Influence of Isotope Substitution on Lattice and

FULL PAPER DOI: 10.1002/asia.201200956

Influence of Isotope Substitution on Lattice and Spin-Peierls-Type Transition Features in One-Dimensional Nickel Bis-dithiolene Spin Systems Guo-Jun Yuan,[a] Shun-Ping Zhao,[a] Can Wang,[a] Jian-Lan Liu,[a] and Xiao-Ming Ren*[a, b] Abstract: Four new 1D spin-Peierlstype compounds, [D5]1-(4’-R-benzyl)pyridinium bis(maleonitriledithiolato)nickelate ([D5]R-Py; R = F, I, CH3, and NO2), were synthesized and characterized structurally and magnetically. These 1D compounds are isostructural with the corresponding non-deuterated compounds, 1-(4’-R-benzyl)pyridinium bis(maleonitriledithiolato)nickelate (RPy; R = F, I, CH3, and NO2). Compounds [D5]R-Py and R-Py (R = F, I, CH3, and NO2) crystallize in the monoclinic space group P21/c with uniform stacks of anions and cations in the high-temperature phase and triclinic

space group P1¯ with dimerized stacks of anions and cations in the low-temperature phase. Similar to the non-deuterated R-Py compounds, a spinPeierls-type transition occurs at a critical temperature for each [D5]R-Py compound; the magnetic character of the 1D S = 1=2 ferromagnetic chain for [D5]F-Py and the 1D S = 1=2 Heisenberg antiferromagnetic chain for others appear above the transition temperaKeywords: deuterium · isotope effects · magnetic properties · nickel · spin-Peierls-type transitions

Introduction

have been widely developed; however, isotope effects, namely, changes in the physical properties of a material caused by isotope substitution, have seldom been discussed and remain poorly understood in the field of molecule magnets,[14] although the isotope effect has been widely investigated in the fields of ferroelectric and phonon-mediated superconducting materials.[15–18] In our previous work, a series of 1D spin-Peierls-type compounds, composed of 1-N-(4’-R-benzyl)pyridinium cations and a bis(maleonitriledithiolato)nickelate monoanion (denoted as [R-BzPy][NiACHTUNGRE(mnt)2]; R = F, Cl, Br, I, NO2, CH3, CN, and CH=H2 ; Bz = benzoyl; mnt = maleonitriledithiolate), were designed, prepared, and their structural, magnetic, and spin-Peierls-type transition properties were studied.[19] It was noted that applied pressure and increased chemical pressure could promote spin-Peierls-type transitions and stabilize the dimerized phase for those magneticchain systems.[19e] Most recently, two isostructural deuterated analogues, [[D5]Br-BzPy][NiACHTUNGRE(mnt)2] and [[D5]Cl-BzPy][NiACHTUNGRE(mnt)2], were prepared by utilizing [D5]pyridine instead of pyridine in 1-N-(4-bromobenzyl)pyridinium and 1-N-(4chlorobenzyl)pyridinium cations, respectively.[20] Structural and magnetic investigations revealed that 1) the cell volumes decreased slightly and 2) the spin-Peierls-type transition temperature, TC, increased when pyridine was replaced with [D5]pyridine in the cation moieties. The isotope effects of deuterated countercations on the phase-transition critical temperature are probably related to an increase in chemical

Molecule-based magnets have been attracting a great deal of academic interest and many achievements have been made over the past three decades. Examples include tuning of the critical temperature, TC, higher than room temperature ferromagnets;[1–3] hard magnets with giant coercivity (a coercive field is 52 kOe);[4] spin bistability materials;[5] guest-tunable spin-crossover nanoporous coordination framework materials;[6] magneto-opto-electronic bistability materials;[7] metallic ferromagnets;[8] giant negative magnetoresistance materials;[9] as well as single-molecule magnets,[10, 11] single-chain magnets,[12] and single-ion magnets[13] with macroscopic quantum tunneling magnetization. The strategies towards the tailoring and fine-tuning of the magnetic behavior through chemical modification techniques

[a] G.-J. Yuan, S.-P. Zhao, C. Wang, Prof. Dr. J.-L. Liu, Prof. Dr. X.-M. Ren State Key Laboratory of Materials-Oriented Chemical Engineering and College of Science, Nanjing University of Technology Nanjing 210009 (P. R. China) Fax: (+ 86) 25-58139481 E-mail: [email protected] [b] Prof. Dr. X.-M. Ren Coordination Chemistry Institute & State Key Laboratory Nanjing University, Nanjing 210093 (P. R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201200956.

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ture. Spin-gap magnetic behavior was observed for all of these compounds below the transition temperature. In comparison to the corresponding R-Py compound, the cell volume is almost unchanged for [D5]F-Py and shows slight expansion for [D5]R-Py (R = I, CH3, and NO2) as well as an increase in the spin-Peierls-type transition temperature for all of these 1D compounds in the order of F > I CH3 NO2. The large isotopic effect of nonmagnetic countercations on the spin-Peierls-type transition critical temperature, TC, can be attributed to the change in w0 with isotope substitution.

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and comparable to those in its analogue I-Py.[19d] The characteristic dihedral angles between the phenyl and pyridyl rings, as well as between the reference plane, defined by N5C14-C15, and the phenyl (pyridyl) ring in the L-shaped [D5]4-I-BzPy + cation are analogous to those in I-Py[19d] (see Table S4 in the Supporting Information). The anions and cations are aligned into segregated columnar stacks along the crystallographic c axis; each anion stack is surrounded by four cation stacks and vice versa. Relative slippage along the long molecular axis of the anion and rotation between two superimposed anions are observed within an anion stack; this kind of overlap pattern provides a more efficient way to minimize repulsions between the neighboring [NiACHTUNGRE(mnt)2] anions. The neighboring cations are arranged in a boat-type conformation, in which the phenyl rings of the [D5]1-N-(4-iodobenzyl)pyridinium cations are approximately parallel to each other and the iodine atoms point towards the pyridyl ring centre of the neighboring cations within a cation stack, indicating that there are probably lone pair···p interactions between iodine atoms with a partial negative charge and electron-deficient pyridyl rings, in addition to p···p stacking interactions between parallel phenyl rings (Figure 1 b). Shorter interatomic contacts are also found between CN groups in the anion moiety and D atoms on the pyridyl ring with distances of dN2···D10 = 2.837 , dN3···D12#1 = 2.852 , and dN3···D13#2 = 2.675 (symmetric codes #1 = 1x, 0.5 + y, 0.5z; #2 = 1 + x, 0.5y, 0.5 + z); these are illustrated in Figure 2. It is unambiguous that there are electrostatic attractions between the above-mentioned N atoms

pressure because the cell volume shrinks or the phonon frequency, w0, changes; however, it is ambiguous which factor plays a crucial role in the isotope effect observed in the phase-transition TC. To better understand this issue, a systematic study of the crystal structures, magnetic behavior, and phase-transition behavior of deuterated analogues of the 1D spin-Peierls-type [R-BzPy][NiACHTUNGRE(mnt)2] family is required. Herein, four deuterated spin-Peierls-type compounds [[D5]R-BzPy][NiACHTUNGRE(mnt)2] (R = F, I, CH3, and NO2 ; Scheme 1) were synthesized and characterized structurally, and the isotope effects of the deuterated countercation on the cell volume, magnetic behavior, and spin-Peierls-type transition features were investigated.

Scheme 1. Structures of compounds [[D5]R-BzPy][NiACHTUNGRE(mnt)2] and [RBzPy][NiACHTUNGRE(mnt)2] studied herein.

Results and Discussion Crystal Structures Compounds [D5]R-Py (R = F, I, CH3, and NO2) are isostructural at room temperature (in the high-temperature (HT) phase) and crystallize in monoclinic space group P21/c. As the four compounds show similar cell parameters (see Table 1) and packing structures, only the crystal structure of [D5]I-Py is described in detail herein. An asymmetric unit of [D5]IPy is comprised of an anion and cation pair (Figure 1 a). The mean-molecule plane of the [NiACHTUNGRE(mnt)2] anion, defined through four-coordinate sulfur atoms, is approximately parallel to the phenyl ring in the cation with a dihedral angle of 14.48. The bond lengths and angles in the planar [NiACHTUNGRE(mnt)2] moiety, listed in Table 2, are normal

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Table 1. Crystallographic data and refinement parameters for [D5]F-Py, [D5]I-Py, [D5]CH3-Py, and [D5]NO2-Py in the HT phase. [D5]F-Py T [K] l [] formula Mr space group CCDC no. crystal system a [] b [] c [] b [8] V [3]/Z 1 [g cm1] FACHTUNGRE(000) abs. coeff. [mm1] q range for data collection [8] index ranges

296(2) 0.71073 C20H6D5N5S4NiF 532.32 P21/c 867566 monoclinic 12.1420(18) 25.952(4) 7.3479(11) 101.746(2) 2266.9(6)/4 1.560 1068 0.0360(15) 1.71–27.46 15 h 15 33 k 30 9 l 9 0.0698 Rint independent reflns/restraints/parame- 5174/0/281 ters 1.029 goodness of fit on F2 R1, wR2[a] [I > 2s(I)] 0.0431, 0.0994 0.0746, 0.1155 R1, wR2[a] [all data] 0.325/0.277 residual [e nm3]

[D5]I-Py

[D5]CH3-Py

[D5]NO2-Py

296(2) 0.71073 C20H6D5N5S4NiI 640.22 P21/c 867567 monoclinic 12.0014(13) 26.638(3) 7.5769(8) 102.6890(10) 2363.1(4)/4 1.799 1244 0.0000(13) 2.32–26.55 15 h 14 33 k 33 9 l 9 0.0498 4920/0/325

296(2) 0.71073 C21H9D5N5S4Ni 528.35 P21/c 867568 monoclinic 12.1779(18) 26.594(4) 7.4202(11) 102.991(2) 2341.6(6)/4 1.499 1068 0.0273(11) 1.72–27.48 14 h 15 34 k 34 9 l 9 0.0540 5353/0/320

296(2) 0.71073 C20H6D5O2N6S4Ni 559.33 P21/c 867569 monoclinic 12.2144(19) 26.587(4) 7.2553(11) 102.920(2) 2296.5(6)/4 1.618 1124 0.0012(2) 1.71–27.47 15 h 15 32 k 34 9 l 9 0.0435 5240/0/343

1.038 0.0648, 0.1363 0.0497, 0.1257 2.072/2.063

1.059 0.0363, 0.0895 0.0533, 0.0996 0.264/0.303

1.021 0.0388, 0.0905 0.0693, 0.1100 0.312/0.359

[a] R1 = j j Fo j j Fc j j / j Fo j , wR2 = [w(F 2oF 2c)2/w(F 2o)2]1/2.

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of CN groups and D atoms on pyridyl rings owing to the corresponding N and D atoms with a partial negative and positive charge, respectively. Note that there is only one type of intermolecular overlap in both the anion and cation stacks, even if there are two anions and two cations per repeat unit along the stack direction, since both anion and cation stacks are uniform. There is an identical center-to-center distance between the adjacent phenyl rings of c1 = c2 = 4.5872(4) within a cation stack as well as an identical Ni···Ni distance between adjacent superimposed anions of d1 = d2 = 3.9655(7) in an anion stack (Table 3). Single-crystal X-ray diffraction data for [D5]R-Py (R = I, CH3, and NO2) in the LT phase were collected at 100 K. Since there are diffuse diffractions in the wide temperature range around the magnetic transition, which arise from strong magnetoelastic interactions and affect the precision of the intensity of the Bragg diffraction,[19d, 25] the RACHTUNGRE(sigma) values of diffraction data for these spin-Peierls-type compounds increase, leading to R1 and wR2 values being higher, as well as the precision of some bonds being lower in the LT phase. Three compounds are also isostructural to each other in the LT phase, with analogous cell parameters and packing structures; thus only the structure of [D5]I-Py in the LT phase is described herein and the structures of [D5]CH3-Py and [D5]NO2-Py are shown in the Supporting Information. From the HT to the LT phase, the space group of the crystal [D5]I-Py degrades from P21/c to P1¯, while the Z values remain the same (Z = 4). The twofold screw axis and glide plane along the c axis disappear on going from the HT to the LT phases, so that the symmetry-related molecules (anions and cations) through the twofold screw axis and glide plane are inequivalent in a unit cell and, as a result, an asymmetric unit switches from an anion and cation pair in the HT phase into two pairs of anions and cations in the LT phase (as shown in Figure 3). By comparison to the crystal structure of [D5]I-Py in the HT phase, the bond lengths and angles in both anion and cation moieties in the LT phase are in agreement with the corresponding values in the HT phase; however, the cation conformation and packing structures of both the anion and cation show significant changes. As displayed in Figure 3 b, the symmetry-breaking phase transition leads to two crystallographically inequivalent cations, exhibiting distinct orientations and uneven shrinkage of anion and cation stacks, as reflected in the interatomic separations, the centroid-tocentroid distances between adjacent phenyl rings, as well as in charge-assisted hydrogen-bonding interactions between hydrogen/deuterium atoms in the cations and nitrogen atoms in the anions (see Figure 4 and Table S3 in the Supporting Information), for instance, d1 = 3.7842 , d2 = 3.8926 , c1 = 4.5975 , c2 = 4.4324 , b1 = 3.6100 , and b1’ = 3.5025 , thereby indicating that intermolecular interactions are strengthened between neighboring anions and cations.

Figure 1. a) Molecular structure showing the labeling of the non-hydrogen atoms and displacement ellipsoids at the 20 % probability level. b) Packing diagram viewed along the a axis, which shows segregated columnar stacks of anions and cations as well as alignment patterns of the neighboring superimposed anions in an anionic stack and the overlapped cations in a cationic stack in the crystal of [D5]I-Py at room temperature.

Figure 2. Illustration of the shorter interatomic contacts between CN groups in the anion moieties and D atoms on the pyridyl rings of cations in the crystal of [D5]I-Py.

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Table 2. CH···p/lone pair···p interactions between substituent R and phenyl/pyridyl rings in the crystals of [D5]R-Py and R-Py (F, I, CH3, or NO2) at room temperature.

Distance []

[D5]F-Py

F-Py

[D5]I-Py

I-Py

[D5]CH3-Py

CH3-Py

[D5]NO2-Py

[D5]NO2-Py

a1 a1’ a2 a2’ d1 d2 c1 c2 b1 b1’ b2 b2’ b3 b3’

4.4078(10) 4.4078(10) 3.9497(12) 3.9497(12) 3.9655(7) 3.9655(7) 3.9157(5) 3.9157(5) 3.2997(21) 3.2997(21) 4.0405(23) 4.0405(23) 3.7905(23) 3.7905(23)

3.6543(17) 3.6543(17) 3.7600(21) 3.7600(21) 3.9642(10) 3.9642(10) 3.9122(1) 3.9122(1) 3.3034(36) 3.3034(36) 4.0394(38) 4.0394(38) 3.7838(38) 3.7838(38)

4.4089(15) 4.4089(15) 4.0847(21) 4.0847(21) 3.9648(9) 3.9648(9) 4.5872(4) 4.5872(4) 3.6259(6) 3.6259(6) 3.9418(6) 3.9418(6) 3.8466(6) 3.8466(6)

4.5843(73) 4.5843(73) 3.9971(64) 3.9971(64) 3.9607(58) 3.9607(58) 4.5764(54) 4.5764(54) 3.6234(46) 3.6234(46) 3.9368(60) 3.9368(60) 3.8449(57) 3.8449(57)

3.6132(10) 3.6132(10) 3.9591(12) 3.9591(12) 3.8303(7) 3.8303(7) 4.2463(5) 4.2463(5) 3.8709(30) 3.8709(30) 3.7539(30) 3.7539(30) 3.6114(31) 3.6114(31)

4.1659(12) 4.1659(12) 3.9423(10) 3.9423(10) 3.8070(7) 3.8070(7) 4.2257(6) 4.2257(6) 3.8554(20) 3.8554(20) 3.7298(23) 3.7298(23) 3.5980(23) 3.5980(23)

3.6662(8) 3.6662(8) 3.9909(10) 3.9909(10) 3.8834(7) 3.8834(7) 4.5116(5) 4.5116(5) 3.9521(32) 3.9521(32) 3.7628(31) 3.7628(31) 3.6981(32) 3.6981(32)

4.4605(14) 4.4605(14) 3.8731(15) 3.8731(15) 3.8652(12) 3.8652(12) 4.4862(9) 4.4862(9) 3.8774(36) 3.8774(36) 3.6979(39) 3.6979(39) 3.7428(39) 3.7428(39)

non-deuterated compounds R-Py (R = F, I, CH3, and NO2) could be analyzed by using an infinite ferromagnetic uniform chain model for F-Py and an infinite uniform antiferromagnetic Heisenberg chain model for R-Py (R = I, CH3, and NO2) in the HT phase, as well as a spin–gap model for R-Py (R = F, I, CH3, and NO2) in the LT phase. Thus, the Baker equation [Eq. (1)],[26] derived from a high-temperature series expansion for a ferromagnetic chain, is used to analyze the magnetic susceptibility data of the deuterated compound [D5]F-Py in the HT phase:

Table 3. Parameters obtained from the fit of magnetic susceptibility in high-temperature (HT) and low-temperature (LT) phases for [D5]R-Py (F, I, CH3, or NO2). Compound

J/kB [K]

T range [K]

D/kB [K]

T [K]

[D5]F-Py [D5]I-Py [D5]CH3-Py [D5]NO2-Py

+ 22.0(2) 42.4(6) 154.7(5) 164.1(7)

100–300 125–300 190–300 186–300

604(20) 671(33) 1027(31) 1071(60)

1.8–88 1.8–105 1.8–164 1.8–152

Magnetic Properties cchain ¼

Plots of magnetic susceptibility versus temperature for [D5]R-Py and R-Py (R = F, I, CH3 and NO2) are displayed in Figure 5. It is observed that the deuterated compounds and corresponding non-deuterated analogues show similar magnetic behavior. By comparison to the corresponding nondeuterated analogues, the spin-Peierls-type transition temperature, TC, increases for [D5]R-Py (R = F, I, CH3, and NO2 ; see the insets in Figure 5 a–d), and the DTC = TC(D)TC(H) value is estimated to be about 5.1 K for [D5]F-Py, 2.1 K for [D5]I-Py, 2.2 K for [D5]CH3-Py, and 2.1 K for [D5]NO2-Py from magnetic susceptibility measurements. Similar behavior is observed for the corresponding nondeuterated compounds R-Py (R = F, I, CH3, and NO2): the magnetic exchange nature is ferromagnetic for [D5]F-Py and antiferromagnetic for [D5]I-Py, [D5]CH3-Py, and [D5]NO2-Py in the HT phase, whereas the magnetic interactions are dominated by antiferromagnetic coupling between [NiACHTUNGRE(mnt)2] anions in the LT phase for four deuterated compounds. In our previous studies,[19b–d, 25] the magnetic behavior of the

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Ng2 m2B C 2=3 ½ 4kB T D

ð1Þ

in which C = 1.0 + 5.7979916y + 16.902653y2 + 29.376885y3 + 29.832959y4 + 14.036918y5, D = 1.0 + 2.7979916y + 7.008678y2 + 8.653644y3 + 4.5743114y4, and y = J/kBT. Equation (2),[27] deduced from a uniform Heisenberg model of a linear chain with S = 1=2 , is utilized to analyze the temperature dependence of the magnetic susceptibility of the deuterated compounds [D5]R-Py (R = I, CH3, and NO2) in the HT phase: cm ¼

Ng2 m2B A þ BX 1 þ CX 2 kB T 1 þ DX 1 þ EX 2 þ FX 3

ð2Þ

in which X = kBT/ j J j , J is the magnetic exchange constant of neighboring spins in a magnetic chain, and the coefficients of A–F in the power series are as follows: A = 0.25, B = 0.14995, C = 0.30094, D = 1.9862, E = 0.68854, F = 6.0626. If the contribution c0 originated from closed atom shells (di-

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Figure 3. a) Molecular structures with non-hydrogen (deuterium) labeling and b) the molecule conformations for two crystallographically inequivalent cations (this plot was obtained by using the keyword OFIT in the SHELXTL program) for [D5]I-Py in the LT phase (at 100 K).

Figure 4. Characteristic distances within a stack of a) anions and b) cations, which demonstrate the changes in the crystal structures of the HT and LT phases of [D5]I-Py.

in which a is a constant corresponding to the dispersion of excitation energy, D/kB is the magnitude of the spin gap, and c0 is the contribution from core diamagnetism and possibly van Vleck paramagnetism. The parameters, obtained from best fits for the magnetic susceptibility data of four deuterated compounds [D5]R-Py (R = F, I, CH3, and NO2) in both HT and LT phases, are summarized in Table 3, which are comparable to parameters in the corresponding non-deuterated compounds R-Py (R = F, I, CH3, and NO2), respectively.

amagnetism) and possible van Vleck paramagnetism, and magnetic impurities arising from lattice defects are also taken into account, then the experimental magnetic susceptibility for [D5]R-Py (R = F, I, CH3, and NO2) in the HT phase is given by Equation (3): cm ¼ cchain þ

C þ c0 T

ð3Þ

In Equation (3), the term cchain is given by Equation (1) for [D5]F-Py and by Equation (2) for [D5]R-Py (R = I, CH3, and NO2). In the LT phase, the magnetic susceptibility exponentially decreases upon cooling; this indicates that a spin gap is opened and the magnetic susceptibility is thermally activated for four deuterated compounds. Accordingly, the temperature dependence of magnetic susceptibility was simulated by using Equation (4) for [D5]R-Py (R = F, I, CH3, and NO2):[19, 28] cm ¼

a C expðD=TÞ þ þ c0 T T

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Temperature-Dependent IR Spectra Four deuterated compounds [D5]R-Py (R = F, I, CH3, and NO2) show similar IR spectra at room temperature. Herein, a detailed discussion is only given for the temperature-dependent IR spectra of [D5]F-Py, which were measured in the temperature range 6–293 K. IR spectra of [D5]F-Py under different temperatures are analogous to each other: most of the vibrational bands do not show any sizable change in either the strength or the central position. The main alterations as the temperature changes concern vibrational bands in five spectroscopy regions; these are displayed in Figures 6 and 7 and described below.

ð4Þ

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at 1463 cm1 with asymmetry at 293 K, and its maximum shifts towards higher frequency with a decrease in temperature and is almost unchanged in the temperature range 100–143 K. Such a trend is similar to that observed for the nCN band. The nC=C band of the mnt2 ligand begins splitting and a higher frequency shoulder appears below 80 K; the relative intensity of the higher frequency part is greater than that on the lower frequency side at 6 K. 3) For vibrational bands between 1115 and 1165 cm1, two vibrational bands centered at 1158 and 1119 cm1 in the IR spectrum at 293 K correspond to the nCC + nCS and pCCN vibrational modes of the mnt2 ligand.[22] It was noted that a shoulder occurred in the Figure 5. Plots of magnetic susceptibility versus temperature of a) [D5]F-Py and F-Py, b) [D5]I-Py and I-Py, lower frequency region of the c) [D5]CH3-Py and CH3-Py, and d) [D5]NO2-Py and NO2-Py (insets: magnifications of selected areas of the nCC + nCS band below 143 K plots). and a blueshift appeared for the pCCN band upon cooling (see Figure 6 e). 4) For vibrational bands between 865 and 900 cm1, these 1) For nCN vibrational bands between 2180 and 1 2 2230 cm , the nCN vibrations of the mnt ligand gives rise are assigned to stretching vibrations, nCS, of the mnt2 to intense vibrational bands in the IR spectrum, and these ligand,[22] as depicted in Figure 6 f. No sizable band shift is stretching vibration frequencies are, in general, uncoupled detected in the lower frequency band and a slight blueshift to other vibrational modes of the molecule; therefore, IR is seen in the higher frequency band as the temperature spectroscopy is particularly appropriate for studying mnt2 drops below about 100 K. 5) Vibrational bands between 2250 and 2320 cm1 are ascompounds. As demonstrated in Figure 6 a, a very intense 1 band centered at 2208 cm together with two shoulder signed to stretching vibrations of nCD.[29] Figure 7 displays 1 bands around 2217 and 2186 cm appeared in the IR specchanges in the nCD bands with temperature in the range of trum of [D5]F-Py at 293 K. Two shoulder bands increase 6–293 K. Four vibrational bands centered at 2266, 2297, 2307, and 2320 cm1 shift slightly towards higher frequencies upon cooling; meanwhile the band maximum shows a blueshift for the band on the lower frequency side, whereas during cooling. there is a redshift for the band in the higher frequency side. Vibrational band shifts indicate changes in the electronic The maximum of the intense band first blueshifts when the state of the molecule because the frequency of a vibration is temperature drops, reverts to its original position in the temdirectly related to the force constant of the bond. As menperature range 80–143 K, and then redshifts a little below tioned above, pretransitional phenomena are observed from 80 K (see Figure 6 b). Clearly, the reflected point of the nCN four intramolecular vibration modes within the magnetic [NiACHTUNGRE(mnt)2] moiety, indicating that electron–molecular viband shift (ca. 143 K; see the inset of Figure 6 b) upon cooling is higher than the critical temperature of the magnetic bration couplings within a [NiACHTUNGRE(mnt)2] moiety cooperate transition. This behavior is related to the pretransitional with spin-Peierls-type transitions. In fact, it was known that phenomenon, which originates from inherent structural flucintramolecular vibrations played an important role in the tuation in a 1D electronic system with a half-filled band and occurrence of superconductivity of organic materials three was identified by superlattice diffraction in the spin-Peierlsdecades ago, for which molecular superconductivity was type transition compound F-Py.[25a] caused by electron–phonon interactions.[30] In addition, shifts 1 in the nCD bands in the cation moiety were also observed, 2) For vibrational bands between 1450 and 1480 cm , Nakamoto and Schlpfer assigned the vibrational bands in this accompanied by a magnetic transition related to changes in region to the nC=C vibration of the mnt2 ligand.[22] As shown the intermolecular interactions between neighboring anions and cations, such as charge-assisted hydrogen-bond interacin Figure 6 c, d, the nC=C band of the mnt2 ligand is located

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tions between hydrogen/deuterium atoms in the pyridyl ring and nitrile groups in the mnt2 ligands. This means that intermolecular interactions between the anions and cations probably play a cooperative role in magnetic transitions. Such a finding could be used to address the issue that the steric nature of a substituent on the phenyl ring of the countercation appears to strongly affect spin-Peierls-type transition features in the series of 1D [R-BzPy][NiACHTUNGRE(mnt)2] (R represents the substituent on the phenyl ring of the cation) spin systems, for example, the variation in TC is dependent upon the size of the substituent group.[19g] The substituent size difference (steric effect) leads to subtle changes in charge-assisted hydrogen-bond interactions between hydrogen atoms in the pyridyl ring of the cation and the nitrile group of the mnt2 ligands; this gives rise to distinction of cooperative interactions in spin-Peierls-type transitions. TC Determined by Thermodynamic Approaches Differential scanning calorimetry (DSC) measurements were Figure 6. Variable-temperature IR spectra of [D5]F-Py in the temperature range 6–293 K, showing changes in 2 further performed for deuteratthe shape and position of characteristic bands: a) and b) the nCN bands of the mnt ligands, c) and d) the nC=C ed and non-deuterated combands of the mnt2 ligands, e) the nCS + nCC bands of the mnt2 ligands and pCCN, and f) the nCS bands of the mnt2 ligands. pounds in the temperature range 98–293 K; the related curves are shown in Figure 8 a– d, from which a l-shaped thermal anomaly was observed for all compounds, apart from F-Py because its magnetic transition temperature of about 90 K was lower than the limit of our instrument. The DTC = TC(D)TC(H) values, in which TC(D) and TC(H) represent the peak temperatures of the DSC event for the deuterated and corresponding non-deuterated compounds, respectively, were calculated to be about 2.6 K for [D5]I-Py, 2.3 K for [D5]CH3-Py, and 2.1 K for [D5]NO2-Py. For F-Py, a l-shaped thermal anomaly was observed in the heat capacity measurement,[25a] and its peak temperature was determined to be 93.1 K; thus the DTC value between [D5]F-Py and F-Py was estimated to be about 8.4 K. The DTC values estimated from thermodynamic apFigure 7. Variable-temperature IR spectra of [D5]F-Py in the 2250– 1 proaches are essentially in agreement with results obtained 2340 cm region, corresponding to the stretching vibration of nCD in the from magnetic susceptibility measurements for [D5]R-Py [D5]pyridine moiety and 6–293 K temperature range.

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tions of [D5]F-Py and F-Py are almost the same; no sizable shift is observed for the positions of the diffraction peaks and the simulated cell parameters for two compounds are rather close to each other, indicating that the cell parameters are almost unaffected by deuteration for F-Py. In comparison, some characteristic diffraction peaks of [D5]I-Py and [D5]NO2Py shift slightly to lower angles than those of non-deuterated IPy and NO2-Py, respectively. Accordingly, this leads to a small expansion in the cell volume of the corresponding deuterated analogues. In relation to non-deuterated CH3-Py, clear shifts in the diffraction peaks towards lower angles are observed in the enlarged PXRD profiles of [D5]CH3-Py; Figure 8. DSC curves of a) [D5]F-Py and F-Py, b) [D5]I-Py and I-Py, c) [D5]CH3-Py and CH3-Py, and this is consistent with expansion d) [D5]NO2-Py and NO2-Py. of the cell volume of [D5]CH3Py. In our previous study, it was and R-Py (R = I, CH3, and NO2), and somewhat higher for found that the cell volumes slightly contracted for deuterat[D5]F-Py and F-Py. ed cations of the two compounds [Br-BzPy][NiACHTUNGRE(mnt)2] (BrPy) and [Cl-BzPy][NiACHTUNGRE(mnt)2] (Cl-Py), which are isostructural to [D5]R-Py (R = F, I, CH3, and NO2),[20] and these results Effect of Deuterium Substitution on Cell Parameters clearly showed the versatile effects of isotopic substitution on cell volume for the series of compounds R-Py (R = F, Cl, When comparing the cell parameters obtained from singleBr, I, CH3, and NO2). crystal X-ray diffraction measurements, it is clear that isotopic substitution significantly affects cell parameters in the The isotope effects on vapor pressure, condensed phase series of compounds R-Py (R = F, I, CH3, and NO2); howevmolar volume or molar density, vapor-phase second virial coefficients, and molecular polarizabilities are closely relater, each individual single crystal cannot provide concrete ed and share a common origin of quantum effects on vibraproof of this fact, especially with small changes in the cell tion properties.[32] It is interesting that six isostructural comparameters because differences may originate from random errors with the devices or environment. To get a clearer picpounds R-Py (R = F, Cl, Br, I, CH3, and NO2) display diture of the effect of isotopic substitution on the cell parameverse isotopic effects of cell volume. Currently, the exact ters, powder X-ray diffraction (PXRD) analyses were perreason for these differences is unclear. formed for [D5]R-Py and R-Py (R = F, I, CH3, and NO2) under the same measuring conditions. The PXRD profiles Effect of Deuterium Substitution on TC over 2q = 5–408 are provided in Figure S9 in the Supporting Information, and the cell parameters obtained from simulaBased on magnetic susceptibility and DSC measurements, tions of PXRD data using the UnitCell program[31] are sumthe isotopic substitution effect of nonmagnetic countercations on the spin-Peierls-type transition temperature, TC, marized in Table 4. Enlarged profiles, which show characteristic diffractions, are displayed in Figure 9 a–h. The diffracwas clearly observed in four [NiACHTUNGRE(mnt)2]-based spin-Peierlstype compounds [D5]R-Py (R = F, I, CH3, and NO2). Results in Table 4. Cell parameters obtained from simulations of PXRD data at 293 K. this work ([D5]R-Py; R = F, I, F-Py [D5]F-Py I-Py [D5]I-Py CH3-Py [D5]CH3-Py NO2-Py [D5]NO2-Py CH 3 and NO2), combined with a [] 12.1080 12.1079 11.9580 11.9516 12.0337 12.1207 12.1520 12.1657 our previous study ([D5]R-Py; b [] 25.9050 25.9038 26.5068 26.5341 26.4163 26.3151 26.4802 26.5070 c [] 7.3237 7.3234 7.5449 7.5581 7.3603 7.3563 7.2158 7.2191 R = Cl and Br), revealed that 101.764 101.758 102.450 102.360 102.671 102.921 102.931 102.952 b [8] changes in spin-Peierls-type 2248.9 2248.7 2335.3 2341.3 2282.8 2286.9 2263.0 2268.8 V [3] transition temperatures, arising

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and they noted that when natCu was substituted for 63Cu and 65 Cu isotopes in the CuGeO3 spin system, the TC value decreased by 0.08(2) and 0.05(2) K, respectively.[33a] When comparing the inorganic CuGeO3 spin-Peierls system and [NiACHTUNGRE(mnt)2]-based spinPeierls-type compounds, two distinctions can be found: 1) TC decreases in CuGeO3, whereas it increases in [NiACHTUNGRE(mnt)2]based spin-Peierls-type compounds; and 2) the change in TC that results from isotopic substitution is much larger in [NiACHTUNGRE(mnt)2]-based spin-Peierlstype compounds than that in CuGeO3. It is noticeable that significant distinctions between [NiACHTUNGRE(mnt)2]-based spin-Peierlstype compounds and the CuGeO3 real spin-Peierls system was also reflected in the influence of nonmagnetic doping on TC.[19d, 34, 35] The spinPeierls transition is destroyed by nonmagnetic impurities for an impurity mole fraction of only x 0.02 for CuGeO3,[35] whereas x > 0.27 for [NiACHTUNGRE(mnt)2]-based spin system in which the magnetic [NiACHTUNGRE(mnt)2] anions were substituted for nonmagnetic analogous [AuACHTUNGRE(mnt)2] anions,[19d] and x > 0.5 for systems in which the magnetic [NiACHTUNGRE(mnt)2] anions were replaced by nonmagnetic analogous [CuACHTUNGRE(mnt)2] anions.[34] Theoretically, within the limit kBT ! pJ, the expression for the spin-Peierls-type transition temperature, TC, is of the Bardeen– Cooper–Schrieffer (BCS) form given by Equations (5) and (6): kB T C ¼ 1:14ðpJÞexpð1=lÞ Figure 9. PXRD profiles obtained at room temperature for F-Py and [D5]F-Py (a, b), I-Py and [D5]I-Py (c, d), CH3-Py and [D5]CH3-Py (e, f), and NO2-Py and [D5]NO2-Py (g, h).

from isotopic substitution, for DTC = TC(D)TC(H) followed the order of F > Cl Br > I CH3 NO2. Kremer and co-workers investigated the isotope effect of an inorganic spin-Peierls system, CuGeO3, several years ago,

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l ¼ 4g2 p2 N 0 =w0 2 g ¼ gðlq, q ¼ 2kf Þ

ð5Þ ð6Þ

in which N0 = 1/pJp and is the density of states at kf for the fermion band, J is the static exchange constant and the only weakly temperature-dependent constant, p = 1.64, and w0 and g represent the phonon frequency in the absence of the

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spin interaction and the spin-phonon coupling constant, respectively. Equation (5) shows that TC increases with the static exchange constant J; this was observed in our previous studies.[19d,e] From Equations (5) and (6), TC is also related to the mass of the vibrating centers through the phonon frequency, w0, and by the spin-phonon coupling constant, g, for which g211m may be assumed in a first approximation, in which m is the mass of the atoms with spins. In the series of [NiACHTUNGRE(mnt)2]-based ion-pair spin-Peierls-type compounds, the [NiACHTUNGRE(mnt)2] anion has a spin of S = 1=2 and the countercation is a nonmagnetic species. It seems that the spin-phonon coupling constant, g, is only correlated to the mass of the [NiACHTUNGRE(mnt)2] anion because only the anion has a spin of S = 1=2 and the spin density is delocalized over the entire anionic skeleton. On the other hand, the phonon frequency, w0, is associated with the mass of both the magnetic anion and nonmagnetic countercations in the R-Py (R = F, Cl, Br, I, CH3, and NO2) spin system. Therefore, the large isotopic effect of nonmagnetic countercations on TC probably arises from the change of w0 with isotope substitution.

Experimental Section Chemicals and Materials All reagents and chemicals were purchased from commercial sources and used without further purification. The starting material, Na2mnt, was prepared as reported in the literature.[21] Compounds [[D5]R-BzPy]X and [[D5]R-BzPy]2[NiACHTUNGRE(mnt)2] (R = F, I, CH3, NO2 ; X = Br or Cl) were synthesized by utilizing a similar procedure to that used for the preparation of [[D5]Br-BzPy]X and [[D5]Br-BzPy]2[NiACHTUNGRE(mnt)2],[20] but instead of the [D5]1-N-(4-bromobenzyl)pyridinium cation the corresponding [D5]1-N(4-R-benzyl)pyridinium (R = F, I, CH3, NO2) cations were used. Preparation of [[D5]F-BzPy][NiACHTUNGRE(mnt)2] ([D5]F-Py) A solution of I2 (150 mg, 0.59 mmol) in methanol (10 mL) was slowly added to a solution of [[D5]F-BzPy]2[NiACHTUNGRE(mnt)2] (726 mg, 1.0 mmol) in methanol (20 mL). The mixture was stirred for 15 min and allowed to stand overnight and then black product microcrystals (450 mg, 85 %) were filtered off, washed with methanol, and dried under vacuum. Elemental analysis calcd (%) for C20H6D5N5FNiS4 : C 45.56, H and D 2.10, N 13.28; found: C 45.05, H and D 2.67, N 13.43; IR (KBr):[22, 23] n˜ = 3070 (w), 3041 (w), and 3012 (vw) attributed to nCH of the phenyl ring; 2217 (sh), 2208 (vs), and 2186 (sh) assigned to nCN of the mnt2 ligands; 1605 (s) 1589 (vs), 1553 (s), and 1507 (s) attributed to the ring-stretching vibration of the pyridyl and phenyl rings in the cation; 1462 (s) arose from nC= 2 ligands; 1226 (s) assigned to nCF of the phenyl ring; 1157 C of the mnt (vs) and 1063 (w) arose from nCS + nCC of the mnt2 ligands; 1119 (s), 1096 (s), and 533 (s) for pCCN ; 887 cm1 (m) attributed to nCS of the mnt2 ligands.

Conclusion Four new 1D [NiACHTUNGRE(mnt)2]-based spin-Peierls-type compounds, [D5]R-Py, in which the substituent group R = F, I, CH3, and NO2, were synthesized and characterized structurally and magnetically. Combined with our previous studies, it was found that the R-Py (R = F, Cl, Br, I, CH3, and NO2) compounds showed versatile isotope effects on the cell volume, but increased spin-Peierls-type transition temperatures when the hydrogen atoms on the pyridyl ring of the nonmagnetic countercation were replaced with deuterium atoms. The increase in TC arising from deuteration was closely related to the nature of the substituent group R, in the order of F > Cl Br > I CH3 NO2. Combined with the crystal structure analysis, the large isotope effect of nonmagnetic countercations on TC could be attributed to the change in parameter w0 with isotope substitution. Analyses of variable-temperature IR spectra revealed that some intramolecular vibrational modes within the anion cooperated with the spin-Peierls-type transition in these [NiACHTUNGRE(mnt)2] magnetic chain compounds. In addition, intermolecular interactions, such as charge-assisted hydrogen-bonding interactions between hydrogen/deuterium atoms in the pyridyl ring and nitrile groups of the mnt2 ligands also played a cooperative role in spin-Peierls-type transitions. These findings are expected to address the issue that the nature of the substituent on the phenyl ring of the countercation can strongly affect the spin-Peierls-type transition features in the 1D [R-BzPy][NiACHTUNGRE(mnt)2] (R represents the substituent in the phenyl ring of cation) spin system, even if the exact relationship between DTC and substituent group R is not clear at this stage.

A similar procedure was used for the preparation of [D5]R-Py (R = I, CH3, and NO2). The yields of the three deuterated compounds were more than 80 %. Elemental analysis calcd (%) for C20H6D5N5INiS4 ([D5]I-Py): C 37.82, H and D 1.75, N 11.03; found: C 37.43, H and D 1.60, N 10.97; IR spectrum (KBr):[22] 3078 (w), 3044 (w), and 3024 (vw) attributed to nCH of the phenyl ring; 2215 (sh) and 2204 (vs) attributed to nCN of the mnt2 ligands; 1581 (vs) and 1550 (m) assigned to the ring-stretching vibration of the pyridyl and phenyl rings in the cation; 1461 (s) arose from nC=C of the mnt2 ligands; 1155 (vs) and 1060 (w) assigned to nCS + nCC of the mnt2 ligands; 1114 (vs), 1100 (sh), and 534 (vs) arose from pCCN ; 888 cm1 (m) attributed to nCS of the mnt2 ligands. Elemental analysis calcd (%) for C21H9D5N5NiS4 ([D5]CH3-Py): C 48.20, H and D 2.70, N 13.38; found: C 47.29, H and D 2.85, N 13.68; IR (KBr):[22] 3093 (vw), 3048 (w), 3031 (w), and 3002 (vw) attributed to nCH of the phenyl ring; 2217 (sh), 2204 (vs), and 2187 (sh) arose from nCN of the mnt2 ligands; 1585 (s) and 1550 (m) assigned to the ring-stretching vibration of the pyridyl and phenyl rings in the cation; 1466 (s) attributed to nC=C of the mnt2 ligands; 1155 (vs) arose from the nCS + nCC of mnt2 ligands; 1114 (s) and 536 (s) assigned to pCCN ; 888 cm1 (m) arose from nCS of mnt2 ligands. Elemental analysis calcd (%) for C20H6D5O2N6NiS4 ([D5]NO2-Py): C 43.34, H and D 2.00, N 15.16; found: C 43.16, H and D 1.84, N 15.07; IR (KBr):[22] 3074 (w), 3042 (w), and 3002 (vw) attributed to nCH of the phenyl ring; 2217 (sh) and 2206 (vs) assigned to nCN of the mnt2 ligands; 1599 (m), 1586 (vs), and 1551 (m) attributed to the ring-stretching vibration of the pyridyl and phenyl rings in the cation; 1462 (s) arose from nC=C of the mnt2 ligands; 1519 (vs) and 1345 (s) attributed to nas and ns of the nitro group in the cation; 1156 (vs) and 1064 (w) assigned to nCS + nCC of the mnt2 ligands; 1123 (s), 1103 (m), and 532 (s) arose from pCCN ; 887 (w) assigned to nCS of the mnt2 ligands; 865 cm1 (w) attributed to nCN of the nitrobenzyl group in the cation. Single crystals suitable for X-ray diffraction analyses were obtained by evaporation of solutions of [D5]R-Py (R = F, I, CH3, and NO2) in MeCN at ambient temperature for 6–8 d, respectively. Physical Measurements Elemental analyses (C, H, and N) were performed with an Elementar Vario EL III analytical instrument. IR spectra were recorded at room

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temperature on a Bruker VERTEX80V FTIR spectrometer (as KBr discs) under vacuum. Temperature-dependent FTIR spectra were recorded on a Thermo Nicolet 8700 spectrometer with a combination of an Oxford Variox AC-TL optical cryostat instrument. The sample temperature was controlled from 6 to 293 K through an ITC503 digital temperature controller. Power X-ray diffraction (PXRD) data were collected on a Bruker D8 Advance powder diffractometer operating at 40 kV and 40 mA for CuKa radiation with l = 1.5418 . Samples were scanned from 2q = 5–508 at 0.028 per step and 1.2 s per step. Magnetic susceptibility data for polycrystalline samples were measured over a temperature range of 1.8–300 K by using a Quantum Design MPMS-5S superconducting quantum interference device (SQUID) magnetometer. DSC measurements were carried out on a Q2000V24.9 Build 121 instrumental in the temperature range of 180 to 20 8C (93–293 K) at a rate of 20 8C min1.

[9] H. Komatsu, M. M. Matsushita, S. Yamamura, Y. Sugawara, K. Suzuki, T. Sugawara, J. Am. Chem. Soc. 2010, 132, 4528 – 4529. [10] R. Sessoli, D. Gatteschi, A. Caneschi, M. A. Novak, Nature 1993, 365, 141 – 143. [11] S. M. J. Aubin, Z. Sun, L. Pardi, J. Krzystek, K. Folting, L.-C. Brunel, A. L. Rheingold, G. Christou, D. N. Hendrickson, Inorg. Chem. 1999, 38, 5329 – 5340. [12] A. Caneschi, D. Gatteschi, N. Lalioti, C. Sangregorio, R. Sessoli, G. Venturi, A. Vindigni, A. Rettori, M. G. Pini, M. A. Novak, Angew. Chem. 2001, 113, 1810 – 1813; Angew. Chem. Int. Ed. 2001, 40, 1760 – 1763. [13] a) S. D. Jiang, S. S. Liu, L. N. Zhou, B. W. Wang, Z. M. Wang, S. Gao, Inorg. Chem. 2012, 51, 3079 – 3087; b) S. D. Jiang, B. W. Wang, H. L. Sun, Z. M. Wang, S. Gao, J. Am. Chem. Soc. 2011, 133, 4730 – 4733; c) M. Jeletic, P. H. Lin, J. J. Le Roy, I. Korobkov, S. I. Gorelsky, M. Murugesu, J. Am. Chem. Soc. 2011, 133, 19286 – 19289. [14] a) P. A. Goddard, J. Singleton, C. Maitland, S. J. Blundell, T. Lancaster, P. J. Baker, R. D. McDonald, S. Cox, P. Sengupta, J. L. Manson, K. A. Funk, J. A. Schlueter, Phys. Rev. B 2008, 78, 052408; b) K. Hosoya, T. Kitazawa, M. Takahashi, M. Takeda, J.-F. Meunier, G. Molnr, A. Bousseksou, Phys. Chem. Chem. Phys. 2003, 5, 1682 – 1688. [15] a) G. A. Samara, Ferroelectrics 1987, 71, 161 – 182; b) S. Koval, J. Kohanoff, J. Lasave, G. Colizzi, R. L. Migoni, Phys. Rev. B 2005, 71, 184102. [16] S. Horiuchi, R. Kumai, Y. Tokura, J. Am. Chem. Soc. 2005, 127, 5010 – 5011. [17] I. Takasu, A. Izuoka, T. Sugawara, T. Mochida, J. Phys. Chem. B 2004, 108, 5527 – 5531. [18] a) E. Maxwell, Phys. Rev. 1950, 78, 477 – 477; b) C. A. Reynolds, B. Serin, W. H. Wright, L. B. Nesbitt, Phys. Rev. 1950, 78, 487 – 487. [19] a) X. M. Ren, Q. J. Meng, Y. Song, C. S. Lu, C. J. Hu, X. Y. Chen, Inorg. Chem. 2002, 41, 5686 – 5692; b) J. L. Xie, X. M. Ren, Y. Song, W. W. Zhang, C. S. Lu, W. L. Liu, C. He, Q. J. Meng, Chem. Commun. 2002, 2346 – 2347; c) D. B. Dang, C. L. Ni, Y. Bai, Z. F. Tian, Z. P. Ni, L. L. Wen, Q. J. Meng, S. Gao, Chem. Lett. 2005, 34, 680 – 681; d) X. M. Ren, T. Akutagawa, S. Nishihara, T. Nakamura, W. Fujita, K. Awaga, J. Phys. Chem. B 2005, 109, 16610 – 16615; e) X. M. Ren, S. Nishihara, T. Akutagawa, S. Noro, T. Nakamura, W. Fujita, K. Awaga, Chem. Phys. Lett. 2007, 439, 318 – 322; f) Z. F. Tian, H. B. Duan, X. M. Ren, C. S. Lu, Y. Z. Li, Y. Song, H. Z. Zhu, Q. J. Meng, J. Phys. Chem. B 2009, 113, 8278 – 8283; g) H. B. Duan, X. M. Ren, Q. J. Meng, Coord. Chem. Rev. 2010, 254, 1509 – 1522. [20] G. J. Yuan, S. P. Zhao, C. Wang, X. M. Ren, J. L. Liu, Chem. Commun. 2011, 47, 9489 – 9491. [21] A. Davison, R. H. Holm, Inorg. Synth. 1967, 10, 8 – 26. [22] C. W. Schlpfer, K. Nakamoto, Inorg. Chem. 1975, 14, 1338 – 1344. [23] W. Zierkiewicz, D. Michalska, B. Czernik-Matusewicz, M. Rospenk, J. Phys. Chem. A 2003, 107, 4547 – 4554. [24] G. M. Sheldrick, SHELX-97, Program for the Refinement of Crystal Structure, University of Gçttingen, Gçttingen (Germany), 1997. [25] a) X. M. Ren, S. Nishihara, T. Akutagawa, S. Noro, T. Nakamura, W. Fujita, K. Awaga, Z. P. Ni, J. L. Xie, Q. J. Meng, R. K. Kremer, Dalton Trans. 2006, 1988 – 1994; b) X. M. Ren, T. Akutagawa, S. Noro, S. Nishihara, T. Nakamura, Y. Yoshida, K. Inoue, J. Phys. Chem. B 2006, 110, 7671 – 7677. [26] a) G. A. Baker, G. S. Rushbrooke, H. E. Gilbert, Phys. Rev. 1964, 135, A1272; b) L. Deakin, A. M. Arif, J. S. Miller, Inorg. Chem. 1999, 38, 5072 – 5077. [27] a) J. C. Bonner, M. E. Fisher, Phys. Rev. A 1964, 135, A640; b) W. E. Hatfield, J. Appl. Phys. 1981, 52, 1985 – 1990. [28] L. C. Isett, D. M. Rosso, G. L. Bottger, Phys. Rev. B 1980, 22, 4739 – 4743. [29] a) L. Corrsin, B. J. Fax, R. C. Lord, J. Chem. Phys. 1953, 21, 1170 – 1176; b) K. N. Wong, S. D. Colson, J. Mol. Spectrosc. 1984, 104, 129 – 151; c) M. Szafran, J. Koput, J. Mol. Struct. 2001, 565, 439 – 448. [30] a) E. Demiralp, S. Dasgupta, W. A. Goddard, J. Am. Chem. Soc. 1995, 117, 8154 – 8158; b) T. Kato, T. Yamabe, J. Chem. Phys. 2003, 119, 5680 – 5689.

Single-crystal X-ray Crystallography Single-crystal X-ray diffraction data for [D5]R-Py (R = F, I, CH3, and NO2) were collected at 296 K with graphite monochromated MoKa (l = 0.71073 ) radiation on a CCD area detector (Bruker-SMART). Data reductions and absorption corrections were performed with SAINT and SADABS software packages, respectively. Structures were solved by a direct method using the SHELXL-97 software package.[24] The non-hydrogen atoms were anisotropically refined by using the full-matrix leastsquares method on F2. All hydrogen/deuterium atoms were placed at the calculated positions and refined as riding on the parent atoms. Details about data collection, structure refinement, and crystallography are summarized in Table 1. CCDC-867566 ([D5]F-Py), 867567 ([D5]I-Py), 867568 ([D5]CH3-Py), and 867569 ([D5]NO2-Py) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgements We thank the Science and Technology Department of Jiangsu Province and the National Nature Science Foundation of China for financial support (grant nos. BK2010551, 91122011, and 21271103).

[1] R. Jain, K. Kabir, J. B. Gilroy, K. A. R. Mitchell, K. C. Wong, R. G. Hicks, Nature 2007, 445, 291 – 294. [2] S. Ferlay, T. Mallah, R. Ouahs, P. Veillet, M. Verdaguer, Nature 1995, 378, 701 – 703. [3] J. M. Manriquez, G. T. Yee, R. S. McLean, A. J. Epstein, J. S. Miller, Science 1991, 252, 1415 – 1418. [4] N. Ishii, Y. Okamura, S. Chiba, T. Nogami, T. Ishida, J. Am. Chem. Soc. 2008, 130, 24 – 25. [5] a) T. Liu, D. P. Dong, S. Kanegawa, S. Kang, O. Sato, Y. Shiota, K. Yoshizawa, S. Hayami, S. Wu, C. He, C. Y. Duan, Angew. Chem. 2012, 124, 4443 – 4446; Angew. Chem. Int. Ed. 2012, 51, 4367 – 4370; b) S. Takaishi, N. Ishihara, K. Kubo, K. Katoh, B. K. Breedlove, H. Miyasaka, M. Yamashita, Inorg. Chem. 2011, 50, 6405 – 6407; c) M. Nihei, H. Tahira, N. Takahashi, Y. Otake, Y. Yamamura, K. Saito, H. Oshio, J. Am. Chem. Soc. 2010, 132, 3553 – 3560; d) R. D. Willett, C. J. Gmez-Garca, B. L. Ramakrishna, B. Twamley, Polyhedron 2005, 24, 2232 – 2237; e) W. Fujita, K. Awaga, Science 1999, 286, 261 – 263; f) O. Kahn, C. J. Martinez, Science 1998, 279, 44 – 48. [6] a) S. M. Neville, G. J. Halder, K. W. Chapman, M. B. Duriska, B. Moubaraki, K. S. Murray, C. J. Kepert, J. Am. Chem. Soc. 2009, 131, 12106 – 12108; b) G. J. Halder, C. J. Kepert, B. Moubaraki, K. S. Murray, J. D. Cashion, Science 2002, 298, 1762 – 1765. [7] M. E. Itkis, X. Chi, A. W. Cordes, R. C. Haddon, Science 2002, 296, 1443 – 1445. [8] E. Coronado, J. R. Galn-Mascars, C. J. Gmez-Gara, V. Laukhin, Nature 2000, 408, 447 – 449.

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[31] Note: the program used for PXRD pattern simulation can be downloaded free of charge from the website http://www.esc.cam.ac.uk/ astaff/holland/UnitCell.html; it is further described in the following paper: T. J. B. Holland, S. A. T. Redfern, Mineral. Mag. 1997, 61, 65 – 77. [32] W. A. Van Hook, L. P. N. Rebelo, M. Wolfsberg, Fluid Phase Equilib. 2007, 257, 35 – 52. [33] a) R. K. Kremer, R. W. Henn, A. Faißt, J. Wosnitza, H. V. Lçhneysen, Czech. J. Phys. 1996, 46, 1977; b) E. Pytte, Phys. Rev. B 1974, 10, 4637 – 4642.

Chem. Asian J. 2013, 8, 611 – 622


[34] X. M. Ren, G. X. Liu, H. Xu, T. Akutagawa, T. Nakamura, Polyhedron 2009, 28, 2075 – 2079. [35] Y. J. Wang, Y. J. Kim, R. J. Christianson, S. C. Lamarra, F. C. Chou, T. Masuda, I. Tsukada, K. Uchinokura, R. J. Birgeneau, J. Phys. Soc. Jpn. 2003, 72, 1544 – 1553. Received: October 15, 2012 Published online: January 9, 2013

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