Synthesis and Reactivity in Inorganic, Metal-Organic

This article was downloaded by: [KIT Library] On: 18 June 2014, At: 04:58 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lsrt20

Synthesis and Structural Characterization of Two New Schiff Bases incorporating a Piperazine Skeleton, and their Reactions with Copper(II) Perchlorate a

a

a

b

b

Liliana Cseh , Ramona Tudose , Otilia Costisor , Ingo Pantenburg , Gerd Meyer & Wolfgang Linert

c

a

Institute for Chemistry Timisoara of the Romanian Academy , Timisoara, Romania

b

Institute of Inorganic Chemistry , University Köln , Köln, Germany

c

Institute of Applied Synthetic Chemistry , Vienna University of Technology , Vienna, Austria Published online: 13 Jun 2008.

To cite this article: Liliana Cseh , Ramona Tudose , Otilia Costisor , Ingo Pantenburg , Gerd Meyer & Wolfgang Linert (2008) Synthesis and Structural Characterization of Two New Schiff Bases incorporating a Piperazine Skeleton, and their Reactions with Copper(II) Perchlorate, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:4, 382-389 To link to this article: http://dx.doi.org/10.1080/15533170802132253

PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:382–389, 2008 Copyright # 2008 Taylor & Francis Group, LLC ISSN: 1553-3174 print/1553-3182 online DOI: 10.1080/15533170802132253

Synthesis and Structural Characterization of Two New Schiff Bases incorporating a Piperazine Skeleton, and their Reactions with Copper(II) Perchlorate Liliana Cseh,1 Ramona Tudose,1 Otilia Costisor,1 Ingo Pantenburg,2 Gerd Meyer,2 and Wolfgang Linert3 1

Institute for Chemistry Timisoara of the Romanian Academy, Timisoara, Romania Institute of Inorganic Chemistry, University Ko¨ln, Ko¨ln, Germany 3 Institute of Applied Synthetic Chemistry, Vienna University of Technology, Vienna, Austria

Downloaded by [KIT Library] at 04:58 18 June 2014

2

The synthesis of Schiff bases N,N0 -bis(4-dodecyloxy-benzylidene-Npropyl)-piperazine (2) and N,N0 -bis-[4-(40 -octyloxy-benzoic)-esterbenzylidene-N-propyl]-piperazine (6) in a multistep process is reported. The intermediates as well as the products were characterized by elemental analysis, melting point and IR, 1H and 13C-NMR spectroscopy. The complex formation of these Schiff bases with copper(II) perchlorate resulted in disruption of the imino bond and yielded N,N0 -bis(3-aminopropyl)piperazineperchloratocopper(II) perchlorate, Cu(L)(ClO4)2, where L stands for N,N0 -bis(3aminopropyl-)piperazine. The nature of the complex is established by elemental analyses, IR and Raman spectroscopy and its structure by X-ray diffraction measurements. The mesomorphic ordering of the ligands have been checked. Keywords

copper(II) complex, perchlorat complex, Schiff base, spectral properties

INTRODUCTION Most studied and applied liquid crystals are pure organic compounds. In the last decades, the introduction of metal ions leads to a new class of liquid crystals: metallomesogens.[1,2] Metal complexes that contain organic mesogens as ligands can retain these properties. Also, the introduction of a metal ion in an organic compound that does not exhibit liquid crystal properties can lead to a complex with liquid crystal properties. Most of the metallomesogens are thermotropics. According to the shape of the molecules, thermotropic crystals are classified in two main groups: calamitic Received 21 April 2007; accepted 1 August 2007. Thanks for financial support are due to the “Fonds zur Fo¨rderung ¨ sterreich” (Project 19335der Wissenschaftlichen Forschung in O N17). Address correspondence to Liliana Cseh, Institute for Chemistry Timisoara of the Romanian Academy, 24 Bv. M. Viteazu, Timisoara 300223, Romania. E-mail: [email protected]

(rod-like) and discotic (disc-like) or columnar. The molecular requirements of liquid crystals have been summarized[3] as i) stucturally anisotropy, ii) the presence of a permanent dipole and iii) a high anisotropy of polarisability. The liquid crystal phases are characterized by anisotropy of the physical properties like refractive indices, which leads to birefringence, dielectric permittivity and magnetic susceptibilities. Basic principles of the liquid crystals including metallomesogenes are described in some representative works.[3,4] Geometric and structural criteria of the mesomorphism of metallomesogenes have been studied[5] and principles to design metallomesogens with specific ligands have been pointed out.[6] The major distinction between metallomesogenes and the most organic mesogens is the presence of the coordinate bonds that are more or less polarized. As a consequence, the metallomesogenes have a greater tendency to exhibit intermolecular interactions, which affects the molecular packing, and hence, the liquid crystalline properties. Additionally, the coordinative unsaturation favors the metal-metal and/or metal – ligand interactions. These interactions can result in phase behavior with kinetic, structural and thermodynamic complexities, but they also provide an opportunity to create useful supramolecular organizations. However, sometimes these interactions must be tamed to avoid the formation of a coordination polymer. Among the ligands, Schiff bases offer the possibility to control the alignment and orientation of metal complexes in their mesophases and to generate liquid crystalline materials of unconventional structures and properties. This can be realized by attaching alkyl- or alkyl-substituted phenyl groups to the complex cores. The nature and the length of these tails, as well as the nature of the linkage units and that of the terminal substituents allow tuning the phase properties. In this respect, we designed and further obtained the Schiff bases ligands N,N0 -bis(4-dodecyloxy-benzylidene-Npropyl)-piperazine (2) and N,N0 -bis-[4-(40 -octyloxy-benzoic)ester-benzyliden-N-propyl]-piperazine (6), which contain two

382

SYNTHESIS AND CHARACTERIZATION OF TWO SCHIFF BASES

N2 donor sets simmetrically separated by a piperazine fragment, a relative rigid unit. In this context, it should be noted that Schiff bases containing saturate cyclic systems as cyclohexane,[7] 1,3-dioxane,[8] or piperazine[9,10] are well known as mesogens. The designed ligands contain benzenic rings as rigid fragments, -CH55N- or -COO- as linkage units and CnH2nþ1O- as terminal substituents. Thanks to these structural features, nematic properties can be expected. In attempt to obtain metallomegens, some first row metal ions, starting with copper(II), are considered.


EXPERIMENTAL Analyses and Physical Measurements Analytical data were obtained by a Perkin Elmer model 240C elemental analyzer for C, N, and H and the metal ion was determined with GBC SENSAA apparatus. Electric conductivity was measured on DMSO solution with a WTW LF 340 – A conductometer. The thin layer chromatography (TLC): Merck 60 F254 plates were used. Detection was by UV fluorescence (254 nm). Column Chromatography: Flash or gravity column chromatography was carried out using Merck Kieselgel C60 230– 240 mesh silica gel. IR spectra were recorded on a Perkin-Elmer Spectrum One FT-IR spectrophotometer, as KBr pellet, in the 400– 4000 cm21 range. NMR analysis was carried out using a JEOL Lambda 400 FT NMR (400 MHz) spectrometer. Thermomicroscopy was realized under polarized light using an Olympus BH-2 polarizing microscope with Mettler FP52 hot stage linked to an FP5 temperature control unit with an accuracy of measurements of + 18C. Preparation of the Ligands All the reagents and solvents were purchased from Merck, Aldrich, Avocado, Fluka and Lancaster Synthesis and used without further purification, except 2-butanone and dichloromethane. 2-Butanone was dried by distillation under nitrogen and the 798C– 808C fraction was collected. Dichloromethane (DCM) was dried over molecular sieves for a week. Synthesis of 4-dodecyloxy-benzaldehyde (1) has been carried out according to the literature.[11]

H-RMN 400 MHz, CDCl3/d [ppm]: 9.84 (s, 1H, H1); 7.81 (m, 2H, H2,3); 6.98 (m, 2H, H4,5); 4.02 (t, 2H, H6); 1.78 (q, 2H, H7); 1.21 2 1.72 (m, 18H, H8-16); 0.88 (t, 3H, H17); IR (film) nmax [cm21]: 2968, 2939, 2879, 2829, 2738, 1691, 1601, 1578, 1511, 1475, 1465, 1428, 1395, 1315, 1305,

1

383

1261, 1216, 1161, 1130, 1112, 1065, 1045, 1013, 975, 912, 906, 859, 833, 766, 651, 642, 616, 516. Synthesis of N,N0 -bis(4-dodecyloxy-benzylidene-n-propyl)piperazine (2)

2.3 g 4-Dodecyloxy-benzaldehyde (1) (8.2 mmol) dissolved in 20 ml dry methanol was treated with 0.85 ml 1,4-bis(3amino-propyl)-piperazine (4.1 mmol) and further with 2 – 3 drops of glacial acetic. The mixture was refluxed for 1 h and then cooled slowly to room temperature. The formed solid was filtered off and purified by recrystallization from ethanol when a slightly yellow solid was obtained. Yield: 1.4 g (47%); mp ¼ 69 – 70 8C; Anal: calcd for C48H80N4O2 (747.17) C 77.37%, H 10.82%, N 7.52%; found C 77.59%, H 11.11%, N 7.67%; 1H-RMN 400 MHz, CDCl3/d [ppm]: 8.19 (s, 1H, H6); 7.63 (m, 2H, H7,8); 6.90 (m, 2H, H9,10); 3.97 (t, 2H, H11); 3.60 (t, 2H, H5); 2.55 (m, 4H, H1,2); 2.46 (t, 2H, H3); 1.90 (q, 2H, H4); 1.78 (q, 2H, H12); 1.22 – 1.47 (m, 18H, H13-21); 0.87 (t, 3H, H22); IR (KBr pellet) nmax [cm21]: 2943, 2919, 2866, 2846, 2813, 2793, 2766, 2739, 1636, 1606, 1575, 1508, 1471, 1435, 1419, 1393, 1384, 1357, 1315, 1305, 1243, 1162, 1139, 1108, 1048, 1027, 996, 969, 861, 834, 813, 797, 719, 658, 638, 616, 538, 528, 520, 497. Synthesis of 4-octyloxy-benzoic acid methyl ester (3) has been carried out according to the literature.[12]

The crude product was recrystallized three times from methanol resuilting in white crystals. The purity of the product was verified by TLC (silica gel; DCM) when Rf ¼ 0.65. Yield: 50 g h (60%). Anal: calcd for C16H24O3 (264.36) C 72.69%, H 9.15%; found C 72.71%, H 9.37%; 1H-NMR 400 MHz, CDCl3/d [ppm]: 7.90 (m, 2H, H2,3); 6.82 (m, 2H, H4,5); 3.93 (t, 2H, H6); 3.81 (s, 3H, H1); 1.72 (m, 2H, H7); 1.20-1.42 (m, 10H, H8-12); 0.81 (t, 3H, H13). Synthesis of 4-octyloxy-benzoic acid (4) has been carried out according to the literature.[12]


384

L. CSEH ET AL.

Recrystallization of the crude product from chloroform/n-heptane (75 ml/330 ml) resulted in white crystals. Yield: 33 g (73%). Anal: calcd for C15H22O3 (250.33) C 71.97%, H 8.86%; found C 80.21%, H 8.75%; 1H-NMR 400 MHz, CDCl3/d [ppm]: 8.05 (m, 2H, H2,3); 6.92 (m, 2H, H4,5); 4.01 (t, 2H, H6); 1.80 (m, 2H, H7); 1.28-1.45 (m, 10H, H8-12); 0.86 (t, 3H, H13); 13C-NMR 400 MHz, CDCl3/d [ppm]: 172, 164, 132, 121, 114, 78, 77, 76, 68, 32, 29(3), 26, 23, 14; IR (KBr pellet) nmax [cm21]: 3436, 2950, 2927, 2870, 2851, 2673, 2559, 1690, 1607, 1578, 1515, 1464, 1428, 1389, 1330, 1316, 1296, 1256, 1207, 1171, 1147, 1130, 1122, 1109, 1067, 1018, 998, 959, 933, 910, 897, 848, 813, 771, 753, 724, 692, 647, 630, 551, 508, 476, 450.

74.21%, H 8.32%, N 6.51%; 1H-NMR 400 MHz, CDCl3/d [ppm]: 8.22 (s, 1H, H6); 8.06 (dd, 2H, H11,12), J ¼ 8.98; 7.70 (dd, 2H, H7,8), J ¼ 8.61; 7.18 (dd, 2H, H9,10), J ¼ 8.61; 6.89 (dd, 2H, H13,14), J ¼ 8.98; 3.95 (t, 2H, H15); 3.58 (t, 2H, H5); 2.49 (m, 4H, H1,2); 2.40 (t, 2H, H3); 1.85 (q, 2H, H4); 1.75 (q, 2H, H16); 1.18–1.45 (m, 10H, H17 – 21); 0.82 (t, 3H, H22); 13 C-NMR 400 MHz, CDCl3/d [ppm]: 164, 163, 160, 152, 133, 132, 129, 122, 121, 114, 77, 76, 68, 59, 56, 53, 31, 29(2), 25, 22, 14; IR (KBr pellet) nmax [cm21]: 2941, 2923, 2869, 2853, 2807, 2775, 1734, 1646, 1604, 1579, 1510, 1467, 1444, 1418, 1395, 1379, 1353, 1314, 1254, 1221, 1192, 1163, 1065, 1017, 1007, 997, 967, 940, 874, 844, 822, 804, 761, 722, 691, 662, 631, 529, 508.

Synthesis of 4-octyloxy-benzoic acid 4-formyl-phenyl ester (5) has been carried out according to the literature[13]

Preparation of [Cu(L)(ClO4)](ClO4)] 0.1 mmol (0.037 g) Cu(ClO4)2 . 6H2O disolved in 1.5 ml tetrahydrofurane (THF) containing 0.1 mmol of (2) (0.747 g) or (6) (0.873 g) was treated with 1 ml THF containing 0.1 mmol (0.037 g) Cu(ClO4).2 . 6H2O. The mixture was stirred at room temperature for 15 minutes and after 24 h, violet crystals appropriate for X-ray analyse were obtained. Yield: 0.0198 g (43%). Microanalysis: Found: C 25.13; H 4.86; N 12.44; Cl 15.68; Cu 13.69; Required for [Cu(L)(ClO4)](ClO4)]: C 25.93; H 5.18; N 12.10; Cu 13.73. IR(KBr) cm21: 2948, 2885, 1734, 1601, 1510, 1470 vw, 1402 vw, 1310vw, 1267, 1215, 1158, 1105, 929, 915, 882, 862, 845, 834, 790, 760, 690, 623, 514, 492, 481. Raman cm21: 2948, 2889, 1735, 1599, 1468, 1306, 1268, 1159, 1100, 931, 624, 517, 481,461, 352, 277.

The crude product was purified by column chromatography (silica gel; DCM) when Rf ¼ 0.51. The product was obtained as a white solid. Yield: 3.84 g (90.28%); mp ¼ 1038C; Anal: calcd for C22H26O4 (354.44) C 74.55%, H 7.39%; found C 74.31%, H 7.55%; 1H-NMR 400 MHz, CDCl3/d [ppm]: 10.01 (s, 1H, H1); 8.13 (m, 2H, H2,3) J ¼ 8.98; 7.96 (m, 2H, H6,7), J ¼ 8.61; 7.39 (m, 2H, H8,9), J ¼ 8.61; 6.98 (m, 2H, H4,5), J ¼ 8.98; 4.04 (t, 2H, H10); 1.82 (q, 2H, H11); 1.241.52 (m, 10H, H12-16); 0.89 (t, 3H, H17). IR (KBr pellet) nmax [cm21]: 2954, 2931, 2911, 2846, 2824, 1733, 1700, 1605, 1577, 1511, 1468, 1421, 1388, 1269, 1215, 1168, 1099, 1070, 1057, 1009, 995, 956, 912, 881, 844, 813, 795, 759, 719, 690, 663, 628, 512. Synthesis of N,N0 -bis-[4-(40 -octyloxy-benzoic)-ester-benzylidene-n-propyl]-piperazine (6)

1.77 g aldehyde (5) (5 mmol) dissolved in 15 ml dry methanol was treated with 0.51 ml 1,4-bis(3-amino-propyl)-piperazine (2.5 mmol) and further with 2–3 drops of glacial acetic. The mixture was refluxed for 1 h and then cooled slowly to room temperature. The solid was filtered off and purified by recrystallization from ethanol. A slightly yellow solid was obtained. Yield: 4.01 g (92%); mp ¼ 133–1348C; Anal: calcd for C57H72N4O6 (873.17) C 74.27%, H 8.31%, N 6.42%; found C

X-ray Crystallography of [Cu(L)(ClO4)](ClO4) A suitable single crystal was carefully selected under a polarizing microscope and mounted in a glass capillary. The scattering intensities were collected by an imaging plate diffractometer (IPDSII, STOE and CIE) equipped with a normal focus, 1.75 kW, sealed tube X-ray source (Mo Ka, l ¼ 71.073 pm) operating at 50 kV and 35 mA. Intensity data were corrected for Lorentz and polarization effects. A numerical absorption correction based on crystal-shape optimization was applied for all data.[14] The programs used in this work are Stoe’s X-Area,[15] including X-RED and X-shape for data reduction and numerical absorption correction,[16] and the WinGX suite of programs,[17] including SIR-92[18] and SHELXL-97[19] for structure solution and refinement. All hydrogen atoms were taken from the difference Fourier map at the end of the refinement. The last cycles of refinement included atomic positions for all the atoms, anisotropic thermal parameters for all the non-hydrogen atoms and isotropic thermal parameters for all of the hydrogen atoms. Details of the refinements are given in Table 1. Crystallographic data for the structure have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 611035. Copies of the

385


TABLE 1 Crystal data and structure refinement parameters for (1,4-bis(3aminopropyl)piperazine)perchloratocopper(II) perchlorate

TABLE 1 Continued

Cu(C10H24N4)(ClO4)2

Cu(C10H24N4)(ClO4)2 Empirical formula Formula mass [g mol21] Data collection Diffractometer Radiation


Temperature [K] Index range

Rotation angle range Increment No. of images Exposure time [min] Detector distance [mm] 2.u range [deg] Total data collected Unique data Observed data Rmerg Absorption correction Transmission min/max Crystallographic data Crystal size [mm] Colour, habit Crystal system Space group a [pm] b [pm] c [pm] Volume [106 pm3] Z rcalc [g cm23] m [mm21] F(000) Structure analysis and refinement Structure determination No. of variables R indexes [I . 2sI] R indexes (all data)

C10H24N4O8Cl2Cu 462.77 STOE IPDS II Mo-Ka (graphite monochromator, l ¼ 71.073 pm) 120(2) 219 h 19 220 k 18 222 l 22 08 v 1808; c ¼ 08 08 v 1268; c ¼ 908 Dv ¼ 28 153 6 100 2.2 –59.5 54644 4900 3738 0.0627 Numerical, after crystal shape optimization[14, 16] 0.4771/0.7962 0.4 . 0.1 . 0.1 Pink, column Orthorhombic Pbca (no. 61) 1442.8(1) 1503.9(1) 1610.1(1) 3493.6(4) 8 1.760 1.604 1912

Goodness of fit (Sall) Largest difference map hole/peak [e 1026pm23] Deposition number

CCDC-611035

R1 ¼ SjjFoj 2 jFcjj/SjFoj, wR2 ¼ [Sw(jFoj2 2 jFcj2)2/Sw(jFoj2)2]1/2; S2 ¼ [Sw(jFoj2 2 jFcj2)2/(n-p)]1/2, with w ¼ 1/[s2(Fo)2 þ 2 2 . . (0.0519 P) þ 0.6685 P], where P ¼ (Fo þ 2F2c )/3. Fc ¼ kFc [1 þ 0.001 . jFcj2 l3/sin(2u)]21/4.

data can be obtained, free of charge, on application to CHGC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: þ44 1223 336033 or E-mail: [email protected]). RESULTS AND DISCUSSION Compounds and related reactions are sketched in Scheme 1 and Scheme 2. The structure of the two Schiff bases as well as those of the intermediates was inferred from satisfactory elemental analyses, IR and 1H-NMR, which are given in the experimental section. N,N0 -bis(4-dodecyloxy-benzylidene-N-propyl)-piperazine (2), a slightly yellow solid, was synthesized by direct condensation of 4-dodecyloxy-benzaldehyde with 1,4-bis-(3-aminopropyl)piperazine in refluxing absolute methanol as solvent and catalytic amount of glacial acid acetic. The first step consists in synthesis of 4-dodecyloxy-benzaldehyde from 4-hydroxybenzaldehyde and an excess of 1-bromo-dodecane and the reaction was controlled by TLC against 4-hidroxybenzaldehyde (Rf ¼ 0.68). The 1H-NMR spectrum of (1) displays a complex system of signals at higher field with small difference of chemical shift values (0.88, 1.21 –1.72, 1.78 and 4.02 ppm), which proves the presence of the C12 tail. The IR spectrum shows bands around 2900 and 2800 cm21, which can be attributed to CH2 and CH3 belonging to the C12 tail. The IR spectrum of the product (2) shows the characteristic

SIR-92 [18] and SHELX-97 [19] 323 R1 ¼ 0.0353 wR2 ¼ 0.0833 R1 ¼ 0.0524 wR2 ¼ 0.897 (continued)

1.040 20.643/0.588

SCH. 1.


386

L. CSEH ET AL.

SCH. 2.

band of the C55N bond at 1636 cm21.[20] Also, it does not contain the characteristic bands of the reactants, namely that at 3360 and 3280 cm21 in the spectrum of 1,4-bis-(3-aminopropyl)piperazine and that of the corresponding aldehyde at 1691 cm21. The 1H-NMR spectrum of the obtained Schiff base displays signals at 3.60, 2.55, 2.46 and 1.90 ppm, which can be assigned to the protons belonging to the bis –(N-propyl)piperazine fragment. The presence of azomethinic bond is associated with the shift of the the 1H-NMR signal at 9.84 ppm in spectrum of (1) to 8.19 ppm for (2). The synthesis of (6) involves several steps in which the intermediate products (3), (4) and (5) were separated and characterized by TLC, elemental analysis and NMR and IR techniques. The first step involves the alkylation of the 4-hydroxy-benzoic acid methyl ester in basic medium resulting in (3). The 1H-NMR spectrum of (3) displays a complex system of signals (0.81, 1.20 – 1.42, 1.72 and 3.93 ppm) at higher fields with small differences of the chemical shift values attributable to the C8 tail protons. The second step refers to the deprotection of the carboxylic group resulting in the intermediate (4). The success of this step was proved by the 1H- and 13C-NMR spectra. Thus, the signal at 3.81 ppm in the 1H-NMR spectrum of (3), assigned to the three methyl protons, disappeared in the spectrum of (4). The IR spectrum shows a strong C55O stretching absorption at 1690 cm21 and a broad OH stretch absorption at 3436 cm21 characteristic of carboxylic group as dimmers.[20] The third step in Scheme 2 refers to the esterification of the acid (4) in the presence of dicyclohexylcarbodiimide (DCC) and 4-(dimethylamino)pyridine

(DMAP). This approach takes the advantage of DCC to bind water and further, the formation of easy-removable product, dicyclohexylurea. Additionally, it is a one-pot reaction that occurs in mild conditions thus preserving the alkoxy and carbonyl groups. However, the formation of N-acylureas as undesired products is possible, thereby reducing the yields. The success of esterification process and the purity of compound (5) were confirmed by 1H-NMR and IR spectra. Indeed the two groups of signals at 10.01 ppm, and 8.13 and 6.98 ppm and the values of the peak’s integration in the 1H-NMR spectrum, support the presence of the aldehydic group proton and that of the new attached benzene ring, respectively. Concerning the IR spectrum, it can be noticed the disappearance of the band at 3436 cm21 and the presence of a new one at 1700 cm21 associated to the new carbonylic group in (5). The last step refers to the Schiff condensation resulting in the new base N,N0 -bis-[4-(40 -octyloxy-benzoic)-ester-benzylidene-N-propyl]piperazine (6). The new band that appears at 1646 cm21 in the IR spectrum of (6) compared to that of (5), is clearly assigned to the new formed C55N bond. Also, the IR spectrum of compound (6) does not contain the characteristic bands of the reactants, namely that at 3360 and 3280 cm21 in the spectrum of 1,4-bis-(3-aminopropyl) piperazine and that of the corresponding aldehyde at 1700 cm21. The identity of the Schiff base was proved by 1H- and 13C-NMR spectroscopy. Thus, the signal at 10.01 ppm in the 1H-NMR spectrum of (5), was shifted in the spectrum of (6) at 8.22 ppm due to the formation of azomethinic bond. In

387



addition, new signals at 3.58, 2.49, 2.40, and 1.85 ppm appear in the spectrum of (6), which is attributed to protons belonging to the bis – (n-propyl)piperazine fragment. The peaks attributable to the solvent, in the 13C-NMR spectrum, can be noticed as a triplet at d 77 ppm. Assuming this signal as reference,[21] the peaks to the left side, at 53, 56, and 59 ppm, can be assigned to the saturated carbons bonded to the nitrogen atoms. Mesomorphic Ordering of Schiff Bases The potential mesogenic properties of (2) and (6) have been checked with a polarizing microscope equipped with a heating stage, and a single melting point has been noticed at 69– 708C and 133– 1348C, respectively. Although the new Schiff bases contain the characteristic structural features, they do not show any mesogenic properties. This behavior may be explained by the flexibility of molecules. However this disadvantage can be overruled if these ligands are included in an appropriate metal complex, as one can expected that the newly formed metal-ligand bonds would decrease the flexibility of the organic molecule. Both (2) and (6) contain four potential donor atoms. Depending on the conformation of the piperazine bridge, they can act as a bis-bidentate ligands or as tetradentate ones. In the first case, piperazine moiety adopts the energetically stable chair conformation, thus leading to binuclear complexes. Mononuclear complexes can be expected when piperazine adopts the bath conformation. The preference for a nature or other is also strongly imposed by the geometry of the metal ion. Thus, our previous works[22] have shown that in the presence of copper(II), mononuclear complexes have been obtained with the piperazine in a bath conformation. Considering this experience and considering our intention to create a more rigid molecule, copper(II) was chosen. In order to obtain copper containing mesogen, an absolute methanolic dry tetrahydrofurane solution of the Schiff base ligand was treated with copper(II) perchlorate. When either (2) or (6) was used, pink-violet crystals were isolated in high yield, the elemental analysis of which was in agreement with N,N0 -bis(3-aminopropyl)piperazineperchloratocopper(II) perchlorate, Cu(L)(ClO4)2, where L stands for N,N0 -bis(3-aminopropyl-)piperazine. The infrared spectrum shows a shift of the n(NH) band (3315 and 3268 cm21) energies lower than those in the free L-ligand (3357 and 3295 cm21), whereas the d(NH) band is observed at 1601 cm21.[23] These bands are also Raman active. The relatively weak bands around 3000 cm21 are assigned to the n(CH2) mode of the propylene groups. The strong absorption bands at 1158 (R 1159) and the weak ones at 929 (R 931) and 481 cm21 (R 481) are present, attributable to the n4, n2 and n6 modes, respectively, of a unidentate perchlorate. The strong and large band at 1105 (R 1100) covers the n3 and n1 modes of the ionic and monodentate perchlorate whereas that at 624 (R 623) cm21overlaps the bending modes n4 and the n3 and n5 of the ionic and and monodentate perchlorate, respectively.[24]

FIG. 1. Central projection of the asymmetric unit of Cu(C10H24N4)(ClO4)2 showing the atom numbering scheme. H atoms have been omitted for clarity.

The pink crystals were suitable for the X-ray analysis. The complex crystallizes in orthorombic, space group Pbca (no. 61) with Z ¼ 8. The structure of the complex with atom numbering scheme is shown in Figure 1 and selected bond lengths and angle data are gathered in Table 2. The structure is consistent with a complex cation and a perchlorate anion. In the complex cation, copper(II) center has a typical square pyramidal geometry made up by the four nitrogen atoms of the organic ligand. The apical position is occupied by an oxygen atom of one of the perchlorate group. The molecular structure of Cu(L)(ClO4)2, has been already described[25] and our data agree well with them. However, the packing diagram presented in Figure 2 shows a strong difference, which may be the result of its formation. It can be noticed that two complex units are associated along a pyramidal line forming a block. The blocks are disposed alternatively so that they describe a zigzag chain. The uncoordinated perchlorate groups are located in the angles formed by these chains. The forces that

TABLE 2 Selected internuclear distances [pm] and angles [deg] for (1,4-bis(3-aminopropyl)piperazine)-perchlorato-copper(II) perchlorate Cu-N1 Cu-N10 Cu-N14 Cu-N5 Cu-O12

199.5(2) 201.4(2) 202.0(2) 206.1(2) 245.6(2)

N1-Cu-N10 N1-Cu-N14 N10-Cu-N14 N1-Cu-N5 N10-Cu-N5 N14-Cu-N5 N1-Cu-O12 N10-Cu-O12 N14-Cu-O12 N5-Cu-O12

166.32(7) 90.82(8) 96.64(8) 95.84(7) 74.35(7) 165.10(7) 85.98(7) 103.76(7) 100.80(7) 92.96(7)

388

L. CSEH ET AL.

REFERENCES


FIG. 2. Perspective view of the unit cell in the crystal structure of Cu(C10H24N4)(ClO4)2.

TABLE 3 Hydrogen bonds with H..A , r(A) þ 2.000 Angstroms and ,DHA. 110 deg d(D-H)

d(H..A)

,DHA

d(D..A)

A

N1-N15 N1-H15

0.947 0.947

2.113 2.832

157.38 131.73

3.009 3.534

O21 Cl2

N1-H19 N1-H19

0.903 0.903

2.632 2.658

119.87 127.85

3.179 3.290

O22 O211

N14-H21

0.913

2.309

152.98

3.150

O21

N14-H23 N14-H23

0.858 0.858

2.449 2.565

139.41 135.57

3.151 3.234

O13 O11

D-H

lead to such a construction are intra- and intermolecular hydrogen bonds, as it results from the data presented in Table 3.

CONCLUSIONS Two new Schiff bases were obtained and characterized. The study of the mesomorphic ordering of Schiff base has shown the flexibility of the molecule that unfortunately does not promote liquid crystal properties. The formation of a rigid core by complexation of the aminic groups failed due to the destruction of the imino groups and formation of N,N,-bis (3-aminopropyl)piperazineperchloratocopper(II) perchlorate, which shows a monodimensional structure. The presence of the trace amounts of water arising from copper(II) perchlorate hexahydrate and the catalytic activity of the copper(II) ions can explain the splitting of the imino bond. Investigations considering other metal ions as well as catalytic effect of the copper(II) are in progress.

1. J.L. Serrano, (ed.), Metallomesogens, 1996, VCH, Weinheim. 2. B. Donnio, D. Guillon, R. Deschenaux, and D.W. Bruce, Metallomesogens, in Comprehensive Coordination Chemistry II, J.A. McCleverty and T.J. Meyer (eds.), Elsevier Ltd, 2004, vol. 7, 357–627. 3. P. Collings and M. Hird, An Introduction to Liquid Crystals: Chemistry and Physics, 1997, Taylor & Francis, London, pp. 300. 4. (a) D. Demus and T. Inukai, Empirical Relation between Order Parameter and Nematic-isotropic Transition Temperature, Mol. Cryst. Liq. Cryst., 2003, 400, 59 – 69 and references therein; (b) D.W. Bruce, Metal-containing Liquid Crystals, In Inorganic Materials, 2nd Edn.; D.W. Bruce and D. O’Hare (eds.), Chichester: Wiley, 1996. 5. (a) A.M. Giroud-Godquin. Metal-containing liquid crystals, in Handbook of Liquid Crystals, Demus, D. (ed.), VCH Verlag GmbH, Weinheim: Wiley, 1998, pp. 901– 932; (b) Y.G. Galyametdinov, I.G. Bikchantaev, and I.V. Ovchinnikov, Influence of Geometry of Chalate Node on the Manifestation of Liquid-crystal Properties in Transition-metal Complexes with the Schiff-Base, Zhur. Obsh. Khim., 1988, 58, 1326– 1331. 6. R.W. Date, E.F. Iglesias, K.E. Rowe, J.M. Elliott, and D.W. Bruce, Metallomesogens by Ligand Design, Dalton Transactions, 2003, 1914 –1931. 7. S. Asahina, M. Sorai, and R. Eidenschink, Calorimetric Study of the Relationship between Molecular Structure and Liquid-crystallinity of Rod-like Mesogens. I. Heat Capacities and Phase Transitions of 40 -propylbiphenyl-4-carbonitrile and trans,trans-40 propylbicyclo-hexyl-4-carbonitrile, Liq. Cryst., 1991, 10, 675–90 and references therein. 8. D. Demus and H. Zaschke, Synthesis and Properties of New Liquid Crystalline Materials, Mol. Cryst. Liq. Cryst., 1981, 63, 129–144. 9. S. Takenaka, T. Hirohata, and S. Kusabayashi, The Thermal Properties of Liquid Crystalline Materials Incorporating a Piperazine Skeleton, Bull. Chem. Soc. Jpn., 1985, 58, 1079. 10. A.S. Angeloni, M. Lans, C. Castellari, G. Galli, P. Ferruti, and E. Chiellini, Liquid Crystalline Poly(aminoester)s Containing Different Mesogenic Groups, Makromol. Chem., 1985, 186, 977–97. 11. G.-W. Gray and B. Jones, Mesomorphism and Chemical Constitution. Part II. The trans-p-n-alkoxycinnamic Acids, J. Chem. Soc., 1954, 1467 –1470. 12. S. Diez, D.A. Dunmur, M.R. de la Fuente, P.K. Karahaliou, G.H. Mehl, T. Mayer, M.A. P. Jubindon, and D.J. Photinos, Dielectric Studies of a Laterally-linked Siloxane Ester Dimer, Liq. Cryst., 2003, 30, 1021– 1030. 13. X.-H. Liu, M.N. Abser, and D.W. Bruce, Synthesis and characterization of rod-like metallomesogens of Mn(I) based on Schiff base ligands, J. Organomet. Chem., 1998, 551, 271– 280. 14. STOE & Cie GmbH, X-Shape 1.06, Crystal Optimisation for Numerical Absorption Correction (C), Darmstadt, Germany, 1999. 15. Stoe & Cie GmbH, X-Area V. 1.16, Darmstadt, Germany, 2003. 16. Stoe & Cie GmbH, X-RED V. 1.22, Stoe Data Reduction Program (C), Darmstadt, Germany, 2001. 17. L.J. Farrugia and V. WinGX, 1.64.02, An Integrated System of Windows Programs for the Solution, Refinement ans Analysis


18.

19. 20. 21.


22.

of Single Crystal X-Ray Diffraction Data, J. Appl. Crystallogr., 1999, 32, 837– 838. A. Altomare, G. Cascarano, and C. Giacovazzo, SIR-92, A Program for Crystal Structure Solution, J. Appl. Crystallogr., 1993, 26, 343– 350. G.M. Sheldrick, SHELXL-97; Programs for Crystal Structure Analysis, 1997, University of Go¨ttingen, Germany. L.J. Bellamy, The Infrared Spectra of Complex Molecules, 3rd Edn., Vol. 2, pp. 320, 1980, Chapman and Hall, London. R.M. Silverstein and F.X. Webster, Spectrometric Identification of Organic Compounds, 6th Edn. 1997, John Wiley & Sons, USA. (a) P. Weinberger, O. Costis¸or, R. Tudose, O. Baumgartner, and W. Linert, A Novel Mixed Valence Copper(I)-copper(II)-bis(antipyril-methyl)-piperazine Complex: Synthesis, Molecular Structure and Spectroscopic Characterization, J. Mol. Struct., 2000,

389

519, 21 –31; (b) O. Costisor, R. Tudose, I. Pantenburg, and G. Meyer, A New Copper(II) Complexes with N,N0 -Bis(antipiryl-4-methyl)-piperazne (BAMP) Ligand, Z. Naturforschung, 2002, 57B, 1454–1460. ´´ zpozan, D. Ku´´c¸u´´kusta, and Z. Bu´´yu´´kmumcu, Vibrational 23. T. O Spectra, Normal Coordinate Treatment and Simulation of the Vibrational Spectra of Piperazine Glyoxime and its Co(III) Complex, J. Mol. Struc., 2003, 661– 662, 647– 657. 24. N.M. Gowda, S.B. Naikar, and G.K.N. Reddy, Perchlorate Ion Complexes, Adv. Inorg. Chem., Radiochem., 1984, 28, 255– 299. 25. S.S. Massoud and F.A. Mautner, Synthesis, Characterization, and Crystal Structure of 1,4-bis(3-aminopropyl)piperazineperchloratocopper(II) Perchlorate, Inorg. Chem. Commun., 2004, 7, 559– 562.