Received: 13 March 2018
Revised: 2 October 2018
Accepted: 11 October 2018
DOI: 10.1002/aoc.4684
REVIEW
Structure, atomic Hirshfeld surface, spectroscopic studies and magnetic and dielectric properties of new mixed solid solution (NH4)2Mn0.17Cu0.83Cl4⋅2H2O Nouha Messoudi1
| Manuel Almeida Valente2 | Essebti Dhahri3 | Mohamed Loukil1
1
Laboratoire des Sciences des Matériaux et d’Environnement, Faculté des Sciences de Sfax, Université de Sfax, BP 1171, Route de Soukra, 3018 Sfax, Tunisia 2
I3N and Physics Department, University of Aveiro, 3810‐193 Aveiro, Portugal 3
Laboratoire de Physique Appliquée, Faculté des Sciences de Sfax, 3000 Sfax, Tunisia Correspondence Nouha Messoudi, Laboratoire des Sciences des Matériaux et d’Environnement, Faculté des Sciences de Sfax, BP 802, 3018 Sfax, Tunisia. Email:
[email protected]
The tetrachlorocupratmanganate dehydrate (NH4)2Mn0.17Cu0.83Cl4⋅2H2O has been prepared and characterized using various physicochemical techniques including Fourier transform infrared and Raman spectroscopies, differential scanning calorimetry and dielectric and magnetic measurements. A preliminary single‐crystal X‐ray diffraction structural analysis reveals that the title compound belongs to the tetragonal system with P4(2)/mnm space group. The unit cell dimensions are: a = b = 7.5817(2), c = 7.9312(2) Å, with Z = 2. Its crystal structure was determined and refined down to R = 2%. The structure of this compound consists of discrete [Cu/MnCl4⋅2H2O]2− octahedra interleaved with alkali cations. The cohesion and stabilization of the structure are provided by hydrogen bond interactions (N─H…Cl and O─H…Cl) between [NH4]+ cation and [Cu/MnCl4⋅2H2O]2− anion. Hirshfeld surface analysis has been performed to explore the behaviour of these weak interactions. Dielectric measurements confirm the transition temperatures determined using differential scanning calorimetry. The temperature dependence of the magnetic susceptibility was measured in the temperature range 10– 300 K at various magnetic field intensities. Magnetic measurements reveal the occurrence of weak ferromagnetic behaviour at low temperature (Tc = 12 K). The ferromagnetic ordering is further confirmed by the presence of hysteresis loops. KEYWORDS dielectric properties, DSC, ferromagnetic–paramagnetic transition, Hirshfeld surface analysis
1 | INTRODUCTION Diammoniumtetrachlorocupratmanganate dehydrate, (NH4)2Mn0.17Cu0.83Cl4⋅2H2O, is a newly synthesized compound. Crystals of dihydrate tetrahalogen metallates (A2BX4⋅2H2O) may contain the following ions: A = NH4, K, Rb, Cs; B = Cu, Mn, Ca, Ni; X = Cl, Br. The crystals from this family can be divided into two classes according to their symmetry and structure. The first class includes compounds with copper Appl Organometal Chem. 2018;e4684. https://doi.org/10.1002/aoc.4684
ions which crystallize at room temperature in tetragonal symmetry with the P4(2)/mnm space group. The crystals with Mn2+, Ca2+ and Ni2+ ions represent the second class with triclinic symmetry and the P‐1 space group. These crystals show a variety of spectroscopic and transport properties, as a function of both temperature and pressure. These types of crystals have attracted considerable interest due to their physical properties and multiple phase transitions (order–disorder, commensurate–
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incommensurate, first order and second order transitions) related to the dynamics of the inorganic cation which may occur in phases with ferroelectric or ferroelastic ordering.[1–4] In this paper, we report the structure of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O at room temperature in order to examine the influence of a partial substitution of Cu2+ by Mn2+ in (NH4)2CuCl4⋅2H2O on crystalline symmetry and physical properties.
TABLE 1
Crystal structure data and experimental conditions for structure determination of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O Summary of crystallographic data T = 293(2) K
2 | EXPERIMENTAL
Formula
(NH4)2Mn0.17Cu0.83Cl4.2H2O
Formula weight
552
Space group
P42/mnm
a = b (Å)
7.5817(2)
c (Å)
7.9312(2)
3
V (Å )
455.90(2) 2
Z
2.1 | Crystal growth
−3
ρcalc (g cm ) −1
Single crystals of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O were grown by the slow evaporation solution growth method. Ammonium chloride, manganese(II) chloride and copper(II) chloride (from Sigma‐Aldrich, 99.9%) were dissolved at a molar ratio of 2:1:1 in distilled water and mixed well using a magnetic stirrer to ensure homogeneous concentration in the solution. The mixture was allowed to evaporate at room temperature for a few days until parallelepiped single crystals of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O were formed. The measured average value of density (Dm = 2.011 g cm−3) is in agreement with that calculated (Dx = 1.998 g cm−3). The reaction involved in the formation of the complex compound is
μ (mm )
3.35 0.20 × 0.12 × 0.04
Crystal shape
Parallelepipedic
F (000)
276.6
Data collection instrument
Bruker Kappa‐APEX II
Radiation: graphite monochromator
λKα
θ range for data collection (°)
3.7–25.4
Index ranges
−7 ≤ h ≤ 9; −5 ≤ k ≤ 9; −8 ≤ l ≤ 9
Total reflections
1354
Reflection with ( F > 4σ( F ))
251
WR2 (%)
H2 O
þ ð1 − x ÞCuCl2 !NH4 Mnx Cu1−x Cl4 ⋅2H2 O
2.2 | Hirshfeld surface analysis The intermolecular interactions[7,8] in the crystal structure were quantified using Hirshfeld surface analysis.
2.011
Crystal size (mm3)
R( F ) (%)
NH4 Cl þ xMnCl2
A suitable single crystal with dimensions of 0.20 × 0.12 × 0.04 mm3 was chosen for structural determination. The data were collected with a Bruker APEXII CCD four circle diffractometer using Mo Kα (λ = 0.71073 Å) radiation at room temperature. The structure was determined by Patterson methods using the SHELXS‐97 program. In the closest solution proposed by the program, only some atoms of manganese and copper were located. Using the SHELXL‐97[5,6] program, refinements followed by Fourier differences are necessary to find the positions of other atoms remaining in the lattice to an R factor of 2% for all reflections. The structure graphics were drawn with Diamond 2.1 supplied by Crystal Impact. A summary of crystallographic data, recording conditions and structure refinement results of the title compound is given in Table 1.
ET AL.
a
b
Rint–Rσ
Mo
(0.71073 Å)
0.0203 0.0554 0.0174–0.0124
R= ║FO│2–│FC║2 ⁄│FO│ 1 = 2 2 ∑½wðjF O j2 −jF C j2 Þ WR2 ¼ 2 ∑½wðjF O j2 Þ
a
b
The molecular Hirshfeld surface calculations, their associated two‐dimensional fingerprint plots[9,10] and the crystal voids were performed using Crystal Explorer 3.0,[11] which accepts a structure input file in the CIF format. This approach has been built on the electron distribution calculated as the sum of spherical atom electron densities.[12]
2.3 | Spectroscopic analysis The Fourier transform infrared (FT‐IR) measurements were performed at room temperature using a PerkinElmer FT‐IR Paragon 1000 PC spectrometer over the range 400–4000 cm−1, with samples in a KBr pellet. Furthermore, Raman spectra were measured with a LABRAMHR 800 triple monochromator at room temperature under a 50× LF objective microscope. A He–Ne ion
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laser operating at about 20 mW was used (on the sample) as an excitation source (514.5 nm), with spectral steps of 3 cm−1. The Raman spectra were recorded in the range 50–500 cm−1.
2.4 | Differential scanning calorimetry (DSC) DSC measurements were carried out using a DSC Q2000 TA calorimeter, by putting a powder sample (about 7.6 mg) in an aluminium capsule. DSC was conducted in two regions, one from 0 to 300 K and the other between 150 and 500 K, with heating/cooling rates of 5 K min−1 in an inert atmosphere (nitrogen gas).
2.5 | Dielectric study
FIGURE 1
Crystals of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O were crushed and pressed to a dense and translucent pellet (8 mm in diameter; 1 mm in thickness) at a pressure of 200 MPa and room temperature. The pellet was sandwiched between metal electrodes. Electrical permittivities were measured in the frequency range 2000 Hz–10 MHz with a TEGAM 3550 ALF automatic bridge monitored by a microcomputer. The measurements were taken over the temperature range 300–500 K.
trans‐positions (Tables 2 and 3). The chlorine ions form a rhombus in the (a–a) plane. The crystal lattice is a layered structure. One layer consists of planar Cu/MnCl4 anions with two long Cu/Mn─Cl(II) bonds of 2.96 Å and two shorter Cu/Mn─Cl(I) bonds of 2.26 Å. The second layer is constituted of oxygen atoms, water molecules and nitrogen atoms from disordered NH4+ ions (Tables 4 and 5). The ammonium NH4+ cations is surrounded by a cage of four water molecules and eight chlorine ions, which form a slightly distorted cube with N─Cl distances very close to that in NH4Cl. Thus, the NH4+ tetrahedron has two almost energetically equivalent configurations and, at room temperature, the system is expected to be in a disordered state with both the orientations almost equally probable. Ammonium cations in this room temperature phase are interposed along the c axis between the Cu/MnCl4O2 octahedra. The nitrogen in the NH4+ cation has a tetrahedral environment surrounded by four hydrogen atoms.
2.6 | Magnetic study Magnetic measurements of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O were performed using a physical property measurement system magnetometer from Quantum Design operating up to 10 T. The magnetic ordering temperature was determined from the temperature dependence of the magnetization measured in magnetic field of 1 T and in a temperature range of 10–300 K.
3 | R E S U L T S AN D D I S C U S S I O N
TABLE 2 Fractional atomic and equivalent thermal parameters
3.1 | Crystal structure The crystal structure of (NH4)2Mn0.17Cu0.83Cl4⋅2H2O is shown in Figure 1. The symmetry is tetragonal with P42/mnm space group. The unit cell contains two formula units, related to each other by the 42 axis parallel to the c axis. The copper and manganese ions at ±0.5,0.5,0, (2b Wyckoff notation), are surrounded by a distorted octahedron of four chlorine ions and two water molecules. The copper manganese sites are an inversion centre. The oxygen ions of water molecules are situated at approximately ±0.5,0.5,−0.245,(4e Wyckoff notation), which occupy
Perspective view of the title compound
x
y
Uiso*/Ueq Occ. ( 425 K, the reorientational dynamics of alkyl cations is activated. The cation gets enough excitation thermal energy to be able to respond to the change in the external electric field more easily. This in turn enhances the contribution to the polarization leading to an increase of dielectric behaviour. The variation of tan δ with temperature is a general tendency in ionic solids. It may be due to space charge polarization caused by impurities or interstitials in the materials. This dielectric anomaly appears when the jumping frequency of localized charge carriers becomes approximately equal to that of the externally applied electric field. Further, as the frequency increases, the peaks become less pronounced. This can be explained by the fact
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that beyond a certain frequency of external field, the charge carriers cannot follow the alternating electric field.
3.6 | Magnetic properties Figure 10 displays the thermal magnetization M(T) curve under an applied magnetic field of 1 T in the temperature range 10–300 K for (NH4)2Mn0.17Cu0.83Cl4⋅2H2O. It is clear that the sample shows a very sharp ferromagnetic transition around the Curie temperature TC = 12 K, which is calculated from the minimum of the dM/dT curve (inset of Figure 10).[19] From the M(T) data, one can also determine the inverse of susceptibility χ−1 as a function of temperature under 1 T (Figure 11). In the paramagnetic region, this curve can be fitted by the modified Curie–Weiss law: χ ¼
C þ χ0 T − θp
The Curie constant (C) and Weiss constant (θp) were obtained by linear fitting χ−1 in this temperature range. Intersection point with the horizontal axis gives the value of θp. The slope gives the value of C (Table 7). The negative value of the Weiss constant reveals antiferromagnetic interactions between near‐neighbour copper and manganese atoms at low temperature. The TC value is higher than θp. Generally, the difference between θp and TC depends on the substance and is associated with the presence of short‐range order slightly above TC, which may be related to the presence of a magnetic inhomogeneity. According to the (NH4)2Mn0.17Cu0.83Cl4⋅2H2O composition, the calculated effective paramagnetic moment (μThe eff ) should be
FIGURE 10
Temperature dependence of magnetization for (NH4)2Mn0.17Cu0.83Cl4⋅2H2O sample at a magnetic field of 1 T
FIGURE 11
Evolution of magnetic susceptibility and its inverse for (NH4)2Mn0.17Cu0.83Cl4⋅2H2O
μThe eff ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi xμ2eff Cu2þ þ ð1 − x Þμ2eff Mn2þ
2+ 2+ The with μThe eff (Cu ) = 1.73 μB and μeff (Mn ) = 5.92 μB. The experimental effective paramagnetic moment values were determined from
μexp eff ¼
pffiffiffiffiffiffi 8C
The constant C is related to the effective paramagnetic moment by the following relation: C¼
N 2g μ2B J ðJ þ 1Þ 3K B
¼
Nμ2B 2 μ 3K B eff
where N = 6.023.1023 mol−1 refers to the Avogadro number, μB = 9.274 × 10−21 emu is the Bohr magneton and KB = 1.38016 × 10−16 erg K−1 is the Boltzmann constant. These values are listed in Table 7. The experimental values can be compared to calculated ones. We conclude that the measured effective magnetic moments in the paramagnetic regime are significantly larger than the calculated ones. This result is commonly observed in manganites and is generally attributed to spin–orbit coupling.[20,21] We also measured hysteresis loops between −10 and 10 T at 10 K. Figure 12 shows the behaviour of magnetization (M) versus the magnetic field (H) for (NH4)2Mn0.17Cu0.83Cl4⋅2H2O. We can deduce that this compound is magnetically soft. A definitely narrow hysteresis loop is observed, in agreement with the existence of a ferromagnetic ordering of these single crystals below the transition temperature TC.[22,23] In order to determine the magnetic behaviour (ferromagnetic state, coexistence of a ferromagnetic and antiferromagnetic state, non‐saturation of the compound,
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TABLE 7
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Magnetic characteristics of the (NH4)2Mn0.17Cu0.83Cl4·2H2O compound
Compound
TC (K)
θp (K)
C (emu K Oe−1 mol−1)
μ The eff (μB)
μ exp eff (μB)
(NH4)2Mn0.17Cu0.83Cl4⋅2H2O
12
−2.49
0.38
2.20
1.74
FIGURE 12 Magnetization hysteresis curve (M versus H) measured at 10 K and in external magnetic fields from −100 to +100 kOe for (NH4)2Mn0.17Cu0.83Cl4⋅2H2O
etc.) of our sample, we carried out magnetization measurements as a function of the magnetic field applied at different temperatures on both sides of the Curie temperature. The isotherms of the magnetization M(H, T) of our compound depicted in Figure 13 show that the studied sample has a ferromagnetic behaviour at low temperature. Note that as the applied magnetic field increases, the material changes from a paramagnetic state to a
FIGURE
13 Isotherm magnetization (NH4)2Mn0.17Cu0.83Cl4⋅2H2O
curves
M(H)
ferromagnetic state. This effect is all the more important when the magnetization is for a field μ0H < 1 T indicating the displacement of the Bloch walls. As soon as the applied magnetic field increases, 1 T < μ0H < 10 T, the magnetic moments remain frozen, and afterwards our materials do not reach saturation. For this sample the magnetization does not reach saturation even for magnetic fields up to 10 T. The observed weak ferromagnetic behaviour could be due to local geometric disorder around the copper and manganese atoms, inside the layer, which will cant the spins. When the temperature increases, the magnetization curves are in the same way standard, but spontaneous magnetization MSP(T) decreases because of thermal agitation. At the Curie temperature TC, MSP(T) is cancelled. For T > TC, the substance is paramagnetic and the magnetization curves according to the magnetic field applied for various temperatures become increasingly linear. To determine with precision the Curie temperature and the nature of the transition, the Arrott plots obtained from the magnetic field dependence of isothermal magnetization are shown in Figure 14. These plots give a positive slope in the complete (H/M) range, which confirms that our sample exhibits a second‐order phase transition. Following the mean‐field theory, the curves in the vicinity of TC should be parallel straight lines and the line at T = TC has to pass through the origin. In this case, the curves are linear and show upward curvature even at high field. All this information shows that the transition
for
FIGURE 14
Arrott curves for (NH4)2Mn0.17Cu0.83Cl4⋅2H2O
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from ferromagnetic to paramagnetic state at TC = 12 K is a second‐order phase transition.
4 | CONCLUSIONS The tetrachlorocupratmanganate dehydrate (NH4)2Mn0.17 Cu0.83Cl4⋅2H2O has been prepared and studied using X‐ ray diffraction, Raman and FT‐IR spectroscopies, DSC and dielectric and magnetic measurements. The (NH4)2Mn0.17Cu0.83Cl4⋅2H2O salt is tetragonal with the P4(2)/mnm space group. The complex exhibits weak antiferromagnetic coupling between the copper(II) and manganese(II) centres. The magnetic susceptibility follows the modified Curie–Weiss law, characterized by a negative Weiss constant (θ = −2.5). At low temperature, the negative Weiss temperature confirms the antiferromagnetic interactions in the (NH4)2Mn0.17Cu0.83Cl4⋅2H2O compound. ACK NO WLE DGE MEN TS This work was supported by the Tunisian National Ministry of Higher Education, Scientific Research and the Portuguese Ministry of Science.
ET AL.
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CCDC 1559942 contains 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. Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/ j.ica.2013.06.046.
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ORCID Nouha Messoudi
https://orcid.org/0000-0003-3666-9948
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[23] H. Forstat, J. N. McElearney, P. T. Baily, XI Int. Conf. Low Temp. Phys., St Andrews 1967, 2, 1349.
How to cite this article: Messoudi N, Valente MA, Dhahri E, Loukil M. Structure, atomic Hirshfeld surface, spectroscopic studies and magnetic and dielectric properties of new mixed solid solution (NH4)2Mn0.17Cu0.83Cl4⋅2H2O. Appl Organometal Chem. 2018;e4684. https://doi.org/ 10.1002/aoc.4684
