Crystal structure of bis­(tetra­methyl­thio­urea-κS)bis­(thio­cyanato-κN)nickel(II)

Jochim, A.; Radulovic, R.; Jess, I.; Näther, C.

doi:10.1107/S2056989020015121

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Volume 76| Part 12| December 2020| Pages 1841-1845

https://doi.org/10.1107/S2056989020015121

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Crystal structure of bis(tetramethylthiourea-κS)bis(thiocyanato-κN)nickel(II)

Aleksej Jochim,^a ^* Rastko Radulovic,^a Inke Jess ^a and Christian Näther ^a

^aInstitut für Anorganische Chemie, Christian-Albrechts-Universität Kiel, Max-Eyth-Str. 2, D-24118 Kiel, Germany
^*Correspondence e-mail: ajochim@ac.uni-kiel.de

Edited by B. Therrien, University of Neuchâtel, Switzerland (Received 29 October 2020; accepted 13 November 2020; online 17 November 2020)

In the course of our investigations regarding transition-metal thiocyanates with thiourea derivatives, the title compound, [Ni(NCS)₂(C₅H₁₂N₂S)₂], was obtained. The asymmetric unit consists of one thiocyanate anion and one tetramethylthiourea molecule on general positions, as well as one Ni^II cation that is located on a twofold rotational axis. In this compound, discrete complexes are formed in which the Ni^II cations are surrounded by two trans-N-bonding thiocyanate anions as well as two trans-S-bonding tetramethylthiourea molecules within a distorted square-planar coordination geometry. The discrete complexes are linked by pairs of weak C—H⋯S hydrogen bonds between the thiocyanate S and one of the tetramethylthiourea methyl hydrogen atoms into chains along the crystallographic a- and c-axis directions, which are combined into layers parallel to the ac plane. X-ray powder diffraction proves that a pure crystalline phase was obtained and measurements using thermogravimetry and differential thermoanalysis reveal that the compound decomposes at about 408 K, where all tetramethylthiourea molecules are lost.

Keywords: crystal structure; nickel thiocyanate; tetramethylthiourea; discrete complexes; thermal properties.

CCDC reference: 2044233

1. Chemical context

Many thiocyanate coordination compounds are reported in the literature, which mostly consist of discrete complexes containing non-bridging N-terminally coordinated thiocyanate anions, while compounds in which the metal cations are bridged by these anionic ligands are comparatively rare. Despite this fact, a variety of coordination modes can be found for bridging thiocyanate anions, which leads to metal–thiocyanate networks with different dimensionalities and topologies (Wöhlert et al., 2014 ; Lin, 2008 ; Li et al., 2014 ; Suckert et al., 2016 ). If these compounds contain paramagnetic metal cations, they are of special interest, because thiocyanate anions can mediate magnetic exchange and thus cooperative magnetic phenomena can be expected (Palion-Gazda et al., 2015 ; Mekuimemba et al., 2018 ; Mousavi et al., 2020 ; Rams et al., 2020 ; Mautner et al., 2018 ). Our interest focuses mainly on transition-metal thiocyanates with the general composition [M(NCS)₂(coligand)₂]_n with M = Mn^II, Fe^II, Co^II or Ni^II that consist of linear chains, in which the metal cations are connected by pairs of N- and S-bonding thiocyanate anions into centrosymmetric M₂(NCS)₂ units, while the remaining sites of the coordination octahedron are occupied by neutral coligands forming a coordination environment in which all ligands are trans (Wöhlert et al., 2014; Werner et al., 2014 , 2015 ; Prananto et al., 2017 ). In this context, it is noted that the Co^II compounds are of special interest, because either ferromagnetic behavior or a slow relaxation of the magnetization is observed (Werner et al., 2015; Neumann et al., 2019 ; Rams et al., 2017 , 2020). Besides these chain compounds with an all-trans coordination environment, several other isomers with different cis–cis–trans arrangements of the ligands can be found in which either the coligand, the N-bonding or the S-bonding thiocyanate are trans, while the other ligands are cis (Maji et al., 2001 ; Shi et al., 2007 ; Rams et al., 2017). For most of these compounds, corrugated chains are observed in which the magnetic exchange is low or negligible (Böhme et al., 2020 ; Jochim et al., 2018 ). In the case of [M(NCS)₂(4-chloropyridine)₂]_n (M = Co, Ni), two isomeric compounds are observed that contain either linear or corrugated chains, which allowed investigations on the influence of the chain geometry on the magnetic behavior, because both compounds contain the same coligand and thus all differences in the magnetic behavior can be attributed to the structural changes (Böhme et al., 2020; Jochim et al., 2018).

However, to investigate the magnetic properties of transition-metal thiocyanate compounds in more detail, the influence of the coligands on the structural and magnetic behavior must be investigated systematically. Most of these compounds contain N-donor coligands, whereas compounds with, for example, O- or S-donor coligands are rare (Groom et al., 2016 ; Amzel et al., 1969 ; Shurdha, et al., 2013 ). This is the reason why we became interested in transition-metal thiocyanate compounds with thiourea derivatives, where a few compounds have been reported for which either octahedral (Amzel et al., 1969) or tetrahedral complexes (Jochim et al., 2020a ,b ) are observed. Furthermore, some polymeric compounds have been reported in which the metal cations are connected by either the coligands (Nardelli et al., 1966a ) or the thiocyanate anions into chains (Nardelli et al., 1966b ; Jochim et al., 2020c ). In the course of our systematic investigations we became interested in tetramethylthiourea as coligand, which upon reaction with nickel thiocyanate leads to the formation of the title compound [Ni(NCS)₂(C₅H₁₂N₂S)₂] that consists of discrete complexes, in which the thiocyanate anions are N-terminally coordinated. Phase pure powders of the title compound could easily be obtained, which is confirmed by X-ray powder diffraction (Fig. S1 in the supporting information). The C—N stretching band of the thiocyanate anion can be found at 2080 cm⁻¹, which proves the presence of terminally bonded thiocyanate anions, in accordance with the results from single crystal X-ray diffraction (Fig. S2). Investigation of the thermal behavior of the title compound shows that it decomposes at about 408 K in one discrete step of 59.0%, which is in agreement with the mass loss calculated for the loss of all coligand molecules of 60.2% (Fig. S3).

2. Structural commentary

The asymmetric unit consists of one Ni^II cation that is located on a twofold rotational axis as well as one thiocyanate anion and one tetramethylthiourea molecule, which both occupy general positions. Each Ni^II cation is fourfold coordinated by two trans N-binding thiocyanate anions and two trans S-binding tetramethylthiourea molecules into discrete complexes. (Fig. 1). The Ni—N bonds are much shorter than the Ni—S bonds and from the angles it is obvious that the Ni cation is in a square-planar coordination geometry (Table 1). Furthermore, a strong deviation from the ideal angles is found in the coordination environment of the Ni cation, which can probably be attributed to the relatively bulky NMe₂ groups of the tetramethylthiourea molecules. This is most pronounced in the N—Ni—N angle, which amounts to 167.47 (16)°. In contrast, for the S—Ni—S angle a smaller deviation with a value of 173.26 (5)° can be found. The tetramethylthiourea molecules are twisted relative to each other with a C=S⋯S=C torsion angle of 135.0 (2)°. Furthermore, while the thiourea unit of each tetramethylthiourea ligand is planar, both NMe₂ groups are rotated out of this plane by angles of 28.8 (2) and 27.3 (2)°.

Table 1
Selected geometric parameters (Å, °)

Ni1—N1	1.844 (3)	Ni1—S11	2.2259 (7)

N1—Ni1—N1ⁱ	167.47 (16)	N1ⁱ—Ni1—S11	93.93 (8)
N1—Ni1—S11	86.80 (8)	S11ⁱ—Ni1—S11	173.26 (5)
Symmetry code: (i) $[-x+1, y, -z+{\script{3\over 2}}]$ .

Figure 1
View of the asymmetric unit of the title compound with atom labeling and displacement ellipsoids drawn at the 50% probability level. Symmetry transformations used to generate equivalent atoms: (i) −x + 1, y, −z + $[{3\over 2}]$ .

3. Supramolecular features

In the crystal structure of the title compound, the discrete complexes are linked by two crystallographically different intermolecular C—H⋯S hydrogen bonds between the thiocyanate S atom S1 and the methyl hydrogen atoms H13C and H12C of the tetramethylthiourea molecule. In both cases, each two neighbouring complexes are linked into pairs containing 18-membered rings that are located on centers of inversion (Fig. 2 and Table 2). These pairs are further linked into chains, which for the hydrogen bonds between S1 and H13C proceed along the crystallographic a-axis direction and for those between S1 and H12b along the c-axis direction (Fig. 2). These two chains condense into layers parallel to the ac plane by centrosymmetric pairs of both crystallographically different C—H⋯S hydrogen bonds (Fig. 3).

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C12—H12B⋯S1ⁱⁱ	0.98	3.01	3.821 (3)	140
C13—H13C⋯S1ⁱⁱⁱ	0.98	2.93	3.798 (3)	148
Symmetry codes: (ii) ; (iii) x+1, y, z.

Figure 2
Crystal structure of the title compound with view of the two different chains formed by intermolecular C—H⋯S hydrogen bonding between S1 and H13C (top) and between S1 and H12B (bottom). Intermolecular C—H⋯S hydrogen bonding is shown as dashed lines.

Figure 3
Crystal structure of the title compound with view along the crystallographic b axis and intermolecular C—H⋯S hydrogen bonding shown as dashed lines.

4. Database survey

In the Cambridge Crystallographic Database (CSD, Version 5.41, last update May 2020; Groom et al., 2016) no transition-metal thiocyanate compounds with tetramethylthiourea are reported, but one such compound with cobalt was published recently (Jochim et al., 2020b). In this compound, discrete tetrahedral complexes are found in which the metal cations are coordinated by two N-bonding thiocyanate anions and two S-bonding tetramethylthiourea molecules. Several compounds with transition-metal cations and tetramethylthiourea are reported in the CSD, of which two contain nickel cations. Both consist of discrete binuclear complexes in which the metal cations are connected by thiolate ligands. These complexes contain either two Ni^II cations with a square-planar coordination geometry (Ito et al., 2009 ) or one Ni^II and one Fe^II cation with square-pyramidal and octahedral coordination geometries (Ohki et al., 2008 ), respectively. Several Ni(NCS)₂ compounds with other thiourea derivatives are also found, including polymeric compounds such as [Ni(NCS)₂(ethylenethiourea)₂]_n (Nardelli et al., 1966b) and discrete complexes like [Ni(NCS)₂(N,N′-diethylthiourea)₄] (Amzel et al., 1969), but only one of those contains nickel cations with a square-planar coordination geometry (Leovac et al., 1995 ).

5. Synthesis and crystallization

General

Ni(NCS)₂ was synthesized using a procedure described in Jochim et al. (2018). The reagents NiSO₄·6H₂O and Ba(NCS)₂·3H₂O, which were used for this, were obtained from Merck and Alfa Aesar, respectively.

Synthesis

To synthesize a powder sample, a mixture of Ni(NCS)₂ (0.50 mmol, 87.4 mg) and tetramethylthiourea (1.00 mmol, 132.2 mg) was stirred in 0.5 mL of ethanol for one day. The black residue was filtered off and washed with n-heptane. Single crystals were grown by slow evaporation of the filtrate obtained from a similar reaction. In this case, Ni(NCS)₂ (0.25 mmol, 43.7 mg) and tetramethylthiourea (1.00 mmol, 132.3 mg) were reacted in 0.5 mL of n-butanol for one day, after which the residue was filtered off. Elemental analysis calculated for C₁₂H₂₄N₆NiS₄ (439.32 g mol⁻¹) C 32.81, H 5.51, N 19.13, S 29.20, found: C 32.77, H 5.42, N 19.07, S 29.18. IR (ATR): ν_max = 3025 (w), 3008 (w), 2954 (w), 2926 (w), 2164 (w), 2080 (s), 1555 (s), 1492 (m), 1461 (m), 1441 (m), 1415 (w), 1378 (s), 1259 (m), 1209 (w), 1156 (s), 1109 (s), 1100 (s), 1060 (m), 1055 (m), 941 (w), 878 (s), 845 (s), 653 (m), 612 (m), 490 (m), 478 (m), 468 (m), 408 (m) cm⁻¹.

Experimental details

Elemental analysis was performed using an EURO EA elemental analyzer fabricated by EURO VECTOR Instruments. The IR spectrum was measured using an ATI Mattson Genesis Series FTIR Spectrometer, control software: WINFIRST, from ATI Mattson. The XRPD measurements were performed with Cu Kα₁ radiation (λ = 1.540598 Å) using a Stoe Transmission Powder Diffraction System (STADI P) that is equipped with a MYTHEN 1K detector and a Johansson-type Ge(111) monochromator. DTA–TG measurements were performed in a dynamic nitrogen atmosphere (5 NL h⁻¹) in Al₂O₃ crucibles using a STA-PT 1000 thermobalance from Linseis. The instrument was calibrated using standard reference materials.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. All non-hydrogen atoms were refined with anisotropic displacement parameters. The C-bound H atoms were positioned with idealized geometry (C—H = 0.98 Å) allowing them to rotate, but not to tip and refined isotropically with U_iso(H) = 1.5U_eq(C).

Table 3
Experimental details

Crystal data
Chemical formula	[Ni(NCS)₂(C₅H₁₂N₂S)₂]
M_r	439.32
Crystal system, space group	Monoclinic, P2/c
Temperature (K)	200
a, b, c (Å)	10.7245 (3), 6.2050 (3), 15.1579 (5)
β (°)	103.140 (3)
V (Å³)	982.28 (6)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	1.42
Crystal size (mm)	0.12 × 0.09 × 0.07

Data collection
Diffractometer	Stoe IPDS2
Absorption correction	Numerical (X-RED and X-SHAPE; Stoe & Cie, 2002 )
T_min, T_max	0.716, 0.874
No. of measured, independent and observed [I > 2σ(I)] reflections	9982, 1945, 1607
R_int	0.070
(sin θ/λ)_max (Å⁻¹)	0.617

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.038, 0.098, 1.05
No. of reflections	1945
No. of parameters	109
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.39, −0.36
Computer programs: X-AREA (Stoe & Cie, 2002), SHELXS97 (Sheldrick, 2008 ), SHELXL2018/3 (Sheldrick, 2015 ), XP (Sheldrick, 2008), DIAMOND (Brandenburg & Putz, 1999 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 2044233

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989020015121/tx2033sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989020015121/tx2033Isup2.hkl

Figure S1. Experimental (top) and calculated (bottom) PXRD pattern of the title compound measured with Cu-radiation. The cell parameters for the calculated pattern were obtained from a Pawley fit for which the parameters obtained from single crystal diffraction were used as initial values. DOI: https://doi.org/10.1107/S2056989020015121/tx2033sup3.tif

Figure S2. IR spectrum of the title compound. Given is the value of the CN stretching vibration of the thiocyanate anions. DOI: https://doi.org/10.1107/S2056989020015121/tx2033sup4.tif

Figure S3. DTG, TG and DTA curve of the title compound measured with 4 C/min. in a dynamic nitrogen atmosphere. DOI: https://doi.org/10.1107/S2056989020015121/tx2033sup5.tif

checkCIF report

Computing details top

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA (Stoe & Cie, 2002); data reduction: X-AREA (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015); molecular graphics: XP (Sheldrick, 2008) and DIAMOND (Brandenburg & Putz, 1999); software used to prepare material for publication: publCIF (Westrip, 2010).

Bis(tetramethylthiourea-κS)bis(thiocyanato-κN)nickel(II) top

Crystal data top

[Ni(NCS)₂(C₅H₁₂N₂S)₂]	F(000) = 460
M_r = 439.32	D_x = 1.485 Mg m⁻³
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71073 Å
a = 10.7245 (3) Å	Cell parameters from 9982 reflections
b = 6.2050 (3) Å	θ = 2.0–26.0°
c = 15.1579 (5) Å	µ = 1.42 mm⁻¹
β = 103.140 (3)°	T = 200 K
V = 982.28 (6) Å³	Block, black
Z = 2	0.12 × 0.09 × 0.07 mm

Data collection top

Stoe IPDS-2 diffractometer	1607 reflections with I > 2σ(I)
ω scans	R_int = 0.070
Absorption correction: numerical (X-Red and X-Shape; Stoe & Cie, 2002)	θ_max = 26.0°, θ_min = 2.0°
T_min = 0.716, T_max = 0.874	h = −13→13
9982 measured reflections	k = −7→7
1945 independent reflections	l = −18→18

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.038	H-atom parameters constrained
wR(F²) = 0.098	w = 1/[σ²(F_o²) + (0.056P)² + 0.1275P] where P = (F_o² + 2F_c²)/3
S = 1.05	(Δ/σ)_max < 0.001
1945 reflections	Δρ_max = 0.39 e Å⁻³
109 parameters	Δρ_min = −0.36 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Ni1	0.500000	0.29112 (8)	0.750000	0.03467 (16)
N1	0.3260 (3)	0.2587 (4)	0.70613 (16)	0.0416 (6)
C1	0.2221 (3)	0.1954 (5)	0.67755 (18)	0.0375 (6)
S1	0.07891 (8)	0.10731 (15)	0.63716 (6)	0.0536 (2)
S11	0.51467 (7)	0.31221 (13)	0.60612 (5)	0.0421 (2)
C11	0.6634 (3)	0.4138 (5)	0.60210 (18)	0.0368 (6)
N11	0.7271 (2)	0.3274 (4)	0.54463 (16)	0.0402 (5)
C12	0.7000 (4)	0.1112 (6)	0.5071 (2)	0.0551 (8)
H12A	0.658143	0.026358	0.546631	0.083*
H12B	0.780347	0.041141	0.502878	0.083*
H12C	0.643405	0.121046	0.446582	0.083*
C13	0.8112 (3)	0.4537 (6)	0.5012 (2)	0.0495 (8)
H13A	0.801002	0.607219	0.513061	0.074*
H13B	0.788670	0.427747	0.435733	0.074*
H13C	0.900282	0.410930	0.525696	0.074*
N12	0.7143 (2)	0.5845 (4)	0.65156 (16)	0.0410 (5)
C14	0.6379 (4)	0.7320 (5)	0.6929 (2)	0.0522 (8)
H14A	0.549871	0.735359	0.656431	0.078*
H14B	0.674874	0.876929	0.695780	0.078*
H14C	0.637766	0.682513	0.754302	0.078*
C15	0.8524 (3)	0.6057 (6)	0.6875 (2)	0.0522 (8)
H15A	0.894942	0.470956	0.677642	0.078*
H15B	0.869414	0.636391	0.752599	0.078*
H15C	0.885381	0.723850	0.656457	0.078*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ni1	0.0307 (3)	0.0413 (3)	0.0316 (3)	0.000	0.00619 (19)	0.000
N1	0.0423 (15)	0.0489 (14)	0.0335 (12)	0.0005 (11)	0.0085 (10)	0.0004 (10)
C1	0.0364 (16)	0.0446 (15)	0.0319 (13)	0.0021 (12)	0.0086 (11)	0.0017 (11)
S1	0.0354 (4)	0.0637 (5)	0.0597 (5)	−0.0076 (4)	0.0063 (4)	−0.0022 (4)
S11	0.0360 (4)	0.0576 (5)	0.0323 (4)	−0.0074 (3)	0.0069 (3)	−0.0023 (3)
C11	0.0337 (14)	0.0430 (14)	0.0327 (13)	0.0007 (12)	0.0052 (11)	0.0045 (11)
N11	0.0399 (13)	0.0451 (13)	0.0368 (12)	0.0015 (10)	0.0112 (10)	0.0024 (10)
C12	0.066 (2)	0.0556 (19)	0.0474 (18)	−0.0026 (17)	0.0204 (16)	−0.0084 (15)
C13	0.0405 (17)	0.065 (2)	0.0471 (17)	0.0022 (15)	0.0188 (14)	0.0113 (14)
N12	0.0391 (13)	0.0417 (13)	0.0418 (13)	−0.0021 (10)	0.0081 (10)	−0.0029 (10)
C14	0.060 (2)	0.0426 (16)	0.0564 (19)	0.0031 (14)	0.0185 (16)	−0.0051 (14)
C15	0.0418 (17)	0.0580 (19)	0.0539 (18)	−0.0090 (15)	0.0050 (14)	−0.0051 (15)

Geometric parameters (Å, º) top

Ni1—N1	1.844 (3)	C11—N12	1.340 (4)
Ni1—S11	2.2259 (7)	N11—C13	1.460 (4)
N1—C1	1.168 (4)	N11—C12	1.460 (4)
C1—S1	1.614 (3)	N12—C14	1.461 (4)
S11—C11	1.729 (3)	N12—C15	1.464 (4)
C11—N11	1.335 (4)

N1—Ni1—N1ⁱ	167.47 (16)	N11—C11—S11	119.3 (2)
N1—Ni1—S11	86.80 (8)	N12—C11—S11	122.0 (2)
N1ⁱ—Ni1—S11	93.93 (8)	C11—N11—C13	122.6 (3)
S11ⁱ—Ni1—S11	173.26 (5)	C11—N11—C12	122.5 (3)
C1—N1—Ni1	166.5 (3)	C13—N11—C12	113.9 (2)
N1—C1—S1	179.4 (3)	C11—N12—C14	122.6 (3)
C11—S11—Ni1	109.10 (9)	C11—N12—C15	121.9 (3)
N11—C11—N12	118.6 (3)	C14—N12—C15	113.7 (3)

Symmetry code: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C12—H12B···S1ⁱⁱ	0.98	3.01	3.821 (3)	140
C13—H13C···S1ⁱⁱⁱ	0.98	2.93	3.798 (3)	148

Symmetry codes: (ii) −x+1, −y, −z+1; (iii) x+1, y, z.

Acknowledgements

We thank Professor Dr Wolfgang Bensch for access to his experimental facilities.

Funding information

This project was supported by the Deutsche Forschungsgemeinschaft (Project No. NA 720/5–2) and the State of Schleswig-Holstein.

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