Synthesis, crystal structure and thermal properties of di­aqua­bis­(4-cyano­pyridine)­dithiocyanato­nickel(II)

Näther, C.

doi:10.1107/S2056989026003373

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ISSN: 2056-9890

Volume 82| Part 5| May 2026| Pages 441-445

https://doi.org/10.1107/S2056989026003373

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Synthesis, crystal structure and thermal properties of diaquabis(4-cyanopyridine)dithiocyanatonickel(II)

Christian Näther ^a ^*

^aInstitut für Anorganische Chemie, Universität Kiel, Germany
^*Correspondence e-mail: [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 25 March 2026; accepted 31 March 2026; online 10 April 2026)

The reaction of Ni(NCS)₂ and 4-cyanopyridine (C₆H₄N₂) in water leads to the formation of single crystals of the title compound, [Ni(NCS)₂(C₆H₄N₂)₂(H₂O)₂]. The asymmetric unit consists of one Ni^II cation, which is located on a center of inversion, as well as one thiocyanate anion, one 4-cyanopyridine coligand and one water molecule in general positions. The nickel cations therefore adopt trans-NiO₂N₄ octahedra, forming discrete complexes. These complexes are linked by O—H⋯S hydrogen bonds into layers that lie parallel to the bc plane. These layers are additionally linked by weak C—H⋯N interactions into a three-dimensional network. Powder X-ray diffraction (PXRD) indicates that an almost pure sample has been obtained. Upon heating, the title compound loses its water molecules and the 4-cyanopyridine ligands in separate steps.

Keywords: synthesis; crystal structure; nickel thiocyanate; discrete aqua complex; 4-cyanopyridine; hydrogen bonding; thermal properties.

CCDC reference: 2542643

1. Chemical context

Investigations on the synthesis of new coordination compounds with specific magnetic properties is still an important field in inorganic chemistry (Ferrando-Soria et al., 2017 ). In this context, compounds in which paramagnetic metal cations are linked by small sized anionic ligands are of special importance (Yue & Gao, 2019 ). Numerous examples of such compounds are reported in the literature and our own work has focused on the synthesis of transition-metal thiocyanate compounds in which the cations are linked by μ-1,3-bridging anionic ligands (Wöhlert et al., 2013 ; Werner et al., 2014 ; Neumann et al., 2018 ). Unfortunately, with less chalcophilic metal cations, the synthesis in solution mostly leads to compounds in which the thiocyanate anions are only terminally coordinated to the N atom.

Therefore, many years ago we developed a new route, which is based on thermal ligand removal from simple precursor complexes (Näther & Greve, 2003 ). We also have found that the corresponding coordination polymers with selenocyanate can be prepared by this route (Wriedt & Näther, 2010 ; Wöhlert et al., 2012 ). This route is therefore one more alternative to the preparation of new coordination compounds by typical solid-state methods such as molecular milling (Braga et al., 2005 , 2006 , James et al., 2012 ; Do & Friščić, 2017 ; Stolar et al., 2017 ) or reactions in melts (Müller-Buschbaum, 2005 ; Höller & Müller-Buschbaum, 2008 ; Zurawski et al., 2012 ).

In view of magnetic properties, compounds based on Co(NCS)₂ and Ni(NCS)₂ are of special interest, because the former can show one-dimensional ferromagnetic ordering if they exhibit chain structures (Mautner et al., 2018 ; Rams et al., 2020 ), whereas the latter show three-dimensional ferromagnetic ordering if they crystallize as layered structures (Suckert et al., 2016 ). In the course of this project, we were particularly interested in pyridine derivatives as ligands and within our systematic investigations we became interested in Ni(NCS)₂ compounds with 4-cyanopyridine (C₆H₄N₂) as coligand.

With this ligand, only one Ni compound is reported: this is Ni(NCS)₂(C₆H₄N₂)₄, which consists of discrete complexes in which the nickel cations are coordinated by two terminal N-bonded thiocyanate anions and four 4-cyanopyridine ligands, which coordinate through the pyridine N atom to the metal center (CSD refcode UBUBOL; Clegg & Harrington, 2016 ). In the course of our investigations, we obtained crystals of a further crystalline phase, Ni(NCS)₂(C₆H₄N₂)₂(H₂O)₂ (I) that was identified by single crystal X-ray diffraction.

2. Structural commentary

The asymmetric unit of (I) is built up of one crystallographically independent nickel(II) cation that is situated on a center of inversion and one thiocyanate anion, one 4-cyanopyridine coligand and one water molecule, with all atoms located in general positions. The nickel cations are sixfold coordinated by two terminally N-bonding thiocyanate anions, two 4-cyanopyridine coligands and two water molecules into discrete complexes (Fig. 1). The 4-cyanopyridine coligand coordinates through its pyridine N atom to the metal center. The bond angles deviate slightly from the ideal values, which demonstrate that the trans-NiO₂N₄ octahedra are slightly distorted (Table 1).

Table 1
Selected geometric parameters (Å, °)

Ni1—N1	2.035 (3)	Ni1—N11	2.108 (3)
Ni1—O1	2.084 (2)

N1—Ni1—O1ⁱ	87.62 (12)	N1—Ni1—N11	89.67 (13)
N1—Ni1—O1	92.38 (12)	O1—Ni1—N11	91.15 (11)
N1ⁱ—Ni1—N11	90.32 (13)	C1—N1—Ni1	166.4 (3)
Symmetry code: (i) .

Figure 1
The molecular structure of (I) with labeling and displacement ellipsoids drawn at the 50% probability level. Symmetry code: (i) −x + 1, −y + 1, −z + 1.

Finally, it may be mentioned that the title compound is isotypic to one of the two modifications of Mn(NCS)₂(C₆H₄N₂)₂(H₂O)₂ already reported in the literature (OJEFAN; Wellm et al., 2020 ).

3. Supramolecular features

In the extended structure of (I), the complexes are linked by O—H⋯S hydrogen bonds between the water H atoms and the thiocyanate S atom into corrugated layers that are arranged parallel to the bc plane (Fig. 2). Within these layers, each S atom acts as acceptor for two hydrogen bonds from two neighboring complexes, and the H atoms of each water molecule act as donors in O—H⋯S hydrogen bonds to two complexes. Therefore, each complex is involved in eight hydrogen bonds to six adjacent complexes (Fig. 2). The H⋯S distances are relatively short and the O—H⋯S angles close to linear, indicating that these are relatively strong interactions (Table 2).

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1O1⋯S1ⁱⁱ	0.84	2.48	3.307 (3)	167
O1—H2O1⋯S1ⁱⁱⁱ	0.84	2.44	3.225 (3)	156
C11—H11⋯N12^iv	0.95	2.44	3.129 (6)	129
Symmetry codes: (ii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (iii) ; (iv) $[-x+2, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Figure 2
Crystal structure of (I) in a view along the crystallographic a-axis direction. The O—H⋯S hydrogen bonds are shown as dashed lines.

The layers are additionally linked by pairs of centrosymmetric C—H⋯N interactions between the pyridine H atom and the N atom of the cyano group into a three-dimensional network (Fig. 3). The C—H⋯N angle is far from linear, showing that this is only a weak interaction (Table 2).

Figure 3
Crystal structure of (I) in a view along the crystallographic c-axis direction. Intermolecular O—H⋯S and C—H⋯N hydrogen bonding is shown as dashed lines.

4. Additional characterization

The purity of (I) was investigated by X-ray powder diffraction. Comparison of the experimental powder pattern with that calculated for the title compound proves that an almost pure crystalline phase has been obtained (Fig. 4). There is a very small additional peak to the left of the most intense reflection, which indicates the presence of a very small amount of a further crystalline phase. The experimental pattern is rather noisy, which can be traced back to a low crystallinity, presumably because of grinding.

Figure 4
Experimental (top) and calculated (bottom) PXRD patterns for (I). Some of the reflections in the calculated pattern are slightly shifted to higher Bragg angles, which originate from the fact that the structure analysis was performed at lower temperatures.

The thermal properties of (I) were investigated using differential thermoanalysis coupled to thermogravimetry (DTA-TG). Upon heating, at least three mass losses are observed in the TG curve that are accompanied with endothermic events in the DTA curve (Fig. 5). The experimental mass loss in the first step of 8.5% is in good agreement with that calculated for the removal of the two water molecules of 8.1%. The DTG curve indicates that the first mass loss can be divided into two different steps, which is a hint that the two water molecules are removed in two different steps. The experimental mass losses in the second and third TG step are in good agreement with those calculated for one 4-cyanopyridine ligand in each step (Δm_calc. = 24.8%). This indicates that in the first TG step a compound with the composition Ni(NCS)₂(C₆H₄N₂)₂ is formed, which decomposes into Ni(NCS)₂(C₆H₄N₂) upon further heating, before the final product of Ni(NCS)₂ is formed.

Figure 5
DTG, TG and DTA curves for (I). The percentage mass loss is given and the peak temperature is in °C.

5. Synthesis and characterization

Ni(NCS)₂ was prepared from the reaction of equimolar amounts of NiSO₄·6H₂O with Ba(NCS)₂·3H2O in water. The white residue of BaSO₄ was filtered off and the filtrate was concentrated until complete dryness. The purity was checked by X-ray powder diffraction (XRPD). Barium thiocyanate trihydrate was purchased from Alfa Aesar and 4-cyanopyridine as well as nickel sulfate hexahydrate from Sigma-Aldrich.

1.00 mmol (174.9 mg) of Ni(NCS)₂ and 2.00 mmol (208.2 mg) of 4-cyanopyridine were reacted in 3 ml of water at room temperature. Within 3 d, crystals of (I) in the form of light-blue blocks suitable for crystal structure analysis were obtained.

Powder X-ray diffraction measurements were performed using a Stoe STADI P transmission powder diffractometer with Cu Kα₁ radiation (λ = 1.540598 Å), a Johann-type Ge(111) monochromator and a MYTHEN 1K detector from Dectris.

Thermogravimetry and differential thermoanalysis (TG–DTA) measurements were performed in a dynamic nitrogen atmosphere in Al₂O₃ crucibles with a heating rate of 4°C min⁻¹ using a STA-PT 1000 thermobalance from Linseis. The TG–DTA instrument was calibrated using standard reference materials.

6. Database survey

Some more compounds with 4-cyanopyridine and transition-metal cations were found in a search of the CSD (version 5.43, last update January 2026; Groom et al., 2016 ) using CONQUEST (Bruno et al., 2002 ). These include Ni(NCS)₂(C₆H₄N₂)₄ already mentioned in the Chemical context section (CSD refcode UBUBOL; Clegg & Harrington, 2016).

Several compounds are reported with Mn(NCS)₂, including Mn(NCS)₂(C₆H₄N₂)₄, that also consists of discrete complexes, but which are not isotypic to Ni(NCS)₂(C₆H₄N₂)₄ (OJEDOZ; Wellm et al., 2020). Discrete complexes with an octahedral coordination are also found in one of the two modifications of Mn(NCS)₂(C₆H₄N₂)₂(H₂O)₂ that is isotypic to the title compound (OJEFAN and OJEFAN01; Wellm et al., 2020). Two further aqua complexes with additional 4-cyanopyridine as solvate ligand are also known (OJEFER and OJEFUH; Wellm et al., 2020). Two Mn(NCS)₂ compounds with bridging thiocyanate anions are also reported. These include Mn(NCS)₂(C₆H₄N₂)₂, in which the manganese cations are octahedrally coordinated by two N- and two S-bonding thiocyanate anions and two 4-cyanopyridine ligands and are linked by pairs of anionic ligands into chains (OJEFIV; Wellm et al., 2020) and Mn(NCS)₂(C₆H₄N₂), in which two Mn^II cations are linked by pairs of thiocyanate anions into dinuclear units that are further connected by single μ-1,3-bridging anionic ligands into layers that condense into a three-dimensional network via the bridging 4-cyanopyridine ligands (OJEDUF and OJEDUF01; Wellm et al., 2020).

With Cu(NCS)₂, one compound with the composition Cu(NCS)₂(C₆H₄N₂)₂ is also found, in which the 4-cyanopyridine coligand is only monocoordinated via the pyridine N atom and in which the copper cations are linked by pairs of thiocyanate anions into chains (ABOVOF; Handy et al., 2017 ). A further solvato complex with the composition Fe(NCS)₂(C₆H₄N₂)₂(H₂O)₂·2(C₆H₄N₂) is also known (Jochim et al., 2017 ).

Finally, two compounds with Cd(NCS)₂ are listed in the CSD, viz. Cd(NCS)₂(C₆H₄N₂)₂ (WUCLUB; Chen et al., 2002 ), which shows the same structure as Mn(NCS)₂(C₆H₄N₂)₂, and Cu(NCS)₂(C₆H₄N₂)₂ (WUCMAI; Chen et al., 2002), in which the 4-cyanopyridine ligand acts as a bridging ligand.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. The C-bound H atoms were positioned with idealized geometry and were refined with U_iso(H) = 1.2U_eq(C) using a riding model. The water H atoms were located in a difference map, their bond lengths were set to standard values and finally they were refined with U_iso(H) = 1.5U_eq(O) using a riding model. The crystal chosen for data collection was found to contain a small amount of at least a second domain, but it was not possible to index them separately to perform a twin refinement.

Table 3
Experimental details

Crystal data
Chemical formula	[Ni(NCS)₂(C₆H₄N₂)₂(H₂O)₂]
M_r	419.13
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	200
a, b, c (Å)	10.6984 (11), 12.2068 (10), 7.3974 (7)
β (°)	103.500 (12)
V (Å³)	939.36 (16)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	1.27
Crystal size (mm)	0.13 × 0.09 × 0.06

Data collection
Diffractometer	Stoe IPDS1
Absorption correction	Numerical (X-SHAPE and X-RED32; Stoe, 2008 )
T_min, T_max	0.844, 0.899
No. of measured, independent and observed [I > 2σ(I)] reflections	5054, 1830, 1464
R_int	0.074
(sin θ/λ)_max (Å⁻¹)	0.617

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.055, 0.150, 1.02
No. of reflections	1830
No. of parameters	115
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	1.24, −1.09
Computer programs: X-AREA (Stoe, 2008), SHELXT (Sheldrick, 2015b ), SHELXL (Sheldrick, 2015a ), DIAMOND (Brandenburg, 1999 ), XP in SHELXTL-PC (Sheldrick, 2008 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 2542643

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989026003373/hb8207sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989026003373/hb8207Isup2.hkl

checkCIF report

Computing details top

Diaquabis(pyridine-4-carbonitrile)dithiocyanatonickel(II) top

Crystal data top

[Ni(NCS)₂(C₆H₄N₂)₂(H₂O)₂]	F(000) = 428
M_r = 419.13	D_x = 1.482 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 10.6984 (11) Å	Cell parameters from 6692 reflections
b = 12.2068 (10) Å	θ = 4.6–26.9°
c = 7.3974 (7) Å	µ = 1.27 mm⁻¹
β = 103.500 (12)°	T = 200 K
V = 939.36 (16) Å³	Block, light blue
Z = 2	0.13 × 0.09 × 0.06 mm

Data collection top

Stoe IPDS-1 diffractometer	1464 reflections with I > 2σ(I)
Phi scans	R_int = 0.074
Absorption correction: numerical (X-Shape and X-Red32; Stoe, 2008)	θ_max = 26.0°, θ_min = 2.6°
T_min = 0.844, T_max = 0.899	h = −13→12
5054 measured reflections	k = −13→15
1830 independent reflections	l = −9→9

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.055	H-atom parameters constrained
wR(F²) = 0.150	w = 1/[σ²(F_o²) + (0.1103P)²] where P = (F_o² + 2F_c²)/3
S = 1.02	(Δ/σ)_max < 0.001
1830 reflections	Δρ_max = 1.24 e Å⁻³
115 parameters	Δρ_min = −1.09 e Å⁻³
0 restraints

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	0.500000	0.500000	0.0212 (2)
N1	0.4116 (3)	0.5615 (3)	0.6935 (4)	0.0322 (7)
C1	0.3433 (3)	0.6039 (3)	0.7731 (4)	0.0228 (7)
S1	0.24664 (9)	0.66118 (9)	0.88587 (14)	0.0356 (3)
N11	0.6437 (3)	0.6209 (2)	0.5724 (4)	0.0259 (7)
C11	0.7680 (3)	0.5930 (3)	0.6064 (6)	0.0324 (8)
H11	0.788824	0.517784	0.598705	0.039*
C12	0.8678 (4)	0.6673 (3)	0.6520 (6)	0.0384 (10)
H12	0.954934	0.644175	0.676692	0.046*
C13	0.8361 (4)	0.7766 (3)	0.6604 (6)	0.0398 (10)
C14	0.7090 (4)	0.8075 (3)	0.6257 (6)	0.0375 (9)
H14	0.686068	0.882410	0.630713	0.045*
C15	0.6155 (4)	0.7275 (3)	0.5833 (6)	0.0304 (8)
H15	0.527780	0.748690	0.561004	0.036*
C16	0.9377 (5)	0.8572 (4)	0.7069 (9)	0.0598 (15)
N12	1.0171 (5)	0.9193 (5)	0.7477 (11)	0.099 (2)
O1	0.6085 (3)	0.3904 (2)	0.6893 (4)	0.0352 (7)
H1O1	0.654313	0.339361	0.663891	0.053*
H2O1	0.639203	0.397151	0.804131	0.053*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ni1	0.0251 (4)	0.0130 (3)	0.0255 (4)	0.0010 (2)	0.0063 (2)	−0.0014 (2)
N1	0.0400 (17)	0.0227 (16)	0.0361 (17)	−0.0037 (13)	0.0131 (14)	−0.0042 (13)
C1	0.0307 (17)	0.0184 (16)	0.0207 (16)	−0.0058 (13)	0.0085 (14)	−0.0014 (13)
S1	0.0338 (5)	0.0416 (6)	0.0342 (5)	0.0045 (4)	0.0135 (4)	−0.0029 (4)
N11	0.0255 (14)	0.0164 (14)	0.0342 (16)	0.0005 (11)	0.0036 (12)	−0.0023 (11)
C11	0.0315 (19)	0.0180 (17)	0.046 (2)	0.0023 (14)	0.0060 (16)	−0.0020 (16)
C12	0.0284 (18)	0.029 (2)	0.053 (2)	−0.0004 (16)	0.0007 (17)	−0.0036 (18)
C13	0.038 (2)	0.026 (2)	0.052 (2)	−0.0102 (16)	0.0027 (18)	−0.0071 (18)
C14	0.043 (2)	0.0168 (17)	0.051 (2)	0.0001 (16)	0.0069 (18)	−0.0087 (16)
C15	0.0303 (17)	0.0194 (17)	0.041 (2)	0.0030 (14)	0.0078 (15)	−0.0047 (15)
C16	0.044 (3)	0.033 (2)	0.098 (4)	−0.007 (2)	0.007 (3)	−0.012 (3)
N12	0.057 (3)	0.052 (3)	0.176 (7)	−0.028 (2)	0.003 (3)	−0.021 (4)
O1	0.0470 (16)	0.0237 (13)	0.0311 (14)	0.0093 (12)	0.0017 (12)	−0.0001 (11)

Geometric parameters (Å, º) top

Ni1—N1ⁱ	2.035 (3)	C11—H11	0.9500
Ni1—N1	2.035 (3)	C12—C13	1.382 (6)
Ni1—O1ⁱ	2.084 (2)	C12—H12	0.9500
Ni1—O1	2.084 (2)	C13—C14	1.376 (6)
Ni1—N11ⁱ	2.108 (3)	C13—C16	1.446 (6)
Ni1—N11	2.108 (3)	C14—C15	1.381 (5)
N1—C1	1.161 (5)	C14—H14	0.9500
C1—S1	1.630 (4)	C15—H15	0.9500
N11—C11	1.339 (5)	C16—N12	1.127 (6)
N11—C15	1.342 (5)	O1—H1O1	0.8400
C11—C12	1.381 (6)	O1—H2O1	0.8400

N1ⁱ—Ni1—N1	180.0	N11—C11—C12	123.8 (4)
N1ⁱ—Ni1—O1ⁱ	92.38 (12)	N11—C11—H11	118.1
N1—Ni1—O1ⁱ	87.62 (12)	C12—C11—H11	118.1
N1ⁱ—Ni1—O1	87.62 (12)	C11—C12—C13	117.5 (4)
N1—Ni1—O1	92.38 (12)	C11—C12—H12	121.3
O1ⁱ—Ni1—O1	180.0	C13—C12—H12	121.3
N1ⁱ—Ni1—N11ⁱ	89.68 (13)	C14—C13—C12	119.9 (4)
N1—Ni1—N11ⁱ	90.33 (13)	C14—C13—C16	120.9 (4)
O1ⁱ—Ni1—N11ⁱ	91.15 (11)	C12—C13—C16	119.2 (4)
O1—Ni1—N11ⁱ	88.85 (11)	C13—C14—C15	118.7 (4)
N1ⁱ—Ni1—N11	90.32 (13)	C13—C14—H14	120.6
N1—Ni1—N11	89.67 (13)	C15—C14—H14	120.6
O1ⁱ—Ni1—N11	88.85 (11)	N11—C15—C14	122.6 (3)
O1—Ni1—N11	91.15 (11)	N11—C15—H15	118.7
N11ⁱ—Ni1—N11	180.00 (11)	C14—C15—H15	118.7
C1—N1—Ni1	166.4 (3)	N12—C16—C13	178.2 (8)
N1—C1—S1	178.9 (3)	Ni1—O1—H1O1	126.0
C11—N11—C15	117.5 (3)	Ni1—O1—H2O1	129.9
C11—N11—Ni1	120.2 (2)	H1O1—O1—H2O1	100.9
C15—N11—Ni1	122.2 (2)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1O1···S1ⁱⁱ	0.84	2.48	3.307 (3)	167
O1—H2O1···S1ⁱⁱⁱ	0.84	2.44	3.225 (3)	156
C11—H11···N12^iv	0.95	2.44	3.129 (6)	129

Symmetry codes: (ii) −x+1, y−1/2, −z+3/2; (iii) −x+1, −y+1, −z+2; (iv) −x+2, y−1/2, −z+3/2.

Acknowledgements

This work was supported by the State of Schleswig-Holstein.

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