Synthesis and Crystal Structure of Hexakis(imidazole) nickel (II) O,O′-diphenyldithiophosphate [Ni(Im)₆](Ph₂O₂PS₂)₂

The X-ray structure of the complex [Ni(Im)₆](dtp)₂ is built up of discrete monomeric molecules. Figure 1 shows a perspective view of the title compound with atomic numbering scheme and Figure 2 a perspective view of the crystal packing in the unit cell. Table 1 contains atomic positions and equivalent temperature factors for non-hydrogen atoms. Selected bond lengths and angles are presented in Table 2.

The crystal structure of the complex consists of [Ni(Im)₆]²⁺ cation and two dtp anions, linked by electrostatic forces and hydrogen bonds (shown as dashed lines in Figure 2). The coordination model of the nickel (II) can be described as being of octahedral geometry. Six imidazole molecules are coordinated through their tertiary nitrogen atoms to each nickel (II) ion, and two dtp anions are out of the coordination sphere and balance the charge. The bond distances of Ni(1)-N(1), Ni(1)-N(3) and Ni(1)-N(5) of [Ni(Im)₆](dtp)₂ are 2.133(3), 2.132(3) and 2.125(3) Å, respectively. These distances are in agreement with those reported for octahedral [Ni(Im)₆]²⁺ complex [2.120(1), 2.124(1), 2.141(1) Å], [Ni(Im)₆](sal)₂ (sal = salicylate) [8]. In the solid state, one dtp sulfur atom forms a N-H∙∙∙S intermolecular hydrogen bond with the nitrogen atom of Ni(Im)₆²⁺ (Figure 2), and the donor and acceptor distances are N(2)∙∙∙S(1) 3.6547, C(17)∙∙∙S(2) ( 2-x, 1-y, 1-z) 3.3052, C(11)∙∙∙S(2) ( 2-x, 1-y, 1-z) 3.7945 and C(20)∙∙∙S(1) (2-x, -y, 1-z) 3.3807 Å (Table 3), the whole complexes forming a 3-dimensional network structure.

The IR spectrum of the complex shows characteristic absorption bands at 3401 and 552 cm^-1, assigned to ν(N-H) and ν(Ni-N) vibrations, respectively. This indicates that the atom coordinated with Ni(II) is the double bond nitrogen (=N) in the imidazole molecule. This result is in agreement with that of X-ray crystal structure determination.

All commercially available chemicals were of analytical reagent grade and used directly without further purification. The C, N and H contents were determined by using an Elementar Vario EL analyzer. Infrared spectra were recorded from KBr pellets on a Midac Prospet IR spectrometer. All operations were carried out under ambient conditions.

To a warm solution of excess imidazole (1.0 g, 15 mmol) in EtOH (50 mL) was added with stirring nickel (II) O, O′-diphenyl dithiophosphate, and the mixture was refluxed for 40 min. The blue solution was filtered and the filtrate was left to stand undisturbed. Upon slow evaporation at room temperature, a blue crystalline solid suitable for X-ray structure determination appeared several weeks later and was separated by filtration. Main IR absorption bands (KBr, cm^-1): 3401 (N-H), 1491 (C=N), 1591, 1530 (phenyl ring stretch), 552 (Ni-N). Anal. Data: Calcd for C₄₂H₄₄N₁₂O₄P₂S₄Ni₁ C, 48.94; H, 4.27; N, 16.31 %. Found: C, 48.93; H, 4.30; N, 16.21 %.

The selected crystal of [Ni(Im)₆](dtp)₂ was mounted on a Nonius CAD4 diffractometer, reflection data for the unit cell determination were measured at 293 K using MoKα radiation (λ= 0.71073 Å) with a graphite monochromator. The technique used was ω-scan with 0.995<θ<25.04° for the complex. Absorption correction was made with π-scans. The structure was solved by direct method and refined by full-matrix least-squares method on F²_obs by using the SHELXTL software package [10]. All non-H atoms were anisotropically refined. The hydrogen atoms were geometrically fixed and allowed to ride on the parent atoms to which they are attached. The final conventional R = 0.0604, wR = 0.1388 for 3843 reflections with I > 2σ(I); w = 1/[σ²(F²_o)+(0.0600P)²+1.4652P] where P = (F²_o+2(F²_c))/3. The molecular graphics were created by SHELXTL. Atomic scattering factors and anomalous dispersion correction were taken from International Table for X-Ray Crystallography [11]. A summary of the key crystallographic information is given in Table 4.