Crystal structure of a new mixed-metal coordination polymer consisting of NiII piperidine-dithiocarbamate and pentanuclear CuI—I cluster units

A novel heterometallic CuI–NiII coordination polymer with an infinite one-dimensional structure was prepared and structurally characterized via X-ray diffraction. This complex consists of a mononuclear nickel(II) unit of NiII(C6H10NS2)2 and a pentanuclear copper(I) cluster unit of Cu5I5(CH3CH2CN).


Chemical context
The crystal engineering of coordination polymers is one of the most attractive areas in the field of materials science because their characteristic assembled structures and electronic states bearing features of organic-inorganic hybrid materials have new chemical and/or physical properties such as catalytic activity (Yaghi et al., 2003), gas adsorption (Kitagawa et al., 2004), conductivity (Givaja et al., 2012), magnetism (Sato et al., 1996) and optical properties (Watanabe et al., 2017). The design and synthesis of coordination polymers have drawn much interest; in particular, the establishment of a rational synthetic method for preparing heterometallic coordination polymers is important in developing the chemistry of coordination complexes because of the unique coordination networks created by the combination of several metal ions with versatile coordination geometries (Ghosh et al., 2018). Metal complexes with dithiocarbamate (dtc) derivatives are some of the most useful building units to form heterometallic coordination polymers (Engelhardt et al., 1988(Engelhardt et al., , 1989Tokoro et al., 1995;Okubo et al., 2012) because one can employ a variety of mononuclear metal complexes as building units for coordination polymers owing to the coordination ability of the sulfur atoms in the dithiocarbamate complexes. In this paper, we report the synthesis and X-ray ISSN 2056-9890 crystal structure of the title new heterometallic Cu I -Ni II coordination polymer.

Structural commentary
The title compound ( Fig. 1) has an infinite chain structure consisting of a mononuclear Ni II dithiocarbamate unit Ni II (Pip-dtc) 2 (Pip-dtc À = piperidine-dithiocarbamate) and a pentanuclear Cu I cluster unit Cu 5 I 5 (CH 3 CH 2 CN). The Ni II ion, which lies on an inversion centre, is surrounded by four S atoms from the dithiocarbamate ligands in a square-planar coordination geometry. The four S atoms in Ni II (Pip-dtc) 2 are also coordinated by the Cu I ions in the Cu I cluster unit, forming an infinite zigzag chain along the b-axis direction (Fig. 2). In the Cu I cluster unit, a mirror plane passes through one Cu I ion (Cu2) and three I ions (I1, I3 and I4). The five Cu I ions in the cluster create a distorted square-pyramidal structure bridged by five iodide ions, where four Cu I ions [Cu1, Cu1 i , Cu3 and Cu3 i ; symmetry code: (i) x, Ày + 1 2 , z] construct the basal plane and atom Cu2 is in the apical position. Atom I3 bridges the four basal Cu I ions to stabilize the plane structure, while atoms I1 and I2 each bridge the two basal Cu I ions and  A packing diagram of the title compound, showing the one-dimensional chain structure: Cu red-brown, Ni green, I purple, S yellow, C white, N blue. H atoms and CH 3 Cl molecules have been omitted for clarity.

Figure 3
A packing diagram of the title compound viewed along the a axis: Cu redbrown, Ni green, I purple, S yellow, C white, N blue. H atoms and CH 3 Cl molecules have been omitted for clarity. the apical Cu I ion (Cu2). Atom I4 bridges the two basal Cu I ions (Cu3 and Cu3 i ). One propionitrile ligand is coordinated to the apical Cu I ion. In this cluster, the Cu1Á Á ÁCu2 and Cu1Á Á ÁCu3 distances of 2.6920 (6) and 2.7883 (3) Å , respectively, are shorter than the sum of the van der Waals radii for CuÁ Á ÁCu (2.80 Å ). In order to confirm the oxidation state of the copper ions, a bond-valence-sum (BVS) calculation was performed (Brese & O'Keeffe, 1991). The estimated BVS values for atoms Cu1, Cu2 and Cu3 are 1.08, 1.10 and 1.08, respectively, indicating their monovalent oxidation states.

Spectroscopic properties
UV-vis-NIR spectra of the mononuclear Ni II dithiocarbamate complex, Ni II (Pip-dtc) 2 , and the title coordination polymer, 1, were acquired using a U-4100 UV/VIS/NIR Spectrophotometer (HITACHI). Fig. 5 shows the diffuse-reflection spectra converted from the diffusion-reflectance (R) spectra using the Kubelka-Munk function: f(R) = (1 À R) 2 /2R (Kubelka, 1948). Ni II (Pip-dtc) 2 shows two small absorption bands originating from the d-d transition of the Ni II ion at 480 and 630 nm, as well as large absorption bands based on the charge-transfer transitions in the region of wavelengths less than 450 nm. On the other hand, 1 shows an absorption band at 680 nm, close to the wavelength (630 nm) of the d-d transition of Ni II (Pip-dtc) 2 , but the absorption edge of the d-d transition shifts to the NIR region because of the formation of the energy band structure.

Poly[[tetra-µ 3 -iodido-µ 2 -iodido-bis(µ 3 -piperidine-1-dithiocarbamato)propionitrilepentacopper(I)nickel(II)] chloroform monosolvate]
Crystal data Special details 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.