Structural, magnetic, high-frequency and high-field EPR investigation of double-stranded heterometallic [{Ni(en)2}2(μ-NCS)4Cd(NCS)2]n•nCH3CN polymer self-assembled from cadmium oxide, nickel thiocyanate and ethylenediamine

A novel heterometallic 1D coordination polymer [{Ni(en)(2)}(2)(mu-NCS)(4)Cd(NCS)(2)](n) center dot nCH3CN (en = ethylenediamine) has been prepared using the self-assembly process in a one-pot reaction of cadmium oxide, nickel and ammonium thiocyanates with an acetonitrile solution of ethylenediamine. The complex consists of an uncommon cis-Cd(SCN)(4)(NCS)(2)(4-) fragment and a rare combination of cis-Ni(en)(2)(2+) and trans-Ni(en)(2)(2+) building blocks linked by mu(1,3)-NCS bridges into a double-stranded zigzag chain structure. Each chain is comprised of [Ni2Cd2(mu-NCS-N, S)(4))] macrocycles with chair-like and rectangular-like shapes arrayed alternately. The shortest intrachain Cd center dot center dot center dot Cd separations are 9.535(1) and 10.868(2) angstrom, while the nearest Ni center dot center dot center dot Ni distances are 5.418(1) and 6.612(2) angstrom. A network of weak N-H center dot center dot center dot S hydrogen bonds, involving the terminal NCS ligands and NH2-groups of en, links the infinite chains and results in the formation of an extended supramolecular three-dimensional framework. Variable-temperature (1.8-300 K) magnetic susceptibilities show a slight change of the mu(B) value at low temperature, indicative of weak antiferromagnetic interactions (J = 1.55 cm(-1)) between magnetic canters. High-field, high-frequency (100-400 GHz) EPR spectra were simulated using S = 1 ground state for separate Ni2+ ions with the spin Hamiltonian parameters g = 2.165, D = 0.45 cm(-1) and E = 0.03 cm(-1). According to DFT calculations, the D and E parameters are -0.35 cm(-1) and 0.049 cm(-1) for the cis arrangement of Ni2+ and 0.58 cm(-1) and 0.012 cm(-1) for trans.