New Family of Thiocyanate-Bridged Re(IV)-SCN-M(II) (M = Ni, Co, Fe, and Mn) Heterobimetallic Compounds: Synthesis, Crystal Structure, and Magnetic Properties

The heterobimetallic complexes of formula [(Me2phen)2M­(μ-NCS)­Re­(NCS)5]·CH3CN [Me2phen = 2,9-dimethyl-1,10-phenanthroline and M = Ni (1), Co (2), Fe (3), and Mn (4)] have been prepared, and their crystal structures have been determined by X-ray diffraction on single crystals. Compounds 1–4 crystallize in the monoclinic C2/c space group, and their structure consists of neutral [(Me2phen)2M­(μ-NCS)­Re­(NCS)5] heterodinuclear units with a Re-SCN-M bridge. Each Re­(IV) ion in this series is six-coordinated with one sulfur and five nitrogen atoms from six thiocyanate groups building a somewhat distorted octahedral environment, whereas the M­(II) metal ions are five-coordinated with four nitrogen atoms from two bidentate Me2phen molecules and a nitrogen atom from the bridging thiocyanate describing distorted trigonal bipyramidal surroundings. The values of the Re···M separation through the thiocyanate bridge in 1–4 vary in the range 5.903(1)–6.117(3) Å. The magnetic properties of 1–4 as well as those of the parent mononuclear Re­(IV) compounds (NBu4)2[Re­(NCS)6] (A1) (NBu4+ = tetra-n-butylammonium cation) and [Zn­(NO3)­(Me2phen)2]2[Re­(NCS)5(SCN)] (A2) were investigated in the temperature range 1.9–300 K. Weak antiferromagnetic interactions between the Re­(IV) and M­(II) ions across the bridging thiocyanate were found in 1–4 [J = −4.3 (1), −2.4 (2), −1.8 (3), and −1.2 cm–1 (4), the Hamiltonian being defined as Ĥ = –JŜRe·ŜM]. The magnetic behavior of A2 is that of a magnetically diluted Re­(IV) complex with a large and positive value of the zero-field splitting for the ground level (DRe = +37.0 cm–1). In the case of A1, although its magnetic behavior is similar to that of A2 in the high-temperature range (DRe being +19.0 cm–1), it exhibits a weak ferromagnetism below 3.0 K with a canting angle of 1.3°.