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°.