Molybdenum(III) Thiocyanate- and Selenocyanate-Based One-Dimensional Heteronuclear Polymers: Coordination Affinity-Controlled Assemblage of Mixed Spin and Mixed Valence Derivatives with Ni(II) and Co(II/III)

One-dimensional coordination polymers constructed with the 4d metallo-ligand [Mo(NCS) 6 ] 3- associated with Ni II and Co II complexes are reported. The first series consists of anionic NCS-bridged [Mo-M II ] - coordination polymers associated with a discrete paramagnetic complex or a diamagnetic Co III complex acting as cations. The latter takes advantage of the coordination preference of the S-ligand for the soft 3d ions and has led to hetero-trimetallic [Mo III Ni II Co III ] and mixed valence [Mo III Co II Co III ] compounds. A second series concerns neutral chains in which trinuclear [Mo M 2 II ] units are bridged by an additional NCS anion. The soft character of the S atom was also the key to a rare example of a compound involving both high-spin and low-spin Co II centers associated with [Mo(NCS) 6 ]. A [Mo-Ni] derivative obtained with [Mo(NCSe) 6 ] 3- has been considered in order to evaluate the effect of Se versus S on the exchange interaction. The spin distribution for selenocyanate metallo-ligand has been assessed by density functional theory calculations. The crystal structures for all compounds have been characterized, and their magnetic behaviors have been investigated. These ferrimagnetic systems are characterized by antiferromagnetic Mo-M II interactions in the range of -40 to -90 cm -1 (based on H = - J S a S b formalism) operative both with Co II and with Ni II , thus demonstrating the potential of the Mo III -NCS combination for molecular systems in which exchange interactions play an important role.