Synthesis and Characterization of 4d and 5d Cyanometallate Compounds for Molecular Magnetism

Abstract

This research describes the synthesis and characterization of cyanometallate compounds based on 4d and 5d transition metal ions. Since the discovery of [Mnv12(CHv3COO)v16(H2O)v4Ov12] (Mnv12OAc) displaying magnetic hysteresis, the pursuit of Single Molecule Magnets (SMMs) has been an active field of research owing to their potential applications in high-density storage, spintronics, quantum computing, and molecular refrigeration technologies. SMM applications are limited by their low operating temperatures, however, and strategies for meeting this challenge are being vigorously pursued. One approach is to take advantage of strong anisotropic coupling between metal ions which can be achieved by using metal ions with large spin-orbit coupling constants and electronic orbital degeneracies. In order to expand on this hypothesis from previous work with Kv4[Mo^III(CN)v7], the synthesis of the [W^III(CN)v7] ^4- was targeted. Synthetic routes towards isolating this moiety were explored, culminating with the synthesis of the previously unknown heptacyanotungstate anion in (Buv4N)v3[W^IV(CN)7]. This seven-coordinate homoleptic species, and its molybdenum analogue (Buv4N)v3[Mo^IV(CN)v7] which was also prepared, constitute the first examples of S = 1 heptacyanometallates in the literature. Attempts to incorporate the heptacyanometallate(IV) moieties into polynuclear cyanide-bridged structures were undertaken to assess the magnetic exchange interactions with other metal spin centers, reactions that inevitably resulted in the decomposition of [M^IV(CN)v7]^ 3- to the diamagnetic [M^IV(CN)v8] ^4- anion. Incorporation of the S = 1/2 [MV (CN)8] 3- anion into discrete complexes was also investigated in order to compare the results with the chemistry of [M^IV (CN)v7]^ 4- . The paramagnetic complexes containing [M^V (CNv)8]^ 3- , indeed, exhibit magnetic exchange coupling. In an effort to further exploit the spin-orbit coupling of the heavier transition elements, the incorporation of trigonal symmetry into 4d and 5d metal complexes with the tris(3,5-dimethylpyrazoyl)borate capping ligand was explored, and starting materials that can be used to prepare cyanometallates are reported.