Preparation and Characterization of Cyanide-Bridged Molecular Clusters and Extended Networks Using the Building-Block Approach

Abstract

The cyanide ligand has frequently been used to prepare clusters with novel magnetic properties due to its ability to provide an efficient pathway for superexchange between metal centers that are bound in an end-to-end fashion. One of the common synthetic approaches in this chemistry is to design suitable cyanide containing precursors and then to react such building blocks with metal complexes consisting of accessible sites. The triphos ligand (triphos: 1,1,1-tris(diphenylphosphinomethyl)ethane) has been employed in this vein to prepare metal complexes, one of which is a five coordinate paramagnetic complex (S = 1/2) with a square pyramidal metal center, [CoII(triphos)(CN)2]. A family of molecular squares, [{MIICl2}2{CoII(triphos)(CN)2}2] (M= Mn (2), Fe (3), Co (4), Ni (5), and Zn (6)), has been synthesized by the reaction of CoII(triphos)(CN)2 and MCl2 (M= Mn, Co, Ni, Zn) or Fe4Cl8(THF)6 in CH2Cl2/EtOH mixture. A series of cyanide-bridged trinuclear complexes, {[Co(triphos)(CN)2]2 [M(MeOH)4]}(ClO4)2 ( M = Mn (7), Fe (8), Co (9), and Ni (10)) and tetranuclear complexes, {[Co(triphos)(CN)2]2[M(MeOH)4]2}(ClO4)4 ([Co2M2] M = Mn (11) and Ni (12)) have been synthesized in a similar fashion by the reaction of CoII(triphos)(CN)2 and M(ClO4)2.6H2O (M= Mn, Fe, Co, Ni) in methanol. The trinuclear compounds (7-9), and tetranuclear complexes (2-6, 11, 12), are characterized by antiferromagnetic coupling between metal centers while magnetic behavior of 10 indicates the presence of ferromagnetic interactions between the paramagnetic metal centers. Interactions between magnetic orbitals of Co(II) and M(II) ions were also investigated by means of the density functional theoretical (DFT) calculations. Another triphos containing building block, [(triphos)Re(CN)3] anion (13), has been employed to prepare derivatives of a cubic SMM cluster with four octahedral Re(II) ions and four tetrahedral Mn(II) sites bridging through cyanide ligand. The reactions of Re(II) precursor with MnI2 and solvated Mn(II) ions resulting in derivatives of Re4Mn4 cube with different ligands attached to the Mn center other than the chloride atom were reported. Our efforts on linking these cubes using organo cyanide ligands such as dicyanamide (dca) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) to form extended networks were also discussed.