Two Cyanide-Bridged MnII-NbIV Coordination Chain Ferrimagnets Promoted by Interchain Ferromagnetic Interactions

Abstract

Two new coordination chain compounds based on octacyanoniobate(IV) are reported: {[MnII(bpy)(H2O)2]2[NbIV(CN)8]·5H2O}n (1) and {[MnII(bpy)(H2O)2][MnII(bpy)2][NbIV(CN)8]·5H2O}n (2) (bpy = 2,2′-bipyridine). Both have the topology of vertex-sharing CN-bridged squares. The Mn2Nb2 units are mutually parallel in 1 and perpendicular in 2. The antiferromagnetic intrachain interactions between the MnII and NbIV centers in 1 and 2, typical for MnII-[NbIV(CN)8] family of compounds, lead to ferrimagnetic ground state of each single chain. Both compounds show bulk ferrimagnetic ordering below their critical temperatures (Tc) of 6.4 K in 1 and 4.7 K in 2. Such a behavior is due to the ferromagnetic interchain interactions, assured by the π-π contacts between the 2,2′-bipyridine rings and by the hydrogen bonds between the terminal cyanide ligands of the [NbIV(CN)8]-building blocks and coordination/crystallization water molecules. 1 and 2 are rare examples of ferrimagnets promoted by interchain ferromagnetic exchange, and the Tc of 1 is one of the highest among similar 1-D coordination polymers.