Mixed azide–carboxylate bridged tri- and tetranuclear MnII clusters in coordination polymers derived from a zwitterionic dicarboxylate ligand: structures and magnetism

Abstract

Two Mn(II) coordination polymers with azide and the zwitterionic dicarboxylate ligand bis(N-carboxymethyl-4-pyridinium) (bcp) were synthesized, and structurally and magnetically characterized. They are formulated as [Mn(3)(bcp)(2)(N(3))(2)(SO(4))(2)(H(2)O)(4)].6H(2)O (1) and [Mn(4)(bcp)(2)(N(3))(8)(H(2)O)(2)].4H(2)O (2). Compound 1 contains anionic linear [Mn(3)(N(3))(2)(COO)(4)(SO(4))(2)(H(2)O)(4)](4-) units with simultaneous mu(2)-EO (end-on) azide, sulfate and carboxylate bridges, while compound 2 contains [Mn(4)(COO)(4)(N(3))(8)(H(2)O)(2)](4-) clusters with mixed mu(2)-EO azide, mu(3)-EO azide and carboxylate bridges. In these compounds, the anionic tri- or tetranuclear units are linked into coordination chains by the cationic bipyridinium spacers, and are also hydrogen bonded into chains by double O-H...O bridges. Magnetic analyses were carried out on temperature-variable susceptibility data for both compounds, and also on isothermal magnetization data for 1. It is revealed that all the mixed double and triple bridges, [(EO-N(3))(COO)(SO(4))] in 1, [(COO)(EO-N(3))(2)] and [(COO)(EO-N(3))] in 2, transmit antiferromagnetic coupling between Mn(II) ions. The [(EO-N(3))(2)] bridge in , with Mn-N-Mn = 96.6 degrees, also transmits antiferromagnetic coupling, providing the first example in the antiferromagnetic regime predicted theoretically for double EO-azide bridges between Mn(II) ions. The double hydrogen bonding [(O-H...O)(2)] bridges in both compounds induce weak antiferromagnetic interactions.