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

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)(SO4)(2)(H2O)(4)]center dot 6H(2)O (1) and [Mn-4(bcp)(2)(N-3)(8)(H2O)(2)]center dot 4H(2)O (2). Compound 1 contains anionic linear [Mn-3(N-3)(2)(COO)(4)(SO4)(2)(H2O)(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)(H2O)(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 center dot center dot center dot 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)(SO4)] 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 2, 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 center dot center dot center dot O)(2)] bridges in both compounds induce weak antiferromagnetic interactions.