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

Two MnII 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 [Mn3(bcp)2(N3)2(SO4)2(H2O)4]·6H2O (1) and [Mn4(bcp)2(N3)8(H2O)2]·4H2O (2). Compound 1 contains anionic linear [Mn3(N3)2(COO)4(SO4)2(H2O)4]4− units with simultaneous μ2-EO (end-on) azide, sulfate and carboxylate bridges, while compound 2 contains [Mn4(COO)4(N3)8(H2O)2]4− clusters with mixed μ2-EO azide, μ3-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-N3)(COO)(SO4)] in 1, [(COO)(EO-N3)2] and [(COO)(EO-N3)] in 2, transmit antiferromagnetic coupling between MnII ions. The [(EO-N3)2] bridge in 2, with Mn–N–Mn = 96.6°, also transmits antiferromagnetic coupling, providing the first example in the antiferromagnetic regime predicted theoretically for double EO-azide bridges between MnII ions. The double hydrogen bonding [(O–H⋯O)2] bridges in both compounds induce weak antiferromagnetic interactions.