Syntheses, structures, and magnetic properties of heterometallic coordination polymers with carboxyphosphonate linkers

Five heterometallic coordination polymers were synthesized utilizing the multifunctional carboxyphosphonate ligand N-(phosphonomethyl)iminodiacetic acid (H₄PMIDA), N(CH₂PO(OH)₂)(CH₂COOH)₂, with a coordinating nitrogen atom and two carboxylate and one phosphonate groups. The compounds were characterized structurally and magnetically. [Cu₂M₂(PMIDA)₂(H₂O)₆]·3H₂O for M = Mn (1-CuMn), Co (2-CuCo), and Cd (3-CuCd) are isostructural (space group P2₁/n) and made of honeycomb-like 2D layers which, in turn, are made of unusual double-stranded meso-helices. [Cu₂Ln₂(PMIDA)₂(C₂O₄)(H₂O)₆]·3.5H₂O for Ln = La (4-CuLa) and Nd (5-CuNd)) are also isostructural (P2₁/c) but with open 3D framework structures. They contain dinuclear CuLn(PMIDA) secondary building units that are bridged by phosphonate tetrahedra and form infinite chains along the c axis. The chains are interconnected via carboxylic groups and form double-decker layers which, in turn, are connected by the oxalate linkers to form the open three-dimensional framework. The magnetic properties of the compounds were measured and analyzed in detail.