Synthesis, crystal structure, and magnetic properties of two-dimensional divalent metal glutarate/dipyridylamine coordination polymers, with a single crystal-to-single crystal transformation in the copper derivative

Hydrothermal reaction of divalent metal chlorides with glutaric acid and 4,4′-dipyridylamine (dpa) has afforded an isostructural family of coordination polymers with formulation [M(glu)(dpa)]n (M=Co (1), Ni (2), Cu (3); glu=glutarate). Square pyramidal coordination is seen in 1–3, with semi-ligation of a sixth donor to produce a “5+1” extended coordination sphere. Neighboring metal atoms are linked into 1D [M(glu)]n neutral chains through chelating/monodentate bridging glutarate moieties with a syn–anti binding mode, and semi-chelation of the pendant carboxylate oxygen. These chains further connect into 2D layers through dipodal dpa ligands. Neighboring layers stack into the pseudo 3D crystal structure of 1–3 through supramolecular hydrogen bonding between dpa amine units and the semi-chelated glutarate oxygen atoms. The variable temperature magnetic behavior of 1–3 was explored and modeled as infinite 1D Heisenberg chains. Notably, complex 3 undergoes a thermally induced single crystal-to-single crystal transformation between centric and acentric space groups, with a conformationally disordered unilayer structure at 293 K and an ordered bilayer structure at 173 K. All materials were further characterized via infrared spectroscopy and elemental and thermogravimetric analyses.