Structural diversity and magnetic properties of Co(ii)/Mn(ii)/Ni(ii) coordination polymers constructed from an unsymmetrical tetracarboxylic acid and varying N-donor ligands

Abstract

Seven new coordination polymers (CPs), namely, [M₂(α-bptc)(phen)·2H₂O]·3H₂O (M = Co, for 1; Mn, for 2), [M₂(α-bptc)(bpea)·7H₂O]·H₂O (M = Co, for 3; Ni, for 4), [Co₃(α-Hbptc)₂(4,4′-bipy)₂·4H₂O]·2H₂O (5), [Co₄(α-bptc)₂(bpee)₃·2H₂O]·2H₂O (6), and [Ni₄(α-bptc)(4,4′-bipy)₂(OH)₄·4H₂O]·13H₂O (7) (α-H₄bptc = 2,3,3′,4′-biphenyl tetracarboxylic acid, phen = 1,10-phenanthroline, bpea = 1,2-bis(4-pyridyl)ethane, 4,4′-bipy = 4,4′-bipyridine, bpee = 1,2-bis(4-pyridyl)ethylene), based on an unsymmetrical tetracarboxylic acid with the aid of varying ancillary N-donor ligands have been synthesized under hydrothermal conditions. Interestingly, the unsymmetrical tetracarboxylate linked Co(II)/Mn(II)/Ni(II) ions to give diverse structural fragments, which were connected by various ancillary N-donor ligands, resulting in the formation of CPs with different structural topologies. Complexes 1 and 2 were isomorphous and showed a 1D tube-like [M₂(α-bptc)·2H₂O] network decorated with phen moiety. Complexes 3 and 4 were also isomorphous and displayed a 1D ladder-like chain structure assembled by [M₂(α-bptc)·7H₂O] metallacycles as nodes and bpea as linkers. Complex 5 featured a 3D CdS net with 4-connected (6⁵·8) topology constructed by the combination of 1D [Co₃(α-Hbptc)₂·3H₂O] zigzag chain and 4,4′-bipy. Complex 6 exhibited a novel 3D framework with (4,4,6)-connected (4²·4²·6) topology formed through the integration of [Co₂(α-bptc)·H₂O] double layers with bpee. Complex 7 possessed a 3D bcu-x net with 4-connected (7⁴·8²) topology, yielded by linking the 4,4′-bipy with left- and right-handed [Ni₄(α-bptc)(OH)₄·4H₂O] helical chains. Magnetic susceptibility measurements indicated the ferromagnetic behaviours of complex 7.