Coordination polymeric materials in binary and ternary Cu(II)- tetracarboxylato-bipy systems: Structure-reactivity correlation in Cu(II)-(O,N) 1D-3D lattice assemblies

Cu(II) is a metal ion, the aqueous chemistry of which with carboxylic acids draws intense interest, targeting new materials and exemplifying diverse and unique structure-reactivity correlations. Driven by the need to explore the interplay of the chemical interactions of Cu(II) with polycarboxylic acid substrates and the association of such reactivity with lattice architecture and physicochemical properties, binary and ternary systems of Cu(II) with 1,2,3,4-cyclobutane-tetracarboxylic acid (H ₄CBTC) and bipy (2,2′-bipyridine) were investigated. To this end, aqueous synthetic reactions of Cu(II) with H ₄CBTC, under pH-specific conditions (pH 3), led to the isolation of the first species in the aforementioned binary system [Cu ₂(CBTC)(H ₂O) ₄)] _n·2nH ₂O (1). Aqueous synthetic chemical reactivity in the ternary Cu(II)-H ₄CBTC-bipy system led to the isolation of the 1D polymer [Cu(NO ₃) ₂(bipy)] _n (2). Complexes 1 and 2 were characterized by elemental analysis, spectroscopic techniques (EPR, FT-IR, UV-Vis and luminescence (2)), magnetic susceptibility, cyclic voltammetry (2) and thermogravimetric studies, and X-ray crystallography. The molecular lattice in 1 reveals the presence of Cu(II) units bound to (a) 1,2,3,4-cyclobutane- tetracarboxylate, and (b) water molecules, in a tetragonal pyramidal geometry, thereby projecting the unique chemical reactivity in the requisite system leading to a 3D lattice assembly. The presence of two types of channels in the solid state lattice of variable hydrophilicity/hydrophobicity signifies their unique nature in the coordination polymer and projects the importance of H ₂O and its H-bonding ability in the assembly of 1. The molecular lattice of 2 reveals the presence of Cu(II) ions bound to nitrate ions and 2,2′-bipy in an octahedral fashion, collectively leading to a 1D lattice assembly. The magnetic susceptibility and solid-state EPR data on 1 and 2 are consistent with the presence of Cu(II) in a tetragonal pyramidal and octahedral environment, respectively. Collectively, the physicochemical profiles of coordination polymers 1 and 2 earmark: (a) the influence of the polycarboxylic acid nature of the ligand on the chemical reactivity in binary and ternary systems, and (b) the critical nature of interactions in binary and ternary discrete Cu(II)-(O,N) species emerging in aqueous media and influencing the lattice assembly of Cu(II)-carboxylato materials of variable dimensionality (1D-3D), architecture and physicochemical properties.