Concentration Gradient-Induced Syntheses and Crystal Structures of Two Copper(II) Coordination Polymer Based on Phthalic Acid and 2,2'-Bipyridine.

The reaction of copper nitrate, phthalic acid (1,2-H2BDC), and bipyridine in ammonia/ethanol media affords two multi-copper (II) cluster-based coordination polymers, namely {[Cu4(bpy)4(OH)2(BDC)2]·2OH·13H2O}n (USC-CP-6) and {[Cu2(BDC)2(bpy)2(H2O)]·3H2O}n (USC-CP-7), under ambient conditions, with CP-6 forming at the bottom and CP-7 at the upper edge of the same beaker. The single-crystal structures reveal that it is a rare case of gradient-induced formation of different multi-copper(II) cluster-based CPs within a single-solution chemical reaction. CP-6 crystallizes in the monoclinic system, sp. gr. P21/c, and is composed of chair-like tetranuclear [Cu4(μ3-OH)2(bpy)4(BDC)2]2+ clusters as secondary building units, bridged by BDC2- ligands to form a two-dimensional layer framework, while CP-7 crystallizes in the monoclinic system, sp. gr. P21/n, with binuclear [Cu2(1,2-BDC)2(bpy)2(H2O)] clusters linked by bridging BDC2- ligands to form a one-dimensional looped double chain. Through intermolecular π-π stacking and hydrogen bonds between the coordination water, lattice water, and free oxygen atoms from carboxylate, both compounds yield a 3D supramolecular structure.