A new copper(II) tubelike metal–organic framework constructed from P,P′-diphenylmethylenediphosphinic acid and 4,4′-bipyridine: Synthesis, structure, and thermal behavior

A new tubular metal–organic framework [Cu2(pcp)2(4,4′-bipy)] · 5H2O (pcp = P,P′-diphenylmethylenediphosphinate) has been synthesized and characterized by single-crystal X-ray analysis, temperature-dependent X-ray powder diffraction (TDXD), thermogravimetric measurements and IR spectroscopy. The structure consists of polymeric nano-sized square channels, whose edges are constituted by infinite chains of metal ions bridged by phosphinate ligands. The chains are linked together by 4,4′-bipyridines, forming the walls of the channels. Solvent water molecules are located inside and outside the channels, all anchored through hydrogen bonds. The cross-section dimensions of the channels are approximately 10 × 10 Å2. The four guest molecules located inside the channels can be eliminated by gentle heating at ca. 80 °C, restored in air, or in turn substituted by DMF through vapour exposition. The monohydrated phase [Cu2(pcp)2(4,4′-bipy)] · H2O, which maintains the same polymeric framework as the title complex, remains stable till 260 °C. Above this temperature the complex undergoes a solid state crystal-to-crystal rapid reaction, via loss of both the 4,4′-bipyridine and the remaining water and rearrangement of the coordinated pcp to give the previously reported [Cu(pcp)] polymeric framework.