Hydrothermal synthesis and structural characterization of metal organophosphonate oxide materials: Role of metal-oxo clusters in the self assembly of metal phosphonate architectures

摘要

Two new metal organophosphonate oxide materials with formulas [Cu~ (II)_ 4Cu~I_ 2(L)_2(2,2′- bpy)_6(HPW_(12)O_(40))]_n·4nH_ 2O (1) and [Cu(2,2′-bpy)VO_2(OH)(H_ 2L)]_n (2) have been synthesized starting from the Cu(II) salts, 2,2′-bipyridine (2,2′-bpy), p-xylylenediphosphonic acid (H_4L), and sodium tungstate (for 1)/ammonium metavanadate (for 2). Both the compounds 1 and 2 are characterized by routine elemental analyses, IR spectroscopy, thermogravimetric (TG) analysis, and unambiguously characterized by single crystal X-ray crystallography. The crystal structure of compound 1 consists of 2D copper phosphonate layers connected by the Keggin heteropolyanion to form a three-dimensional (3D) framework. The copper phosphonate layers in compound 1 are fabricated by the rare copper hexanuclear clusters in which the four terminal Cu(II) centers form two eight-membered Cu-dimer (Cu_ 2P_2O_4) rings (top and the bottom) that are connected to each other by the two central Cu(I) atoms of four-membered Cu_ 2O_2 rings. These hexanuclear assemblies are connected to each other along the plane through the p-xylyl linkers to form a two-dimensional (2D) layer. Compound 1 is a unique example in terms of the existence of a hexanuclear copper phosphonate cluster in the 3D coordination matrix. Compound 2 has a 2D structure, in which the one-dimensional [Cu(2,2′-bpy)(H_ 2L)]_n chains are connected by the VO_2OH subunits to from a 2D layer. The formation of VO_2OH in compound 2 ceases the formation of eight-membered Cu-dimer rings. The self-assembly of the polyoxometalates plays an important role in the formation of the metal organophosphonate phases.