Hydrothermal Synthesis and Structural Characterization of Metal Organophosphonate Oxide Materials: Role of Metal-Oxo Clusters in the Self Assembly of Metal Phosphonate Architectures

Two new metal organophosphonate oxide
materials with formulas [CuII4CuI2(L)2(2,2′-bpy)6(HPW12O40)]n·4nH2O (1) and [Cu­(2,2′-bpy)­VO2(OH)­(H2L)]n (2) have been synthesized starting from the Cu­(II) salts, 2,2′-bipyridine
(2,2′-bpy), p-xylylenediphosphonic acid (H4L), 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 (Cu2P2O4) rings (top and the bottom) that are connected
to each other by the two central Cu­(I) atoms of four-membered Cu2O2 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)­(H2L)]n chains are connected by the
VO2OH subunits to from a 2D layer. The formation of VO2OH 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.