VANADYL(IV) PHOSPHONATES, VOCNH2N+1PO3-CENTER-DOT-XH(2)O (N=0-4, X=1 OR 1.5), AS PRECURSORS OF VANADYL(IV)PYROPHOSPHATE, (VO)(2)P2O7

Vanadyl(N) phosphonates with the formula VOCnH2n+1PO3 . xH(2)O (n = 0-4, x = 1 or 1.5) have been synthesized in organic medium by reaction of V2O5 with the corresponding phosphonic acid. The low-temperature magnetic susceptibility of vanadyl(IV) phosphite (n = 0) and n-butylphosphonate (n = 4) was indicative of antiferromagnetically exchange-coupled V2O9 vanadyl dimers similar to previously reported results for n = 1-3 phosphonates and vanadyl(IV) hydrogen phosphate hemihydrate (VOHPO4 . 0.5H(2)O). Raman spectroscopy of vanadyl(IV) phosphonates (n = 0-4) also suggested the similar local crystalline order in these solids. The close structural relationship between these phosphonates and VOHPO4 . 0.5H(2)O is further substantiated by the thermal transformation of the former phases in the presence of oxygen into vanadyl(IV) pyrophosphate. Kinetic measurements of the n-butane selective oxidation to maleic anhydride demonstrated that vanadyl methylphosphonate (n = 1) and phoshite (n = 0) produced vanadyl pyrophosphate catalysts with comparable (the methylphosphonate) and even superior performance (vanadyl phosphite) compared to the conventional unpromoted vanadium-phosphorus-oxide (VPO) catalyst.