A NEW TETRATUNGSTATE, [W4O4CL10 (NBU(T)4]2-, AND ITS DEGRADATION TO THE MONONUCLEAR COMPLEX [WOCL2(NBU(T) (BIPY)] OR [WCL2(NBU(T)2(BIPY)] (BIPY = 2,2'-BIPYRIDINE)

The [NBu(n)4]+ and [P(CH2Ph)Ph3]+ salts of the tetranuclear tungstate [W4O4Cl10(NBu(t))4]2- have been prepared from WOCl4 and NH2Bu(t) in the presence of chloride ions. The crystal structure of the phosphonium salt has been determined and shows bridging oxo ligands [W-0 1.88 angstrom (av.) and WOW 159.6-degrees (av.)] and terminal tert-butylimido groups [W-N 1.70 angstrom (av.) and WNC 174.9-degrees (av.)]. Two mu-chloro ligands occupy positions trans to the imido groups [W-Cl 2.66 angstrom (av.) and WCIW 115.6-degrees (av.) ] while the remaining chlorides are terminal [W-Cl 2.41 A (av.)]. The structure is stable towards 1,2-dimethoxyethane but is degraded on addition of 2,2'-bipyridine (bipy). At lower temperatures, treatment of [W4O4Cl10(NBu(t)4]2- with bipy gives [WOCl2(NBu(t))(bipy)], whereas [WCl2(NBu(t))2(bipy)] is crystallised from a similar reaction carried out in refluxing toluene. In the oxo complex W-N 1.741 (6), W-0 1.716(5) and W-N(bipy) 2.313(5) (trans to 0) and 2.335(5) angstrom (trans to NBu(t). In the bis(imido) complex W-N 1.754(5) and 1.747(5) and W-N(bipy) 2.373(5) and 2.370(5) angstrom. These results are compared with crystal structures of related complexes in an effort to understand the bond-length variations in terms of the trans influences and steric properties of the pi-bonding imido and oxo ligands.