Some studies of Nb6Cl14,7H2O and analogous compounds

Abstract

The previously known staphylonuclear halides, Nb6Cl14,7H2O; Nb6Brl4,7H2O (in trifling yield) ; Ta6Cl14,7H2O ; and Ta6Br14,7H2O have been prepared, but intended studies of these have been frustrated by their instability and insolubility. It has been possible, however, to obtain approximate molar conductivities in water and ethanol which support the formulation of (Nb6Cl12)Cl2,7H2O as a 2 : 1 electrolyte, and evidence by pH titration of the existence of the complex ion [(Nb6Cl12)(OH)4- (H2O)p]2- in alkaline solution. The absorption spectra of the four halides have been obtained over the range 8-50 kK in neutral and alkaline aqueous solution and in the solid state. It is proposed that the very strong bands in the visible and infrared region result from transitions from metal-to-metal bonding to metal-to-metal anti-bonding levels. Excellent agreement can be obtained between the experimental frequencies of the (Nb6Cl12) group and those predicted from the molecular orbital energy diagram of Cotton and Haas. It is proposed that Harned's brown chloride is a similar material to the green Nb6Cl14,7H2O but additionally contains μ-hydroxo derivatives of the type [Nb6Cl(12-n)(OH)n]Cl2, resulting from the mode of preparation of the material.