ANOMALOUS BEHAVIOR OF [NB(CO)6]- AND [TA(CO)6]- TOWARDS PROTONS - CRYSTAL AND MOLECULAR-STRUCTURE OF THE ORGANO-METALLIC ACID [C4H8OH]+[NB2(CO)8CL3]-.C4H8O

Treatment of [M(CO)J - with HX (X = CI, AcO) under anhydrous conditions or in aqueous buffered solution yielded the diamagnetic [M2(C0)8X3-] anions of d4 niobium([) and tantalum(!); the crystal and molecular structure of the title compound was solved by X-ray diffraction methods, showing that each niobium centre is heptaco-ordinated to four terminal carbonyl groups and to three bridging chlorides