SYNTHESIS AND CHEMICAL BEHAVIOR OF THE [CO6NI2C2(CO)16]2- CLUSTER - ELECTROGENERATION OF THE [CO6NI2C2(CO)16]N- (N=1, 3, 4) CLUSTER ANIONS - CRYSTAL AND MOLECULAR-STRUCTURES OF [NET4]2[CO6NI2C2(CO)16] AND [NET4]2[CO6NI2C2(CO)14(CH3CN)2]