SYNTHESIS AND STRUCTURAL INVESTIGATION OF POLYOXOMOLYBDATE COORDINATION-COMPOUNDS DISPLAYING A TETRANUCLEAR CORE - CRYSTAL AND MOLECULAR-STRUCTURES OF [N-BU4N]2[MO4O10(OME)4X2] (X = -OME, -CL) AND THEIR RELATIONSHIP TO THE CATECHOLATE DERIVATIVE [N-BU4N]2[MO4O10(OME)2(OC6H4O)2] AND TO THE DIAZENIDO COMPLEXES OF THE O-AMINOPHENOLATE AND THE NAPHTHALENE-2,3-DIOLATE DERIVATIVES [N-BU4N]2[MO4O6(OME)2(HNC6H4O)2(NNC6H5)4] AND [N-BU4N]2[MO4O6(OME)2(C10H6O2)2(NNC6H5)4] - COMPARISON TO THE STRUCTURE OF A BINUCLEAR COMPLEX WITH THE [MO2(OME)2(NNC6H5)4]2+ CORE, [MO2(OME)2(H2NC6H4O)2(NNC6H5)4]4