Salze des neuen Pentacyano‐oxo‐molybdän(IV)‐Anions wurden dargestellt: das blaue Cs2H[MoO(CN)5], und blaues [(CH3)4N]2H[MoO(CN)5] · 2 H2O und [Cr(en)3] [MoO(CN)5] · 4 H2O (grün). Das grüne [(C6H5)4P]3[MoO(CN)5] · 7 H2O kristallisiert triklin in der Raumgruppe P1. Das Molybdän(IV) ist von einer terminalen Oxo‐Gruppe (d(MoO): 1,705(4) Å) sowie einer trans‐ständigen CN−‐Gruppe (d(MoC): 2,373(6) Å) und vier äquatorialen CN−‐Gruppen (mittlerer d(MoC): 2,178 Å umgeben. Die blauen und grünen Salze haben unterschiedliche v(MoO)‐Valenzschwingungen: blau 948 cm−1, grün 920 cm−1. Blaue und grüne Salze des Anions [MoO(OH2)(CN)4]2− mit [(C6H5)4P]+‐ sowie [(C6H5)4As]+‐Kationen wurden dargestellt und ihre Strukturen röntgenographisch bestimmt. [(C6H5)4P]2[MoO(OH2)(CN)4] · 4 H2O (grün) und [(C6H5)4As]2 [MoO(OH2)(CN)4] · 4 H2O (blau) kristallisieren isotyp in der Raumgruppe C 2h5—P21/n. Es handelt sich um Distorsionsisomere des Anions [MoO(OH2)(CN)4]2−: die grüne Form hat d(MoO) = 1,72(2)Å während in der blauen Form ein MoO‐Abstand von 1,60(2) Å gefunden wird; die entsprechenden v(MoO) Valenzschwingungen liegen bei 920 cm−1 und 980 cm−1.

Two remarkable molybdenum complexes have been isolated on recation of aqueous solutions of MoVI oxo anions with H2NOH or MeHNOH: the yellow NO complex (1) and the colorless NO‐free neutral complex (2). This shows that many yellow Mo complexes characterized only in solution pribably contain NO ligands.

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The reaction of [0(V0(R2N0)2)2] (R = ethyl, benzyl) with oxalic acid in ethanol yields colorless neutral complexes of vanadium(V) containing a bridging u4-oxalato ligand: [(V0(R2N0)2)2(C204)]. The reaction of MoG2(Et2NO)2 (Et = ethyl) in ethanol with oxalic acid yields pale yellow crystals of (Et2HNOH)2[Mo204(Et2NO)2(C204)2], This complex has been characterized by a single-crystal X-ray diffraction study. The complex crystallizes in the monoclinic space group P2,/c (Cl*-No. 14) with a = 11.593 (3) A, b = 12.120 (3) A, c = 12.045 (3) A, ß = 102.75 (2)°, V= 1650 A1 23, and Pcaicd = L587 g cm"3 for Z = 2 and mol wt 788.5. Diffraction data were collected on a Syntex R3 diffractometer using 9-26 scan and Mo Ka radiation, and the structure was solved by conventional methods, resulting in a final R factor of 0.051 for 2314 independent reflections. The structure consists of Ar,7V-diethylhydroxylammonium cations and of binuclear dianions, [Mo204(Et2NO)2(C204)2]2 567", upon which a center of symmetry is imposed crystallographically. the Mo(VI) ions are in a distorted pentagonal-bipyramidal environment containing an , -coordinated TV.A-diethylhydroxylamido ligand, a bidentate oxalate anion, and a terminal and two bridging oxo ligands. The two terminal oxo ligands are in a trans position with respect to each other. The structure of the dianion may be regarded as two pentagonal bipyramids sharing an equatorial edge.