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Keywords: Vanadium / Oxo complexes / NMR spectroscopy / Hydrazones / N ligands / O ligands The dioxovanadium(V) complexes M[VO 2 (L)solv] (2, 5, 6) have been isolated along with dimeric, oxo-bridged monooxovanadium complexes with the formula [{VOL} 2 µ-O] (1, 4), and characterised by their spectral and thermogravimetric properties and reactivity patterns. H 2 L is the hydrazone H 2 {(R-sal)-iNH} [sal derives from salicylaldehyde (R = H) or p-Cl-salicylaldehyde (R = Cl)] or H 2 hap-iNH,where hap is the o-hydroxyacetophenone moiety, and iNH stands for isonicotinic acid hydrazide. In the isolated potassium (M = K) complexes 2a, 5 and 6, solv is a water molecule, [a]

where H 2 sal-sbdt are the Schiff bases formed between salicylaldehyde and dithiocarbazates) have been synthesised, and the structures of 1 and 2 revealed by X-ray diffraction analyses. The ligands coordinate in the tridentate ONS fashion out of the enethiolate tautomeric form. The potassium counterions, coordinated to water molecules, the phenolate-O, the oxo groups on vanadium and, in the case of 1, to the thiolate, provide interlinkages between the

Vanadium complexes containing [VO] 2+ , [VO] 3+ , [VO 2 ] + and [VO(O 2 )] + cores with ligands (LH) derived from 2-acetylpyridine and S-benzyldithiocarbazate (Hacpy-sbdt, I) or Smethyldithiocarbazate (Hacpy-smdt, II) are introduced. The dioxovanadium(V) complexes [VO 2 L] [HL = I (2), II (5)] were isolated from the reaction between LH and [VO(acac) 2 ] in the presence of air and KOH in dry methanol. Treatment of II with aerated [VO(acac) 2 ] in wet methanol yielded the malonato complex [VO(acpy-smdt)mal] (6), with the malonate ligand originating from acetylacetonate. Under anaerobic reaction conditions, LH replaced one of the acac(1−) ligands to yield the oxovanadium(IV) complexes [VO(acac)L] [HL = I (1), II (4)]. Treatment of these complexes with H 2 O 2 , catechol or benzhydroxamic acid gave rise to oxo(peroxo)vanadium complexes [VO(O 2 )L] [HL = I (3), II (7)], catecholato com-

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