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The syntheses of dioxomolybdenum(VI) complexes were attempted using the Schiff base ligands HL1 and HL2. The ligands were prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicyl aldehyde (for HL1) and o-hydroxy acetophenone (for HL2). When MoO2(acac)2 was used as a metal precursor, HL1 yielded the normal ligand exchange product [MoO2(L1)Cl] (1) in a medium acidified by HCl. However, instead of the normal product, HL2 produced two bis chloro dioxomolybdenum(VI) complexes [MoO2(L3)Cl2] (2) and [Mo2O5(L3)Cl2] (3) in the same reaction medium. Here, L3 is a bidentate neutral ligand 2-(3,5-dimethyl-1-pyrazolyl) 4,6-dimethyl pyrimidine, which is afforded by a transformation of the used ligand. This ligand transformation reaction is probably triggered by molybdenum mediated C N bond cleavage in the hydrazone part of HL2 followed by cyclization with acetylacetone released from the metal precursor. Again, when MoO2(acac)2 was reacted with another related ligand H 2 L 1 ′ , a bis salicyl hydrazone of 2,4-dihydrazino pyrimidine, in acidic medium, [MoO2(L4)Cl] (4) was produced as the only product. Here, also a similar ligand transformation, but only to a partial extent, leads to the formation of the ligand HL4, the salicyl hydrazone of 2-hydrazino-4-(3,5-dimethyl-1-pyrazolyl) pyrimidine. HL4, thus produced in the reaction medium binds in a monoanionic fashion to the MoO22+ core to form the complex [MoO2(L4)Cl] (4). The complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1, 2, 3 and 4, as well as the ligand HL2, have been crystallographically characterized in order to probe into the structures and the ligand transformation process in a comprehensive way. |
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