Synthesis and Characterization of Vanadium(IV) and (V) Complexes with 2‐Hydroxy‐acetophenone‐semicarbazone (H 2 hasc) as Ligand. X‐Ray Crystal Structures of [VO 2 (H 2 hasc)] and [VO 2 (Hhasc)]

Three novel vanadium complexes with pharmacologically active ligands were synthesized and characterized: [V IV O(acac)(Hhasc)], [V IV O 2 (H 2 hasc)], and [V V O 2 (Hhasc)], where H 2 hasc = 2‐Hydroxy‐acetophenone‐semicarbazone. The analytical methods used included FTIR, 1 H‐, 13 C‐, 51 V‐NMR and EPR spectroscopies, elemental analysis and X‐ray diffractometry from single crystals. The crystal and molecular structures of [V IV O 2 (H 2 hasc)] and [V V O 2 (Hhasc)] were determined. [V IV O 2 (H 2 hasc)] crystallizes monoclinic [P2 1 /c, Z = 4, a = 783.4(2), b = 1024.9(2), c = 1365.5(3) pm, β = 99.506(14)°]. The (VO 2 ) 2+ core is coordinated to a neutral O , N , O ‐tridentate unit of the H 2 hasc ligand, with the vanadium atom showing a square pyramidal coordination sphere. In the crystal of [V V O 2 (Hhasc)], triclinic [ ${\rm P}{\bar 1}$ , Z = 4, a = 858.73(11), b = 967.39(5), c = 1318.63(12) pm, α = 97.423(5), β = 101.590(6), γ = 98.144(5)°], two symmetry independent (VO 2 ) + cores are observed. Each of them coordinates to a monodeprotonated Hhasc − unit, in a O , N , O ‐tridentate mode. One assumes a square pyramidal geometry for the pentacoordinate vanadium(V) center. An additional interaction is observed for the other one, involving the phenolate oxygen atom from a symmetry related unit, resulting in a [5+1]‐coordination number for the transition metal atom.