Structural and Electron Paramagnetic Resonance Studies of the Square Pyramidal to Trigonal Bipyramidal Distortion of Vanadyl Complexes Containing Sterically Crowded Schiff Base Ligands

[ N, N ‘-Ethylenebis( o -( tert -butyl- p -methylsalicylaldiminato)]oxovanadium(IV) ( 1 ), [ N, N ‘-propanediylbis( o -( tert -butyl- p -methylsalicylaldiminato)]oxovanadium(IV) ( 2 ), bis( N -methylsalicylaldiminato)oxovanadium(IV) ( 3 ), bis( N -isopropyl- o -methylsalicylaldiminato)oxovanadium(IV) ( 4 ), and, bis( N -methyl- o -( tert -butyl- p -methylsalicylaldiminato)oxovanadium(IV) ( 5 ) were prepared and characterized by X-ray crystallography and EPR spectroscopy. Complexes 1 and 2 are best described as square pyramids, while complexes 3 − 5 are distorted trigonal bipyramids, demonstrating that oxovanadium(IV) complexes can readily adopt a trigonal bipyramidal geometry. All five compounds give nearly the same parallel hyperfine coupling constant ( A z ) regardless of the fact that the geometry about the vanadium changes from square pyramidal to trigonal bipyramidal. Crystal data for 1: space group P 1̄, a = 7.9382(3) Å, b = 12.6749(7) Å, c = 13.8353(7) Å, α = 109.608(5)°, β = 96.552(5)°, γ = 96.589(5)°, Z = 2. Crystal data for 2: space group I 4 1 / a, a = 16.1895(6) Å, b = 16.1895(6) Å, c = 41.117(3) Å, Z = 16. Crystal data for 3: space group C 2/ c, a = 18.8230(17) Å, b = 7.5118(5) Å, c = 11.7460(10) Å, β = 112.229(7)°, Z = 4. Crystal data for 4: space group P 2 1 / c, a = 9.7086(6) Å, b = 11.4554(7) Å, c = 20.866(2) Å, β = 103.943(6)°, Z = 4. Crystal data for 5: space group Pbca, a = 10.667(3) Å, b = 25.549(5) Å, c = 18.322(4) Å, Z = 8.