Conformational Diversity of Thiosemicarbazonatovanadium(V) Complexes in the Solid State: From Polymorphism to Isostructurality

New alkoxooxovanadium(V) complexes, [VO(L)(OR)] (OR = OMe (1), OEt (2), OPr (3)), were synthesized by the reaction of assorted vanadium precursors and 4-methoxysalicylaldehyde 4-phenylthiosemicarbazone (H2L) in appropriate alcohols. Complexes 2 and 3 crystallized each in two polymorphic forms, which can be selectively prepared by using either a vanadium(IV) or a vanadium(V) precursor. The conformational flexibility of these complexes manifests itself in conformational polymorphism (2a and 2b, 3a, and 3b), conformational isomorphism (2b, 3a, and 3b), and conformational synmorphism (3a and 3b). The largest conformational differences are found in the spatial arrangements of the coordinated alkoxo groups and the phenyl rings of the ligand. The isostructurality of complexes 2b and 3a reflects, on the other hand, their conformational similarity, with nearly the same pattern of intermolecular interactions dominating within their crystal architectures. However, unlike the case in 3a, the structure of 2b exhibits disorder in the stacking of molecular layers, which can be tentatively correlated with the crystallization rate. All compounds were thoroughly investigated by various solid-state methods, while the thermodynamic relation of polymorphs 2 and 3 was assessed via competitive slurry and thermal experiments.