Polymorphism in dinuclear Cu(II) compounds – polymorphism caused by different degrees of hydration: the structures of [Cu(HL)]2Cl24H2O (I), [Cu(HL)]2Cl2 · 2H2O (II), [Cu(HL)]2)(NO3)2 · 4H2O (III), [Cu(HL)]2)(NO3)2 · 2H2O (IV) and [Cu(HL)]2)(ClO4)2 · 2H2O

Compounds of composition [Cu(HL)]2Cl2 · 4H2O (I), [Cu(HL)]2Cl2 · 2H2O (II), [Cu(HL)]2)(NO3)2 · 4H2O (III), [Cu(HL)]2)(NO3)2 · 2H2O (IV) and [Cu(HL)]2)(ClO4)2 · 2H2O (V) (HL=[(3-aminopropyl)-di-(2-hydroxopropyl)]-amine anion) were prepared and their crystal structures determined. Compounds I, IV and V crystallize in the same space group, P21/n, and are very close to being isomorphous and isostructural. II Crystallizes in space group Pcab, while III crystallizes in C2/c. The pairs of compounds I–II and III–IV are examples of hydration polymorphism. Efforts to obtain polymorphic forms of V have, thus far, been negative. All five compounds contain a central bi-metallic core consisting of two Cu(II) cations bridged by two oxygens. The resulting species are antiferromagnetically coupled and can nicely be fitted to a Bleany–Bowers model with great precision. Electron spin resonance studies were carried out in solid powders and in frozen solutions, at 77 K in both instances. The g-factors obtained from the latter studies were used in the fitting of the magnetism measurements, which were made between 5 and 295 K. Counter anions were changed on purpose in order to ascertain the manner in which counter ions exert an effect in the selection of the crystallization pathway chosen. Also, solvent changes were made which resulted in the polymorphism observed, and which was due to variations in the ratios of the solvent components (e.g., methanol–water). All five cations contain one Cu(II)–OH2 bond; and, the length of this bond is the primary difference in the stereochemistry of the cations. They range from 2.731 to 3.959 Å. A discussion is given of the arguments for and against considering the two longest distances (3.827 and 3.959 Å) as true bonds.