Solvatomorphism with polar protic/aprotic and non-polar solvents in a series of complexes derived from the 5-phenylimidazole/tetrafluoroborate/copper(ii) reaction system

Abstract

In a search to explore the structural landscape of possible copper(II) complexes with the 4-phenylimidazole/ tetrafluoroborate combination, considerable solvatomorphism has emerged. The utilization of a wide variety of crystallization solvents (polar protic, polar and non-polar aprotic) resulted in a series of seventeen crystalline solvatomorphs with the general formulae [Cu(BF₄)₂(HL)₄]·x(solvent) [HL = 5-phenylimidazole, x(solvent) = 2(acetone)·2(water) (1), 2(methanol) (2), 2(ethanol) (3), 2(1-propanol) (4), 1.4(2-propanol) (5), 2(1-butanol) (6), 2(iso-butanol) (7), 1.33(tert-butanol) (8), 2(1-pentanol) (9), 2(dimethylformamide) (10), 1.2(acetone) (11), 2(tetrahydrofurane) (12), 1.85(1,4-dioxane) (13), 0.86(ethyl acetate) (14), 1(diethyl ether) (15), 0.7(diisopropyl ether) (16), 1(n-hexane) (17)]. A reaction using the CH₂Cl₂/MeCN solvent system produced crystals of the [Cu(HL)₄(MeCN)(H₂O)_0.4](BF₄)₂ complex (18). Crystallization with nitromethane yielded [Cu{SiF₂O(OMe)}₂(HL)₄]·0.8MeNO₂ (19·0.8MeNO₂), due to the in situ reaction of fluoride ions from BF₄⁻ ions with the glass surface of the vial used to grow crystals. The structures have been solved by single-crystal X-ray diffraction and the complexes were characterized by thermal analysis and infrared spectroscopy. The crystallization solvents are located in channels, with the exception of 1.33(tert-butanol) (8) and 1.2(acetone) (11) residing in lattice pockets. An analysis to understand the role of the solvents in the molecular self-assembly process is described. Depending on the hydrogen-bond functionalities of each solvent, three distinct cases emerge i) the solvents link neighboring [Cu(BF₄)₂(HL)₄] molecules via N–H⋯O_solvent–H⋯F intermolecular associations (polar protic solvents, compounds 1–9), ii) they are terminally connected to [Cu(BF₄)₂(HL)₄] molecules (polar aprotic solvents, compounds 10–13) and iii) they simply reside in channels without any involvement in supramolecular motifs (non-polar solvents, compounds 14–17). The final crystal packings result from the concerted action of robust N–H⋯F synthons and the above described interactions involving the solvent molecules.