The imidazole influence in strontium b-diketonate complex formation

A selection of new strontium beta-diketonate derivatives (imH(2))(2)[Sr-2(beta-dike)(6)] [where imH = imidazole and beta-dike = tfac (tfacH = 1,1,1-trifluoro-2,4-pentanedione), tfbz (tfbzH = 1,1,1-trifluoro-4-phenyl-2,4-butanedione), or hfac (hfacH = 1, 1, 1, 5,5,5-hexafluoro-2,4-pentanedione)], [Sr-2(tfac)(4)(Meim)(2)(H2O)(2)], (MeimH)(2)[Sr(beta-dike)(4)] (where Meim = 1-methylimidazole and beta-dike = tfbz or hfac), [Sr-2(thd)(4)(imH)(2)(EtOH)], and [Sr-2(thd)(4)(Meim)(2)(EtOH)] (where thdH = 2,2,6,6-tetramethyl-3,5-heptanedione) have been synthesized and fully characterized. (imH(2))(2)[Sr-2(beta-dike)(6)] and (MeimH)(2)[Sr(beta-dike)(4)] are di- and mononuclear Sr anionic complexes, respectively, while [Sr-2(tfac)(4)(Meim)(2)(H2O)(2)], [Sr-2(thd)(4)(imH)(2)(EtOH)], and [Sr-2(thd)(4)(Meim)(2)(EtOH)] are neutral dinuclear molecular derivatives. The derivative (imH(2))(2)[Sr-2(hfaC)(6)] slowly decomposes in solution under aerobic conditions, giving (imH(2))(2)[Sr(H2O)(2)(tfa)(3)](tfa) (tfaH = trifluoroacetic acid), which is an ionic compound containing polynuclear anionic chains composed of Sr(H2O)(2)(tfa)(3) units. When a deficiency of imH is employed, the thdH proligand forms not only the dinuclear derivative [Sr-2(thd)(4)(imH)(2)(EtOH)] but also an additional product with the formula [Sr(thd)(2)(H2O)(2)(EtOH)], in which the Sr atom is seven-coordinated. A complete solid-state characterization has been accomplished by comparing X-ray and solid-state C-13 NMR data. Elucidation of the H-bond interaction between the heterocyclic rings and metal complexes by cross-polarization magic-angle-spinning N-15 NMR is also reported.