Polynuclear CoII,III compounds containing pivalate and hexafluoroacetylacetonate anions in the ligand shell and their heterospin complexes with nitroxides

Abstract

The reaction of cobalt(II) bis(hexafluoroacetylacetonate) (Co(hfac)2) with polynuclear CoII or CoII,III pivalates, [Na2Co4(OH)2(Piv)8(EtOH)4], [Co2(H2O)(Piv)4(HPiv)4], and [CoIII2CoII4(O)2(Piv)10(H2O)(THF)3]·1.5THF (Piv is pivalate), affords the previously unknown cobalt compounds containing coordinated Piv and hfac anions in the ligand shell, viz., the dinuclear complex [Na2Co2(hfac)4(Piv)2(Me2CO)4], the tetranuclear complex [Co4(Piv)4(hfac)2(OH)2(HPiv)4]·HPiv, and the tetradecanuclear complex [CoIII4CoII10(Piv)10(hfac)4(OH)14(O)2(HPiv)4]·2HPiv·2H2O·3C7H16, respectively. The tetradecanuclear complex has an unusual ability to precipitate nitroxides from solution, due to which the following new heterospin crystalline solids were synthesized: [Co14(Piv)10(hfac)4(OH)14(O)2(H2O)2(HPiv)2]·2NIT-Me·2HPiv·C6H14, [Co14(Piv)10(hfac)4(OH)14(O)2(HPiv)4]·2NIT-Et·2CHCl3, [Co14(Piv)10(hfac)4(OH)14(O)2(HPiv)4]·2NIT-Ph·2C6H14, [Co14(Piv)10(hfac)4(OH)14(O)2(HPiv)4]·2L1·2CH2Cl2, and [Co14(Piv)10(hfac)4(OH)14(O)2(HPiv)4]·2L2·C6H14, where NIT-Me, NIT-Et, and NIT-Ph are 2-imidazoline nitroxides, L1 is 3-imidazoline nitroxide, and L2 is di-tert-butyl nitroxide. The X-ray diffraction study showed that the efficient binding of nitroxides is provided by the specific arrangement of the μ3-OH groups in the [Co14(Piv)10(hfac)4(OH)14(O)2(HPiv)4] molecule, which is spatially complementary for the formation of numerous hydrogen bonds with the nitroxide moiety. The coordination of the nitroxides by terminal cobalt ions is impossible because this would lead to the impermissible spatial overlap of the atoms of the tetradecanuclear moiety and the nitroxide. The spatial characteristics of only NIT-H containing the H atom in position 2 of the 2-imidazoline ring are suitable for the direct coordination of the nitroxide, which made it possible to synthesize the complex [Co14(Piv)10(hfac)4(OH)14(O)2(H2O)4(NIT-H)2]·4HPiv·2H2O.