Novel coordination polymers generated from angular 2,2′-dipyridyl ligands and bis(hexafluoroacetylacetonate) copper(II):: Crystal structures and magnetic properties

The synthesis of the ligand 2,5-bis(2-pyridylethynyl)thiophene (L2) is described and the coordination chemistry of the 2,2'-long conjugated bidentate ligands 1,2-di(2-pyridyl)butadiyne (L1), 2,5-bis(2-pyridylethynyl)thiophene (U), and 2,2'-dipyridyl disulfide (L3) with Cu(hfaC)(2) (hfac = hexafluoroacetylacetonate) is investigated. Three new coordination polymers {[Cu(hfac)(2)L](n) (1 for L = L1, 2 for L = L2 and 3 for L = L3)} are prepared and fully characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and X-ray diffraction. They are obtained by a combination of L1, L2, or L3 with Cu(hfac)(2)(H2O)-H-. in dichloromethane (CH2Cl2) as the solvent. When CH2Cl2 solutions of 3 were left standing for longer than one day or were refluxed for two days, rearrangements took place and 3 was transformed into 4 and 5. Compounds 1-3 adopt a one-dimensional chain structure with the copper atom in a six-coordinate 4 + 2 pseudooctahedral geometry. In 1 and 2, four equatorial sites Cu-O/N and two axial sites Cu-O are found with an unusual cis orientation of two L-1 or L-2 ligands, respectively, while in 3 the four equatorial sites are defined by four oxygen atoms from two hfac chelating ligands and the axial sites by two nitrogen donors from two trans-L3 ligands. Compound 4 contains a (1-hydro-2-pyridinio)thio group that is bound to a hexafluoroacetylacetonate anion through a S-C bond and 5 is a molecular compound where the Cu-II ion is pentacoordinate to two oxygen atoms of the hfac anion, two nitrogen atoms of two 2-pyridyl sulfide fragments, and one carbon atom of the CC(O)CF3 fragment, which has been inserted into the S-S bond of the 2,2'-dipyridyl disulfide ligand, giving a new tridentate ligand. The reaction of L3 with copper acetate leads to the molecular 1:2 adduct Cu-2(mu-OAC)(4)(L3)(2) (6), where the Cu-II ion is pentacoordinate to four oxygen atoms of four different acetate anions and one nitrogen atom from the pyridine ring of L3 to form a square-pyramidal geometry. (c) Wiley-VCH Verlag GmbH & Co.