Novel Coordination Polymers Generated from Angular 2,2′‐Dipyridyl Ligands and Bis(hexafluoroacetylacetonate) Copper(<scp>II</scp>): Crystal Structures and Magnetic Properties

Abstract

Abstract 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 ( L2 ), 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 · H 2 O in dichloromethane (CH 2 Cl 2 ) as the solvent. When CH 2 Cl 2 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)CF 3 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 (μ‐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. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)