Versatility of copper(II) coordination compounds with 2,3-bis(2-pyridyl)pyrazine mediated by temperature, solvents and anions choice

Tuning reaction temperatures as well as the variation in starting copper salts and solvents led to the formation of a new series of Cu(II) coordination compounds with 2,3-bis(2-pyridyl)pyrazine (dpp): a mononuclear [Cu(acac)(dpp)(NO3)] (1) complex, two dinuclear [Cu2(acac)2(dpp)(NO3)(H2O)]NO3 (2) and [Cu2(Hdpp)2(ox)(Cl)2(H2O)2]Cl2·6(H2O) (4) complexes, and four coordination polymers {[Cu4(dpp)2(ox)(Cl)6]}n (3), {[Cu4(dpp)2(ox)(NO3)6(H2O)2]∙1.2(H2O)}n (5), {[Cu(dpp)(NO3)](NO3)·(H2O)}n (6) and {[Cu(dpp)(SO4)(H2O)2]}n (7), where acac− = acetylacetonate, ox2− = oxalate. Remarkably, the treatment of Cu(II) chloride dihydrate with dpp in methanol solution led to an unusual in situ condensation of dpp with acac− to produce [Cu2(acdpp)2(Cl)4]·2(MeOH) (8). The structure of 1 consists of neutral, mononuclear [Cu(acac)(dpp)(NO3)] units with acac− and dpp acting as bidentate ligands. In 2, the dpp ligand coordinates in a bis-chelating mode to two Cu(II) ions and bridges them into a dimeric entity, whereas an oxalate linker joins [Cu(Hdpp)(Cl)2(H2O)]+ units into a dimer in 4. Compounds 3, 5, 6 and 7 are 1D chain coordination polymers, which incorporate two symmetry independent metal centers and different bridging ligands: Hdpp+ as a protonated cationic or dpp as a neutral chelating ligand and oxalate, Cl− anions or sulfate di-anions as bridging ligands. Magnetic studies were performed on samples 1 and 2, and the analysis reveals a very weak magnetic exchange coupling mediated via the dpp ligand.