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 [Cu-2(acac)(2)(dpp)(NO3)(H2O)]NO3 (2) and [Cu-2(Hdpp)(2)(ox)(Cl)(2)(H2O)(2)]Cl-2 center dot 6(H2O) (4) complexes, and four coordination polymers {[Cu-4(dPP)(2)(ox)(Cl)(6)]}(n) (3), {[Cu-4(dpp)(2)(Ox) (NO3)(6)(H2O)(2)]center dot 1.2 (H2O)In (5), {[Cu(dPP)(NO3)] (NO3)center dot(H2O)}(n) (6) and {[Cu(dPP)(SO4) (H2O)(2)]}(n) (7), where acac(-) = acetylacetonate, ox(2-) = 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 [Cu-2(acdpp)(2)(Cl)(4)]center dot 2(MeOH) (8). The structure of 1 consists of neutral, mononuclear [Cu(acac)(dpp)(NO3)] units with acac(-) and dpp acing 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.