Synthesis, X-ray crystal structure and magnetic properties of oxalate-bridged copper(II) complexes with 2,3-bis(2-pyridyl)pyrazine, 2,3-bis(2-pyridyl)quinoxaline and 2,2’-bipyrazine as peripheral ligands

Click on the DOI link to access the article (may not be free).Five oxalate-containing copper(ii) complexes of formula [Cu(dpq)(H2O)(ox)]·5H2O (1), [Cu(dpp)(H2O)(ox)]·H2O (2), [Cu(bpz)(ox)]n (3), [Cu2(dpp)2(H2O)2(NO3)2(ox)]·4H2O (4) and [Cu2Cl2(bpz)2(H2O)2(ox)][Cu(bpz)(H2O)2(ox)]·2H2O (5) [dpq = 2,3-bis(2-pyridyl)quinoxaline; dpp = 2,3-bis(2-pyridyl)pyrazine; bpz = 2,2′-bipyrazine; ox = oxalate] were prepared and their structures were determined by X-ray diffraction on single crystals. Complexes 1 and 2 are discrete mononuclear complexes with oxalate and dpq (1)/dpp (2) acting as bidentate ligands. Complex 3 is a neutral oxalato-bridged (2,2′-bipyrazine)copper(ii) chain where the oxalate adopts a bidentate/monodentate coordination mode, whereas 4 is an oxalato-bridged copper(ii) dinuclear complex with ox and dpp acting as bis-bidentate and bidentate ligands, respectively. The structure of 5 contains neutral [Cu(bpz)(H2O)2(ox)] (mononuclear) and [Cu2(bpz)2(H2O)2Cl2(ox)] (dinuclear) units where the bpz acts as a bidentate ligand and the oxalate group adopts the bidentate (mononuclear) and bis-bidentate (dinuclear) coordination modes. The copper atoms have distorted square pyramidal (1 and 2) and elongated octahedral (3−5) geometries: two nitrogen atoms from heterocyclic N-donors and two oxalate-oxygen atoms occupy the equatorial positions (1−5) and a water molecule (1 and 2), two oxalate-oxygen atoms (3), a water molecule and a nitrate-oxygen (4), and either two water molecules (5), mononuclear) or a chlorine atom and a water molecule (5, dinuclear) fill the axial ones. Magnetic susceptibility measurements for 3−5 in the temperature range 1.9−290 K reveal the occurrence of weak (J = −1.4 cm−1, 3) and strong (−312 and −345 cm−1 for 4 and 5, respectively; Hˆ = −J·SˆA·SˆB) antiferromagnetic interactions between the copper(ii) atoms in agreement with the out-of-plane (3) and in-plane (4 and 5) exchange pathways involved