Effect of N-donor ancillary ligands on structural and magnetic properties of oxalate copper(II) complexes

Through varying the auxiliary N-donor ligands under similar synthetic conditions nine new compounds: [Cu(C2O4)(pz)]n (1), [Cu(C2O4)(apz)2]n·(3H2O)n (2), [Cu2(μ-C2O4)2(H2O)2(ampz)4] (3), [Cu(C2O4)(mpz)2]n (4), [Cu(C2O4)(aind)2]n (5), [Cu2(C2O4)2(bpzm)2]n·(3.5H2O)n (6), [Cu(C2O4)(ampy)(H2O)]n (7) {[Cu2(μ-C2O4)(aepy)2][Cu(C2O4)2(H2O)2]}n·(2H2O)n (8) and [Cu4(μ-C2O4)3(aepy)4(H2O)2]Cl2 (9) (pz = pyrazole, apz = 3(5)-aminopyrazole, mpz = 3(5)-methylpyrazole, ampz = 3(5)-amino-5(3)-methylpyrazole, aind = 7-azaindole, bpzm = bis(pyrazol-1-yl)methane, ampy = 2-aminomethylpyridine and aepy = 2-(2-pyridyl)ethylamine) have been synthesized and characterised structurally (by single crystal X-ray analysis) and spectroscopically. On the basis of structural data, the influence of neutral N-donor ligands on the control of the final complex structures and the role of weak intermolecular interactions in the creation of molecular architectures have been discussed in detail. The two independent oxalate anions in 1, adopting μ3-oxalato-1κ2O1,O2:2κO1:3κO2a and a relatively rare μ4-oxalato-1κ2O1,O2:2κO1:3κO1a,O2a:4κO2a coordination mode, connect the Cu centers into a two-dimensional net extending along the crystallographic plane (100). Simultaneous existence of both amino and methyl groups in the ampz ligand results in the formation of a 0D dimeric structure of 3. Compounds 2 and 4–8 display one-dimensional coordination structures, and the most significant differences between these structures concern the geometry around the copper(II) center and the coordination mode of the oxalate bridge. The structures of 2–9 are stabilized by the extensive hydrogen-bonding interactions that give rise to the supramolecular architectures. Additionally, the magnetic properties of the complexes 1–9 have been investigated and discussed in the context of their structures