[Cr(AA)(C2O4)2]− and [Cu(bpca)]+ as building blocks in designing new oxalato-bridged CrIIICuII compounds [AA=2,2′-bipyridine and 1,10-phenanthroline; bpca=bis(2-pyridylcarbonyl)amide anion]

The monouclear complex PPh4[Cr(bipy)(ox)2]·H2O (1) and the heterodinuclear compounds [Cu(bpca)(H2O)Cr(bipy)(ox)2]·2.5H2O (2) and [Cu(bpca)(H2O)Cr(phen)(ox)2]·2H2O (3) [PPh4+=tetraphenylphosphonium cation, bpca=bis(2-pyridylcarbonyl)amide anion, ox=oxalate dianion, bipy=2,2′-bipyridine and phen=1,10-phenanthroline] have been synthesized and characterized by single-crystal X-ray diffraction. Discrete [Cr(bipy)(ox)2]− mononuclear anions and tetraphenylphosphonium cations are present in 1 whereas the structures of 2 and 3 are made up neutral oxalato-bridged bimetallic CrIIICuII units. The chromium environment is distorted octahedral in the three complexes: two nitrogen atoms from a bidentate bipy (1 and 2) or phen (3) ligand and four oxygen atoms from two oxalate groups (1–3) build the coordination polyhedron around the chromium atom. The CrN(bipy) [2.055(3) and 2.078(3) Å for 1 and and 2.060(3) and 2.066(3) Å for 2] and CrN(phen) bond lengths [2.056(5) and 2.069(5) Å (3)] are somewhat longer than the CrO(ox) ones [values in the ranges 1.944(2)–1.955(2) (1), 1.948(2)–1.960(2) (2) and 1.945(4)–1.953(4) Å (3)]. The copper atom in 2 and 3 exhibits a distorted square-pyramidal surrounding: three bpca-nitrogen atoms [values of the CuN(bpca) bonds in the ranges 1.922(3)–2.017(3) (2) and 1.918(5)–2.004(6) Å (3)] and a water molecule [CuOw=1.952(3) (2) and 1.952(5) Å (3)] define the equatorial positions whereas an oxalate-oxygen atom occupies the axial site [CuOox=2.253(2) (2) and 2.325(4) Å (3)]. The oxalate bridge in 2 and 3 exhibits a unusual bidentate/monodentate coordination mode, the metalmetal separation across this bridge being 5.283(1) (2) and 5.407(1) Å (3). Magnetic susceptibility measurements of 1–3 in the temperature range 1.9–290 K reveal a Curie law behavior for the three complexes. The preparation of bimetallic systems by using [Cr(AA)(ox)2]− (AA=α-diimine type ligand) as a complex ligand towards coordinatively unsaturated metal complexes is analyzed and discussed.