[Cr(bpym)(C2O4)2]− in designing heterometallic complexes. Crystal structures and magnetic properties of PPh4[Cr(bpym)(C2O4)2]·H2O and [Ag(bpym)][Cr(C2O4)2](H2O)2]·2H2O (bpym=2,2′-bipyrimidine)

The preparation, crystal structure and magnetic properties of PPh4[Cr(bpym)(C2O4)2]·H2O (1) and [Ag(bpym)][Cr(C2O4)2(H2O)2]·2H2O (2) (C2O4 2−=oxalate dianion, bpym=2,2′-bipyrimidine and PPh4 +=tetraphenylphosphonium cation) are described. The structure of 1 is made up of discrete (2,2′-bipyrimidine)bis(oxalato)chromate(III) anions, teraphenylphosphonium cations and uncoordinated water molecules. The structure of 2 consists chains of univalent silver cations bridged by bis-chelating 2,2′-bypyrimidine, cis-diaquabis(oxalato)chromate(III) anions and crystallisation water molecules. The chromium atom in 1 and 2 has a slightly distorted octahedral geometry with two bidentate oxalate groups (1 and 2), and one bidentate bpym ligand (1) or two cis-coordinated water molecules (2). The CrO(ox) bonds are in the ranges 1.951(3)–1.981(3) Å (1) and 1.9575(12)–1.9585(14) Å (2), values which are shorter than the CrO(w) bonds in 2 [1.9999(16) Å]. The CrN(bpym) bond lengths are 2.064(4) and 2.090(4) Å for 1. The silver atom in 2 is disordered with two different four-coordinated environments from two bpym groups. One of these environments can be defined as a flattened tetrahedron with AgN(bpym) distances of 2.331(2) Å (x2) and 2.360(2) Å (x2) and the second one is distorted with values of the AgN(bpym) bonds in the range 2.132(18) and 2.59(2) Å. The silver–silver separation across bridging bpym is 6.1854(8) Å. Magnetic susceptibility measurements of 1 and 2 in the temperature range 1.9–290 K reveal the occurrence of weak antiferromagnetic interactions together with zero-field splitting effects. The use of the [Cr(bpym)(C2O4)2]− unit of 1 as a ligand towards different univalent and divalent metal ions is discussed in the light of the available structural information.