Synthesis, crystal structure and magnetic properties of two oxalato-bridged dimetallic trinuclear complexes combined with a polar cationElectronic supplementary information (ESI) available: Crystal packing of 1and field dependence of Mof 1and 2. CCDC reference numbers 762572and 762573. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c002468f

Two isostructural heterometallic trinuclear oxalato-bridged complexes of formula C4[MCr2(ox)6(H2O)2]·nH2O (C+= 4-aminopyridinium; ox2−= oxalate dianion; M2+= Mn2+, n= 3, 1; M2+= Co2+, n= 3.25, 2) have been synthesized by using direct self-assembly methods combining C3[Cr(ox)3] and the chloride salts of the corresponding metal ion. The crystal structures of both compounds have been resolved by single-crystal X-ray diffraction. They crystallize in the C2/cspace group [a= 11.5113(15) Å, b= 20.250(3) Å, c= 21.810(4) Å, β= 100.447(10)°, V= 5161.6(3) Å3, and Z= 4 for 1, and a= 11.4334(16) Å, b= 20.243(2) Å, c= 21.805(3) Å, β= 101.113(9)°, V= 4951.9(11) Å3, and Z= 4 for 2]. The structures of 1and 2consist of discrete linear [MCr2(ox)6]4−bimetallic trinuclear units, pyridinium cations and crystallization water molecules. The linear trinuclear unit is built from a central trans-diaquametal(ii), linked to two Cr(ox)3]3−entities by oxalate bridges. One of the oxalate ions is coordinated to the central metal ion whereas the other two oxalate ligands are non-bridging. In the crystal, intermolecular hydrogen bonds involving oxalate ligands, water molecules and pyridinium cations, build a complex three-dimensional network. Variable-temperature magnetic susceptibility measurements for 1and 2indicate a weak ferromagnetic interaction (J= +1.16 and +2.62/+2.70 cm−1for 1and 2, respectively) between the two terminal CrIII(SCr= 3/2) and the central high-spin MnII(SMn= 5/2) and CoII(SCo= 3/2) ions. The nature and the amplitude of the exchange interaction are rationalized using DFT calculations and orbital interpretations. [ABSTRACT FROM AUTHOR]