Two isostructural oxalato-bridged dimetallic heptanuclear [BaII3MIII4] complexes (M = Cr; Fe) associated with 3-aminopyridinium cations: Synthesis, crystal structure and magnetic properties

Abstract Two heterometallic heptanuclear oxalato-bridged [BaII3MIII4] complexes, (Org-H)6[Ba3(H2O)5.1Cr4(C2O4)12]·5H2O (1) and (Org-H)6[Ba3(H2O)5.3Fe4(C2O4)12]·5H2O (2) (Org-H = C5H7N2+: 3-aminopyridinium cation), have been synthesized through an ion-exchange reaction strategy by combining {Ba6(H2O)17[MIII(C2O4)3]4}·7H2O (M = Cr; Fe) with (C5H7N2)2C2O4 in a 1:3 M ratio. They have been characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction and variable temperature magnetic susceptibility measurements. The hybrid salts 1 and 2 are isostructural and they crystallize in the monoclinic space group C2/c. Their structures consist of [Ba3(H2O)5M4(C2O4)12]6− dimetallic heptanuclear units (M = Cr, Fe), six 3-aminopyridinium cations and five crystallization water molecules. The d-metal atom is located in a distorted (2 + 2 + 2) octahedral environment of six O atoms from three chelating oxalato(2−) ligands. In the crystal, intermolecular N H⋯O and O H⋯O hydrogen bonds link the anions and 3-aminopyridinium cations and lattice water molecules into a three-dimensional framework. In addition, π-π stacking interactions [centroid-centroid distances of 3.680 to 3.938 A] between the pyridine rings contribute to the stabilization of the framework. The magnetic properties of the two salts have been investigated and they revealed weak antiferromagnetic coupling between d-metal atoms.