Two isostructural oxalato-bridged dimetallic heptanuclear [(Ba3M4III)-M-II] complexes (M = Cr; Fe) associated with 3-aminopyridinium cations: Synthesis, crystal structure and magnetic properties

摘要

Two heterometallic heptanuclear oxalato-bridged [(Ba3M4III)-M-II] complexes, (Org-H)(6)[Ba-3(H2O)(5.1)Cr-4(C2O4)(12)]center dot 5H(2)O (1) and (Org-H)(6)[Ba-3(H2O)(5.3)Fe-4(C2O4)(12)]center dot 5H(2)O (2) (Org-H = C5H7N2+ : 3-aminopyridinium cation), have been synthesized through an ion-exchange reaction strategy by combining {Ba-6(H2O)(17)[M-III(C2O4)(3)](4)}center dot 7H(2)O (M = Cr; Fe) with (C5H7N2)(2)C2O4 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 [Ba-3(H2O)(5)M-4(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 center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonds link the anions and 3-aminopyridinium cations and lattice water molecules into a three-dimensional framework. In addition, pi-pi stacking interactions [centroid-centroid distances of 3.680 to 3.938 angstrom] 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. (C) 2020 Elsevier Ltd. All rights reserved.