A first exploration of isostructurality in transition metal nitroprussides: X-ray analysis, magnetic properties and DFT calculations

Abstract

Five new transition metal nitroprussides with 1-methylimidazole (1-MeIm) have been synthesized and characterized by IR, XPS and UV-vis spectroscopy, thermal analysis, and powder and single-crystal X-ray diffraction. The structural analyses have revealed that the complexes Mn(1-MeIm)₂[Fe(CN)₅NO] (1), Fe(1-MeIm)₂[Fe(CN)₅NO] (2), Cu(1-MeIm)₄[Fe(CN)₅NO] (3), Zn(1-MeIm)₂[Fe(CN)₅NO] (4) and Cd(1-MeIm)₂[Fe(CN)₅NO] (5) are 2D coordination polymers. The supramolecular self-assembly of all the five complexes is governed by non-classical C–H⋯N hydrogen bonds and lone-pair(O)⋯π interactions. N⋯O chalcogen and π⋯π contacts are also present in the crystal packing of complexes 1, 2, 4 and 5. A detailed analysis of four geometric descriptors revealed the existence of a high degree of isostructurality for the molecular pair 1/2, and a moderate one for the pairs 1/5 and 2/5. The dissimilarity index was also calculated for molecular pairs in two series of related compounds, showing that the degree of similarity is lower than those found in the pairs 1/2, 1/5 and 2/5. The results herein discussed for first time in the literature may be useful to understand property/structure relationships in these types of complexes. By using DFT calculations at the PBE0-D3/def2-TZVP level of theory and discrete models of the coordination polymers, we have analyzed cooperative lp–π/π–π/π–lp assemblies that are observed in the solid state of these compounds. This interesting assembly has been further analyzed by a combination of QTAIM, NCIplot and MEP surface calculations. The magnetic measurements indicate that compounds 1–3 are paramagnetic at 300 K and the Curie–Weiss constants are negative, suggesting weak antiferromagnetic coupling between the metal centers, at very low temperatures.