Electron Density Distribution of an Oxamato Bridged Mn(II)−Cu(II) Bimetallic Chain and Correlation to Magnetic Properties

Abstract

The electron density distribution of the ferrimagnetic MnCu(pba)(H2O)3.2H2O chain compound, where pba stands for 1,3-propylenebis(oxamato), has been derived from high resolution X-ray diffraction measurements at 114 K using a multipolar model. The analysis of the chemical bonding has been carried out through the "Atoms in Molecules" formalism and thoroughly interpreted with regards to the strong intrachain and weak interchain magnetic couplings. The topological properties of the electron density on the oxamato bridge indicate large electron delocalization and conjugation effects, in addition to high charge transfer from both metals to the bridge. The resulting positive charges on Mn (+1.45 e) and Cu (+1.56 e) induce charge polarization of the bridge, leading to a shift of electron density from the central C atoms to the metal coordinating O and N atoms. The Mn-bridge interactions are mainly closed-shell interactions with low electron density at the corresponding bond critical points, whereas the Cu-bridge interactions exhibit significant covalent character. The Cu-N bonds are moreover stronger than the Cu-O bonds. The 3d Cu and Mn orbital populations are consistent with pyramidal and regular octahedral environments, respectively, in agreement with the loss of degeneracy due to ligand field effects. Interchain interaction pathways are evidenced by the existence of four bond critical points in hydrogen bond regions. Finally, these intrachain and interchain bonding features are correlated to the results of experimental and theoretical spin density distributions, as well as magnetic measurements.

Magnetic superexchange interactions: trinuclear bis(oxamidato) versus bis(oxamato) type complexes

“…However, precise statements on the magnetic coupling path were not derived, although it is at least implied that the N⋯C⋯O unit of the C 2 NO 3 containing oxamato bridge contributes to a larger extent to the magnetic superexchange coupling compared to the O⋯C⋯O unit. 22,23 Certainly, polymeric [{MnCu( pba)-(OH)•2H 2 O} n ] compares marginally with the situation to be discussed here.…”

Towards understanding π-stacking interactions between non-aromatic rings

“…While metalloaromaticity is a somewhat contentious issue (Milčić et al, 2007;Feixas et al, 2013;Masui, 2014;Malenov et al, 2017), it may be expected only in some rare cases of complexes of transition metals with unsaturated , 0 -and , 0 -ligands (Masui, 2014); there is no way that chelate rings with decidedly non-aromatic ligands, such as 2,5-DHQs, can display metalloaromaticity. Moreover, accurate X-ray charge-density data confirmed the nature of metal-ligand bonds for first-row transition metals and the most common N-and O-donor ligands: due to a low electron density at the critical points (mostly >0.5 e Å À3 ) and positive values of the Laplacian, they can be classified as borderline cases between ionic and highly polar covalent interactions (Poulsen et al, 2004;Pillet et al, 2004;Bianchi et al, 2005;Wang, 2014;Vologzhanina et al, 2015;Chuang et al, 2017;Gajda & Woźniak, 2017). M-O bonds in Cu and Mn complexes of 2,5-DHQs [ Fig.…”

Charge density research: from inorganic and molecular materials to proteins

“…The resultant magnetic properties at the macroscopic scale depend on the nature and strength of those interactions. Despite their potentiality, surprisingly only few X-ray high resolution studies have been devoted to these materials [see for example 15,[42][43][44][45][46][47][48]. Among the work performed in our laboratory in this field, we will describe two coordination compounds:…”