Related Experiment Video
Updated: May 15, 2026
Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
Published on: June 9, 2023
Magnetostructural correlation for rational design of Mn(II) hybrid-spin complexes
Anela Ivanova1, Julia Romanova, Alia Tadjer
1Department of Physical Chemistry, Faculty of Chemistry and Pharmacy, University of Sofia, 1 James Bourchier Avenue, 1164 Sofia, Bulgaria. aivanova@chem.uni-sofia.bg
Abstract:
The magnetic properties of a series of manganese(II) diacetylacetonate and dihexafluoroacetylacetonate hybrid-spin complexes with neutral pyridine-based organic radicals were characterized theoretically by DFT calculations. Three stable radicals, in which a radical group is bound in either para or meta position with respect to the pyridine nitrogen atom, were considered. The correct stable structures and multiplets of the complexes were obtained by full geometry optimization starting from an ideal structure. A total of three important geometry descriptors of the complexes were monitored and related to their magnetic characteristics. These structural parameters are (i) the torsion angle governing the conjugation of the organic radical m-PyNO (anti versus gauche), (ii) the coordination geometry of the acetyl acetonate ligands around the metal ion (square versus rhombic), and (iii) the relative orientation of the organic radical with respect to the acetyl acetonate plane (parallel versus perpendicular). It was found that the magnetic properties are not sensitive to the orientation of the radicals with respect to the equatorial plane but do depend on the conformation of the organic radicals. Even a spin switch between the ferromagnetic (S = (7)/(2)) and antiferromagnetic (S = (3)/(2)) ground state was found to be feasible for one of the complexes upon variation of the organic radical geometry, namely, the dihedral angle between the organic radical moiety and the pyridine ring. The pattern of molecular orbital overlap was determined to be the key factor governing the exchange coupling in the modeled systems. Bonding π-type overlap provides antiferromagnetic coupling in all complexes of the para radicals. In the meta analogues, the spins are coupled through the σ orbitals. A low-spin ground state occurs whenever a continuous σ-overlap pathway is present in the complex. Ferromagnetic interaction requires σ-π orthogonality of the pyridine atomic orbitals and/or π-antibonding Mn-pyridine natural orbital overlap. Using an estimate of the donor-acceptor energy stabilization, the affinity of a given Mn(II) d-orbital to mix with the sp(2) orbital from pyridine can be predicted.
Related Concept Videos
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:42Valence Bond Theory
02:34Structural Isomerism
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can be...
02:57Coordination Number and Geometry
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...