Related Experiment Video
Updated: Aug 5, 2026
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Uncovering Correlations between Structure and Valence Tautomerism in Cobalt-o-Dioxolene Crystals
Marcelo Francis Fernandes Alecrim1, Ludmila Leroy1,2, Lucas Gustavo Gonçalves Pimenta1
1Physics Department, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte, Minas Gerais 31270-901, Brazil.
Abstract:
Bistability in transition-metal complexes can originate from several phenomena, including mixed valence (MV), spin-crossover (SCO), and valence tautomerism (VT). In the latter case, valence-tautomeric interconversion (VTI) generates pairs of switchable redox isomers whose physical properties can be controlled by external stimuli, such as light, temperature, and pressure, making these systems promising candidates for molecular devices, spintronics, and chemosensing. Although several strategies exist to modulate VTI in crystalline materials, tuning intermolecular interactions has emerged as a particularly effective route. In cobalt-o-dioxolene complexes of the type [Co-(dioxolene)2(PyL)2] (PyL = pyridyl-like ancillary ligands), VTI is extremely sensitive to crystal packing and the local chemical environment, and its occurrence can be promoted or suppressed by solvation. Here, we show that, in addition to the intrinsic metal-ligand distance changes across VTI, torsion of the pyridyl ancillary ligands in [Co-(dioxolene)2(Py)2] stabilizes specific electrostatic interactions and acts as a structural trigger for VTI, establishing a direct geometric-electronic coupling mechanism. This conclusion is supported by single-crystal X-ray diffraction (SCXRD) data collected on distinct solvated [Co-(dioxolene)2(Py)2] crystals, complemented by DFT calculations performed with the SIESTA package and benchmarked against experimental magnetic susceptibility data using the local density approximation (LDA) functional. DFT spin-polarization analyses reveal that the torsion angle of the PyL plane in [Co-(dioxolene)2(Py)2] correlates directly with the spin state of the system. This behavior extends to all trans-[Co-(dioxolene)2(PyL)2] derivatives with 3D structures deposited in the Cambridge Structural Database (CSD). Our findings establish a coherent picture of the redox and spin-state dynamics in VT complexes and provide concrete design guidelines for their use in practical solid-state applications.
Related Concept Videos
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...
02:42Valence Bond Theory
02:45Valence Bond Theory
01:29Determination of Crystal Structures
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...
02:46Crystal 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,...