The Role of Coulomb Interactions for Spin Crossover Behaviors and Crystal Structural Transformation in Novel Anionic Fe(III) Complexes from a π-Extended ONO Ligand

Abstract

Abstract:To investigate the π-extension effect on an unusual negative-charged spin crossover (SCO) Fe III complex with a weak N 2 O 4 first coordination sphere, we designed and synthesized a series of anionic Fe III complexes from a π-extended naphthalene derivative ligand. Acetonitrile-solvate tetramethylammonium (TMA) salt 1 exhibited an SCO conversion, while acetone-solvate TMA salt 2 was in a high-spin state. The crystal structural analysis for 2 revealed that two-leg ladder-like cation-anion arrays derived from π-stacking interactions between π-ligands of the Fe III complex anion and Coulomb interactions were found and the solvated acetone molecules were in one-dimensional channels between the cation-anion arrays. A desolvation-induced single-crystal-to-single-crystal transformation to desolvate compound 2' may be driven by Coulomb energy gain. Furthermore, the structural comparison between quasi-polymorphic compounds 1 and 2 revealed that the synergy between Coulomb and π-stacking interactions induces a significant distortion of coordination structure of 2.

High-Temperature Cooperative Spin Crossover Transitions and Single-Crystal Reflection Spectra of [FeIII(qsal)2](CH3OSO3) and Related Compounds

“…The literature [9] disclosed that [Fe(qsal) 2 ](NCSe)•solv were transformed into [Fe(qsal) 2 ](NCSe) by desolvation. Moreover, the time-dependence of the spin-states in [Fe(qsal) 2 ](NCS) was reported in the literature [8], suggesting that the desolvation from [Fe(qsal) 2 ](NCS)•solv to [Fe(qsal) 2 ](NCS) took place at 286 K. Very recently, similar desolvation-induced crystal structure transformations in the charged Fe(II) and Fe(III) compounds were reported [57,58], which seemed to be driven by Coulomb interactions. In general, the Coulomb interaction is much stronger than other intermolecular interactions.…”

“…The Mössbauer spectra were recorded on a constant acceleration spectrometer with a source of 57 Co/Rh in the transmission mode. The measurements at low temperature were performed with a closed-cycle helium refrigerator (Iwatani Co., Ltd., Japan).…”

Spin-Singlet Transition in the Magnetic Hybrid Compound from a Spin-Crossover Fe(III) Cation and π-Radical Anion

“…Recently we found strong intermolecular interactions such as hydrogen-bonding and Coulomb interactions prevented Fe(III) complexes from exhibiting SCO [47,48]. As these observations are compared with functional SCO hybrid compounds [5,7,22,23], the competition of intermolecular interactions between SCO and functional units play a key role in the development of a synergistic functional SCO compound.…”

Cation modulated spin state and near room temperature transition within a family of compounds containing the same [FeL2]2− center

“…As far as we are aware, these currently include several Fe II compounds fabricated with three coordination sites chelated by tripodal pyridine ligands and their derivatives with the other three sites ligated by three SCN − anions, 55–59 and only two Fe III compounds by O,N,O-tridentate ligands. 60,61 Very recently, we reported another type of anionic [FeL 2 ] 2− (H 2 L = pyridine-2,6-bi-tetrazolate) SCO compound that assembles through deprotonation self-assembly, which is further linked into a molecular square with an enhanced SCO property by coordination-directed self-assembly. 33 Given that the tetrazolate group of ligand H 2 L is a hydrogen-bonding acceptor-rich unit, we anticipated that the substitution of various organic amine cations would allow us to tune the SCO properties by adjusting the H-bond numbers between the spin-inactive amine cations and spin-active anionic Fe II centers, as well as the spatial arrangement of the Fe II centers.…”