Abundant Solvatomorphism-Tuned Spin Crossover in a Dinuclear Fe(II) Compound: Computational Insights on Molecular Distortion and Packing Effects

Abstract

A series of solvates based on a dinuclear Fe­(II) complex [(TPA)2Fe2(μ-DHBQ)]­[BF4]2·S [S = CH3OH (1·CH 3 OH), 2CH3OH (2·2CH 3 OH), 4DMF (3·4DMF), 2Et2O (4·2Et 2 O), Et2O·MeCN (5·Et 2 O·MeCN), and 2CH2Cl2 (6·2CH 2 Cl 2 )] were synthesized. Upon solvent removal, single-crystal-to-single-crystal (SC-to-SC) transitions could occur for the first four solvates to give 1, 2, 3, and 4·0.5Et 2 O. Within the temperature range of 400–10 K, these compounds exhibited abundant variations in their spin crossover (SCO) properties. 2,5·Et 2 O·MeCN and 6·2CH 2 Cl 2 displayed half high-spin (HS) to low-spin (LS) transitions, and 4·2Et 2 O underwent incomplete LS-to-HS conversion, whereas other solvatomorphs showed complete SCO. As all these solvatomorphs possessed the identical [(TPA)2Fe2(μ-DHBQ)]­[BF4]2 core, these variations in SCO behavior emphasized the critical role of the crystal lattice contributions. With the aim of deciphering their origin, periodic DFT+U+D3 computations were performed on these solvatomorphs to quantify the importance of all possible intramolecular and intermolecular effects on their spin-state energetics. Computationally, the isolated [(TPA)2Fe2(μ-DHBQ)]2– molecule in the gas phase would undergo SCO around 350 K in one step intrinsically. However, distinctive roles of the crystal-lattice effects in the solid state resulted in varying SCO behaviors. Different reasons were discovered for the incomplete spin transitions of different solvatomorphs. For 2, although serious volume shrinkage of the LS state caused efficient packing of the overall crystal-lattice organization, the originally close-packing SCO cations got loose and thus strongly destabilized its LS state. For 5·Et 2 O·MeCN and 6·2CH 2 Cl 2 , severe molecular distortions kinetically trapped their LS state. These computationally magneto-structural studies on dinuclear solvatomorphs have great importance for designing SCO compounds with selected properties, which is critical for their actual application.

Solvatomorphism, polymorphism and spin crossover in bis[hydrotris(1,2,3-triazol-1-yl)borate]iron(ii)

“…32 On the other hand, numerous examples of solvatomorphs in SCO complexes have also been reported mainly in the polymeric Fe(II) Hofmann type and in molecular Fe(II) and Fe(III) compounds. [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] These solvatomorphs result from a mixture of crystals obtained serendipitously, by a vapor-induced single-crystal-to-single-crystal transformation or growing crystals by liquid-liquid diffusion methods. In the present case, solvatomorphs were obtained by changing the solvent during the recrystallization procedure.…”

Heteroleptic iron(ii) complexes of chiral 2,6-bis(oxazolin-2-yl)-pyridine (PyBox) and 2,6-bis(thiazolin-2-yl)pyridine ligands – the interplay of two different ligands on the metal ion spin sate

“…5, top). 41 The equilibrium is complete around 170 K, and the material is fully low-spin below that temperature.…”

Two-Dimensional Spin-Crossover Molecular Solid Solutions with Tunable Transition Temperatures across 90 K

“…ΔH elec was the major factor affecting T c , while the other three terms (ΔH vib , ΔS elec and ΔS vib ) were similar for these halogen-substituted analogs. 35 Isolated Molecules. From a ligand field strength perspective, it is important to note that the F atom possesses greater electronegativity than the Cl atom.…”

“…These effects can initially perturb subtle energy distinctions between spin states, and their contribution to the energy difference (Δ H ) can be of comparable magnitude to that of Δ H itself. The integration of periodic density functional theory (DFT) calculations augmented with the Hubbard U term and D3 dispersion correction (DFT + U + D 3) has demonstrated greater efficacy and plays a significant role in elucidating the connections between molecular structure and observed properties. , …”

“…The integration of periodic density functional theory (DFT) calculations augmented with the Hubbard U term and D3 dispersion correction (DFT + U + D3) has demonstrated greater efficacy and plays a significant role in elucidating the connections between molecular structure and observed properties. 34,35 Inspired by pioneering research, this study introduced a novel solid-solution SCO system characterized by distinct Detailed analysis of the X-ray single-crystal structure revealed the exact position of the halogen atoms between the layers. Additionally, the interlayers exhibited both weaker and stronger F-involved hydrogen bonds.…”