%AÜngör, Ökten [Department of Chemistry and Biochemistry, Florida State University, 95 Chieftan Way, Tallahassee, FL 32306, USA]%AChoi, Eun [National High Magnetic Field Laboratory, 1800 E Paul Dirac Dr, Tallahassee, FL 32310, USA]%AShatruk, Michael [National High Magnetic Field Laboratory, 1800 E Paul Dirac Dr, Tallahassee, FL 32310, USA]%BJournal Name: Chemical Science; Journal Volume: 12; Journal Issue: 32 %D2021%I %JJournal Name: Chemical Science; Journal Volume: 12; Journal Issue: 32 %K %MOSTI ID: 10304012 %PMedium: X %TOptimization of crystal packing in semiconducting spin-crossover materials with fractionally charged TCNQ δ anions (0 < δ < 1) %XCo-crystallization of the prominent Fe( ii ) spin-crossover (SCO) cation, [Fe(3-bpp) 2 ] 2+ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ δ − radical anion has afforded a hybrid complex [Fe(3-bpp) 2 ](TCNQ) 3 ·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ RT = 3.1 × 10 −3 S cm −1 , and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ − anions, [Fe(3-bpp) 2 ](TCNQ) 2 ·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy) 2 ](TCNQ) 6 ·2Me 2 CO (4) and [Fe(bzimpy) 2 ](TCNQ) 5 ·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ RT = 9.1 × 10 −2 S cm −1 and 1.8 × 10 −3 S cm −1 , respectively. %0Journal Article