101257-38-9Relevant articles and documents
Extension of Azine-Triazole Synthesis to Azole-Triazoles Reduces Ligand Field, Leading to Spin Crossover in Tris-L Fe(II)
Brooker, Sally,Singh, Sandhya
, (2020)
The first examples of azole-Triazole Rat ligands, bidentate L4NMeIm(3-(1-methyl-1H-imidazol-4-yl)-5-phenyl-4-(p-Tolyl)-4H-1,2,4-Triazole) and L4SIm (4-(5-phenyl-4-(p-Tolyl)-4H-1,2,4-Triazol-3-yl)thiazole), have been prepared, by extension of the general synthesis used to access many examples of azine-Triazoles. The tris-L FeII complexes of the azine-Triazoles are consistently low spin (LS). As intended, these new azole-Triazole ligands provide lower field strengths, resulting in high-spin (HS) [FeII(L4NMeIm)3](BF4)2 (1·4H2O) and spin crossover (SCO) active [FeII(L4SIm)3](BF4)2 (2·0.5H2O). Single-crystal structure determinations revealed that at 100 K 1·solvents is HS whereas 2·solvents is LS. Solid-state variable temperature magnetic studies of air-dried crystals showed that the methylimidazole-Triazole complex 1·4H2O remains HS while the thiazole-Triazole complex 2·0.5H2O undergoes a two-step gradual SCO (T1/2 approximately 275 and 350 K). Variable-Temperature Evans method NMR studies of 2, in five different solvents (CD3NO2, CD3CN, CD3COCD3, CD2Cl2, and CDCl3) gave T1/2 values in a relatively narrow range, 214-259 K. These T1/2 values did not correlate with the solvent polarity index P′ (R2 = 0.25) but did correlate with the solvent basicity parameter SB (R2 = 0.90). Variable-Temperature UV-vis studies on a golden yellow CH3CN solution of 2, with monitoring of the d-d transition at 530 nm (? = 39 L mol-1 cm-1 at 293 K) while the solution was heated from 253 to 303 K, showed that the high-spin fraction increased from 0.51 to 0.77. Cyclic voltammetry studies in CH3CN revealed a Fe(III)/Fe(II) redox process that was reversible for 1 and irreversible for 2, with significant tuning of the Epa value: The methylimidazole-Triazole complex 1 is significantly easier to oxidize (0.46 V) than the thiazole-Triazole complex 2 (0.68 V; both vs 0.01 M Ag/AgNO3).