Iron(II) complexes of 2,6-di(1-alkylpyrazol-3-yl)pyridine derivatives – The influence of distal substituents on the spin state of the iron centre
作者:Thomas D. Roberts、Marc A. Little、Laurence J. Kershaw Cook、Simon A. Barrett、Floriana Tuna、Malcolm A. Halcrow
DOI:10.1016/j.poly.2013.01.057
日期:2013.11
2,6-Di(1-methyl-pyrazol-3-yl)pyridine (L-Me), 2,6-di(1-allyl-pyrazol-3-yl)pyridine (L-All), 2,6-di(1-benzylpyrazol-3-yl)pyridine (L-Bz) and di(1-isopropyl-pyrazol-3-yl)pyridine (L-iPr) have been synthesized by alkylation of deprotonated di1H-pyrazol-3-yl}pyridine (3-bpp), and converted to salts of the corresponding [Fe(L-R)(2)](2+) complexes (R = Me, All, Bz and iPr). Crystal structures of [Fe(L-Me)(2)]X-2 (X- = BF4-, ClO4- and PF6-), [Fe(L-All)(2)][BF4](2), [Fe(L-Bz)(2)][BF4](2) and [Fe(L-iPr)(2)][PF6](2) have been determined at 150 K. All of these contain high-spin iron centres except [Fe(L-Me)(2)][BF4](2)center dot xH(2)O, which is predominantly low-spin at that temperature. All the complexes are high-spin between 5 and 300 K as solvent-free bulk powders, and are also high-spin in (CD3)(2)CO solution between 193 and 293 K. This was unexpected, since the parent complex [Fe(3-bpp)(2)](2+) undergoes spin-crossover in the same solvent with T-1/2 = 247 K [40]. The high-spin nature of the [Fe(L-R)(2)](2+) complexes in solution must reflect a subtle balance of steric and electronic factors involving the ligand 'R' substituents. (C) 2013 Elsevier Ltd. All rights reserved.