posted on 2014-12-03, 00:00authored byYuan-Zhu Zhang, Philip Ferko, Diana Siretanu, Rodica Ababei, Nigam P. Rath, Michael
J. Shaw, Rodolphe Clérac, Corine Mathonière, Stephen M. Holmes
Two
structurally related and photoresponsive cyanide-bridged Fe/Co
square complexes, {Fe2Co2}, are reported: {[(TpMe)Fe(CN)3]2[Co(bpy)2]2[(TpMe)Fe(CN)3]2}·12H2O (2) and {[(TpMe)Fe(CN)3]2[Co(bpy)2]2[BPh4]2}·6MeCN (3), where TpMe and bpy
are hydridotris(3-methylpyrazol-1-yl)borate and 2,2′-bipyridine,
respectively. Through electrochemical and spectroscopic studies, the
TpMe ligand appears to be a moderate σ donor in comparison
to others in the [NEt4][(TpR)FeIII(CN)3] series [where TpR = Tp, hydridotris(pyrazol-1-yl)borate;
TpMe = hydridotris(3-methylpyrazol-1-yl)borate; pzTp =
tetrakis(pyrazol-1-yl)borate; Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate;
Tp*Me = hydridotris(3,4,5-trimethylpyrazol-1-yl)borate].
The spectroscopic, structural, and magnetic data of the {Fe2Co2} squares indicate that thermally-induced intramolecular
electron transfer reversibly converts {FeIILS(μ-CN)CoIIILS} pairs into {FeIIILS(μ-CN)CoIIHS} units near
ca. 230 and 244 K (T1/2) for 2 and 3, respectively (LS: low spin; HS: high spin).
These experimental results show that 2 and 3 display light-induced {FeIIILS(μ-CN)CoIIHS} metastable states that relax to thermodynamic
{FeIILS(μ-CN)CoIIILS} ones at ca. 90 K. Ancillary TpR ligand donor strength
appears to be the dominant factor for tuning electron transfer properties
in these {Fe2Co2} complexes.