Mononuclear and dinuclear iron thiocyanate and selenocyanate complexes of tris-pyrazolyl methane ligands

Treatment of Fe(NCE)(2) (E = S or Se) with 1 equiv. of tris-(3,5-dimethylpyrazol-1-yl)methane (tpm') yields dimeric [{Fe(NCE)(mu-NCE)(tpm')}(2)]. These dinners are cleaved in MeCN solution, yielding isolable [Fe(NCE)(2)(tpm')(NCMe)], whose solvent ligands can be substituted by moderately basic heterocycle donors to give [Fe(NCE)(2)(tpm')(py)], [Fe(NCS)(2)(tpm')(im)] or [{Fe(NCE)(2)(tpm')}(2)(mu-4,4'-bipy)]. The monodentate heterocycles in the latter compounds are readily lost in most solvents, regenerating the dimeric starting materials. [Fe(NCS)(2)(tpm')(py)] was also prepared by reacting [Fe(NCS)(2)(py)(4)] with tpm'. The mononuclear compounds are all high-spin between 5 and 300 K, despite mostly having regular coordination geometries and tpm' ligand conformations that should in principal favour spin-crossover. Analogous products containing unsubstituted tris-(pyrazol-1-yl)methane (tpm) could not be isolated, but the crystal structure of the double salt [Fe(tpm)(2)][Fe(NCS)(5)(py)], containing a new iron(III) anion, is described. (C) 2008 Elsevier Ltd. All rights reserved.