A powdered crystalline mixture of iron(II) chloride tetrahydrate (FeCl2·4H2O) and 1,10-phenanthroline (phen) was subjected to mechanical stressing in Ar by a planetary ball-mill. By milling for 3h, the mixture turned completely non-crystalline. New IR absorption bands appeared simultaneously at 358cm-1 due to Fe-N(phen) stretching and at 207cm-1 due to N-Fe-N(phen) bending for [Fe(phen)3]2+. Only a doublet peak due to [Fe(phen)3]Cl2·nH2O was detected in the Mössbauer spectrum. All these results indicate consistently the formation of [Fe(phen)3]Cl2·nH2O by milling with an almost quantitative yield. Disproportionation of the hydrated water molecules was observed after milling FeCl2·4H2O alone for 3h. The molecular strain triggers a solid-state exchange reaction between H2O and phen at the contact point of two dissimilar solid particles under mechanical stressing, and promotes formation of [Fe(phen)3]Cl2·nH2O in the solid state.
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