Phase transformation induced mechanochromism in a platinum salt: a tale of two polymorphs

Abstract

Red crystals of [Pt(tpy)Cl]NO₃·HNO₃ show mechanochromic behaviour turning yellow when pressure is applied. The electronic character and spectroscopic signature of the red and yellow polymorphs change as a result of slipping of the molecular stacking planes in the solid state. The slippage alters the Pt⋯Pt intermolecular distances from a linear stacked motif with <3.5 Å separations in the red polymorph to a less stacked motif of alternating short intradimer and long interdimer interactions in the yellow polymorph.