Polymorphism in P,P-[3]ferrocenophanes: insights from an NMR crystallographic approach

Abstract

Polymorphism phenomena in P,P-[3]ferrocenophanes were studied by ³¹P and ¹³C solid-state NMR spectroscopy and suitable DFT calculations. “No-bond” indirect ³¹P⋯³¹P spin–spin coupling constants serve as a rather sensitive tool for the characterization of such systems, particularly since this NMR observable strongly depends on intermolecular P⋯P distances and mutual orientations of the phosphorus lone pairs. Indeed, the structure of a previously unknown pseudo-polymorphism of a P,P-[3]ferrocenophane was determined via the emerging tool kit of “NMR crystallography”, where structural inputs and constraints determined by modern solid-state NMR techniques, aided by DFT calculations, are used for faster and more reliable structure solution or refinement of X-ray powder diffraction patterns. Based on this approach it is demonstrated that the observed pseudo polymorphism is related to reversible incorporation of dichloromethane in the crystal structures.