Experimental charge density of ferrocenyl derivative of β-lactam

Abstract A single crystal of a ferrocenyl derivative – cis-4-(2-ferrocenylphenyl)-3-hydroxyazetidin-2-one (FER), combining two chemically and biologically important systems (ferrocene and β-lactam), has been analysed from the structural, energetic and experimental charge density distribution perspectives. Investigated compound crystallizes in the chiral orthorhombic P212121 space group. Molecules of FER are arranged in a “zig-zag” manner and participate in a network of N–H⋯O and O–H⋯O hydrogen bonds as well as C–H···π contacts. The R 2 2 ( 9 ) ring motif of H-bonds, atypical for the mono−β−lactams, was observed. An experimental charge density model was obtained using the Hansen-Coppens multipole formalism. Energy density descriptors at bond critical points allowed classification of Fe–C interactions in FER as intermediate type with some features of covalency. The charge distribution for the ferrocenyl moiety is analogous to those previously reported, however in the case of the β-lactam substantial differences are present. Conjugation of ferrocenyl with β-lactam does not significantly affect the charge density distribution in either of these fragments. The unique R 2 2 ( 9 ) system of H-bonds was found to elude a typical topological H-bond classification.