M₆O₄(OH)₄ of M = Sn, Pb: Single Crystal Growth and Crystal Structure Determinations Far Away from Routine

Abstract

Single crystals of Sn6O4(OH)4 have been grown over a period of more than a decade in hermetically sealed flasks of various triorganotin(IV)-trihydrides in toluene/N,N-dimethylformamide and those of Pb6O4(OH)4 on a petri dish within some days from the reaction of Pb(ClO4)2 with Sr(OH)2·8H2O. High-resolution X-ray diffraction data of the tetragonally crystallizing compounds have been collected conventionally at 100 K. Crystal structure determinations have been performed in space groups P4/mnc and P4¯21c with different structure models because of a pretended specific systematic extinction condition. Its violation was routinely overseen because of the very low intensities of the respective reflections, an effect reinforced by crystal size. The non-existence of this systematic extinction was experimentally confirmed by studying the datasets in more detail, including the simulation of layer photographs. The importance of additional information obtained from dataset analysis tools and structure validation programs to assess the different structure models is demonstrated. Structures of both molecules are analyzed with respect to the molecules as a whole as well as to their constructive building units: two crystallographic different prototypes of {MO4} coordination polyhedra with a bent seesaw conformation, one μ3-OH- and one μ3-O- group, each trigonal-pyramidally coordinated.

Keywords

• crystal growth
• systematic extinction condition
• space group determination
• refinement strategies
• structure validation
• building units