Five- and six-fold coordinated silicon in silicodiphosphonates: short range order investigation by solid-state NMR spectroscopy?

New Journal of Chemistry Pub Date: 2020-02-24 DOI: 10.1039/C9NJ05943A

Abstract

The structure of amorphous silicodiphosphonates made from diphosphonic acids and tetraethoxysilane was investigated by 1H, 13C, 29Si, and 31P single pulse and cross polarization (CP) MAS NMR spectroscopy as well as 1H–31P{29Si} REDOR, 1H–31P–29Si and 1H–29Si–13C double CP MAS experiments. The combination of these solid-state NMR techniques leads to a structural understanding of the short range order. The structure is dominated by [Si(OP)6] units. Besides a few [SiO4] groups, we noticed that HEDP based silicodiphosphonate possesses further five- and sixfold coordinated silicon moieties. Another synthesis route to obtain Si–O–P compounds with higher coordinated silicon species is the reaction of trimethylsilyl-substituted diphosphates and diphosphonates with tetramethoxysilane. The 29Si CP NMR spectra also demonstrate polymeric structures with different [SiO4] units in the solids. Both silyl-substituted phosphorus precursors show a surprising triplet signal in the 29Si INEPT NMR spectra that we interpret using higher order coupling patterns.

Graphical abstract: Five- and six-fold coordinated silicon in silicodiphosphonates: short range order investigation by solid-state NMR spectroscopy
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