Characterization of local environments in crystalline borophosphates using single and double resonance NMR

Abstract

11B and 31P magic-angle spinning as well as 11B{ 31P} and 31P{ 11B} rotational echo double resonance (REDOR) NMR have been applied to characterize the local environments in the crystalline borophosphates K 3[BP 3O 9(OH) 3], NH 4[ZnBP 2O 8] and Rb 3[B 2P 3O 11(OH) 2]. Dipolar second moment values extracted from the REDOR curves at short evolution times (Δ S/ S 0⩽0.2) are in reasonable agreement with those calculated from the internuclear distances in the corresponding crystal structures. In particular, the method is found to be useful for distinguishing between boron and phosphorus local environments with different numbers of B–O–P connectivities, making REDOR a well-suited tool for medium-range order investigations in glasses.