In N,N'-di-tert-butyl-N",N"-dimethylphosphoric triamide, C10H26N3OP, (I), and N,N',N",N'"-tetra-tert-butoxybis(phosphonic diamide), C16H40N4O3P2, (II), the extended structures are mediated by P(O)…(H—N)2 interactions. The asymmetric unit of (I) consists of six independent molecules which aggregate through P(O)…(H—N)2 hydrogen bonds, giving R21(6) loops and forming two independent chains parallel to the a axis. Of the 12 independent tert-butyl groups, five are disordered over two different positions with occupancies ranging from 1/6 to 5/6. In the structure of (II), the asymmetric unit contains one molecule. P(O)…(H—N)2 hydrogen bonds give S(6) and R22(8) rings, and the molecules form extended chains parallel to the c axis. The structures of (I) and (II), along with similar structures having (N)P(O)(NH)2 and (NH)2P(O)(O)-P(O)(NH)2 skeletons extracted from the Cambridge Structural Database, are used to compare hydrogen-bond patterns in these families of phosphoramidates. The strengths of P(O)[…H—N]x (x = 1, 2 or 3) hydrogen bonds are also analysed, using these compounds and previously reported structures with (N)2P(O)(NH) and P(O)(NH)3 fragments.

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