Two new XP(O)[NHC(CH3)3]2 phosphoramidates, with X = (CH3)2N and [(CH3)3CNH]2P(O)(O).

In N,N'-di-tert-butyl-N'',N''-dimethylphosphoric triamide, C(10)H(26)N(3)OP, (I), and N,N',N'',N'''-tetra-tert-butyl[oxybis(phosphonic diamide), [corrected] C(16)H(40)N(4)O(3)P(2), (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 R(2)(1)(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 R(2)(2)(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)(2)P(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)(2)P(O)(NH) and P(O)(NH)(3) fragments.