Conformational flexibility in amidophosphoesters: a CSD analysis completed with two new crystal structures of (C6H5O)2P(O)X [X = NHC7H13 and N(CH2C6H5)2].

The crystal structures of diphenyl (cycloheptylamido)phosphate, C19H24NO3P or (C6H5O)2P(O)(NHC7H13), (I), and diphenyl (dibenzylamido)phosphate, C26H24NO3P or (C6H5O)2P(O)[N(CH2C6H5)2], (II), are reported. The NHC7H13 group in (I) provides two significant hydrogen-donor sites in N-H...O and C-H...O hydrogen bonds, needed for a one-dimensional hydrogen-bond pattern along [100] in the crystal, while (II), with a (C6H5CH2)2N moiety, lacks these hydrogen bonds, but its three-dimensional supramolecular structure is mediated by C-H...π interactions. The conformational behaviour of the phenyl rings in (I), (II) and analogous structures from the Cambridge Structural Database (CSD) were studied in terms of flexibility, volume of the other group attached to phosphorus and packing forces. From this study, synclinal (±sc), anticlinal (±ac) and antiperiplanar (±ap) conformations were found to occur. In the structure of (II), there is an intramolecular Cortho-H...O interaction that imposes a +sc conformation for the phenyl ring involved. For the structures from the CSD, the +sc and ±ap conformations appear to be mainly imposed by similar Cortho-H...O intramolecular interactions. The large contribution of the C...H/H...C contacts (32.3%) in the two-dimensional fingerprint plots of (II) is a result of the C-H...π interactions. The differential scanning calorimetry (DSC) analyses exhibit peak temperatures (Tm) at 109 and 81 °C for (I) and (II), respectively, which agree with the strengths of the intermolecular contacts and the melting points.