Two new CCl3C(O)NHP(O)X compounds [X = NH(CH2)3NH (1) and NHCH2C(CH3)2CH2NH (2)] were synthesized and characterized by spectroscopic methods and X-ray crystallography. In each of 1 and 2, the phosphoryl and carbonyl groups are gauche relative to one another and the P atom is in a tetrahedral environment. The 1,3-diazaphosphorinane moiety adopts conformation between chair and envelope with the P=O in an equatorial position. In the structure 1, the asymmetric unit contains one molecule; whereas, the asymmetric unit of 2 is composed of two independent molecules. In the crystal packing of 1 and 2, the N-H...O hydrogen bonds lead to two-dimensional arrangements along (-101) plane for 1 and (010) plane for 2. In order to precise assignments of different N-H units stretching frequencies in compounds 1 and 2, quantum chemical calculations were performed, with B3LYP method using 6-311++G(d,p) basis set. Theoretical procedure was performed for the individual molecule (monomer) and also for the hydrogen-bonded clusters of the molecules. In the H-bonded molecules, the effect of hydrogen bonds formation and their strengths in different N-H...O=P and N-H...O=C units were considered to close the theoretical frequencies of absorption bands to the real values. It is found that the stronger N-H...O=P hydrogen bond creates more changes in the N-H stretching frequency than the weaker N-H...O=C hydrogen bond makes. The natural bond orbital analysis showed a positive character for H atom and a negative character for N and O atoms. The hydrogen bond formation was studied by the AIM method through the Laplacian analysis.

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