Four new crystal structures, P(O)(OC6H5)2(NHNHC6H5) (I), P(S)(OCH3)2(NHCH(CH3)2) (II), P(S)(OCH3)2(NH-cyclo-C5H9) (III) and [2–Cl–C6H4CH2NH3]2[(CH3S)P(O)(O)–O–P(O)(O)(SCH3)] (IV) were studied. The P–O–C angles were analyzed, considering phosphoryl compound (I) and thiophosphoryl compounds (II) and (III) and their analogous structures deposited in the Cambridge Structural Database (CSD), including 282 P(O)(O)2(N) structures (706 P–O–C angles) and 186 P(S)(O)2(N) structures (518 P–O–C angles) with at least one P–O–C angle. The maximum populations of P–O–C angles are within 120°–122° in both P(O)(O)2(N) and P(S)(O)2(N) families of structures, confirming the hybridization state close to sp2 for the oxygen atom of P–O–C. A survey on the CSD resulted in 11 P(O)(O)2(S–C) structures (11 P–S–Cangles), and the structure (IV) belonging to this family of compounds is the first diffraction study of a salt with a (S)P(O)(O)–O–P(O)(O)(S) skeleton in the anion component. For the P–S–C angles, the maximum population was found in the range of 100°–104° showing the angles within those related to unhybridized pure p orbitals (p3) and hybridized sp3 for the sulfur atom of P–S–C. The analysis of 187 P(O)–O–P(O) structures (with no restriction on the other two atoms attached to phosphorus) including 538 P–O–P angles yielded the maximum population of P–O–P angles within132°–134°, showing the more pronounced ‘‘s’’ character of the orbital (with respect to the sp2 and toward sp) for the oxygen atom at the P–O–P moiety.

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