The effect of replacing oxygen with sulphur and selenium has been investiga
ted in terms of successive protonation of phosphate (PO43(-)), thiophosphat
e (SPO33(-)), and selenophosphate (SePO33(-)). Ab initio conformational ana
lysis has been performed on the partially protonated HPO42(-), HPSO32(-), H
PSeO32(-), as well as on H2PO4(-), H2PSO3(-), and H2PSeO3(-), and fully pro
tonated species. Topological analysis of the electron density has been perf
ormed by Bader's Atoms in Molecule (AIM) approach. (C) 2000 Elsevier Scienc
e B.V. All rights reserved.