Pentavalent P compound having the structure (X=C*)-P(=X) or (cyano*)-P(=X) where X is chalcogen, * indicates a direct bond of the C of the C=X group or of the C of the cyano group directly to the P atom, and the other atoms bonded directly to the P atom are either carbon and hydrogen (9/53A9; 9/53P; 9/53Y)