Hydrogen Bonds Involving P-H Linkages

The evidence for the existence of P-H bonding is in general a little conflicting, but at best it is a very weak linkage. 

A drastic reduction in the amount of H bonding in PH3 compared with that in NH3 is indicated by the much lower melting and boiling points of the phosphorus compound (Fignre 13.1). 

Neutron diffraction studies of crystalline PH4Br and PHJ indicate the presence of weak P-H -halogen bonding. Each iodine atom in the iodide structure is surrounded by fonr H atoms at 3.35 A (corresponding to the van der Waal radius sum) and four H atoms at a closer distance of 2.87 A. The latter may involve weak bent H bonds with P/H/1 180°. 

Ring anions (HPOjH) (13.45a) and (HPOjH) (13.45b) are found in the aystalline acid phosphites Fe(H2P03)3 and Cn(H2P03)2, respectively [42,43], and no significant P-H bonding is indicated by the experimental interatomic distances. 

A highly symmetrical hexagonal structure exists in crystalline FcjCHPOjlj which contains 3 A diameter channels lined with H atoms and lying parallel to a six-fold axis. The H atoms do not appear to take part in any bonding [41], Similar hexagonal channels lined with H atoms are found in the salts M (HP03)8(0H)g M = Fe,Mn,Zn (13.46b). 

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