title: Crystallographic evidence for oxygen acceptor directionality in oxyanion hydrogen bonds.
abstract: A survey of 2632 D-H...O-A hydrogen bonds in crystal structures (where D is any atom and A is the central atom of a trigonal planar (A = C, N) or tetrahedral (A = P, S, Cl, As, Se, Cr, Mo) oxyanion, has established the existence of a distinct directionalities at the oxygen atom acceptors. The directionality depends primarily on the geometry of the oxyanion. With the trigonal planar oxyanions NO3-, HCO3-, and CO32-, the average H...O-A angle is 115 +/- 12 degrees and there is a clear preference for the hydrogen to lie within the plane of the anion. With the tetrahedral oxyanions H2PO4-, HPO42-, HSO4-, SO42-, ClO4-, H2AsO4-, HAsO42-, AsO43-, HSeO4-, SeO42-, CrO42-, and MoO42-, the average H...O-A angle is 122 +/- 12 degrees , and there is a weak preference for eclipsed H...O-X-O dihedral angles. The observed directionality closely coincides with minima on electrostatic potential surfaces calculated for the anions.
authors.affiliation: W. R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, USA. ben.hay@pnl.gov
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Hay
authors.forename: David A
authors.initials: DA
authors.lastname: Dixon
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Bryan
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Moyer