Phosphate anion-metal cation complexes of (OH)2PO2− with Li+, Na+, Be2+, and Mg2+ have been studied by using ab initio self-consistent field methods with an extended, double ζ plus polarization, basis set. The most stable binding site for all cations is a symmetric C2v complex with the metal interacting with two phosphate oxygen atoms, consistent with previous calculations. Significant electron transfer was found for all complexes except that involving Na+, implying that Li+, Be2+, and Mg2+ interactions with phosphate are not totally electrostatic. Hydration of Li+ and Be2+ does not significantly alter the extent of covalency of the metal-phosphate bond, although it weakens the direct complex formation by partial neutralization of the cation. All cations are found to affect both the geometry and electronic charge distribution of the phosphate group, consistent with their key role in determining nucleic acid conformational stability. © 1982, American Chemical Society. All rights reserved.