INTERACTIONS BETWEEN C-H AND N-H BONDS AND D(8) SQUARE-PLANAR METAL-COMPLEXES - HYDROGEN-BONDED OR AGOSTIC

The structural characteristics of C-H...M and N-H...M groups in square planar d(8)-ML(4) metal complexes are examined and compared with thos e for C-H...M groups in unambiguously agostic d(6)-ML(5) systems. The N-H...M(d(8)) systems have the linear geometry typical of hydrogen bon ds, not the bent geometry typical of agostic species. As proposed by B rammer, the N-H...M(d(8)) systems are best regarded as hydrogen bonds, but the C-H...M(d(8)) systems are intermediate in geometry between th e hydrogen bonded N-H...M systems and the true agostic C-H...M of the d(6) cases and are neither typical of hydrogen bonds nor typical agost ic species.