Transition metals as hydrogen bond acceptors: a theoretical study

The ability of the (CO)(4)Co- organometallic complex as a HE acceptor has b een studied. For this theoretical study, several standard HE donors such as HF, HCN and HNC have been used. The inclusion of the HN(CH3)(3)(+) cation as HE donor, allows the comparison of theoretical and experimental results. In order to consider the importance of the formal negative charge of (CO)( 4)Co- in the interaction with other systems, the isoelectronic neutral (CO) (4)Ni organometallic complex has been considered as HE acceptor. The electr onic changes, within the Atoms in Molecules (AIM) and Natural Bond Orbitals (NBO) methodologies, have been evaluated. Geometry, protonation energy, in teraction energy, and electron density results confirm that the stability a s a protonated species of the organometallic complexes (i.e. their gas-phas e basicity) studied here gives an indication of their ability to act as a H E acceptor. It can be concluded that the Co organometallic anion seems to b e a better HE acceptor than the Ni derivative, due to the formal charge of the former, more than the corresponding electronic distribution. (C) 2001 E lsevier Science B.V. All rights reserved.