Structure and bonding of the remarkable donor acceptor complexes XBeO X NH NMe CO N C H C H H H CO O 3 3 2 2 2 2 4 2 2 2

• Published in: Molecular physics Vol. 89; no. 5; pp. 1245 - 1263
• Main Author: GERNOT FRENKING STEFAN DAPPRICH KLAUS F KOHLER WOLFRAM KOCH JACK R COLLINS
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01-12-1996
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/002689796173156

Quantum mechanical calculations at the MP4/6-311G(2df,2pd)//MP2/6-31G(d,p) level of theory are reported for the compounds XBeO with X = NH
3
, NMe
3
, CO, N
2
, C
2
H
2
, C
2
H
4
, H
2
, H
2
CO and O
2
. The calculations show that BeO is a very strong Lewis acid. The X-BeO bond strength is between D
e
=69*5 kcal mo1
-1
for Me
3
NBeO and D
3
= 11*2 kcal mo1
-1
for π-bonded N
2
BeO. The calculated bond strength for the yet unknown donor-acceptor complex Me
3
NBeO is significantly higher than the strongest experimentally known main-group donor-acceptor complex Me
3
NA1C1
3
(D
o
= 47*5 kcal mo1
-1
). Even the weak donor H
2
is bonded with D
e
= 18*5 kcal mo1
-1
. The compounds O
2
BeO and its isomer berylliumozonide BeO
3
should not be considered as donor-acceptor complexes. The results of the CDA method show that the donor-acceptor interactions in terms of orbital mixing are mainly described by the mixing of occupied orbitals of X with vacant orbitals of BeO, while the mixing of occupied orbitals of BeO with vacant orbitals of X is negligible. The topological analysis of the electronic charge distribution and the NBO partitioning scheme demonstrate that the X-BeO bonds have little or no covalent character; the bonds are caused by electrostatic attraction. The charge concentration at the donor atoms in the stronger bonded compounds is significantly deformed towards the beryllium atom.