Can four-center two-electron bonding alone provide stability of a molecule?

Mikhail N. Glukhovtsev, Paul Von R. Schleyer, Andreas Stein

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Ab initio calculations on the Li42+ and Na42+ Td structures show that two valence electrons are capable of binding four alkali metal centers. These structures have positive binding energies (Eb/n = 4.62 (Li42+, QCISD-(T)(full)/6-311G(2d)//MP2(full)/6-311G(2d); 4.74 MP4SDQ(full)/6-31+G(3d)//MP2(full)6-311G(2d)) and 1.66 kcal/mol (Na42+, QCISD(T)(full)/6-31G(d)//MP2(full)/6-31G(d)). However, they are thermodynamically unstable with respect to the dissociations into different two sets of cations, i.e. into M3+ (D3h) and M+ and into 2M2+. The decomposition barriers into M3+ and M+ are 3.4 kcal/mol for Li42+ (QCISD(T)(full)/6-311G(2d)//MP2(full)/6-311G(2d) + ZPE(MP2/6-31G(2d)) and 2.3 kcal/mol for Na42+ (MP4SDTQ(fc)/6-31G(2df)/6-31G(d)//MP2(full)/6-31G(d) + ZPE(HF/6-31G(d))), respectively. Four-center, two-electron (4c-2e) bonding suffices to stabilize an otherwise unsupported molecule. Alternative geometries of the M42+ clusters (e.g., linear (D∞h), Y-type (D3h), square (D3h), and rhombus (D2h)) are not minima. In contrast to H42+, the relative stabilities of the Li42+ forms strongly disagree with the expectations based on the charge alternation model. Effective 4c-2e bonding in Li42+ (Td) depends on the 2p lithium orbitals. When these orbitals are excluded from the basis set, Li42+ behaves somewhat similarly to H42+; in particular, the Td form is not a minimum. Topological analysis (AIM) of the electron charge density shows the existence of a nonnuclear maximum (attractor, in this case pseudoatom) in the center of the Li42+ tetrahedron. There is no direct Li-Li bonding. The electronic structure analysis shows that Li42+ (Td) is not very stable; this is consistent with the low dissociation barrier.

Original languageEnglish (US)
Pages (from-to)5541-5546
Number of pages6
JournalJournal of physical chemistry
Issue number21
StatePublished - 1993


Dive into the research topics of 'Can four-center two-electron bonding alone provide stability of a molecule?'. Together they form a unique fingerprint.

Cite this