ic0c00138_si_001.pdf (2.38 MB)
Unsymmetrical Coordination of Bipyridine in Three-Coordinate Gold(I) Complexes
journal contribution
posted on 2020-02-25, 16:43 authored by Lucy M.
C. Luong, Michael M. Aristov, Alexandria V. Adams, Daniel T. Walters, John F. Berry, Marilyn M. Olmstead, Alan L. BalchThe unsymmetrical
coordination of gold(I) by 2,2′-bipyridine
(bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational
studies. The salts [(Ph3P)Au(bipy)]XF6 (X =
P, As, Sb) form an isomorphic series in which the differences in Au–N
distances range from 0.241(2) to 0.146(2) Å. A second polymorph
of [(Ph3P)Au(bipy)]AsF6 has also been found.
Both polymorphs exhibit similar structures. The salts [(Et3P)Au(bipy)]XF6 (X = P, As, Sb) form a second isostructural
series. In this series the unsymmetrical coordination of the bipy
ligand is maintained, but the gold ions are disordered over two unequally
populated positions that produce very similar overall structures for
the cations. Although many planar, three-coordinate gold(I) complexes
are strongly luminescent, the salts [(R3P)Au(bipy)]XF6 (R = Ph or Et; X = P, As, Sb) are not luminescent as solids
or in solution. Computational studies revealed that a fully symmetrical
structure for [(Et3P)Au(bipy)]+ is 7 kJ/mol
higher in energy than the observed unsymmetrical structure and is
best described as a transition state between the two limiting unsymmetrical
geometries. The Au–N bonding has been examined by natural resonance
theory (NRT) calculations using the “12 electron rule”.
The dominant Lewis structure is one with five lone pairs on Au and
one bond to the P atom, which results in a saturated (12 electron)
gold center and thereby inhibits the formation of any classical, 2
e– bonds between the gold and either of the bipy
nitrogen atoms. The nitrogen atoms may instead donate a lone pair
into an empty Au–P antibonding orbital, resulting in a three-center,
four-electron (3c/4e) P–Au–N bond.
The binuclear complex, [μ2-bipy(AuPPh3)2](PF6)2, has also been prepared
and shown to have an aurophillic interaction between the two gold
ions, which are separated by 3.0747(3) Å. Despite the aurophillic
interaction, this binuclear complex is not luminescent.