Noncoordinating anions, which generally play a subordinate role in coordination chemistry, alter the structure, the luminescence, as well as the thermochromic and vapochromic behaviors of salts of the two-coordinate cation, [(C 6 H 11 NC) 2 Au] + . Thus whereas the yellow polymorphs of [(C 6 H 11 NC) 2 Au](PF 6 ) and [(C 6 H 11 NC) 2 Au](AsF 6 ) contain single chains of cations and are vapochromic, yellow [(C 6 H 11 NC) 2 Au](SbF 6 ) does not form the same polymorph and is not vapochromic but contains two distinct chains of cations connected through aurophilic interactions. Mixed crystals such as [(C 6 H 11 NC) 2 Au](PF 6 ) 0.50 (AsF 6 ) 0.50 have been prepared by adding diethyl ether to a dichloromethane solution containing equimolar amounts of [(C 6 H 11 NC) 2 Au](PF 6 ) and [(C 6 H 11 NC) 2 Au](AsF 6). The initial (kinetic) product for the three combinations of anions ((PF 6 ) − /(AsF 6 ) − , (PF 6 ) − /(SbF 6 ) − , and (AsF 6 ) − /(SbF 6 ) − ) was a precipitate of fine yellow needles with a green emission, which were gradually transformed at rates that depended on the anions present into colorless crystals with a blue emission. Whereas neither polymorph of [(C 6 H 11 NC) 2 Au](PF 6 ) nor [(C 6 H 11 NC) 2 Au](SbF 6 ) is thermochromic, the colorless mixed crystal [(C 6 H 11 NC) 2 Au](PF 6 ) 0.50 (SbF 6 ) 0.50 is thermochromic and converts from blue-emitting to green-emitting at 87−95 °C. The temperature required to transform a crystal of the type [(C 6 H 11 NC) 2 Au](PF 6 ) n (AsF 6 ) 1−n from colorless (blue-emitting) to yellow (green-emitting) increases as the fraction of hexafluorophosphate ion in the crystal increases. The yellow crystals of [(C 6 H 11 NC) 2 Au](PF 6 ) 0.75 (AsF 6 ) 0.25 , [(C 6 H 11 NC) 2 Au](PF 6 ) 0.50 (AsF 6 ) 0.50 , and [(C 6 H 11 NC) 2 Au](PF 6 ) 0.25 (AsF 6 ) 0.75 are vapochromic, whereas the yellow crystals of [(C 6 H 11 NC) 2 Au](PF 6 ) 0.50 (SbF 6 ) 0.50 and [(C 6 H 11 NC) 2 Au](AsF 6 ) 0.50 (SbF 6 ) 0.50 are not.
The 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 [(Ph 3 P)Au(bipy)]XF 6 (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 [(Ph 3 P)Au(bipy)]AsF 6 has also been found. Both polymorphs exhibit similar structures. The salts [(Et 3 P)Au(bipy)]XF 6 (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, threecoordinate gold(I) complexes are strongly luminescent, the salts [(R 3 P)-Au(bipy)]XF 6 (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 [(Et 3 P)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, [μ 2bipy(AuPPh 3 ) 2 ](PF 6 ) 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.
Non-luminescent, isostructural crystals of C6H6•[(C6H11NC)2Au](EF6) (E = As, Sb] lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies...
The mono‐ and di‐chloroform solvates of [Au2(μ‐1,2‐bis(diphenylarsino)ethane)2](AsF6)2 undergo single‐crystal‐to‐single‐crystal transformations that result in gain (over 12 hours) or slow loss (over five years) of only one chloroform molecule. The change in solvation results in changes in the structure and luminescence of the digold cation. The cation consists of a pair of slightly bent As‐Au‐As units that are connected through the two bridging dpae ligands and by aurophilic interactions with Au⋅⋅⋅Au contacts of 3.05152(15) Å in the disolvate or 2.9570(5) Å in the monosolvate.
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