Reaction of 1,3-bis(2-pyridinylmethyl)-1H-imidazolium salt, [H(pyCH(2))(2)im]X (X = BF(4)(-) or Cl(-)), with silver oxide in acetonitrile readily yields yellow-brown [((pyCH(2))(2)im)(2)Ag]X, 1.BF(4) or 1.Cl. The chloride salt crystallizes with 3.650 A intermolecular Ag...Ag interactions while 1.BF(4) shows no short intermolecular interaction. Addition of excess Ag(BF(4)) produces the homoleptic carbene bridged trimetallic species, [(mu-NHC)(3)Ag(3)](BF(4))(3), 2. This species contains very short Ag-Ag separations between 2.7249(10) and 2.7718(9) A. In solution, these complexes are photoluminescent.

The deep-red, air-stable mixed-metal metallocryptands, [AuPdTl(P2phen)3](PF6)2, 1.(PF6)2, and [AuPtTl(P2phen)3](PF6)2, 2.(PF6)2, are easily prepared in good yield (60-70%) by reacting 3 equiv of P2phen with 1 equiv of Au(THT)Cl, excess thallous acetate, and the appropriate amount of either Pd2(dba)3 for 1 or Pt(dba)2 for 2 in acetonitrile where P2phen is 2,9-bis(diphenylphosphino)-1,10-phenanthroline, THT is tetrahydrothiophene, and dba is dibenzylidineacetone. Compared to the more symmetrical bimetallic metallocryptands, these trimetallic species show shorter than expected Au(I)-Tl(I), Pt(0)-Tl(I), and Pd(0)-Tl(I) separations. The enhanced bonding interaction is attributed to the incorporation of the dissimilar capping metals introducing dipole moments that strengthen the dispersion forces responsible for maintaining the metallophilic interactions.

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 remarkable, vapor-induced transformation of the yellow polymorphs of [(C(6)H(11)NC)(2)Au(I)](AsF(6)) and [(C(6)H(11)NC)(2)Au(I)](PF(6)) into the colorless forms are reported along with related studies of the crystallization of these polymorphs. Although the interconversion of these polymorphs is produced by vapor exposure, molecules of the vapor are not incorporated into the crystals. Thus, our observations may have broad implications regarding the formation and persistence of other crystal polymorphs where issues of stability and reproducibility of formation exist. Crystallographic studies show that the colorless polymorphs, which display blue luminescence, are isostructural and consist of linear chains of gold(I) cations that self-associate through aurophilic interactions. Significantly, the yellow polymorph of [(C(6)H(11)NC)(2)Au(I)](AsF(6)) is not isostructural with the yellow polymorph of [(C(6)H(11)NC)(2)Au(I)](PF(6)). Both yellow polymorphs exhibit green emission and have the gold cations arranged into somewhat bent chains with significantly closer Au···Au separations than are seen in the colorless counterparts. Luminescence differences in these polymorphs clearly enhance the ability to detect and monitor their phase stability.

The deep-red, air-stable complexes [Pt(2)Hg(2)(P(2)phen)(3)](PF(6))(2), 1, or [Pd(2)Hg(2)(P(2)phen)(3)](PF(6))(2), 2, (P(2)phen is 2,9-bis(diphenylphosphino)-1,10-phenanthroline) are most conveniently prepared by the stoichiometric reaction of either Pt(dba)(2) or Pd(2)(dba)(3).CHCl(3) (dba is dibenzylideneacetone) with P(2)phen and a single drop of elemental mercury in refluxing dichloromethane under an atmosphere of nitrogen. The (31)P[(1)H] NMR spectrum (CD(3)CN) of 1 shows a single sharp resonance at 43.1 ppm for the phosphorus atoms of the P(2)phen ligand with both (195)Pt ((1)J(P-Pt) = 4350 Hz) and (199)Hg ((2)J(P-Hg) = 620 Hz) satellites indicating the Hg(2)(2+) unit is dynamic. Compound 2 has a similar resonance at 44.9 ppm with (199)Hg satellites ((2)J(P-Hg) = 638 Hz). The (199)Hg NMR (CD(2)Cl(2), vs Hg(OAc)(2)) spectrum of 2 shows a heptet pattern at 833 ppm while for 1 a heptet superimposed on a doublet of heptets is observed at 770.8 ppm. The (195)Pt NMR spectrum of 1 displays a quartet at -3071 ppm with (199)Hg satellites and a (1)J(Pt-Hg) value of 1602 Hz. Characterization of 1 and of 2(BF(4)(2) by single-crystal X-ray diffraction studies confirms the metallocryptand structure consisting of three phosphine-imine ligands forming a D(3) symmetric cage with a Hg(2)(2+) ion in its center coordinated to two phenanthroline rings with the Hg-Hg bond (1, 2.7362(6); 2(BF(4)(2), 2.6881(4) A) oriented perpendicular to the vector between the trigonally coordinated Pt(0) or Pd(0) atoms on each end. The Pt-Hg separations in 1 average 2.8143(6) A while in 2(BF(4)(2) the average Pd-Hg separation is 2.7698(5) A. Excitation into the low energy excitation bands of 1 (475 nm) and 2 (430 nm) produces weak emissions centered at 593 nm with shoulders at 530 and 654 nm in 1 and centered at 524 nm with a shoulder at 545 nm in 2.