Syntheses, Structures, and Spectroscopic Properties of Gold(I) Complexes of l, 3, 5-Triaza-7-phosphaadamantane (TPA). Correlation of the Supramolecular Au•••Au Interaction and Photoluminescence for the Species (TPA)AuCl and [(TPA-HCl)AuCl]

Zerihun Assefa, Brian G. McBurnett, Richard J. Staples, John P. Fackler, Bernd Assmann, Klaus Angermaier, Hubert Schmidbaur

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Abstract

The reaction of the cage-type ligand l, 3, 5-triaza-7-phosphaadamantane (TPA) with (dimethyl sulfide)gold(I) chloride in a molar ratio 1:1 in aprotic polar solvents affords the complex (TPA)AuCl, 1, in high yield. Similarly, reacting the protonated TPA ligand in MeOH/CH3CN (2:1) with (tetrahydrothiophene)AuCl gives the protonated product (TPA-HCl)AuCl, 1P, in excellent yield. The cation of 1P becomes deprotonated above about pH 4.5. The structures and temperature-dependent photoluminescence properties of 1 and 1P have been determined. Protonation of the TPA ligand remarkably lengthens the solid state, auriophilic Au•••Au interaction in 1P, where the Au•••Au separation is 3.322(1) Å, compared with 3.092(1) Å in 1. The luminescence spectra of the two compounds are substantially different, clearly a consequence of the change in the Au•••Au separation associated with the “supramolecular” auriophilic dimerization. While the Cl-Au-P angles are nearly linear in both compounds, 177.4 (1) and 175.8 (1)°, respectively, a “crossed” dimerization (dihedral angle P-Au-Au′-P′ about 105°) occurs. The small cone angle of the TPA ligand allows this Au•••Au interaction to occur, a dimerization absent for many other tertiary phosphine complexes of LAuX which have been structurally characterized to date. At 78 K compound 1P luminesces yellow (596 nm), while compound 1 luminesces intensely red (674 nm). The emission band of 1 is red-shifted by about 2000 cm−1 when compared to that of 1P. The emission bands in both compounds blue-shift as the temperature is increased. Between 78 and 298 K the emission band of 1P blue-shifts by about 400 cm−1 and that of 1 by 700 cm11. Neither complex is luminescent in solution. A solution absorption band has been observed at energies >40 000 cm−1 (242 nm). The interpretation of the changes in the low-energy visible emission in the solid state upon changing the auriophilic Au•••Au contact is supported by extended Hückel MO calculations wherein, upon shortening the Au•••Au separation, the HOMO (σu) orbital is destabilized, causing a decrease in the HOMO-LUMO gap. (TPA)AuCl is readily converted into the corresponding bromide, 2, or iodide, 3, by treating it with HBr(aq) or KI in acetone, respectively. The complex (TPA)AuCH3, 4, is obtained from (TPA)AuCl and equimolar quantities of MeLi in diethyl ether. An N-methylated complex [(TPAMe)AuCl]-oso2cf3, 5, is formed in the reaction of (TPA)AuCl with CF3SO3Me in dichloromethane. Crystal data: (TPA-HCl)AuC1•0.5H2O, 1P-0.5H2O, monoclinic, space group C2/c with a = 15.060(2) Å, b = 12.663(2) Å, c = 13.775(3) Å, β = 120.60(2)°, V = 2261.0 (6) Å3, Z = 8, R = 0.0317 (Rw = 0.0415); (TPA)AuCl-CH3CN, 1•CH3-CN, orthorhombic, space group Pbcn, with a = 14.334(2) Å, b = 13.924(3) Å, c = 11.776(2) Å, V= 2350.3 Å3, Z = 8, R = 0.038 (Rw = 0.0467); (TPA)AuBrCH3CN, 2•CH3CN, orthorhombic, space group Pbcn, a = 14.546-(3) Å, b = 14.138(3) Å, c = 11.898(3) Å, V = 2431.9(9) Å, Z = 8, R = 0.544 (Rw = 0.075).

Original languageEnglish
Pages (from-to)75-83
Number of pages9
JournalInorganic Chemistry
Volume34
Issue number1
DOIs
StatePublished - 1 Sep 1995
Externally publishedYes

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