A Detailed Study of the Vapochromic Behavior of {Tl[Au(C₆Cl₅)₂]}_n

Abstract

The linear-chain polymer [Tl[Au(C(6)Cl(5))(2)]](n), 1, reacts in the solid state and in solution with different volatile organic compounds such as tetrahydrofuran, acetone, tetrahydrothiophene, 2-fluoropyridine, acetonitrile, acetylacetone, and pyridine. Solid-state exposure of 1 to vapors of the above VOCs produces a selective and reversible change in its color that is perceptible to the human eye and even deeper under UV irradiation, allowing 1 to function as a sensor for these VOCs. Heating the samples exposed to the VOCs for a few minutes at 100 degrees C regenerates the original material without degradation, even after several exposure/heating cycles. The reversibility is further confirmed by X-ray powder diffraction measurements of complex 1 before and after exposure to vapors and again after heating the samples. The products obtained by reactions of complex 1 with the above VOCs as ligands in solution contain extended linear chains of alternating gold and thallium centers with two molecules of the organic ligands attached to each thallium atom. The stoichiometry of these materials has been confirmed by single-crystal X-ray diffraction as [Tl(THF)(2)[Au(C(6)Cl(5))(2)]](n), 3, and [Tl(acacH)(2)[Au(C(6)Cl(5))(2)]](n), 5. Comparison of FT-IR, UV-vis, and luminescence spectra at room temperature and at 77 K of the solid samples of complexes 2-9 with the spectra of complex 1 after its exposure to VOCs suggests interaction occurs between the organic VOCs and thallium in each case. Thermogravimetric analyses data indicate that all the thallium centers in these derivatives of complex 1 are neither fully nor equally coordinatively saturated. The materials formed appear to be intermediates between complex 1 with no VOCs attached and complexes 3-9 which contain two organic ligands coordinated to each thallium. A crystal structure analyses of one of these intermediates, [Tl(THF)(0.5)[Au(C(6)Cl(5))(2)]](n), 1.0.5THF, confirms this. Density functional calculations are in accord with the observed experimental results. Analysis reveals a substantial participation of the metal atoms in transitions that give rise to the observed emissions. Crystallographic data are as follows. For 1.0.5THF: triclinic, P1, a = 8.9296(1) A, b = 11.2457(1) A, c = 21.2465(3) A, alpha = 96.7187(7) degrees, beta = 92.5886(6) degrees, gamma = 98.5911(8) degrees, V = 2090.87(4) A(3), and Z = 2. For 3: monoclinic, P2(1)/c, a = 26.4163(6) A, b = 12.1619(2) A, c = 28.0813(6) A, alpha = 90 degrees, beta = 161.9823(6) degrees, gamma = 90 degrees, V = 2790.51(10) A(3), and Z = 4. For 5: monoclinic, P2(1)/c, a = 9.8654(2) A, b = 29.8570(5) A, c = 11.6067(2) A, alpha = 90 degrees, beta = 114.5931(6) degrees, gamma = 90 degrees, V = 3108.64(10) A(3), and Z = 4.

Gold–Heterometal Interactions and Bonds

“…These channels are large enough to accommodate different volatile organic compounds (VOCs) which can enter the lattice. Indeed, exposure of 31 in the solid state to VOCs (e.g., tetrahydrofuran, acetone, tetrahydrothiophene, 2-fluoropyridine, acetonitrile, acetylacetone, pyridine) resulted in a perceptible change in the color of the solid, which reverts to that of the starting material upon heating the solid adducts [56,59]. In all complexes the process is completely reversible with no detectable degradation, even after 10 exposure/heating cycles [59].…”

“…Exposure of the solid [Tl{Au(C 6 Cl 5 ) 2 }] n 31 to vapors of THF provided crystals of [Tl (THF) 0.5 {Au(C 6 Cl 5 ) 2 }] n 40 for which an X-ray diffraction study revealed that part of the empty channels available in the crystal of the parent compound 31 are occupied by solvent molecules [59]. The polymeric structure is preserved but the alternating Au and Tl atoms form a zigzag chain.…”

“…Thus, while Tl(1) remained uncoordinated to THF with only intermetallic interactions and an angular Au-Tl-Au fragment (4) Å], but in this case each thallium atom is coordinated by two THF molecules [Tl-O 2.653(7)/2.648(6) Å] in a distorted pseudo-trigonal bipyramidal geometry (Figure 4.15b) [59]. The coordination sphere of each Tl(I) being complete, the crystal of 41 no longer presents interchain Tl-Cl contacts and free channels [59]. The yellow complex [Tl(MeCN) 2 {Au(C 6 Cl 5 ) 2 }] n 42 was prepared similarly [59].…”

“…The coordination sphere of each Tl(I) being complete, the crystal of 41 no longer presents interchain Tl-Cl contacts and free channels [59]. The yellow complex [Tl(MeCN) 2 {Au(C 6 Cl 5 ) 2 }] n 42 was prepared similarly [59]. Compounds of the same stoichiometry, that is [Tl(L) 2 {Au(C 6 Cl 5 ) 2 }] n , but different colors, were also obtained when 31 was reacted in a 1 : 2 molar ratio with other pure organic ligands as solvents [59]: yellow -THT 43, 2-fluoropyridine 44, NEt 3 45; red -pyridine 46 [59].…”

Chromo- and Fluorogenic Organometallic Sensors

“…The incorporation of halogenated and small polar solvents is favoured by the formation of relatively strong CH-p, p-p, CH-X and X-X interactions, whereas the size of the voids may be too small to host aromatic VOCs. In the case of derivatives 10b and 10c ( with channels into which the VOCs can diffuse [93,94]. Reversible changes of colour are observed when the solid is exposed to a variety of VOCs, such as acetone, acetonitrile, triethylamine, acetylacetone, tetrahydrothiophene, 2-fluoropyridine, tetrahydrofuran, and pyridine vapours.…”