Syntheses, Structure, and Photoluminescence Properties of the 1-Dimensional Chain Compounds [(TPA)2Au][Au(CN)2] and (TPA)AuCl (TPA = 1,3,5-Triaza-7-phosphaadamantane)

Abstract

The structures and temperature-dependent photoluminescence properties of the one-dimensional compounds [(TPA)₂Au][Au(CN)₂], 1, and (TPA)AuCl, 2, are reported. An extended linear chain with weak Au···Au interactions along the c-axis is evident in the structure of 1, and a helical chain with a pitch of 3.271 Å is seen for 2. The intrachain Au···Au separation is 3.457(1) and 3.396(2) Å in 1 and 2, respectively. As a result of this weak Au···Au interaction, the physical properties of these compounds are anisotropic. Scanning electron microscopy (SEM) studies indicate that single crystals of both compounds are noninsulating. Single crystals of 1 do not luminesce visibly, but grinding the crystals finely initiates a strong green emission under UV irradiation at room temperature. Further interesting optical properties include the dependence of the emission profile of the powder on the exciting wavelength and luminescence thermochromism. When excited at wavelengths < 360 nm, the powder exhibits a blue emission at 425 nm while excitation with longer wavelengths leads to a green emission near 500 nm. While the green emission dominates at ambient temperature, cooling to cryogenic temperatures leads to the dominance of the blue emission. Fibers of 2 are luminescent at 78 K with an emission band centered at 580 nm. Compound 1 crystallizes in the orthorhombic space group Cccm (No. 66), with Z = 2, a = 6.011(1) Å, b = 23.877(6) Å, c = 6.914(1) Å, V = 992.3(3) ų, and R = 0.0337. Compound 2 crystallizes in the trigonal space group R3̄ (No. 148), with Z = 18, a = 22.587(2) Å, b = 22.587(2) Å, c = 9.814(2) Å, V = 4336 ų, and R = 0.0283.