Tri-[Pt2Tl]3- and polynuclear chain [Pt−Tl]∞- Complexes based on nonbridged PtII−TlI bonds: Solid state and frozen solution photophysical properties

Abstract

Treatment of (NBu4)2[PtR4] (R = C6F5) with 1 or 0.5 equiv of TlNO3 in EtOH/H2O produces colorless crystals of trinuclear complex (NBu4)3[Tl{PtR4}2], 1, in which the Tl+ center is complexed by two [PtR4]2- fragments (Pt−Tl = 2.9777(4) and 3.0434(4) Å). The expected mixed complex with a Pt/Tl composition of 1:1, 2, is generated as an orange microcrystalline solid by treating [PtR4]2- with a large excess of TlNO3 (8 equiv). Crystallographic analysis of 2 reveals the formation of a novel one-dimensional (1D) heterometallic linear chain (NBu4)∞[Tl{PtR4}]∞, 2, formed by alternating a [PtR4]2- fragment and a Tl+ center with a uniform Pt−Tl bond separation along the chain of 3.0321(2) Å. Surprisingly, treatment of (NBu4)2[PtR4] with 1 equiv of TlPF6 in EtOH yields pale greenish-yellow needles of an unusual adduct, 2·{(NBu4)(PF6)}∞ (3), which was found to form a similar extended linear chain, {TlPtR4}∞, constructed by two alternating Pt−Tl separations, a shorter (3.1028(6) Å) one and a longer (3.2306(6) Å) one. The solid state and solution photophysical properties have been examined. While complex 1 shows a high-energy MM‘CT blue phosphorescence (450 nm), the extended chain in 2 exhibits a lower-energy emission (582 nm) than that in adduct 3 (505 nm). For products 2 and 3, interesting luminescence thermochromism is observed in frozen solutions. The emissions are found to be strongly dependent on the solvent, concentration, and excitation wavelength.