Reaction of the neat elements in tantalum containers at 400 degrees C and then 150 degrees C gives the pure title phase. X-ray crystallography shows that the hexagonal structure (P6(3)/mmc, Z = 2, a = 11.235(1) Angstrom, b = 30.133(5) Angstrom) contains relatively high symmetry clusters Tl-5(7-) (D-3h), Tl-4(8-) (C-3v, similar to T-d), and the new Tl-3(7-) (D-infinity h) plus Tl5-, the last two disordered over the same elongated site in 1:2 proportions. Cation solvation of these anions is tight and specific, providing good Coulombic trapping of weakly bound electrons on the isolated cluster anions. The observed disorder makes the compound structurally a Zintl phase with a closed shell electron count. EHMO calculations on the novel Tl-3(7-) reveal some bonding similarities with the isoelectronic CO2, with two good sigma(s,p) bonding and two weakly bonding pi MO’s. The Tl-Tl bond lengths therein (3.14 Angstrom) are evidently consistent with multiple bonding. The weak temperature-independent paramagnetism and metallic conductivity (rho(293) similar to 90 mu Omega . cm) of the phase are discussed.