Osmotic and activity coefficients of perrhenic acid and perrhenate salts

Osmotic and activity coefficients are reported for the aqueous solution of perrhenic acid and for its lithium, sodium and tetramethylguanidinium slats at 25°C. These coefficients are similar in order of magnitude but smaller than the coefficients of the corresponding perchorates. Evidence is submitted for the ion pairing of the perrhenate ion with both hydronium and tetramethylguanidinium ions in fairly dilute aqueous solutions. The association with hydronium ion decreases in more concentrated solutions.     

The crystal structure of β-Thallium perrhenate

β-TlReO₄, the room temperature modification of thallium perrhenate, has been investigated by means of single crystal X-ray diffraction. It crystallizes in the monoclinic space group P112₁/a with a = 5.636(1), b = 17.428(3), c = 13.353(3) Å, γ = 89.86(2)° and Z = 12. The structure has been refined to R = 0.063 (wR = 0.053) using 2 020 absorption-corrected reflections. The title compound can be described as an intergrowth of β-CsReO₄ and scheelite type blocks at unit cell level. The structure of β-TlReO₄ consists of isolated ReO₄ tetrahedra linked together by TlO₈ and TlO₉ polyhedra. Based upon group theoretical considerations the structural relationships between β-TlReO₄, β-CsReO₄, α-CsReO₄ and scheelite type are discussed.