Two phases of {[CsPH(eta(6)-2,4,6-(Bu3C6H2)-Bu-t)](2)(eta(3)-toluene)(0.5)}(x): their structures and interconversions

The solvent-bridged caesium phosphide ([CsPH(eta(6)-2,4,6-(Bu3C6H2)-Bu-t)]( 2)(eta(3)-toluene)(0.5)}(x), catena-[(mu-eta(3)-toluene)-bis[caesium(2,4,6- tri-tert-butylphenylphosphide)]], undergoes a reversible solid-state, order -disorder phase transition characterized by the doubling of the unit-cell v olume at low temperature achieved by doubling one unit-cell vector. The uni t-cell parameters at 293 (2) K (form A) are: a = 11.147 (4), b = 14.615 (4) , c = 14.806 (5) Angstrom, alpha = 70.57 (3), beta = 71.85 (3), gamma = 72. 93 (2)degrees, V = 2112.5 (12) Angstrom(3), Z = 2, rho(calc) = 1.362 g cm(- 3), R-1 = 0.0513 for 5462 reflections, wR(2) = 0.0947 for all data. The uni t-cell parameters at 173 (2)K (form B) are: a = 14.6241 (3), b = 14.7393 (3 ), c = 22.0720 (4) Angstrom, alpha = 72.2117 (7), beta = 73.3659 (8), gamma = 70.2953 (7)degrees, V = 4174.8 (2) Angstrom(3), Z = 4, rho(calc) = 1.379 g cm(-3) R-1 = 0.0405 for 14 010 reflections, wR(2) = 0.1326 for all data. With a minor change, the key structural features discussed previously for form A [Rabe et al. (1998). Inorg. Chem. 37, 4235-4245] remain unchanged. T he eta(3)-toluene ligand is observed to be disordered at 293(2)K and ordere d at 173 (2! K, with the order-disorder phase transition occurring at appro ximately 278 (2) K.