Rhenium trichloride, ReCl 3 , and its 5/3‐hydrate synthesis, crystal structure, and thermal expansion

Single crystals of ReCl 3 were grown by vacuum sublimation and the crystal structure (trigonal, R 3 m, a = 1020.62(5), c = 2035.3(2) pm, V m = 61.430(8) cm 3 mol −1 ) was refined to R = 0.049, R w = 0.031. From hydrochloric acid solutions of ReCl 3 containing me 4 NCl, the hydrete ReCl 3 · 5/3 H 2 O is salted out: hexagonal, P 6 2 c , a = 944.89(3), c = 1470.07(9) pm, V m = 114.09(1) cm 3 mol −1 . The crystal structure (R = 0.079, R w = 0.051) contains hexagonally closest‐packed [Re 3 Cl 9 (H 2 O) 3 ] molecules held loosely together by two molecules of crystal water positioned between the clusters in the [00.1] direction thereby forming chains that are shifted against each other by 1/2c. Thermal expansion of ReCl 3 , ReCl 3 . 5/3 H 2 O and RbReCl 4 has been recorded and is discussed in connection with the crystal structures.