Comprehensive structural study of lanthanide(III) chloride hydrates: [ RE Cl 3 · x H 2 O ( RE = La–Nd, Sm–Lu; x = 6, 7)]

A comprehensive crystallographic study is presented of the complete series of rare-earth(III) chloride hydrates. Early lanthanides form dimeric [(H 2 O) 7 RE (μ-Cl) 2 RE (H 2 O) 7 ] 4+ binuclear complexes in which each RE atom ( RE = La 3+ , Ce 3+ ) is coordinated by seven H 2 O molecules and two bridging inner-sphere chloride ions. Di-μ-chlorido-bis[heptaaqualanthanide(III)] tetrachloride, [(H 2 O) 7 RE (μ-Cl) 2 RE (H 2 O) 7 ]Cl 4 , crystallizes in the triclinic space group P 1 . Heavier lanthanides exhibit monomeric [ RE Cl 2 (H 2 O) 6 ] + units where each RE atom ( RE = Pr 3+ , Nd 3+ , Sm 3+ –Lu 3+ ) is coordinated by six H 2 O molecules and two inner-sphere chloride ions. Hexaaquadichloridolanthanide(III) chlorides, [ RE Cl 2 (H 2 O) 6 ]Cl, adopt the monoclinic space group P 2/ c. In both structures, the cationic inner-sphere complex is counter-charged by the corresponding number of outer-sphere Cl − anions, in which the metal ion and outer-sphere chloride ion lie on crystallographic twofold axes. Crystal structures for all compounds were determined in high quality with refined H-atom positions and were collected at the same temperature (100 K), providing a uniform structural dataset and addressing discrepancies in previous reports. The crystal structure of [HoCl 2 (H 2 O) 6 ]Cl is reported for the first time.