An unexpected lanthanum chloride carbonate hydrate: synthesis, crystal structure, vibrational spectra and thermal degradation of LaCl[CO3]•3H2O

Microcrystalline powders of LaCl[CO3] center dot 3H(2)O were precipitated and isolated from stoichiometric aqueous solutions of LaCl3 center dot 7H(2)O and Na-2[CO3] center dot 10H(2)O. This confirmed the surprising emergence of corresponding single crystals during a reaction of equimolar aqueous solutions of LaCl3 center dot 7H(2)O and Na[N-3] under ambient conditions by the uptake of atmospheric CO2. According to the X-ray structure analysis of colorless, transparent and rectangular single-crystals, LaCl[CO3] center dot 3H(2)O adopts an orthorhombic structure, space group Pbca with the unit-cell parameters a = 856.82(5), b = 1598.57(9) and c = 967.68(6) pm for Z = 8. The tenfold coordination polyhedron around Le+ consists of two monodentate as well as two bidentate [CO3](2-) anions together with three oxygen atoms from coordinating water molecules and one chloride anion. According to DSC/TG studies and X-ray powder diffraction, LaCl[CO3] center dot 3H(2)O loses first its water and then carbon dioxide under thermal treatment up to 900 degrees C to leave LaOCI behind. Vibrational infrared and Raman spectra confirmed the presence of H2O and [CO3](2-) in LaCI[CO3] center dot 3H(2)O and its stepwise degradation at elevated temperatures.