Single crystal structures of lanthanide carbonate and hydroxy-carbonate compounds have been previously reported in the literature, with the majority of these compounds being extended one- to three-dimensional compounds. Very few lanthanide compounds have been isolated that contain molecular moieties, and none have been reported for either erbium or dysprosium. Single crystals of the tetra-carbonate complexes, [C(NH(2))(3)](5)[Er(CO(3))(4)].11H(2)O (I) and [C(NH(2))(3)](4)[Dy(CO(3))(4)(H(2)O)](H(3)O).13H(2)O (II), were isolated from concentrated guanidinium carbonate solutions and characterized by single crystal X-ray diffraction studies. Compounds I and II are the first reported molecular carbonate structures for Er and Dy to be characterized via single crystal X-ray diffraction studies. Crystallographic data for I: monoclinic, space group P21/n, a = 8.8160(6) A, b = 21.0121(14) A, c = 19.6496(14) A, Z = 4. Data for II: tetragonal, space group P4/n, a = b = 15.3199(11) A, c = 7.5129(11) A, Z = 2.

Single crystals of [C(NH2)3]5 [Er(CO3)4]·11H2O (I) and [C(NH2)3]4 [Dy(CO3)4(H2O)] (H3O)·13H2O (II) are prepared by evaporation at 3 °C of aqueous solutions of Ln(NO3)3 (Ln: Er, Dy) and guanidinium carbonate.