Synthesis and crystal structure of three-dimensional open-framework lanthanide oxalates containing either the guanidinium or tetramethylammonium ions

Single crystals of three new lanthanide oxalate complexes, (CN₃H₆)₂[Nd(H₂O)]₂(C₂O₄)₄3H₂O I, [N(CH₃)₄][Nd₂(H₂O)₃](C₂O₄)_3.54H₂O II and [N(CH₃)₄][Yb(C₂O₄)₂] III, have been synthesized hydrothermally in presence of either the guanidinium or tetramethylammonium TMA ions. A relevant feature of III is the complete absence of water. For all the complexes, the three-dimensional framework structure is built up by the connections of the lanthanide and the oxalate units, forming cavities and channels where the guest species, guanidinium and TMA ions and free water molecules, are localized. Thus, the above complexes present a very open architecture. For I and II, the neodymium atoms are 9-coordinated, forming a distorted monocapped square antiprism while for III, the ytterbium atom is 8-coordinated forming a quite regular dodecahedron. For I, the dehydration process is partially reversible. All the complexes will be characterized by infrared spectroscopy and thermal analysis. I has been extended to other lanthanide forming a family, Ln = La–Eu.