Chiral open-framework uranyl molybdates. 1. Topological diversity: synthesis and crystal structure of [(C2H5)2NH2]2[(UO2)4(MoO4)5(H2O)](H2O)

Crystals of a new framework uranyl molybdate, [(C2H5)2NH2]2[(UO2)4(MoO4)5(H2O)](H2O), were synthesized from a solution of UO2(CH3COO)2 · 2H2O, MoO3, diethylamine and HCl in H2O at 220 °C. The structure was studied at −127 °C. The compound is hexagonal, space group P6522, a = 11.3612(13), c = 52.698(8) Å, V = 5890.7(13) Å3, Z = 3. The structure has been refined to R1 = 0.050 (wR2 = 0.100; S = 0.985) on the basis of 3103 unique observed reflections. The structure consists of a three-dimensional framework of composition [(UO2)4(MoO4)5(H2O)]2− that consists of UO7 pentagonal bipyramids that share equatorial corners with MoO4 tetrahedra. The framework contains a three-dimensional system of channels. The first system of channels is parallel to [0 0 1] and has the dimensions 7.0 × 7.0 Å, which result in a crystallographic free diameter (effective pore width) of 4.3 × 4.3 Å (based on an oxygen radius of 1.35 Å). Other channels run parallel to [1 0 0], [1 1 0] and [0 1 0] and have dimensions 5.2 × 7.1 Å (giving an effective pore width of 2.5 × 4.4 Å). One symmetrically unique [(C2H5)2NH2]+ cation and H2O molecule reside in the framework cavities. The channels parallel to [0 0 1] are chiral and are centered about a 65 screw axis. The uranyl framework with U:Mo = 4:5 in the structure of [(C2H5)2NH2]2[(UO2)4(MoO4)5(H2O)](H2O) represents the third known type of chiral uranyl molybdate framework. Its relationships to the frameworks with U:Mo = 5:7 and 6:7 can be understood in terms of fundamental chains that have related but yet different topological structure.