Solvothermal synthesis and structural characterization of ultralight metal coordination networks

Two lithium-based coordination polymers and a framework Li ₃(C₇H₃O₄N)₂-0.21(H ₂O) (C₂H₈N) [1]; ULCP-1 (ULCP = ultralight coordination polymer); Li₃(C₇H₃O ₄N)·(C₆H₃O₂N) [2]; [ULCP-1A]; and Li₂(C₇H₃O₄N) [3]; ULMOF-4 (ULMOF = ultralight metal organic framework) were synthesized using solvothermal techniques. The compounds were characterized using single-crystal X-ray diffraction methods and thermal analysis techniques. Compound [1] [space group P2₁/c, a = 11.51(2) Å, b = 15.33(3) Å, c = 10.93(2) Å, β = 99.98(3)°] consists of trimeric corner- and edge-sharing lithium tetrahedral chains. Organic linkers connect each of these chains to form a two-dimensional (2-D) layered structure. Positively charged dimethyl amine (DMA) molecules and sites partially occupied by water molecules are present between the layers. Compound [2] [space group P2₁/c, a = 10.190(2) Å, b = 13.390(3) Å, c = 10.450(2) Å, β = 106.02(3)°] contains trimeric clusters of cornerand edge-sharing lithium tetrahedra. Each of these clusters is connected by the organic linkers to form an overall 2-D structure. Compound [3] [space group C2/c, a = 12.692(2) Å, b = 10.977(2) Å, c = 11.200(2) Å, β = 105.83(3)°] consists of edge- and corner shared one-dimensional (1-D) chains of lithium tetrahedra. The lithium polyhedral chains are then connected by the organic linkers to form a dense three-dimensional (3-D) network. All compounds are stable above 300 °C under N₂ atmosphere, with [3] stable to 550 °C.