K<sub>2</sub>Ca<sub>4</sub>[(UO<sub>2</sub>)(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>]: A Uranyl Silicate with a One-Dimensional Chain Structure

A new uranyl silicate, K<sub>2</sub>Ca<sub>4</sub>[(UO<sub>2</sub>)­(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>], with a 1D chain structure has been synthesized from a solution of mixed alkali- and alkaline-earth-metal cations under hydrothermal conditions at 550 °C and 1400 bar and characterized by single-crystal X-ray diffraction and photoluminescence spectroscopy. It crystallizes in the triclinic space group <i>P</i>1̅ (No. 2) with <i>a</i> = 6.6354(2) Å, <i>b</i> = 6.6791(2) Å, <i>c</i> = 9.6987(3) Å, α = 98.324(2)°, β = 93.624(2)°, γ = 112.310(2)°, and <i>Z</i> = 1. Its crystal structure consists of a 1D chain of uranyl disilicate formed of corner-sharing UO<sub>6</sub> tetragonal bipyramids and Si<sub>2</sub>O<sub>7</sub> double groups. The adjacent chains are separated by K<sup>+</sup> and Ca<sup>2+</sup> cations. It is the first example of uranyl silicate with a 1D chain structure.