Rb₃[C₆N₇(NCN)₃]·3H₂O and Cs₃[C₆N₇(NCN)₃]·3H₂O – Synthesis, Crystal Structure and Thermal Behavior of Two Novel Alkali Melonates

Abstract

Abstract Rubidium melonate trihydrate Rb 3 [C 6 N 7 (NCN) 3 ]·3H 2 O and cesium melonate trihydrate Cs 3 [C 6 N 7 (NCN) 3 ]·3H 2 O were obtained by ion exchange reactions in aqueous solution. The structure of the cesium salt was determined by single‐crystal X‐ray diffraction ( Pna 2 1 , a = 687.34(14), b = 2196.5(4), c = 1232.6(3) pm, V = 1860.9(7)·10 6 pm 3 , Z = 4, T = 200 K). The crystal structure of the isotypic rubidium salt was refined from X‐ray powder diffraction data by the Rietveld method ( Pna 2 1 , a = 674.48(2), b = 2146.4(1), c = 1207.5(1) pm, V = 1753.4(6)·10 6 pm 3 , Z = 4, T = 298 K). In the crystal structure planar melonate ions and alkali cations as well as water molecules are arranged in alternating layers. The melonate entities are interconnected by a dense hydrogen bonding network. Rb 3 [C 6 N 7 (NCN) 3 ]·3H 2 O and Cs 3 [C 6 N 7 (NCN) 3 ]·3H 2 O were investigated by FT‐IR spectroscopy, TG and DTA measurements.