ИСТИНА

Anhydrous transition metal nitrates stand out by peculiar properties stemming from the frustration of leading exchange interactions. Recently, the investigation of physical properties of these systems has been focused on M(NO3)2 (M = Co, Ni), Rb3Ni2(NO3)7 and (NO)M(NO3)3 (M = Co, Ni, Cu) [1-5]. This work represents highly disordered nitrosonium manganese nitrate (NO)Mn6(NO3)13. It demonstrates the correlated disorder in magnetic and anionic subsystems at temperatures exceeding 12.8 K and 192 K, correspondingly. Its crystal structure was established in a broad temperature range at T  100 K. It is described by space group P63/m with unit cell parameters a = 10.630(2) Å, c = 15.150(8) Å, V = 194.3(0) Å3 at T = 300 K. It contains quantum tubes of corner shared MnO6 octahedra strengthened with nitrate groups NO3 - inside and outside. The space between the tubes is occupied with intermediate NO+ groups. One of nitrate groups outside the tubes may occupy two positions and orders at 190 K. The antiferromagnetic ordering of the magnetic subsystem occurs after antiferromagnetic low-dimensional correlations with characteristic temperature Tmax = 25 K in two steps at TN1 = 12.8 K and TN2 = 8.3 K. The structural and magnetic phase transitions are confirmed by the anomalies in specific heat shown in Fig. 1, magnetic susceptibility, dielectric constant and ESR data.