Sequence of Structural and Magnetic Phase Transitions in (NO)Mn 6 (NO 3 ) 13 .

New nitrosonium manganese(II) nitrate, (NO)Mn 6 (NO 3 ) 13 , has been synthesized and structurally characterized. In the temperature range of 45-298 K, the crystal is hexagonal (centrosymmetric sp. gr. P 6 3 / m ). Mn 2+ ions are assembled into tubes along axis c with both NO 3 - filling and coating. The nitrosonium cation is located in the framework cavity and is disordered by a 3-fold axis. At the temperature T S1 = 190 K, a structural phase transition related to the libration of the intertube NO 3 group and a small variation of Mn polyhedron is observed. Moreover, the anomalies in physical properties of (NO)Mn 6 (NO 3 ) 13 allow suggesting that ordering of NO + units occurs at low temperatures. The antiferromagnetic ordering in this compound is preceded by the formation of a short-range correlation regime at about 25 K and takes place in two steps at T N1 = 12.0 K and T N2 = 8.4 K.