The crystal structure shows the formation of symmetric and asymmetric cationic hydroxo-bridged uranyl dimers. <...> The uranium atoms adopt a distorted pentagonal bipyramidal configuration with a UO4N3 coordination environment formed by two uranyl O atoms, three N atoms from the terpy ligand, and two O atoms from the hydroxide anions. <...> The complexation of uranyl ions with 2,2:6,2-terpyridine has been studied recently [ 2—6]. <...> This tridentate N-donor ligand, shorthanded here as terpy, can provide variously organized systems with the 2 UO2 cation. <...> The formation of some simple complexes, e.g., [UO2(NO3)2(terpy)] [ 7 ], [UO2(OTf)2(terpy)], and [UO2(terpy)2](OTf)2 [ 8 ], is favored in anhydrous organic solvents and with weakly coordinating counterions. <...> In addition, a dimeric complex [{UO2(NO3)(terpy)}2(-O2)] with a bridging peroxide ion has been isolated [ 6 ]. <...> The stock solution of uranyl perchlorate in acetonitrile was obtained in the following manner: uranyl nitrate hexahydrate (0.10 g, 0.19 mmol) was dissolved in 10 ml of concentrated perchloric acid (11 M) and evaporated to dryness 3 times with the addition of 2 ml of HClO4. <...> Acetonitrile solution (1 ml) of terpyridine (0.02 g, 0.086 mmol) was added dropwise to the solution of uranyl ions (0.04 M) in acetonitrile (1 ml). <...> Mirror-monochromated MoKh radiation (y = 0.7107 Е) from a micro-focus Nova X-ray source was used for the measurement. <...> One of the perchlorate anions (Cl(3) 4O ) was disordered over two positions with the occupancy ratio refined to 0.46:0.54. <...> In addition, the acetonitrile molecule was also disordered over two possible orientations sharing the C atom of the methyl group, with partial occupancy refined to about 0.40. <...> The H atoms associated with the solvent molecule were not located. <...> RESULTS AND DISCUSSION [{UO2(OH)(terpy)}2]2+ cations, perchlorate anions, and acetonitrile molecules. <...> Each uranium atom is surrounded by seven donor atoms. <...> Two of them belong to tightly bonded oxygen atoms of the uranyl Description of the molecular and crystal structure. <...> The structure consists of dimeric 110 K. LYCZKO, L. STECZEK Fig. 1. <...> Hydrogen atoms, perchlorate anions, and a solvent molecule <...>