Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions

Abstract

Two compounds with unusual architectures of uranyl complexes were synthesized and then studied by single-crystal X-ray diffraction and FTIR spectroscopy. Compound Ba 2 [UO 2 (C 3 H 5 COO) 3 ] 4 ·2C 3 H 5 COOH·7H 2 O (I) is constructed of neutral hexanuclear clusters {Ba 2 [UO 2 (C 3 H 5 COO) 3 ] 4 -(C 3 H 5 COOH) 2 (H 2 O) 4 } containing crotonate ions. Compound Sr(H 2 O) 6 {Na[UO 2 (i-C 3 H 7 COO) 3 ] 3 } (II) is constructed of anionic tetranuclear clusters {Na[UO 2 (i-C 3 H 7 COO) 3 ] 3 } 2containing isobutyrate ions. These and other examples of heteronuclear clusters imply that the alkali and alkaline-earth metal atoms in these structures are not just charge-balancing ions, but truly [a]

Uranyl Coordination Compounds with Alkaline Earth Metals and Crotonate Ligands

“…Being the only distinguishing feature in the syntheses of compounds 1–4 (See syntheses in Supporting Information) the M atoms serve as the driving force of formation of certain building units (mono‐, tri‐ or hexanuclear) as opposed to simply responding to a space filling opportunity in crystal structures. In that sense this work continues our studies to reveal the role of the secondary metals in the formation of bimetallic polynuclear units …”

“…However, it seems that the elongation of hydrocarbon chain increases the tendency of binding of such smaller [UO 2 L 3 ] – units into larger heteronuclear clusters (in the presence of secondary metals). This tendency was proposed and discussed earlier, and recently we were able to solve crystal structures of several heteronuclear uranyl complexes with up to eight nuclei in the single cluster …”

“…Hydrogen bonds in compound 4 were reported earlier . Hydrogen bonds in 1–3 form between H atoms of water molecules (coordinated and crystallization) as well as of molecules of crotonic acid in 3 from one side and O atoms of crotonate ions, of water molecules and even of uranyl ions from the other side.…”

“…The only difference between crystal structures of 3 and 4 that restricts calling them isostructural is in the amount of molecules of crystallization water: three and a half and three respectively. Similarly to earlier published Ba compound 4 , the newly synthesized Sr compound 3 includes large hexanuclear neutral {Sr 2 (H 2 O) 4 (crtH) 2 [UO 2 (crt) 3 ] 4 } complex units (Figure ). Such units consist of four typical building units [UO 2 L 3 ] – bound with two Sr atoms one of which being hydrated by four water molecules and solvated by two molecules of crotonic acid.…”

“…Here we present the newly solved crystal structures of Mg, Ca and Sr containing compounds: [Mg(H 2 O) 6 ][UO 2 (crt) 3 ] 2 ⋅H 2 O ( 1 ), {Ca(H 2 O) 3 [UO 2 (crt) 3 ] 2 }⋅1.5H 2 O ( 2 ), {Sr 2 (H 2 O) 4 (crtH) 2 [UO 2 (crt) 3 ] 4 }⋅3.5H 2 O ( 3 ), where crt=C 3 H 5 COO – . The crystal structure of Ba containing compound {Ba 2 (H 2 O) 4 (crtH) 2 [UO 2 (crt) 3 ] 4 }⋅3H 2 O ( 4 ) was published earlier in the paper in ref., which also features the full systematics of all known to date heteronuclear clusters under discussion. Unfortunately, Be containing compound forms clusters of crystals under thermal evaporation of solutions and we were not able to grow an X‐ray quality single crystal yet, although we have evidence of its existence in the solid state.…”