Sulfonate complexes of actinide ions: structural diversity in uranyl complexes with 2-sulfobenzoate

The reaction of uranyl nitrate hexahydrate with 2-sulfobenzoate (SB(2-)) in the presence of various amines gave the series of complexes [UO(2)(SB)(H(2)O)] (1), [UO(2)(SB)(H(2)O)](2)·pyz (2), [2,2'-bipyH](2)[UO(2)(SB)(2)(H(2)O)]·4H(2)O (3), [4,4'-bipyH(2)](2)[UO(2)(SB)(2)](2) (4), [4,4'-bipyH](2)[(UO(2))(2)(SB)(3)(H(2)O)]·4H(2)O (5), [NMe(4)](2)[(UO(2))(2)(SB)(3)(H(2)O)(1.15)]·1.35H(2)O (6), [NMe(4)](2)[(UO(2))(3)(SB)(2)O(2)] (7), and [H(2)DABCO](2)[(UO(2))(5)(SB)(4)O(2)(OH)(2)]·4H(2)O (8), where pyz = pyrazine, bipy = bipyridine, and DABCO = 1,4-diazabicyclo[2.2.2]octane, with all compounds but 5 having been obtained under hydrothermal conditions. The crystal structures of these complexes display a common motif in which uranyl is chelated by the carboxylate and sulfonate groups of SB, giving a seven-membered ring. Structure-directing effects due to the amine and the presence in 7 and 8 of additional μ(3)-oxo or μ(2)-hydroxo bridges result in much structural variety, with different bridging by the carboxylate and sulfonate groups giving rise to zero- (3, 4), one- (1, 5-8), or two-dimensional (2) assemblies. Some unusual uranyl secondary building units are observed, such as the pentanuclear [(UO(2))(5)O(2)(OH)(2)] discrete motif. Addition of 3d-block metal cations (Cu(2+), Ni(2+)) in the presence of nitrogen donors gave the heterometallic molecular complex [UO(2)Cu(SB)(2)(2,2'-bipy)(2)](2)·2H(2)O (9), the heterogeneous compound [Cu(4,4'-bipy)(H(2)O)(3)](2)[UO(2)(SB)(2)](2)·2H(2)O (10), in which molecular uranyl dimers are encompassing copper-containing chains, and the heterometallic one-dimensional polymers [(UO(2))(2)Cu(2)(SB)(4)(bipym)(H(2)O)(4)] (11) and [UO(2)Ni(SB)(2)(bipym)(H(2)O)(2)]·3H(2)O (12), where bipym = bipyrimidine. The latter two complexes display two different arrangements: in 11, bipym bridges two [UO(2)Cu(SB)(2)] chains to give a ladderlike assembly, while the uranyl cations are merely decorating species in 12. In contrast to those of phosphonates, the actinide complexes of sulfonates in the solid state have been little investigated up to now. The present results show that sulfocarboxylates such as 2-sulfobenzoate, in which sulfonate coordination is promoted by chelate effects, are of interest in the synthesis of uranyl-organic coordination polymers.