Sulfonate Complexes of Actinide Ions: Structural Diversity in Uranyl Complexes with 2‑Sulfobenzoate

The reaction of uranyl nitrate hexahydrate with 2-sulfobenzoate
(SB2–) in the presence of various amines gave the
series of complexes [UO2(SB)­(H2O)] (1), [UO2(SB)­(H2O)]2·pyz (2), [2,2′-bipyH]2[UO2(SB)2(H2O)]·4H2O (3), [4,4′-bipyH2]2[UO2(SB)2]2 (4), [4,4′-bipyH]2[(UO2)2(SB)3(H2O)]·4H2O (5), [NMe4]2[(UO2)2(SB)3(H2O)1.15]·1.35H2O (6), [NMe4]2[(UO2)3(SB)2O2] (7), and [H2DABCO]2[(UO2)5(SB)4O2(OH)2]·4H2O (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 μ3-oxo or μ2-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
[(UO2)5O2(OH)2] discrete
motif. Addition of 3d-block metal cations (Cu2+, Ni2+) in the presence of nitrogen donors gave the heterometallic
molecular complex [UO2Cu­(SB)2(2,2′-bipy)2]2·2H2O (9), the heterogeneous
compound [Cu­(4,4′-bipy)­(H2O)3]2[UO2(SB)2]2·2H2O
(10), in which molecular uranyl dimers are encompassing
copper-containing chains, and the heterometallic one-dimensional polymers
[(UO2)2Cu2(SB)4(bipym)­(H2O)4] (11) and [UO2Ni­(SB)2(bipym)­(H2O)2]·3H2O
(12), where bipym = bipyrimidine. The latter two complexes
display two different arrangements: in 11, bipym bridges
two [UO2Cu­(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.

硝酸铀酰六水合物（uranyl nitrate hexahydrate）与2-磺基苯甲酸根（2-sulfobenzoate, SB²⁻）在多种胺类存在下反应，得到一系列配合物：[UO₂(SB)(H₂O)] (1)、[UO₂(SB)(H₂O)]₂·pyz (2)、[2,2′-联吡啶氢][UO₂(SB)₂(H₂O)]·4H₂O (3)、[4,4′-联吡啶二氢]₂[UO₂(SB)₂]₂ (4)、[4,4′-联吡啶氢]₂[(UO₂)₂(SB)₃(H₂O)]·4H₂O (5)、[四甲基铵]₂[(UO₂)₂(SB)₃(H₂O)₁.₁₅]·1.35H₂O (6)、[四甲基铵]₂[(UO₂)₃(SB)₂O₂] (7)以及[二氢三亚乙基二胺]₂[(UO₂)₅(SB)₄O₂(OH)₂]·4H₂O (8)，其中pyz为吡嗪（pyrazine），bipy为联吡啶（bipyridine），DABCO为1,4-二氮杂双环[2.2.2]辛烷（1,4-diazabicyclo[2.2.2]octane）。除化合物5外，所有产物均通过水热条件（hydrothermal conditions）制备得到。
这些配合物的晶体结构具有共同的结构基元：铀酰（uranyl）被SB的羧酸根与磺酸根螯合，形成七元环。胺类的结构导向效应，以及7和8中额外的μ3-氧桥（μ3-oxo）或μ2-羟桥（μ2-hydroxo）的存在，造就了丰富的结构多样性；羧酸根与磺酸根的不同桥联方式，可形成零维（3、4）、一维（1、5–8）或二维（2）的组装体。我们观察到了一些罕见的铀酰次级结构基元（secondary building units），例如离散的五核[(UO₂)₅O₂(OH)₂]结构基元。
在氮给体存在下引入3d区金属阳离子（3d-block metal cations，如Cu²+、Ni²+），可得到异金属分子配合物[UO₂Cu(SB)₂(2,2′-联吡啶)₂]₂·2H₂O (9)、异金属配合物[Cu(4,4′-联吡啶)(H₂O)₃]₂[UO₂(SB)₂]₂·2H₂O (10)——该化合物中分子级铀酰二聚体包覆着含铜链——以及异金属一维聚合物[(UO₂)₂Cu₂(SB)₄(bipym)(H₂O)₄] (11)和[UO₂Ni(SB)₂(bipym)(H₂O)₂]·3H₂O (12)，其中bipym为联嘧啶（bipyrimidine）。后两种配合物呈现两种不同的排布方式：在11中，联嘧啶桥联两条[UO₂Cu(SB)₂]链，形成梯状组装体；而在12中，铀酰阳离子仅作为修饰性物种存在。
与膦酸盐（phosphonates）体系不同，目前固态磺酸盐锕系配合物（actinide complexes）的研究仍较少。本研究结果表明，诸如2-磺基苯甲酸根这类磺基羧酸盐（sulfocarboxylates，其磺酸根的配位可通过螯合效应得到强化）在铀酰有机配位聚合物（uranyl–organic coordination polymers）的合成中具有研究价值。