Ionic liquid gel materials offer a way to further utilise ionic liquids in technological applications. Combining the controlled and directed assembly of gels, with the diverse applications of ionic liquids, enables the design of a heady combination of functional tailored materials, leading to the development of task specific/functional ionic liquid gels.

Reaction of the mononuclear Ni(II) thiolate complexes [Ni(L)]hydrogenase ͉ iron ͉ nickel ͉ thiolates ͉ density functional theory calculations H ydrogenases catalyze the reversible oxidation of molecular hydrogen and play a vital role in anaerobic metabolisms of a wide variety of microorganisms (1, 2).[NiFe]hydrogenases are particularly interesting because of their heterobinuclear active site and have been studied extensively (3-12). Thiolate-bridged heterobimetallic Ni-Fe complexes, therefore, have also received considerable attention because of their importance as structural, spectroscopic, and functional models for the active site of the enzyme (13-15). The structure of the oxidized inactive form of [NiFe]hydrogenase in Desulfovibrio gigas has been determined by x-ray crystallography (4, 5) and confirms an unusual heterobimetallic Ni-Fe core incorporating two terminal thiolates and two bridging thiolates at the Ni ion, with the bridging thiolates binding to a Fe(CN) 2 (CO) fragment with a Ni-Fe separation of 2.9 Å (Fig. 1). The vast majority of low-molecular-weight mimics have sought to model these structural patterns and this Ni-Fe separation (13-15).Of particular interest to us was the reported x-ray absorption study of [NiFe]hydrogenase from Chromatium vinosum that estimated the Ni-Fe separation as 2.5-2.6 Å in the reduced and active Ni-SI form of the enzyme (16). This finding was further supported by theoretical (17) and mechanistic (18, 19) studies that suggest a shorter Ni-Fe separation (2.5 Å) in the active form of the enzyme compared with that observed in the structure of its oxidized, inactive form (2.9 Å) (4). Furthermore, recent crystal structure determinations of [NiFe]hydrogenases from Desulfovibrio vulgaris Miyazaki F (8) and D. gigas (11) also exhibit shorter Ni-Fe separations (2.55 and 2.53 Å, respectively), while Cramer and coworkers (20) have identified spin-state changes brought about by stereochemical distortion and͞or addition of further ligands at the active site. We therefore were challenged to synthesize low-molecular-weight heterobinuclear Ni-Fe complexes that would mimic not only the short Ni-Fe distance of the Ni-SI, Ni-C, and related reduced centers, but also to model the proposed stereochemical distortions and spin-state changes at the Ni center on binding to Fe fragment(s). Materials and MethodsAll operations were carried out at room temperature under a pure argon atmosphere by using standard Schlenk techniques. [Ni(pdt) (dppe)] (21, 22) and [Fe(CO) 3 (BDA)] (23) (pdt, propanedithiolate; dppe, 1,2-diphenylphosphinoethane; BDA, benzylidene acetone) were prepared by methods described in the literature. Fe 2 (CO) 9 and Fe 3 (CO) 12 were purchased from Aldrich and used as received. All solvents were dried and distilled before use. CH 2 Cl 2 was distilled from CaH 2 and benzene from Na͞benzophenone ketyl under argon. All calculations on complex 3 were carried out with the program ORCA (24). The functional for the geometry optimization was BP86 (25,26), and the basis set was TZVP on lig...

In entrapment an active species, which is often a catalyst, is trapped within a material by a solid or gel forming event; thus, it becomes dispersed within the solid or...