Model complexes of [FeFe]-hydrogenase bearing carboxylic acid functionalities have been designed for applications toward immobilization of hydrogen production electrocatalysts on amino-functionalized carbon electrode surfaces. Using carboxylic acid-substituted thiols, complexes incorporating the −COOH moiety into the thiolate linkers have been synthesized:  (μ-SCH2CH2COOH)2[Fe(CO)3]2 (1) and the previously known (μ-(SCH2)2CHCOOH)[Fe(CO)3]2 (2). Carboxylic acid units have also been introduced via ligand substitution with a tricarboxyethyl phosphine to generate (μ-pdt)[Fe(CO)3][Fe(CO)2{P(C2H4COOH)3}] (3). To mimic the linkage of complexes of these types to amino-functionalized monolayers, it has been demonstrated that 2 can be coupled with aniline in solution to generate (μ-(SCH2)2CHCONHPh)[Fe(CO)3]2 (4), and the stability of this linkage has been addressed. The carboxylic acid-substituted complex 2 undergoes ligand substitution with PMe3 to generate (μ-(SCH2)2CHCOOH)[Fe(CO)2(PMe3)]2 (5). Complex 5 can then be protonated in either methanol or tetrahydrofuran solvent to generate (μ-(SCH2)2CHCOOMe)(μ-H)[Fe(CO)2(PMe3)]2}PF6 (6) and (μ-(SCH2)2CHCOOH)(μ-H)[Fe(CO)2(PMe3)]2}PF6 (7), respectively, demonstrating that a range of carboxy-functionalized complexes can be synthesized. Structural characterization and cyclic voltammetry of these complexes indicate that the carboxylic acid functionality has little effect on the structure and reactivity of the diiron dithiolate core.

The reaction of 2‐(aminomethyl)pyridine (2‐amp) with silver(I) salts of triflate (OTf–), trifluoroacetate (tfa–), and tetrafluoroborate (BF4–) produce monomeric, dimeric, bridged, and polymeric structural motifs. The structural characteristics are dependent upon the ratio of ligand/metal in the structure as well as the ability of the anion to coordinate to the metal centers and form hydrogen bonds to the bound ligands. The silver coordination environment takes on several geometries including near linear (6), trigonal (4), tetrahedral (1), and both trigonal‐bipyramidal and square‐based pyramidal in a single structure (2). Structures 2, 3, and 5 also display short Ag–Ag contacts ranging from 2.8958(3) to 3.0305(4) Å. The species with metal–metal interactions, which are connectively very similar to their metal‐isolated counterparts of 1, 4, and 6, are held together only by weak π‐stacking interactions or hydrogen bonds to their respective anions. Low‐temperature luminescence spectra were collected for all compounds and are compared. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The dianionic NiN2S2 complex, Ni(ema)2-, ema=N,N'-ethylenebis-2-mercaptoacetamide, known as a reasonable model of the tripeptide complex Ni(CGC)2- (C=cysteine; G=glycine) with respect to the two carboxyamido nitrogens and cis-dithiolates in a (N2S2)4- ligand scaffold as found in acetyl CoA synthase, has been explored for S-based reactivity toward oxygenation and alkylation. The isolation and structural characterization of a sulfinato species, [Et4N]2[Ni(ema).O2], prepared through a unique direct reaction of molecular O2 with crystalline [Et4N]2[Ni(ema)] is described. Reaction of [Et4N]2[Ni(ema)] with Br(CH2)3Br yields a neutral N2S2 macrocyclic complex shown by DFT computations and electrostatic-potential mapping to be opposite in electron distribution from the neutral NiN2S2 complexes in which the anionic charge is localized on sulfur.

The reaction of the asymmetric 3-aminomethylpyridine (3-amp) ligand with silver(I) tetrafluoroborate (AgBF4) produces an array of structural motifs that depend on the ratio of the reactants present and crystallization temperature. With a 1:1 ratio of 3-amp to silver, either a folded macrocycle, 1a, or a linear coordination polymer, 1, is formed, depending upon whether the crystals are grown at -35 or 5 degrees C. A 3:2 ratio forms two-dimensional sheets of 2 regardless of temperature of crystallization. The 2:1 ratio of ligand to metal again sees a temperature dependence with either a one-dimensional, 3a, or two-dimensional, 3, coordination polymer formed upon crystallization at low and high temperatures, respectively. Addition of 2,2'-bipyridine to any of the previous reaction mixtures stops the formation of their respective structures, instead constructing the discrete Ag-Ag-linked 4.