The synthesis of the selenium-based ligand (LSeSeL1)-Se-1 (2,2'-diselanediylbis(N,N-bis(pyridin-2-ylmethyl)ethan-1-amine) is described along with its reactivity with cobalt(II) salts. The cobalt(II... Show moreThe synthesis of the selenium-based ligand (LSeSeL1)-Se-1 (2,2'-diselanediylbis(N,N-bis(pyridin-2-ylmethyl)ethan-1-amine) is described along with its reactivity with cobalt(II) salts. The cobalt(II)-diselenide complex [Co-2((LSeSeL1)-Se-1)Cl-4] was obtained in good yield, and its spectroscopic properties closely resemble that of its sulfur analog. Reaction of (LSeSeL1)-Se-1 with Co(II) thiocyanate results in the formation of the cobalt(III) compound [Co((LSe)-Se-1)(NCS)(2)], similar to reaction of (LSSL1)-S-1. The redox-conversion reactions from the Co(II)-diselenide compound [Co((LSeSeL1)-Se-1)Cl-4] using external triggers such as removal of the halide ions or the addition of the strong-field ligand 8-quinolinolate resulted in good yields of the Co(III)-selenolate complexes [Co((LSe)-Se-1)(MeCN)(2)](SbF6)(2) and [Co((LSe)-Se-1)(quin)]Cl. Our computational studies show that the ligand-field splitting energy of the selenium compounds is smaller than their sulfur analogs, indicating that redox-conversion of cobalt(II)-diselenide to cobalt(III)-selenolate complexes may be more arduous than that for the related sulfur compounds. Show less
For the technological integration of molecular switches in electronic devices, self-assembling nanomaterials of such switches are highly sought after. The syntheses of a new tetrapyridyl ligand... Show moreFor the technological integration of molecular switches in electronic devices, self-assembling nanomaterials of such switches are highly sought after. The syntheses of a new tetrapyridyl ligand bearing a C12 alkyl chain and two N-H bridges (compound 1) and of its iron(II) complex [Fe(1)(NCS)(2)] (compound 2), are described. Magnetic susceptibility data for bulk samples of 2 confirmed their gradual spin-crossover properties. The self-assembly of 1 and 2 on highly ordered pyrolytic graphite surfaces (HOPG) was investigated by Scanning Tunneling Microscopy (STM). Both compounds 1 and 2 formed ordered monolayers after deposition by drop casting. The patterns of the two compounds are very different, which is attributed to the fundamentally different hydrogen bonding networks before and after coordination of Fe(NCS)(2) to the tetradentate chelate. Two possible models for the self-assembly of 1 and 2 are provided. This work suggests that it is possible to design molecular switches that self-assemble on surfaces in highly ordered monolayer films. This is a significant step in the development of spin-switching materials, which may streamline the integration of molecular switches in for example memory and sensing devices. Show less
Olivares, M.; Ham, C.J.M. van der; Mdluli, V.; Schmidtendorf, M.; Müller-Bunz, H.; Verhoeven, T.W.G.M.; ... ; Albrecht, M. 2020
Based on previous work that identified iridium(III) Cp* complexes containing a C,N-bidentate chelating triazolylidene-pyridyl ligand (Cp* = pentamethylcyclopentadienyl, C5Me5-) as efficient... Show moreBased on previous work that identified iridium(III) Cp* complexes containing a C,N-bidentate chelating triazolylidene-pyridyl ligand (Cp* = pentamethylcyclopentadienyl, C5Me5-) as efficient molecular water oxidation catalysts, a series of new complexes based on this motif has been designed and synthesized in order to improve catalytic activity. Modifications include specifically the introduction of electron-donating substituents into the pyridyl unit of the chelating ligand (H, a; 5-OMe, b; 4-OMe, c; 4-tBu, d; 4-NMe2, e), as well as electronically active substituents on the triazolylidene C4 position (H, 8; COOEt, 9; OEt, 10; OH, 11; COOH, 12). Chemical oxidation using cerium ammonium nitrate (CAN) indicates a clear structure-activity relationship with electron-donating groups enhancing catalytic turnover frequency, especially when the donor substituent is positioned on the triazolylidene ligand fragment (TOFmax = 2500 h(-)(1) for complex 10 with a MeO group on pyr and a OEt-substituted triazolylidene, compared to 700 h(-)(1) for the parent benchmark complex without substituents). Electrochemical water oxidation does not follow the same trend, and reveals that complex 8b without a substituent on the triazolylidene fragment outperforms complex 10 by a factor of 5, while in CAN-mediated chemical water oxidation, complex 10 is twice more active than 8b. This discrepancy in catalytic activity is remarkable and indicates that caution is needed when benchmarking iridium water oxidation catalysts with chemical oxidants, especially when considering that application in a potential device will most likely involve electrocatalytic water oxidation. Show less
Three pyridyl‐amide substituted (benz)imidazolium salts H2L1Cl, H2L2Cl and H2L3Cl were synthesized and successfully employed as ligand precursors for the syntheses of novel nickel(II) and cobalt... Show moreThree pyridyl‐amide substituted (benz)imidazolium salts H2L1Cl, H2L2Cl and H2L3Cl were synthesized and successfully employed as ligand precursors for the syntheses of novel nickel(II) and cobalt(III) complexes. The compounds H2L1Cl and H2L2Cl are precursors to tetradentate ligands and differ in the nature of the N‐heterocyclic carbene (NHC) functionality, being imidazole‐based and benzimidazole‐based, respectively. The ligand precursor H2L3Cl resembles H2L1Cl, but with one of the pyridyl groups replaced with a benzyl group, thus yielding a potential tridentate ligand. The nickel(II) compounds [Ni(L1)]Cl and [Ni(L2)]PF6 were obtained, bearing tetradentate ligands comprising an amidate and two pyridine nitrogen donor atoms and an (NHC) carbon donor. Single crystal X‐ray crystallography revealed that the nickel ions in both compounds are in slightly distorted square‐planar geometries. Reactions of cobalt salts with the ligands H2L1Cl and H2L3Cl resulted in the cobalt(III) compounds [Co(L1)2]Cl and [Co(L3)2]PF6; the cobalt ions in both complexes are in octahedral geometries, bound by two tridentate ligands in a meridional binding mode, with two dangling pyridine and benzyl groups, respectively. The four compounds show electrocatalytic activity in proton reduction in dimethylformamide solutions in presence of acetic acid; their activity is compared using cyclic voltammetry and quantified with gas chromatography. Show less
