Larisa Oresmaa

Argentophilic interactions in multinuclear Ag complexes of imidazole containing Schiff bases

The reactions of imidazole groups containing Schiff bases, 1,2-bis[(1-methyl-2-imidazolyl)-methyleneamino]ethane (bmimen) and 1,3-bis[(1-methyl-2-imidazolyl)-methyleneamino]propane (bmimpn), with silver salts AgCF3SO3 and AgClO3 were studied. Five new silver complexes, [Ag2(bmimen)2][CF3SO3]2·CH3OH·CH3CN (1), [Ag2(bmimen)2][CF3SO3]2 ·0.5H2O (2), [Ag2(bmimen)2][ClO3]2·CH3OH (3), [Ag3(bmimen)2(μ-CF3SO3)2]2[CF3SO3]4 (4) and [Ag(bmimpn)]n[CF3SO3]n (5), were synthesized and characterized. The Ag⋯Ag distances in compounds 1–5 depend on the length of the alkyl chain separating the imidazole ends of the ligand and the coordination mode of the bmimen and bmimpn. The shortest Ag⋯Ag distance of 2.7842(2) A was found in 4. Such a short distance indicates a strong argentophilic interaction. Argentophilic interactions exist in each of the dinuclear structures 1–3 (Ag⋯Ag distances are 3.3348(5), 3.1873(3) and 3.0680(2) A, respectively). The distance depends on crystal packing, which is determined by the counter ion and solvent molecules in the structure. In polymeric structure 5, the longer alkyl chain between the imidazole end units of the ligand pushes the metal centres further apart, the Ag⋯Ag separations being 3.6088(4) and 3.5279(4) A. The results show that imidazole-based Schiff bases can be used to build multinuclear Ag compounds with variable silver–silver interactions.

Ruthenium imidazole oxime carbonyls and their activities as CO-releasing molecules.

Carbon monoxide has been found to possess various beneficial effects in living organisms. To study the effects of CO further and to develop potential pharmaceutical agents, a meaningful method for delivering CO to the target organ is needed. It has been found that under physiological conditions various metal carbonyl complexes release carbon monoxide. In this study six novel ruthenium carbonyl complexes Ru(IMOX)(CO)(2)(COOR)Cl(1) (IMOX: imidazolecarbaldehyde oxime, R: Me, Et) were prepared and tested as carbon monoxide releasing molecules (CORMs). Synthesis of the complexes was performed under mild conditions in alcoholic solutions. The ability to release CO was tested spectrophotometrically by following the transformation of deoxymyoglobin to carbonmonoxy myoglobin. All of the complexes studied were found to release CO. Compared to formerly studied ruthenium-based CORMs these complexes offer a way for slower CO release.

Metallophilic interactions in stacked dinuclear rhodium 2,2′-biimidazole carbonyl complexes

Non-covalent metallophilic interactions were studied by investigating the stacking of two neutral rhodium complexes [Rh2I(R2bim)Cl2(CO)4] (R = Et, ethyl or Pr, propyl) in the solid state. Both dinuclear complexes formed infinite arrays of square planar d8 rhodium centres with intramolecular Rh⋯Rh distances of 3.1781(5) A (R = Et) and 3.1469(3) A (R = Pr) and the intermolecular Rh⋯Rh distances of 3.4345(6) A (R = Et) and 3.4403(3) A (R = Pr) between the adjacent molecules. The crystalline solids were stable and did not contain any solvent of crystallization. The effect of the metallophilic interactions on the absorption properties were studied using TD-DFT methods. The computational results indicate a red shift with a shortening Rh⋯Rh distance. Experimentally, bathochromic effects were also observed. The colour of the crystals was found to be dependent on the temperature, shape of the crystal, and the direction of the incoming light. The general appearance of the crystal was strongly affected by the linearly arranged metal atoms. Both crystalline materials had a metallic lustre typical of chain-like metal systems with metal–metal interactions.

Electro- and Photo-driven Reduction of CO2 by a trans-(Cl)-[Os(diimine)(CO)2Cl2] Precursor Catalyst: Influence of the Diimine Substituent and Activation Mode on CO/HCOO− Selectivity

A series of [OsII(NN)(CO)2Cl2] complexes where NN is a 2,2′‐bipyridine ligand substituted in the 4,4′ positions by H (C1), CH3 (C2), C(CH3)3 (C3), or C(O)OCH(CH3)2 (C4) has been studied as catalysts for the reduction of CO2. Electrocatalysis shows that the selectivity of the reaction can be switched toward the production of CO or HCOO− with an electron‐donating (C2, C3) or ‐withdrawing (C4) substituent, respectively. The electrocatalytic process is a result of the formation of an Os0‐bonded polymer, which was characterized by electrochemistry, UV/Visible and EPR spectroscopies. Photolysis of the complexes under CO2 in DMF+TEOA produces CO as a major product with a remarkably stable turnover frequency during 14 h of irradiation. Our results suggest that electrocatalysis and photocatalysis occur through two distinct processes, starting mainly from an OsI dimer precatalyst if the reduction is performed by an electrode and an OsI mononuclear species in case of a photoreduction process.