Diruthenium aryl compounds – tuning of electrochemical responses and solubility

The variation of the substituents (X = 3,5-(OMe)2; 3-iPrO) on the bridging ligand results in improved solubility of Ru2-aryl compounds, while the aryl substitution significantly influences the potentials of the Ru2-based redox couples.

Partial synthetic models of FeMoco with sulfide and carbyne ligands: Effect of interstitial atom in nitrogenase active site

Nitrogen-fixing organisms perform dinitrogen reduction to ammonia at an Fe-M (M = Mo, Fe, or V) cofactor (FeMco) of nitrogenase. FeMco displays eight metal centers bridged by sulfides and a carbide having the MFe7S8C cluster composition. The role of the carbide ligand, a unique motif in protein active sites, remains poorly understood. Toward addressing how the carbon bridge affects the physical and chemical properties of the cluster, we isolated synthetic models of subsite MFe3S3C displaying sulfides and a chelating carbyne ligand. We developed synthetic protocols for structurally related clusters, [Tp*M’Fe3S3X]n−, where M’ = Mo or W, the bridging ligand X = CR, N, NR, S, and Tp* = Tris(3,5-dimethyl-1-pyrazolyl)hydroborate, to study the effects of the identity of the heterometal and the bridging X group on structure and electrochemistry. While the nature of M’ results in minor changes, the chelating, μ3-bridging carbyne has a large impact on reduction potentials, being up to 1 V more reducing compared to nonchelating N and S analogs.

The first coordination complex of (5R,6R,7S)-5-(furan-2-yl)-7-phenyl-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidin-6-amine with zinc(II) acetate-chloride

The title complex, systematic name catena-poly[[[acetatochloridozinc(II)]-μ-(5R,6R,7S)-5-(furan-2-yl)-7-phenyl-4,5,6,7-tetrahydro[1,2,4]triazolo[1,5-a]pyrimidin-6-amine] monohydrate], {[Zn(C2H3O2)Cl(C15H15N5O)]·H2O} n , is the first coordination complex in which the neutral tetrahydrotriazolopyrimidine derivative acts as bridging ligand between two zinc molecules. As a result, polymeric chains of the coordination complex are found. The coordination of the zinc metal atom occurs with the lone pairs of the triazolo nitrogen atom and amino group. The positive charge of the zinc atom is compensated by the chlorine anion and deprotonated acetic acid. The coordination complex exists as a monohydrate in the crystalline phase. The water molecules bind neighbouring polymeric chains by the formation of O—H...O, O—H...Cl and N—H...O hydrogen bonds.

Which bridge to cross, which mountain to climb – Supramolecular Photocatalysis Outpacing Conventional Catalysis

Unequivocal assignment of rate limiting steps in supramolecular photocatalysts is of utmost importance to rationally optimize photocatalytic activity. By spectroscopic and catalytic analysis of a series of three structurally similar [(tbbpy) 2 Ru-BL-Rh(Cp*)Cl] 3+ photocatalysts just differing in the central part (alkynyl, triazole or phenazine) of the bridging ligand (BL) we were able to derive design strategies for improved photocatalytic activity of this class of compounds (tbbpy = 4,4´-tert-butyl- 2,2´-bipyridine, Cp* = pentamethylcyclopentadienyl). Most importantly, not the rate of the transfer of the first electron towards the Rh III center but rather the rate at which a two-fold reduced Rh I species is generated can directly be correlated with the observed photocatalytic formation of NADH from NAD + . Interestingly, the complex which exhibited the fastest intramolecular electron transfer kinetics for the first electron is not the one that allowed the fastest photocatalysis. With the photocatalytically most efficient alkynyl linked system, it was even possible to overcome the rate of thermal NADH formation. Moreover, for this photocatalyst loss of the alkynyl functionality under photocatalytic conditions was identified as an important deactivation pathway.

The Influence of Aryl Substituents on the Supramolecular Structures and Photoluminescence of Cyclic Trinuclear Pyrazolato Copper(I) Complexes

Cyclic trinuclear complexes with group 11 metal (I) ions are fascinating and important to coordination chemistry. One of the ligands known to form these cyclic trinuclear complexes is pyrazolate, which is a bridging ligand that coordinates many transition metal ions in a Npz–M–Npz linear mode (Npz = pyrazolyl nitrogen atom). In these group 11 metal (I) ions, copper is the most abundant metal. Therefore, polynuclear Copper(I) complexes are very important in this field. The cyclic trinuclear Copper(I) complex [Cu(3,5-Ph2pz)]3 (3,5-Ph2pz– = 3,5-diphenyl-1-pyrazolate anion) was reported in 1988 as a landmark complex, but its photoluminescence properties have hitherto not been described. In this study, we report the photoluminescence and two different polymorphs of [Cu(3,5-Ph2pz)]3 and its derivative [Cu(3-Me-5-Phpz)]3 (3-Me-5-Phpz– = 3-metyl-5-phenyl-1-pyrazale anion). The substituents in [Cu(3-Me-5-Phpz)]3 cause smaller distortions in the solid-state structure and a red-shift in photoluminescence due to the presence of intermolecular cuprophilic interactions.

Kinetic and Thermodynamic Control in Rare Earth Cyamelurates Synthesis

If various compounds exist in the metal cation – C6N7O33– – H2O system, the synthesis temperature can affect the isolation of a particular product. Low temperatures favor the release of metastable kinetic products, and high temperatures, on the contrary, of thermodynamic ones. It is found that several structural types exist in the row of rare-earth cyamelurates. Room temperature synthesis leads to the formation of [Ln(H2O)7C6N7O3] (Ln=Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er), an increase in temperature yields thermodynamically more stable [Ln(H2O)4C6N7O3]n·nH2O (Ln=Y, Ho, Er, Tm, Yb, Lu) and [Ln(H2O)5C6N7O3]n (Ln = Pr, Nd). The change in the synthesis temperature did not affect the structures of Sm, Eu, Gd, Tb, Dy cyamelurates, as well as the structure of lanthanum cyamelurate [La(H2O)6C6N7O3]·H2O.In synthesized at increased temperature [Ln(H2O)4C6N7O3]n·nH2O and [Ln(H2O)5C6N7O3]n cyamelurates polymeric chains exist due to the fact that the cyamelurate anion acts as a bridging ligand. Kinetically trapped Y, Pr, Nd, Ho, Er cyamelurates, in contrast, consist of individual complex molecules [Ln(H2O)7C6N7O3]. Probably, steric difficulties caused a decrease in the coordination number of Y, Ho, Er from 9 to 8 in the thermodynamic product. The coordination number of Pr and Nd remains equal to 9 in both types of compounds.

Pyrimidoquinxoalinophenanthroline opens next chapter in design of bridging ligands for artificial photosynthesis

Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand that bridges the gap of already existing systems is synthesized. By the usage of versatile cross-coupling reactions two different coordination spheres are included in the ligand architecture. Due to the twisted geometry of the novel ditopic ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)3]2+ (bpy = 2,2´-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier molecular orbitals apparent by e.g., luminescence quenching. Thus, the new bridging ligand motif offers electronic properties which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru-Rh complex, visible light-driven reduction of NAD+ to NADH was achieved, highlighting the potential of this system for photocatalytic applications.

Pyrimidoquinxoalinophenanthroline opens next chapter in design of bridging ligands for artificial photosynthesis

Using a dehydrogenative chemistry on the complex approach, a new polypyridine bridging ligand that bridges the gap of already existing systems is synthesized. By the usage of versatile cross-coupling reactions two different coordination spheres are included in the ligand architecture. Due to the twisted geometry of the novel ditopic ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)3]2+ (bpy = 2,2´-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier molecular orbitals apparent by e.g., luminescence quenching. Thus, the new bridging ligand motif offers electronic properties which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru-Rh complex, visible light-driven reduction of NAD+ to NADH was achieved, highlighting the potential of this system for photocatalytic applications.

Quantum Chemical Study of Spin Transitions in the Bimetallic Fe/Co Complexes with the Bis(catecholate) Bridging Ligand

The computational modeling of the spatial and electronic structures, energy characteristics, and magnetic properties of the bimetallic iron and cobalt complexes with 9,10-dimethyl-9,10-ethano-9,10-dihydro-2,3,6,7-tetrahydroxyanthracene and terminal tris(2-pyridylmethyl)amine bases is performed using the density functional theory method (DFT UTPSSh/6-311++G(d,p)). The chosen tetradentate redox ligand is shown to be a promising precursor for the production of magnetically active compounds. The calculations make it possible to establish a relationship between the relative energies of the electronic isomers of the complexes and the structures of the ancillary N-donor moieties. The coordination compounds prone to the manifestation of spin transitions accompanied by a change in the magnetic properties are revealed.