Presence Of Counteranions Research Articles

Counter-Anions Rendered Weak-Interactions Perturb the Stability of Tyrosinase-Mimicked Peroxo-Dicopper(II) Active Site: Unraveling Computational Indicators.

It has been observed in literature that the stability of tyrosinase-mimicked μ-η2 :η2 -peroxo-dicopper(II) (P) can be perturbed in presence of counter-anions (CAs) such as PhCO2 - , CF3 SO3 - , TsO- and SbF6 - . In this work, we unravel computational indicators using density functional theory to screen and study the stability of P in experimentally-reported cases. These indicators are Gibbs energies, geometrical parameters such as distances and angles, independent gradient model based on Hirshfeld partition (IGMH) generated data, orbitals' overlap, and distortion-interaction (DI) energies. Our DFT computed Gibbs energies indicate that P is stable in case of PhCO2 - and TsO- . CF3 SO3 - allows P and its isoelectronic species bis-μ-oxo-dicopper (O) to coexist. SbF6 - shows that O is in excess. Our indicators reveal that the stability of P in case of PhCO2 - and TsO- is due to the better placing of P and its CA, thus leading to better interactions and overlap of orbitals. Other indicator displays that the plane of Cu2 O2 core in P is more bend in PhCO2 - and TsO- cases as compared to the plane in the other two cases. In addition, the IGMH-based indicator displays higher values in the case of PhCO2 - and TsO- than the other CAs.

Exploring the structural diversities of three Co(II) complexes constructed from a new quinoline-containing N3O-cavity half-salamo type ligand and various counteranions

Three new Co(II) complexes containing half-salamo type ligand HL viz. [Co(L)Cl] (1), [Co(L)(NO3)] (2) and [Co(L)(NCS)] (3) were synthesized and characterized by single crystal X-ray diffraction. The results showed that the central Co(II) atoms in mononuclear complexes 1–3 are all located in the N3O cavity of the deprotonated ligand (L)− unit, while coordinated with different counteranions. The presence of counteranions in complexes 1–3 are Cl−, NO3− and NCS−, respectively. The spectral properties of these complexes were investigated in detail. In addition, the structural descriptions were corroborated with theoretical calculations. The Hirshfeld surface analysis combined with 2D fingerprint plots revealed the short-range intermolecular interactions of these complexes.

Aryliodonium Ylides as Novel and Efficient Additives for Radical Chemistry: Example in Camphorquinone (CQ)/Amine Based Photoinitiating Systems

Diaryliodonium salts are well-established compounds in free radical chemistry and are already used as photoinitiators (free radical or cationic polymerization), but the presence of counter anions is a strong drawback. Indeed, a counter anion is always required (e.g., SbF6−) leading to potential toxicity issues or release of HF. In the present paper, counter anion-free and fluoride-free aryliodonium salts are proposed, that is, aryliodonium ylides (AY) are studied here as new and efficient additives for radical chemistry and an example is provided for the camphorquinone (CQ)/amine based photoinitiating systems (PISs) for the polymerization of thick (1.4 mm) and thin (20–13 µm) methacrylates under air and blue light irradiation. The newly proposed PISs, for example, CQ/amine/AY, presented excellent polymerization performances and good bleaching properties were obtained after polymerization. Real-time Fourier transform infrared spectroscopy (RT-FTIR) was used to monitor the photopolymerization profiles. The chemical mechanisms involved were investigated using electron spin resonance (ESR).

Anion‐Templated Assembly of Half‐Sandwich Rhodium‐Based Multinuclear Metallamacrocycles

A series of half-sandwich rhodium-based metallamacrocycles with tetra- and hexanuclearities have been synthesized. They are assembled by linking the deprotonated 2,4-diacetyl-5-hydroxy-5-methyl-3-(3-pyridinyl)cyclohexanone (HL) ligand in the presence of counteranions. When the counteranion was the tetrahedral BF(4)(-) ion, tetranuclear metallamacrocycle [(Cp*RhL)(4)][BF(4)](4) (1d) was formed. However, the larger OTf(-) , PF(6)(-) , and SbF(6) (-) counterions favored the formation of hexanuclear metallamacrocycles [(Cp*RhL)(6)⊃2OTf][OTf](4) (1a), [(Cp*RhL)(6)⊃2PF(6)][PF(6)](4) (1b), and [(Cp*RhL)(6)⊃2SbF(6)][SbF(6)](4)⋅6CH(3)CN (1c) when the reactions were performed under the same conditions. Single-crystal X-ray analysis indicated that, in the solid state, two counteranions were encapsulated in each belt-like host molecule of hexanuclear metallamacrocycles 1a, b, and c. Based on the results of (1)H NMR analysis in methanol, the nuclearities of 1a-c and the two encapsulated anions in each molecular cavity were maintained in solution. In addition, tetranuclear metallamacrocycle 1d was converted into the hexanuclear metallamacrocycles 1a', b, and c after addition of the appropriate anion as its [NBu(4)](+) salt. The compound 1a' was characterized by single-crystal X-ray diffraction to have the formula [(Cp*RhL)(6)⊃2OTf][BF(4)](4) ⋅2MeOH⋅2H(2) O. From the interconversion of the hexanuclear metallamacrocycles, we have concluded that the hexanuclear belt-like host in 1a-c has an clear selectivity for larger anions, in the sequence SbF(6) (-) ≈PF(6) (-) >OTf(-) >BF(4) (-) >Cl(-) .

Nature of anion-templated π+–π+ interactions

Interaction between positively charged aromatic groups (π(+)-π(+)) is characterized by anti-parallel, displaced-stacked structures in the presence of counteranions. Binding energies of pyridinium, N-methylpyridinium and N-methylimidazolium dimers are much larger than that of benzene-pyridine (π-π) and pyridinium-benzene (π(+)-π). Stabilization is attributed to attractive electrostatic interaction with significant dispersion contribution.

Ab initio inter-radical potential for p-phenylenediamine radical cation dimer

Ab initio molecular orbital calculations were carried out to investigate the inter-radical interaction of the paired p-phenylenediamine radical cations in the singlet state. After initial optimization of the dimer in the parallel sandwich ( D 2 h ) and parallel displaced ( C s ) configurations at the B3LYP/6-31G* theoretical level, the MP2/6-31G* and B3LYP/6-31G* single energies of the dimer were calculated as a function of the inter-radical distance R. The depths of the potential minima near R=3.2 Å were estimated to be in the order of the hydrogen bonding energy, assuming that the electrostatic contribution between the cations is canceled out by the attractive contributions due to the counter anions on the aspect of a simple electrostatic model. This can be related to the indications of the cation dimer formation in solution in the presence of counter anions at a low temperature reported previously in the literature by resonance Raman and electronic absorption spectra. The inter-radical (Raman active) frequencies of the dimer were calculated, one of which corresponds to the reported value at 161 cm −1 observed in the resonance Raman spectrum in ethanol at 200 K by Yokoyama and Maeda (Chem. Phys. Lett. 48 (1977) 59).