With the aim of enhancing the biological activity of ruthenium-nitrosyl complexes, new compounds with four equatorially bound indazole ligands, namely, trans-[RuCl(Hind)(NO)]Cl·HO ([3]Cl·HO) and trans-[RuOH(Hind)(NO)]Cl·HO ([4]Cl·HO), have been prepared from trans-[Ru(NO)(Hind)] ([2]). When the pH-dependent solution behavior of [3]Cl·HO and [4]Cl·HO was studied, two new complexes with two deprotonated indazole ligands were isolated, namely [RuCl(ind)(Hind)(NO)] ([5]) and [RuOH(ind)(Hind)(NO)] ([6]). All prepared compounds were comprehensively characterized by spectroscopic (IR, UV-vis, H NMR) techniques. Compound [2], as well as [3]Cl·2(CH)CO, [4]Cl·2(CH)CO, and [5]·0.8CHCl, the latter three obtained by recrystallization of the first isolated compounds (hydrates or anhydrous species) from acetone and dichloromethane, respectively, were studied by X-ray diffraction methods. The photoinduced release of NO in [3]Cl and [4]Cl was investigated by cyclic voltammetry and resulting paramagnetic NO species were detected by EPR spectroscopy. The quantum yields of NO release were calculated and found to be low (3-6%), which could be explained by NO dissociation and recombination dynamics, assessed by femtosecond pump-probe spectroscopy. The geometry and electronic parameters of Ru species formed upon NO release were identified by DFT calculations. The complexes [3]Cl and [4]Cl showed considerable antiproliferative activity in human cancer cell lines with IC values in low micromolar or submicromolar concentration range and are suitable for further development as potential anticancer drugs. p53-dependence of Ru-NO complexes [3]Cl and [4]Cl was studied and p53-independent mode of action was confirmed. The effects of NO release on the cytotoxicity of the complexes with or without light irradiation were investigated using NO scavenger carboxy-PTIO.

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Abstract"Kramers pairs symmetry breaking" is evaluated at the 2-component (2c) Kramers unrestricted and/or general complex Hartree-Fock (GCHF) level of theory, and its analogy with "spin contamination" at the 1-component (1c) unrestricted Hartree-Fock (UHF) level of theory is emphasized. The GCHF "Kramers pairs symmetry breaking" evaluation is using the square of overlaps between the set of occupied spinorbitals with the projected set of Kramers pairs. In the same fashion, overlaps between α and β orbitals are used in the evaluation of "spin contamination" at the UHF level of theory. In this manner, UHFŜ 2 expectation value is made formally extended to the GCHF case. The directly evaluated GCHF expectation value of theŜ 2 operator is considered for completeness. It is found that the 2c GCHF Kramers pairs symmetry breaking has a very similar extent in comparison to the 1c UHF spin contamination. Thus higher excited states contributions to the 1c so 2c unrestricted wave functions of open shell systems have almost the same extent and physical consequences. Moreover, it is formally shown that a single determinant wave function in the restricted open shell Kramers case has the expectation value ofK 2 operator equal to the negative number of open shell electrons, while the eigenvalue ofK 2 for the series of simple systems (H, He, He*-triplet, Li and Li*-quartet) are found to be equal to minus the square of the number of open shell electrons. The concept of unpaired electron density is extended to the GCHF regime and compared to UHF and restricted open shell Hartree-Fock spin density. The "collinear" and "noncollinear" analogs of spin density at the GCHF level of theory are considered as well. Spin contamination and/or Kramers pairs symmetry breaking, spin

Mixing of ionic liquids provides new opportunities for their tuning, enabling the applications of ionic liquid mixtures to expand. At the same time, the genesis of the fundamental properties of ionic liquid mixtures is still poorly understood. In this study we carried out a molecular dynamics simulation of binary mixtures of 1-buthyl-3-methylimidazolium hexafluorophosphate, 1-buthyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-buthyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate ([C4mim][PF6] + [C4mim][NTf2], [C4mim][PF6] + [C4mim][FAP], [C4mim][FAP] + [C4mim][NTf2]) in a wide concentration range at 303.15 K and complemented it with quantum mechanical calculations. Three pure ionic liquids underwent the same kind of analysis for comparison purposes. We found that the addition of the [FAP]--anion to a mixture enhances the segregation of non-polar domains and weakens the hydrogen-bond network. The H-bonds in the studied mixtures are rather weak, as follows from QTAIM analysis, with the rarest occurrence for the [FAP]--anion. The competition of two anions in the mixtures for the most acidic hydrogen of the 1-butyl-3-methylimidazolium cation is reported. In most of the cases, the smaller anion ([PF6]- or [NTf2]-) with stronger charge concentration displaces the bigger one ([NTf2]- or [FAP]-) from the preferred coordination site. The existing nano-segregation in some mixtures notably slows down ion diffusion. Our results show that the differences in anion size, shape and nature are the main reasons for nano-segregation and the non-ideal behavior of ionic liquid mixtures.

Chromium species are the active sites in a variety of heterogeneous catalysts, such as the Phillips catalyst, which is composed of Cr ions supported by SiO2 and is used to produce polyethylene. Among the catalytically relevant oxidation states of chromium is CrIV. Families of neutral, homoleptic, four-coordinate complexes, CrL4, with a variety of monoanionic, monodentate ligands, such as L = alkyls, aryls, amides, ketimides (R2C = N–), alkoxides, and siloxides, are available and can provide information regarding Cr sites in heterogeneous materials. For example, the previously reported siloxide, Cr­(DTBMS)4, where DTBMS = –OSiMe t Bu2 (di-tert-butylmethylsiloxide), may be considered a molecular analogue of CrIV supported by SiO2. Such CrL4 complexes can have either a singlet (S = 0) or triplet (S = 1) spin ground state, and the spin state preferences of such complexes are not fully understood. A truly tetrahedral d2 S = 1 complex would exhibit no zero-field splitting (zfs), and the zfs is indeed small and observable by X-band EPR for several CrR4 and Cr­(OR)4 complexes. In contrast, Cr­(DTBMS)4 has zfs beyond the range amenable to X-band EPR so that high-frequency and high-field EPR (HFEPR) is appropriate. HFEPR of Cr­(DTBMS)4 in the solid state shows the presence of three very similar triplet species with the major component having D = +0.556 cm–1. Classical ligand-field theory (LFT) and quantum chemical theory (QCT), including ab initio methods, use EPR and electronic absorption spectra to give a complete picture of the electronic structure of Cr­(DTBMS)4, and other complexes of formula Cr­(ER n )4, E = C, n = 3; E = N, n = 2; E = O, n = 1; E = F, n = 0. Computations show the importance of ligand steric bulk and of π-bonding in controlling the subtleties of electronic structure of CrL4 species. These electronic structure results, including zfs, which is a measure of excited state accessibility, for both triplet and singlet excited states, might be related to the catalytic activity of paramagnetic Cr species.

High-resolution HFEPR indicates weak exchange interactions between MnIII ions in agreement with DFT calculations.

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