Boere, Rene

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    Hydrogen bonds stabilize chloroselenite anions: crystal structure of a new salt and donor-accepting bonding to SeO2
    (MDPI, 2023) Boeré, René T.
    The single-crystal X-ray diffraction structure characterizing a new 4-methylbenzamidinium salt of chloroselenite [C8H11N2][ClSeO2] is reported. This is only the second crystal structure report on a ClSeO2− salt. The structure contains an extended planar hydrogen bond net, including a double interaction with both O atoms of the anion (an 𝑅22(8) ring in Etter notation). The anion has the shortest Se–Cl distances on record for any chloroselenite ion, 2.3202(9) Å. However, the two Se–O distances are distinct at 1.629(2) and 1.645(2) Å, attributed to weak anion–anion bridging involving the oxygen with the longer bond. DFT computations at the RB3PW91-D3/aug-CC-pVTZ level of theory reproduce the short Se–Cl distance in a gas-phase optimized ion pair, but free optimization of ClSeO2− leads to an elongation of this bond. A good match to a known value for [Me4N][ClSeO2] is found, which fits to the Raman spectroscopic evidence for this long-known salt and to data measured on solutions of the anion in CH3CN. The assignment of the experimental Raman spectrum was corrected by means of the DFT-computed vibrational spectrum, confirming the strong mixing of the symmetry coordinate of the Se–Cl stretch with both ν2 and ν4 modes.
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    N,N'-diaryl-sulfurdiimides are strongly redox tuned
    (Wiley, 2024) Hill, Nathan D. D.; Boeré, René T.
    The synthesis and extensive characterization of nine aryl sulfur diimides (SDIs, Ar−NSN−Ar) are presented with a robust computational and experimental investigation of the fundamental properties of these important members of the thiazyl family of compounds, with particular attention paid to their highly tunable electrochemical behaviour. This is the first work to undertake a systematic comparison of the electrochemical profiles of a coherent series of SDIs to demonstrate and quantify the response of their reduction potentials to substituent electron-donating and -withdrawing properties. This effect is found to be not only exceptionally strong, but also correlates very closely with computed orbital energies. Electron paramagnetic resonance spectroscopy is used to determine the nature, localization, and qualitative lifetimes of the radical anions of SDIs. This work also addresses significant misconceptions about physical properties of SDIs. Experimental data and modern computational methods are employed to provide a resolute answer to the long-standing contention of the solution-state conformations of SDIs, and to correct historical mistakes in the assignment of infrared spectroscopic data. High-quality crystal structures of all SDIs in this work showcase the utility of the recently introduced structural refinement software NoSpherA2, enabling full anisotropic refinement of H-atoms with accurate C−H bond lengths.
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    Lewis acid behavior of MoF5 and MoOF4: syntheses and characterization of MoF5(NCCH3), MoF5(NC5H5)n, and MoOF4(NC5H5)n (n- 1, 2)
    (ACS Publications, 2021) Bykowski, Janelle; Turnbull, Douglas; Hahn, Nolan R. J.; Boeré, René T.; Wetmore, Stacey D.; Gerken, Michael
    The Lewis acid–base adducts MoF5(NC5H5)n and MoOF4(NC5H5)n (n = 1, 2) were synthesized from the reactions of MoF5 and MoOF4 with C5H5N and structurally characterized by X-ray crystallography. Whereas the crystal structures of MoF5(NC5H5)2 and MoOF4(NC5H5)2 are isomorphous containing pentagonal-bipyramidal molecules, the fluorido-bridged, heptacoordinate [MoF5(NC5H5)]2 dimer differs starkly from monomeric, hexacoordinate MoOF4(NC5H5). For the weaker Lewis base CH3CN, only the 1:1 adduct, MoF5(NCCH3), could be isolated. All adducts were characterized by Raman spectroscopy in conjunction with vibrational frequency calculations. Multinuclear NMR spectroscopy revealed an unprecedented isomerism of MoOF4(NC5H5)2 in solution, with the pyridyl ligands occupying adjacent or nonadjacent positions in the equatorial plane of the pentagonal bipyramid. Paramagnetic MoF5(NC5H5)2 was characterized by electron paramagnetic resonance (EPR) spectroscopy as a dispersion in solid adamantane as well as in a diamagnetic host lattice of MoOF4(NC5H5)2; EPR parameters were computed using ZORA with the BPW91 functional using relativistic all-electron wave functions for Mo and simulated using EasySpin. Density functional theory calculations (B3LYP) and natural bond orbital analyses were conducted to elucidate the distinctive bonding and structural properties of all adducts reported herein and explore fundamental differences observed in the Lewis acid behavior of MoF5 and MoOF4.
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    Synthesis, characterization and anticancer activities of cationic η6-p-cymene ruthenium(II) complexes containing phosphine and nitrogenous ligands
    (Elsevier, 2022) Guimaraes, Ivelise D. L.; Marszaukowski, Flávia; Rutka, Priscila B.; Borge, Luis F.; Ribeiro, Renan A. P.; Ricardo de Lazaro, Sergio; Castellen, Patrícia; Sagoe-Wagner, Araba; Golsteyn, Roy M.; Boeré, René T.; Wohnrath, Karen
    Ruthenium-based anticancer agents have created a center of attention in the field of inorganic medicinal chemistry. The first fully characterized cationic ruthenium(II)-arene complexes [Ru(η6-p-cymene) (PAr3)LNCl]+ with highly lipophilic PAr3 ligands where Ar = 3,5-((CH3)3C)2C6H3– (L1), 3,5-(CH3)2C6H3– (L2), 4-CH3O-3,5-(CH3)2C6H2– (L3) and 4-CH3O-C6H4– (L4) with N = 3-methylpyridine (1–4, respectively), or L4 and 4-methylpyridine (5), or L4 and CH3CN (6) were obtained (yields 67–91%) as solids stable to light and air. Electrical conductance indicates that all the complexes are 1:1 electrolytes in solution. Their composition and purity have been unambiguously established by single-crystal X-ray diffraction, NMR spectroscopy and elemental analysis. The coordination geometries are uniform for all six complexes and each structure consist of a unipositive complex cation bearing the phosphine ligands L1-L4 and LN = 3-methylpyridine, 4-methylpyridine or CH3CN attached to the organometallic fragment. The equivalent unit cell volumes per formula unit decrease with 1 > 3 > 2 > 4 > 5 > 6, accurately reflecting the decreasing sizes of the phosphines L1-L4, and a greater occupied volume for 3-methyl- vs. 4-methylpyridine, and the smallest volume contribution from CH3CN. Electrochemical studies showed mixed electrochemical mechanisms (EC/ECE) from partial substitution of p-cymene by CH3CN ligands from the solvent. A large electrochemical stability window (>2.2 V) for Ru(II) was observed extending beyond the physiological E° range. The complexes were cytotoxic against human cancer cell lines in vitro, and some complexes altered cell morphology.
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    Frustrated and realized hydrogen bonding in 4-hydroxy-3,5- ditertbutylphenylphosphine derivatives
    (ACS Publications, 2022) Marszaukowski, Flávia; Boeré, René T.; Wohnrath, Karen
    Synthesis and molecular and supramolecular structures of a series of triarylphosphines P(Ph)3–n{4-RO-3,5-(tBu)2-C6H2}n (n = 1, 3; R = SiMe3, H) are reported. Chemical oxidation products E=P(Ph)3–n{4-RO-3,5-(tBu)2-C6H2}n (E = O, S, and Se; n = 1, 3; R = SiMe3, H) are also reported. Crystal structures of the reported compounds were determined by single-crystal X-ray diffraction, using a Hirshfeld atom refinement with NoSpherA2 through OLEX2, which provides an average improvement in C–C bond distance precision of 35%. Phosphine basicity for the phosphines with n = 1, R = H and n = 3, R = SiMe3, H was determined using the 1JP,Se values of the respective selenides; 1JP,Se = 699 Hz for E = Se, n = 3, and X = H identifies the most basic triarylphosphine ever reported. Intermolecular interactions allow classification of the 17 structures into 4 categories: those with only dispersion-induced short contacts, those with frustration of H-bonding, those with only classic H-bonding, and those with combinations of classic and frustration of H-bonding. A “double phenol embrace” classified by an R22(4) graph set is a weak intermolecular synthon organizing lattices with 2,6-ditertbutylphenol functional groups. Classic H-bonding occurs only when E = O.