Boere, Rene
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- ItemDispersion in crystal structures of 1-chloro-3-aryl-5-trihalomethyl-1λ4,2,4,6-thiatriazines: towards an understanding of the supramolecular organization of covalent thiazyl chlorides(Thieme, 2023) Kondage, Savini S.; Roemmele, Tracey L.; Boeré, René T.The syntheses of five new 1-chloro-3-aryl-5-trichloromethyl-1λ4,2,4,6-thiatriazines, aryl = 4-R-C6H4- (R = CH3O, CH3, H, Cl and CF3), are reported with full characterization. Single-crystal X-ray diffraction structure determinations on all, as well as the 5-CF3 analogue which also has R = CF3, with models produced by Hirshfeld atom refinement, produced high-accuracy structures. All six exemplars form lateral dimers with short contacts that define a centrosymmetric {δ+S···Nδ−}2 motif, with interaction distances from 3.0473(9) to 3.422(3) Å, which do not vary in an expected manner with R. Normal population analysis charges computed by B3LYP-D3/6-311++G(d,p) DFT methods show small variations, and entirely as expected from the inductive effects of R. Gas-phase minimization of the dimers with M06-2X/aug-cc-pVDZ or B3LYP-D3/6-311++G(d,p) methods, with full counterpoise correction, replicate the experimental geometries for the 5-CF3, the 5-CCl3/CH3OC6H4 and the 5-CCl3/CH3C6H4 experimental structures, but diverge for other CCl3 exemplars. Interaction energies are more than double those computed for [(HC)2N2S]2. Using a geometry-optimized model with H in place of CX3, the interaction energy reduces to a very realistic –22 to –24 kJ/mol for just the {δ+S···Nδ−}2 motif, suggesting that CX3 interactions contribute 21% (CF3) to 37% (CCl3) of the total.
- ItemAccurate crystal structures of C12H9CN, C12H8(CN)2, and C16H11CN valence isomers using nonspherical atomic scattering factors(RSC Publishing, 2022) Hill, Nathan D. D.; Lilienthal, Elaura; Bender, Christopher O.; Boeré, René T.Fourteen crystal structures, mostly from good-quality datasets but including some marginal and twinned exemplars, from a series of novel polycyclic benzo- and naphtho-fused organic nitriles are presented and accurately described, including some related structures of a bromo-substituted and partially hydrogenated analogues. These structures represent a considerable increase in the number of published structures within their archetypes. This work highlights the significant advancement in structural refinement software proffered by NoSpherA2, which enables Hirshfeld Atom Refinement (HAR) of the structures within Olex2 v1.5. This results in the determination of C–H bond lengths with near to neutron diffraction accuracies at far lower experimental cost, and with an average improvement in C–C bond precision of 42% compared to Independent Atom Model refinements. H-atoms (apart from disordered components) refined well with anisotropic displacement parameters. Nonclassical H-bonding (C–H···N≡C) in this series is analyzed, and dipolar nitrile–nitrile interactions (C≡N···C≡N) in three major motifs described by (Wood, P. A. Acta Cryst. B, 2008, 64, 393−396) are found in 9 out of 13 nitrile-containing compounds of this series, a much higher proportion than the global average of 21% of nitrile-containing compounds. The HAR/NoSpherA2 approach shows increasing benefits with better data quality without apparent discontinuities.
- ItemChalcogen controlled redox behaviour in peri-substituted S, Se and Te naphthalene derivatives(RSC Publishing, 2022) Roemmele, Tracey L.; Knight, Fergus R.; Crawford, Ellis; Robertson, Stuart D.; Bode, Bela E.; Bühl, MIchael; Slawin, Alexandra M. Z.; Woollins, J. Derek; Boeré, René T.Cyclic and square wave voltammetry of (PhE)2peri-disubstituted naphthalene[1,8-cd]dichalcoganyls and acenaphthene[5,6-diyl]dichalcoganyls (E = S, Se, Te, 12 compounds) is reported. Mixed (E1 = Se, Te; E2 = Br, I) naphthalene[1,8-cd]halochalcoganyls were also investigated, as well as an exemplar bearing two PhS([double bond, length as m-dash]O) groups and another bearing one PhSe and one Ph2P([double bond, length as m-dash]S) substituent. The voltammetry, in CH2Cl2/0.4 M [nBu4N][PF6] at both platinum and glassy carbon macro-disk working electrodes, shows two sequential chemically reversible and electrochemically quasi-reversible oxidation processes, and the lack of accessible reductions. Additional oxidations above +1.5 V vs. Fc+/0 have not been investigated in detail. In situ and ex situ EPR spectroscopy conclusively demonstrate that both anodic processes are 1e transfers; persistent radical cations could be generated for all the dichalcoganyls except when E1 = E2 = Te; for the latter case thermally stable dications are generated instead. The complex possible solution conformations of these compounds in 0, +1 and +2 charge states were modelled with DFT at the B3LYP-D3(BJ)/6-31+G(d) level of theory in a CH2Cl2 PCM continuum solution model and adiabatic ionisation energies calculated, which correlate linearly (R = 0.88) with the Ea1p values. Crystal structures of four solvolysis and hydrolysis products of the ditellurium dications are reported and were modelled computationally. Interpretative comparisons to unsubstituted naphthalene[1,8-cd]dichalcogenoles are reported and the crystal structure of naphtho(1,8-cd)(1,2-dithiolium) tetrafluoroborate has been obtained. This is the first structure reported for any salt of this cation radical. Electron transfer mechanisms of both the (PhE)2 and E2peri-disubstituted naphthalene series are correlated using a redox molecular orbital interpretative framework.
- ItemCrystal structures of CuCl2·2H2O (Eriochalcite) and NiCl2∙6H2O (Nickelbischofite) at low temperature: full refinement of hydrogen atoms using non-spherical atomic scattering factors(MDPI, 2023) Boeré, RenéNew structure determinations of CuCl2∙2H2O and NiCl2∙6H2O are reported from 100 K X-ray diffraction experiments using both Mo Kα and Cu Kα radiation. Combined density functional theory (ORCA) and non-spherical atomic scattering factor (NoSpherA2) computations enabled Hirshfeld atom refinements (HAR) using custom atom scattering factors based on accurately polarized atom electron densities. The water hydrogen atoms could be positionally refined resulting in distinctly longer O–H bond lengths than those reported from previous X-ray diffraction experiments, but in good agreement with legacy neutron diffraction studies. Anisotropic displacement factors were employed, for the first time in these compounds by any technique. The outcomes from using the different X-ray sources with this new HAR method are compared, and the precision of the H-atom refinements evaluated where possible.
- ItemAre monophospha(III)amidines and -guanidines with ionizable hydrogens tautomeric? Towards a deeper understanding of two related hetero-element functional groups(Wiley, 2023) Masuda, Jason D.; Amrei, Leila M.; Boeré, René T.This paper presents definitive structural evidence for N,P(III)-monophosphaamidines in P=C and N=C isomeric forms from a combination of new syntheses, single-crystal X-ray diffraction (SC-XRD), solid-state NMR and FTIR. Evidence is also provided for C-amino-(σ2,λ3)-phosphaalkene and C-(σ3,λ3)-phosphinoimine tautomerism in solution using multi-nuclear NMR methods. Synthesis and SC-XRD structure determination of a trisubstituted N,N’,P(III)-monophosphaguanidine is presented, the first structure of a phospha(III)guanidine with two ionizable H atoms. The structural evidence is convincing for an N=C geometry, resulting in both N−H and P−H in the molecule. A detailed computational investigation using DFT methods is presented, with the goal of understanding the tautomeric structure preferences both at the fundamental level (parent molecules with all substituents on the heteroatoms being hydrogen) and using the full structures containing the very bulky 2,6-diisopropylphenyl (Dipp) substituents employed in this study. Arguments are espoused for treating phospha(III)amidines and -guanidines as new types of functional groups, similar to but distinct from the familiar organic analogues. Limited reactivity studies and a voltammetry study of one phospha(III)amidine are included with the supporting information.