Gerken, Michael

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    Fluoride-ion acceptor properties of WSF4: synthesis, characterization, and computational study of the WSF5¯ and W2S2F9¯ anions and 19F NMR spectroscopic characterization of the W2OSF9¯ anion
    (American Chemical Society, 2012) Nieboer, Jared; Haiges, Ralf; Hillary, William; Yu, Xin; Richardet, Tyler; Mercier, Hélène P. A.; Gerken, Michael
    The new [N(CH3)4][WSF5] salt was synthesized by two preparative methods: (a) by reaction of WSF4 with [N(CH3)4][F] in CH3CN and (b) directly from WF6 using the new sulfide-transfer reagent [N(CH3)4][SSi(CH3)3]. The [N(CH3)4][WSF5] salt was characterized by Raman, IR, and 19F NMR spectroscopy and [N(CH3)4][WSF5]·CH3CN by X-ray crystallography. The reaction of WSF4 with half an aliquot of [N(CH3)4][F] yielded [N(CH3)4][W2S2F9], which was characterized by Raman and 19F NMR spectroscopy and by X-ray crystallography. The WSF5– and W2S2F9– anions were studied by density functional theory calculations. The novel [W2OSF9]− anion was observed by 19F NMR spectroscopy in a CH3CN solution of WOF4 and WSF5–, as well as CH3CN solutions of WSF4 and WOF5–.
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    The solid-state structure of SF4: the final piece of the puzzle
    (Wiley, 2013) Goettel, James T.; Kostiuk, Nathan; Gerken, Michael
    Solved at last: The crystal structure of solid SF4, which has a melting point of −121 °C, has been obtained. It exhibits weak intermolecular S⋅⋅⋅F interactions. A similar structural motif was observed within a layer of SF4 in [HNC5H3(CH3)2+]2F−⋅⋅⋅SF4[SF5−]⋅3 SF4. The latter structure contains a range of bonding modes between S and F, namely SF5−, F4S⋅⋅⋅F−, F4S⋅⋅⋅FSF4−, and F4S⋅⋅⋅FSF3.
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    Lewis acid behavior of SF4: synthesis, characterization, and computational study of adducts of SF4 with pyridine and pyridine derivatives
    (Wiley, 2015) Chaudhary, Praveen; Goettel, James T.; Mercier, Hélène P. A.; Sowlati-Hashjin, Shahin; Hazendonk, Paul; Gerken, Michael
    Sulfur tetrafluoride was shown to act as a Lewis acid towards organic nitrogen-bases, such as pyridine, 2,6-dimethylpyridine, 4-methylpyridine, and 4-dimethylaminopyridine. The SF4·NC5H5, SF4·2,6-NC5H3(CH3)2, SF4·4-NC5H4(CH3), and SF4·4-NC5H4N(CH3)2 adducts can be isolated as solids that are stable below –45 °C. The Lewis acid-base adducts were characterized by low temperature Raman spectroscopy and the vibrational bands were fully assigned with the aid of density-functional-theory (DFT) calculations. The electronic structures obtained from the DFT calculations were analyzed by the quantum theory of atoms in molecules (QTAIM). The crystal structures of SF4·NC5H5, SF4·4-NC5H4(CH3), and SF4·4-NC5H4N(CH3)2 revealed weak S---N dative bonds with nitrogen coordinating in the equatorial position of SF4. Based on the QTAIM analysis, the non-bonded valence shell charge concentration on sulfur, which represents the lone pair, is only slightly distorted by the weak dative S---N bond. No evidence for adducts between quinoline or isoquinoline with SF4 was found by low-temperature Raman spectroscopy.
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    The structure of trimethyltin fluoride
    (Royal Society of Chemistry, 2015) Chaudhary, Praveen; Bieringer, Mario; Hazendonk, Paul; Gerken, Michael
    The solid-state structure of (CH3)3SnF was reinvestigated by X-ray diffraction techniques as well as by multi-nuclear solid-state NMR spectroscopy. Trimethyltin fluoride crystallizes from hot ethanol in the orthorhombic space group Pnma at room temperature and changes to a low-temperature orthorhombic phase (space group: Cmcm) below −70 °C. In both modifications, trimethyltin fluoride adopts a linear chain structure with symmetric fluorine bridges, in contrast to previous reports. During its synthesis, (CH3)3SnF precipitates in another, poorly crystalline modification, as shown by powder X-ray diffraction. Solid-state MAS NMR experiments of both room-temperature phases of (CH3)3SnF (non-recrystallized and recrystallized) were carried out for the 1H, 13C, 19F, and 119Sn nuclei. The 119Sn{19F, 1H} and 19F{1H} NMR spectra offer unambiguous determination for the 19F and 119Sn shielding tensors. The 119Sn{1H} solid-state NMR spectra are in agreement with pentacoordination of Sn in this compound for the non-recrystallized and the recrystallized modifications. Based on the solid-state NMR results, the non-recrystallized modification of (CH3)3SnF also consists of linear, symmetrically fluorine-bridged chains, and differs from the recrystallized orthorhombic phase only in packing of the chains.
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    A new synthetic route to rhenium and iodine oxide fluoride anions: The reaction between oxoanions and sulfur tetrafluoride
    (Elsevier, 2015) Goettel, James T.; Turnbull, Douglas; Gerken, Michael
    Sulfur tetrafluoride is a reagent for the one-step syntheses of [ReVIIO2F4]−, [IVOF4]−, and [IVIIO2F4]− salts. Pure Ag[ReO2F4] as well as its CH3CN coordination compounds were obtained from CH3CN solvent. The Ag[ReO2F4], [Ag(CH3CN)2][ReO2F4], and [Ag(CH3CN)4][ReO2F4] salts were characterized by Raman spectroscopy. The [Ag(CH3CN)4][ReO2F4]·2CH3CN coordination compound was characterized by single-crystal X-ray diffraction. The reaction of SF4 with KIO4 in anhydrous HF gave the known K[IO2F4] salt. The reaction of [N(CH3)4]IO3 with SF4 in CH3CN yielded the new [N(CH3)4][IOF4] salt, which was characterized by Raman spectroscopy.
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    Synthesis and characterization of adducts between SF4 and oxygen bases: examples of O···S(IV) chalcogen bonding
    (American Chemical Society, 2016) Goettel, James T.; Gerken, Michael
    Lewis acid–base adducts between SF4 and the oxygen bases tetrahydrofuran, cyclopentanone, and 1,2-dimethoxyethane were synthesized and characterized by Raman spectroscopy and X-ray crystallography. Crystal structures of (SF4·OC4H8)2, SF4·(OC4H8)2, SF4·CH3OC2H4OCH3, and SF4·(O═C5H8)2 show weak S···O chalcogen bonding interactions ranging from 2.662(2) to 2.8692(9) Å. Caffeine, which has three Lewis basic sites, was reacted with SF4 and one aliquot of HF forming C8H10N4O2·2SF4·HF, which was also characterized by X-ray crystallography. Density functional theory calculations aided in the assignment of the vibrational spectra of (SF4·OC4H8)2, SF4·(OC4H8)2, SF4·CH3OC2H4OCH3, and SF4·(O═C5H8)2. Bonding was studied by natural bond order and the quantum theory of atoms in molecules analyses.
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    Single-core PAHs in petroleum- and coal-derived asphaltenes: size and distribution from solid-state NMR spectroscopy and optical absorption measurements
    (American Chemical Society, 2016) Majumdar, R. Dutta; Bake, K. D.; Ratna, Y.; Pomerantz, A. E.; Mullins, O. C.; Gerken, Michael; Hazendonk, Paul
    Using solid-state 13C NMR spectroscopy of two different asphaltenes, one derived from petroleum and the other from coal liquids, it was shown that the asphaltene molecular architecture consists of a spectrum of sizes, ranging from smaller polyaromatic hydrocarbons (PAHs; <5 condensed rings) to much larger ones (>9 condensed rings), but their distribution varies between the two. It is shown that smaller PAHs are likely more abundant in the coal-derived asphaltenes, while the largest PAH cores of the two different asphaltenes are similar in size. These observations are reinforced by optical absorption. The coal-derived asphaltenes were found to contain a small fraction of archipelago-type structures, where a small PAH is tethered to the larger PAH core via an aryl linkage, which are less evident, and likely less abundant, in the petroleum asphaltenes. An important difference between the two asphaltenes lies in their alkyl fraction, with the petroleum asphaltenes possessing significantly longer and more mobile alkyl side chains, on average ∼7 carbons long, as opposed to an average chain length of ∼3–4 in the coal asphaltenes. The petroleum asphaltenes also possess a larger fraction of alicyclics. The longer length increases the propensity of the petroleum asphaltene alkyl side chains to intercalate between the aromatic rings of adjacent asphaltene aggregates, which is not observed in coal-derived asphaltenes. This work demonstrates the utility of combining cross-polarization dynamics and directly polarized 13C solid-state NMR spectroscopy in studying asphaltenes, while adding to the body of evidence supporting the single-core model of asphaltenes, which appears to be the dominant structural motif for this fraction of petroleum.
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    Interactions between SF4 and fluoride: a crystallographic study of solvolysis products of SF4·nitrogen-base adducts by HF
    (American Chemical Society, 2016) Goettel, James T.; Kostiuk, Nathan; Gerken, Michael
    Adducts between SF4 and a nitrogen base are easily solvolyzed by HF, yielding the protonated nitrogen base and fluoride. Salts resulting from the solvolysis of SF4·NC5H5, SF4·NC5H4(CH3), SF4·NC5H3(CH3)2, and SF4·NC5H4N(CH3)2 have been studied by Raman spectroscopy and X-ray crystallography. Crystal structures were obtained for pyridinium salts [HNC5H5+]F–·SF4 and [HNC5H5+]F–[HF]·2SF4, the 4-methylpyridinium salt [HNC5H4(CH3)+]F–·SF4, the 2,6-methylpyridinium salt [HNC5H3(CH3)2+]2[SF5–]F–·SF4, and 4-(dimethylamino)pyridinium salts [HNC5H4N(CH3)2+]2[SF5–]F–·CH2Cl2 and [NC5H4N(CH3)2+][HF2–]·2SF4. In addition, the structure of [HNC5H4(CH3)+][HF2–] was obtained. 4,4′-Bipyridyl reacts with SF4 and 1 and 2 equiv of HF to give the 4,4′-bipyridinium salts [NH4C5–C5H4NH+]F–·2SF4 and [HNH4C5–C5H4NH2+]2F–·4SF4, respectively. These structures exhibit a surprising range of bonding modalities and provide an extensive view of SF4 and its contacts with Lewis basic groups in the solid state. The interactions range from the strong F4S–F– bond in the previously observed SF5– anion to weak F4S---F–, F4S(---F–)2, and F4S(---FHF–)2 dative bonds.
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    Syntheses and characterization of W(NC6F5)F5– and W2(NC6F5)2F9– salts and computational studies of the W(NR)F5– (R = H, F, CH3, CF3, C6H5, C6F5) and W2(NC6F5)2F9– anions
    (American Chemical Society, 2017) Turnbull, Douglas; Wetmore, Stacey D.; Gerken, Michael
    Convenient preparative routes to fluorido[(pentafluorophenyl)imido]tungstate(VI) salts have been developed. The reaction of WF6·NC5H5 or [N(CH3)4][WF7] with C6F5NH2 results in quantitative formation of the C5H5NH+ or N(CH3)4+ salt of the W(NC6F5)F5– anion, respectively. The dissolution of [C5H5NH][W(NC6F5)F5] in anhydrous HF results in the formation of [C5H5NH][W2(NC6F5)2F9]. These salts have been comprehensively characterized in the solid state by X-ray crystallography and Raman spectroscopy and in solution by 19F and 1H NMR spectroscopy. The crystal structures of the W(NC6F5)F5– salts reveal conformational differences in the anions, and the 19F NMR spectra of these salts in CH3CN reveal coupling of the axial fluorido ligand to the 14N nucleus of the imido ligand. In addition, density functional theory (DFT-B3LYP) calculations have been performed on a series of W(NR)F5– anions (R = H, F, CH3, CF3, C6H5, C6F5) and the W2(NC6F5)2F9– anion, including gas-phase geometry optimizations, vibrational frequencies, molecular orbitals, and natural bond orbital (NBO) analyses.
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    Solid-state structure of a protonated ketones and aldehydes
    (Wiley, 2017) Stuart, Daniel; Wetmore, Stacey D.; Gerken, Michael
    Protonated carbonyl compounds have been invoked as intermediates in many acid-catalyzed organic reactions. To gain key structural and electronic data about such intermediates, oxonium salts derived from five representative examples of ketones and aldehydes are synthesized in the solid state, and characterized by X-ray crystallography and Raman spectroscopy for the first time. DFT calculations were carried out on the cations in the gas phase. Whereas an equimolar reaction of the carbonyl compounds, acetone, cyclopentanone, adamantanone, and acetaldehyde, with SbF5 in anhydrous HF yielded mononuclear oxonium cations, the same stoichiometry in a reaction with benzaldehyde resulted in formation of a hemiprotonated, hydrogen-bridged dimeric cation. Hemiprotonated acetaldehyde was obtained when a 2:1 ratio of aldehyde and SbF5 was used. Experimental and NBO analyses quantify the significant increase in electrophilicity of the oxonium cations compared to that of the parent ketones/aldehydes.
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    Syntheses, characterisation, and computational studies of tungsten hexafluoride adducts with pyridine and its derivatives
    (Elsevier, 2018) Turnbull, Douglas; Kostiuk, Nathan; Wetmore, Stacey D.; Gerken, Michael
    The reactions of WF6 with pyridine, 4-methylpyridine, 4-(dimethylamino)pyridine, and 4,4′-bipyridine (4,4′-bipy) in CH2Cl2 afford the Lewis-acid-base adducts WF6(4-NC5H4R) (R = H, CH3, N(CH3)2) and F6W(4,4′-bipy)WF6 as solids in quantitative yields. These adducts have been characterised in the solid state by Raman spectroscopy at ambient temperature and, in the cases of the mononuclear adducts, by X-ray crystallography at −173 °C. Furthermore, density-functional-theory (DFT-B3LYP) studies have been conducted to aid in predicting the structure of F6W(4,4′-bipy)WF6, assigning the vibrational frequencies of the adducts, and comparing their electronic properties.
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    Syntheses, characterization, and computational study of AsF5 adducts with ketones
    (Elsevier, 2019) Stuart, Daniel; Wetmore, Stacey D.; Gerken, Michael
    Lewis acid-base adducts between AsF5 and the ketones, acetone, cyclopentanone, and adamantanone, were synthesized from SO2 and CH2Cl2 solutions. These adducts, which contain O---As pnictogen bonding interactions, were found to be stable in solutions at room temperature. Raman and NMR spectroscopy of the solid adducts showed a characteristic decrease in the C=O stretching frequency, as well as dramatic deshielding of the 13C resonance of the carbonyl group upon adduct formation. Fluorine-19 NMR spectroscopy showed the two fluorine environments of the O–AsF5 moiety. Optimization of the gas-phase geometry using DFT calculations yielded geometries with essentially planar CC=OAs moieties. NBO analyses of the adducts and the free ketones show the polarization of the C=O bond upon adduct formation. The lowering of the LUMO energies upon adduct formation is more dramatic than what was found for protonation of ketones and reflects the substantially enhanced electrophilicity of the adducted ketones.
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    Synthesis, characterization, and Lewis acid behavior of [W(NC6F5)F4]x and computational study of W(NR)F4 (R = H, F, CH3, CF3, C6H5, C6F5), W(NC6F5)F4(NCCH3), and W(NC6F5)F4(NC5H5)n (n = 1, 2)
    (American Chemical Society, 2019) Turnbull, Douglas; Wetmore, Stacey D.; Gerken, Michael
    Amorphous [W(NC6F5)F4]x has been synthesized by the reaction of [C5H5NH][W(NC6F5)F5] with AsF5 in CH2Cl2. The reaction of [W(NC6F5)F4]x with CH3CN yields monomeric W(NC6F5)F4(NCCH3), whereas reaction with a sub-2-fold excess of C5H5N in CH3CN results in quantitative conversion to W(NC6F5)F4(NC5H5). Meanwhile, the reaction of W(NC6F5)F4(NCCH3) with a large excess of C5H5N results in the precipitation of W(NC6F5)F4(NC5H5)2. These compounds have been characterized in the solid state by Raman spectroscopy and in solution by multinuclear NMR spectroscopy. The crystal structures of W(NC6F5)F4(NCCH3) and W(NC6F5)F4(NC5H5), as well as improved structures of WOF4(NC5H5)n (n = 1, 2), have been obtained at low temperatures. Furthermore, density functional theory (DFT-B3LYP) calculations have been conducted on the W(NR)F4 (R = H, F, CH3, CF3, C6H5, C6F5) series as well as W(NC6F5)F4(NCCH3) and W(NC6F5)F4(NC5H5)n (n = 1, 2), providing optimized gas-phase geometries, vibrational frequencies, molecular orbitals, fluoride-ion affinities, and natural bond orbital (NBO) analyses.
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    Stabilization of [WF5]+ by bidentate N-donor ligands
    (Wiley, 2019) Turnbull, Douglas; Wetmore, Stacey D.; Gerken, Michael
    Transition-metal hexafluorides do not exhibit fluoride-ion donor properties in the absence of donor ligands. We report the first synthesis of donor-stabilized [MF5]+ derived from a transition-metal hexafluoride via fluoride-ion abstraction using WF6(L) (L=2,2′-bipy, 1,10-phen) and SbF5(OSO) in SO2. The [WF5(L)][Sb2F11] salts and [WF5(1,10-phen)][SbF6]⋅SO2 have been characterized by X-ray crystallography, Raman spectroscopy, and multinuclear NMR spectroscopy. The reaction of WF6(2,2′-bipy) with an equimolar amount of SbF5(OSO) reveals an equilibrium between [WF5(2,2′-bipy)]+ and the [WF4(2,2′-bipy)2]2+ dication, as determined by 19F NMR spectroscopy. The geometries of the cations in the solid state are reproduced by gas-phase geometry optimizations (DFT-B3LYP), and NBO analyses reveal that the positive charges of the cations are stabilized primarily by compensatory σ-electron donation from the N-donor ligands.
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    Synthesis and characterization of SF4 adducts with polycyclic amines
    (American Chemical Society, 2020) Kostiuk, Nathan; Goettel, James T.; Gerken, Michael
    Chalcogen-bonding interactions of SF4 with the polycyclic amines DABCO (C6H12N2) and HMTA (C6H12N4) were studied by low-temperature Raman spectroscopy and X-ray crystallography, revealing the 2:1 adducts C6H12N2·2SF4 and C6H12N4·2SF4 obtained from SF4 solvent. In C6H12N2·2SF4, the sulfur in each SF4 molecule is pentacoordinate with each SF4 coordinated by a single amine group, whereas C6H12N4·2SF4 forms a one-dimensional coordination polymer with three of the four nitrogen atoms in HMTA exhibiting N---S chalcogen bonds: one terminal N---SF4 and one experimentally unprecedented bridging N---(SF4)---N moiety. Solvolysis of C6H12N2·2SF4 by HF yielded crystals of [C6H12N2H]+2F–[SF5]−·6SF4, in which SF4 acts as a chalcogen-bond donor toward N as well as F. Solvolysis of C6H12N4·2SF4 resulted in the formation of the monoprotonated HMTA salt [C6H12N4H]+[HF2]−·SF4. Excess HF also led to isolation of monoprotonated HTMA, as seen in the crystal structure of the [C6H12N4H]+[H2F3]−·HF salt. The reaction of bicyclic, monobasic quinuclidine with SF4 and HF gave [C7H13NH]+F–·3.5SF4, which contains N–H---F–---SF4 interactions, as well as an interstitial, disordered SF4 molecule.
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    Reactions of molybdenum and tungsten oxide tetrafluoride with sulfur(IV) Lewis bases: structure and bonding in [WOF4]4, MOF4(OSO), and [SF3][M2O2F9] (M = Mo, W)
    (American Chemical Society, 2020) Turnbull, Douglas; Chaudhary, Praveen; Leenstra, Dakota; Hazendonk, Paul; Wetmore, Stacey D.
    The structure of [WOF4]4 has been reinvestigated by low-temperature X-ray crystallography and DFT (MN15/def2- SVPD) studies. Whereas the W4F4 ring of the tetramer is planar and disordered in the solid state, the optimized gas-phase geometry prefers a disphenoidally puckered W4F4 ring and demonstrates asymmetric fluorine bridging. Dissolution of MOF4 (M = Mo, W) in SO2 and SF4 results in the formation of MOF4(OSO) and [SF3][M2O2F9], respectively. Both SO2 adducts and [SF3]- [Mo2O2F9] have been characterized by X-ray crystallography. The crystal structure of [SF3][Mo2O2F9] reveals dimerization of the ion pair that results in a rare heptacoordinate sulfur center. Optimization of the {[SF3][M2O2F9]}2 dimers in the gas phase, however, results in the elongation of one contact such that the sulfur centers are effectively hexacoordinate. Meanwhile, the crystal structure of [SF3][W2O2F9]·HF instead demonstrates hexacoordinate sulfur centers and a highly unusual coordination to [SF3]+ from [W2O2F9]−through an oxido ligand. While [SF3][W2O2F9] does not decompose at ambient temperature, MOF4(OSO) and [SF3][Mo2O2F9] are unstable toward evolution of SO2 or SF4. Computational studies reveal that the monomerization of [WOF4]4 in the gas phase at 25 °C is thermodynamically unfavorable using SO2, but favorable using SF4, consistent with the relative thermal stabilities of WOF4(OSO) and [SF3][W2O2F9].
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    Stabilisation of [WF5]+ and WF5 by pyridine: facile access to [WF5(NC5H5)3]+ and WF5(NC5H5)2
    (Wiley, 2020) Turnbull, Douglas; Hazendonk, Paul; Wetmore, Stacey D.
    The enhanced reactivity of [WF5]+ over WF6 has been exploited to access a neutral derivative of elusive WF5. The reaction of WF6(NC5H5)2 with [(CH3)3Si(NC5H5)][O3SCF3] in CH2Cl2 results in quantitative formation of trigonal-dodecahedral [WF5(NC5H5)3]+, which has been characterised as its [O3SCF3]− salt by Raman spectroscopy in the solid state and variable-temperature NMR spectroscopy in solution. The salt is susceptible to slow decomposition in solution at ambient temperature via dissociation of a pyridyl ligand, and the resultant [WF5(NC5H5)2]+ is reduced to WF5(NC5H5)2 in the presence of excess C5H5N, as determined by 19F NMR spectroscopy. Pentagonal-bipyramidal WF5(NC5H5)2 was isolated and characterised by X-ray crystallography and Raman spectroscopy in the solid state, representing the first unambiguously characterised WF5 adduct, as well as the first heptacoordinate adduct of a transition-metal pentafluoride. DFT-B3LYP methods have been used to investigate the reduction of [WF5(NC5H5)2]+ to WF5(NC5H5)2, supporting a two-electron reduction of WVI to WIV by nucleophilic attack and diprotonation of a pyridyl ligand in the presence of free C5H5N, followed by comproportionation to WV.
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    Crystal structure of an ordered [WOF5]¯ salt: (1,10-phenH) [WOF5] (1,10-phen = 1, 10-phenanthroline
    (2020) Turnbull, Douglas; Gerken, Michael
    Crystals of 1,10-phenanthrolinium penta­fluorido­oxidotungstate(VI), (1,10-phen-H)[WOF5] (1,10-phen = 1,10-phenanthroline, C12H8N2), were obtained upon hydrolysis of WF6(1,10-phen) in CH3CN at 193 K. The (1,10-phen-H)[WOF5] salt contains a rare example of a [WOF5]− anion in which the oxygen and fluorine atoms are ordered. This ordering was verified by bond-valence determinations and structural comparisons with [Xe2F11][WOF5] and Lewis acid-base adducts of WOF4 with main-group donor ligands. The crystal packing is controlled by N—H⋯F hydrogen bonding that is directed exclusively to the axial F atom as a result of its increased basicity caused by the trans influence of the oxido ligand.
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    Synthesis and characterizations of fluorophosphoryl diazide and diisocyanate
    (Elsevier, 2021) Song, Chao; Chu, Xianxu; Zhu, Bifeng; Gerken, Michael; Zeng, Xiaoqing
    Two fluorine-substituted phosphoryl pseudohalides including the highly explosive diazide FP(O)(N3)2 and dii-socyanate FP(O)(NCO)2 have been synthesized and fully characterized with IR (gas-phase and noble-gas matrices), Raman (liquid), and NMR (19F and 31P) spectroscopy. The vibrational spectra of FP(O)(N3)2 and FP (O)(NCO)2 were analyzed with the aid of the B3LYP/6
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    Chalcogen versus dative bonding in [SF3] + Lewis acid−base adducts: [SF3(NCCH3)2] +, [SF3(NC5H5)2] +, and [SF3(phen)]+ (phen = 1,10-phenanthroline)
    (American Chemical Society, 2021) Turnbull, Douglas; Chaudhary, Praveen; Hazendonk, Paul; Wetmore, Stacey D.; Gerken, Michael
    The Lewis-acid behavior of [SF3][MF6] (M = Sb, As) salts toward mono- and bidentate nitrogen bases was explored. Reactions of [SF3][MF6] with excesses of CH3CN and C5H5N yielded [SF3(L)2]+ (L = CH3CN, C5H5N) salts, whereas the reaction of [SF3][SbF6] with equimolar 1,10-phenanthroline (phen) in CH3CN afforded [SF3(phen)][SbF6]·2CH3CN. Salts of these cations were characterized by low-temperature X-ray crystallography and Raman spectroscopy in the solid state as well as by 19F NMR spectroscopy in solution. In the solid state, the geometries of [SF3(NC5H5)2]+ and [SF3(phen)]+ are square pyramids with negligible cation–anion contacts, whereas the coordination of CH3CN and [SbF6]− to [SF3]+ in [SF3(NCCH3)2][SbF6] results in a distorted octahedral coordination sphere with a minimal perturbation of the trigonal-pyramidal SF3 moiety. 19F NMR spectroscopy revealed that [SF3(L)2]+ is fluxional in excess L at −30 °C, whereas [SF3(phen)]+ is rigid in CH2Cl2 at −40 °C. Density functional theory (DFT-B3LYP) calculations suggest that the S–N bonds in [SF3(NC5H5)2]+ and [SF3(phen)]+ possess substantial covalent character and result in a regular AX5E VSEPR geometry, whereas those in [SF3(NCCH3)2]+ are best described as S···N chalcogen-bonding interactions via σ-holes on [SF3]+, which is consistent with the crystallographic data.