Liquid clathrate media containing transition metal halocarbonyl anions; formation and crystal structures of [K+ · 18-crown-6][Cr(CO)5Cl], [H3O+ · 18-crown-6][W(CO)5Cl], [H3O+ · 18-crown-6][W(CO)4Cl3], and [H2O · bis-aza-18-crown-6 · (H+)2][W(CO)4Cl3]2

Insights into Ionic Liquid/Aromatic Systems from NMR Spectroscopy: How Water Affects Solubility and Intermolecular Interactions

Hydrocarbon solubility and chemical interactions in ten imidazolium- and pyridinium-based ionic liquids (ILs) with four different anions (thiocyanate [SCN]^- , dicyanamide [DCA]^- , tricyanomethanide [TCM]^- , and bis(trifuoromethylsulfonyl)imide [NTf₂ ]^- ) have been studied by ¹ H and ¹³ C NMR spectroscopy. The anion structure has the main influence on the anion-aromatic chemical interaction strength; it is directly correlated to the NMR chemical shift deviations but not to the hydrocarbon solubility. The [TCM]^- anion shows the largest chemical shift deviations, but the [NTf₂ ]^- anion has the highest hydrocarbon solubility due to steric effects. Higher water contents decrease the hydrocarbon solubility in ILs. Ion-water solvation mainly occurs until 1 mol_water /mol_IL with the saturation limit at 10 mol_water /mol_IL . Toluene-ion interactions are stronger than water-ion interactions in [DCA]^- and [TCM]^- -based ILs, but they have a similar or even lower strength in [SCN]^- -based ILs.

Impacts of Oxo Interactions on Np(V) Crown Ether Complexes

Intermolecular interactions between the oxo group of an actinyl cation and other metal cations (i.e., cation-cation interactions) are dependent on the strength of the actinyl bond. These cation-cation interactions are prominently observed for the neptunyl cation [Np(V)O₂]⁺ and are sufficiently stable enough to explore using a variety of chemical techniques. Herein, we investigate these intermolecular interactions in the neptunyl 18-crown-6 system, because this macrocyclic ligand provides both stable coordination and the proper sterics to engage the oxo group in bonding with both low-valent metal cations and neighboring neptunyl units. We report the structural and spectroscopic characterization of five neptunyl, [Np(V,VI)O₂]^+,2+, compounds: Np1a ([NpO₂(18-crown-6)]ClO₄), Np1b ([NpO₂(18-crown-6)]AuCl₄), Na-Np ([Np(V)O₂(18-crown-6)(Na(H₂O)(18-crown-6)][Np(VI)O₂Cl₄], Np-Np ([NpO₂(18-crown-6)](NpO₂Cl₂NO₃)], and Np-Cl (NpO₂Cl(H₂O)_1.75). Each of these compounds were prepared from the ambient reactions of Np(V) in HX (where X = Cl, NO₃) with the 18-crown-6 ether molecule. Structural information obtained from single-crystal X-ray diffraction data was paired with solid-state and solution Raman spectroscopy to provide information on the interaction of the neptunyl oxo atom with neighboring cations. Neptunyl (Np═O) bond lengths are not perturbed upon interaction with the Na⁺ cation (Na-Np), but elongation is observed upon formation of a neptunyl-neptunyl interaction (Np-Np). This is also the first structurally characterized isolated, molecular complex that contains a simple T-shaped neptunyl-neptunyl interaction. Raman spectroscopy indicates little perturbation to the neptunyl bond until the formation of the neptunyl-neptunyl motif, which also results in activation of the ν₃ asymmetric stretch. Additional spectroscopic studies indicated that the neptunyl 18-crown-6 inclusion complexes form in solution and persist in the presence of other low-valence cations.

Element misidentification in X-ray crystallography: a reassessment of the [MCl2(diazadiene)] (M = Cr, Mo, W) series

A series of reports describing the syntheses and structures of [MCl2(diazadiene)] (M = Cr, Mo, W) complexes is reassessed in the context of known chemistry of low-valent Group VI metal complexes, crystallographic trends such as M-Cl bond lengths and unit cell volumes, and calculated metal-ligand bond lengths. Crystallographic data and computational results are inconsistent with any of these species being second or third row transition metal complexes. A review of the crystallographic information files accompanying the [MCl2(diazadiene)] (M = Mo, W) published structures reveals that the metal atoms were inappropriately treated with partial site occupancy factors (0.775 for Mo; 0.4005 and 0.417 for W), the effect of which was to manifest lighter-element behavior and better refinement in accord with the metal atoms' correct identity. A deliberate synthesis and characterization by X-ray diffraction of [ZnCl2((Mes)dad(Me))] ((Mes)dad(Me) = 1,4-bis(2,4,6-trimethylphenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene) are reported. Refinement of this structure with the same combination of second or third row metal and offsetting partial site occupancy is shown to provide final refinement statistics essentially the same as with the correct model employing M = Zn at site occupancy 1.00. Use of the published method for synthesis of [WCl2(diazadiene)] with (Mes)dad(Me) and [WBr4(MeCN)2] in lieu of [WCl4(MeCN)2] is shown to produce [ZnBr2((Mes)dad(Me))], which has also been characterized by X-ray diffraction. It is concluded that the unusual putative 12-electron [MCl2(diazadiene)] (M = Cr, Mo, W) complexes are in all cases the corresponding [ZnCl2(diazadiene)] complexes, Zn having been commonly employed as reducing agent in their synthesis.

(Salen)tin complexes: syntheses, characterization, crystal structures, and catalytic activity in the formation of propylene carbonate from CO(2) and propylene oxide

A series of (salen)tin(II) and (salen)tin(IV) complexes was synthesized. The (salen)tin(IV) complexes, (salen)SnX(2) (X = Br and I), were prepared in good yields via the direct oxidation reaction of (salen)tin(II) complexes with Br(2) or I(2). (Salen)SnX(2) successfully underwent the anion-exchange reaction with AgOTf (OTf = trifluoromethanesulfonate) to form (salen)Sn(OTf)(2) and (salen)Sn(X)(OTf) (X = Br). The (salen)Sn(OTf)(2) complex was easily converted to any of the dihalide (salen)SnX(2) compounds using halide salts. All complexes were fully characterized by (1)H NMR spectroscopy, mass spectrometry, and elemental analysis, while some were characterized by (13)C, (19)F, and (119)Sn NMR spectroscopy. Several crystal structures of (salen)tin(II) and (salen)tin(IV) were also determined. Finally, both (salen)tin(II) and (salen)tin(IV) complexes were shown to efficiently catalyze the formation of propylene carbonate from propylene oxide and CO(2). Of the series, (3,3',5,5'-Br(4)-salen)SnBr(2), 3i, was found to be the most effective catalyst (TOF = 524 h(-)(1)).

Oxonium ions from aqua regia: isolation by hydrogen bonding to crown ethers

The preparation and structures of a variety of oxonium ion tetrachloroaurate(III) salts isolated from aqua regia are reported. The new compounds are [(H(5)O(2))(2)(12-crown-4)(2)][AuCl(4)](2) (1), [(H(7)O(3))(15-crown-5)][AuCl(4)] (2), [(H(5)O(2))(benzo-15-crown-5)(2)][AuCl(4)] (3), [(H(3)O)(18-crown-6)][AuCl(4)] (4), [(H(5)O(2))(dibenzo-24-crown-8)][AuCl(4)] (5), [(H(5)O(2))(4-nitrobenzo-15-crown-5)(2)][AuCl(4)] (6), [(H(3)O)(4-nitrobenzo-18-crown-6)][AuCl(4)] (7), [(H(11)O(5))(tetrachlorodibenzo-18-crown-6)(2)][AuCl(4)] (8), and [(H(7)O(3))(dinitrodibenzo-30-crown-10)][AuCl(4)] (9). A significant correlation between the degree of proton hydration and crown ether size is observed. Aryl crown ethers are nitrated in concentrated aqua regia, but nonnitrated products may be obtained in a dilute solution of aqua regia by reaction with aqueous HAuCl(4).

Formation of Lanthanide and Actinide Oxonium Ion Complexes with Crown Ethers from a Liquid Clathrate Medium

Reaction of MCl(3).nH(2)O (M = La, Eu) with 18-crown-6 in HCl/toluene affords the crystalline oxonium complexes (H(9)O(4))[LaCl(2)(H(2)O)(18-crown-6)]Cl(2) (1) and (H(3)O)[EuCl(H(2)O)(2)(18-crown-6)]Cl(2) (2). In complex 1 the H(9)O(4)(+) cation is of the unusual linear chain type with O.O contacts of 2.560(9), 2.430(9), and 2.483(9) Å. The analogous reaction with YbCl(3).6H(2)O results in the isolation of the known species (H(5)O(2))[H(3)O.(18-crown-6)]Cl(2). Analogous reaction of YbCl(3).6H(2)O with 15-crown-5 gives [Yb(H(2)O)(8)]Cl(3).(15-crown-5) (5). Reaction of uranyl acetate with 15-crown-5 within a toluene/HCl mixture results in the formation of a yellow liquid clathrate layer from which crystals of (H(5)O(2))[UO(2)(H(2)O)(2)Cl(3)].2(15-crown-5) (6) are deposited. The H(5)O(2)(+) ion in this material exhibits a particularly short O.O separation of 2.371(8) Å. On standing, loss of HCl results in the transformation of 6 into a species of empirical formula [UO(2)(H(2)O)(3)Cl(2)].(15-crown-5) (7) which has been shown by X-ray crystallography to contain 16 unique uranium complexes, arranged in infinite hydrogen-bonded chains in the solid state. Crystal data for 1: monoclinic, P2(1)/c, a = 7.6950(2) Å, b = 21.2160(16) Å, c = 15.8650(10) Å, beta = 92.866(2) degrees, V = 2586.8(3) Å(3), Z = 4. 2: orthorhombic, Pbn2(1), a = 10.2267(6) Å, b = 14.7231(9) Å, c = 29.8565(18) Å, V = 4495.5(5) Å(3), Z = 4. 5: monoclinic, P2(1)/n, a = 9.1740(3) Å, b = 17.1900(3) Å, c = 15.2450(5) Å, beta = 92.643(2) degrees, V = 2401.60(12) Å(3), Z = 4. 6: orthorhombic, Pmcn, a = 12.1740(5) Å, b = 14.7740(7) Å, c = 18.4920(11) Å, V = 3325.9(3) Å(3), Z = 4. 7: trigonal, P3(2), a = 35.3500(2) Å, c = 21.3755(2) Å, V = 23 132.7(3) Å(3), Z = 48.