Synthesis, Characterization, and Properties of Weakly Coordinating Anions Based on tris-Perfluoro-tert-Butoxyborane.

A convenient method for the preparation of strongly Lewis acidic tris-perfluoro-tert-butoxyborane B(ORF)3 (1), (ORF = OC(CF3)3) was developed, and its X-ray structure was determined. 1 was used as a precursor, guided by density functional theory (DFT) calculations and volume-based thermodynamics, for the synthesis of [NEt4][NCB(ORF)3] (3) and [NMe4][FB(ORF)3] (5) and the novel large and weakly coordinating anion salts [Li 15-Crown-5][B(ORF)4] (2) and [NEt4][CN{B(ORF)3}2] (4). The stability of [B(ORF)4]- was compared with that of some related known weakly coordinating anions by appropriate DFT calculations.

Absorption of SO2(g) by TDAE[O2SSO2](s) to Give TDAE[O2SS(O)2SO2](s): Related Reactions of [NR4]2[O2SSO2](s) (R = CH3, C2H5).

One mole equivalent of gaseous SO2 is absorbed by purple TDAE[O2SSO2](s), producing red, essentially spectroscopically pure TDAE[O2SS(O)2SO2](s); under prolonged evacuation, the product loses SO2(g), regenerating TDAE[O2SSO2](s). Similarly, [NR4]2[O2SS(O)2SO2](s) (R = Et, Me) can be prepared, albeit at lower purity, from the corresponding tetraalkylammonium dithionites (prepared by a modification of the known [NEt4]2[O2SSO2](s) preparation). While the [NEt4](+) salt is stable at rt; the [NMe4](+) salt has only limited stability at -78 °C. Vibrational spectra assignments for the anion in these salts were distinctly different from those for the anion in salts containing the long-known [O3SSSO3](2-) dianion, the most thermodynamically stable form of [S3O6](2-) (we prepared TDAE[O3SSSO3]·H2O(s) and obtained its structure by X-ray diffraction and vibrational analyses). The best fit between the calculated ((B3PW91/6-311+G(3df) and PBE0/6-311G(d)) and experimental vibrational spectra were obtained with the dianion having the [O2SS(O)2SO2](2-) structure. Vibrational analyses of the three [O2SS(O)2SO2](2-) salts prepared in this work showed that the corresponding [O3SSO2](2-) salts were present as a ubiquitous decomposition product. The formation of these new [O2SS(O)2SO2](2-) dianion salts was predicted to be favorable for [NMe4](+) and larger cations using a combination of theoretical calculations (B3PW91/6-311+G(3df)) and volume based thermodynamics (VBT). Similar methods accounted for the greater stabilities of the TDAE(2+) and [NEt4](+) salts of [O2SS(O)2SO2](2-) compared to [NMe4]2[O2SS(O)2SO2](s) toward irreversible decomposition to the corresponding [O3SSO2](2-) salts. These salts represent the first known examples of a new class of poly(sulfur dioxide) dianion, [SO2]n(2-) in which n > 2.

Reactions of a cyclodimethylsiloxane (Me2SiO)6 with silver salts of weakly coordinating anions; crystal structures of [Ag(Me2SiO)6][Al] ([Al] = [FAl{OC(CF3)3}3], [Al{OC(CF3)3}4]) and their comparison with [Ag(18-crown-6)]2[SbF6]2.

Two silver-cyclodimethylsiloxane cation salts [AgD6][Al] ([Al] = [Al(ORF)4](1) or [FAl(OR(F))3](2), R(F) = C(CF3)3, D = Me2SiO) were prepared by the reactions of Ag[Al] with D6 in SO2(l). For a comparison the [Ag(18-crown-6)]2[SbF6]2(3) salt was prepared by the reaction of Ag[SbF6] and 18-crown-6 in SO2(l). The compounds were characterized by IR, multinuclear NMR, and single crystal X-ray crystallography. The structures of 1 and 2 show that D6 acts as a pseudo crown ether toward Ag(+). The stabilities and bonding of [MDn](+) and [M(18-crown-6)](+) (M = Ag, Li, n = 4-8) complexes were studied with theoretical calculations. The calculations predicted that D6 adopts a puckered C(i) symmetric structure in the gas phase in contrast to previous reports. 18-Crown-6 was calculated to bind more strongly to Li(+) and Ag(+) than D6. (29)Si[(1)H] NMR results in solution, and calculations in the gas phase established that a hard Lewis acid Li(+) binds more strongly to D6 than Ag(+). A comparison of the [MD(n)](+) complex stabilities showed D7 to form the most stable metal complexes in the gas phase and the solid state and explained why [AgD7][SbF6] was isolated in a previous reaction where ring transformations resulted in an equilibrium of [AgD(n)](+) complexes. In contrast, the isolations of 1 and 2 were possible because the corresponding equilibrium of [AgD(n)](+) complexes was not observed with [Al](-) anions. The formation of the dinuclear complex salt 3 instead of the corresponding mononuclear complex salt was shown to be driven by the gain in lattice enthalpy in the solid state. The bonding to Li(+) in D6 and 18-crown-6 metal complexes was described by a quantum theory of atoms in molecules (QTAIM) analysis to be mostly electrostatic while the bonding to Ag(+) also had a significant charge transfer component. The charge transfer from both D6 and 18-crown-6 to Ag(+) and Li(+) metal ions was depicted by the QTAIM analysis to be of similar strength, and the difference in the stabilities of the complexes was attributed mostly to more attractive electrostatic interactions between 18-crown-6 and the metal ions despite the more negative oxygen atomic charges calculated for D6.

Synthesis of [N(CH3)4]2O3SOSO2(s) and [N(CH3)4]2[(O2SO)2SO2]·SO2(s) containing (SO4)(SO2)x(2-) x = 1, 2, members of a new class of sulfur oxydianions.

One mole equivalent of SO2 reversibly reacts with [N(CH3)4]2SO4(s) to give [N(CH3)4]2S2O6(s) (1) containing the [O3SOSO2](2-), shown by Raman and IR to be an isomer of the [O3SSO3](2-) dianion. The experimental and calculated (B3PW91/6-311+G(3df)) vibrational spectra are in excellent agreement, and the IR spectrum is similar to that of the isoelectronic O3ClOClO2. Crystals of [N(CH3)4]2(O2SO)2SO2·SO2 (2) were isolated from solutions of [N(CH3)4]2SO4 in liquid SO2. The X-ray structure showed that 2 contained the [(O2SO)2SO2](2-) dianion. The characterized N(CH3)4(+) salts 1 and 2 are the first two members of the (SO4)(SO2)x(2-) class of sulfur oxydianions analogous to the well-known small cation salts of the SO4(SO3)x(2-) polysulfates.

Synthesis of (TDAE)(O2SSO2)(s) and discovery of (TDAE)(O2SSSSO2)(s) containing the first polythionite, [O2SSSSO2]2-.

Gaseous SO2 reacts with tetrakis(dimethylamino)ethylene (TDAE) in acetonitrile in a 2:1 stoichiometric ratio to give analytically pure insoluble purple (TDAE)(O2SSO2) (1) in about 80% yield. Crystals of (TDAE)(O2SSSSO2) (2) were obtained from orange solution over the purple solid. The Raman spectrum of [TDAE](2+) was established using (TDAE)(A) salts [A = 2Br(-), 2Br(-)·2H2O (X-ray), 2[Br3](-) (X-ray)]. Vibrational spectroscopy showed that [O2SSO2](2-) in 1 has C2h geometry. The X-ray structure of 2 showed that it contained [O2SSSSO2](2-), the first example of a new class of sulfur oxyanions, the polythionites. The geometry of [O2SSSSO2](2-) consists of S2 with an S-S bond length of 2.003(1) Å connected to two terminal SO2 moieties by much longer S-S bonds of 2.337(1) Å. Calculations (B3PW91/6-311+G(3df)) show that the structural units in [O2SSSSO2](2-) are joined by the interaction of electrons in two mutually perpendicular π* SOMOs of the triplet-state diradical S2 with unpaired electrons in the π*-antibonding orbitals of the two terminal [SO2](•-) and polarized to delocalize the negative charge equally onto the three fragments. Thermodynamic estimates show 2 to be stable with respect to loss of sulfur and formation of 1, in contrast to [O2SSSSO2](2-) salts of small cations that are unstable toward the related dissociation. Reaction of TDAE with an excess of liquid SO2 led to (TDAE)(O3SOSO3)·SO2 (preliminary X-ray, Raman), (TDAE)(O3SSSSO3)·2SO2 (preliminary X-ray, Raman), and (TDAE)(O3SSO2) (Raman).

Evidence for [18-Crown-6 Na]2[S2O4] in methanol and dissociation to Na2S2O4 and 18-Crown-6 in the solid state; accounting for the scarcity of simple oxy dianion salts of alkali metal crown ethers in the solid state.

[18-Crown-6 Na](2)S(2)O(4) complex was prepared in methanol solution but dissociates into 18-Crown-6 ((s)) and Na(2)S(2)O(4 (s)) on removal of the solvent. Evidence for complexation in methanol is supported by a quantitative mass analysis and the dissociation in the solid state by vibrational spectroscopy and powder X-ray diffraction. These observations are accounted for by investigating the energetics of complexation in solution and dissociation in the solid state using calculated density functional theory (DFT) gas phase binding enthalpies and free energies combined with conductor-like screening model (COSMO) solvation energies and lattice enthalpy and free energy terms derived from volume based thermodynamics (VBT). Our calculations show that complexation of alkali metal dianion salts to crown ethers are much less favorable than that of the corresponding monoanion salts in the solid state and that the formation of alkali metal crown complexes of stable simple oxy-dianion (e.g., CO(3)(2-), SO(4)(2-)) salts is unlikely. The roles of complexation with 18-Crown-6 and ion pair formation in the process of dissolution of Na(2)S(2)O(4) to methanol are discussed.

Preparation and characterization of (CNSSS)2(A)2 (A = AsF6(-), SbF6(-), Sb2F11(-)) containing the O2-like 5,5'-bis(1,2,3,4-trithiazolium) dication: the second example of a simple nonsterically hindered main-group diradical that retains its paramagnetism in the solid state.

The reaction of NC-CN with a 1:1 mixture of S(4)(MF(6))(2) and S(8)(MF(6))(2) (M = As, Sb) (stoichiometrically equivalent to four "S(3)MF(6)" units) results in the quantitative formation of S(3)NCCNS(3)(MF(6))(2) [7(MF(6))(2)], which is the thermodynamic sink in this reaction. The Sb(2)F(11)(-) salt 7(Sb(2)F(11))(2) is prepared by the addition of an excess of SbF(5) to 7(AsF(6))(2). Crystal structure determinations for all three salts show that 7(2+) can be viewed as two R-CNS(3)(+) radical cations joined together by a C-C single bond. The two rings are coplanar and in a trans orientation due to electrostatic N(delta-)...S(delta+) interactions. The classically bonded alternative (quinoidal structure), in which the octet rule is obeyed, is not observed and is much higher in energy based on calculated estimates and a simple comparison of pi bond energies. Calculated molecular orbitals (MOs) support this, showing that the MO corresponding to the quinoidal structure lies higher in energy than the nearly degenerate singly occupied MOs of 7(2+). The vibrational spectra of 7(2+) in all salts were assigned based on a normal-coordinate analysis and theoretical vibrational frequencies calculated at the PBE0/6-31G* level. In the solid state, 7(2+) is a planar disjoint diradical with essentially degenerate open-shell singlet and triplet states. The disjoint nature of the diradical cation 7(2+) is established by magnetic susceptibility studies of the Sb(2)F(11)(-) salt doped in an isomorphous diamagnetic host material (CNSNS)(2)(Sb(2)F(11))(2) [10(Sb(2)F(11))(2)]. Intramolecular spin coupling is extremely weak corresponding to a singlet-triplet gap (DeltaE(ST) = 2J) of <+/-2 cm(-1). CASPT2[12,12]/6-311G* calculations support a triplet ground state with a small singlet-triplet gap. The single-crystal electron paramagnetic resonance (EPR) of 7(Sb(2)F(11))(2) doped in 10(Sb(2)F(11))(2) is in agreement with the triplet state arising from the weak coupling between the unpaired electrons residing in p(pi) orbitals in each of the rings. Variable-temperature susceptibility data for bulk samples of 7(A)(2) (A = SbF(6)(-), AsF(6)(-), Sb(2)F(11)(-)) are analyzed by employing both 1D chain and 2D sheet magnetic models. These studies reveal significant intermolecular exchange approximating that of a 1D chain for the SbF(6)(-) salt with |J| = 32 cm(-1). The exchange coupling is on the same order of magnitude as that for the AsF(6)(-) salt, although in this case it is likely that there are complex exchange pathways where no particular one is dominant. Intermolecular exchange in the Sb(2)F(11)(-) salt is an order of magnitude weaker. In solution, the EPR spectrum of 7(2+) shows a broad triplet resonance as well as a sharp resonance that is tentatively attributed to a rotomer of the 7(2+)/anion pair, which is likely the origin of the green species given on dissolution of the red 7(2+) salts in SO(2)/AsF(3)/MF(5). We account for the many similarities between O(2) and 7(2+), which are the only simple nonsterically hindered nonmetal diradicals to retain their paramagnetism in the solid state. 7(2+) is also the first isolable, essentially sulfur-based diradical as evidenced by calculated spin densities.

Silver(I) complexes of the weakly coordinating solvents SO(2) and CH(2)Cl(2): crystal structures, bonding, and energetics of [Ag(OSO)][Al{OC(CF(3))(3)}(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(CH(2)Cl(2))(2)][SbF(6)].

Pushing the limits of coordination chemistry: The most weakly coordinated silver complexes of the very weakly coordinating solvents dichloromethane and liquid sulfur dioxide were prepared. Special techniques at low temperatures and the use of weakly coordinating anions allowed structural characterization of [Ag(OSO)][Al{OC(CF(3))(3)}(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(Cl(2)CH(2))(2)][SbF(6)] (see figure). An investigation of the bonding shows that these complexes are mainly stabilized by electrostatic monopole-dipole interactions.The synthetically useful solvent-free silver(I) salt Ag[Al(pftb)(4)] (pftb=--OC(CF(3))(3)) was prepared by metathesis reaction of Li[Al(pftb)(4)] with Ag[SbF(6)] in liquid SO(2). The solvated complexes [Ag(OSO)][Al(pftb)(4)], [Ag(OSO)(2/2)][SbF(6)], and [Ag(CH(2)Cl(2))(2)][SbF(6)] were prepared and isolated by special techniques at low temperatures and structurally characterized by single-crystal X-ray diffraction. The SO(2) complexes provide the first examples of coordination of the very weak Lewis base SO(2) to silver(I). The SO(2) molecule in [Ag(OSO)][Al(pftb)(4)] is eta(1)-O coordinated to Ag(+), while the SO(2) ligands in [Ag(OSO)(2/2)][SbF(6)] bridge two Ag(+) ions in an eta(2)-O,O' (trans,trans) manner. [Ag(CH(2)Cl(2))(2)][SbF(6)] contains [Ag(CH(2)Cl(2))(2)](+) ions linked through [SbF(6)](-) ions to give a polymeric structure. The solid-state silver(I) ion affinities (SIA) of SO(2) and CH(2)Cl(2), based on bond lengths and corresponding valence units in the corresponding complexes and tensimetric titrations of Ag[Al(pftb)(4)] and Ag[SbF(6)] with SO(2) vapor, show that SO(2) is a weaker ligand to Ag(+) than the commonly used weakly coordinating solvent CH(2)Cl(2) and indicated that binding strength of SO(2) to silver(I) in the silver(I) salts increases with increasing size of the corresponding counteranion ([Al(pftb)(4)](-)>[SbF(6)](-)). The experimental findings are in good agreement with theoretical gas-phase ligand-binding energies of [Ag(L)(n)](+) (L=SO(2), CH(2)Cl(2); n=1, 2) and solid-state enthalpies obtained from Born-Fajans-Haber cycles by using the volume-based thermodynamics (VBT) approach. Bonding analysis (VB, NBO, MO) of [Ag(L)(n)](+) suggests that these complexes are almost completely stabilized by electrostatic interaction, that is, monopole-dipole interaction, with almost no covalent contribution by electron donation from the ligand orbitals into the vacant 5s orbital of Ag(+). All experimental findings and theoretical considerations demonstrate that SO(2) is less covalently bound to Ag(+) than CH(2)Cl(2) and support the thesis that SO(2) is a polar but non-coordinating solvent towards Ag(+).

77Se NMR spectroscopic, DFT MO, and VBT investigations of the reversible dissociation of solid (Se6I2)[AsF6]2.2SO2 in Liquid SO2 to solutions containing 1,4-Se6I2(2+) in equilibrium with Se(n)2+ (n = 4, 8, 10) and seven binary selenium iodine cations: preliminary evidence for 1,1,4,4-Se4Br4(2+) and cyclo-Se7Br+.

The composition of a complex equilibrium mixture formed upon dissolution of (Se(6)I(2))[AsF(6)](2).2SO(2) in SO(2)(l) was studied by (77)Se NMR spectroscopy at -70 degrees C with both natural-abundance and enriched (77)Se-isotope samples (enrichment 92%). Both the natural-abundance and enriched NMR spectra showed the presence of previously known cations 1,4-Se(6)I(2)(2+), SeI(3)(+), 1,1,4,4-Se(4)I(4)(2+), Se(10)(2+), Se(8)(2+), and Se(4)(2+). The structure and bonding in 1,4-Se(6)I(2)(2+) and 1,1,4,4-Se(4)I(4)(2+) were explored using DFT calculations. It was shown that the observed Se-Se bond alternation and presence of thermodynamically stable 4ppi-4ppi Se-Se and 4ppi-5ppi Se-I bonds arise from positive charge delocalization from the formally positively charged tricoordinate Se(+). The (77)Se chemical shifts for cations were calculated using the relativistic zeroth-order regular approximation (ZORA). In addition, calculations adding a small number of explicit solvent molecules and an implicit conductor-like screening model were conducted to include the effect that solvent has on the chemical shifts. The calculations yielded reasonable agreement with experimental chemical shifts, and inclusion of solvent effects was shown to improve the agreement over vacuum values. The (77)Se NMR spectrum of the equilibrium solution showed 22 additional resonances. These were assigned on the basis of (77)Se-(77)Se correlation spectroscopy, selective irradiation experiments, and spectral simulation. By combining this information with the trends in the chemical shifts, with iodine, selenium, and charge balances, as well as with ZORA chemical shift predictions, these resonances were assigned to acyclic 1,1,2-Se(2)I(3)(+), 1,1,6,6-Se(6)I(4)(2+), and 1,1,6-Se(6)I(3)(+), as well as to cyclic Se(7)I(+) and (4-Se(7)I)(2)I(3+). A preliminary natural-abundance (77)Se NMR study of the soluble products of the reaction of (Se(4))[AsF(6)](2) and bromine in liquid SO(2) included resonances attributable to 1,1,4,4-Se(4)Br(4)(2+)(.) These assignments are supported by the agreement of the observed and calculated (77)Se chemical shifts. Resonances attributable to cyclic Se(7)Br(+) were also observed. The thermal stability of (Se(6)I(2))[AsF(6)](2).2SO(2)(s) was consistent with estimates of thermodynamic values obtained using volume-based thermodynamics (VBT) and the first application of the thermodynamic solvate difference rule for nonaqueous solvates. (Se(6)I(2))[AsF(6)](2).2SO(2)(s) is the first example of a SO(2) solvate for which the nonsolvated parent salt, (Se(6)I(2))[AsF(6)](2)(s), is not thermodynamically stable, disproportionating to Se(4)I(4)(AsF(6))(2)(s) and Se(8)(AsF(6))(2)(s) (DeltaG degrees for the disproportion reaction is estimated to be -17 +/- 15 kJ mol(-1) at 298 K from VBT theory).

Characterisation of the thermally accessible spin triplet state in dimers of the 7pi ClCNSSS+* in the solid state.

[ClCNSSS]2(2+) is the first example of a thiazyl radical dimer where population of a thermally excited spin triplet state has been detected, as is proved by VT-powder and single-crystal EPR spectroscopy.

Evolution of the pseudo-1,3-dipolar cycloaddition chemistry of SNSMF6 (M = As, Sb) leading to 2,5-dihydroxybenzo-1,3,2-dithiazolylium and 2,7-dicarbonylnaphtha-1,3,2-dithiazolylium salts and their corresponding radicals.

We report the unprecedented formation of a benzo-fused 1,3,2-dithiazolylium [AsF6-] salt by a one step, quantitative, cycloaddition of SNSAsF6 with 1,4-benzoquinone. In contrast, the reaction of SNSSbF6 with 1,4-naphthaquinone results in 2,7-dicarbonylnaphtha-1,3,2-dithiazolylium [SbF6-]. Both were reduced to the corresponding 7pi radicals.

Thermal hysteresis in dithiadiazolyl and dithiazolyl radicals induced by supercooling of paramagnetic liquids close to room temperature: a study of F3CCNSSN and an interpretation of the behaviour of F3CCSNSCCF3.

The trifluoromethyl-substituted dithiadiazolyl and dithiazolyl radicals, F3CCNSSN (1) and F3CCSNSCCF3 (2) associate through pi*-pi* covalent and electrostatic S delta+...N delta- interactions in the solid state, but melt with a dramatic volume increase to generate paramagnetic liquids; these radicals exhibit thermal hysteresis, which arises through a meta-stable super-cooled liquid state, close to room temperature.

Identification of the 1,3,2,4-Dithiadiazolyl RCNSNS(*) Radical Dimers in Solution, Their Dimeric Concerted Photochemically Symmetry-Allowed Rearrangement to 1,2,3,5-Dithiadiazolyl RCNSSN(*) by the Net Exchange of Adjacent Cyclic Sulfur and Nitrogen Atoms, and the Photolysis of RCNSNS(*).

The 1,3,2,4-dithiadiazolyl RCNSNS(*) radicals undergo an unprecedented concerted rearrangement to the thermodynamically more stable 1,2,3,5-dithiadiazolyl RCNSSN(*) radicals by the net exchange of adjacent cyclic sulfur and nitrogen atoms. The UV-visible spectra of RCNSNS(*) (R = Ph, p-O(2)NC(6)H(4), 3,5-(O(2)N)(2)C(6)H(3), CF(3)) in solution show bands at 250 nm (strong) and 680 nm (very weak) attributable to monomer and two dimer bands at 376 and 480 nm, the positions of which are independent of the substituents, providing direct identification of the radical dimers in solution. The dimerization equilibrium constant (K(298) approximately 0.7 for R = Ph) at room temperature was derived from the enthalpy and entropy changes for the dimerization of PhCNSNS(*) (DeltaH(d) degrees = -19.0 kJ/mol, DeltaS degrees = -66.5 J/mol) estimated by a variable-temperature ESR spectroscopic study. In addition, RCNSNS(*) (R = Bu(t), Ph) undergo an apparent unimolecular photolysis to RCN and possibly SNS(*) (analogue of ONO(*)). The photochemical rearrangement and dissociation (for R = Ph and 3,5-(O(2)N)(2)C(6)H(3)) were shown to proceed by irradiation of the radical dimer (376 and 480 nm) and monomer (250 nm), respectively. Thus, the radical rearrangement reasonably occurs via a concerted dimeric pathway shown by molecular orbital calculations (CNDO) to be photochemically symmetry-allowed. In addition, we propose that the radical dissociation proceeds via a concerted unimolecular photochemically symmetry-allowed process.

Relationships among Ionic Lattice Energies, Molecular (Formula Unit) Volumes, and Thermochemical Radii.

The linear generalized equation described in this paper provides a further dimension to the prediction of lattice potential energies/enthalpies of ionic solids. First, it offers an alternative (and often more direct) approach to the well-established Kapustinskii equation (whose capabilities have also recently been extended by our recent provision of an extended set of thermochemical radii). Second, it makes possible the acquisition of lattice energy estimates for salts which, up until now, except for simple 1:1 salts, could not be considered because of lack of crystal structure data. We have generalized Bartlett's correlation for MX (1:1) salts, between the lattice enthalpy and the inverse cube root of the molecular (formula unit) volume, such as to render it applicable across an extended range of ionic salts for the estimation of lattice potential energies. When new salts are synthesized, acquisition of full crystal structure data is not always possible and powder data provides only minimal structural information-unit cell parameters and the number of molecules per cell. In such cases, lack of information about cation-anion distances prevents use of the Kapustinskii equation to predict the lattice energy of the salt. However, our new equation can be employed even when the latter information is not available. As is demonstrated, the approach can be utilized to predict and rationalize the thermochemistry in topical areas of synthetic inorganic chemistry as well as in emerging areas. This is illustrated by accounting for the failure to prepare diiodinetetrachloroaluminum(III), [I(2)(+)][AlCl(4)(-)] and the instability of triiodinetetrafluoroarsenic(III), [I(3)(+)][AsF(6)(-)]. A series of effective close-packing volumes for a range of ions, which will be of interest to chemists, as measures of relative ionic size and which are of use in making our estimates of lattice energies, is generated from our approach.

Metastable Se6 as a ligand for Ag+: from isolated molecular to polymeric 1D and 2D structures.

Attempts to prepare the hitherto unknown Se(6)(2+) cation by the reaction of elemental selenium and Ag[A] ([A](-) = [Sb(OTeF(5))(6)](-), [Al(OC(CF(3))(3))(4)](-)) in SO(2) led to the formation of [(OSO)Ag(Se(6))Ag(OSO)][Sb(OTeF(5))(6)](2)1 and [(OSO)(2)Ag(Se(6))Ag(OSO)(2)][Al(OC(CF(3))(3))(4)](2)2a. 1 could only be prepared by using bromine as co-oxidant, however, bulk 2b (2a with loss of SO(2)) was accessible from Ag[Al(OC(CF(3))(3))(4)] and grey Se in SO(2) (chem. analysis). The reactions of Ag[MF(6)] (M = As, Sb) and elemental selenium led to crystals of 1/∞{[Ag(Se(6))](∞)[Ag(2)(SbF(6))(3)](∞)} 3 and {1/∞[Ag(Se(6))Ag](∞)}[AsF(6)](2)4. Pure bulk 4 was best prepared by the reaction of Se(4)[AsF(6)](2), silver metal and elemental selenium. Attempts to prepare bulk 1 and 3 were unsuccessful. 1-4 were characterized by single-crystal X-ray structure determinations, 2b and 4 additionally by chemical analysis and 4 also by X-ray powder diffraction, FT-Raman and FT-IR spectroscopy. Application of the PRESTO III sequence allowed for the first time (109)Ag MAS NMR investigations of 4 as well as AgF, AgF(2), AgMF(6) and {1/∞[Ag(I(2))](∞)}[MF(6)] (M = As, Sb). Compounds 1 and 2a/b, with the very large counter ions, contain isolated [Ag(Se(6))Ag](2+) heterocubane units consisting of a Se(6) molecule bicapped by two silver cations (local D(3d) sym). 3 and 4, with the smaller anions, contain close packed stacked arrays of Se(6) rings with Ag(+) residing in octahedral holes. Each Ag(+) ion coordinates to three selenium atoms of each adjacent Se(6) ring. 4 contains [Ag(Se(6))(+)](∞) stacks additionally linked by Ag(2)(+) into a two dimensional network. 3 features a remarkable 3-dimensional [Ag(2)(SbF(6))(3)](-) anion held together by strong Sb-FAg contacts between the component Ag(+) and [SbF(6)](-) ions. The hexagonal channels formed by the [Ag(2)(SbF(6))(3)](-) anions are filled by stacks of [Ag(Se(6))(+)](∞) cations. Overall 1-4 are new members of the rare class of metal complexes of neutral main group elemental clusters, in which the main group element is positively polarized due to coordination to a metal ion. Notably, 1 to 4 include the commonly metastable Se(6) molecule as a ligand. The structure, bonding and thermodynamics of 1 to 4 were investigated with the help of quantum chemical calculations (PBE0/TZVPP and (RI-)MP2/TZVPP, in part including COSMO solvation) and Born-Fajans-Haber-cycle calculations. From an analysis of all the available data it appears that the formation of the usually metastable Se(6) molecule from grey selenium is thermodynamically driven by the coordination to the Ag(+) ions.

Preparation, structure and analysis of the bonding in the molecular entity (OSO)2Li{[AlF(ORF)3]Li[Al(ORF)4]} (RF = C(CF3)3).

The (SO(2))(2)Li[AlF(OR(F))(3)]Li[Al(OR(F))(4)] (1) (R(F) = C(CF(3))(3)) molecular entity was obtained by thermal decomposition of Li[Al(OR(F))(4)] followed by crystallization from liquid SO(2). 1, containing two SO(2) molecules eta(1)-O coordinated to Li(+), was structurally characterized by single crystal X-ray diffraction and NMR spectroscopy in SO(2)(l). Bonding analyses of 1 (bond valency units, AIM analysis, atomic charges, bond orders) show that 1 can be either considered as a Li(OSO)(2)(+) complex stabilized by the large WCA [AlF(OR(F))(3)](-)Li(+)[Al(OR(F))(4)](-) or as consisting of 2 SO(2), 2 Li(+), [AlF(OR(F))(3)](-), and [Al(OR(F))(4)](-) joined by electrostatic interactions into the discrete molecular entity 1. The bonding between Li(+) and SO(2) molecules is shown to be almost completely attributable to monopole-induced dipole electrostatic interactions. Theoretical gas phase lithium ion affinity of SO(2) is determined to be stronger than its silver(I) ion affinity owing largely to the shorter lithium SO(2) contacts in the calculated structures that increase the electrostatic interaction.