Synthesis and Properties of Cobalt Complexes with [B11H11]4- Ligands.

The unusually high oxidation state + IV of cobalt is stabilized by ligands based on [B11H11]4- in dark blue colored Cs4[Co(B11H10.11(OH)0.75)2]·4.56H2O, K4[Co(B11H9.19(OH)1.81)2]·2H2O, Cs8[Co{(B11H6)2(O)(O2BOH)4}]2·4H2O and K4[Co{(B11H6)2(O2BOH)5}]·7H2O. These compounds were obtained by reacting Co2+ salts with [B11H14]- under alkaline conditions. In the absence of oxygen, Co(+III) compounds such as the light brownish K4[Co(B11H11)(CN)3]·KCl·2.5H2O are formed. The title compounds were characterized by X-ray crystallography. Cs8[Co{(B11H6)2(O)(O2BOH)4}]2·4H2O and K4[Co(B11H11)(CN)3]·KCl·2.5H2O were also characterized using IR-, UV-vis and cyclovoltammetry. Magnetic measurements of Cs4[Co(B11H10.11(OH)0.75)2]·4.56H2O and ESR measurements of Cs8[Co{(B11H6)2(O)(O2BOH)4}]2·4H2O show that in these Co(+IV) low-spin d5 complexes the unpaired electron is on the dx2-y2, dxy (E2g) orbitals.

Binding Properties of Small Electrophilic Anions [B6 X5 ]- and [B10 X9 ]- (X=Cl, Br, I): Activation of Small Molecules Based on π-Backbonding.

Superelectrophilic anions constitute a special class of molecular anions that show strong binding of weak nucleophiles despite their negative charge. In this study, the binding characteristics of smaller gaseous electrophilic anions of the types [B6 X5 ]- and [B10 X9 ]- (with X=Cl, Br, I) were computationally and experimentally investigated and compared to those of the larger analogues [B12 X11 ]- . The positive charge of vacant boron increases from [B6 X5 ]- via [B10 X9 ]- to [B12 X11 ]- , as evidenced by increasing attachment enthalpies towards typical σ-donor molecules (noble gases, H2 O). However, this behavior is reversed for σ-donor-π-acceptor molecules. [B6 Cl5 ]- binds most strongly to N2 and CO, even more strongly than to H2 O. Energy decomposition analysis confirms that the orbital interaction is responsible for this opposite trend. The extended transition state natural orbitals for chemical valence method shows that the π-backdonation order is [B6 X5 ]- >[B10 X9 ]- >[B12 X11 ]- . This predicted order explains the experimentally observed red shifts of the CO and N2 stretching fundamentals compared to those of the unbound molecules, as measured by infrared photodissociation spectroscopy. The strongest red shift is observed for [B6 Cl5 N2 ]- : 222 cm-1 . Therefore, strong activation of unreactive σ-donor-π-acceptor molecules (commonly observed for cationic transition metal complexes) is achieved with metal-free molecular anions.

Face-Fusion of Icosahedral Boron Hydride Increases Affinity to γ-Cyclodextrin: closo,closo-[B21 H18 ]- as an Anion with Very Low Free Energy of Dehydration.

The supramolecular recognition of closo,closo-[B21 H18 ]- by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass-spectrometric measurements and computations, which indicated the formation and stability of CD ⋅ B21 H18- complexes in the gas phase. The thermodynamic signature of solution-phase binding is exceptional, the association constant for the γ-CD complex with B21 H18- reaches 1.8×106  M-1 , which is on the same order of magnitude as the so far highest observed value for the complex between γ-CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum-mechanical computational protocols. These suggest that the desolvation penalty, which is particularly low for the B21 H18- anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution.

Properties of gaseous closo-[B6X6]2- dianions (X = Cl, Br, I).

Electronic structure, collision-induced dissociation (CID) and bond properties of closo-[B6X6]2- (X = Cl-I) are investigated in direct comparison with their closo-[B12X12]2- analogues. Photoelectron spectroscopy (PES) and theoretical investigations reveal that [B6X6]2- dianions are electronically significantly less stable than the corresponding [B12X12]2- species. Although [B6Cl6]2- is slightly electronically unstable, [B6Br6]2- and [B6I6]2- are intrinsically stable dianions. Consistent with the trend in the electron detachment energy, loss of an electron (e- loss) is observed in CID of [B6X6]2- (X = Cl, Br) but not for [B6I6]2-. Halogenide loss (X- loss) is common for [B6X6]2- (X = Br, I) and [B12X12]2- (X = Cl, Br, I). Meanwhile, X˙ loss is only observed for [B12X12]2- (X = Br, I) species. The calculated reaction enthalpies of the three competing dissociation pathways (e-, X- and X˙ loss) indicated a strong influence of kinetic factors on the observed fragmentation patterns. The repulsive Coulomb barrier (RCB) determines the transition state for the e- and X- losses. A significantly lower RCB for X- loss than for e- loss was found in both experimental and theoretical investigations and can be rationalized by the recently introduced concept of electrophilic anions. The positive reaction enthalpies for X- losses are significantly lower for [B6X6]2- than for [B12X12]2-, while enthalpies for X˙ losses are higher. These observations are consistent with a difference in bond character of the B-X bonds in [B6X6]2- and [B12X12]2-. A complementary bonding analysis using QTAIM, NPA and ELI-D based methods suggests that B-X bonds in [B12X12]2- have a stronger covalent character than in [B6X6]2-, in which X has a stronger halide character.

Stepwise Introduction of Cyano Groups into nido- and closo-Undecaborate Clusters.

Eleven-vertex closo and nido boron clusters with one or two exo-cyano groups were obtained by a series of consecutive cage-opening and cage-closure reactions starting from K2 [closo-B11 H11 ] (K2 1). In the first step, K2 1 reacts with KCN in water at elevated temperatures to yield [7-NC-nido-B11 H12 ]2- (5 a). Oxidation of 5 a with PbO2 gives [NC-closo-B11 H10 ]2- (2). In analogous subsequent reactions, dianion 2 was converted with KCN regioselectively to [7,9-(NC)2 -nido-B11 H11 ]2- (6 a), which was further oxidized to [(NC)2 -closo-B11 H9 ]2- (3). The {nido-B11 } dianions 5 a and 6 a were protonated to yield [7-NC-nido-B11 H13 ]- (5 b) and [7,9-(NC)2 -nido-B11 H12 ]- (6 b). All anions were studied by NMR spectroscopy and, except for 6 b, salts of all anions were characterized by IR and Raman spectroscopy and by elemental analysis. The position of the cyano group(s) in 5 a and 6 a were confirmed by NMR data and single-crystal X-ray diffraction studies on [Ph4 P]2 5 a⋅CH2 Cl2 and [Et4 N]2 6 a. The {closo-B11 } clusters are fluxional in solution. In the crystal of [EMIm]2 2 the BCN vertex is in the 2-position. Two isomers of dianion 3, [2,3-(NC)2 -closo-B11 H9 ]2- and [2,6-(NC)2 -closo-B11 H9 ]2- , were identified in the crystal of its [Et4 N]+ salt. The peak oxidation potentials Epa of anions 1-3, 5 a, 6 a, 5 b, and [nido-B11 H14 ]- (4 b), determined by cyclic voltammetry, increase with increasing number of cyano groups. Increasing Epa in the order 1<2<3 parallels the increasing reactivity toward cyanide anions.

Reaction of the Tricyanoborate Dianion [B(CN)3]2- with HgCl2.

The very reactive [B(CN)3]2- dianion has a strongly nucleophilic boron atom and can be used for the synthesis of tricyanoborates, which otherwise are difficult to access. Herein the reaction of this anion with HgCl2 is reported. The main product is the anionic mercury complex [Hg(B(CN)3)2]2-. Heteronuclear NMR spectroscopic experiments shows that the reaction proceeds via the intermediate [ClHgB(CN)3]2-. Even though [Hg(B(CN)3)2]2- is the main product, it is difficult to obtain it in pure form, because it slowly decomposes in the presence of water and air to [(NC)HgB(CN)3]-. All three anions were fully characterized by hetereonuclear NMR spectroscopy (11B, 13C, and 199Hg). Single-crystal X-ray diffraction studies of the salts K[ClHgB(CN)3], [Ph4P]2[Hg(B(CN)3)2], K[(NC)HgB(CN)3], and [Ph4P][(NC)HgB(CN)3] revealed linear coordination environments around mercury for all anions. The Hg-B bonds range from 2.219(5) Å in [Hg(B(CN)3)2]2- to 2.148(11) Å in [ClHgB(CN)3]-, are in accord with the sum of the covalent radii of mercury and boron, and can be described as covalent single bonds. A comparison with related complexes indicates that the [B(CN)3]2- dianion is a stronger ligand than chloride, cyanide, or carbenes. [Hg(B(CN)3)2]2- hydrolyses in solution only in the presence of oxygen. It is suggested that cis-[Hg(OH)2(B(CN)3)2]2- is formed as a very unstable intermediate, which decomposes very fast to [(NC)HgB(CN)3]- and other products. The anion cis-[Hg(OH)2(B(CN)3)2]2- would contain mercury in the unusual oxidation state +IV. Quantum-chemical calculations were performed to support this assumption.

Binary twinned-icosahedral [B21H18]- interacts with cyclodextrins as a precedent for its complexation with other organic motifs.

The weakly coordinating binary macropolyhedral anion closo,closo-[B21H18]- (B21; D3h symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with ß- and γ-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, α-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical computations, showing that ß- and γ-CD are able to interact with B21 due to their larger cavities, in contrast to the smaller α-CD. The hydridic B-H vectors of the B21 anion interact with K+ counterions and, via dihydrogen bonding, also with the partially positively charged hydrogens of the CD sugar units in the modeled ß- and γ-CD complexes. In summary, it has been shown by combined spectrometric/computational analysis that macropolyhedral boron hydride anions with two counterions can form stable complexes with ß- and γ-CD in the gas phase, offering a new perspective for the future investigation of this remarkable anion in the areas of supramolecular and medicinal chemistries.

Methanesulfonyl Azide: Molecular Structure and Photolysis in Solid Noble Gas Matrices.

The parent sulfonyl azide CH3SO2N3 has been characterized in a neat form by IR (gas, matrix-isolation) and Raman (solid) spectroscopy, and its structure has been established by X-ray crystallography. In both gas phase and solid state, the azide exhibits single conformation with the azido ligand being synperiplanar to one of the two S═O groups. In the crystal molecules of CH3SO2N3 are interconnected through three-dimensional O···H-C-H···O hydrogen bonds. Upon an ArF laser (193 nm) photolysis, the azide in solid noble gas matrices splits off N2 and yields the sulfonyl nitrene CH3SO2N in the triplet ground state. Subsequent photolysis with UV light (266 nm) causes the transformation from the nitrene to the pseudo-Curtius rearrangement product CH3NSO2. The identification of the photolysis intermediates by matrix-isolation IR spectroscopy is supported by quantum chemical calculations with DFT methods.

The hexacyanodiborane(6) dianion [B2(CN)6](2-).

Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron-precise B-B σ-bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B2 (CN)6 ](2-) that is chemically very robust is reported. The dianion is air-stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H3 O)2 [B2 (CN)6 ] starts at 200 °C. The [B2 (CN)6 ](2-) dianion is readily accessible starting from 1) B(CN)3 (2-) and an oxidant, 2) [BF(CN)3 ](-) and a reductant, or 3) by the reaction of B(CN)3 (2-) with [BHal(CN)3 ](-) (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an SN 2 mechanism.

Spectroscopic characterization and constitutional and rotational isomerism of ClC(O)SCN and ClC(O)NCS.

Chlorocarbonylthio- and isothiocyanate (ClC(O)SCN and ClC(O)NCS) have been isolated and characterized by IR (Ar matrix, gas), Raman (liquid), (13)C NMR and UV-visible spectroscopies. Vibrational and quantum chemical studies suggest the presence of the syn and anti conformers (SCN group with respect to the C═O bond) in the gas phase for both constitutional isomers. syn-ClC(O)SCN is preferred by ΔH° (anti/syn) = 1.3(0.3) kcal mol(-1). The solid-state structure of ClC(O)SCN has been determined by single crystal X-ray diffraction analysis at low temperature. The crystalline solid consists exclusively of molecules in the syn conformation. On the other hand, the anti form is more stable for the ClC(O)NCS isomer. The structure of ClC(O)NCS and its conformational composition were determined by gas electron diffraction. An unusual low syn → anti interconversion energy barrier of 0.98 (0.15) kcal mol(-1) was detected for ClC(O)NCS at cryogenic temperatures. The photochemistry of both constitutional isomers isolated in solid argon at 15 K was studied. Rearrangement of ClC(O)SCN to ClC(O)NCS was observed in the neat liquid and under UV-vis irradiation of ClC(O)SCN isolated in solid argon. Properties have been discussed in terms of the valence electronic structure, including the analysis of the He(I) photoelectron spectrum of ClC(O)SCN.

Syntheses and crystal structures of the closo-borate M[B8H9] (M = [PPh4]+ and [N(n-Bu4)]+).

Protonation of M(2)[B(8)H(8)] with HCl or NEt(3)·HCl resulted in M[B(8)H(9)] (M = [PPh(4)](+) or [N(n-Bu(4))](+)). The monoanion was isolated and characterized by (1)H, (1)H{(11)B}, (11)B, and (11)B{(1)H} NMR spectroscopy. The "protonated" form [B(8)H(9)](-) showed a dynamic behavior in solution, which was analyzed by NMR spectroscopy and compared with theoretical calculations. The structures of [B(8)H(9)](-) as well as [B(8)H(8)](2-) were determined by single-crystal X-ray diffraction.

Equilibrium acidities of superacids.

In this paper, we report the most comprehensive equilibrium superacidity scale that is available to date. Contrary to most of the past works, this scale is set up in a medium of constant composition and the obtained acidity values characterize the acidities of molecules rather than acidities of media. The current scale is thus complementary to the well-known H(0) scale in the information that it provides. The solvent used is 1,2-dichloroethane (DCE). DCE has very weak basic properties (but sufficiently high polarity) and is an appropriate solvent for measuring acidities of very strong acids of diverse chemical nature. DCE acidities of well-known superacids (CF(3)SO(2)OH, (CF(3)SO(2))(2)NH, cyanocarbon acids, etc.) as well as common mineral acids (H(2)SO(4), HI, HBr, etc.) are reported. Acidities of altogether 62 acids have been determined from 176 interlinked relative acidity measurements. The scale spans 15 orders of magnitude (from picric acid to 1,1,2,3,3-pentacyanopropene) and is expected to be a useful tool in design, use, and further acidity measurements of superacidic molecules.

Syntheses and crystal structures of the closo-borates M2[B7H7] and M[B7H8] (M = PPh4, PNP, and N(n-Bu4)): the missing crystal structure in the series [B(n)H(n)]2- (n = 6-12).

Oxidation of [N(n-Bu(4))](2)[B(9)H(9)] with oxygen in a mixture of dimethoxyethane and CH(2)Cl(2) leads to salts of the [B(7)H(7)](2-) dianion. This is the first convenient synthesis for a seven-vertex hydro-closo-borate anion. Protonation with NEt(3)·HCl resulted in salts of the [B(7)H(8)](-) monoanion. Both closo-borate anions were isolated and characterized by (1)H, (1)H{(11)B}, (11)B, and (11)B{(1)H} NMR spectroscopy. The temperature-dependent (1)H{(11)B}, (11)B, and (11)B{(1)H} NMR spectra of [B(7)H(8)](-) were also measured. The structure of [B(7)H(7)](2-) as well as of [B(7)H(8)](-) were determined by single-crystal X-ray diffraction.

Synthesis and characterization of sulfuryl diazide, O2S(N3)2.

Sulfuryl diazide, O(2)S(N(3))(2), previously described as an "exceedingly explosive" compound, has been isolated and characterized by IR (Ar matrix, gas) and Raman (solid) spectroscopy, and its structure has been determined by X-ray crystallography. It has a melting point of -15 °C and can be handled in small quantities in gas, liquid, and solid states. Vibrational spectroscopic studies suggest the presence of only one conformer in both gas and solid states, and the X-ray crystallography revealed an anti conformation of the two azido groups with respect to the NSN plane. Calculations predict the anti (C(2)) conformer to be 6.6 kJ mol(-1) lower in energy than the syn (C(s)) one at the CBS-QB3 level of theory. The related chlorosulfuryl azide, ClSO(2)N(3), has also been prepared and characterized by IR and Raman spectroscopy.

Synthesis and characterization of the phosphorus triazides OP(N3)3 and SP(N3)3.

Two explosive triazides of phosphorus(V), OP(N(3))(3) and SP(N(3))(3), have been prepared as neat substances and structurally characterized. Both compounds can be handled in gas, liquid, and solid states in submillimolar quantities. The melting points of OP(N(3))(3) and SP(N(3))(3) are +22 and -30 °C, respectively. The two triazides have been characterized by IR (Ar matrix and gas phase) and Raman (solid) spectroscopies. Their single-crystal structures were obtained by X-ray diffraction and found to be significantly distorted from the predicted ideal C(3) symmetry because of intermolecular interactions. The spectroscopic and structural properties are discussed in combination with density functional theory calculations.

Mechanistic study on the fluorination of K[B(CN)4] with ClF enabling the high yield and large scale synthesis of K[B(CF3)4] and K[(CF3)3BCN].

The fluorination of K[B(CN)(4)] with ClF is studied by millimolar test reactions in aHF and CH(2)Cl(2) solution and by subsequent identification of intermediates such as B-CF═NCl, B-CF(2)-NCl(2), and B-CF(3) species as well as NCl(3) by (19)F, (11)B NMR, and Raman spectroscopy, respectively. At first one cyano group of K[B(CN)(4)] is converted fast into a CF(3) group, and with increasing fluorination the reaction becomes slower and several intermediates could be observed. On the basis of these results, a synthesis was developed for K[B(CF(3))(4)] on a 0.2 molar scale by treatment of K[B(CN)(4)] diluted in aHF with ClF. The course of the reactions was followed by (i) monitoring the vapor pressure inside the reactor, (ii) observing the heat dissipation during ClF uptake, and (iii) measuring the volume of the released nitrogen gas. Since the fluorination of the last cyano group proceeds very slowly, the selective synthesis of K[(CF(3))(3)BCN] on a 0.2 molar scale is possible, as well. The analysis of the mechanisms, thermodynamics, and kinetics of the fluorination reactions is supported by density functional theory (DFT) calculations.

Synthesis and characterization of phosphorous(III) diisocyanate and triisocyanate.

Two phosphorous(iii) isocyanates, ClP(NCO)2 and P(NCO)3 were isolated as neat substances and characterized with IR (gas-phase and Ne-matrix), Raman (solid), and 31P NMR spectroscopy. Their vibrational spectra were analyzed in terms of a single conformer with the aid of quantum chemical computations at the B3LYP/6-311+G(3df) level of theory. In line with the theoretically computed favorable syn-configuration of the NCO ligands with the sterically active lone-pair electrons on the central phosphorous atom (nP), low-temperature single-crystal X-ray diffraction (XRD) of solid ClP(NCO)2 reveals a Cs symmetric syn-configuration for both NCO ligands with weak CO (r = 2.9692(4) Å) van der Waals (vdW) interactions. In the binary isocyante P(NCO)3, all the three NCO ligands adopt similar syn-configuration with nP, leading to a propeller-shaped structure with slightly distorted C3v symmetry due to steric repulsion of the NCO ligands and the PO vdW interactions (r = 3.1901(1) Å) in the solid state.

Syntheses and characterization of (C2F5)3BCO and (C3F7)3BCO.

The new tris(perfluoroalkyl)borane carbonyls, (C(2)F(5))(3)BCO and (C(3)F(7))(3)BCO, were prepared by means of a novel synthetic route using commercially available precursors by reacting K[(C(2)F(5))(3)BCOOH] and K[(C(3)F(7))(3)BCOOH] with concentrated sulfuric acid in the last step. The carboxylic acids, K[(C(2)F(5))(3)BCOOH] and K[(C(3)F(7))(3)BCOOH], were prepared by oxidative cleavage of the C[triple bond]C triple bonds in Cs[(C(2)F(5))(3)BC[triple bond]CPh] and Cs[(C(3)F(7))(3)BC[triple bond]CPh] in a two-step process to yield K[(C(2)F(5))(3)BCO-COPh] and K[(C(3)F(7))(3)BCO-COPh] as isolable intermediates. Crystal structures were obtained of K[(C(2)F(5))(3)BCO-COPh], K[(C(2)F(5))(3)BCOOH].H(2)O, (C(2)F(5))(3)BCO, K[(C(3)F(7))(3)BCOOH].2H(2)O, and (C(3)F(7))(3)BCO. In the crystal structures of (C(2)F(5))(3)BCO and (C(3)F(7))(3)BCO the C[triple bond]O bond lengths are 1.109(2) and 1.103(5) A, respectively, which are among the shortest observed to date. Tris(pentafluoroethyl)borane carbonyl and (C(3)F(7))(3)BCO slowly decompose at room temperature to yield CO, difluoroperfluoroalkylboranes and perfluoroalkenes. The decomposition of (C(2)F(5))(3)BCO was found to follow a first-order rate law with E(a)=107 kJ mol(-1).

Vibrational spectra, crystal structures, constitutional and rotational isomerism of FC(O)SCN and FC(O)NCS.

Fluorocarbonyl thio- and isothiocyanate, FC(O)SCN and FC(O)NCS, were fully characterized by IR (gas, Ar and N(2) matrixes), Raman (liquid and solid), UV (gas), and (13)C NMR (liquid) spectroscopy, as well as single-crystal X-ray diffraction. Their vibrational and conformational properties were analyzed using matrix isolation techniques guided by quantum chemical calculation at the ab initio [MP2 and CCSD(T)], density functional theory B3LYP, and CBS-QB3 levels of theory. A complete assignment of the fundamental modes of FC(O)SCN was performed. In both the gas and liquid states, FC(O)SCN and FC(O)NCS were found to exist as two conformers (C(s) symmetry), in which the carbonyl double bond (C═O) adopts a synperiplanar (syn) and an antiperiplanar (anti) orientation with respect to either the SCN or NCS group. For FC(O)SCN, the conformational enthalpy difference, ΔH° = H°(anti) - H°(syn), was determined by matrix IR experiments to be 0.9 ± 0.2 kcal mol(-1). The conformational equilibria were evaluated by fast-cooling gaseous samples highly diluted in argon at different temperatures as cryogenic matrixes. The conformational properties of both molecules were analyzed in terms of the hyperconjugative electronic effect applying the natural bond orbital method. The kinetics of the thermal conversion of the high-energy anti into the syn FC(O)NCS conformer was studied in Ar and N(2) matrixes at cryogenic temperatures. The reversed syn → anti photoisomerization was observed using UV-vis light. Rearrangement of FC(O)SCN into FC(O)NCS was observed in the neat liquid and in solution. Under 193 nm (ArF excimer laser) irradiation, FC(O)NCS isolated in cryogenic Ar matrixes forms FC(O)SCN. At low temperature, single crystals of the two constitutional isomers were obtained using a miniature zone melting procedure. According to X-ray diffraction, they exclusively crystallize in their syn forms (C(s) symmetry) in the orthorhombic crystal system.

Phase transition and structures of the twinned low-temperature phases of (Et4N)[ReS4].

The title compound, tetraethylammonium tetrathiorhenate, [(C2H5)4N][ReS4], has, at room temperature, a disordered structure in the space group P63mc (Z = 2, α-phase). A phase transition to the monoclinic space group P21 (Z = 2, γ-phase) at 285 K leads to a pseudo-merohedral twin. The high deviation from the hexagonal metric causes split reflections. However, the different orientations could not be separated, but were integrated using a large integration box. Rapid cooling to 110-170 K produces a metastable ß-phase (P63, Z = 18) in addition to the γ-phase. All crystals of the ß-phase are contaminated with the γ-phase. Additionally, the crystals of the ß-phase are merohedrally twinned. In contrast to the α-phase, the ß- and γ-phases do not show disorder.