A Comprehensive Experimental and Theoretical Study on the [{(η5-C5H5)2Zr[P(µ-PNEt2)2P(NEt2)2P]}]2O Crystalline System.

The structure of tetraphosphetane zirconium complex C52H100N8OP10Zr21 was determined by single crystal X-ray diffraction analysis. The crystal belongs to the monoclinic system, space group P21/c, with a = 19.6452(14), b = 17.8701(12), c = 20.7963(14)Å, α = γ = 90°, ß = 112.953(7)°, V = 6722.7(8)Å3, Z = 4. The electronic structure of the organometallic complex has been characterized within the framework of Quantum Chemical Topology. The topology of the Electron Localization Function (ELF) and the electron density according to the Quantum Theory of Atoms in Molecules (QTAIM) show no covalent bonds involving the Zr atom, but rather dative, coordinate interactions between the metal and the ligands. This is the first reported case of a Zr complex stabilized by an oxide anion, anionic cyclopentadienyl ligands and rare tetraphosphetane anions.

Synthesis of compounds with C-P-P and C[double bond, length as m-dash]P-P bond systems based on the phospha-Wittig reaction.

A reactivity study of a ß-diketiminate titanium(iii) phosphanylphosphido complex [MeNacNacTi(Cl){η2-P(SiMe3)-PtBu2}] (1) towards ketones such as benzophenone, 9-fluorenone, acetophenone, cyclopentanone, cyclohexanone and cycloheptanone is reported. The reactions of 1 with aromatic ketones (without α-protons) directly lead to the Ti(iii) complex [MeNacNacTi(µ2-Cl)(OSiMe3)] (5) and Ti(iv) complexes with the pinacol condensation product [MeNacNacTi(OSiMe3)(η2-pinacolate)] (3), and phosphanylphosphaalkenes Ph2C[double bond, length as m-dash]P-PtBu2 (2) and (fluorenyl)C[double bond, length as m-dash]P-PtBu2 (6), respectively. The reaction with acetophenone leads to the titanium(iii) complex with the aldol condensation product as ligand [MeNacNacTi(Cl){OC{Me(Ph)}CH2(C[double bond, length as m-dash]O)Ph}] (8) and in parallel to phosphanylphosphaalkene (Ph)MeC[double bond, length as m-dash]P-PtBu2 (9) and 5. The reactions of 1 with cyclic ketones (cyclopentanone and cyclohexanone) lead to Ti(iii) complexes [{(ArN[double bond, length as m-dash]C(Me)CHC(Me)[double bond, length as m-dash]NAr)((CH2)4CO)}Ti(Cl){PtBu2-P(SiMe3)((CH2)4CO)}] (10) and [{(ArN[double bond, length as m-dash]C(Me)CHC(Me)[double bond, length as m-dash]NAr)((CH2)5CO)}Ti(Cl){PtBu2-P(SiMe3)((CH2)5CO)}] (11), which are formed via the successive insertion of two molecules of ketone to one molecule of 1. The stability investigation of complexes 10 and 11 in a polar solvent (THF) revealed that under these conditions, the complexes decompose, resulting in titanium(iii) complexes with aldol condensation products and the expected phosphanylphosphaalkenes (CH2)4C[double bond, length as m-dash]P-PtBu2 (10a) and (CH2)5C[double bond, length as m-dash]P-PtBu2 (11a). In the reaction of 1 with cycloheptanone, only the Ti(iii) complex with the aldol condensation product [MeNacNacTi(Cl){OC(CH2)6}CH(C[double bond, length as m-dash]O)(CH2)5] (12) was isolated. The structures 3, 5, 8, 10, 11, 11b and 12 were characterized by X-ray spectroscopy, while all the phosphanylphosphaalkenes were characterized by NMR spectroscopy.

Homoleptic mono-, di-, and tetra-iron complexes featuring phosphido ligands: a synthetic, structural, and spectroscopic study.

We report the first series of homoleptic phosphido iron complexes synthesized by treating either the ß-diketiminato complex [(Dippnacnac)FeCl2Li(dme)2] (Dippnacnac = HC[(CMe)N(C6H3-2,6-iPr2)]2) or [FeBr2(thf)2] with an excess of phosphides R2PLi (R = tBu, tBuPh, Cy, iPr). Reaction outcomes depend strongly on the bulkiness of the phosphido ligands. The use of tBu2PLi precursor led to an anionic diiron complex 1 encompassing a planar Fe2P2 core with two bridging and two terminal phosphido ligands. An analogous reaction employing less sterically demanding phosphides, tBuPhPLi and Cy2PLi yielded diiron anionic complexes 2 and 3, respectively, featuring a short Fe-Fe interaction supported by three bridging phosphido groups and one additional terminal R2P- ligand at each iron center. Further tuning of the P-substrates bulkiness gave a neutral phosphido complex 4 possessing a tetrahedral Fe4 cluster core held together by six bridging iPr2P moieties. Moreover, we also describe the first homoleptic phosphanylphosphido iron complex 5, which features an iron center with low coordination provided by three tBu2P-P(SiMe3)- ligands. The structures of compounds 1-5 were determined by single-crystal X-ray diffraction and 1-3 by 1H NMR spectroscopy. Moreover, the electronic structures of 1-3 were interrogated using zero-field Mössbauer spectroscopy and DFT methods.

The Reactivity of Phosphanylphosphinidene Complexes of Transition Metals Toward Terminal Dihaloalkanes.

The reactivities of phosphanylphosphinidene complexes [(DippN)2W(Cl)(η2-P-PtBu2)]- (1), [(pTol3P)2Pt(η2-P═PtBu2)] (2), and [(dppe)Pt(η2-P═PtBu2)] (3) toward dihaloalkanes and methyl iodide were investigated. The reactions of the anionic tungsten complex (1) with stochiometric Br(CH2)nBr (n = 3, 4, 6) led to the formation of neutral complexes with a tBu2PP(CH2)3Br ligand or neutral dinuclear complexes with unusual tetradentate tBu2PP(CH2)nPPtBu2 ligands (n = 4, 6). The methylation of platinum complexes 2 and 3 with MeI yielded neutral or cationic complexes bearing side-on coordinated tBu2P-P-Me moieties. The reaction of 2 with I(CH2)2I gave a platinum complex with a tBu2P-P-I ligand. When the same dihaloalkane was reacted with 3, the P-P bond in the phosphanylphosphinidene ligand was cleaved to yield tBu2PI, phosphorus polymers, [(dppe)PtI2] and C2H4. Furthermore, the reaction of 3 with Br(CH2)2Br yielded dinuclear complex bearing a tetraphosphorus tBu2PPPPtBu2 ligand in the coordination sphere of the platinum. The molecular structures of the isolated products were established in the solid state and in solution by single-crystal X-ray diffraction and NMR spectroscopy. DFT studies indicated that the polyphosphorus ligands in the obtained complexes possess structures similar to free phosphenium cations tBu2P+═P-R (R = Me, I) or (tBu2P+═P)2.

Syntheses and Structures of Transition Metal Complexes with Phosphanylphosphinidene Chalcogenide Ligands.

The reactivity of the phosphanylphosphinidene complex [(DippN)2W(Cl)(η2-P-P tBu2)]- (1) toward chalcogens (Ch = Se, S) was studied. Reactions of stoichiometric amounts of 1 with chalcogens in DME yielded monomeric tungsten complexes with phosphanylphosphinidene chalcogenide ligands of the formula tBu2P-P-Ch (Ch = Se (in 2) and S (in 5)), which can be regarded as products of the addition of a chalcogen atom to a P═W bond in starting complex 1. The dissolution of selenophosphinidene complex 2 in nondonor solvents led to the formation of a dinuclear complex of tungsten (3) bearing a tBu2P(Se)-P ligand together with [ tBuSe2Li(dme)2]2 and polyphosphorus species. Under the same reaction conditions, thiophosphinidene complex 5 dimerized via the formation of transient complex 7, possessing a thiotetraphosphane-diido moiety tBu2P(S)-P-P-P tBu2. The elimination of the tBu2PS group from 7 yielded stable dinuclear tungsten complex 8 with an unusual phosphinidene tBu2P-P-P ligand. The reaction of 1 with excess chalcogen led to the cleavage of the P-P bond in the tBu2P-P ligand and the formation of [(DippN)2W(PCh4)]22- and [ tBuCh2Li(dme)2]2. The isolated compounds were characterized by NMR spectroscopy and X-ray crystallography. Furthermore, the calculated geometries of the free selenophosphinidenes, tBu2P-P-Se and tBu2P(Se)-P, were compared with their geometries when serving as ligands in complexes 2 and 3.

Reactions of (Ph)tBuP-P(SiMe3)Li·3THF with [(PNP)TiCl2] and [MeNacNacTiCl2·THF]: synthesis of first PNP titanium(iv) complex with the phosphanylphosphinidene ligand [(PNP)Ti(Cl){η2-P-P(Ph)tBu}].

Herein, the lithium derivative of diphosphane, (Ph)tBuP-P(SiMe3)Li (1), is isolated for the first time and investigated in reactions with ß-diketiminate (MeNacnac- = [Ar]NC(Me)CHC(Me)N[Ar]; Ar = 2,6-iPr2C6H3) and PNP-pincer (PNP = N[2-PiPr2-4-methylphenyl]2) Ti(iii) complexes. The ß-diketiminate titanium(iii) complex containing the phosphanylphosphido ligand [MeNacNacTi(Cl){η2-P(SiMe3)-P(Ph)tBu}] (2) is prepared via the reaction of [MeNacNacTiCl2·THF] with (Ph)tBuP-P(SiMe3)Li in toluene solution with good yield and purity. The corresponding titanium(iv) complex involving the phosphanylphosphinidene ligand [MeNacNacTi(Cl){η2-P-P(Ph)tBu}] (3) is synthesized via the oxidation of complex (2) with [iBu3PAgCl]4. Interestingly, an analogous PNP titanium(iv) complex, [(PNP)Ti(Cl){η2-P-P(Ph)tBu}] (4), is obtained in the reaction of [(PNP)TiCl2] with (Ph)tBuP-P(SiMe3)Li in toluene solution and a 1 : 1 molar ratio instead of the expected titanium(iii) complex with the phosphanylphosphido ligand. The solid-state structures of (Ph)tBuP-P(SiMe3)Li·3THF (1), [MeNacNacTi(Cl){η2-P(SiMe3)-P(Ph)tBu}] (2), [MeNacNacTi(Cl){η2-P-P(Ph)tBu}] (3) and [(PNP)Ti(Cl){η2-P-P(Ph)tBu}] (4) are determined by single-crystal X-ray diffraction, which reveals that in all obtained complexes, both the phosphanylphosphinidene (Ph)tBuP-P and phosphanylphosphido (Ph)tBuP-P(SiMe3) ligands are bidentate-coordinated to the metal center.

Synthetic, Structural, and Spectroscopic Characterization of a Novel Family of High-Spin Iron(II) [(ß-Diketiminate)(phosphanylphosphido)] Complexes.

This work describes a series of iron(II) phosphanylphosphido complexes. These compounds were obtained by reacting lithiated diphosphanes R2PP(SiMe3)Li (R = t-Bu, i-Pr) with an iron(II) ß-diketiminate complex, [LFe(µ2-Cl)2Li(DME)2] (1), where DME = 1,2-dimethoxyethane and L = Dippnacnac (ß-diketiminate). While the reaction of 1 with t-Bu2PP(SiMe3)Li yields [LFe(η1-Me3SiPP-t-Bu2)] (2), that of 1 with equimolar amounts of i-Pr2PP(SiMe3)Li, in DME, leads to [LFe(η2-i-Pr2PPSiMe3)] (3). In contrast, the reaction of 1 with (i-Pr2N)2PP(SiMe3)Li provides not an iron-containing complex but 1-[(diisopropylamino)phosphine]-2,4-bis(diisopropylamino)-3-(trimethylsilyl)tetraphosphetane (4). The structures of 2-4 were determined using diffractometry. Thus, 2 exhibits a three-coordinate iron site and 3 a four-coordinate iron site. The increase in the coordination number is induced by the change from an anticlinal to a synclinal conformation of the phoshpanylphosphido ligands. The electronic structures of 2 and 3 were assessed through a combined field-dependent 57Fe Mössbauer and high-frequency and -field electron paramagnetic resonance spectroscopic investigation in conjunction with analysis of their magnetic susceptibility and magnetization data. These studies revealed two high-spin iron(II) sites with S = 2 ground states that have different properties. While 2 exhibits a zero-field splitting described by a positive D parameter (D = +17.4 cm-1; E/D = 0.11) for 3, this parameter is negative [D = -25(5) cm-1; E/D = 0.15(5)]. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations provide insights into the origin of these differences and allow us to rationalize the fine and hyperfine structure parameters of 2 and 3. Thus, for 2, the spin-orbit coupling mixes a z2-type ground state with two low-lying {xz/yz} orbital states. These interactions lead to an easy plane of magnetization, which is essentially parallel to the plane defined by the N-Fe-N atoms. For 3, we find a yz-type ground state that is strongly mixed with a low-lying z2-type orbital state. In this case, the spin-orbit interaction leads to a partial unquenching of the orbital momentum along the x axis, that is, to an easy axis of magnetization oriented roughly along the Fe-P bond of the phosphido moiety.

The reactivity of 1,1-dichloro-2,2-di-tert-butyldiphosphane towards lithiated metal carbonyls: a new entry to phosphanylphosphinidene dimers.

Reactions of [Cp*(OC)3M]Li (Cp* = C5Me5, M = Mo, W) towards t-Bu2P-PCl2 lead to the formation of phosphanylphosphinidene dimers [Cp*(OC)3M(η(2)-t-Bu2P-P)]2 in fairly good yields. The formation of a tetraphosphorus ligand proceeds via reductive dimerization of t-Bu2P-P units. NMR, X-ray investigations and DFT calculations show that the resulting tetraphosphorus ligand has a structure of dication t-Bu2P(+)=P-P=P(+)t-Bu2.

An investigation on the chemistry of the R2P = P ligand: reactions of a phosphanylphosphinidene complex of tungsten(VI) with electrophilic reagents.

The nucleophilic properties of the title compound [(2,6-i-Pr2C6H3N)2(Cl)W(η(2)-t-Bu2P = P)]Li·3DME (1) were investigated in reactions with selected electrophilic reagents such as MeI, M(CO)5THF (M = Cr, Mo, W), AlCl3, and GaCl3. Methylation of 1 by MeI yields phosphanylphosphido complexes [(2,6-i-Pr2C6H3N)2W(X)(1,2-η-t-Bu2P = P-CH3)] (X = Cl, I) (2-Cl/2-I) with the formation of a new P-C bond. Moreover, 1 reacts with electrophilic compounds [(OC)5M·THF] (M = Cr, Mo, W) to yield a series of novel dinuclear phosphanylphosphinidene complexes [(2,6-i-Pr2C6H3N)2(Cl)W(1,2-η-t-Bu2P = P-M(CO)5)]Li·3DME (3, 4, 5) with very long P-M distances. Adducts [(2,6-i-Pr2C6H3N)2(Cl)W(1,2-η-t-Bu2P = P-MCl3)]Li·3DME (6, 7) formed by reaction of 1 with GaCl3 and AlCl3 are labile and dissociate into 1 and MCl3 (M = Ga, Al). The outcomes of reactions were monitored by (31)P-NMR spectroscopy. Furthermore, the structures of the isolated complexes 2-Cl/2-I, 3, 4, and [(2,6-i-Pr2C6H3N)2(Cl)W(1,2-η-t-Bu2P = P-W(t-Bu2PH)(CO)3COLi·2DME] (5-P) were confirmed unambiguously by X-ray diffraction studies.

Reactivity of Phosphanylphosphinidene Complex of Tungsten(VI) toward Phosphines: A New Method of Synthesis of catena-Polyphosphorus Ligands.

The reactivity of an anionic phosphanylphosphinidene complex of tungsten(VI), [(2,6-i-Pr2C6H3N)2(Cl)W(η(2)-t-Bu2P═P)]Li·3DME toward PMe3, halogenophosphines, and iodine was investigated. Reaction of the starting complex with Me3P led to formation of a new neutral phosphanylphosphinidene complex, [(2,6-i-Pr2C6H3N)2(Me3P)W(η(2)-t-Bu2P═P)]. Reactions with halogenophosphines yielded new catena-phosphorus complexes. From reaction with Ph2PCl and Ph2PBr, a complex with an anionic triphosphorus ligand t-Bu2P-P((-))-PPh2 was isolated. The main product of reaction with PhPCl2 was a tungsten(VI) complex with a pentaphosphorus ligand, t-Bu2P-P((-))-P(Ph)-P((-))-P-t-Bu2. Iodine reacted with the starting complex as an electrophile under splitting of the P-P bond in the t-Bu2P═P unit to yield [(1,2-η-t-Bu2P-P-P-t-Bu2)W(2,6-i-Pr2C6H3N)2Cl], t-Bu2PI, and phosphorus polymers. The molecular structures of the isolated products in the solid state and in solution were established by single crystal X-ray diffraction and NMR spectroscopy.

Bis(diethyl-amido-κN)(diethyl-amine-κN)bis-(2,6-diisopropyl-phenyl-amido-κN)zirconium(IV).

In the title compound, [Zr(C(12)H(18)N)(2)(C(4)H(10)N)(2)(C(4)H(11)N)] or [Zr(HNC(6)H(3) (i)Pr(2))(2)(NEt(2))(2)(HNEt(2))], which was obtained by the reaction of Zr(NEt)(4) with (i)Pr(2)C(6)H(3)NH(2), the Zr(IV) atom is in a trigonal-bipiramidal geometry in which the N atoms from two (i)Pr(2)C(6)H(3)NH and one NEt(2) ligand occupy the equatorial positions, and the N atoms of an NEt(2) and an Et(2)NH ligand occupy the apical positions. An intra-molecular N-H⋯N contact occurs. There are two independent molecules in the asymmetric unit.

Hunting for the magnesium(I) species: formation, structure, and reactivity of some donor-free Grignard compounds.

Magnesium bromide radicals have to be prepared as high-temperature molecules and trapped as a metastable solution because a seemingly simple reduction of donor-free Grignard compounds failed. However, the essential role of magnesium(I) species during the formation of Grignard compounds could be demonstrated experimentally.

Syntheses and structures of the first terminal phosphanylphosphido complex of hafnium [Cp2Hf(Cl){η(1)-(Me3Si)P-P(NEt2)2}] and the first zirconocene-phosphanylphosphinidene dimer [Cp2Zr{µ(2)-P-P(NEt2)2}2ZrCp2].

Reactions of (Et(2)N)(2)P-P(SiMe(3))Li with [Cp(2)MCl(2)] (M = Zr, Hf) in toluene or pentane yield the related terminal phosphanylphosphido complexes [Cp(2)M(Cl){η(1)-(Me(3)Si)P-P(NEt(2))(2)}]. The solid state structure of [Cp(2)Hf(Cl){η(1)-(Me(3)Si)P-P(NEt(2))(2)}] was established by single crystal X-ray diffraction. The reaction of (Et(2)N)(2)P-P(SiMe(3))Li with [Cp(2)ZrCl(2)] in THF or DME solutions leads to the formation of deep red crystals of the first neutral diamagnetic zirconocene-phosphanylphosphinidene dimer [Cp(2)Zr{µ(2)-P-P(NEt(2))(2)}(2)ZrCp(2)]. The molecular structure of this compound was confirmed by X-ray diffraction. The reactions of (R(2)N)(2)P-P(SiMe(3))Li with [CpZrCl(3)] yield the related tetraphosphetanes R(2)NP(µ(2)-PSiMe(3))(2)PNR(2), which apparently are formed as a result of a transfer of NR(2) groups from a P atom to the Zr atom.

[N,N'-Bis(2,6-diisopropyl-phen-yl)pentane-2,4-diamine-(1-)-2κN,N']-µ(2)-chlorido-1:2κCl:Cl-chlorido-2κCl-bis-(1,2-di-methoxy-ethane-1κO,O')iron(II)lithium.

In the title compound, [FeLi(C(29)H(41)N(2))Cl(2)(C(4)H(10)O(2))(2)], the Fe(II) atom is coordinated by two N and two Cl atoms, generating a distorted FeN(2)Cl(2) tetra-hedral geometry. Additionally, one of the chloride atoms bridges to a lithium ion, which is solvated by two dimethoxy-ethane mol-ecules and is coordinated in a distorted trigonal-bipyramidal environment. The central Fe, Cl (× 2) and Li atoms are coplanar with a maximum deviation of 0.034 Å.

5,5-Dimethyl-2-methyl-seleno-1,3,2-dioxaphospho-rinan-2-one.

The title compound, C(6)H(13)O(3)PSe, was obtained in the reaction of 5,5-dimethyl-2-oxo-2-seleno-1,3,2-dioxaphospho-r-inane potassium salt with methyl iodide. The seleno-methyl group is in the axial position in relation to the six-membered dioxaphospho-rinane ring.

catena-Poly[[(tetra-hydro-furan-κO)lithium(I)]-bis-(µ-trimethyl-silanolato-κO:O)-gallium(III)-bis-(µ-trimethyl-silanolato-κO:O)-[(tetra-hydro-furan-κO)lithium(I)]-µ-bromido].

The title chain polymer compound, [GaLi(2)Br(C(3)H(9)OSi)(4)(C(4)H(8)O)(2)](n), was obtained in the reaction of GaBr(3) with Me(3)SiOLi in toluene/tetra-hydro-furan. The Ga(III) atom, located on a twofold rotation axis, is coordinated by four trimethyl-silanolate ligands and has a distorted tetra-hedral geometry. The Li(I) atom is four coordinated by one bridging Br atom located on an inversion centre, two trimethyl-silanolate ligands and one tetra-hydro-furane mol-ecule in a distorted tetra-hedral geometry. The polymeric chains extend along [001]. The tetra-hydro-furane mol-ecule is disordered over two positions with site-occupancy factors of 0.57 (2) and 0.43 (2).

Trichloridobis(ethyl-diphenyl-phosphine)(tetra-hydro-furan)-molybdenum(III).

In the mononuclear title compound, [MoCl(3)(C(4)H(8)O)(C(14)H(15)P)(2)], obtained by the reaction of trichloro-tris-(tetra-hydro-furan)-molybdenum(III) and ethyl-diphenyl-phosphine in tetra-hydro-furan (THF) solution, the Mo(III) atom is six-coordinated by one O atom of a THF mol-ecule, two P atoms from two ethyl-diphenyl-phosphine ligands and three Cl atoms in a distorted octa-hedral geometry. The C atoms of the THF molecule are disordered over two positions in a 0.55 (2):0.45 (2) ratio.

Dispiro-[cyclo-propane-1,5'-endo-tricyclo-[5.2.1.0]deca-3,8-diene-10',1''-cyclo-propane].

The title compound, C(14)H(16), is built up from three five-membered rings. Two of the five-membered rings display an envelope conformation and the third one is almost planar (r.m.s. deviation = 0.014 Å).

Chlorido(η-cyclo-penta-dien-yl)[(4a,4b,8a,9,9a-η)-fluoren-yl](fluorenyl-κC)zirconium(IV) toluene solvate.

In the title compound, [Zr(C(5)H(5))(C(13)H(9))(2)Cl]·C(7)H(8), the Zr(IV) atom is coordinated by a Cl atom, a cyclo-penta-dienyl (Cp) ligand [Zr-centroid (Cp) = 2.199 (3) Å] and two fluorenyl ligands (Fl) [Zr-centroid (Fl) = 2.273 (2) Šand Zr-CH from fluorenyl = 2.355 (2) Å] in a distorted tetra-gonal geometry. The dihedral angles between the mean planes of the fluorenyl ring systems and the Cp ring are 36.62 (6)° for the η(1)-coordinated fluorenyl and 52.85 (6)° for the η(5)-coordinated fluorenyl, while the dihedral angle between the mean planes of the two fluorenyl ring systems is 76.18 (7)°.

catena-Poly[{µ-η:η-1-[2-(dimethyl-amino)-ethyl-κN]cyclo-penta-dien-yl}-lithium(I)-(µ-1,1,3,3-tetra-tert-butyl-triphosphane-κP:P,P)lithium(I)].

The title compound, [Li(2)(C(9)H(14)N)(C(16)H(36)P(3))](n), is a by-product of the reaction of [Cp(C(5)H(4)CH(2)CH(2)NMe(2))ZrCl(2)](n) with (t)Bu(2)P-P(SiMe(3))Li in toluene. It is a coordination polymer composed of infinite chains running along [010]. One Li(I) atom is chelated by the cyclo-penta-dienyl ring and and the N atom of the scorpionate ligand and a P atom, whereas the other Li(I) atom is coordinated by the backside of the cyclo-penta-dienyl ring and two P atoms. Both Li(I) atoms adopt a distorted trigonal coordination. The structure was determined from a twinned crystal, but only the data from the main twin component was used. The fraction of components in the crystal was 0.555:0.445 and the twin matrix corresponds to twofold rotation about the c axis (00/00/001).