Synthesis, structure, and ligand-based reduction reactivity of trivalent organosamarium benzene chalcogenolate complexes (C(5)Me(5))(2)Sm(EPh)(THF) and [(C(5)Me(5))(2)Sm(mu-EPh)](2)

To compare the ligand-based reduction chemistry of (EPh)(-) ligands in a metallocene environment to the sterically induced reduction chemistry of the (C(5)Me(5))(-) ligands in (C(5)Me(5))(3)Sm, (C(5)Me(5))(2)Sm(EPh) (E = S, Se, Te) complexes were synthesized and treated with substrates reduced by (C(5)Me(5))(3)Sm: cyclooctatetraene; azobenzene; phenazine. Reactions of PhEEPh with (C(5)Me(5))(2)Sm(THF)(2) and (C(5)Me(5))(2)Sm produced THF-solvated monometallic complexes, (C(5)Me(5))(2)Sm(EPh)(THF), and their unsolvated dimeric analogues, [(C(5)Me(5))(2)Sm(mu-EPh)](2), respectively. Both sets of the paramagnetic benzene chalcogenolate complexes were definitively identified by X-crystallography and form homologous series. Only the (TePh)(-) complexes show reduction reactivity and only upon heating to 65 degrees C.     

Synthesis,characterization and luminescent properties of three-coordinate copper(I) halide complexes containing diphenylamino monodentate phosphine ligand

Three-coordinate copper halide complexes with a bidentate phosphine ligand have received much attention. Here, a series of three-coordinate dinuclear copper halide complexes containing a diphenylamino monodentate phosphine ligand, [CuX(dpnp)]₂ (dpnp = N-[2-(diphenylphosphino)-4,5-dimethylphenyl]-N-phenylaniline, X = I (1), Br (2) and Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. The structural analysis reveals that two copper(I) centers are bridged by two halogen ligands to form a dinuclear structure with a four-membered Cu₂X₂ ring. Crystal structures of 1–3 contain 1-D supramolecular arrays constructed by intermolecular C–H?π interactions. These complexes exhibit blue emission in the solid state at room temperature and have peak emission wavelengths at 483–487 nm with microsecond lifetimes (τ = 13.9–38.1 μs) and low emission quantum yields (<0.01%). The emission of complex 1 mainly originates from intraligand (IL) transition, whereas the emissions of complexes 2 and 3 are from a combination of MLCT, XLCT and IL transitions. The three complexes displayed good thermal stability.     

Organometallic Fluorides of Zirconium and Hafnium in the Synthesis of Carboxylate Complexes: Molecular Structures of [{(eta(5)-C(5)Me(5))ZrF(OCOCF(3))(2)}(2)] and [(eta(5)-C(5)Me(5))(2)Zr(OCOCF(3))(2)

The reaction of [(eta(5)-C(5)Me(5))ZrF(3)] and [(eta(5)-C(5)Me(5))HfF(3)] with Me(3)SiOCOCF(3) yields the dinuclear complexes [{(eta(5)-C(5)Me(5))ZrF(OCOCF(3))(2)}(2)] (1) and [{(eta(5)-C(5)Me(5))HfF(OCOCF(3))(2)}(2)] (2), regardless of the molar ratio employed. [(eta(5)-C(5)Me(5))(2)ZrF(2)] reacts with 1 and 2 equiv of Me(3)SiOCOCF(3) to form the mononuclear compounds [(eta(5)-C(5)Me(5))(2)Zr(OCOCF(3))(2)] (3) and [(eta(5)-C(5)Me(5))(2)ZrF(OCOCF(3))] (4), respectively. The molecular structures of 1 and 3 have been determined by single-crystal X-ray analysis: 1, triclinic, P&onemacr;, a = 9.508(3) ?, b = 11.002(4) ?, c = 17.528(3) ?, alpha = 78.55(4), beta = 76.80(2), gamma = 87.51(2) degrees, V = 1750(1) ?(3), Z = 2, R = 0.0378; 3, monoclinic, C2/c, a = 18.553(4) ?, b = 9.110(2) ?, c = 16.323(3) ?, beta = 114.88(3) degrees, V = 2503(1) ?(3), Z = 4, R = 0.0457. Compound 1 shows bridging bidentate and chelating carboxylate ligands as well as bridging fluorine atoms. The zirconium atoms are seven coordinated and have an 18-electron configuration. X-ray studies of 3 reveal two structural components where the carboxylate ligands coordinate in a monodentate (major component) and a chelating manner (minor component).     

Synthesis,characterization, and luminescent properties of three-coordinate copper(I) halide complexes containing a carbazolyl monodentate phosphine ligand

Abstract

A series of three-coordinate dinuclear copper halide complexes containing acarbazolyl monodentate phosphine ligand, [CuX(dppc)]₂ (dppc =3,6-di-tert-butyl-9-[2-(diphenylphosphino)phenyl]carbazole, X?=?I (1), Br (2), and Cl (3)), were synthesized, and their molecular structures and photophysical properties were investigated. The structural analysis reveals that two copper(I) centers are bridged by two halogen ligands to form a dinuclear structure with a four-membered Cu₂X₂ ring. Crystal structures of 1-3 contain 1-D supramolecular arrays constructed by intermolecular C–H···π interactions. These complexes exhibit blue to green emission in the solid state at room temperature and have peak emission wavelengths at 492–495?nm with microsecond lifetimes and low emission quantum yields (< 0.01%). The emission of 1-3 mainly originates from MLCT, XLCT, and IL (intraligand) transitions. The three complexes displayed good thermal stability.     

On the electronic origins of structural isomerism in the iron-sulfur cubane, [(C(5)H(5))(4)Fe(4)S(4)](2+)

Density functional theory provides new insights into the structural isomerism observed in the cyclopentadienyl-capped iron-sulfur cluster, [(C(5)H(5))(4)Fe(4)S(4)](2+). Two distinct, closely spaced minima have been located, a triplet with D(2) symmetry and a C(2)-symmetric singlet, both of which correspond closely to the structure of one of the known crystal forms of the cation. Thus, the structural diversity in these species reflects genuine molecular bistability rather than simple solid-state packing effects. In contrast, no stable D(2)(d)()-symmetric minimum has been located, suggesting that the reported D(2)(d)() symmetry of the cation in [(C(5)H(5))(4)Fe(4)S(4)][PF(6)](2) may be a crystallographic artifact. In the ruthenium analogue, the more diffuse 4d orbitals stabilize the C(2)-symmetric singlet, which is unambiguously the ground state, but the D(2)-symmetric potential energy surface provides a viable low-energy pathway for the dynamic exchange of the Ru-Ru bonds.     

Synthesis,molecular structure,and C-C coupling reactions of carbeneruthenium(II) complexes with C5H5Ru(=CRR') and C5Me5Ru(=CRR') as molecular units

The ethene derivatives [(eta(5)-C(5)R(5))RuX(C(2)H(4))(PPh(3))] with R=H and Me, which have been prepared from the eta(3)-allylic compounds [(eta(5)-C(5)R(5))Ru(eta(3)-2-MeC(3)H(4))(PPh(3))] (1, 2) and acids HX under an ethene atmosphere, are excellent starting materials for the synthesis of a series of new halfsandwich-type ruthenium(II) complexes. The olefinic ligand is replaced not only by CO and pyridine, but also by internal and terminal alkynes to give (for X=Cl) alkyne, vinylidene, and allene compounds of the general composition [(eta(5)-C(5)R(5))RuCl(L)(PPh(3))] with L=C(2)(CO(2)Me)(2), Me(3)SiC(2)CO(2)Et, C=CHCO(2)R, and C(3)H(4). The allenylidene complex [(eta(5)-C(5)H(5))RuCl(=C=C=CPh(2))(PPh(3))] is directly accessible from 1 (R=H) in two steps with the propargylic alcohol HC triple bond CC(OH)Ph(2) as the precursor. The reactions of the ethene derivatives [(eta(5)-C(5)H(5))RuX(C(2)H(4))(PPh(3))] (X=Cl, CF(3)CO(2)) with diazo compounds RR'CN(2) yield the corresponding carbene complexes [(eta(5)-C(5)R(5))RuX(=CRR')(PPh(3))], while with ethyl diazoacetate (for X=Cl) the diethyl maleate compound [(eta(5)-C(5)H(5))RuCl[eta(2)-Z-C(2)H(2)(CO(2)Et)(2)](PPh(3))] is obtained. Halfsandwich-type ruthenium(II) complexes [(eta(5)-C(5)R(5))RuCl(=CHR')(PPh(3))] with secondary carbenes as ligands, as well as cationic species [(eta(5)-C(5)H(5))Ru(=CPh(2))(L)(PPh(3))]X with L=CO and CNtBu and X=AlCl(4) and PF(6), have also been prepared. The neutral compounds [(eta(5)-C(5)H(5))RuCl(=CRR')(PPh(3))] react with phenyllithium, methyllithium, and the vinyl Grignard reagent CH(2)=CHMgBr by displacement of the chloride and subsequent C-C coupling to generate halfsandwich-type ruthenium(II) complexes with eta(3)-benzyl, eta(3)-allyl, and substituted olefins as ligands. Protolytic cleavage of the metal-allylic bond in [(eta(5)-C(5)H(5))Ru(eta(3)-CH(2)CHCR(2))(PPh(3))] with acetic acid affords the corresponding olefins R(2)C=CHCH(3). The by-product of this process is the acetato derivative [(eta(5)-C(5)H(5))Ru(kappa(2)-O(2)CCH(3))(PPh(3))], which can be reconverted to the carbene complexes [(eta(5)-C(5)H(5))RuCl(=CR(2))(PPh(3))] in a one-pot reaction with R(2)CN(2) and Et(3)NHCl.     

Synthesis of (C5Me5)2(C5Me4H)UMe, (C5Me5)2(C5H5)UMe, and (C5Me5)2UMe[CH(SiMe3)2] from cationic metallocenes for the evaluation of sterically induced reduction

To probe the correlation of unusual (C5Me5)(1-) reactivity with steric crowding in complexes such as (C5Me5)3UMe and (C5Me5)3UCl, slightly less crowded (C5Me5)2(C5Me4H)UX analogues (X = Me, Cl) were synthesized and their reactivity was evaluated. The utility of the cationic precursors [(C5Me5)2UMe](1+), 1, and [(C5Me5)2UCl](1+), 2, in the synthesis of (C5Me5)2(C5Me4H)UMe, 3, and (C5Me5)2(C5Me4H)UCl, 4, was also explored. Since the use of precursor [(C5Me5)2UMe][MeBPh3], 1a, is complicated by the equilibrium between 1a and (C5Me5)2UMe2/BPh3, the reactivity of [(C5Me5)2UMe(OTf)]2, 1b, (OTf = O3SCF3) prepared from (C5Me5)2UMe2 and AgOTf, was also studied. Both 1a and 1b react with KC5Me4H to form 3. Complex 4 readily forms by addition of KC5Me4H to [(C5Me5)2UCl][MeBPh3], generated in situ from (C5Me5)2UMeCl and BPh3. Complex 1b was preferred to 1a for the synthesis of (C5Me5)2(C5H5)UMe, 5, and (C5Me5)2UMe[CH(SiMe3)2], 6, from KC5H5 and LiCH(SiMe3)2, respectively. Complex 6 is the first example of a mixed alkyl uranium metallocene complex. Sterically induced reduction (SIR) reactivity was not observed with 3-6 although the methyl displacements from the (C5Me5)(1-) ring plane for 3 are the closest observed to date to those of SIR-active complexes. The (1)H NMR spectra of 3 and 4 are unusual in that all of the (C5Me4H)(1-) methyl groups are inequivalent. This structural rigidity is consistent with density-functional theory calculations.     

Synthesis and dynamic NMR studies of Pt(eta(5)-C(5)Me(5))(CO){C(O)NR(2)} complexes

The formation of Pt(eta(5)-C(5)Me(5))(CO){C(O)NR(2)} (R=Me, Et) complexes was established by spectroscopic analysis. The infrared spectra of these complexes showed a sharp absorption due to the presence of coordinated carbonyl group in the region 2017-2013cm(-1). The N,N-dialkylcarbamoyl ligands showed a characteristic CO stretching absorption in the range 1609-1616cm(-1). The proton NMR spectra of these complexes revealed the expected singlet arising from five equivalent methyl groups on the cyclopentadienyl ring with satellites due to coupling to (195)Pt. The N-methyl and N-ethyl protons exhibited very broad resonances due to restricted rotation about the N-C bond at room temperature. On cooling to -30 degrees C, the N,N-dimethyl protons for complex Pt(eta(5)-C(5)Me(5))(CO){C(O)NMe(2)} showed two sharp singlets at delta 2.86 and 3.09ppm as expected for the static structure. For the N,N-diethyl derivative, Pt(eta(5)-C(5)Me(5))(CO){C(O)NEt(2)}, the methyl protons exhibited only a single triplet at delta 1.06ppm at -10 degrees C due to coupling with the methylene protons. This single resonance arises through accidental overlap as the methylene protons of the ethyl groups are inequivalent at this temperature and each exhibited a quartet at delta 3.33 and 3.70ppm due to coupling with the methyl protons. The singlet resonances for the methyl and ring carbons of the eta(5)-C(5)Me(5) group found in (13)C{(1)H} NMR spectra are illustrative of the chemical equivalence of all the carbon atoms caused by free rotation of the ring in these complexes. The signals attributable to the carbonyl and carbamoyl carbon atom resonances are found downfield as two singlets each with a large coupling constant to platinum. The platinum coupling constants of the downfield resonances could not be identified for Pt(eta(5)-C(5)Me(5))(CO){C(O)NMe(2)} due to presence of impurities.     

Synthesis and structural characterization of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)C(Ph)], generated via an alkyne-Ti benzyne coupling reaction

The thermolysis of [(C₅H₄)SiMe₂(N-t-Bu)]TiPh₂ in the presence of diphenylacetylene proceeds at 80 °C in cyclohexane solution with the sole formation of the titanacyclic complex [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph)C(Ph)], which has been characterized by solution NMR measurements and X-ray crystallographic analysis. This reaction is accompanied by the elimination of benzene and presumably occurs via coupling of a titanium benzyne intermediate with diphenylacetylene. The two chemically inequivalent Ti-C bonds of 2.081(7) and 2.103(6) Å in [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph)C(Ph)] reflect the increased electrophilicity of the d⁰ Ti(IV) center arising from the presence of the bifunctional ansa-cyclopentadienyldimethylsilylamido ligand.     

Synthesis and structural characterization of Be(eta 5-C5Me5)(eta 1-C5Me4H). Evidence for ring-inversion leading to Be(eta 5-C5Me4H)(eta 1-C5Me5)

The mixed-ring beryllocene Be(C5Me5)(C5Me4H), that contains eta 5-C5Me5 and eta 1-C5Me4H rings, the latter bonded to the metal through the CH carbon atom (X-ray crystal structure) reacts at room temperature with CNXyl (Xyl = C6H3-2,6-Me2) to give an iminoacyl product, Be(eta 5-C5Me4H)[C(NXyl)C5Me5] derived from the inverted beryllocene structure Be (eta 5-C5Me4H)(eta 1-C5Me5).     

Synthesis, structural characterization, and electrophosphorescent properties of rhenium(I) complexes containing carrier-transporting groups

Two novel diimine rhenium(I) carbonyl complexes with the formula [Re(CO)(3)(L)Br], where L = 1-(4-5'-phenyl-1,3,4-oxadiazolylbenzyl)-2-pyridinylbenzoimidazole (1) and 1-(4-carbazolylbutyl)-2-pyridinylbenzoimidazole (2), have been successfully synthesized and characterized by elemental analysis, (1)H NMR, and IR spectra. Their electrochemical, photophysical, and electroluminescent behaviors, along with the X-ray crystal structure analysis of 2, are also described. White electrophosphorescent devices were fabricated using 1 and 2 as emitters. The devices based on carbazole-containing (hole-transporting group) 2 with the structure ITO/m-MTDATA (30 nm)/NPB (20 nm)/2:CBP (8%, 30 nm)/Bphen (20 nm)/Alq(3) (20 nm)/LiF (0.8 nm)/Al (200 nm) exhibit Commission Internationale de L'Eclairage coordinates of x = 0.34, y = 0.33 with a maximum brightness of 2300 cd/m(2) at 580 mA/cm(2). When a brightness of 1500 cd/m(2) appears at 230 mA/cm(2), the devices based on 10 wt % 2 still possess 56% of the maximum efficiency which appeared at 2.7 mA/cm(2). These performances are among the best reported for devices using Re(I) complexes as emitters. By comparison of the electroluminescent properties of the devices based on 1 and 2, we conclude that the introduction of the carbazole group into the ligand improves the performance of 1-doped devices.     

Synthesis and characterization of chiral polyamides derived from glycine and (S)-5-amino-4-methoxypentanoic acid

Stereoregular, enantiomerically pure, chiral polyamides of the –AB– type, containing a natural (glycine) and a synthetic [(S)-5-amino-4-methoxypentanoic acid (AMP)] component have been prepared by the active ester polycondensation method. Thus, polyamide 7 was obtained by polycondensation of the conveniently activated H₂NGly–AMPCO₂R unit ( 6 ). In this reaction, 7 appeared accompanied by a considerable amount of cyclic (Gly–AMP)₂ ( 8 ), which makes the isolation and purification of 7 difficult. The formation of cyclic byproducts could be avoided by preparing and polymerizing the oligoamide H₂NGly–AMP–AMPCO₂R ( 11 ), which has the terminal carboxyl group activated as the pentachlorophenyl ester. The resulting polyamide ( 12 ) was obtained in 85% yield and free of macrolactams, such as 8 . The new polyamides 7 and 12 were characterized by elemental analysis and infrared and ¹H- and ¹³C-nuclear magnetic resonance spectroscopies. Thermal studies revealed that 12 is crystalline and yields films with spherulitic texture by slow evaporation of formic acid solutions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2741–2748, 1998     

Biferrocenium tetrabromoferrate, [(C5H5)Fe(C5H4)- (C5H4)Fe(C5H5)]FeBr4. The X-ray structural characterization of a mixed-valence compound

Biferrocenium tetrabromoferrate, [(C₅H₅)Fe(C₅H₄)-(C₅H₄)Fe(C₅H₅)]FeBr₄ (1) obtained as a by-product in the synthesis of biferrocenium trihalide salts, crystallizes in the noncentrosymmetric orthorhombic space group, P2₁2₁2₁: (at 296 K) a 7.492(2), b 9.903 (2), c 31.604(9) Å, V 2345(1) ų, and Z = 4. The cation, similar to other structurally characterized biferrocenium salts, adopts a trans-configuration, but, in contrast, possesses no crystallographically imposed symmetry relating the two ferrocenyl environments. Different average Fe-ring distances at the two environments: Fe(1), 2.02(2) and Fe(2), 2.08(2) Å are typical of iron(II) and iron(III) states, respectively, indicating the presence of trapped oxidation states. Interionic contacts are both shorter and more numerous for the iron(III) ferrocenyl fragment than for the iron(II) fragment. Both ferrocenyl units have non-eclipsed ring configurations, with a staggering angle of 6.5(3)° at Fe(1) and 23.5(3)° at Fe(2). The FeBr₄⁻ counterion is tetrahedral and ordered.     

Synthesis,structural characterization,and thermal properties of alkaline (earth) compounds derived from 2,4-dinitroimidazole

Eight alkaline and alkaline-earth compounds derived from 2,4-dinitroimidazole (2,4-HDNI) were synthesized and characterized by elemental analysis, FT-IR, and TG–DSC, of which K(2,4-DNI) (1), Rb(2,4-DNI)(2,4-HDNI)(H₂O)₂ (2), and Ba(2,4-DNI)₂(H₂O)₄ (3) were characterized by single-crystal X-ray diffraction analysis. All the three compounds were crystallized from water, but 1 was an anhydrate. The coordination number in 1 and 3 is 10, but in 2 is 9. The 2,4-DNI adopts either η³, η², or η¹ coordination modes depending on the metal cation. In 3, there is an inversion center located on the metal. Only in 2 does water play an important role for the construction of the structure; in 3 it is a hydrogen bonding participant. TG–DSC analyses of 1 were also performed, and non-isothermal decomposition reaction kinetics were obtained.     

Synthesis, structural characterization, and photophysical properties of palladium and platinum(II) complexes containing 7,8-benzoquinolinate and various phosphine ligands

A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine ligands, namely, [M(bzq)ClL] (L=PPh2H, Pt 1, Pd 2; PPh2CCPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2CCPh)]ClO4 5, [Pt(bzq)(PPh2C(Ph)=C(H)PPh2)]ClO4 6, and [Pt(bzq)(CCPh)(PPh2CCPh)] (7a, 7b), were synthesized. The X-ray crystal structures of 1, 6.CH3COCH3.1/2CH3(CH2)4CH3, and 7b.CH3COCH3 have been determined. In 1, the metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(mu-Cl)]2 with PPh2H and excess of NEt3 leads to the phosphide-bridge platinum dimer [Pt(bzq)(mu-PPh2)]2 8 (X-ray). Moderate pi-pi intermolecular interactions and no evident Pt-Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at high energy due to the intraligand transitions (1IL pi --> pi) and absorptions at lower energy which are attributed to MLCT (5d) pi --> pi (CLambdaN) transition. Platinum complexes show strong luminescence in both solid state and frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined by absorption and emission spectroscopy.     

Synthesis and structural characterization of C(OTeF5)4 and a comparative structural study of the isoelectronic B(OTeF5)4- anion

Tetrakis(pentafluoroorthotellurate)carbon(IV), C(OTeF5)4, was synthesized by reaction of CBr4 with BrOTeF5 in SO2ClF solution at -78 degrees C and was isolated as a colorless, crystalline solid that is room-temperature stable in SO2ClF and in the solid state. Both natural abundance and 99% 13C-enriched C(OTeF5)4 have been characterized in SO2ClF solution by 13C, 19F, and 125Te NMR spectroscopy. In contrast, C(OTeF5)4 undergoes rapid decomposition to O(TeF5)2 and CO2 in CH3CN at 10 degrees C but is stable at -40 degrees C. The X-ray crystal structures of C(OTeF5)4 and [N(CH3)4][B(OTeF5)4] were determined at -30 and -170 degrees C, respectively. The averages of four smaller C/B-O-Te bond angles and O...O contacts and two larger C/B-O-Te bond angles and O...O contacts of C(OTeF5)4 and the isoelectronic B(OTeF5)4- anion are consistent with local S4 symmetry, as predicted by ligand close packing considerations. The existence of three sets of Te-O-C/B-O torsion angles and the energy-minimized geometries of C(OTeF5)4 and B(OTeF5)4- also confirm their local S4 symmetries. The low-temperature, solid-state Raman spectra of 12/13C(OTeF5)4 and B(OTeF5)4- were assigned and compared. The energy-minimized geometries, vibrational frequencies, natural charges, and natural bond orders of both species have been calculated using density functional theory methods. The calculated geometries are in accord with the S4 symmetries assigned for the experimental structures.     

Alkyl complexes of strontium and barium: synthesis and structural characterization of [(Me3Si)2(MeOMe2Si)C]2Sr(THF) and [(Me3Si)2(MeOMe2Si)C]2Ba(MeOCH2CH2OMe)

Metathesis between either SrI2 or BaI2 and 2 equiv of {(Me3Si)2(MeOMe2Si)C}K in THF yields the novel heavier alkali metal dialkyls {(Me3Si)2(MeOMe2Si)C}2M(L) [M(L) = Sr(THF) (2), Ba(DME) (3) (DME = 1,2-dimethoxyethane)] after recrystallization.     

Synthesis,spectroscopic and structural characterization of the first mixed fluoro-bromo group 4 organometallic complex [{Cp*ZrF2Br}4] (Cp* = C5Me5)

[{Cp*ZrF₂Br}₄] is conveniently prepared in high yield from the reaction of [{Cp*ZrF₃}₄] with four equivalents of Me₃SiBr. In contrast the reaction of [{Cp*ZrF₃}₄] with Me₃SiI under identical reaction conditions leads to a mixture of [Cp*ZrI₃] and unreacted [{Cp*ZrF₃}₄]. The crystal structure of [{Cp*ZrF₂Br}₄] has been determined by X-ray diffraction studies. The compound crystallizes in the orthorhombic crystal system [a = 9.325(1), b = 23.483(3), c = 27.016(5) Å, α = β = γ = 90°, space group Ibam, Z = 4]. The tetrameric core structure of [{Cp*ZrF₂Br}₄] contains four zirconium atoms linked by alternating single and triple fluorine bridges. One terminal bromine atom is bonded to each zirconium. ¹H and ¹⁹FNMR spectroscopic data and structural features of the title compound are compared with those for the mixed fluoro-chloro complexes [{Cp*ZrF₂Cl}₄], [{Cp*ZrF₂Cl}₂{Cp*ZrFCl₂}₂] and the trifluoro complex [{Cp*ZrF₃}₄].