Lewis acidic titanium species: the synthesis, structure, bonding and molecular modelling considerations of the complexes Ti(NR2)3Cl (R = Me, Et)

1991 ◽  
Vol 69 (2) ◽  
pp. 357-362 ◽  
Author(s):  
David G. Dick ◽  
Roger Rousseau ◽  
Douglas W. Stephan
Keyword(s):  
Molecular Modelling ◽  
Energy Minimization ◽  
Variable Temperature ◽  
Structural Data ◽  
Steric Effects ◽  
Monoclinic Space Group ◽  
Nmr Studies ◽  
Space Group ◽  
H Nmr ◽  
Multiple Bonding

Reaction of simple amides with TiCl4 affords mixed amido-chloride species Ti(NR2)4−nCln. The trisamide-chloride species Ti(NR2)3Cl can be prepared directly employing three equivalents of amide or by reaction Ti(NR2)4 with TiCl4. The compound Ti(NMe2)3Cl, 1, crystallizes in the trigonal space group [Formula: see text] with a = 11.525(5), c = 14.939(3) Å, Z = 6, and V = 1718(1) Å3. The compound Ti(NEt2)3Cl, 2, crystallizes in the monoclinic space group P21/c, with a = 8.385(2) Å, b = 15.958(2) Å, c = 14.230(4) Å, β = 107.79(1)°, Z = 4, and V = 1813(1) Å3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. The structural data are consistent with Ti—N multiple bonding. Preliminary results of EHMO calculations are consistent with dπ—pπ Ti—N bonding. Attempts to replace the halides with phosphides (LiPR2, R = Me, Et, Ph) led not to the Ti(IV) phosphido species, but rather to redox chemistry yielding Ti(III) amides and P2R4. The barrier to rotation about the Ti—N bonds has been considered. Variable temperature 1H NMR studies reveal that the barrier is small. Extended Hückel total energy minimization calculations have been performed. In addition, MMX calculations of the barrier to Ti—N rotation are reported. The results of these calculations imply that the rotational barrier is dominated by steric effects. Key words: titanium amides, structures, Ti—N bonding

Manganese, molybdenum, and tungsten carbonyl derivatives incorporating the dimethylbis(1-pyrazolyl)gallate ligand, [Me2Ga(N2C3H3)2]−

1981 ◽  
Vol 59 (22) ◽  
pp. 3123-3135 ◽  
Author(s):  
Sharon E. Anslow ◽  
Kenneth S. Chong ◽  
Steven J. Rettig ◽  
Alan Storr ◽  
James Trotter
Keyword(s):  
Mirror Symmetry ◽  
Variable Temperature ◽  
Nmr Studies ◽  
Space Group ◽  
H Nmr ◽  
Carbonyl Derivatives ◽  
Distorted Octahedral Coordination Geometry ◽  
Distorted Octahedral ◽  
Tungsten Carbonyl ◽  
And Tungsten

The synthesis of a number of six-coordinate manganese, molybdenum, and tungsten carbonyl compounds incorporating both the bidentate bispyrazolyl gallate ligand, [Me2Ga(N2C3H3)2]−, and a neutral pyrazole ligand in a facial coordination arrangement are described. Variable temperature 1H nmr studies have revealed interestingly different behaviours in solution for the valence isoelectronic species [Me2Ga(N2C3H3)2](N2C3H4)Mn(CO)3 and [Me2Ga(N2C3H3)2](N2C3H4)Mo(CO)3−. X-ray structural analyses of crystalline samples of the two compounds have been carried out in an effort to shed light on these behavioural differences. Crystals of [Me2Ga(N2C3H3)2](N2C3H4)Mn(CO)3 are monoclinic, a = 31.053(2), b = 8.0503(4), c = 15.8629(8) Å, β = 108.164(2)°, Z = 8, space group C2/c and crystals of [(C2H5)4N]+{[Me2Ga(N2C3H3)2](N2C3H4)Mo(CO)3}− are monoclinic, a = 10.058(1), b = 20.6488(5), c = 13.533(1) Å, β = 93.800(5)°, Z = 4, space group P21/n. Both structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to final R values of 0.028 and 0.023 for 2613 and 4388 observed reflections for the Mn and Mo complexes, respectively. The neutral Mn complex and the complex Mo anion both have approximate mirror symmetry and both metal atoms have trigonally distorted octahedral coordination geometry. Important bond distances (corrected for thermal vibration) are: Mn—N, 2.074(3)–2.086(3), Mn—C, 1.795(4)–1.809(5), Mo—N, 2.291(2)–2.295(2), and Mo—C, 1.918(3)–1.936(3) Å. Although structural differences between these two species do offer plausible explanations for the differences observed in solution, it appears that other factors are more important.

Hydrolysis of chlorophosphine ligands on platinum and palladium. 31P and 195Pt nmr studies and the crystal and molecular structures of cis-[PtCl2(PPh2OH)2]•C4H8O and [Pd2(µ-Cl)2{(P(OEt)2O)2H}2]

1985 ◽  
Vol 63 (11) ◽  
pp. 2949-2957 ◽  
Author(s):  
David Eric Berry ◽  
Kathryn Anne Beveridge ◽  
Gordon William Bushnell ◽  
Keith Roger Dixon
Keyword(s):  
Molecular Structures ◽  
Monoclinic Space Group ◽  
X Ray Diffraction ◽  
Nmr Studies ◽  
Space Group ◽  
X Ray ◽  
H Nmr ◽  
Hydrolysis Products ◽  
Hydrolysis Of ◽  
Controlled Hydrolysis

Controlled hydrolysis of cis-[PtCl2(PPh2Cl)2] gives cis-[PtCl2(PPh2OH)2] which crystallizes as a tetrahydrofuran solvate in the monoclinic space group P21/n, with a = 14.647(3), b = 15.089(3), c = 13.107(2) Å, β = 91.22(3)°. This is the first example of a complex containing a cis-M(PR2OH)2 group to be structurally characterized since further reaction to [Formula: see text] ligand systems is the more usual outcome of such hydrolyses. An example of the latter type, [Pd2(μ-Cl)2-{(P(OEt)2O)2H}2], crystallizes in the monoclinic space group P21/c, a = 9.674(2), b = 20.722(5), c = 8.578(2) Å, β = 92.75(3)°. Complete X-ray diffraction studies are reported for both crystals. Synthesis and 31P{1H} and 195Pt{1H} nmr studies are reported for the complexes [PtCl2(PEt3)(PR2Cl)], R = OEt, Ph, Cy, Et, or Bu′, which have cis stereochemistry except when R = Bu′, and for cis-[PtCl2(PR2Cl)2], R = OEt, Ph, or Et, and also for the hydrolysis products, cis-[PtCl2(PEt3)(PR2OH)], R = OEt or Ph, and cis-[PtCl2(PR2OH)2], R = OEt, Ph, or Et. Analogous products for palladium are generally less stable and more difficult to characterize. The complex of products from hydrolysis of palladium/P(OEt)2Cl compounds is discussed in detail.

Platinum(II) complexes of the tridentate thioether ligands RS(CH2)3S(CH2)3SR (R = Et, iPr, Ph). Structures of [PtCl (iPrS(CH2)3S(CH2)3SiPr)][BF4], [PtI(PhS(CH2)3S(CH2)2SPh)][BF4], and [Pt(PPh3)(iPrS(CH2)3S(CH2)3SiPr)][BF4]2•CH2Cl2

1996 ◽  
Vol 74 (7) ◽  
pp. 1377-1390 ◽  
Author(s):  
Stephen J. Loeb ◽  
James R. Mansfield
Keyword(s):  
Variable Temperature ◽  
Monoclinic Space Group ◽  
Complex Structures ◽  
Triclinic Space Group ◽  
Space Group ◽  
H Nmr ◽  
Racemic Form ◽  
Line Shape Analysis ◽  
Square Planar ◽  
Chloride Ligand

The tridentate thioether ligands RS(CH2)3S(CH2)3SR (L1, R = Et; L2, R = iPr, L3, R = Ph) were synthesized by nucleophilic addition of thiolate, SR−, to the ditosylate TsO(CH2)3S(CH2)3OTs. The complexes [PtX(Ln)][BF4] were prepared by displacement of 1,5-COD from [PtX2(1,5-COD)] (X = Cl, I) in the presence of one equivalent of AgBF4 and one equivalent of thioether ligand. [PtCl(L2)][BF4] crystallized in the monoclinic space group P21/c with a = 10.409(6), b = 14.180(4), c = 13.726(8) Å, β = 104.49(4)°, V = 1961(2) Å3 and Z = 4. The structure refined toR = 5.62% and Rw = 6.86% for 2121 reflections with F02 > 3σ(Fo2). [PtI(L3)][BF4] crystallized in the monoclinic space group P21/n with a = 13.415(4), b = 12.350(5), c = 14.316(5) Å, β = 107.48(3)°, V = 2262(1) Å3 and Z = 4. The structure refined to R = 4.85% and Rw = 6.33% for 2168 reflections with Fo2 > 3σ(Fo2). In both compounds, the thioether ligand acts as a tridentate chelator occupying three of the four sites of the square-planar Pt(II) complex. Variable temperature 13C{1H} NMR verified that there are three possible stereoisomers for these complexes resulting from inversion at sulphur: meso-A, meso-B, and racemic. Thermodynamic parameters were calculated for the interconversion among isomers of [PtCl(L2)][BF4] by a full line-shape analysis. Removal of chloride ligand from [PtCl(L2)][BF4] with Ag+ in the presence of PPh3 yielded the phosphine adduct [Pt(PPh3)(L2)][BF4]2, which crystallized in the triclinic space group [Formula: see text] with a = 13.266(3), b = 11.315(2), c = 13.970(2) Å, α = 106.04(2)°, β = 84.95(2)°, γ = 86.56(2)°, V = 1999.7(7) Å3 and Z = 2. The structure refined to R = 4.22% and Rw = 5.38% for 4493 reflections with Fo2 > 3σ(Fo2). Unlike the two halide complex structures, which crystallized in the meso-B form, [Pt(PPh3)(L2][BF4]2 crystallized in the racemic form. Key words: tridentate thioether ligand, crystal structure, platinum(II) halide, dynamic NMR spectroscopy.

Supramoleküle aus Kronenethern und geminalen Sulfonen: Synthese von vier binären Komplexen und Kristallstruktur von (CH2CH2O)4·2H 2C(SO2C2H5)2/Supramolecules of Crown Ethers with Geminal Sulfones: Synthesis of Four Binary Complexes and Crystal Structure of (CH2CH2O )4·2H2C(SO2C2H5)2

1995 ◽  
Vol 50 (7) ◽  
pp. 1018-1024 ◽  
Author(s):  
Axel Michalides ◽  
Dagmar Henschel ◽  
Armand Blaschette ◽  
Peter G. Jones
Keyword(s):  
Monoclinic Space Group ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Binary Complexes ◽  
Cyclic Polyethers ◽  
Adjacent Unit ◽  
Methylene Group

In a systematic search for supramolecular complexes involving all combinations of the cyclic polyethers 12-crown-4 (12C4), 15-crown-5 (15C 5), 18-crown-6 (18C 6) and dibenzo- 18-crown-6 (DB -18C6), and the geminal di- or trisulfones H2C(SO 2Me)2, H2C (SO2Et)2 and HC (SO2Me)3-n (SO2Et)n (n = 0 -3 ) , only the following four complexes could be isolated and unequivocally characterized by elemental analysis and 1H NMR spectroscopy: [(12C4){H2C (SO2Et)2}2] (3), [(18C6){H2C (S O2Me)2}] (4), [(DB -18C 6){H2C (SO2Et)2}] (5) and [(D B -18C 6)2{HC (SO2Me )(SO2Et)2}3] (6). The structure of 3 (triclinic, space group P1̄) consists of crystallographically centrosymmetric formula units, in which the disulfone molecules are bonded on each side of the ring by two C -H ··· O(crown) interactions originating from the central methylene group (H···O 213 pm) and from the methylene group of one EtSO2 moiety ( H ··· O 237 pm). Formula units related by translation are connected into parallel strands by a third type of reciprocal C -H ···O bond (H ···O 232 pm) between the second H atom of the central methylene group and a sulfonyl oxygen atom of the adjacent unit. The structure of 4 (monoclinic, space group C2/c) showed severe disorder of the crown ether and could not be refined satisfactorily. Compounds 5 and 6 crystallized as long and extremely thin fibres, indicative of linear-polymeric supramolecular structures; single crystals for X-ray crystallography were not available.

Anion-directed assembly of lanthanide coordination polymers with SMMs properties based on a dihydrazone ligand

2018 ◽  
Vol 233 (1) ◽  
pp. 51-59
Author(s):  
Lina Zhang ◽  
Peigao Duan ◽  
Yang Liu ◽  
Jingxian Sun ◽  
Dan Zhao ◽  
...  
Keyword(s):  
Coordination Polymers ◽  
Single Molecule ◽  
Variable Temperature ◽  
Ac Susceptibility ◽  
Directed Assembly ◽  
Magnetization Measurement ◽  
Vital Role ◽  
Diffusion Method ◽  
Monoclinic Space Group ◽  
Space Group

AbstractFour new Ln(III)-based coordination polymers (CPs), [Eu(HL)Cl2(DMF)2]·(H2L) (1), [Dy(HL)Cl2(DMF)2]·(H2L) (2), [Er(HL)Cl2(DMF)(CH3OH)]·(DMF) (3) and [Yb(HL)Cl2(DMF)(H2O)]·(DMF) (4) (H2L=2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine) have been synthesized through the reaction of Ln(III) chloride and H2L by using the vapour diffusion method. Interestingly, Cl−as a template agent plays a vital role in the formation of the target complexes. Single-crystal X-ray diffraction studies indicate that1and2are isostructural and crystallize in triclinic space groupP1̅, while complexes3and4are isostructural and crystallize in monoclinic space groupC2/c. Variable temperature magnetization measurement (χMT–T) demonstrates possible antiferromagnetic interactions in complex2. Alternating-current (ac) susceptibility measurement furthermore indicated frequency dependence for both the in-phase (χ′) and out-of-phase (χ″) components in2, suggesting that there is a slow relaxation behavior of the magnetization, which is typical of single-molecule magnets (SMMs). This is the first time that Ln(III) CPs based on such a dihydrazone ligand has been reported so far.

Chiral "basket handle" binaphthyl porphyrins: synthesis, catalytic epoxidation and NMR conformational studies

2010 ◽  
Vol 14 (07) ◽  
pp. 646-659 ◽  
Author(s):  
Eric Rose ◽  
Emma Gallo ◽  
Nicolas Raoul ◽  
Léa Bouché ◽  
Ariane Pille ◽  
...  
Keyword(s):  
Time Scale ◽  
Room Temperature ◽  
Conformational Equilibrium ◽  
Variable Temperature ◽  
Conformational Exchange ◽  
Iron Catalysts ◽  
Nmr Studies ◽  
Conformational Studies ◽  
H Nmr ◽  
Catalytic Epoxidation

Three "basket handle" porphyrins have been prepared by condensation of tetrakis-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy, -3,3′-dicarbonylchloride, -3,3′-diacetylchloride and -3,3′-dipropanoylchloride. The epoxidation of styrene with the three iron catalysts, obtained after metalation of the free porphyrins, occurs with good yields and moderate ee up to 54%. These porphyrins showed unexpected conformational differences, as revealed by NMR spectroscopy. In particular, variable temperature NMR studies showed that the methoxy group in one of them undergoes intermediate conformational exchange on the 1H NMR time scale at room temperature. Lowering the temperature to -50 °C revealed the presence of four states in slow exchange on the NMR time scale. These results evidence a dynamic conformational equilibrium of the binaphthyl handles that adopt different, asymmetric positions with respect to the porphyrin plane.

scholarly journals Chemie polyfunktioneller Moleküle, 114 [1]. Synthese und Struktur eines ionischen und nichtionischen, cyclischen Carbaphosphazens und eines Cobalt(III)phosphazen-Komplexes / Chemistry of Polyfunctional Molecules, 114 [1]. Synthesis and Structure of an Ionic and Non Ionic Cyclic Carbaphosphazene and of a Cobalt(III)phosphazene Complex

1994 ◽  
Vol 49 (12) ◽  
pp. 1763-1773 ◽  
Author(s):  
Jochen Ellermann ◽  
Jörg Sutter ◽  
Falk A. Knoch ◽  
Matthias Moll ◽  
Walter Bauer
Keyword(s):  
Mass Spectra ◽  
Monoclinic Space Group ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
Lattice Constants ◽  
H Nmr

Reaction of (1) in CH2Cl2 with benzimidazole yields . The salt [4]+BPh4- has been prepared in THF by metathesis of [4]+Cl- with NaBPh4. Deprotonation of the cationic ring in [4]+BPh4- was accomplished using 1,8-diazabicyclo[5.4.01,7]undec-7-ene and resulted in the six-membered carbacyclophosphazene (6). Treating 1 with 8 -hydroxyquinoline in CH2Cl2 yields the octahedral cis-complex = 8-oxyquinolinate group). The com pounds [4]+BPh4-, 6 and 7 are characterized by their IR, Raman, 31P{1H} NMR, 13C{1H} NMR, 1H NMR and mass spectra. Crystals suitable for X-ray structure analyses have been obtained for [4]+BPh4- and 7×0.5 CH2Cl2. The colourless plates of [4]+BPh4- crystallize in the triclinic space group P1̄, with the lattice constants a = 1172.7(3), b = 1326.2(3), c = 1806.1(6) pm; α = 100.79(2), β = 103.71(3), γ = 108.18(2)°. The black blocks of 7×0.5 CH2Cl2 crystallize in the monoclinic space group P 21/c with the lattice constants a = 1159.0(10), b = 2008.9(10), c = 2034.6(12) pm; β = 105.86(5)°.

Coordinated fluoride in rhenium(I) carbonyl complexes

1984 ◽  
Vol 37 (1) ◽  
pp. 35 ◽  
Author(s):  
E Horn ◽  
MR Snow
Keyword(s):  
Hydrogen Bonding ◽  
Least Squares ◽  
Mass Spectra ◽  
Structural Data ◽  
Monoclinic Space Group ◽  
Carbonyl Complexes ◽  
Full Matrix ◽  
Space Group ◽  
Corrected Data ◽  
R Value

Bromide abstraction from the complexes Re(CO)3L2Br (where L = SbPh3 and L2 = bpy, dpe, tmen)* by AgF2H gives the corresponding fluoro compounds Re(CO)3L2F. Mass spectra and structural data show that the fluoride in these complexes is coordinated to the metal. The structures of Re(CO)3(tmen)F and [Re(CO)3(tmen)F]2H.HOBF3 are reported here. Crystals of Re(CO)3(tmen)F are monoclinic, space group P21/c, with a 8.202(2), b 13.115(9), c 12.048(4) � and β 102 24(3)�. A full-matrix least-squares refinement by using the absorption corrected data gave a conventional R value of 0.041. [Re(CO)3(tmen)F]2H.HOBF3 also crystallizes in the space group P21/c. The lattice parameters are: a 17.495(2), b 10.772(2), c 15.447(1) � and β ( 101.409(8)�. The final R value of a blocked least-squares calculation converged at 0.061. In these two complexes the simple Re-F distance is 2.040(4) �, in Re(CO)3(tmen)F. The Re-F distance is increased to 2.236(10)�, as a result of hydrogen bonding between the fluoride and HOBF3 in the latter compound.

Magnetic, Spectral and Structural Aspects of Spin Transitions in Iron(II) Complexes of 2-(Pyrazol-3-yl)pyridine and 3-(Thiazol-2-yl)pyrazole

1999 ◽  
Vol 52 (2) ◽  
pp. 109 ◽  
Author(s):  
Lucia S. Harimanow ◽  
Kristian H. Sugiyarto ◽  
Donald C. Craig ◽  
Marcia L. Scudder ◽  
Harold A. Goodwin
Keyword(s):  
Hydrogen Bonding ◽  
Hysteresis Loop ◽  
Room Temperature ◽  
Thermal Hysteresis ◽  
Structural Data ◽  
Monoclinic Space Group ◽  
Space Group ◽  
Thermal Hysteresis Loop ◽  
Lower Temperature ◽  
Structural Aspects

Tris(ligand)iron(II) complexes of 2-(pyrazol-3-yl)pyridine (3ppH) and 3-(thiazol-2-yl)pyrazole (3tpH) undergo temperature-induced singlet (1A1) ⇔ quintet (5T2) transitions. The transition in [Fe(3ppH)3] [CF3SO3]2.2H2O is continuous and centred above room temperature while that in the anhydrous triflate salt is discontinuous and is centred below room temperature. The latter transition occurs via a thermal hysteresis loop of width 12 K, Tc↓ and Tc↑ being 229 and 241 K, respectively. The displacement of the transition to lower temperature in the anhydrous salt is believed to be associated with the loss of hydrogen bonding involving the uncoordinated pyrazole >NH group and solvate water. In [Fe(3tpH)2(3tp)] [ClO4].2H2O and [Fe(3tpH)2(3tp)] [BF4].2H2O (3tp is the deprotonated ligand) continuous transitions are observed, centred below room temperature. In these instances the displacement is consistent with the intrinsically weaker field of the bidentate system containing two five-membered heterocycles. Structural data were obtained for [Fe(3ppH)3][CF3SO3]2.2H2O, [Fe(3tpH)3] [BF4]2.1·5H2O and [Ni(3tpH)3] [BF4]2.2(3tpH). The average metal–nitrogen distances in the complexes are 1·97, 2·18 and 2·09 Å, severally. The large difference in the distances for the two iron complexes arises from the different ground states: a singlet for the 3ppH complex and a quintet for the 3tpH complex. In all three salts there is extensive hydrogen bonding involving the pyrazole >NH groups, the anions and the solvate molecules. [Fe(3ppH)3] [CF3SO3]2.2H2O: monoclinic, space group P21/c, a 12·33(1), b 24·44(1), c 12·55(1) Å, β 115·27(4)°, Z 4. [Fe(3tpH)3] [BF4]2.1·5H2O: monoclinic, space group C 2/c, a 41·56(2), b 16·418(3), c 18·154(7) Å, β 106·94(2)°, Z 8. [Ni(3tpH)3] [BF4]2.2(3tpH):P bcn, a 14·928(2), b 15·310 (3), c 17·882 (3) Å, Z 4.

Structural Systematics of Metal Acetylide Complexes: X-Ray Studies of Some 'Extended-Chain' Gold σ-Acetylide Complexes

1997 ◽  
Vol 50 (10) ◽  
pp. 991 ◽  
Author(s):  
Ian R. Whittall ◽  
Mark G. Humphrey ◽  
David C. R. Hockless
Keyword(s):  
Ground State ◽  
Structural Data ◽  
Monoclinic Space Group ◽  
Confidence Limits ◽  
X Ray Diffraction ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
Back Bonding ◽  
Ground State Geometry

The structures of Au(4-C≡CC6H4XYC6H4-4′-NO2)(PPh3) (XY = (E )-CH=CH (1), (Z)-CH=CH (2), C≡C (3), N=CH (4)) have been determined by single-crystal X-ray diffraction analyses, refining by full-matrix least-squares analysis. For (1), crystals are triclinic, space group P-1, with a8·847(1), b 17·870(4), c 19·705(3) Å, α116·25(1), β 93·33(1), γ 92·64(2)˚, Z 4, 6747 unique reflections (703 parameters), converging at R 0·025 and Rw 0·029. For (2), crystals are monoclinic, space group P 21/a, with a 10·718(6), b 19·398(5), c14·469(3) Å, β 108·96(2)˚, Z 4, 3295 unique reflections (352 parameters), converging atR 0·040 and Rw 0·034. For (3), crystals are triclinic, space group P-1, with a 10·671(4), b 17·599(7), c 18·220(8) Å, α 116·31(3), β 105·00(4), γ 95·08(4)˚, Z 4, 4828 unique reflections (703 parameters), converging at R 0·043 and Rw 0·030. For (4), crystals are triclinic, space group P-1, with a 8·8314(6), b 17·834(2), c 20·001(2) Å, α 115·249(7), β 90·930(7), γ 94·082(7)˚, Z 4, 4724 unique reflections (703 parameters), converging at R 0·035 and Rw 0·034. Despite the [ligated metal donor]-bridge-[nitro acceptor] composition of these complexes, Au–C and C≡C distances are normal and consistent with minimal allenylidene contribution to the ground-state geometry. Within the 3σ confidence limits, the structural data do not provide evidence for π*-back-bonding in these complexes

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