A photoluminescent copper(I) complex with an exceptionally high Cu(II)/Cu(I) redox potential: [Cu(bfp)2]+ (bfp = 2,9-bis-(trifluoromethyl)-1,10-phenanthroline)

Article abstract of DOI:10.1002/(SICI)1521-3773(19980619)37:11<1556::AID-ANIE1556>3.0.CO;2-W

Unprecedented stabilization of the copper(I) oxidation state is demonstrated for the complex cation [Cu(bfp)₂]⁺ (1) due to the steric and electronic effects of the CF₃ groups (E(1/2)(Cu(II)/Cu(I)) = + 1.55 V vs. SCE). The redox existence range of the copper(I) species is remarkably high at 2.77 V. It is emissive in solution at room temperature and shows great potential as a photocatalyst; in the excited state it is a very potent photooxidant.

Full text of DOI:10.1002/(SICI)1521-3773(19980619)37:11<1556::AID-ANIE1556>3.0.CO;2-W

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ligand charge transfer (MLCT) excited states.[2] Since these
states are best described as copper in the ‡2 oxidation state, it
is believed that these pseudotetrahedral copper(i) complexes
reorganize towards square-planar geometry in the excited
state.[3] Substituents at the 2 and 9 positions reduce the degree
of excited-state distortion,[3, 4] leading to room-temperature
emission for most copper(i) complexes of 2,9-disubstituted-
1,10-phenanthrolines.[5] Photochemical studies of [Cu(N ±
calculations, but parameters were not refined. Methyl and methylene
hydrogen atoms were placed in calculated positions. Hydrogen atoms
were assigned isotropic displacement values based approximately on
the value for the attached atom. The largest peak maximum and
minimum on a final difference electron density map were 0.21 and
0.25 e Š 3. Scattering factors for hydrogen atoms for both 5 and 6
were obtained from Stewart et al.[19] and those for other atoms were
taken from ref. [19]. Programs used in this work include locally
modified versions of the following programs: CARESS (Broach,
Coppens, Becker, and Blessing), peak-profile analysis, Lorentzian and
polarization corrections; ORFLS (Busing, Martin, and Levy), struc-
ture-factor calculation and full-matrix least-squares refinement;
SHELXL (Sheldrick), crystal structure refinement; SHELX86 (Shel-
drick), crystal structure solution; ORTEP (Johnson). Crystallographic
data (excluding structure factors) for the structures reported in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication no. CCDC-101178. Copies of
the data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk).
‡
N)2] complexes (N ± N ˆ 1,10-phenanthroline ligand) with
2,9-dialkyl and 2,9-diaryl substituents have demonstrated that
the steric bulk of the substituents has a profound effect on the
ground-state electrochemistry and the emission properties of
the complexes in solution.[3, 4, 5b,g, 6] Bulkier substituents in-
crease the CuII/CuI redox potential by stabilization of the
copper(i) species, and increase both the lifetimes and energies
of the MLCT excited states.
Metal complexes of electron-deficient ligands are often
studied as catalysts due to their high chemical stability and, in
certain cases, enhanced reactivity.[7] Since copper(i) complexes
have been widely studied in photocatalytic processes,[1b,c, 8] the
effects of electron-withdrawing groups on the photochemistry
of these complexes are of interest. Here we report the first
[12] a) K. Burak, Z. Ciunik, T. Glowiak, J. Chem. Cryst. 1994, 24, 503 ± 506;
b) P. D. Robinson, Acta Crystallogr. Sect. C 1994, 50, 1728 ± 1732.
[13] a) M. L. Greer, H. Sarker, M. E. Mendicino, S. C. Blackstock, J. Am.
Chem. Soc. 1995, 117, 10460 ± 10467; b) R. Glaser, R. K. Murmann,
C. L. Barnes, J. Org. Chem. 1996, 61, 1047 ± 1058, and references
therein.
[14] V. V. Grushin, V. I. Bregadze, V. N. Kalinin, J. Organomet. Chem.
Libr. 1988, 20, 1 ± 68, and references therein.
[15] H. Nakamura, M. Sekido, Y. Yamamoto, J. Med. Chem. 1997, 40,
2825 ± 2830.
[16] a) P. N. Rylander, Catalytic Hydrogenation over Platnium Metals,
Academic Press, New York, 1967, pp. 139Ð157; b) M. Freifelder,
Catalytic Hydrogenation in Organic Synthesis Procedures and Com-
mentary, Wiley, New York, 1978, pp. 53 ± 64.
[17] Accidental overlap of the signals, judged by an HMQC NMR study of
5 in [D6]benzene.
[18] R. F. Stewart, E. R. Davidson, W. T. Simpson, J. Chem. Phys. 1965, 42,
3175 ± 3183.
[19] J. A. Ibers, W. C. Hamilton, The International Tables for X-ray
Crystallography, Vol. IV, Kynoch, Birmingham, 1974.
‡
investigation of the copper(i) complex cation [Cu(bfp)2]
(bfp ˆ 2,9-bis(trifluoromethyl)-1,10-phenanthroline). In com-
‡
parison to previously studied luminescent [Cu(N ± N)2]
complexes, the trifluoromethyl groups dramatically perturb
the electronic structure of the complex, and consequently
enhance the ability of the copper(i) complex to act as a
photooxidant.
The air-stable complex [Cu(bfp)2](PF6) was characterized
by 1H NMR spectroscopy, mass spectrometry, and X-ray
crystallography.[9] An ORTEP view of the cation is shown in
‡
Figure 1. The structure of [Cu(bfp)2] resembles the known
‡
structures of the [Cu(dmp)2] complex (dmp ˆ 2,9-dimethyl-
1,10-phenanthroline).[10] However, there are notable differ-
‡
ences. In the solid state, the [Cu(dmp)2] cation tends to show
variable degrees of distortion from D2d symmetry, which has
A Photoluminescent Copper(i) Complex
with an Exceptionally High Cuii/CuI Redox
‡
Potential: [Cu(bfp)2] (bfp ˆ 2,9-bis-
(trifluoromethyl)-1,10-phenanthroline)**
Mark T. Miller, Peter K. Gantzel, and
Timothy B. Karpishin*
The continued exploration of copper(i) bis(1,10-phenan-
throline) complexes primarily results from their interesting
photophysical properties.[1] In these systems it has been
established that emission originates from low-lying metal-to-
[*] Prof. T. B. Karpishin, M. T. Miller, P. K. Gantzel
Department of Chemistry and Biochemistry
University of California, San Diego
La Jolla, CA 92093-0358 (USA)
Fax: (‡1)619-534-5383
‡
E-mail: tkarpish@ucsd.edu
Figure 1. ORTEP diagram of the complex cation [Cu(bfp)2] . Selected
[**] This work was supported in part by a Hellman Faculty Fellowship
(T.B.K.). We thank Professor Y. Tor for the use of his emission
spectrometer and Professor D. Magde for the use of his laser
equipment.
bond distances [Š] and angles [8]: Cu1 N1A 2.037(6), Cu1 N2A 2.052(6),
Cu1 N1B 2.025(6), Cu1 N2B 2.063(7); N1A-Cu1-N2A 83.3(3), N1B-Cu1-
N1A 134.6(3), N1A-Cu1-N2B 118.4(3), N1B-Cu1-N2A 124.2(3), N2A-
Cu1-N2B 117.0(3), N1B-Cu1-N2B 83.2(3).
1556
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been attributed to crystal packing forces.[11] The primary
distortion usually seen is a flattening of the two ligands
relative to one another (towards a square-planar geometry),
with a dihedral angle of 72 ± 838 between the ligand planes.
However, in the structure of [Cu(bfp)2] the interligand
dihedral angle is 878, closer to 908, to minimize the inter-
radiative decay rates. These results indicate that kr values in
these systems increase as excited-state energies increase,
which is consistent with theory.[16]
Cyclic voltammetry[17] of [Cu(bfp)2](PF6) displays two
reversible waves (both single-electron processes) that are
‡
assigned to a ligand-based redox couple[18] (E1/2
ˆ
1220 mV
actions between the CF3 groups on opposing ligands. In
vs. saturated calomel electrode (SCE); DEp ˆ 70 mV; ipa/ipc ˆ
0.92) and the CuII/CuI couple[2h, 5g, 18] (E1/2 ˆ ‡1550 mV vs.
SCE; DEp ˆ 62 mV; ipa/ipc ˆ 0.93). To the best of our knowl-
edge, this is the highest potential ever measured for a
reversible CuII/CuI couple in a mononuclear copper complex
(Figure 3).[19] The highly efficient electron-withdrawing na-
ture of the CF3 groups combined with their steric bulk result
in a remarkable stabilization of the copper(i) oxidation state
‡
addition, the structure of the complex [Cu(bfp)2] is signifi-
cantly distorted from D2d symmetry with a coordination
geometry best described as distorted trigonal pyramidal
(Figure 1).[12] Unlike what is typically seen with complexes
‡
of [Cu(dmp)2] , there are no intermolecular ligand stacking
interactions in [Cu(bfp)2](PF6).
The absorption and corrected emission spectra of
[Cu(bfp)2](PF6) in dichloromethane at room temperature
are shown in Figure 2. The absorption bands centered at
‡
for [Cu(bfp)2] ; the redox existence range (RER) of the
copper(i) species is 2.77 V. The largest RER value previously
1
‡
462 nm (e462 ˆ 10900 m 1 cm ) are assigned to MLCT tran-
reported for a [Cu(N ± N)2] system is 2.69 V.[5g]
‡
sitions, analogous to those of [Cu(dmp)2] .[2f] The excitation
spectrum measured at 650 nm (not shown) parallels the
absorption spectrum in the range of 400 ± 500 nm. From the
room-temperature emission spectrum, the free energy of the
excited state is estimated to be 2.1 eV[13] (Figure 2).
Figure 3. Cyclic voltammogram (two cycles) of [Cu(bfp)2](PF6) in CH2Cl2.
Conditions: 5mm [Cu(bfp)2](PF6), 0.1m (Bu4N)(PF6), glassy carbon work-
1
ing electrode, scan rate 0.3 Vs
,
internal reference E1/2(ferrocene/
Figure 2. Absorption spectrum and corrected emission spectrum (lex
450 nm) of [Cu(bfp)2](PF6) in CH2Cl2 at room temperature.
ˆ
ferrocenium) ˆ ‡450 mV.
‡
Excited-state lifetimes and quantum yields were deter-
mined at room temperature in deoxygenated dichlorome-
Estimates of the energetics of [Cu(bfp)2] in the excited
‡
state, *[Cu(bfp)2] , reveal the potential use of the complex in
‡
thane. Data for the two well-studied complexes [Cu(dmp)2]
photocatalytic and electron-transfer quenching processes. The
excited-state potentials are E(CuI*/Cu0) ˆ ‡920 mV and
E(CuII/CuI*) ˆ 590 mV (vs. SCE).[20] These data signify that
‡
and [Cu(dpp)2] (dpp ˆ 2,9-diphenyl-1,10-phenanthroline)
provide useful comparisons.[5a,b] The lifetime of the excited
state of [Cu(bfp)2](PF6) was 165 ns, which is approximately
twice that of [Cu(dmp)2](PF6) (t ˆ 83 ns), yet shorter than
that of [Cu(dpp)2](PF6) (t ˆ 243 ns).[14] Significantly, the
‡
*[Cu(bfp)2] is a very potent photooxidant, and also an
‡
effective photoreductant. For *[Cu(bfp)2] to act as a photo-
oxidant however, a significant barrier to reductive quenching
may limit the electron-transfer kinetics. This barrier results
from the high inner-sphere reorganization energy associated
with the repopulation of a ds* orbital.[6, 21] On the other hand,
‡
quantum yield for [Cu(bfp)2] is approximately four times
‡
that for [Cu(dpp)2] , and approximately fourteen times that
‡
‡
for [Cu(dmp)2] .[15] The quantum yield for [Cu(bfp)2] in
‡
dichloromethane is clearly one of the highest ever measured
oxidative quenching of *[Cu(bfp)2] , which involves removal
‡
for a [Cu(N ± N)2] system, although the uncertainties asso-
of an electron from a ligand orbital with primarily p*
character, is expected to occur with much faster kinet-
ics.[2h, 21, 22] In addition, oxidative quenching with viologens
can be anticipated to occur with very high cage-escape
yields.[2h] Thus, a photocatalytic cycle that generates the
highly oxidizing [Cu(bfp)2]2‡ complex in the ground state can
ciated with the determination of quantum yield preclude
absolute ranking.[5g] Among the three complexes, the trend
observed for the quantum yields (dmp < dpp < bfp) is also the
trend observed for the energies of the associated excited
states.[13] Examination of the nonradiative (knr ˆ (1 f)/t)
and radiative (kr ˆ f/t) decay rate constants reveals that the
trend in quantum yields is primarily due to changes in the
‡
be envisioned. Investigations of [Cu(bfp)2] in photocatalytic
processes are in progress.
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Experimental Section
4.0s(F)); Lp correction, SHELXTL refinement: 475 parameters, H
atoms included at calculated positions (C H ˆ 0.96 Š), R ˆ 0.0589,
Rw ˆ 0.0681, refined against F, min./max. residual electron density ˆ
0.781/ 0.269 eŠ 3. Further details on the crystal structure investiga-
tion may be obtained from the Fachinformationszentrum Karlsruhe,
D-76344 Eggenstein-Leopoldshafen, Germany (fax: (‡49)7247-808-
666; e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository
number CSD-408014.
[Cu(dmp)2](PF6) and [Cu(dpp)2](PF6) were prepared according to refer-
ence [2h].
[Cu(bfp)2](PF6): Ligand bfp[24] (2 equiv) is added to [Cu(CH3CN)4](PF6)[23]
(1 equiv) in deoxygenated CH2Cl2, and the solution is taken to dryness.
Recrystallization (CH2Cl2/Et2O) affords bright orange crystals in 76%
yield. 1H NMR (CDCl3): d ˆ 8.35 (d, H4,7), 8.42 (s, H5,6), 9.00 (d, H3,8); FAB-
‡
[10] The Cambridge Structural Database reference codes for the crystal
MS: m/z (%): 695 (100) [M ].
‡
structures of [Cu(dmp)2] are CABKEV, DAWKOB, DMPNCU,
DMPNCU01, DMPRCU, MPHCUN, MPHCUN01.
[11] a) J. F. Dobson, B. E. Green, P. C. Healy, C. H. L. Kennard, C.
Pakawatchai, A. H. White, Aust. J. Chem. 1984, 37, 649 ± 659; b) K. V.
Goodwin, D. R. McMillin, W. R. Robinson, Inorg. Chem. 1986, 25,
2033 ± 2036.
Received: November 28, 1997 [Z11209IE]
German version: Angew. Chem. 1998, 110, 1659 ± 1661
Keywords: copper ´ cyclic voltammetry ´ electrochemistry ´
N ligands ´ photochemistry
[12] Distorted trigonal-pyramidal geometry is also observed in the
‡
structure of [Cu(ocp)2] (ocp ˆ octachloro-1,10-phenanthroline): C.
Titze, W. Kaim, Z. Naturforsch. B 1996, 51, 981 ± 988.
[13] The excited-state energy, DGES, is estimated ( Æ 5%) with a tangent
drawn on the high-energy side of the emission band: D. R. Arnold,
N. C. Baird, J. R. Bolton, J. C. D. Brand, P. W. M. Jacobs, P. DeMayo,
W. R. Ware, Photochemistry: An Introduction, Academic Press, New
York, 1974.
[1] a) D. R. McMillin, J. R. Kirchhoff, K. V. Goodwin, Coord. Chem. Rev.
Â
1985, 64, 83 ± 92; b) C. Kutal, ibid. 1990, 99, 213 ± 252; c) O. Horvath,
ibid. 1994, 135/136, 303 ± 324.
[2] a) J. R. Kirchhoff, R. E. Gamache, Jr., M. W. Blaskie, A. A. Del Pag-
gio, R. K. Lengel, D. R. McMillin, Inorg. Chem. 1983, 22, 2380 ± 2384;
b) J. J. McGarvey, S. E. J. Bell, J. N. Bechara, ibid. 1986, 25, 4325 ±
4327; c) C. E. A. Palmer, D. R. McMillin, C. Kirmaier, D. Holten, ibid.
1987, 26, 3167 ± 3170; d) J. J. McGarvey, S. E. J. Bell, K. C. Gordon,
ibid. 1988, 27, 4003 ± 4006; e) W. L. Parker, G. A. Crosby, J. Phys.
Chem. 1989, 93, 5692 ± 5696; f) R. M. Everly, D. R. McMillin, ibid.
1991, 95, 9071 ± 9075; g) N. Armaroli, M. A. J. Rodgers, P. Ceroni, V.
Balzani, C. O. Dietrich-Buchecker, J.-M. Kern, A. Bailal, J.-P.
Sauvage, Chem. Phys. Lett. 1995, 241, 555 ± 558; h) M. Ruthkosky,
F. N. Castellano, G. J. Meyer, Inorg. Chem. 1996, 35, 6406 ± 6412.
[3] R. M. Everly, R. Ziessel, J. Suffert, D. R. McMillin, Inorg. Chem. 1991,
30, 559 ± 561.
[14] Lifetimes of the exicted states ( Æ 5%) were measured in deoxygen-
ated CH2Cl2 (at concentrations of 50 Æ 5mm) at several wavelengths
‡
with excitation at 445 nm. The
t
values for [Cu(dmp)2] and
[Cu(dpp)2] are in good agreement with literature values.[2h, 4, 6]
[15] Quantum yields ( Æ 20%) were determined from the corrected
emission spectra in deoxygenated CH2Cl2 with [Ru(bpy)3](PF6)2
(bpy ˆ 2,2'-bipyridine) as the standard (f ˆ 0.042 in H2O): J. V.
‡
Caspar, T. J. Meyer, J. Am. Chem. Soc. 1983, 105, 5583 ± 5590. For
[Cu(bfp)2](PF6) f ˆ 3.3  10 3 and for [Cu(dpp)2](PF6) f ˆ 8.7  10
.
4
The quantum yield for [Cu(dmp)2](PF6) has been reported as f ˆ
4
[2h]
2.3 Â 10
.
[16] T. J. Meyer, Pure Appl. Chem. 1986, 58, 1193 ± 1206.
[17] See Figure 3 for experimental conditions.
[4] A. K. Ichinaga, J. R. Kirchhoff, D. R. McMillin, C. O. Dietrich-
Buchecker, P. A. Marnot, J.-P. Sauvage, Inorg. Chem. 1987, 26,
4290 ± 4292.
[18] P. Federlin, J.-M. Kern, A. Rastegar, C. Dietrich-Buchecker, P. A.
Marnot, J.-P. Sauvage, New J. Chem. 1990, 14, 9 ± 12.
[5] a) M. W. Blaskie, D. R. McMillin, Inorg. Chem. 1980, 19, 3519 ± 3522;
b) C. O. Dietrich-Buchecker, P. A. Marnot, J.-P. Sauvage, J. R.
Kirchhoff, D. R. McMillin, J. Chem. Soc. Chem. Commun. 1983,
513 ± 515; c) N. Armaroli, V. Balzani, F. Barigelletti, L. De Cola, J.-P.
Sauvage, C. Hemmert, J. Am. Chem. Soc. 1991, 113, 4033 ± 4035; d) N.
Armaroli, L. De Cola, V. Balzani, J.-P. Sauvage, C. O. Dietrich-
Buchecker, J.-M. Kern, A. Bailal, J. Chem. Soc. Dalton Trans. 1993,
3241 ± 3247; e) C. O. Dietrich-Buchecker, J.-F. Nierengarten, J.-P.
Sauvage, N. Armaroli, V. Balzani, L. De Cola, J. Am. Chem. Soc. 1993,
115, 11237 ± 11244; f) N. Armaroli, V. Balzani, F. Barigelletti, L.
De Cola, L. Flamigni, J.-P. Sauvage, C. Hemmert, ibid. 1994, 116,
5211 ± 5217; g) M. K. Eggleston, D. R. McMillin, K. S. Koenig, A. J.
Pallenberg, Inorg. Chem. 1997, 36, 172 ± 176; h) M. K. Eggleston, P. E.
Fanwick, A. J. Pallenberg, D. R. McMillin, ibid. 1997, 36, 4007 ± 4010.
[6] A. K. I. Gushurst, D. R. McMillin, C. O. Dietrich-Buchecker, J.-P.
Sauvage, Inorg. Chem. 1989, 28, 4070 ± 4072.
[19] The potential of the CuII/CuI couple in the nonluminescent complex
‡
cation [Cu(ocp)2] (ocp ˆ octachloro-1,10-phenantroline) has been
‡
reported to be ‡1040 mV vs. ferrocenium/ferrocene (Fc /Fc) in
‡
‡
CH2Cl2.[12] Versus Fc /Fc) in CH2Cl2, the [Cu(bfp)2]2‡/[Cu(bfp)2]
couple is ‡1100 mV. For other high-potential Cu complexes with N
ligands, see refs. [5g, 18] and a) B. R. James, R. J. P. Williams, J. Chem.
Soc. 1961, 2007 ± 2019; b) T. N. Sorrell, D. L. Jameson, Inorg. Chem.
1982, 21, 1014 ± 1019; c) D. Datta, A. Chakravorty, ibid. 1983, 22,
1085 ± 1090; d) E. Müller, C. Piguet, G. Bernardinelli, A. F. Williams,
ibid. 1988, 27, 849 ± 855; e) S. M. Carrier, C. E. Ruggiero, R. P. Houser,
W. B. Tolman, ibid. 1993, 32, 4889 ± 4899; f) J. McMaster, R. L.
Beddoes, D. Collison, D. R. Eardley, M. Helliwell, C. D. Garner,
Chem. Eur. J. 1996, 2, 685 ± 693.
[20] E(CuI*/Cu0) ˆ E(CuI/Cu0) ‡ DGES; E(CuII/CuI*) ˆ E(CuII/CuI)
DGES: C. R. Bock, J. A. Connor, A. R. Gutierrez, T. J. Meyer, D. G.
Whitten, B. P. Sullivan, J. K. Nagle, J. Am. Chem. Soc. 1979, 101,
4815 ± 4824. The value of DGES is estimated to be 2.14 Æ 0.11 eV.[13]
[21] K. L. Cunningham, C. R. Hecker, D. R. McMillin, Inorg. Chim. Acta
1996, 242, 143 ± 147.
[22] R. E. Gamache, Jr., R. A. Rader, D. R. McMillin, J. Am. Chem. Soc.
1985, 107, 1141 ± 1146.
[23] G. J. Kubas, Inorg. Synth. 1979, 19, 90 ± 91.
[7] a) P. E. Ellis, Jr., J. E. Lyons, Coord. Chem. Rev. 1990, 105, 181 ± 193;
b) T. G. Traylor, K. W. Hill, W.-P. Fann, S. Tsuchiya, B. E. Dunlap, J.
Am. Chem. Soc. 1992, 114, 1308 ± 1312; c) M. W. Grinstaff, M. G. Hill,
J. A. Labinger, H. B. Gray, Science 1994, 264, 1311 ± 1313.
[8] a) A. Edel, P. A. Marnot, J.-P. Sauvage, Nouv. J. Chim. 1984, 8, 495 ±
498; b) S. Sakaki, G. Koga, F. Sato, K. Ohkubo, J. Chem. Soc. Dalton
Trans. 1985, 1959 ± 1962; c) S. Sakaki, G. Koga, K. Ohkubo, Inorg.
Chem. 1986, 25, 2330 ± 2333; d) J.-M. Kern, J.-P Sauvage, J. Chem. Soc.
Chem. Commun. 1987, 546-548; e) S. Sakaki, G. Koga, S. Hinokuma, S.
Hashimoto, K. Ohkubo, Inorg. Chem. 1987, 26, 1817 ± 1819; f) N.
Negishi, M. Matsuoka, H. Yamashita, M. Anpo, J. Phys. Chem. 1993,
97, 5211 ± 5212; g) F. Franceschi, M. Guardigli, E. Solari, C. Floriani,
A. Chiesi-Villa, C. Rizzoli, Inorg. Chem. 1997, 36, 4099 ± 4107; h) J.
Sykora, Coord. Chem. Rev. 1997, 159, 95 ± 108.
[24] R. H. Beer, J. Jimenez, R. S. Drago, J. Org. Chem. 1993, 58, 1746 ±
1747.
[9] Crystal data: 1.0 Â 0.5 Â 0.2 mm3, orthorhombic, space group P212121,
a ˆ 12.551(5), b ˆ 13.673(5), c ˆ 17.910(5) Š, Vˆ 3074(2) Š3, Z ˆ 4,
1calcd ˆ 1.817gcm 3, 2qmax ˆ 558, l(MoKa) ˆ 0.71073 Š, w collection,
293 K; of 4229 independent reflections, 2572 were observed (F >
1558
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Angew. Chem. Int. Ed. 1998, 37, No. 11