(433 mg, 90%) was obtained as colourless crystals by layering
the resulting solution with diethyl ether (20 cm3). M.p. 299–
300 ЊC (decomp.) (Found: C, 60.78; H, 4.43; Ag, 7.70. C72H60-
1
AgAs4BF4 requires C, 60.91; H, 4.22; Ag, 7.60%). NMR: H
(CDCl3) δ 7.35 (4 H, t, JH H = 7.32, para-Ph), 7.07 (8 H, t,
JH H = 7.7, meta-Ph) and 7.01 (8 H, d, JH H = 7.0 Hz, ortho-Ph).
13C-{1H} (CDCl3) δ 134.78 (s, ipso-C), 133.28 (s, para-C),
129.82 (s, meta-C) and 129.26 (s, ortho-C).
Tetrakis(triphenylarsine)gold(I) tetrafluoroborate, [Au(As-
Ph3)4]BF4. A solution of AgBF4 (32.6 mg, 0.16 mmol) in tetra-
hydrofuran (thf) (5 cm3) was added with stirring to a clear
solution of [Au(AsPh3)Cl] (90 mg, 0.16 mmol) in dichloro-
methane (10 cm3) and stirring was continued for 15 min at room
temperature. A solution of AsPh3 (153 mg, 0.50 mmol) in
dichloromethane (10 cm3) was then added to the resulting reac-
tion mixture and stirred at ambient temperature for 3 h. Separ-
ation of precipitated AgCl by filtration, followed by removal of
volatiles under reduced pressure (25 ЊC, 0.8 Torr ≈ 106.6 Pa)
afforded the product (237 mg, 95%). The product was crystal-
lised by dissolving in dichloromethane and layering with diethyl
ether. M.p. 268–269 ЊC (decomp.) [Found: C, 57.07; H, 4.06;
Au, 13.10. The compound contains no significant amounts of
silver (as determined by AAS). C72H60As4AuBF4 requires: C,
57.33; H, 3.98; Au, 13.06%]. NMR: 1H (CDCl3) δ 7.39 (4 H, t,
JH H = 7.5, para-Ph), 7.15 (8 H, t, JH H = 7.5, meta-Ph) and 7.06
(8 H, d, JH H = 7.3 Hz, ortho-Ph). 13C-{1H } (CDCl3) δ 135.01 (s,
ipso-C), 133.09 (s, para-C), 130.30 (s, meta-C) and 129.38 (s,
ortho-C).
Fig. 2 Structure of the cation [Au(AsPh3)4]ϩ in complex 2 (ORTEP,
50% probability ellipsoids; phenyl hydrogen atoms omitted for clarity).
Selected bond lengths (Å) and angles (Њ): Au᎐As(1) 2.5663(10), Au᎐As
2.5882(6); As᎐Au᎐As(1) 109.36(2), As᎐Au᎐AsЈ 109.58(2)
r(As) = 1.20 Å for four-co-ordinate arsenic as the presently
accepted value,19 the covalent radius of four-co-ordinate gold()
(1.366 Å) is thus found to be ca. 6% smaller than the covalent
radius of four-co-ordinate silver() (1.455 Å).
This result agrees well with the trend observed in two- and
three-co-ordinate complexes (Introduction), which clearly indi-
cates that silver is the larger of the two metals, and confirms the
data of pertinent calculations.20,21
In the absence of structural data of an isomorphous copper()
arsenic compound, no direct comparison of the radii of all
three coinage metals can be made. The data of several pairs of
Cu/Ag compounds with other ligands5–7,9 leave no doubt, how-
ever, that copper() is the smallest of the coinage metals also in a
four-co-ordinate environment. The covalent radius for CuI is
estimated to be 1.29 Å. With this entry, the radii of the unival-
ent Group 11 metals should be tabulated in reference treatises
as: (a) two-co-ordinate:2 Cu: 1.13, Ag: 1.33, Au: 1.25 Å. (b)
four-co-ordinate: Cu: 1.29, Ag: 1.46, Au: 1.37 Å. These values
are based here on currently accepted covalent radii of four-co-
ordinated PIII (1.11 Å) and AsIII (1.20 Å), but similar data are
also found for complexes with isocyanide22 or ketimine lig-
ands,23 where carbon or nitrogen atoms are the donor sites,
respectively.
Crystallography
Suitable crystals of the compounds were sealed into glass capil-
laries and used for measurement of precise cell constants and
intensity data collection. During data collection, three standard
reflections were measured periodically as a general check of
crystal and instrument stability. No significant changes were
observed for either compound. Diffraction intensities were cor-
rected for Lorentz-polarization and absorption effects
(empirically). The structures were solved by direct methods and
refined by full-matrix least-squares calculations25 against F 2.
The thermal motion of all non-hydrogen atoms was treated
anisotropically. All hydrogen atoms were calculated in idealized
positions and allowed to ride on their corresponding carbon
atom. Their isotropic thermal parameters were tied to that of
the adjacent carbon atom by a factor of 1.5. The boron atoms
(s.o.f. 0.17) of the tetrafluoroborate anions are located at
¯
centres of 3 symmetry and the anions are therefore crystallo-
graphically disordered. The cation in the silver compound is
disordered in two positions with very different site occupation
factors (s.o.f. 0.93 and 0.07, respectively). The silver atom shows
no sign of disorder (s.o.f. 1). For the molecule with the low s.o.f.
only the arsenic atoms could be found and successfully refined.
Important interatomic distances and angles are given in the
corresponding figure captions. Experimental details are sum-
marized in Table 1.
Experimental
Stringent precautions were taken to exclude moisture from the
solvents and reactants, as well as from the glassware employed
throughout the investigation. All experiments were carried out
under a purified nitrogen atmosphere.
The compound [Au(AsPh3)Cl] was prepared by following the
literature procedure.24 Other starting materials, AsPh3 and
AgBF4, were commercially available.
CCDC reference number 186/627.
Proton (399.8 MHz) and 13C-{1H} (100.5 MHz) NMR
spectra were recorded on a JEOL GX 400 Fourier-transform
NMR spectrometer using SiMe4 as internal standard. Micro-
analyses of the compounds were performed in-house by com-
bustion and atomic absorption spectroscopic (AAS) techniques.
Acknowledgements
This work was supported by Deutsche Forschungsgemeinschaft
and Fonds der Chemischen Industrie. U. M. T. is grateful to the
Alexander von Humboldt Foundation for a research fellowship.
Support by Degussa AG and Heraeus GmbH through the
donation of chemicals is acknowledged. Mr. J. Riede is thanked
for collecting the X-ray data sets.
Preparations
Tetrakis(triphenylarsine)silver(I) tetrafluoroborate, [Ag(As-
Ph3)4]BF4. To a suspension of AgBF4 (66 mg, 0.34 mmol) in
dichloromethane (20 cm3), AsPh3 (415 mg, 1.36 mmol) was
added and the reaction mixture was stirred for 3 h. After remov-
ing 10 cm3 of dichloromethane under vacuum, the product
References
1 N. Kaltsoyannis, J. Chem. Soc., Dalton Trans., 1997, 1 and refs.
therein.
J. Chem. Soc., Dalton Trans., 1997, Pages 2865–2868
2867
Tripathi, Upendra M.
