Synthesis and Crystal Structure of a trans-Diaquabis(amidato) Complex of Platinum(II)

Full text of DOI:10.1021/ic951014m

Inorg. Chem. 1996, 35, 1715-1717
Table 1. Crystallographic Data for Compound 5‚1/3H2O
1715
Synthesis and Crystal Structure of a
trans-Diaquabis(amidato) Complex of
Platinum(II)
mol formula
mol wt
C10H24N2O4Pt‚1/3H2O
437.36
cryst syst
trigonal
space group
radiation (λ, Å)
R3h
graphite-monochromated
Mo KR (0.71073)
Francesco P. Intini,‡ Maurizio Lanfranchi,†
Giovanni Natile,*,‡ Concetta Pacifico,‡ and
Antonio Tiripicchio†
a, Å
R, deg
V, Å3
Z
12.752(2)
114.96(2)
1165(1)
3
1.871
634
Dipartimento Farmaco-Chimico, Universita` di Bari, Via E.
Orabona 4, I-70125 Bari, Italy, and Dipartimento di Chimica
Generale ed Inorganica, Chimica Analitica e Chimica Fisica,
Universita` di Parma and Centro di Studio per la Strutturistica
Diffrattometrica del CNR, Viale delle Scienze 78,
I-43100 Parma, Italy
D
calcd, g cm-3
F(000)
cryst dimens, mm
linear abs, cm-1
Ra
0.17 × 0.23 × 0.27
90.43
0.0257
0.0314
b
Rw
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
ReceiVed August 4, 1995
Experimental Section
Introduction
Starting Materials. Commercial reagent grade chemicals were used
without further purification. The complexes trans-[PtCl2{HNdC-
(OH)R}2] (R ) Me, 1; But, 2, and Ph, 3) were prepared by hydrolysis
of the corresponding nitriles by the reported procedures.11
Platinum(II) complexes with terminal aqua and/or hydroxo
groups are generally assumed to occur in aqueous solution.1-3
Moreover hydrolysis of the first chloro ligand appears to be
the rate-limiting step in the complexation to DNA of dichlorobis-
(amine)platinum complexes which are of particular interest
because of their remarkable antitumor activity.4
Preparation of Complexes. trans-[Pt{HNdC(O)R}2(H2O)2] (R
) Me, 4; But, 5, and Ph, 6). Trans-[PtCl2{HNdC(OH)R}2] (1 mmol),
suspended in 10 mL of water, was treated with KOH (0.6 g, 10.7 mmol).
The reaction mixture was stirred for 12 h at 45 °C and then filtered to
obtain a clear solution. The solvent was evaporated under reduced
pressure and the solid residue was treated with absolute ethanol; the
resulting solution was filtered, to separate KCl, the solvent was
evaporated and the residue, containing the complex K2{trans-[Pt(OH)2-
{HNdC(O)R}2]}, was washed carefully with pentane and dried (yield
80%). The compound (0.3 g), dissolved in 1 mL of water, was treated
with HNO3 1 N at 0 °C until neutral pH, and a white precipitate formed
that was collected by filtration of the mother liquor, washed with water,
and dried. Yield: 70%. Anal. Calcd for C4H12N2O4Pt (4): C, 13.8;
H, 3.5; N, 8.1. Found: C, 13.5; H, 3.5; N, 8.1. Calcd for C10H24N2O4-
Pt (5): C, 27.8; H, 5.6; N, 6.5. Found: C, 27.8; H, 5.6; N, 6.5. Calcd
for C14H16N2O4Pt (6): C, 35.7; H, 3.4; N, 5.9. Found: C, 36.0; H,
3.4; N, 5.9.
Physical Measurements. IR spectra in the range 4000-400 cm-1
were recorded as KBr pellets; spectra in the range 400-200 cm-1 were
recorded as polythene pellets on Perkin-Elmer 283 and FT 1600
spectrophotometers. 1H NMR spectra were obtained with Varian XL
200 and Bruker AM 300 spectrometers. The pKa of the amide ligands
in 1 were determined according to the method of Albert and Serjeant
in aqueous solution in the presence of 10-2 M KCl to suppress
solvolysis; pH measurements were performed with a CRISON micropH
2002.15
X-ray Crystal Structure Determination of trans-[Pt{HNdC(O)-
But}2(H2O)2]‚1/3H2O (5‚1/3H2O). Crystals of 5 suitable for X-ray
diffraction analysis were grown from methanol/water. The crystal-
lographic data are summarized in Table 1. Data were collected at room
temperature on a Philips PW 1100 single-crystal diffractometer using
graphite-monochromated Mo KR radiation and the ω/2θ scan mode.
All reflections with θ in the range 3-27° were measured; of 1715
independent reflections, 1539, having I > 2σ(I), were considered
observed and used in the analysis. The individual profiles have been
analyzed according to Lehmann and Larsen.16 The intensity of one
standard reflection was measured after 50 reflections as a general check
on crystal and instrument stability; no significant change in the measured
intensities was observed during the data collection. A correction for
absorption was applied (maximum and minimum values for the
transmission factors were 1.000 and 0.742.17 Only the observed
reflections were used in the structure solution and refinement.
Only a few crystallographic studies of compounds containing
platinum(II) or palladium(II) complexes with one water molecule
coordinated directly to the metal ion have been published.5-8
In addition to this an X-ray absorption edge and EXAFS study
has been performed on the tetraaqua cation [Pt(H2O)4]2+ 9
.
In the course of our systematic studies on complexes of
platinum with amides10,11 and iminoethers12,13 which are related
to platinum-ammine complexes and are of particular interest
because of the remarkable antitumor activity of some of them
with features that violate the “classical” structure-activity
relationships,14 we have obtained crystals of trans-[Pt{HNdC-
(O)But}2(H2O)2]‚1/3H2O in which two amidato ligands and two
water molecules are coordinated to platinum.
This appears to be the first diaquaplatinum(II) species to have
been structurally characterized.
‡ Universita` di Bari. Fax (39) 80 544 2724.
† Universita` di Parma. Fax (39) 521 905 557.
(1) Hartley, F. R. The Chemistry of Platinum and Palladium; Wiley: New
York, 1973; p 169 and references therein.
(2) Elding, L. I. Inorg. Chim. Acta 1978, 28, 255.
(3) Lim, M. C.; Martin, R. B. J. Inorg. Nucl. Chem. 1976, 38, 1911.
(4) Prestayko, A. W. In Cis-platinsCurrent Status and New DeVelop-
ments; Crooke, S. T., Carter, S. K., Eds.; Academic Press: New York
1980, pp 1-527.
(5) Britten, J. F.; Lippert, B.; Lock, C. J. L.; Pilon, P. Inorg. Chem. 1982,
21, 1936.
(6) Meinema, H. A.; Verbeek, F.; Marsman, J. W.; Bulten, E. J.;
Dabrowiak, J. C.; Krishnan, B. S.; Spek, A. L. Inorg. Chim. Acta 1986,
114, 127.
(7) Rochon, F. D.; Melanson, R. Inorg. Chem. 1987, 26, 989.
(8) Castan, P.; Jaud, J.; Wimmer, S.; Wimmer, F. J. Chem. Soc., Dalton
Trans. 1991, 1155.
(9) Hellquist, B.; Bengtsson, L. A.; Holmberg, B.; Hedman, B.; Persson,
I.; Elding, L. I. Acta Chem. Scand. 1991, 45, 449.
(10) Cini, R.; Fanizzi, F. P.; Intini, F. P.; Natile, G. J. Am. Chem. Soc.
1991, 113, 7807.
(11) Cini, R.; Fanizzi, F. P.; Intini, F. P.; Maresca, L.; Natile, G. J. Am.
Chem. Soc. 1993, 115, 5123.
(12) Cini, R.; Caputo, P. A.; Intini, F. P.; Natile, G. Inorg. Chem. 1995,
34, 1130.
(13) Fanizzi, F. P.; Intini, F. P.; Natile, G. J. Chem. Soc., Dalton Trans.
1989, 947.
(14) Coluccia, M.; Nassi, A.; Loseto, F.; Boccarelli, A.; Mariggio`, M. A.;
Giordano, D.; Intini, F. P.; Caputo, P.; Natile, G. J. Med. Chem. 1993,
36, 510.
(15) Albert, A.; Serjeant, E. P. Ionization Constants of Acids and Bases;
Methuen: London, 1962; pp 1-42.
(16) Lehmann, M. S.; Larsen, F. K. Acta Crystallogr., Sect. A 1974, 30,
580.
0020-1669/96/1335-1715$12.00/0 © 1996 American Chemical Society

1716 Inorganic Chemistry, Vol. 35, No. 6, 1996
Notes
Table 2. Atomic Coordinates (×104) and Equivalent Isotropic
Thermal Parameters (Å2 × 104) Defined as One-Third of the Trace
of the Orthogonalized Uij Tensor, for the Non-Hydrogen Atoms of
the Compound 5‚1/3H2O
atom
x/a
y/b
z/c
U
Pt
5000
0
5000
373(3)
552(36)
694(43)
502(37)
507(41)
719(58)
1139(106)
1434(138)
1550(107)
2270(88)a
O(1)
O(2)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
O(3)
4200(4)
2013(5)
3497(5)
2318(6)
1291(7)
1469(13)
1841(14)
-576(11)
0
-18(4)
6065(4)
3927(5)
3395(5)
3098(6)
1794(7)
2643(11)
970(11)
489(14)
0
-3154(4)
-2493(4)
-3600(5)
-5465(6)
-6001(9)
-5809(8)
-6476(11)
0
Figure 1. Perspective view of he molecular structure of the complex
trans-[Pt{HNdC(O)But}2(H2O)2] showing the atomic numbering scheme.
The thermal ellipsoids are drawn at the 30% probability level.
5.8, respectively. Values in the same range were found for other
a Isotropic Thermal Parameter (Å2 × 104).
amide complexes such as [Co(NH3)5{HNdC(OH)Me}]3+ and
[Pt(H2NCH2CH2NHCH2CH2NH2){HNdC(OH)Me}]2+ 22,23
.
The structure was solved by Patterson and Fourier methods and
refined by full-matrix least-squares methods first with isotropic and
then with anisotropic thermal parameters in the last cycles for all the
non hydrogen atoms, excepting for the water of crystallization, lying
on the 3h symmetry site. The hydrogen atoms of the coordinated water
molecules and of the amidato groups were found in the final ∆F map
and refined isotropically, those of the But group were placed at their
geometrically calculated positions (C-H ) 0.96 Å) and refined “riding”
on the corresponding carbon atoms, whereas those of the water of
crystallization were not introduced being disordered. The final cycles
of refinement were carried out on the basis of 81 variables; after the
last cycles, no parameters shifted by more than 0.85 esd. The biggest
remaining peak in the final difference map was equivalent to about
0.37 e/Å3. In the final cycles of refinement a weighting scheme, w )
Deprotonation of the N-coordinated iminol ligands could be
favored by the delocalization of the electron charge accumulated
on the oxygen upon the N‚ ‚C‚ ‚O moiety, X-ray data support
this conclusion (Vide infra). O-bonded amides have a much
lower acidity, with a pKa of 11.6 as compared to 3.0.23
The region about 1600 cm-1 was very diagnostic for
distinguishing between amide and amidato complexes.24,25 The
amide complexes 1-3 were characterized by having intense IR
absorption bands above 1600 cm-1 (at 1645, 1630, and 1630
cm-1 for 1, 2 and 3, respectively; CH2Cl-CH2Cl solution). In
contrast, the corresponding amidato species 4-6 gave intense
IR absorption bands below 1600 cm-1 (at 1570, 1560, and 1550
cm-1 for 4, 5, and 6, respectively; KBr pellets). Both type of
complexes gave rather sharp and intense bands in the region
between 3300 and 3400 cm-1 assignable to N-H stretching
(at 3330, 3350, and 3340 cm-1 for 1, 2, and 3, respectively,
CH2Cl-CH2Cl solution; at 3340, 3400, and 3380 cm-1 for 4,
5, and 6, respectively, KBr pellets). Amide complexes gave
also rather broad and intense bands in the region between 3000
and 3100 cm-1 assignable to O-H stretching (at 3040, 3070,
and 3060 cm-1 for 1, 2, and 3, respectively, CH2Cl-CH2Cl
solution). The low solubility of the diaquabisamidato species
prevented a NMR study of these compounds.
2
1/[σ2(Fo) + gFo ], was used with g ) 0.0024. The atomic scattering
factors, corrected for the real and imaginary parts of anomalous
dispersion, were taken from ref 18.
All calculations were carried out on the GOULD POWERNODE
6040 and ENCORE 91 computers of the Centro di Studio per la
Strutturistica Diffrattometrica del CNR, Parma, using the SHELX-76
and SHELXS-86 systems of crystallographic computer programs.19 The
final atomic coordinates for the non-hydrogen atoms are given in Table
2. The atomic coordinates of the hydrogen atoms are given in Table
SI and the thermal parameters in Table SII.
Results and Discussion
Synthesis and Solution Behavior. The diaquabisamidato
platinum(II) compounds described in this paper have been
synthesized by base hydrolysis of the corresponding dichlorobis-
(amide) species. Under basic conditions, beside deprotonation
of the amides to amidato anions, also substitution of hydroxide
for chloride ions takes place. Most probably the reaction
proceeds through aquation and subsequent deprotonation of the
solvato species. Neutralization with nitric acid affords the
sparingly soluble diaquabisamidato complexes. The molecular
formula would also be in agreement with a bis(hydroxo)
complex containing two amide ligands; however, previous
workers have proved that coordinated amides are rather acidic
ligands, probably more acidic than coordinated water mol-
ecules.3,5,20,21
Crystal Structure of trans-[Pt{HNdC(O)But}2(H2O)2]‚
1/3H2O (5‚1/3H2O). In the crystals, trans-[Pt{HNdC(O)But}2-
(H2O)2] complexes, having a crystallographically imposed Ci
symmetry with platinum lying on the inversion center and water
molecules of crystallization, lying on the 3h site symmetry, are
present, separated by van der Waals contacts only. The structure
of the complex is shown in Figure 1 together with the atomic
numbering scheme; bond distances and angles are given in Table
3. The square planar coordination around platinum involves
two N atoms from the amidato ligands [Pt-N ) 2.006(4) Å]
and two O atoms from water molecules [Pt-O ) 2.016(7) Å],
which are trans to each other. The four coordinated atoms and
the Pt atom are coplanar for symmetry restrictions. The Pt-O
bond distances are very similar to those found for Pt-O bonds
trans to oxygen donor ligands in other platinum complexes (in
the range 1.99-2.01 Å in nitrato, squarato and oxalato
complexes).26-28 The calculated value for this bond in the
tetraaqua cation [Pt(H2O)4]2+ (X-ray absorption edge and
A solution of trans-[PtCl2{HNdC(OH)Me}2], 1, was titrated
with 1 and 2 equiv of base to give trans-[PtCl2{HNdC(O)-
Me}{HNdC(OH)Me}]- and trans-[PtCl2{HNdC(O)Me}2]2-
,
respectively. The pKa’s for the deprotonation of the first and
second coordinated amide ligands were determined as 3.8 and
(22) Buckingham, D. A.; Keene, R. F.; Sargeson, A. M. J. Am. Chem.
Soc. 1973, 95, 5649.
(17) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
Ugozzoli, F. Comput. Chem. 1987, 11, 109.
(18) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
(19) Sheldrick, G. M. SHELX-76 Program for crystal structure determi-
nation. University of Cambridge, U. K., 1976; SHELXS-86 Program
for the solution of crystal structures, University of Go¨ttingen, 1986.
(20) Jensen, K. A. Z. Anorg. Allg. Chem. 1939, 242, 87.
(21) Perumareddi, J. R.; Adamson, A. W. J. Phys. Chem. 1968, 72, 414.
(23) Woon, T. C.; Fairlie, D. P. Inorg. Chem. 1992, 31, 4069.
(24) Kerridge, D. H. Chem. Soc. ReV. 1988, 17, 181.
(25) Bellamy, L. J. The Infrared Spectra of Complex Molecules; Methuen
and Co. Ltd.: London, 1975; pp 231-262.
(26) Elding, L. I., Oskarsson, A. Inorg. Chim. Acta 1985, 103, 127.
(27) Kobayashi, A.; Sasaki, Y.; Kobayashi, H. Bull. Chem. Soc. Jpn. 1979,
52, 3862.
(28) Simonsen, O.; Toftlund, H. Inorg. Chem. 1981, 20, 4044.

Notes
Inorganic Chemistry, Vol. 35, No. 6, 1996 1717
Table 3. Bond Distances (Å) and Angles (deg) for Compound
5‚1/3H2O
they form with the adjacent water molecules. The O(1)‚‚‚O(2)
distance is as short as 2.484(6) Å, and the O(1)-H(1)‚‚‚O(2)
angle is as large as 150(8)°. This very strong H bond is favored
by the geometry and the in plane orientation of the amidato
ligand and the disposition of the water proton [displacements
of H(1) from the planes through Pt, N(1), and O(1) and H(3),
N(1), C(1), and O(2) atoms of 0.37(11) and 0.11(11) Å,
respectively] and does not require any narrowing of the
N-Pt-O angle which is 91.7(2)°. There appears to be a
relationship between the strength of the hydrogen bond and the
coplanarity of the interacting ligands as measured by the dihedral
angle between the plane through the amidato anion and that of
coordination. The hydrogen bond between the amidato and the
ammine ligands observed in trans-[Pt(NH3)2(NtCMe){HNdC-
(O)Me}]+ was weaker than that observed in the present case
[N‚‚‚O distance of 2.94(2) Å] and the dihedral angle was of
40.8(7)° to be compared with the 7.7(2)° observed in the present
study.30 A rather similar situation was that observed in [Co-
(NH3)5{HNdC(O)Me}]2+ [N‚‚‚O distances of 2.988(10) and
2.900(10) Å and dihedral angles of 49.9(3)° and 40.3(3)°].32
An intermediate situation was that of [PtCl{HNdC(Ph)N-
(But)CH2CH2NHBut}{HNdC(O)Ph}] with a shorter N‚‚‚O
distance [2.789(11) Å] and a smaller dihedral angle [16.1(4)°].31
It has been postulated that stable aqua complexes require the
formation of two strong hydrogen bonds in which the water
molecule donates its protons. This was observed in the
structures we have referred to in the introduction.5-8 Such a
requirement is adequately fulfilled in the present compound. In
fact, beside the H(1) atom which is involved in a very strong
H-bond with the amidato ligand, the H(2) hydrogen atom is
also involved in a strong H bond with the O(2) atom of another
molecule with a O(1)‚‚‚O(2) (z, x, y + 1) distance of 2.588(9)
Å and an O(1)-H(2)‚‚‚O(2) angle of 149(14)°.
Pt-O(1)
2.016(7)
1.272(11)
1.527(8)
1.496(18)
1.11(7)
Pt-N(1)
2.006(4)
1.293(9)
1.511(22)
1.534(14)
0.98(17)
O(2)-C(1)
C(1)-C(2)
C(2)-C(3)
O(1)-H(1)
N(1)-H(3)
N(1)-C(1)
C(2)-C(4)
C(2)-C(5)
O(1)-H(2)
0.86(12)
O(1)-Pt-N(1)
91.7(2)
120.7(8)
117.8(5)
107.0(6)
112.5(6)
109.0(8)
115(6)
Pt-N(1)-C(1)
129.6(4)
121.5(6)
111.7(11)
106.9(8)
109.5(8)
O(2)-C(1)-N(1)
O(2)-C(1)-C(2)
C(1)-C(2)-C(5)
C(1)-C(2)-C(4)
C(1)-C(2)-C(3)
Pt-N(1)-H(3)
N(1)-C(1)-C(2)
C(4)-C(2)-C(5)
C(3)-C(2)-C(5)
C(3)-C(2)-C(4)
C(1)-N(1)-H(3)
Pt-O(1)-H(1)
115(8)
104(7)
Pt-O(1)-H(2)
H(1)-O(1)-H(2)
104(8)
99(10)
Hydrogen Bonds
O(1)‚‚‚O(2)
H(1)‚‚‚O(2)
2.484(6) O(1)‚‚‚O(2i)
2.588(9)
1.70(16)
1.46(10) H(2)‚‚‚O(2i)
O(1)-H(1)‚‚‚O(2) 150(8)
O(1)-H(2)‚‚‚O(2i) 149(14)
a Symmetry: (i) z, x, y + 1.
EXAFS) was 2.01(1) Å.9 Longer Pt-O bond distances have
been observed in other aqua platinum complexes in which the
water molecules were trans to a nitrogen-donor ligand: 2.052-
(8) Å in cis-[Pt(NH3)2(1-methylcytosine-N3)(H2O)](NO3)2‚H2O,5
2.099(5) Å in [Pt{1,1-bis(aminomethyl)cyclohexane}(H2O)-
(SO4)]‚H2O,6 and 2.078(6) Å in [Pt{N,N ′-dimethylethylene-
diamine}(H2O)(SO4)]‚H2O,7 thus indicating a larger ground-
state trans-influence for nitrogen than for oxygen atoms.
The Pt-N bond distances are shorter than those found in
amine complexes trans to other amine ligands, which usually
are ca. 2.06 Å.29 This is due to the sp2 hybridization of the
amidic nitrogen and to the possibility of back-bonding from
filled metal d-orbitals to empty π*-orbitals of the amidato, which
might further shorten the bond.
It is noteworthy that in the packing of the complexes the
hydrophobic But groups are orientated in such a way to leave
large channels into which water molecules of crystallization are
inserted (Figure 2, of Supporting Information).
The planarity of the amidato group is preserved upon
coordination [the maximum deviation from the mean plane being
0.01(1) Å]. The value of the Pt-N(1)-C(1) angle, 129.6(4)°,
is larger than expected (120°) and is a common feature of
amidato ligands. A large angle was also observed in trans-
[Pt(NH3)2(NtCMe){HNdC(O)Me}]+ [132.1(12)°],30 in [PtCl-
{HNdC(Ph)N(But )CH2 CH2 NHBut }{HNdC(O)Ph}]
[131.3(7)°],31 and in [Co(NH3)5{HNdC(O)Me}]2+ [131.0(7)°].32
The N(1)-C(1) and C(1)-O(2) bond distances, 1.293(9) and
1.272(11) Å respectively, are comparable and denote a double
bond delocalization over the N‚ ‚C‚ ‚O moiety which contrib-
utes to the releasing of the formal negative charge accumulated
on the oxygen atom as a consequence of its deprotonation. This
could contribute to increasing the acidity of the coordinated
amide ligands.31 The mean plane of the amidato ligand is tilted
by only 7.7(2)° with respect to the coordination plane. This is
an unusual feature since normally ligands which extend in a
plane prefer to assume a conformation with the ligand plane at
roughly a right angle to the square coordination plane. The
preference for an upright position appears to stem from steric
rather than electronic reasons since such a conformation
minimizes the interligand steric interactions with cis ligands.33
In the present case the almost in-plane orientation of the amidato
ligands is dictated by the strong intramolecular hydrogen bonds
Conclusions
The first X-ray structure of a platinum(II) diaqua species is
reported. Accurate values of Pt-O [2.016(7) Å] and Pt-N
distances [2.006(4) Å] indicate that water oxygen exerts a
smaller ground state trans-influence than amine nitrogen.
Extensive electron delocalization upon the N‚ ‚C‚ ‚O moiety
stabilizes the amidato anion contributing substantially to the high
acidity of coordinate amide ligands. A very strong H bond
between cis amidato and water ligands is responsible for the
in-plane orientation of the amidato ligand [dihedral angle
between the plane through the amidato anion and the platinum
coordination plane of 7.7(2)°]. Analogous interactions between
cis amidato and amine ligands appear to be significantly weaker
and, consequently, the dihedral angles between amidato and
metal-coordination planes are bigger.
Acknowledgment. This work was supported by the Minis-
tero della Universita` e della Ricerca Scientifica e Tecnologica
(MURST, quota 40%) the Italian National Research Council
(CNR) and European Community (EC, contract Cl1-CT92-
0016 and COST Chemistry project D1/02/92). The authors
gratefully acknowledge Prof L. G. Marzilli (Emory University,
Atlanta, Georgia) for helpful discussion.
(29) Lock, C. J. L.; Zvagulis, M. Inorg. Chem. 1981, 20, 1817.
(30) Erxleben, A.; Mutikainen, I.; Lippert, B. J. Chem. Soc., Dalton Trans.
1994, 3667.
(31) Maresca, L.; Natile, G.; Intini, F. P.; Gasparrini, F.; Tiripicchio, A.;
Tiripicchio- Camellini, M. J. Am. Chem. Soc. 1986, 108, 1180.
(32) Schneider, M. L.; Ferguson, G.; Balahura, R. J. Can. J. Chem. 1973,
51, 2180.
Supporting Information Available: Coordinates for the hydrogen
atoms (Table SI), anisotropic thermal parameters for the non-hydrogen
atoms (Table SII), crystallographic data (Table SIII), and crystal packing
(Figure 2) (4 pages). Ordering information is given on any current
masthead page.
(33) Albright, T. A.; Hoffmann, R.; Thibeault, J. C.; Thorn, D. L. J. Am.
Chem. Soc. 1979, 101, 3801.
IC951014M