Saccharinate as a versatile polyfunctional ligand. Four distinct coordination modes, misdirected valence, and a dominant aggregate structure from a single reaction system

Article abstract of DOI:10.1021/ic010300x

The reaction system consisting of copper, saccharinate, and the auxiliary ligands H₂O, PPh₃, and NH₃ produces a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex trans-[Cu(sacch)₂(H₂O)₄] (2) (produced by thermal dehydration of trans-[Cu(sacch)₂(H₂O)₄] ·2H₂O (1)) reacts with triphenylphosphine in CH₂Cl₂ to produce any or all of three Cu(I) complexes, depending upon conditions. The three Cu(I) compounds are Cu(sacch)(PPh₃)₃ (3), in which saccharinate binds to copper through the carbonyl group of the ligand, Cu(sacch)(PPh₃)₂ (4), in which sacch binds to Cu through its charge-bearing nitrogen atom; and [Cu(sacch)(PPh₃)]₂ (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products reacts with NH₃ in CH₂Cl₂ solution to produce trans-[Cu(sacch)₂(NH₃)₄] (6), an unstable Cu(II) complex that exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH₃)₄](sacch)·H₂O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7 by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis of 1 establishes the substitution of the auxiliary ligand H₂O by NH₃ in the Cu(II) products.

Full text of DOI:10.1021/ic010300x

Inorg. Chem. 2001, 40, 4455-4463
4455
Saccharinate as a Versatile Polyfunctional Ligand. Four Distinct Coordination Modes,
Misdirected Valence, and a Dominant Aggregate Structure from a Single Reaction System
Larry R. Falvello,*,† Julio Gomez,‡ Isabel Pascual,† Milagros Toma´s,†
Esteban P. Urriolabeitia,† and Arthur J. Schultz§
Department of Inorganic Chemistry, University of Zaragoza-CSIC, Plaza San Francisco s/n,
E-50009 Zaragoza, Spain, Department of Chemistry, University of La Rioja, Complejo Cient´ıfico
Tecnolo´gico, Calle Madre de Dios, 51, 26006 Logron˜o, Spain, and Intense Pulsed Neutron Source,
Argonne National Laboratory, Argonne, Illinois 60439-4814
ReceiVed March 19, 2001
The reaction system consisting of copper, saccharinate, and the auxiliary ligands H2O, PPh3, and NH3 produces
a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex
trans-[Cu(sacch)2(H2O)4] (2) (produced by thermal dehydration of trans-[Cu(sacch)2(H2O)4]‚2H2O (1)) reacts
with triphenylphosphine in CH2Cl2 to produce any or all of three Cu(I) complexes, depending upon conditions.
The three Cu(I) compounds are Cu(sacch)(PPh3)3 (3), in which saccharinate binds to copper through the carbonyl
group of the ligand, Cu(sacch)(PPh3)2 (4), in which sacch binds to Cu through its charge-bearing nitrogen atom;
and [Cu(sacch)(PPh3)]2 (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate
nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they
exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products
reacts with NH3 in CH2Cl2 solution to produce trans-[Cu(sacch)2(NH3)4] (6), an unstable Cu(II) complex that
exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH3)4]-
(sacch)‚H2O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked
by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of
the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of
saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7
by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis
of 1 establishes the substitution of the auxiliary ligand H2O by NH3 in the Cu(II) products.
Introduction
environment, mostly through hydrogen bonding. The often
countermanding energetic requirements of the crystalline sur-
roundings and the transition-metal center can generate stresses
that lead to the stabilization of species, stoichiometries, or
conformations which in solution would not be expected to
predominate.
Complexes of polyfunctional ligands thus serve as probes into
several interesting phenomena, as well as being potential sources
of new molecular materials. We have observed, for example,
changes in the expression of the Jahn-Teller effect in molecular
solid solutions of a chromium nicotinate complex dissolved
in the solid in a zinc-nicotinate host (nicotinate ) m-carboxylato-
pyridine).3a,b With saccharinate, we have observed that trans-
[Cr/Zn(sacch)2(H2O)4]‚2H2O (sacch ) saccharinate, C7H4NO3S-,
I), forms molecular solid solutions in which the anisotropic
Saccharine and saccharinate have been studied in detail in
several scientific contexts, largely because of their commercial
use in noncaloric food sweeteners. While the large majority of
studies on saccharine have been related to the gustatory
responses that it evokes, and to possible carcinogenesis and
DNA-altering ability,1 research has been conducted into quite
varied properties and uses of saccharine, such as in molecular
materials2a-c and metallurgy.2d
Our own interest in saccharine and saccharinate lies in the
use of the latter as a polyfunctional ligand in transition-metal
chemistry. Polyfunctional ligandssligands of a predominantly
organic nature that possess several functional groupssare
capable of being ligated to metal centers and, at the same time,
of forming relatively strong interactions with a crystalline
† University of Zaragoza-CSIC.
‡ University of La Rioja.
§ Argonne National Laboratory.
(1) (a) Cohen, S. M.; Arnold, L. L.; Cano, M.; Ito, M.; Garland, E. M.;
Shaw, R. A. Carcinogenesis 2000, 21, 783-792. (b) Yang, J.;
Duerksen Hugues, P. Carcinogenesis 1998, 19, 1117-1125. (c)
Jeffrey, A. M.; Williams, G. M. Food Chem. Toxicol. 2000, 38, 335-
338.
(2) (a) Williams-Seton, L.; Davey, R. J.; Lieberman, H. F. J. Am. Chem.
Soc. 1999, 121, 4563-4567. (b) Lieberman, H. F.; Williams, L.;
Davey, R. J.; Pritchard, R. G. J. Am. Chem. Soc. 1998, 120, 686-
691. (c) Davey, R. J.; Williams-Seton, L.; Lieberman, H. F.; Blagden,
N. Nature 1999, 402, 797-799. (d) Benballa, M.; Nils, L.; Sarret,
M.; Muller, C. Surface Coatings Technol. 2000, 123, 55-61.
displacement parameters derived from diffraction data indicate
a subtle, progressive disorder, as a function of chromium
concentration, in the ligand atoms affected by Jahn-Teller
10.1021/ic010300x CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/19/2001

4456 Inorganic Chemistry, Vol. 40, No. 17, 2001
Falvello et al.
distortion.3c,d The intramolecular strain created in each case is
the result of intermolecular interactions involving the polyfunc-
tional ligands and mediated largely by hydrogen bonding. The
same intramolecular strain has also been introduced into systems
not containing polyfunctional ligands, such as solid solutions
of the chromium and zinc ammonium Tutton salts4 (NH4)2[Crx-
Zn1-x(H2O)6](SO4)2 and single crystals of chromium or copper
hexahydrate hexafluorosilicate.5
atom in a solid-state system dominated by a supramolecular
aggregate. In this series of products, the coordination properties
of saccharinate are adapted on a case-by-case basis to the steric
properties of the complex and/or to the stabilization of the
crystalline environment.
Experimental Section
Solvents and Reagents. Solvents were dried over a Na amalgam
and distilled under nitrogen before use unless otherwise stated.
Elemental analyses were carried out on a Perkin-Elmer 240B microana-
lyzer. IR spectra (4000 to 200 cm-1) were recorded on a Perkin-Elmer
883 infrared spectrophotometer from Nujol mulls between polyethylene
sheets. 1H (300.13 MHz), 13C{1H} (75.47 MHz), and 31P{1H} (121.49
MHz) NMR spectra were recorded in CDCl3, CD2Cl2, or C6D5CD3
solutions, at the temperatures stated in the text, on a Bruker ARX300
spectrometer. 1H and 13C{1H} spectra were referenced using the solvent
signals as internal standard, and 31P{1H} spectra were externally
referenced to H3PO4 (85%). Mass spectra (positive ion FAB) were
recorded on a VG AutoSpec spectrometer. In-solution molecular weight
measurements were performed on a Knauer vapor pressure osmometer
over CDCl3 solutions.
The coordination chemistry of saccharinate as a ligand,
meanwhile, has been explored for several transition metals.
Saccharinate (o-sulfobenzoimidate), which has sulfonyl and
carbonyl groups as well as a charge-bearing nitrogen atom in
its five-membered ring, is already known to be able to ligate to
metal atoms through any of these moieties, as well as to bridge
two transition metals through the amidato-like -NCdO system.
The most common coordination mode is ligation through the
nitrogen atom, which has been observed in hydrates of the 3d
series, as well as in mercury saccharinate.6 Saccharinate has
also been found to bind through the carbonyl oxygen in a hydrate
of neodymium7 and in a pyridine adduct of vanadium,6b in which
it appears that steric hindrance impedes binding through the
ring nitrogen atom. As a three-atom amidato-like moiety,
saccharinate is able to bridge a long Cr-Cr quadruple bond,8
and it has also been observed to bridge a dinuclear copper
complex.9 The most unusual contact so far observed between
saccharinate and a metal atom is what might be described as
semicoordination to leadsa weak contact which may possess
some degree of covalencysthrough a sulfonyl oxygen atom,
an atom not expected to be sufficiently basic to coordinate.10
Theoretical and spectroscopic studies have been reported in
which nuances in the spectroscopic properties and structural
features of saccharinate have been related to its coordination
modes.11
Syntheses. Compound 1, [Cu(sacch)2(OH2)4]‚2H2O, was prepared
as previously published elsewhere.6a Complex 2 has been described12
as the dehydrated product [Cu(sacch)2(H2O)4], although it has not been
fully characterized.
[Cu(sacch)(PPh3)3] (3). Over a refluxing solution of 0.2 g (0.8
mmol) of PPh3 in 40 mL of CH2Cl2 was added 0.1 g (0.2 mmol) of 1
that had previously been desiccated in an oven at 120 °C for 24 h (this
heating converts 1 into 2). The greenish blue suspension was refluxed
with stirring for 12 h, until it had become a colorless solution. The
solution was washed with several aliquots of diethyl ether in order to
eliminate the excess of PPh3 and was then dried under vacuum. The
white powder isolated was air stable. Yield: 0.15 g (73%). Anal.
Calcd: H, 4.73; C, 70.98; N, 1.34; S: 3.07. Found: H, 4.51; C, 70.39;
N, 1.33; S, 3.21. IR (cm-1): 1612 s, 1586 s, 1153 s, 750 s, 743 m, 603
s, 544 s. See the structure of compound I in the Introduction for a
labeling scheme for NMR assignments. 1H NMR (ppm): 7.75 (d, 1H,
H(4)), 7.60 (d, 1H, H(1)), 7.58-7.50 (m, 2H, H(2), H(3)), 7.34-7.19
(m, 45H, H-phosphines). 31P{1H} NMR (ppm): 166.36 (all phosphorus
atoms are chemically equivalent in solution). 13C{1H} NMR (ppm):
166.36 (C(1)), 142.18 (C(7)), 131.35 (C(2)), 130.59 (C(4)), 130.31
(C(5)), 121.84 (C(3)), 118.50 (C(6)), 132.47-132.25 (C-ortho PPh3),
132.04-132.77 (C-ipso PPH3), 128.11 (C-para PPh3), 127.07 (C-meta
PPh3). Crystals were obtained by slow evaporation of a solution of 3
in CH2Cl2.
In this report we describe a reaction system that produces
complexes of saccharinate displaying all four coordination
modes, including semicoordination through a sulfonyl oxygen
(3) (a) Cotton, F. A.; Falvello, L. R.; Ohlhausen, E. L.; Murillo, C. A.;
Quesada, J. F. Z. Anorg. Allg. Chem. 1991, 598/599, 53-70. (b)
Falvello, L. R. J. Chem. Soc., Dalton Trans. 1997, 4463-4475. (c)
Cotton, F..A.; Falvello, L. R.; Murillo, C. A.; Valle, G. Z. Anorg.
Allg. Chem. 1986, 540/541, 67-79. (d) Cotton, F. A.; Falvello, C.
A.; Murillo, C. A.; Pascual, I. Unpublished results.
[Cu(sacch)(PPh3)2] (4) Method a. To a solution of 0.40 g (0.61
mmol) of [Cu(PPh3)2(NO3)] in 30 mL of CH2Cl2 was added 0.13 g
(0.61 mmol) of Nasacch‚H2O (molar ratio 1:1). The suspension was
kept stirring for 12 h, after which the NaNO3‚nH2O formed was
removed by filtration. The solution was then reduced to dryness under
vacuum, and the solid obtained was washed several times with
n-pentane and dried. The white powder is air-stable. Yield: 0.44 g
(94%).
Method b. Treatment of 1 with 3 equiv of PPh3 under the same
reaction conditions as those used for 3 or 5 generated mixtures of 3, 4,
and 5, from which 4 was isolated in low yields. Anal. Calcd: H, 4.38;
C, 67.07; N, 1.79; S, 4.1. Found: H, 4.07; C, 65.62; N, 1.73; S, 3.49.
IR (cm-1) 1661 s, 1589 m, 1285 s, 1250 m, 1158 s, 1152 m, 1120 m,
1095 s, 965 m, 782 w, 745 s, 706 s, 601 s, 529 m, 518 s, 505 s, 394
w. 1H NMR (ppm): 7.75 (d, 1H, H(4)), 7.61 (d, 1H, H(1)), 7.58-7.51
(m, 2H, H(2), H(3)), 7.34-7.16 (m, 30H, H-phosphine). 31C{1H} NMR
(ppm): 167.79 (C(1)), 143,53 (CV(7)), 132.73 (C(2)), 132.07 (C(4)),
131.79 (C(5)), 131.18 (C(3)), 119.94 (C(6)), 133.80 (C-ortho PPh3),
131 (over C(5)) (C-ipso PPh3), 129.98 (C-para PPh3), 128.65 (C-meta
PPh3). 31P{1H} NMR (ppm): -0.713 (all phosphorus atoms are
equivalent in solution). Good-quality crystals can be obtained by careful
(4) (a) Araya, M. A.; Cotton, F. A.; Daniels, L. M.; Falvello, L. R.;
Murillo, C. A. Inorg. Chem. 1993, 32, 4853-4860. (b) Cotton, F. A.;
Daniels, L. M.; Falvello, L. R.; Murillo, C. A.; Schultz, A. J. Inorg.
Chem. 1994, 33, 5396-5403.
(5) (a) Cotton, F. A.; Falvello, L. R.; Murillo, C. A.; Quesada, J. F. J.
Solid State Chem. 1992, 96, 192-198. What appears to be a
suppression of the Jahn-Teller effect at the chromium center can be
interpreted in terms of a reexpression as a dynamic Jahn-Teller effect
with a Jahn-Teller radius of 0.32 Å.3b (b) Cotton, F. A.; Daniels, L.
M.; Murillo, C. A.; Quesada, J. F. Inorg. Chem. 1993, 32, 4861-
4867.
(6) (a) Haider, S. Z.; Malik, K. M. A.; Ahmed, K. J.; Hess, H.; Riffel,
H.; Hursthouse, M. B. Inorg. Chim. Acta 1983, 72, 21-27. (b) Cotton,
F. A.; Falvello, L. R.; Llusar, R.; Libby, E.; Murillo, C. A.; Schwotzer,
W. Inorg. Chem. 1986, 25, 3423-3428. (c) Kamenar, B.; Jovanovski,
G.; Grdeniæ, D. Cryst. Struct. Commun. 1982, 11, 263-268.
(7) Starynowicz, P. Acta Crystallogr., Sect. C 1991, C47, 2063-2065.
(8) Cotton, F. A.; Falvello, L. R.; Schwotzer, W.; Murillo, C. A.; Valle-
Bourrouet, G. Inorg. Chim. Acta 1991, 190, 89-96.
(9) Liu, S.-X.; Huang, J.-L.; Li, J.-M.; Lin, W.-B. Acta Crystallogr., Sect.
C 1991, C47, 41-43.
(10) Jovanovski, G.; Hergold-Brundic, A.; Kamenar, B. Acta Crystallogr.,
Sect. C 1988, C44, 63-66.
(11) (a) Naumov, P.; Jovanovski, G. Struct. Chem. 2000, 11, 19-33. (b)
Naumov, P.; Grupce, O.; Jovanovski, G. J. Raman Spectrosc. 2000,
31, 475-479. (c) Jovanovski, G. Croat. Chem. Acta 2000, 73, 843-
868. (d) Naumov, P.; Jovanovski, G.; Grupce, O. J. Mol. Struct. 1999,
483, 121-124. (e) Jovanovski, G.; Naumov, P.; Grupce, O.; Kaitner,
B. Eur. J. Solid State Inorg. Chem. 1998, 35, 231-242.
(12) (a) Yugeng, Z. Transition Met. Chem. 1994, 19, 446-448. (b) Icbudak,
H.; Yilmaz, V. T.; Olmez, H. J. Therm. Anal. Calorim. 1998, 53, 843-
854.

Saccharinate as a Versatile Polyfunctional Ligand
Inorganic Chemistry, Vol. 40, No. 17, 2001 4457
Table 1. Crystal Data for Cu(sacch)(PPh3)3 (3), Cu(sacch)(PPh3)2‚3/4CHCl3 (4‚3/4CHCl3), [Cu(sacch)(PPh3)]2‚CH2Cl2 (5‚CH2Cl2),
trans-[Cu(sacch)2(NH3)4] (6), and [Cu(sacch)(NH3)4](sacch)‚H2O (7)
7
3
4
5
6
X-ray
neutron
formula
CuC61H49P3NO3S
C43H34CuNO3P2S‚
3/4CHCl3
859.02
triclinic
P1h
colorless
13.3164(2)
14.1508(2)
23.6548(4)
80.8106(9)
86.3813(8)
78.8322(8)
4314.54(12)
295(2)
C50H38Cu2N2O6P2S2‚
CH2Cl2
1100.89
monoclinic
C2/c
colorless
19.8920(13)
16.6168(10)
15.2411(8)
90
90.561(8)
90
5037.6(5)
293(2)
4
0.0370
0.0992
C14H20CuN6O6S2
C14H22CuN6O7S2
fw
1032.52
orthorhombic
Pbca
colorless
20.294(3)
19.784(2)
24.974(3)
90
496.02
monoclinic
P21/c
sky blue
7.374(2)
12.775(3)
10.327(3)
90
98.94(3)
90
961.1(5)
298(2)
2
514.04
triclinic
P1h
cryst syst
space group
cryst color
a (Å)
b (Å)
c (Å)
royal blue
7.045(1)
10.578(2)
13.967(3)
98.05(3)
92.39(3)
99.08(3)
1015.5(3)
293(2)
6.998(1)
10.528(2)
13.881(2)
97.55(2)
92.46(2)
99.35(2)
998.1(2)
20(1)
R (deg)
â (deg)
γ (deg)
V (Å3)
temp (K)
Z
90
90
10027(2)
293(2)
8
0.1040
0.1984
0.961
4
2
2
R1a
0.0709
0.2152
1.019
0.1042
0.1967
1.022
0.0296
0.0692
1.045
0.098d
wR2b
0.057e
GOFc
1.031
1.896
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, calculated using reflections with (Fo)2 > 2σ[(Fo)2]. b wR2 ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2, for all reflections used
in the refinement. c GOF ) [∑w(Fo2 - Fc2)2/(n - p)]1/2, for all reflections used in the refinement; n ) no. of observations; p ) no. of parameters.
2
d R(F) ) ∑||Fo| - |Fc||/∑|Fo|, using reflections with Fo > 3σ(Fo). e Rw(F) ) [∑w(Fo - Fc)2/∑wFo ]1/2, for all reflections used in the refinement to
the neutron data (Fo > 3σ(Fo)).
evaporation of a concentrated solution of [Cu(sacch)(PPh3)2] in CHCl3
under a reduced-pressure N2 atmosphere.
The light blue suspension gave way to a dark blue precipitate that was
filtered and isolated. Yield: 0.23 g (95%).
Method c. A colorless solution of [Cu(sacch)(PPh3)x] (x ) 1-3; 5,
4, 3) in 30 mL of CH2Cl2 was kept under a constant pressure of 1.0
bar of NH3(g). The initial product, 6, quickly evolves to 7, which can
be isolated in high yield. Anal. Calcd: H, 4.31; C, 32.71; N, 16.35, S,
12.47. Found. H, 4.09; C, 32.27; N, 16.10; S, 12.43. IR (cm-1): 3610
m, 3351 vs, 3181 s, 1668-1587 vs, 1271 vs, 1227 s, 1154 vs, 1119
vs, 1054 s, 970 vs, 957 s, 786 s, 772 m, 747 s, 676 s, 648 m, 633 m,
604 s, 544 s, 532 s, 461 w, 401 m, 339 m. A large crop of high-quality
crystals can be obtained from the mother liquor of any of the
preparations (method a, b, or c) after 48 h or by recrystallization of 7
in concentrated aqueous ammonia. Larger crystals for use in the neutron
diffraction experiment were obtained from solutions produced by
methods a and b, after 2 weeks at room temperature.
X-ray Structure Analyses. All data for the five structures were
collected at room temperature (Table 1). A Stoe AED2 four-circle
diffractometer13 was used for the data collection for complex 7, a Nonius
CAD-4 was used for 3, 5, and 6,14 and a Nonius KappaCCD was used
for 4.14
After data reduction and application of absorption corrections, the
structures were solved by either Patterson interpretation or direct
methods15 and were refined by full-matrix least-squares.16 For the
structure of 4, for which two independent molecules were found in the
asymmetric unit of the triclinic cell, a further test for higher symmetry
was conducted; a list of Fo and Fc, ordered on 2θ, was examined visually
[Cu(sacch)(PPh3)]2 (5). The method used was the same as that for
3, using 0.16 g (0.33 mmol) of 1 (previously desiccated in an oven at
120 °C) and 0.17 g (0.66 mmol) of PPh3. Compound 5 is stable as a
white powder if kept dry; the colorless solution of 5 is oxidized within
several hours if left open to the air. Anal. Calcd: H, 3.68; C, 59.12; N,
2.69; S, 6.17. Found: H, 3.89; C, 59.05; N, 2.74; S, 6.17. IR (cm-1):
1637 vs, 1591 m, 1307 s, 1262 m, 1168 m, 1157 s, 1124 s, 734 m, 694
m, 678 m, 596 m, 530 m, 394 m. 1H NMR (ppm): 7.57 (d, 1H, H(4)),
7.60(d, 1,1 H(1)), 7.58-7.51 (m, 2H, H(2), H(3)), 7.32-7.16 (m, 16H,
H-phosphines). 31P{1H} NMR (ppm): -1.26 (all phosphorus atoms are
equivalent in solution). 13C{1H} NMR: 167.68 (C(1)), 143.55 (C(7)),
132.71 (C(2)), 132.05 (C(4)), 131.80 (C(5)), 123.28 (C(3)), 119.94
(C(6)), 133.77 (C-ortho PPh3), 132.71-132.05 (C-ipso PPh3), 129.85
(C-para PPh3), 128.61 (C-meta PPh3). Crystals for X-ray analysis were
obtained by slow diffusion of n-pentane into a dilute solution of 5 in
CH2Cl2.
[Cu(sacch)2(NH3)4] (6). This rather unstable complex was isolated
by crystallization in an inert atmosphere using Schlenk techniques. A
colorless solution of 3 in freshly distilled CH2Cl2 was kept at +3 °C
under a constant pressure of NH3 (g). After 16 h under these conditions
a crop of small, flat crystals of 6 can be harvested from a solid residue,
the other components of which have not been identified. These crystals
must be collected in the absence of air; otherwise, they evolve to 7.
This evolution of 6 to 7 takes place both in CH2Cl2 solution in the
presence of air and in the solid state in the presence of air, once the
crystals have been isolated from solution. The formation of compound
7 can easily be monitored by the difference in color of the crystals (6
is sky blue, 7 is royal blue). IR for 6 (cm-1): 3355 vs, 1686-1612 vs,
1332 m, 1288 s, 1258 vs, 1236 vs, 1142 vs, 1137 vs, 1117 vs, 1053 s,
965 vs, 797 w, 774 m, 757 s, 634 s, 603 s, 546 s, 532 s, 402 m, 346
m. Because of the insolubility of 6 in most common solvents, no
physical or spectroscopic measurements were made in solution.
(13) Stoe AED-4 control program: DIF4; Stoe & Cie GmbH, Darmstadt,
Germany.
(14) (a) CAD-4 control program: CAD4/PC Version 1.5c (1994) and
Version 2.0 (1996), Nonius BV, Delft, The Netherlands. (b) Kap-
paCCD control program: Collect, 1997-2000, Nonius BV, Delft, The
Netherlands.
(15) (a) Data were processed on a Local Area VAXCluster (VMS V5.5-2)
using the commercial package SHELXTL-PLUS Release 4.21/V
(1990), Siemens Analytical X-ray Instruments, Inc., Madison, WI, and
on an AlphaStation 200 4/166 (OpenVMS/Alpha V6.2) using the
commercial package SHELXTL Relat. 5.05/VMS (1996), Siemens
Analytical X-ray Instruments, Inc., Madison, WI. Further calculations
were done on a Hewlett-Packard 9000 Model 715/50 (HP-UX V9.05
and V10.20). (b) AED-4 data reduction: REDU4 Rev. 7.03; Stoe &
Cie GmbH, Darmstadt, Germany. (c) Data reduction for the CAD-4:
XCAD4B (K. Harms, 1996). (d) Data reduction for the KappaCCD:
HKL Denzo and Scalepack (Otwinowski & Minor, 1997). (e) Structure
solution: Sheldrick, G. M. SHELXS-86: Fortran Program for Crystal
Structure Solution; University of Go¨ttingen, Go¨ttingen, Germany, 1986.
[Cu(sacch)(NH3)4](sacch)‚H2O (7). Method a. NH3(g) was bubbled
through a solution of 0.15 g (0.60 mmol) of CuCl2‚6H2O in 30 mL of
EtOH until the solution became dark blue. Once the species [Cu-
(NH3)4]2+ had been thus formed, 0.26 g (1.2 mmol) of Na(sacch)‚H2O
was dissolved in 30 mL of MeOH/EtOH (20/80) and added to the dark
blue solution with constant stirring. After 10 min the product
precipitated as a dark blue microcrystalline powder. Yield: 75%.
Method b. In a solution of 0.26 g (0.48 mmol) of [Cu(sacch)2-
(H2O)4]‚2H2O (1) in 30 mL of EtOH or THF was bubbled NH3(g).

4458 Inorganic Chemistry, Vol. 40, No. 17, 2001
Falvello et al.
for systematic pairing of similar intensities. Such pairing, which would
be present if the Laue group were really of higher symmetry, was not
observed. The distinct conformational parameters involving the phenyl
groups at the peripheries of the two molecules served to verify their
crystallographic independence.
Scheme 1
Neutron Experiment. Neutron diffraction data were collected on
the Single Crystal Diffractometer (SCD) beam line at the Intense Pulsed
Neutron Source (IPNS) at Argonne National Laboratory. The SCD, a
time-of-flight energy-dispersive diffractometer, is equipped with a
6
spatially fixed, time- and position-sensitive detector containing a Li
glass scintillator with dimensions of 30 × 30 cm2. The SCD instrument
uses the entire thermal spectrum of neutrons from each pulse of the 30
Hz IPNS spallation source. For a given crystal setting, data are stored
in three-dimensional histograms which comprise measurements of
blocks of reciprocal space. Each point in a given histogram has
coordinates x, y, and t, which are the horizontal and vertical detector
positions and the time of flight, respectively. Time of flight, t, is related
to the neutron wavelength λ by the de Broglie equation λ ) (h/m)(t/l),
in which h is Planck’s constant, m is the neutron mass, and l is the
path length traversed in time t. The 120 time-of-flight channels in each
histogram, which correspond to neutron wavelengths in the range of
0.7-4.2 Å, are constructed in such a way that ∆t/t has a constant value
of 0.015. The details of the SCD instrument and beamline, along with
data collection and analysis procedures, have been described previ-
ously.17,18 The temperature of the sample is controlled by a Displex
closed-circuit He refrigerator (Air Products and Chemicals, Inc. Model
CS-202).
For [Cu(sacch)(NH3)4](sacch)‚H2O (7) the orientation matrix of the
crystal was obtained from an automated autoindexing algorithm19 using
the peaks in one histogram. In all, 40 histograms were measured,
covering half of reciprocal space. The Bragg peaks in each histogram
were integrated in three dimensions about their predicted positions and
corrected for the incident beam spectral dispersion and detector
efficiency. Lorentz and absorption corrections were also applied. The
initial structural model consisted of the atomic coordinates for all of
the non-hydrogen atoms, taken from the X-ray structure determination.
This model was refined using isotropic displacement parameters, and
then all hydrogen atoms were located in a difference Fourier map. For
the final refinement, an extinction correction was included; with the
exception of one sulfonyl sulfur atom, all atoms including hydrogen
were refined anisotropically using the program GSAS.20
Results
In the three Cu(I) complexes 3-5, saccharinate adopts three
distinct coordination modes, occupying a lesser fraction of the
space immediately around the metal as the number of triph-
enylphosphine ligands increases. In the unstable Cu(II) complex
6, the saccharinate ligand is only weakly coordinated through
N, and in the very stable Cu(II) complex 7, which evolves from
6, one saccharinate is N-coordinated and another participates
in a dominant aggregate structure while making a weak contact
to the copper center through one of the sulfonyl oxygen atoms.
Scheme 1 shows the saccharinate coordination modes that are
displayed in the Cu/sacch/{H2O,PPh3,NH3} reaction system. It
is possible, beginning with complex 1, [Cu(sacch)2(H2O)4]‚
2H2O, to traverse the entire system synthetically, with alternative
pathways through the Cu(I) complexes, before arriving at
compound 7. As described below, the three Cu(I) complexes
appear to establish an equilibrium in solution, and the predomi-
nance of one or the other depends on the specific conditions
imposed.
The topologies of the different coordination modes will be
described with reference to the crystal structure determinations.
In compound 3, [Cu(sacch)(PPh3)3], in which the presence of
three ligated PPh3 groups imposes the greatest steric hindrance
to saccharinate coordination found in any of these complexes,
the saccharinate adopts the full coordination mode that puts its
bulk farthest from the metal, namely coordination through the
carbonyl oxygen atom (Figure 1). Unlike the sulfonyl semico-
ordination mode found for 7 (see below), binding through Cd
O in this case involves an intimate contact at a short distance
(Cu(1)-O(1) ) 2.113 (8) Å). The remaining coordination sites
in the distorted tetrahedron about copper are occupied by the
three phosphorus atoms of the three PPh3 ligands. Distances
and angles around the metal center are listed in Table 2. It is
possible, alternatively, to view the coordination about the copper
center as a triangular pyramid with the ligated oxygen atom at
(16) (a) Sheldrick, G. M.; SHELXL-93: FORTRAN-77 Program for the
Refinement of Crystal Structures from Diffraction Data; University
of Go¨ttingen, Go¨ttingen, Germany, 1993. (b) Sheldrick, G. M.
SHELXL-97: FORTRAN Program for Crystal Structure Refinement,
1997.
(17) Schultz, A. J.; Van Derveer, D. G.; Parker, D. W.; Baldwin, J. E.
Acta Crystallogr., Sect. C 1990, C46, 276-279.
(18) Schultz, A. J. Trans. Am. Crystallogr. Assoc. 1987, 23, 61-69.
(19) Jacobson, R. A. J. Appl. Crystallogr. 1986, 19, 283-286.
(20) Larson, A. C.; Von Dreele, R. B. GSAS-General Structure Analysis
System; Los Alamos National Laboratory, Los Alamos, NM, 1994.

Saccharinate as a Versatile Polyfunctional Ligand
Inorganic Chemistry, Vol. 40, No. 17, 2001 4459
O(1a)-Cu(1)-P(1), 100.30(6)°). This obviates steric crowding
between the phenyl groups of triphenylphosphine, on one hand,
and the ring and sulfonyl functions of the saccharinate. The
sacch ligands bridge the two metal centers through the amidate-
like system -N-CdO-, as has been observed previously for
saccharinate bridging copper atoms9 and also for metal-metal
bonds.8,22 In the present case, the Cu-N bond, at 1.933(2) Å,
is stronger than the bond from Cu to the neutral carbonyl oxygen
atom (Cu(1)-O(1a) ) 2.130(2) Å). Taken together, the two
copper atoms with their two bridges form an eight-membered
ring with a boat conformation. The nonbonded Cu‚‚‚Cu distance
is 2.9978(8) Å. The coordination planes about the two copper
centers are not parallel to each other but, rather, make an angle
of 46.49(7)°, with the phosphorus atoms pushed away from each
other, apparently to avoid steric crowding of the phenyl groups.
In addition, the two ends of the molecule are not eclipsed; the
torsion angle P(1)-Cu(1)‚‚‚Cu(1a)-P(1a) has a value of
(73.63(6)°. (Both hands are present in the crystal.) The Cu-P
distance, at 2.1884(9) Å, is shorter than those found in
complexes 3, and 4, thus following the trend of shorter Cu-P
distances with decreasing number of PPh3 ligands about the
metal.
Figure 1. Drawing of Cu(sacch)(PPh3)3 (3), indicating the atom-
labeling scheme. Phenyl hydrogen atoms have been omitted. Saccha-
rinate hydrogen and phenyl carbon atoms are drawn as circles. Other
atoms are represented by their 50% probability ellipsoids.
the apex. The triangular base formed by the three P atoms is
nearly equilateral; the copper atom is approximately 0.5 Å above
the base, and the Cu-O vector makes an angle of 13.6° with
the line perpendicular to the base. The three Cu-P distances
(average value 2.347[13] Å)21 are significantly longer than Cu-
O.
Compound 6, trans-[Cu(sacch)2(NH3)4], has the six-coordi-
nate structure and trans arrangement of the polyfunctional
ligands found for a series of related first-row complexes of sacch
and NH323 and also for the analogous sacch/aqua complexes.6a
Despite the relative stability of the other saccharinate complexes
with the same topology, 6 is unstable and evolves spontaneously
either in solution or in the solid to the dark blue color
characteristic of complex 7. Indeed, if reaction conditions are
not carefully controlled, any of the Cu(I) complexes and the
Cu(II) starting material 1 will yield the more stable product 7
upon reaction with NH3. A drawing of the neutral molecule 6
is shown in Figure 4a. The copper atom sits on a crystallographic
inversion center. The two sacch ligands are only weakly bound
to copper (Cu(1)-N(1) ) 2.508(12) Å). The obvious interpreta-
tion of this is in terms of the Jahn-Teller theorem, although
we note that in the analogous complexes [M(sacch)2(H2O)4]‚
2H2O (M ) Mn, Fe, Co, Ni, Zn, Cd) and [M(sacch)2(NH3)4]
(M ) Mn, Co, Ni, Cd), the values of M-N(sacch) range from
2.1 to 2.3 Å. Complex 6 also has a shape distortion in the solid,
as can be appreciated from Figure 4b, which shows a side-on
view of one molecule. The saccharinate ligands are pitched out
of a central plane of the coordination environment in a concerted
fashion, so that the molecule retains its center of symmetry.
The misdirected valence parameter, defined as the angle between
the Cu-N vector and the external bisector of the C(1)-N(1)-
S(1) angle, has a value of 14.5°. This sort of effect can be seen
in systems in which highly stabilizing phenomena in the crystal,
such as aggregate structures, predominate over the natural
tendencies of individual molecules, but in the present case crystal
effects likely meet little resistance from the weak and probably
nonrigid Cu-N(sacch) bond.
Compound 4, Cu(sacch)(PPh3)2, is a three-coordinate Cu(I)
complex in which the presence of only two bulky PPh3 ligands
permits the saccharinate to move in closer, binding now through
its imido nitrogen atom at a distance of approximately 2.0 Å
(Table 2). This arrangement binds saccharinate to copper directly
through an atom of the ring system of the ligand, rather than
through an atom one bond displaced from it, as is the case in
complex 3. The crystallographic asymmetric unit of 4 consists
of two independent, but chemically nearly identical, molecules
of the neutral complex. The major differences between the two
molecules lie in the relative orientations of the phenyl rings,
which are not of central importance for present purposes. A
drawing of one molecule is shown in Figure 2. The planar
coordination environment about the copper center deviates in
two ways from regularitysfirst, the PPh3 ligands are splayed
back away from each other (P-Cu-P ) 129.07(6), 128.43-
(6)°) and the Cu-N distance is about 0.25 Å shorter than the
Cu-P distances (Table 2). Therefore, the immediate coordina-
tion environment of the copper atom has approximate C2V
symmetry, with the 2-fold axis parallel to the Cu-N vector.
The Cu-P distances, with an average value of 2.247[5] Å, are
significantly shorter than those found in the tris-PPh3 complex
3, a further indication of the lesser degree of steric crowding in
complex 4.
Complex 5, with formula [Cu(µ-sacch)(PPh3)]2, is a neutral
dimeric complex in which the presence of only one PPh3 ligand
per saccharinate now permits the latter to approach the metal
even more closely, forming a bridge between the two Cu(I)
centers (Figure 3). The complex sits on a crystallographic 2-fold
axis in space group C2/c. Each copper atom is three-coordinate,
ligated by the P atom of one PPh3 ligand, the carbonyl atom of
one saccharinate, and the imido nitrogen atom of another sacch
ligand. The planar environment at each metal is, however,
severely distorted, with the phosphorus atom tilted toward the
coordinated carbonyl oxygen (N(1)-Cu(1)-P(1) ) 151.61(8)°,
Complex 7, [Cu(sacch)(NH3)4](sacch)‚H2O, can be synthe-
sized directly from CuCl2‚6H2O and ammonia or, alternatively,
by reaction of the aqua complex 1 with NH3 or starting from
any of the Cu(I) complexes 3-5. It is also formed by evolution
of 6, with the latter either in solution or as a solid exposed to
air. Figure 5 shows one complete formula unit of 7, which
(21) The deviation of an average value, given in square brackets, is
(22) Alfaro, N. M.; Cotton, F. A.; Daniels, L. M.; Murillo, C. A. Inorg.
Chem. 1992, 31, 2718-2723.
(23) (a) Pascual, I. Doctoral Thesis, University of Zaragoza, 1996. (b)
Pascual, I. Acta Crystallogr., Sect. C 1995, C51, 2028-2030.
1/2
(d - d)
∑
i
i
calculated as
in which di is the ith of the n values
[
]
n(n - 1)
being averaged and d is the average.

4460 Inorganic Chemistry, Vol. 40, No. 17, 2001
Falvello et al.
1.610(10)
Table 2. Selected Bond Distances (Å) and Angles (deg) for Cu(sacch)(PPh3)3 (3), Cu(sacch)(PPh3)2‚3/4CHCl3 (4‚3/4CHCl3),
[Cu(sacch)(PPh3)]2‚CH2Cl2 (5‚CH2Cl2), trans-[Cu(sacch)2(NH3)4] (6), and [Cu(sacch)(NH3)4](sacch)‚H2O (7)a
Cu(sacch)(PPh3)3 (3)
Cu(1)-O(1)
Cu(1)-P(1)
2.113(8)
2.334(3)
Cu(1)-P(2)
Cu(1)-P(3)
2.373(3)
2.335(4)
C(2)-O(1)
C(2)-N(1)
1.243(12)
1.332(13)
N(1)-S(1)
O(1)-Cu(1)-P(1)
O(1)-Cu(1)-P(3)
113.8(2)
103.4(2)
P(1)-Cu(1)-P(3)
O(1)-Cu(1)-P(2)
111.12(13)
90.2(2)
P(1)-Cu(1)-P(2)
P(3)-Cu(1)-P(2)
117.33(13)
118.18(13)
C(2)-O(1)-Cu(1)
129.8(8)
Cu(sacch)(PPh3)2‚3/4CHCl3 (4‚3/4CHCl3)
Cu(1)-N(1)
Cu(1)-P(2)
Cu(1)-P(1)
1.976(5)
2.2375(16)
2.2472(16)
N(1)-C(1)
N(1)-S(1)
C(1)-O(1)
1.371(8)
1.621(5)
1.231(7)
Cu(2)-N(2)
Cu(2)-P(4)
Cu(2)-P(3)
2.012(5)
2.2441(16)
2.2591(17)
N(2)-C(44)
N(2)-S(2)
C(44)-O(4)
1.344(8)
1.620(5)
1.227(8)
N(1)-Cu(1)-P(2)
N(1)-Cu(1)-P(1)
P(2)-Cu(1)-P(1)
C(1)-N(1)-S(1)
116.07(15)
114.82(15)
129.07(6)
112.2(4)
C(1)-N(1)-Cu(1)
S(1)-N(1)-Cu(1)
O(1)-C(1)-N(1)
N(2)-Cu(2)-P(4)
122.0(4)
124.6(3)
122.7(6)
117.62(16)
N(2)-Cu(2)-P(3)
P(4)-Cu(2)-P(3)
C(44)-N(2)-S(2)
113.94(16)
128.43(6)
112.9(4)
C(44)-N(2)-Cu(2)
S(2)-N(2)-Cu(2)
O(4)-C(44)-N(2)
113.5(4)
132.7(3)
123.2(7)
[Cu(sacch)(PPh3)]2‚CH2Cl2 (5‚CH2Cl2)b
Cu(1)-N(1)
1.933(2)
2.130(2)
Cu(1)-P(1)
2.1884(9)
2.9978(8)
N(1)-C(1)
N(1)-S(1)
1.348(4)
1.644(2)
C(1)-O(1)
1.240(3)
124.1(3)
Cu(1)-O(1)#1
Cu(1)-Cu(1)#1
N(1)-Cu(1)-O(1)#1 107.28(10) N(1)-Cu(1)-Cu(1)#1
81.81(7) C(1)-N(1)-S(1)
76.32(6) C(1)-N(1)-Cu(1) 126.6(2)
111.72(3) S(1)-N(1)-Cu(1) 121.39(14)
111.86(19) O(1)-C(1)-N(1)
N(1)-Cu(1)-P(1)
O(1)#1-Cu(1)-P(1) 100.30(6)
151.61(8)
O(1)#1-Cu(1)-Cu(1)#1
P(1)-Cu(1)-Cu(1)#1
C(1)-O(1)-Cu(1)#1 123.78(19)
trans-[Cu(sacch)2(NH3)4] (6)c
Cu(1)-N(2)
Cu(1)-N(3)
2.027(12)
2.042(12)
Cu(1)-N(1)
N(1)-C(1)
2.508(12)
1.365(19)
N(1)-S(1)
1.591(12)
C(1)-O(1)
1.259(17)
N(2)-Cu(1)-N(3)
N(2)-Cu(1)-N(3)#1
N(2)-Cu(1)-N(1)#1
93.1(5)
86.9(5)
95.5(4)
N(3)-Cu(1)-N(1)#1
N(2)-Cu(1)-N(1)
N(3)-Cu(1)-N(1)
87.7(4)
84.5(4)
92.3(4)
C(1)-N(1)-S(1)
C(1)-N(1)-Cu(1)
111.2(11)
128.1(10)
S(1)-N(1)-Cu(1)
O(1)-C(1)-N(1)
118.5(7)
125.5(15)
[Cu(sacch)(NH3)4](sacch)‚H2O (7)
Cu(1)-N(3)
Cu(1)-N(4)
Cu(1)-N(6)
Cu(1)-N(5)
Cu(1)-N(1)
2.017(2)
2.033(2)
2.030(3)
2.033(2)
2.030(3)
2.041(2)
2.035(3)
2.050(2)
2.328(2)
2.309(2)
Cu(1)-O(5)
S(1)-O(2)
S(1)-O(3)
S(1)-N(1)
2.715(2)
2.705(3)
1.441(2)
1.458(5)
1.451(2)
1.457(5)
1.611(2)
1.596(5)
N(1)-C(1)
C(1)-O(1)
S(2)-O(5)
S(2)-O(6)
1.363(3)
1.371(2)
1.228(3)
1.223(3)
1.441(2)
1.434(5)
1.448(2)
1.454(5)
S(2)-N(2)
S(2)-C(14)
N(2)-C(8)
C(8)-O(4)
1.609(2)
1.635(4)
1.764(3)
1.748(5)
1.363(3)
1.362(2)
1.231(3)
1.238(3)
N(3)-Cu(1)-N(4)
N(3)-Cu(1)-N(6)
N(4)-Cu(1)-N(6)
N(3)-Cu(1)-N(5)
N(4)-Cu(1)-N(5)
N(6)-Cu(1)-N(5)
N(3)-Cu(1)-N(1)
87.79(11)
87.16(9)
172.82(12)
172.49(11)
89.72(12)
90.04(9)
90.08(12)
90.07(8)
172.34(12)
171.94(11)
91.51(12)
91.76(9)
N(4)-Cu(1)-N(1)
N(6)-Cu(1)-N(1)
N(5)-Cu(1)-N(1)
N(3)-Cu(1)-O(5)
N(4)-Cu(1)-O(5)
N(6)-Cu(1)-O(5)
93.23(10)
93.80(8)
94.49(10)
94.90(8)
94.22(10)
93.87(9)
96.28(10)
96.82(9)
81.89(10)
82.38(9)
76.69(10)
75.89(8)
N(5)-Cu(1)-O(5)
N(1)-Cu(1)-O(5)
C(1)-N(1)-S(1)
C(1)-N(1)-Cu(1)
S(1)-N(1)-Cu(1)
O(1)-C(1)-N(1)
91.03(10)
90.45(9)
169.87(7)
169.96(9)
111.9(2)
112.09(19)
124.9(2)
124.32(12)
122.62(11)
122.76(17)
124.1(2)
S(2)-O(5)-Cu(1)
O(5)-S(2)-O(6)
O(5)-S(2)-N(2)
O(6)-S(2)-N(2)
C(8)-N(2)-S(2)
O(4)-C(8)-N(2)
126.97(12)
125.6(2)
113.44(13)
113.8(3)
111.58(13)
111.4(3)
111.11(13)
109.7(3)
111.4(2)
111.3(2)
124.4(2)
124.45(19)
124.60(19)
92.38(10)
92.24(9)
a For 7, the distances and angles from the neutron diffraction analysis are given in italics. b Symmetry transformations used to generate equivalent
1
atoms for 5: (#1) -x, y, -z + /2. c Symmetry transformations used to generate equivalent atoms for 6: (#1) -x, -y, -z.
corresponds to the crystallographic asymmetric unit and consists
of the copper atom with its four NH3 ligands, one imido-bound
saccharinate (Cu-Nimido ) 2.328(2) Å from the X-ray analysis),
one semicoordinated saccharinate (Cu-Osulfonyl ) 2.715(2) Å),
and one unligated molecule of water. The copper center has a
distorted-octahedral environment, in which the N-bound sac-
charinate is closer to the metal than in complex 6 and the
sulfonyl oxygen atom trans to this moiety is farther away. Table
2 presents selected distances and angles about the metal center.
The presence of the unusual molecular entity [Cu(sacch)(NH3)4]-
(sacch), with one saccharinate semicoordinated through a
sulfonyl oxygen atom, is the result of the formation of a
supramolecular aggregate (Figure 6) consisting of two formula
units of 7, in which the “semicoordinated” saccharinate par-
ticipates in three hydrogen bonds and one electrostatic inter-
action that approximates hydrogen bonding. The unligated water
molecule is the donor in two hydrogen bonds that bind the
aggregate, and it is the acceptor in a further electrostatic
interaction which must also contribute significantly to stabilizing
the overall structure. The aggregate structure sits across a
crystallographic inversion center, and as shown in Figure 6, the
extensive set of hydrogen bonds and purely electrostatic contacts
binds the disparate and chemically unusual features of the
molecular structure into a more symmetrical pattern in which

Saccharinate as a Versatile Polyfunctional Ligand
Inorganic Chemistry, Vol. 40, No. 17, 2001 4461
Figure 5. One asymmetric unit of [Cu(sacch)(NH3)4](sacch)‚H2O (7),
from the neutron diffraction analysis. Atom S(1) was refined isotro-
pically. All other atoms are represented by their 50% probability
ellipsoids.
Figure 2. One molecule of Cu(sacch)(PPh3)2 (4), from the crystal
structure of 4‚3/4CHCl3. Carbon and hydrogen atoms are shown as
circles. Other atoms are represented by their 50% probability ellipsoids.
Figure 3. Drawing of [Cu(sacch)(PPh3)]2 (5), from the crystal structure
of 5‚CH2Cl2. Phenyl group hydrogen atoms have been omitted. Phenyl
carbon atoms and the hydrogen atoms of saccharinate are represented
as circles. Other atoms are drawn as their 50% probability ellipsoids.
Figure 6. Drawing of the supramolecular aggregate formed by two
asymmetric units of [Cu(sacch)(NH3)4](sacch)‚H2O (7), from the
neutron diffraction analysis. Atoms with “A” appended to their names
are related to their congeners by a crystallographic inversion center.
longer, on average, than those observed using X-ray diffraction;
this is the expected difference between the internuclear distance
observed by neutron diffraction and the difference between the
centers of electron density observed using X-rays. The dimin-
ished libration at the lower temperature of the neutron structure
determination is also expected to contribute to this difference,
albeit to a lesser extent. The C-H bond distances also differ
by 0.16[2] Å on average. Of the two O-H bonds in the water
molecule, one is about 0.1 Å longer in the neutron diffraction
results, and the other is essentially identical in the neutron and
X-ray analyses; the latter is likely an artifact of an anomalously
large value from the X-ray determination, which is more prone
to inaccuracies in hydrogen atom positions.
IR Spectroscopy. Table 4 lists the most important IR bands
for compounds 3-7. The vibrational energies are well correlated
with what is seen in the crystal structures. The CdO stretch of
saccharinate is shifted to lower energy in compound 5 as
compared to 4, because in the former the carbonyl group is
bound to one metal as part of the bridging system. The carbonyl
stretch is found at even lower energy in 3, in which sacch binds
to copper exclusively through CdO. The other relevant IR
bandssM-N, SdO2, N-H, and O-Hsare all consistent with
the structures found by diffraction. It appears that the CdO bond
distances tend to longer values as the carbonyl oxygen becomes
more involved in coordination, although the statistical signifi-
cance of slight differences in the relevant CdO and C-N bond
distances does not permit rigorous discrimination among the
values observed for 3-5. We simply note that the CdO and
C-N bonds tend to follow the expected trend11 of longer Cd
Figure 4. Structure of trans-[Cu(sacch)2(NH3)4] (6): (a) thermal
ellipsoid plot (50% probability), with the atom-labeling scheme
indicated; (b) side-on view, showing the distortion caused by pitching
of the saccharinate ligands.
none of the potential donor or acceptor atoms in electrostatic
interactions remain unused.
The neutron structure determination of 7 serves the dual
purpose of providing a clear distinction between NH3 and H2O
in the structure and of supplying accurate parameters for the
hydrogen-bonding pattern. Table 3 lists the H-bonds and purely
electrostatic interactions, as characterized by both X-ray and
neutron diffraction. We note that the N-H bond distances that
emerge from the neutron structure determination are 0.16[2] Å

4462 Inorganic Chemistry, Vol. 40, No. 17, 2001
Falvello et al.
Table 3. Noncovalent Interactions within the Supramolecular Aggregate Formed by [Cu(sacch)(NH3)4](sacch)‚H2O (7)a
D-H‚‚‚A
D‚‚‚A, Å
D-H, Å
H‚‚‚A, Å
D-H‚‚‚A (deg)
acceptor coord
x, y, z
O(7) - H(71) ‚‚‚N(2)
2.862(3)
2.869(3)
3.038(4)
3.017(3)
3.142(4)
3.107(3)
3.150(4)
3.116(3)
2.915(3)
2.911(3)
0.85(4)
0.972(6)
0.97(6)
0.961(7)
0.81(4)
1.022(6)
0.92(5)
1.014(6)
0.93(4)
1.016(5)
2.01(4)
1.898(5)
2.07(6)
2.056(5)
2.36(4)
2.123(5)
2.28(5)
2.173(5)
2.00(4)
1.904(5)
176(4)
177.3(4)
174(4)
178.9(5)
163(4)
160.9(4)
157(4)
153.9(5)
173(3)
170.3(4)
O(7) - H(72) ‚‚‚N(2)
N(5) - H(52) ‚‚‚O(7)
N(5) - H(53) ‚‚‚O(4)
N(3) - H(32) ‚‚‚O(4)
1 - x, 1 - y, 1 - z
1 - x, 1 - y, 1 - z
1 - x, 1 - y, 1 - z
1 - x, 1 - y, 1 - z
a Values from the neutron structure determination are given in italics.
Table 4. Principal IR Bands (cm-1) for Compounds 3-7
Complex 6, trans-[Cu(sacch)2(NH3)4], was the original target
of this chemistry. It was expected that its preparation would
present no special problems, by analogy with the facile syntheses
of the analogous aqua complexes of first-row transition elements,
including copper, and of the ammine complexes of first-row
elements other than copper. The instability of 6 can be attributed
in large part to the availability of a highly stable alternative, 7;
however, the structure of 6 itself belies the presence of inherent
physical instability. The [Cu(NH3)4]2+ moiety is chemically
stable, but the weak bonding to saccharinatesenabled as one
of the possible expressions of the Jahn-Teller effect and
observed in the long bond distance and especially in the
misdirected valencesundoubtedly confers a high degree of
lability on the complex. It is noteworthy that although the loss
of both sacch ligands from 6 would yield the stable entity [Cu-
(NH3)4]2+, in the actual event the formation of 7 brings one of
the sacch ligands closer to the copper center.
Scheme 1 summarizes the whole reaction system. The powder
blue tetraaquabis(saccharinato)copper(II) dihydrate (1) turns
deep green upon dehydration in an oven, presumably through
loss of the waters of hydration, yielding 2. This complex is the
point of departure for the three Cu(I) complexes 3-5, in which
saccharinate is fully coordinated but with its bulk either nearer
the center of the complex or farther away, depending on the
steric permittivity of the remaining ligand arrangement. Any
of the three Cu(I) complexes reacts with NH3 in the absence of
water to give the sky blue tetraamminobis(saccharinato)copper-
(II) (6) which evolves rapidly to the royal blue complex 7 if
water is not rigorously excluded. Except for the three colorless
Cu(I) complexes, all of the compounds can be distinguished
easily from each other by their colors.
assignt
3
4
5
6
7
CdO str 1612 1661
1637
397
1686-1612 1668-1587
402, 346 401
M-N
SdO
394
1153 1158, 1152 1168, 1157 1142, 1137, 1154, 1119,
1117 1054
3355 3351
3610
N-H
O-H
O and shorter C-N distances as the carbonyl becomes more
involved in coordination (i.e., on going from 4 to 5 to 3).
Discussion
The most important result to emerge from this study of the
Cu/sacch/{H2O,PPh3,NH3} system is the manner in which
saccharinate employs its polyfunctional nature to adapt to the
steric needs of the complexes. Each of the three full coordination
modes possible for sacchsbridging through the amidato-like
system, coordinated through the imido nitrogen atom, and
coordinated through the carbonyl oxygensimposes distinct steric
encumbrances on the complex formed; in each of the Cu(I)
compounds saccharinate adopts the coordination mode appropri-
ate to its surroundings. The Cu(I) compounds appear to
participate in a complex equilibrium in solution, but we have
found that the principal Cu(I) product isolated from a given
reaction of 2 with PPh3 possesses one fewer phosphine moiety
than the number used in the preparation. Thus, for example, if
a sacch:PPh3 ratio of 1:4 is used in the preparation, the principal
product isolated is complex 3, Cu(sacch)(PPh3)3. Except for 6,
all of the compounds are stable enough to be handled without
unusual precautions, and except for 6 all can be isolatedseither
from this reaction system or from parallel preparationssin yields
ranging from moderate (about 50% for 5) to nearly quantitative
(complexes 4 and 7). This signifies that the observed bonding
modes are stable as well as interchangeable.
The semicoordination mode observed for one sacch moiety
in 7sthat is, the formation of a long contact to copper through
a sulfonyl oxygen atomsis unusual and requires explanation,
especially in light of the fact that all of the other products evolve
easily to 7 in the presence of the appropriate reagents. The
formation of the aggregate structure (Figure 6) in the solid state
must be the source of the special stability of 7scrystals can
even be kept under hard vacuum for periods of at least minutes
without losing the unligated water. We do not expect that an
isolated chemical entity such as that shown in Figure 5 has a
significant lifetime in solution. We attempted to prepare complex
6, trans-[Cu(sacch)2(NH3)4], by various means beginning with
7; we were unsuccessful in all cases, showing that dehydration
of 7 and rearrangement of one saccharinate do not yield a more
stable product. Although the aggregate does not possess any
exceptionally strong hydrogen bonds, its overall stability is
sufficient to make it a dominant feature of this chemistry.
The very stable complex 1, with four aqua ligands in its
central plane, gives way at the bottom of the reaction system
to products 6 and 7, in which the equatorial plane is populated
by four NH3 ligands. The identities of the auxiliary ligands H2O
in 1 and NH3 in 7 have been established by single-crystal
neutron diffraction analyses. (The neutron structure determina-
tion of 1 was reported previously.24) The neutron analysis was
particularly useful for 7, which has both ammine ligands and
unligated water, although the identity of the water is clear from
its role as acceptor in electrostatic interactions. The identity of
the four auxiliary ligands NH3 in complex 6 is inferred from
their identity in complex 7.
Conclusion
Saccharinate, as a ligand in coordination chemistry, has
previously been observed to approach transition metal centers
in four different ways, although coordination through the imido
(24) Cotton, F. A.; Falvello, L. R.; Murillo, C. A.; Schultz, A. J. Eur. J.
Solid State Inorg. Chem. 1991, 29, 311-320.

Saccharinate as a Versatile Polyfunctional Ligand
Inorganic Chemistry, Vol. 40, No. 17, 2001 4463
nitrogen atom is by far the most commonly observed bonding
mode. In the present study, the results with the [CuI(sacch)x-
(PPh3)y] complexes demonstrate that with a given transition
metal and chemical environment, the coordination mode of
saccharinate is highly adaptable to the steric requirements of
the complex formed. The formation of the ammine complex 7
shows that the most basic atoms of saccharinate can be used in
the formation of a structurally dominant supramolecular ag-
gregate while its weakest electron donor, a sulfonyl oxygen
atom, is directed at the transition metal.
NH3 system was suggested by Prof. Carlos Murillo. We thank
Prof. Juan Fornie´s for generous logistical support throughout
the course of this work. Work at Argonne National Laboratory
was supported by the U.S. Department of Energy, Office of
Basic Energy Sciences, Division of Materials Sciences, under
Contract No. W-31-109-ENG-38.
Supporting Information Available: A Crystallographic Informa-
tion File (CIF) containing crystal data, experimental parameters, and
structural results for the X-ray analyses of 3-7 and for the neutron
structure determination of 7. This material is available free of charge
via the Internet at http://pubs.acs.org.
Acknowledgment. Funding from the Directorate General
for Higher Education (Spain) under Grant PB98-1593 is
gratefully acknowledged. The potential interest of the Cu/sacch/
IC010300X