Stabilization of copper(II) thiosulfonate coordination complexes through cooperative hydrogen bonding interactions

Article abstract of DOI:10.1021/ic801234c

A series of copper(II) thiosulfonate complexes have been prepared via the reaction of [Cu(Me₃tren)(OH₂)](ClO₄) ₂ (Me₃tren = tris(2-methylaminoethyl)amine) with three thiosulfonate ligands (RSO₂S^-, where R = Me, Ph, and MePh) and characterized by microanalysis, FTIR spectroscopy, and X-ray crystallography. In these complexes, the distorted trigonal bipyramidal copper(II) coordination sphere is occupied by four amine nitrogen atoms from the tripodal tetramine ligand and an apically bound sulfur atom from the thiosulfonate ligand. By using the tripodal tetramine ligand the oxidation of the thiosulfonate has been restricted, allowing the isolation of the complexes. The Cu-S distances were found to be similar to those in related thiosulfate complexes, indicating coordinative interactions of similar strength. Two types of intramolecular hydrogen bonding interactions were evident which enhance the binding of the thiosulfonate to the copper(II) center. These interactions, which involve two amine N-H groups and either one or two thiosulfonate oxygens, were found to be weaker than in the corresponding thiosulfate complexes. The complex formation constants for the thiosulfonate complexes (log K_f = 0.3-0.7) were found to be two orders of magnitude lower than compared to the thiosulfate analogues. This correlates well with a lower strength of intramolecular hydrogen bonding.

Full text of DOI:10.1021/ic801234c

Inorg. Chem. 2008, 47, 10565-10574
Stabilization of Copper(II) Thiosulfonate Coordination Complexes
Through Cooperative Hydrogen Bonding Interactions
Adam J. Fischmann, Craig M. Forsyth, and Leone Spiccia*
School of Chemistry, Monash UniVersity, Victoria 3800, Australia
Received July 3, 2008
A series of copper(II) thiosulfonate complexes have been prepared via the reaction of [Cu(Me3tren)(OH2)](ClO4)2
(Me3tren ) tris(2-methylaminoethyl)amine) with three thiosulfonate ligands (RSO2S-, where R ) Me, Ph, and
MePh) and characterized by microanalysis, FTIR spectroscopy, and X-ray crystallography. In these complexes, the
distorted trigonal bipyramidal copper(II) coordination sphere is occupied by four amine nitrogen atoms from the
tripodal tetramine ligand and an apically bound sulfur atom from the thiosulfonate ligand. By using the tripodal
tetramine ligand the oxidation of the thiosulfonate has been restricted, allowing the isolation of the complexes. The
Cu-S distances were found to be similar to those in related thiosulfate complexes, indicating coordinative interactions
of similar strength. Two types of intramolecular hydrogen bonding interactions were evident which enhance the
binding of the thiosulfonate to the copper(II) center. These interactions, which involve two amine N-H groups and
either one or two thiosulfonate oxygens, were found to be weaker than in the corresponding thiosulfate complexes.
The complex formation constants for the thiosulfonate complexes (log Kf ) 0.3-0.7) were found to be two orders
of magnitude lower than compared to the thiosulfate analogues. This correlates well with a lower strength of
intramolecular hydrogen bonding.
Introduction
The rapid oxidation of thiosulfate by copper(II) ions is a
well-known reaction, and it is generally accepted that a
copper(II)-thiosulfate complex is a reactive intermediate that
Figure 1. Structures of (a) thiosulfate, (b) thiosulfonates, and (c) thiosul-
fonate esters.
promotes this reaction. As a direct consequence of this
reactivity, there have been few reported examples of stable
copper(II)-thiosulfate coordination complexes.1-3 In each
of these examples, the copper(II) ion was five-coordinate and
the thiosulfate anion was coordinated in a monodentate
fashion via the terminal sulfur atom. The coordination sphere
of the copper(II) center was completed by four nitrogen donor
atoms, either from two ethylenediamine (en) ligands1,2 or
from a tripodal tetraamine ligand (e.g., tren, tris(2-amino-
ethyl)amine, and derivatives thereof).3
the study of the coordination chemistry of thiosulfonates
(RS2O2 ), organic derivatives of thiosulfate in which one of
-
the oxygen atoms is formally replaced by an organic group
(Figure 1). (We note that both thiosulfonate esters (Figure
1c) and thiosulfonate anions (Figure 1b) have been referred
to as thiosulfonates; herein, “thiosulfonate” refers to the
anion). The bond angles around the central sulfur atom are
close to tetrahedral (thiosulfate possesses C3V symmetry
whereas thiosulfonates are at most Cs). As is the case for
thiosulfate, the common coordination mode for thiosulfonates
is via the terminal sulfur atom.
Most previous research on thiosulfonates has had a
biological emphasis. Thiosulfonate salts have been investi-
gated as more effective antidotes for cyanide poisoning than
thiosulfate, in combination with the enzyme rhodanese
Further insights into the structure and properties of these
reactive copper(II) thiosulfate complexes can be gained via
* To whom correspondence should be addressed. E-mail: leone.spiccia@
sci.monash.edu.au. Fax: +61-3-9905-4597.
(1) Podberezskaya, N. V.; Borisov, S. V.; Bakakin, V. V. J. Struct. Chem.
(Engl. Transl.) 1971, 12, E770-774.
(2) Fu, A.-Y.; Wang, D.-Q.; Wang, F.-M. Acta Crystallogr., Sect. E:
Struct. Rep. Online 2004, 60, 1527–1529.
(3) Fischmann, A. J.; Warden, A. C.; Black, J.; Spiccia, L. Inorg. Chem.
2004, 43, 6568–6578.
10.1021/ic801234c CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 22, 2008 10565
Published on Web 10/24/2008

Fischmann et al.
(thiosulfate:cyanide sulfur transferase).4-6 Biological forma-
tion of thiosulfonate compounds, such as thiotaurine (2-
aminoethanethiosulfonate)7 and alaninethiosulfonate,8 has
also been established. Some deep-sea invertebrates that live
near hydrothermal vents produce thiotaurine from hypotau-
rine (2-aminoethanesulfinate), to detoxify the high concentra-
tions of H2S.6,9 Thiotaurine has been used as a pretreatment
for sulfur mustard (mustard gas) poisoning10 while thiosul-
fonic acids (and their S-esters) are biologically active as
fungicides and bactericides.11
The coordination chemistry of thiosulfonates has not
been extensively studied. The limited examples of thiosul-
fonate-metal complexes include Au(I),12-17 Cu(I),18,19
Fe(II),20 Ru(II),21,22 Ag(I),23 Hg(II),23 Pt(II),24,25 and Ir(III)26
complexes. To our knowledge there have not been any
quantitative studies on the formation of Cu(II) thiosulfonates
complexes. The monothiosulfonato-Cu(I) complexes
(CuMeS2O2, CuEtS2O2, and CuPrS2O2) were, however,
obtained via reduction of copper(II) by thiosulfonates.18,19
In an extension of our previous work, in which a series of
thiosulfate complexes were stabilized through the use of the
tripodal tetradentate ligand tris(2-aminoethyl)amine (tren) and
several N-functionalized derivatives of tren,3 we present
herein the first detailed investigation of copper(II) thiosul-
fonate complexes. We report the syntheses, characterization,
and X-ray crystal structures of three copper(II) complexes
of composition [Cu(Me3tren)(RS2O2)](ClO4), where Me3tren
) tris(2-methylaminoethyl)amine and R ) Me, Ph, and
MePh, and compare structural features of these complexes,
for example, intramolecular hydrogen bonding, with those
of thiosulfate copper(II) complexes bearing these tripodal
polyamine ligands.3 Taking advantage of the fact that, as
was the case for thiosulfate, coordination of thiosulfonate
to copper(II) is characterized by an intense L f Cu(II) charge
transfer transition in the 300-400 nm spectral region,
-
constants for binding of methanethiosulfonate (MeS2O2 ) to
the tren and Me3tren copper(II) complexes have been
determined and are compared to those reported previously
for the corresponding thiosulfate complexes.3
Experimental Section
Materials and Reagents. Me6tren, Bz3tren, [Cu(tren)(H2O)]-
(ClO4)2, [Cu(Me6tren)(H2O)](ClO4)2, [Cu(Me3tren)(H2O)](ClO4)2,
and [Cu(Bz3tren)(H2O)](ClO4)2 were synthesized as described
previously (tren ) tris(2-aminoethyl)amine, Me3tren ) tris(2-
methylaminoethyl)amine, and Me6tren ) tris(2,2-dimethylamino-
ethyl)amine).3 The syntheses of NaMeS2O2 ·H2O,7 NaPhS2O2,8 and
NaMePhS2O28 were based on literature procedures. Other chemicals
were used as received from commercial suppliers. Deoxygenated
water was prepared by boiling freshly distilled water under nitrogen
for 2 h.
Instrumentation. UV-visible-NIR spectra were recorded on
a Varian Cary 5G spectrophotometer fitted with a water-jacketed
cell holder. An externally circulating water bath (Varian) maintained
the temperature to a precision of (0.1 °C. FTIR spectra were
recorded using either a Perkin-Elmer 1600 FTIR or a Bruker
Equinox IFS 55 FTIR to a resolution of 4 cm-1. A Bruker Equinox
IFS 55 FTIR fitted with a Specac Goldengate ATR stage was used
for recording ATR-IR spectra. The pH of stock solutions for
spectrophotometric studies was fixed using a Titrando autoburette,
fitted with a Metrohm electrode. Elemental analyses were performed
by Campbell Microanalytical Services, University of Otago, New
Zealand.
[Cu(Me3tren)(MePhS2O2)]ClO4. [Cu(Me3tren)(H2O)](ClO4)2 (9
mg, 0.02 mmol) was dissolved in a minimum amount of MeCN to
give a blue solution, and NaMePhS2O2 (10 mg, 0.050 mmol) was
added. The mixture was filtered, yielding a green solution. Slow
diffusion of Et2O into the filtrate resulted in crystallization of green
plates after several days. Analysis via single crystal X-ray crystal-
lography confirmed the formation of [Cu(Me3tren)(MePhS2O2)]-
ClO4. Yield: 1 mg (11%).
(4) Petrikovics, I.; Pei, L.; McGuinn, W. D.; Cannon, E. P.; Way, J. L.
Fundam. Appl. Toxicol. 1994, 23, 70–75.
(5) Frankenberg, L. Arch. Toxicol. 1980, 45, 315–323.
(6) Pruski, A. M.; Fiala-Me´dioni, A. J. Exp. Biol. 2003, 206, 2923–2930.
(7) Cavallini, D.; de Marco, C.; Mondovi, B. J. Biol. Chem. 1959, 234,
854–857.
(8) So¨rbo, B. Biochim. Biophys. Acta 1957, 24, 324–329.
(9) Rosenberg, N. K.; Lee, R. W.; Yancey, P. H. J. Exp. Zool. 2006, 305A,
655–622.
(10) Baskin, S. I.; Prabhaharan, V.; Bowman, J. D.; Novak, M. J. J. Appl.
Toxicol. 2000, 20, S3-S5.
(11) Janota, H.; Zakrzewski, A. Pol. J. Appl. Chem. 1991, 35, 265–271.
(12) Roembke, P.; Schmidbaur, H.; Cronje, S.; Raubenheimer, H. J. Mol.
Catal. A: Chem. 2004, 212, 35–42.
(13) Ro¨mbke, P.; Schier, A.; Wiesbrock, F.; Schmidbaur, H. Inorg. Chim.
Acta 2003, 347, 123–128.
(14) Cleary, B. P.; Lok, R.; White, W. W. U.S. Patent, EP1388536A1,
2004, 13 pages.
(15) Lok, R.; White, W. W. U.S. Patent, US 5620841, 1997, 9 pages.
(16) Lok, R.; White, W. W. U.S. Patent US 5700631, 1997, 9 pages.
(17) Lok, R.; White, W. W.; Marshall, M. W. U.S. Patent, US 5939245,
1999, 9 pages.
(18) Gundorina, A. A. Russ. J. Org. Chem. 1986, 31, 689–690.
(19) Gundorina, A. A.; Sergeeva, A. N. Koord. Khim. 1978, 4, 522–526.
(20) El-khateeb, M.; Shaver, A.; Lebuis, A.-M. J. Organomet. Chem. 2001,
622, 293–296.
(21) El-khateeb, M.; Wolfsberger, B.; Schenk, W. A. J. Organomet. Chem.
2000, 612, 14–17.
(22) Shaver, A.; Plouffe, P.-Y. J. Am. Chem. Soc. 1991, 113, 7780–7782.
(23) Dundorina, A. A.; Sergeeva, A. N. Russ. J. Inorg. Chem. 1974, 19,
181–183.
A better yielding synthesis of this compound was developed as
follows. [Cu(Me3tren)(H2O)](ClO4)2 (0.18 g, 0.40 mmol) was
dissolved in 15 mL of hot iPrOH, and NaMePhS2O2 (0.083 g, 0.40
mmol) was added in portions while stirring. Upon addition of the
first portion of the thiosulfonate salt, an immediate blue to green
color change occurred. At the completion of the addition of the
thiosulfonate salt, the solution was dark green and clear. Stirring
was continued for a few minutes, and a green solid was found to
precipitate. The solid was collected by filtration of the solution after
it had been allowed to stand at room temperature (RT) for a few
minutes. The microcrystalline green product was dried at the pump
and washed with Et2O. Yield: 0.12 g (56%). Characterization.
Microanalyses: Found (%): C, 35.8; H, 5.8; N, 10.4. Calculated
for C16H31ClCuN4O6S2 (%): C, 35.7; H, 5.8; N, 10.4. Selected IR
bands [KBr disk: ν (cm-1)]: 3254 s, 2883 m, 1251 m, 1124 s,
1102 s, 1066 s, 988 m, 856 m, 825 m, 708 m, 662 s, 624 m.
[Cu(Me3tren)(PhS2O2)]ClO4. [Cu(Me3tren)(H2O)](ClO4)2 (9
mg, 0.02 mmol) was dissolved in minimum MeCN to give a blue
solution, and NaPhS2O2 (10 mg, 0.05 mmol) was added. Slow
diffusion of Et2O into the green filtrate obtained following filtration
of this mixture caused green blocks of the desired product to
crystallize after several days, along with white/colorless needles,
which were assumed to be NaPhS2O2. Analysis of the green blocks
(24) Weigand, W.; Wu¨nsch, R. Chem. Ber. 1996, 129, 1409–1419.
(25) Stachel, H.-D.; Eckl, E.; Immerz-Winkler, E.; Kreiner, C.; Weigand,
W.; Robl, C.; Wu¨nsch, R.; Dick, S.; Drescher, N. HelV. Chim. Acta
2002, 85, 4453–4467.
(26) Strope, D.; Shriver, D. F. Inorg. Chem. 1974, 13, 2652–2655.
10566 Inorganic Chemistry, Vol. 47, No. 22, 2008

Stabilization of Cu(II) Thiosulfonate Coordination Complexes
Table 1. Crystal Data for [CuL(MePhS2O2)]ClO4 (I), [CuL(PhS2O2)]ClO4 (II), and [CuL(MeS2O2)]ClO4 (III) (L ) Me3tren)
crystal data
I
II
III
empirical formula
C16H31ClCuN4O6S2
538.56
monoclinic
P21/n
11.302(1)
8.598(1)
24.084(3)
96.490(3)
2325.2(5)
4
C15H29ClCuN4O6S2
524.53
monoclinic
P21/n
7.9481(5)
21.598(1)
12.8819(8)
106.872(3)
2116.2(2)
4
C10H27ClCuN4O6S2
462.27
monoclinic
P21/c
10.5593(8)
23.073(2)
16.117(1)
107.938(2)
3735.8(5)
8
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
ꢁ (deg)
V (Å3)
Z
Fcalcd (g cm-3
)
1.538
1.273
55.4
23438
1.646
1.396
60.0
28997
1.643
1.569
55.0
39905
µ Mo KR (mm-1
2θmax (deg)
)
reflections collected
unique reflections (Rint
)
5426 (0.0563)
5117
1.394
7145 (0.0291)
6774
1.313
0.0494, 0.0894
0.748, -0.528
8573 (0.0555)
7720
1.349
0.0841, 0.1498
1.099, -0.975
“observed” [I > 2σ(I)] reflections
GOF on F2
R1,a wR2b [I > 2σ(I)]
0.0808, 0.1378
0.566, -0.728
2
maximum difference peak, hole (e Å-3
)
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
2
2
by X-ray diffraction confirmed that the compound was
[Cu(Me3tren)(PhS2O2)]ClO4. Insufficient compound was obtained
to permit further characterization.
measurements were prepared immediately prior to use. For the
-
[Cu(tren)(H2O)]2+-MeS2O2 binding studies, four stock solutions
were prepared from deoxygenated water: (i) a buffer solution
prepared from the free acid of MOPS (0.140 M) and sufficient
NaClO4 ·H2O to obtain an ionic strength (I) of 0.150 M after titration
to pH 7.5 with ∼2 M NaOH; (ii) a CuL2+ solution containing 1.20
A slightly higher yielding synthesis was based on the preparation
of [Cu(Me3tren)(MePhS2O2)]ClO4. [Cu(Me3tren)(H2O)](ClO4)2 (0.10
g, 0.21 mmol) and 1 equiv of NaPhS2O2 (0.042 g, 0.20 mmol) were
dissolved in a minimal amount of hot iPrOH, and the solution was
heated at ∼80 °C for 5 min. The solution was then filtered while
hot, allowed to slowly cool to RT, and then stored overnight at 4
°C. Small green crystals formed after one week, which were
collected by vacuum filtration and washed with Et2O. The green
color of the filtrate indicated that significant amounts of the
compound remained in solution. Yield: 10 mg (9%). Charac-
terization. Microanalyses: Found (%): C, 34.3; H, 5.5; N, 10.5.
Calculated for C15H29ClCuN4O6S2 (%): C, 34.4; H, 5.6; N, 10.7.
Selected IR bands [KBr disk: ν (cm-1)]: 3286 (m), 3255 (m),
2969 (m), 2926 (m), 2886 (m), 1250 (s), 1124 (s), 1102 (s),
1065 (s), 986 (m), 964 (m), 856 (m), 824 (m), 761 (m), 718
(m), 691 (m), 618 (s), 610 (m).
-
mM [Cu(tren)(H2O)](ClO4)2 (I ) 3.60 mM); (iii) a MeS2O2
solution consisting of 0.200 M NaMeS2O2 ·H2O (I ) 0.200 M),
which was filtered through a 0.22 µm Millipore membrane to
remove traces of suspended solids, such as elemental sulfur, prior
to use; and (iv) a 0.200 M NaClO4 · H2O solution. Solutions with
different MeS2O2- concentrations (I ) 0.200 M) were prepared
by mixing appropriate volumes of the MeS2O2- and ClO4- stock
solutions. The buffer, CuL2+, and MeS2O2- solutions were then
mixed in the ratio 1/3:1/6:1/2, which resulted in a final ionic
strength of 0.15 M. Prior to mixing the three solutions, the
-
MeS2O2 solution was equilibrated at 25 °C in the thermostatted
spectrophotometer cell block, and the CuL2+ and MOPS solutions
were mixed and equilibrated at 25 °C in a thermostatted water bath.
For the [Cu(Me3tren)(H2O)]2+-MeS2O2- and [Cu(Me6tren)(H2O)]2+
-
[Cu(Me3tren)(MeS2O2)]ClO4. NaMeS2O2 · H2O (28 mg, 0.18
mmol) was dissolved, with gentle heating, in 5 mL of 95% EtOH.
To this solution was added 1 mL of a 25 mM MeOH solution of
[Cu(Me3tren)(H2O)](ClO4)2 (0.025 mmol). The solution was taken
to dryness by rotary evaporation and the residue dissolved in ∼1
-
MeS2O2 systems, the stock solutions and samples were prepared
as described for [Cu(tren)(H2O)](ClO4)2 but using [Cu(Me3tren)-
(H2O)](ClO4)2 and [Cu(Me6tren)(H2O)](ClO4)2 with a few minor
differences as outlined below. The concentration of the
Cu(Me3tren)2+ stock solution was 2.99 mM rather than 1.20 mM
to achieve a sufficient change in the spectrum with increasing
[MeS2O2-] to allow measurement of the binding constant.
i
mL of PrOH to give a green solution (after gentle heating). A
further 1 mL of iPrOH was added, and slow diffusion of Et2O into
this solution yielded small green crystals after a few hours. One
crystal was analyzed by X-ray diffraction and found to be
[Cu(Me3tren)(MeS2O2)]ClO4. Insufficient compound was obtained
for further characterization.
Crystallography. Single-crystal X-ray data were collected on a
Bruker X8 Apex diffractometer with monochromated Mo KR
radiation (λ ) 0.71073 Å) at 123(2) K using ꢀ and/or ω scans
(Table 1). Data were corrected for Lorentz and polarization effects,
and absorption corrections were applied using SADABS.27 The
structures were solved by conventional methods and refined using
the full-matrix least-squares method using the SHELXS-9728 and
SHELXL-9729 programs, respectively. The program X-Seed30 was
used as an interface to the SHELX programs and to prepare the
A larger batch was prepared by dissolving [Cu(Me3tren)(H2O)]-
(ClO4)2 (10 mg, 0.21 mmol) and NaMeS2O2 ·H2O (31 mg, 0.20
i
mmol) in a minimum amount of hot PrOH. The solution was
filtered while hot, slowly cooled to RT, and then stored at 4 °C for
several hours. Green crystals formed which were collected by
filtration and washed with Et2O. Yield: 7 mg (7%). Characterization.
Microanalyses: Found (%): C, 26.2; H, 5.8; N, 12.1. Calculated
for C10H27ClCuN4O6S2 (%): C, 26.0; H, 5.9; N, 12.1. Selected IR
bands [KBr disk: ν (cm-1)]: 3257 s, 2966 m, 2926 m, 2881 m,
1459 m, 1257 m, 1206 m, 1076 br s, 990 m, 958 m, 859 m, 829 m,
747 m, 624 m.
(27) Sheldrick, G. M. SADABS; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
(28) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(29) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(30) Barbour, L. J. J. Supramol. Chem. 2001, 1, 189–191.
Spectrophotometric Studies. Due to the slow decomposition
of the thiosulfonate solutions, all solutions for spectrophotometric
Inorganic Chemistry, Vol. 47, No. 22, 2008 10567

Fischmann et al.
Table 2. Position of ν(SO2) Vibrations in Thiosulfonate Compounds
ligand
compound
ν(SO2) (cm-1
)
ref
-
MeS2O2
NaL·H2O
1196, 1084
1220-1180 (br),
1100-1075 (br)
this work
32
NaL
[Cu(Me3tren)(L)]ClO4 1257, 1206, 1076
[Ru(Cp)(dppe)(L)]
this work
21
33
1266a
1190, 1120, 1070
-
MePhS2O2 NaL
[Cu(Me3tren)(L)]ClO4 1251, 1122, 1089
this work
22
[Ru(Cp)(Ph3P)(CO)(L)] 1266a
-
PhS2O2
NaL
NaL
1225, 1191, 1121,
1067
1220, 1120,
this work
33, 34
1070 1190, 1117, 1063
[Cu(Me3tren)(L)]ClO4 1250, 1123, 1065
[Ru(Cp)(dppe)(L)]
1253a
a Some stretches obscured by other ligand vibrations.
this work
21
figures. Non-hydrogen atoms were refined with anisotropic thermal
parameter forms. Hydrogen atoms attached to carbon were placed
in calculated positions using a riding model and with Uiso(H) )
1.2-1.5Uiso(C); otherwise, they were located on Fourier difference
maps and refined with isotropic thermal parameters (N-H distances
were restrained to reasonable values in III, while for I the amine
hydrogen atoms, H(1), H(2), and H(3), were constrained to have
identical thermal motion). In the structure of III, one SO2Me group
was modeled as disordered, with the methyl carbon and one oxygen
atom occupying two alternate positions, having refined occupancies
of 0.88:0.12. The anisotropic refinement of the minor disordered
component was restrained to be the same as that of the major
component. The data for I and II showed several significant
systematic absence violations for the space group P21/n; however,
refinement in lower symmetry space groups was less satisfactory.
Figure 2. Section of FT IR spectra of (a) [Cu(Me3tren)(H2O)](ClO4)2; (b)
NaPhS2O2; and (c) [Cu(Me3tren)(PhS2O2)]ClO4.
The comparison of IR spectra in Figure 2 illustrates the
changes that occur on coordination of thiosulfonates to
Cu(II). The two bands associated with the split νas(SO2) mode
at 1225 and 1191 cm-1 (NaPhS2O2, spectrum b) combine
and shift to 1251 cm-1 for Cu(Me3tren)(PhS2O2)]ClO4
(spectrum c). This band is absent in the spectrum of
[Cu(Me3tren)(H2O)](ClO4)2 (spectrum a), whereas a number
of other vibrations in the spectrum of [Cu(Me3tren)-
(PhS2O2)]ClO4 are common to NaPhS2O2 (1121 and 1067
cm-1) or [Cu(Me3tren)(H2O)](ClO4)2 (988, 963, 858, and 829
cm-1) The broad perchlorate bands in [Cu(Me3tren)-
(PhS2O2)](ClO4) (1000-1100 cm-1 region) are less intense
than the νs(SO2) bands.
Results and Discussion
Synthesis and Characterization. Generally, copper(II)
thiosulfonate complexes were prepared by dissolving the
precursor copper(II) tripodal amine complex and the sodium
i
thiosulfonate salt in hot PrOH, and allowing the resulting
green solution to slowly cool to RT. Isolated product yields
were relatively low due to the low stability of the thiosul-
fonate complexes (vide infra) and the fact that significant
amounts of the product remained in solution. The complexes
were characterized by IR spectroscopy, elemental analysis,
and X-ray crystallography.
The thiosulfonate complexes exhibited significant shifts of
the νas(SO2) and νs(SO2) vibrations on coordination to Cu(II)
when compared with those of the sodium salts of these ligands
(Table 2). The antisymmetric stretch, νas(SO2), is particularly
sensitive to metal ion coordination,21 generally shifting to higher
energy on coordination via the terminal sulfur. As for thiosulfate
compounds, the νs(SO2) mode shows only minor changes.31
The ν(SR) is less diagnostic, apart from being difficult to assign
in the aromatic thiosulfonates, although it seems to shift to lower
energy in thiosulfonate complexes. For example, the band at
768 cm-1 in NaMeS2O2 ·H2O shifts to 747 cm-1 in [Cu-
(Me3tren)(MeS2O2)]ClO4.
X-ray Crystal Structures. The molecular structures of
the copper(II)-thiosulfonate complexes [Cu(Me3tren)-
(RS2O2)]ClO4, determined by X-ray crystallography (Figures
3, 4, and 5 for R ) Ph, MePh, and Me, respectively),
confirmed that the thiosulfonate ligands coordinate to the
copper(II) center via the terminal sulfur atom. For the
-
MeS2O2
complex, two independent [Cu(Me3tren)-
(MeS2O2)]ClO4 units were found within the unit cell. The
Cu(II) geometry in each complex is slightly distorted trigonal
bipyramidal; τ values35 lie in the 83-93% range. Two of
the amine protons are aligned with the SO2R group, thereby
facilitating intramolecular N-H · · · O hydrogen bonding,
which is discussed further below.
Bond distances and angles (Table 3) around the Cu(II)
centers are comparable to those in [Cu(Me3tren)(MeCN)]-
(ClO4)2 (Cu-Nax 2.030(2) Å; Cu-Neq 2.080(2), 2.093(2),
and 2.111(3) Å; Neq-Cu-Neq 123.2(1), 124.1(1), and
110.2(1)°; Nax-Cu-Neq 85.3(1), 84.72(9), and 84.0(1)°).3
(31) Freedman, A. N.; Straughan, B. P. Spectrochim. Acta, Part A 1971,
27, 1455–1465.
(32) Macke, J. D.; Field, L. J. Org. Chem. 1988, 53, 396–402.
(33) Sato, R.; Goto, T.; Takikawa, Y.; Takizawa, S. Synthesis 1980, 8,
615.
(35) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C.
J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
(36) Foss, O.; Hordvik, A. Acta Chem. Scand. 1964, 18, 619–626.
(37) Cooper, G. K.; Bloxham, D. P.; Webster, M. J. Chem. Res. 1982,
(M), 1164–1172.
(34) Mintel, R.; Westley, J. J. Biol. Chem. 1966, 241, 3381–3385.
10568 Inorganic Chemistry, Vol. 47, No. 22, 2008

Stabilization of Cu(II) Thiosulfonate Coordination Complexes
-
-
-
MePhS2O2 , PhS2O2 , and the two independent MeS2O2
complexes, respectively. The displacements are in excellent
agreement with that observed for the copper(II) ion in the
MeCN complex (0.194(2) Å).
Relative to the corresponding thiosulfonate salts (Table
4), the S-S distances show the greatest change upon
coordination to Cu(II), increasing by 0.070 Å for the
MePhS2O2- complex and 0.033 Å for the PhS2O2- complex.
There is therefore significant donation of electron density
onto the Cu(II) center. The S-O distances are essentially
unchanged from the respective salts, despite the increase in
the energy of the νa(SO2) vibration evidenced by the IR
spectra.
The Cu-S distances for the thiosulfonate complexes are
the same (within 3σ) as for the thiosulfate complexes (Table
4), despite the lesser negative charge of the thiosulfonates
compared to the doubly charged thiosulfate. Table 5 sum-
marizes some key geometric parameters for known X-ray
structures of thiosulfonate complexes. The S-S and M-S
distances for the [Cu(Me3tren)(RS2O2)]ClO4 complexes are
the same as those found in the Au(I), Ru(II), Fe(II), and Pt(II)
complexes (corresponding distances are 2.03 ( 0.01 and 2.33
( 0.04 Å, respectively). The greatest variation is found
among the M-S-S angles, suggesting that thiosulfonate
complexes can adopt a range of M-S-S angles; the small
angle for the Pt(II) complex arises because the SO2R moiety
is part of a six-membered chelate ring.
Figure 3. Molecular structure of [Cu(Me3tren)(PhS2O2)]ClO4 (thermal
ellipsoids drawn at 50% level, non-amine hydrogen atoms omitted for
clarity).
Intramolecular Hydrogen Bonding Interactions. In the
thiosulfonate complexes and the previously reported thio-
sulfate complexes,3 the proximity of amine hydrogen atoms
on the tren-based ligands to the thiosulfonate/thiosulfate
oxygen atoms accommodates the formation of moderate to
weak intramolecular hydrogen bonds (Table 6). In the
discussion that follows we use the classification of hydrogen
bonding proposed by Jeffrey,38 which defines strong, moder-
ate, and weak hydrogen bonds based on measurable physical
Figure 4. Molecular structure of [Cu(Me3tren)(MePhS2O2)]ClO4 (thermal
ellipsoids drawn at 50% level, non-amine hydrogens omitted for clarity).
1
properties, such as shifts in IR and H NMR spectra, in
addition to bond lengths and angles. Analysis of the available
structures indicates that two hydrogen bonding modes are
adopted (Figure 6), for simplicity designated type I and type
II. In both cases, two N-H· · ·O hydrogen bonds are present,
but in type I two different oxygen atoms on the oxoanion
act as acceptors while in type II one oxygen atom accepts
both hydrogen bonds.
The two hydrogen bonding interactions can be classified
in terms of the alignment of the SO2R moiety relative to the
CuSSO/R plane (designated type I and type II; Figure 7).
Ideally, type I would be characterized by two Cu-S-S-O
torsion angles of ( 60° (i.e., the two S-O bonds are at (60°
to the Cu-S bond for the oxygens that point up toward the
Cu) and type II by one torsion angle close to 0° (i.e., one of
the S-O bonds is aligned with the Cu-S bond, and this
oxygen atom points up toward the Cu). For the thiosulfonate
complexes, [Cu(Me3tren)(PhS2O2)]ClO4 exhibits the type I
hydrogen bonding mode whereas the type II mode is found
in [Cu(Me3tren)(MePhS2O2)]ClO4 (Figure 6b, Table 6). For
Figure 5. Molecular structure of the two independent complexes in
[Cu(Me3tren)(MeS2O2)]ClO4 (thermal ellipsoids drawn at 50% level, non-
amine hydrogen atoms omitted for clarity, major (88%) disorder component
of O1′, S2′, and C10′ shown).
The Cu-Nax bonds are the shortest of the four Cu-Me3tren
bonds in all cases, as for [Cu(Me3tren)(MeCN)](ClO4)2. All
of the Nax-Cu-Neq angles are less than 90° and as a
consequence the Cu(II) center is displaced out of the
equatorial plane away from the bridge-head nitrogen by
0.195(2), 0.195(1), 0.205(3), and 0.213(3) Å for the
(38) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University
Press: New York, 1997; p 303.
Inorganic Chemistry, Vol. 47, No. 22, 2008 10569

Fischmann et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for [Cu(Me3tren)(RS2O2)]ClO4 Complexesa
MePh
Ph
Me
Meb
Cu-Nax
Cu-Neq
Cu-N(4)
Cu-N(1)
Cu-N(2)
Cu-N(3)
Cu-S(1)
S(2)-S(1)
S(2)-O(1)
S(2)-O(2)
S(2)-C(10)
2.049(4)
2.138(4)
2.093(4)
2.082(4)
2.317(1)
2.020(2)
1.451(4)
1.459(4)
1.773(4)
2.0416(2)
2.116(2)
2.079(2)
2.136(2)
2.2989(6)
2.0108(7)
1.447(2)
1.452(2)
1.772(2)
2.063(4)
2.051(4)
2.132(5)
2.120(5)
2.324(2)
2.010(2)
1.454(4)
1.445(4)
1.760(6)
2.064(5)
2.064(5)
2.131(5)
2.129(5)
2.317(2)
2.014(2)
1.449(5)
1.473(5)
1.760(6)
Cu-S
S-S
S-O
S-C
Neq-Cu-Nax
N(1)-Cu-N(4)
N(2)-Cu-N(4)
N(3)-Cu-N(4)
N(1)-Cu-N(2)
N(1)-Cu-N(3)
N(2)-Cu-N(3)
N(1)-Cu-S(1)
N(2)-Cu-S(1)
N(3)-Cu-S(1)
N(4)-Cu-S(1)
S(2)-S(1)-Cu
84.5(2)
84.6(2)
84.9(2)
120.4(2)
112.7(2)
124.3(2)
96.9(1)
95.8(1)
93.3(1)
178.1(1)
103.02(6)
85.60(7)
84.67(7)
83.86(7)
121.72(7)
112.13(8)
123.60(8)
98.40(5)
96.11(5)
91.35(5)
174.67(5)
105.54(3)
84.5(2)
84.4(2)
84.3(2)
120.0(2)
126.7(2)
110.4(2)
94.8(1)
92.6(1)
99.2(1)
176.0(1)
102.26(7)
84.8(2)
84.0(2)
83.8(2)
123.7(2)
121.0(2)
112.2(2)
96.8(1)
Neq-Cu-Neq
Neq-Cu-S
90.0(1)
100.5(1)
173.7(1)
107.97(7)
Nax-Cu-S
Cu-S-S
a Nax ) axial nitrogen; Neq ) equatorial nitrogen. b Data for major conformation of second complex.
Table 4. Comparison of Geometric Parameters in Cu(II)-Thiosulfonate
and Cu(II)-Thiosulfate Complexes and Thiosulfonate Salts
complexes with a tren-based ligand and a coordinated
tetrahedral XY(O)2Z anion were found in the Cambridge
Structural Database. The most closely related compound in
the CSD is [Zn(tren)(BNPP)]ClO4 (BNPP ) bis(p-nitrophe-
nyl)phosphate).39 However, no hydrogen bonding is evident
in this compound, because the Zn-O-P angle is too large
to bring the oxygen atom(s) close enough to allow hydrogen
bonding with the amine protons. The closest nontrigonal
bipyramidal analogues are cis-NH4[Co(en)2(SO3)(S2O3)] ·
3H2O,40 [Cu(en)2(S2O3)],2 and [trans-Co(en)2Cl2][[trans-
Co(en)2(S2O3)2].41 Although two of these complexes are
octahedral and the other square pyramidal, all three exhibit
hydrogen bonding interactions to the thiosulfate SO3 group
that can be described as type I (shown in Figure 8 for two
of the complexes). In each case, these interactions appear to
contribute to the conformation adopted by the molecule.
A common feature of all these complexes is a tight
M-X-Y angle (ca. 100°). This is necessary for the oxygen
atoms to be close enough to accept a hydrogen bond from
the amine ligands. Figure 9 plots the distribution of M-X-Y
angles for XY(O)2Z anions (and esters) in the CSD and
shows that if X ) oxygen, the majority of oxoanion
coordination complexes have an M-X-Y angle >120°,
whereas the corresponding angle in SXO3n- compounds (X
) sulfur) is smaller. The larger M-X-Y angle, typically
found when X ) oxygen, would leave the uncoordinated
oxygen atoms too far from the tren ligand amine hydrogen
atoms to act as hydrogen bond acceptors (see Figure S1,
Supporting Information). On the other hand, S-coordinated
monothio-arsenate, -silicate, -phosphate, and -selenate
complexes of [Cu(R3tren)(H2O)]2+, R ) H, Me, Bz, would
be expected to form intramolecular hydrogen bonds with the
amine co-ligand.
Cu-S
(Å)
S-S
(Å)
Cu-S-S
(deg)
Thiosulfonate Complexes
[Cu(Me3tren)(MePhS2O2)]ClO4
[Cu(Me3tren)(PhS2O2)]ClO4
[Cu(Me3tren)(MeS2O2)]ClO4
2.317(1) 2.020(2) 103.02(6)
2.2989(6) 2.0108(7) 105.54(3)
2.324(2) 2.010(2) 102.26(7)
2.317(2) 2.014(2)a 107.97(7)a
Thiosulfate Complexes
[Cu(tren)(S2O3)]·H2O
2.3158(8) 2.0513(8) 103.28(3)
(H3Me3tren)[Cu(Me3tren)(S2O3)]2(ClO4)3 2.330(3) 2.042(3) 97.1(1)
2.280(3) 2.014(3) 109.5(1)
[Cu(Bz3tren)(S2O3)]·MeOH
2.301(1) 2.061(2) 102.52(6)
Thiosulfonate Salts
NaMeS2O2 ·H2Ob
1.979(6)
1.954(1)
c
NH4MeS2O2
a 1.96(1) Å and 98.8(4)° in the minor conformation. b Reference 36.
c Reference 37.
Table 5. Geometric Parameters for Non-Cu(II) Thiosulfonate
Complexes
M-S
(Å)
S-S <M-S-S
(Å) (deg)
complex
ref
[Au(Me3P)(MePhS2O2)]
2.340(1) 2.033(2) 99.73(7) 13
2.332(1) 2.039(2) 103.15(6)
[Au(Ph3P)(MePhS2O2)]
2.3286(7) 2.043(1) 103.35
13
[Au(Me3CNC)(MePhS2O2)]
2.288(1) 2.045(1) 102.80(5) 13
[Ru(Cp)(PPh3)(CO)(MePhS2O2)] 2.383(2) 2.023(3) 110.0(1) 22
[Ru(Cp)(dppe)(ClPhS2O2)]
[Fe(Cp)(CO)2(CCl3PhS2O2)]
[PtL(PPh3)2]a
2.393(2) 2.032(2) 104.23(8) 21
2.280(1) 2.022(2) 109.43(6) 20
2.362(2) 2.034(2) 92.6
24, 25
a L is a cyclic thiosulfonate (no esd reported for Pt-S-S angle); Cp )
cyclopentadienyl; dppe ) 1,2-bis(diphenylphosphino)ethane; (CH2)3tu )
trimethylenethiourea; Me4tu ) N,N,N′,N′-tetramethylthiourea; (CH2)2tu )
dimethylenethiourea.
[Cu(Me3tren)(MeS2O2)]ClO4, the Cu-S-S-O torsion angles
lie between the type I and type II ranges, resulting in an
intermediate intramolecular hydrogen bonding geometry.
Analogous but slightly stronger hydrogen bonding interac-
tions are evident in the structures of the previously reported
copper(II)-thiosulfate complexes.3 These particular combi-
nations of coordination and hydrogen bonding are otherwise
unprecedented. No other trigonal bipyramidal transition metal
(39) Ibrahim, M. M.; Shimomura, N.; Ichikawa, K.; Shiro, M. Inorg. Chim.
Acta 2001, 313, 125–136.
(40) Kastner, M. E.; Smith, D. A.; Kuzmission, A. G.; Cooper, J. N.; Tyree,
T.; Yearick, M. Inorg. Chim. Acta 1989, 158, 185–199.
(41) Sharma, R. P.; Sharma, R.; Bala, R.; Quiros, M.; Salas, J. M. J. Coord.
Chem. 2005, 58, 1099–1104.
10570 Inorganic Chemistry, Vol. 47, No. 22, 2008

Stabilization of Cu(II) Thiosulfonate Coordination Complexes
Table 6. Intramolecular Hydrogen Bonding in Cu(II)-Me3tren-RS2O2 Complexesa
-
bond
N-H (Å)
H · · ·O (Å)
N · · ·O (Å)
<(NHO) (deg)
torsion(s)
H-bonding mode
type II
[Cu(Me3tren)(MePhS2O2)]ClO4
N(1)-H(1)· · ·O(2)
N(2)-H(2)· · ·O(2)
0.95(5)
0.84(6)
2.52(5)
2.37(6)
3.171(5)
3.072(6)
126(4)
142(5)
+10
+10
[Cu(Me3tren)(PhS2O2)]ClO4
3.227(3)
N(1)-H(1)· · ·O(1)
N(2)-H(2)· · ·O(2)
0.84(3)
0.84(3)
2.75(3)
2.52(3)
118(2)
140(3)
-62
+69
type I
3.203(2)
[Cu(Me3tren)(MeS2O2)]ClO4
3.010(6)
N(1)-H(1)· · ·O(2)
N(1′)-H(1′)· · ·O(2′)
0.83(2)
0.84(2)
2.30(4)
2.44(5)
143(6)
142(6)
+25
intermediate
type II
type II
type I
3.149(6)
[Cu(tren)(S2O3)]c
2.969(2)
3.077(3)
[Cu(Bz3tren)(S2O3)]c
2.866(5)
3.178(5)
[Cu(Me3tren)(S2O3)] (a)c
2.95(1)
-18b
N(3)-H(18)· · ·O(3)
N(4)-H(8)· · ·O(2)
0.83(2)
0.87(3)
2.69(2)
2.34(3)
101(2)
143(2)
-67
+54
N(2)-H(2)· · ·O(1)
N(3)-H(3)· · ·O(2)
0.83(4)
0.80(3)
2.06(4)
2.62(4)
163(3)
129(3)
-59
+61
N(3)-H(3)· · ·O(1)
N(2)-H(2)· · ·O(1)
0.93
0.93
2.29
2.56
128
115
+6
3.07(1)
[Cu(Me3tren)(S2O3)] (b)c
3.09(1)
N(3′)-H(3′)· · ·O(1′)
0.93
2.34
137
-16
type I
a Torsion(s) ) Cu-S-S-O angle. b Major conformation (34.0° for the minor conformation). c Reference 3.
Figure 7. Torsion angles describing the orientation of the SO2R group
relative to the Cu-S bond: (a) type I (-50° < θ1 < -70°, 50° < θ2
70°) and (b) type II (-10° < θ < 10°).
<
Figure 8. Intramolecular amine-thiosulfate hydrogen bonding in (a)
[Cu(en)2(S2O3)]2 and (b) NH4[Co(en)2(SO3)(S2O3)]·3H2O;40 non-amine
protons, counterions, and water omitted for clarity.
Figure 6. (a) Intramolecular hydrogen bonding modes (broken lines)
observed in thiosulfate complexes, [CuL(S2O3)] (R ) H, Me, and Bz and
X ) O), and thiosulfonate complexes, [CuL(S2O3R′)] (R ) Me and X )
Me, Ph, and MePh). (b) Examples of type I and type II hydrogen bonding
modes found in [Cu(Me3tren)(PhS2O2)]ClO4 and [Cu(Me3tren)(MePhS2O2)]-
ClO4, respectively.
sulfite42 and has been used to prepare [Cu(en)2(SeSO3)], the
only literature example of a selenosulfate-copper(II) com-
plex. The X-ray crystal structure1 shows that SeSO3
2-
coordinates weakly to Cu(II) in the apical position of a square
pyramid. The Cu-Se distance (2.89 Å) is within the range
of covalent radii overlap defined by the CSD as a bonding
The closest analogues of thiosulfate, monothioselenate and
selenoselenate, are unfortunately not stable.42 Selenosulfate,
however, can be prepared from elemental selenium and
(42) Ball, S.; Milne, J. Can. J. Chem. 1995, 73, 716–724.
Inorganic Chemistry, Vol. 47, No. 22, 2008 10571

Fischmann et al.
Cu(II) LMCT centered at ∼350 nm. This intense transition
was useful for determining the strength of the interaction
between the copper(II) center and the thiosulfate anion. In
-
aqueous solution, the coordination of MeS2O2 to some
Cu(II)-tren complexes was sufficiently strong to allow
-
determination of the formation constants, whereas PhS2O2
and MePhS2O2- coordinated more weakly and the complex
formation could not quantified.
-
The spectrophotometric data for the Cu(II)-L-MeS2O2
system (L ) tren and Me3tren, Figure 10) show the
appearance of the LMCT in the same region as for the
corresponding thiosulfate complexes.3 The similar energy of
the LMCT for the two classes of complexes provides
evidence that the chromophores are similar, namely, S f
Cu(II). The complex formation constants were determined
as described in our previous study;3 additionally, the forma-
tion constant for [Cu(tmpa)(S2O3)] was measured (tmpa )
tris(pyridin-2-ylmethyl)amine, see Supporting Information,
Figure S8). The concentration of the [Cu(L)(H2O)]2+ present
in solution was corrected for the effect of hydrolysis to
[Cu(L)(OH)]+ at the pH of study using the acid dissociation
constant for each complex (pKa ) 9.08(2) for [Cu-
(Me3tren)(H2O)]2+,44 9.40(5) for [Cu(tren)(H2O)]2+,45 and
8.51(1) for [Cu(Bz3tren)(H2O)]2+; note that this pKa value
was previously reported incorrectly3 as 7.10(9)). The values
for the thiosulfate complexes3 were also recalculated to
account for partial deprotonation of the complex and are
compared with the thiosulfonates in Table 7.
Coordination of MeS2O2 to [Cu(Me6tren)(H2O)]2+ and
-
[Cu(tmpa)(H2O)]2+ was also examined. While a LMCT was
-
observed for the Cu(II)-tmpa-MeS2O2 system (see Sup-
porting Information, Figure S9) the change in intensity of
-
this band with [MeS2O2 ] was linear over the accessible
-
ranges of MeS2O2 concentration. For the Cu(II)-Me6tren-
-
MeS2O2 system no spectral change was evident. Conse-
quently, the binding of MeS2O2 was too weak to be
quantifiable for either system.
Figure 9. Distribution of M-X-Y angles for oxoanion coordination
-
complexes (number of structures) of (a) sulfate (999); (b) arsenate (495);
n-
(c) perchlorate (1223); (d) phosphate (6502); and (e) SXO3 (198) (X )
S, P, Si, and esters thereof).
The complex formation constants for the thiosulfonate
complexes are two orders of magnitude smaller than those
interaction.43 The Cu-Se-S angle in this compound (100°)
is favorable for the formation of intramolecular N-H · · · O
hydrogen bonds, leading to an N· · · O close contact of 2.81
Å.1 The Cu-Se-S-O torsion angles (+46° and -82°) mean
that the hydrogen bonding interaction is best described as
distorted type I, but with the formation of only one of the
two possible hydrogen bonds.
Intermolecular Interactions. The three complexes exhibit
a variety of CH/π interactions that have a significant
influence on crystal packing of [Cu(Me3tren)(MePhS2O2)]-
ClO4 (see Figures S2-S7 and Tables S1-S3 in Supporting
Information).
-
for corresponding thiosulfates, and in the case of MeS2O2 ,
coordination to the Me6tren complex could not be detected.
The weaker binding affinity of thiosulfonate for Cu(II)
when compared with thiosulfate implies that less electron
density is available on the terminal sulfur of thiosulfonates
for ligation. It would therefore be expected that the S-S
and Cu-S distances in the X-ray crystal structures would
reflect this; however, this was not the case. The lower
strength of intramolecular N-H · · · O hydrogen bonding
of the thiosulfonate complexes when compared with the
thiosulfate complexes, which is clearly evident in the solid
state compounds, is postulated to be responsible for the
variation in the complex formation constants. The strength
of the hydrogen bonding is influenced by the polarization
Thiosulfonate Binding Constants. In previous studies,
we reported that the addition of thiosulfate to copper(II)-tren
complexes in aqueous and nonaqueous solution caused a
color change, from blue to green,3 arising from a new S f
(44) Thaler, F.; Hubbard, C. D.; Heinemann, F. W.; van Eldik, R.; Schindler,
S.; Fa´bia´n, I.; Dittler-Klingemann, A. M.; Hahn, F. E.; Orvig, C. Inorg.
Chem. 1998, 37, 4022–4029.
(43) Cambridge Crystallographic Data Centre, Radii & Bond Lengths,
2004.http://www.ccdc.cam.ac.uk/products/csd/radii/table.php (accessed
July 2006).
(45) Anderegg, G.; Gramlich, V. HelV. Chim. Acta 1994, 77, 685–690.
10572 Inorganic Chemistry, Vol. 47, No. 22, 2008

Stabilization of Cu(II) Thiosulfonate Coordination Complexes
-
Figure 10. Changes in the UV spectrum with MeS2O2 concentration for [Cu(L)(H2O)]2+ complexes: measured (+) and calculated (-) spectra for (a) L
) tren; (b) L ) Me3tren; measured (O) and calculated (s) data at λmax for (c) L ) tren, λmax ) 354 nm, and (d) L ) Me3tren, λmax ) 363 nm. The spectra
were recorded in aqueous solution at pH 7.5 and T ) 25 °C.
Table 7. Stability Constants and Spectral Data for the
Table 8. Measures of N-H Polarization for Tripodal Tetraamine
2-
[CuL]2+-MeS2O2-/S2O3 Systems Measured in Water at pH 7.5 and
Ligands
25 °Ca
a
ligand
pKa
δ(NH)
-
2-
MeS2O2
S2O3
tren
Me3tren
Bz3tren
10.42(1), 9.88(1), 8.915(5)
10.93(1), 10.24(1), 9.17(1)
9.16(1), 8.56(2), 7.17(3)
1.36
1.30
1.64
λmax
εmax
log
Kf
λmax
εmax
log
ligand (nm) (M-1 cm-1
)
(nm) (M-1 cm-1
)
Kf
a For the protonated ligand at 25 °C; I ) 1.0 M (NaClO4) for tren45 and
tren
Me3tren 363
Me6tren
Bz3tren
tmpa
354
6700
4500
0.68 ((0.06) 356
7050
6450
5780
5600
5500
2.74 ((0.02)b
2.77 (0.01)b
1.2 ((0.1)b
Me3tren;44 I ) 0.1 M (KNO3) for Bz3tren.3
0.3 ((0.1)
364
410
367
388
4.29 ((0.03)b
2.65 ((0.02)
engage in intramolecular hydrogen bonding with the SO3/
SO2R moiety.
385
a Values in parentheses are two standard deviations; Kf ) Kapp(1 +
(Ka/[H+])). b Values recalculated from previous study to account for
hydrolysis of the complex and converted from an activity to a concentration
scale;3 see Supporting Information.
Conclusions
We have carried out the first detailed investigation of
copper(II) thiosulfonate complexes. Through the application
of an N-substituted derivative of the tripodal tetramine ligand,
tris(2-aminoethyl)amine ligand, we have been able to sta-
bilize and synthesize three copper(II) thiosulfonate com-
plexes. The choice of ligands is critical since, as was the
case of a series of thiosulfate copper(II) complexes reported
recently by our group,3 tripodal tetramine ligands are able
to minimize oxidation of these oxoanions, thereby allowing
their isolation and characterization. The structures of these
complexes revealed that the Cu-S distances were similar
to those in the related thiosulfate complexes, indicating a
coordinative interaction of similar strength. In these thio-
sulfonate and thiosulfate complexes, two types of intramo-
lecular hydrogen bonding interactions are evident, involving
two amine N-H groups and one or two thiosulfonate
of both the N-H bond of the amine ligand (the donor)
and of the S-O bond of the thiosulfate/thiosulfonate anion
(the acceptor).
The polarization of the N-H bond can be approximated
by the chemical shifts of the amino hydrogen atoms in the
1H NMR spectra of the neutral ligands (in CDCl3) and by
the pKa values of the protonated ligands (in water). Lower
pKa and higher δ(NH) indicate greater polarization; accord-
ingly, Bz3tren has a larger δ(NH) and lower pKa values than
tren and Me3tren (Table 8) and forms a significantly more
stable thiosulfate complex with the shortest N · · ·O intramo-
lecular hydrogen bonding distance. For tmpa and Me6tren,
the low stability of the corresponding thiosulfate and
thiosulfonate complexes can be attributed to the fact that
neither tripodal ligand possesses amine protons that can
Inorganic Chemistry, Vol. 47, No. 22, 2008 10573

Fischmann et al.
Supporting Information Available: Crystallographic data for
[Cu(Me3tren)(MePhS2O2)]ClO4, [Cu(Me3tren)(PhS2O2)]ClO4, and
[Cu(Me3tren)(MeS2O2)]ClO4 in CIF format. Figure S1 (effect of
the size of <MXY on intramolecular hydrogen bonding); Figures
S2-S7, and Tables S1-S3 (CH/π interactions, intermolecular
hydrogen bonding interactions, and crystal packing diagrams for
[Cu(Me3tren)(MePhS2O2)]ClO4, [Cu(Me3tren)(PhS2O2)]ClO4, and
[Cu(Me3tren)(MeS2O2)]ClO4. Experimental details of spectropho-
tometric titrations for the [Cu(tmpa)(H2O)]2+-S2O32- and [Cu(tmpa)-
(H2O)]2+-MeS2O3- systems and the resultant data (Figures S8 and
S9). This material is available free of charge via the Internet at
http://pubs.acs.org.
oxygens. These interactions appear to be stronger in the
thiosulfate complexes, and we postulate that this could be
responsible for the generally higher affinity of thiosulfate,
cf., thiosulfonates, for copper(II) centers. The variation in
the thiosulfonate binding constant with the amine ligand was
also the same as was observed for the thiosulfonate com-
plexes. In both cases, intramolecular hydrogen bonding is
proposed to tune the strength of the Cu(II)-S coordination
and results in the following trend for Kf: Bz3tren . Me3tren
) tren > tmpa > Me6tren.
Acknowledgment. We are grateful to the Australian
Postgraduate Award Scheme (A.J.F) and the Australian
Institute for Nuclear Science and Engineering (AINSE) for
financial support.
IC801234C
10574 Inorganic Chemistry, Vol. 47, No. 22, 2008