Synthesis of novel S-bridged heterotrinuclear complexes containing six-membered chelate rings: Structural, spectroscopic, and electrochemical properties of [Co{Rh(apt)3}2]3+ (apt = 3-aminopropanethiolate)

Article abstract of DOI:10.1002/ejic.200500701

A bidentate ligand, 3-aminopropanethiolate (apt), was synthesized and treated with RhCl₃·3H₂O in basic water to yield a novel mononuclear complex, fac(S)-[Rh(apt)₃] (1), which was characterized by spectroscopic methods. Furthermore, the reaction of 1 with CoCl₂·6H₂O in water formed the linear-type, S-bridged trinuclear complexes ΔΛ-[Co{Rh(apt)₃} ₂]³⁺ (2a) and ΔΔ/ΛΛ-[Co{Rh(apt) ₃}₂]³⁺ (2b), which were characterized by stereochemical, spectrochemical, and electrochemical methods. 2a and 2b are stable and exhibit trivalency in water. X-ray crystallographic analysis of 2a and 2b showed that all of the bridging sulfur atoms are fixed in the R configuration for the Δ unit and in the S configuration for the Λ unit, and each complex has six six-membered chelate rings, all of which are in the chair conformation. The crystal structure of the corresponding 2-aminoethanethiolate (aet) trinuclear complex ΔΛ-[Co{Rh(aet) ₃}₂]³⁺ (4a) was also determined. The structures of 2a and 2b have some differences from that of 4a as a result of the six-membered chelate rings. The Co...Rh distances in 2a and 2b [3.0490(4) and 3.063(1) A] are significantly longer than this distance in the aet complex 4a [2.9139(2) A]. The UV/Vis absorption spectra of 2a and 2b indicate a shift to higher energies as compared with 4a and ΔΔ/ ΛΛ-[Co{Rh(aet)₃}₂]³⁺ (4b). The chemical shifts for the NCH₂ and SCH₂ carbon atoms in 2a and 2b are shifted to higher fields than those for 4a and 4b in the NMR spectra. The Co^III/II redox potential values are -0.56 V (2a) and -0.57 V (2b) compared with -0.35 V (4a) and -0.36 V (4b). This shows that the Co ^III state is more stable in 2a and 2b than it is in 4a and 4b. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200500701

FULL PAPER
DOI: 10.1002/ejic.200500701
Synthesis of Novel S-Bridged Heterotrinuclear Complexes Containing Six-
Membered Chelate Rings: Structural, Spectroscopic, and Electrochemical
3
+
Properties of [Co{Rh(apt) } ] (apt = 3-Aminopropanethiolate)
3
2
[a]
[a]
[a]
[a]
Nagina Amir,* Masaru Motonishi, Mitsuharu Fujita, Yoshitaro Miyashita,*
[a]
[a]
Kiyoshi Fujisawa, and Ken-ichi Okamoto*
Keywords: 3-Aminopropanethiolate / Heterometallic complexes / Crystal structures / Six-membered chelate rings / Spec-
troscopy / Electrochemistry
A bidentate ligand, 3-aminopropanethiolate (apt), was syn-
thesized and treated with RhCl ·3H O in basic water to yield
a novel mononuclear complex, fac(S)-[Rh(apt) ] (1), which
was characterized by spectroscopic methods. Furthermore,
the reaction of 1 with CoCl ·6H O in water formed the linear-
type, S-bridged trinuclear complexes ∆Λ-[Co{Rh(apt)
mined. The structures of 2a and 2b have some differences
from that of 4a as a result of the six-membered chelate rings.
The Co···Rh distances in 2a and 2b [3.0490(4) and 3.063(1) Å]
are significantly longer than this distance in the aet complex
4a [2.9139(2) Å]. The UV/Vis absorption spectra of 2a and 2b
3
2
3
2
2
3
+
3
}
2
]
indicate a shift to higher energies as compared with 4a and
3
+
3+
(
2a) and ∆∆/ΛΛ-[Co{Rh(apt)
3
}
2
]
(2b), which were charac-
∆∆/ΛΛ-[Co{Rh(aet)
NCH and SCH
higher fields than those for 4a and 4b in the NMR spectra.
3
}
2
]
(4b). The chemical shifts for the
terized by stereochemical, spectrochemical, and electro-
chemical methods. 2a and 2b are stable and exhibit trival-
ency in water. X-ray crystallographic analysis of 2a and 2b
showed that all of the bridging sulfur atoms are fixed in the
R configuration for the ∆ unit and in the S configuration for
the Λ unit, and each complex has six six-membered chelate
rings, all of which are in the chair conformation. The crystal
structure of the corresponding 2-aminoethanethiolate (aet)
2
2
carbon atoms in 2a and 2b are shifted to
III/II
The Co
redox potential values are –0.56 V (2a) and
–0.57 V (2b) compared with –0.35 V (4a) and –0.36 V (4b).
III
This shows that the Co state is more stable in 2a and 2b
than it is in 4a and 4b.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
3
+
trinuclear complex ∆Λ-[Co{Rh(aet)
3
}
2
]
(4a) was also deter-
Introduction
the central metal ions and the metal ions in the terminal
building blocks (Scheme 1).
[
1–5]
The chemistry of sulfur-bridged metal complexes has at-
tracted much interest because of the importance of coordi-
nated thiolato groups in a variety of systems ranging from
inorganic to organic and biological chemistry. It has been
recognized that, because of their high Lewis basicity, coor-
dinated thiolato groups have an affinity to form S-bridged
polynuclear structures with transition-metal ions. There-
III
fore, mononuclear complexes, fac(S)-[M(aet) ] (M = Co ,
3
III
III
Rh , Ir ; aet = 2-aminoethanethiolate), could function as
metalloligands to other transition-metal ions, using sulfur
atoms. The polynuclear complexes obtained so far have
shown unique stereochemical, spectrochemical, and electro-
chemical properties, depending highly upon the nature of
[
1]
Scheme 1.
The complex [Co(tn)3]3+ (tn = 1,3-propanediamine) con-
taining an additional methylene group shows some interest-
ing differences in properties when compared with the corre-
[
a] Department of Chemistry, Graduate School of Pure and Ap-
plied Sciences, University of Tsukuba,
Tsukuba 305–8571, Japan
sponding complex [Co(en)3]3 (en = ethylenediamine).
+
[6–13]
For example, six-membered chelate rings give rise to a
Fax: +81-29-853-4323-6503
E-mail: nagina@chem.tsukuba.ac.jp
larger bite angle (N···N distances in chelates) than five-
ymiya@chem.tsukuba.ac.jp
[6–9]
membered rings.
It was reported that both the confor-
okamoto@chem.tsukuba.ac.jp
mational flexibility and the structural bulkiness are larger
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
in [M(tn)3]3 than in [M(en)3]
+
3+
(M = Co
III
or Cr
III
Eur. J. Inorg. Chem. 2006, 1041–1049
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1041

N. Amir, M. Motonishi, M. Fujita, Y. Miyashita, K. Fujisawa, K. Okamoto
FULL PAPER
ion).[10,11] It was also observed that the ring–ring interac- a few Co , Ni , Zn , Cd , Hg , and Fe complexes have
tions, which give rise to the energy differences between con- been reported.[14,15,20,21] The polynuclear complexes ob-
formations, are more severe and more numerous in the six- tained were homopolynuclear complexes only, and to the
membered chelate ring complexes than in five-membered best of our knowledge, there is no report of heteropolynu-
III
II
II
II
II
III
[
10]
systems. Moreover, the absorption maxima in the first d– clear complexes. The choice of apt is based on the simplicity
d transition region in the tn complexes shift to lower ener- of the ligand and the fact that the ligand had been poorly
[
12,13]
3+
gies than those in the corresponding en complexes.
studied. Turning to six-membered rings in the mononuclear
3
+
Similar to the complexes [Co(tn)3] and [Co(en)3] with unit, we are interested in the effects of changes in the three-
N–N donor ligands, complexes containing five- and six- dimensional structure on the metal, spectroscopic, and elec-
membered chelate rings with N–S donor ligands also show trochemical properties.
interesting differences in properties. For example, an ad-
In this paper, we report on the stepwise synthesis of
ditional methylene group led to differences in reactivity: all aptH·HCl from 3-aminopropanol following literature meth-
[
22–24]
the attempts to synthesize [Co(apt) ] (apt = 3-aminopro- ods with some modifications.
After synthesis,
3
III
panethiolate) were unsuccessful, unlike the corresponding aptH·HCl was treated with the Rh ion to obtain a mono-
[
14]
complex [Co(aet) ], which was obtained easily. Similarly, nuclear complex fac(S)-[Rh(apt) ] (1), which reacts with the
3
3
II
[
[
Ni(apt) ] was obtained under more drastic conditions than Co
ion
to
form
heterotrinuclear
complexes
2
3
+
Ni(aet) ]. Moreover, differences in chemical properties were [Co{Rh(apt)3}2] in meso (2a) and racemic (2b) forms.
also observed: [Ni(apt) ] gave [Ni{Ni(apt) } ] when dis- Crystal structural analysis and spectrochemical characteri-
2
2
+
2
2 2
solved in polar solvents, whereas [Ni(aet) ] remained practi- zation have been described comparatively for the corre-
2
2+
cally insoluble. The aqueous solutions of [Ni{Ni(apt) } ] sponding aet complexes. Electrochemical measurements
were less stable than those of the homologous trinuclear were also performed.
The solubility of complexes
with six-membered chelate rings, e.g. [Ni{Ni(apt) } ] , was
2
2
2
+ [15]
complex [Ni{Ni(aet) } ] .
2
2
2
+
2
2
lower than that of complexes with five-membered chelate
Results and Discussion
2
+ [16]
rings, e.g. [Ni{Ni(aet) } ] . As far as structure was con-
2
2
cerned, the most striking difference resulting from the pres-
ence of an additional methylene group was found to be the
opening of the dihedral angle by 30°. This can be attributed
to the steric requirements of the enlargement of the chelate ture methods.
Synthesis of Ligand
The ligand aptH·HCl was prepared by modified litera-
[
22–24]
There was only a very simple descrip-
ring. The electronic properties are also influenced by the tion for the synthesis of the aminoalkanethiol series in the
additional methylene group, which could be explained in literature. Therefore, the synthesis of aptH·HCl was exam-
terms of different bond lengths and angles of the chromo- ined in detail and improved. The ligand was obtained by
phores in these complexes.[
15]
the three-step reaction shown in Scheme 2. Each compound
It has been well explained in the literature that the varia- was characterized by elemental analysis and NMR spec-
tions in the bridging ligands provide remarkable control troscopy.
over the electronic structures and photophysics of com-
plexes. In one of the reports it was found that bpa dimers fore carried out in an ice bath. From this step, the com-
bpa = 1,2-bis(4-pyridyl)ethane] exhibit a broad, low-energy pound 1-amino-3-propylsulfate (I) was obtained. The sec-
The first step of the reaction was vigorous and was there-
[
3
emission from a metal-centered LF excited state, whereas ond step gave tetrahydro-1,3-thiazine-2-thione (II) with the
the bpe and bpy dimers [bpe = trans-1,2-bis(4-pyridyl)ethyl- ring-formation reaction of I and carbon disulfide. Com-
ene, bpy = 4,4Ј-bipyridyl] exhibit structured emission from pound II is a thione-thiol tautomer that consists of tetra-
the lowest pyridyl-centered 3(π–π*) excited state.[ In an- hydro-1,3-thiazine-2-thione and 5,6-dihydro-1,3-thiazine-2-
17]
II
other report, complexes of 4-pyridine thiolate with Co , thiol (Figure 1). The X-ray crystal structure of II is shown
II
II
II
II
II
IV
III
Ni , Zn , Cd , Hg , Pt , Sn , and Bi involve bonding in Figure 2, and bond lengths and angles are listed in
through sulfur rather than nitrogen,[ while complexes of Table 1. The six-membered ring is not a planar structure
-(2-mercaptoethyl)pyridine with Co , Ni , Pd , and Pt
involve bonding through sulfur as well as nitrogen.
18]
II
II
II
II
3
3
2
because of the sp carbon atoms C1 and C2, and the sp
[
19]
It sulfur atom S1, although the C1, S1, C4, N1, C3, and S2
can therefore be demonstrated that the modifications of the atoms are almost on the same plane. The S2–C4 distance
bridging ligand provide exquisite control over the electronic [1.692(3) Å] is shorter than the length of the single bond
structures and photophysics of the compounds, including S1–C1 [1.814(4)] and S1–C4 [1.729(3) Å]. It is reported that
the orbital character of the lowest emissive state. It is also the length of the single bond S–C of typical thiol com-
assumed that the complexes using apt, which has an ad- pounds is 1.82 Å, and that of typical thione compounds is
[
25–28]
ditional methylene group as compared with aet, can lead to 1.56 Å.
somewhat different structural, spectrochemical, or electro- shorter than the length of the single bond N1–C3
chemical properties, which might be quite interesting. [1.471(5) Å], which suggests multibonding. Thus, the C4
Similarly, the N1–C4 distance [1.321(4) Å] is
2
No doubt metal complexes of aet ligands have been atom is in an sp hybridized state. The S1–C4 distance in II
widely studied, many of them form stable chelates, but is similar to the corresponding S–C distance [1.722(7) Å] in
those of apt have received little attention up to now. Only N,NЈ-trimethylenethiourea.
[
29]
1042
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1041–1049

S-Bridged Heterotrinuclear Complexes Containing Six-Membered Chelate Rings
FULL PAPER
Scheme 2.
under nitrogen. However, in this work, the apt was added
at the end and gave a higher yield than a similar method
for synthesizing the aet mononuclear complex. The re-
sulting yellow powder was found to be 1. This neutral com-
plex is not soluble in general solvents, but soluble in acidic
water following the protonation of the sulfur atoms of the
coordinated thiolato group. Complex 1 was obtained more
Figure 1. Two tautomers of II.
easily and in
a
purer form than the complexes
fac(S)-[Co(apt) ] and trans(S)-[Ni(apt) ], which were ob-
3
2
15]
[
tained under more drastic conditions.
Scheme 3.
The trinuclear complexes ∆Λ-[Co{Rh(apt) } ](NO )
3 3
3
2
Figure 2. Crystal structure of II.
[
2a(NO ) ] and ∆∆/ΛΛ-[Co{Rh(apt) } ]Br (2bBr ) were
3 3 3 2 3 3
synthesized by the reported procedure, but using aptH in-
Table 1. Bond lengths [Å] and angles [°] of II.
[
33]
stead of aetH.
It was found that, in the case of
III
S1–C1
S2–C4
N1–C4
C2–C3
1.814(4)
1.692(3)
1.321(4)
1.513(5)
S1–C4
N1–C3
C1–C2
1.729(3)
1.471(5)
1.502(5)
2
a(NO ) and 2bBr , the reaction gave the trivalent Co
3
3
3
complexes under nitrogen or air. This result is different
from the case of ∆Λ-[Co{Rh(aet) } ](NO ) [4a(NO ) ] and
3
2
3 3
3 3
∆
∆/ΛΛ-[Co{Rh(aet) } ]Br (4bBr ), which gave divalent
3 2 3 3
II
C1–S1–C4
S1–C1–C2
N1–C3–C2
S1–C4–N1
105.2(2)
110.9(2)
112.1(3)
122.2(2)
C3–N1–C4
C1–C2–C3
S1–C4–S2
S2–C4–N1
127.0(3)
111.7(3)
115.1(2)
122.7(2)
Co complexes under such conditions, in which case H O
was used for oxidation.
2 2
[33]
This difference in reactivity can
be related to the difference in the redox potential of the
III
Co ion in trinuclear structures (vide infra). Complexes 2a
and 2b (Scheme 4) were obtained both in meso and racemic
The third step in the reaction of II gave aptH·HCl as a forms similar to 4a and 4b. Selective crystallization using
result of ring opening. This ligand is hygroscopic and solu- suitable counter anions was achieved. This is different from
ble in water, methanol, ethanol, and acetone, and less solu- the case of the CoIII complexes in which [Co-
ble in other solvents. The overall process was carried out in {Co(aet) } ]Cl gave both meso and racemic forms while
3
2
3
[
14,21]
a manner similar to that of the synthesis of 1-Meaet (1- [Co{Co(apt) } ]Cl gave only the meso form.
3
2
3
Meaet = 1-amino-2-propanethiolate).[
30]
Crystal Structures of Complexes 2a, 2b, and 4a
Syntheses of Complexes
The results of the ICP analysis and elemental analysis
Preparation of the apt mononuclear complex fac(S)- confirmed that the ratio of Co to Rh was 1:2 in 2a and 2b.
[
Rh(apt) ] (1) (Scheme 3) was carried out by a modified The values obtained for the molar conductivity in aqueous
3
method of the synthesis of the aet mononuclear complex, solution for the apt complexes 2a and 2b (329 and
[
31,32]
2
–1
fac(S)-[Rh(aet) ] (3).
The difference between the syn- 363 S·cm ·mol , respectively) are comparable to the values
3
2
–1
theses was the order in which the starting materials were of the aet complexes 4a and 4b (384 and 401 S·cm ·mol ,
added. For the synthesis of the aet mononuclear complex, respectively). These values are also within the range nor-
RhCl ·3H O was added to a basic aqueous solution con- mally observed for other trivalent trinuclear complexes con-
3
2
2
taining the ligand, and the mixture was heated to reflux taining
fac(S)-[Rh(aet)3]
units
(323–404 S·cm ·
Eur. J. Inorg. Chem. 2006, 1041–1049
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1043

N. Amir, M. Motonishi, M. Fujita, Y. Miyashita, K. Fujisawa, K. Okamoto
FULL PAPER
Figure 5. Crystal structure of 4a.
Scheme 4.
in the aet complex 4a [2.9139(2) Å]. The Rh–S [av.
2
.322(1) Å], Rh–N [av. 2.133(5) Å], and Co–S [av.
The structures of 2a, 2b, and 4a, determined 2.291(1) Å] distances in 2a are slightly longer than those in
by X-ray structural analysis, are shown in Figures 3, 4, and 4a [av. 2.306(8), av. 2.121(3), and av. 2.290(9) Å]. The S–
, respectively. The crystal structure of 4a was determined Rh–S (av. 80.43(4)°), N–Rh–N [av. 88.2(2)°], and S–Co–S
–
1 [2,3,34,35]
mol ).
5
for purposes of comparison. The selected bond lengths and [av. 81.71(4)°] angles in 2a are more acute than those in 4a
angles are summarized in Table 2 and Table 3. Compounds [av. 83.75(3), av. 96.2(1), and av. 84.45(3)°] while Co–S–Rh
2a and 2b consist of two approximately octahedral fac(S)- angles [av. 82.73(4)°] in 2a are more obtuse than those in
[
Rh(apt) ] units and one Co atom, forming the completely 4a [av. 78.67(3)°]. These differences in the bond lengths and
3
linear-type,
S-bridged
trinuclear
structures,
∆Λ- angles are attributed to the presence of six-membered che-
3
+
3+
[
Co{Rh(apt) } ] (for 2a) and ∆∆/ΛΛ-[Co{Rh(apt)3}2]
late rings that are formed between the metal and ligands in
3
2
(for 2b). Only the ΛΛ configuration of 2b is shown in Fig- the case of apt complexes 2a and 2b compared with the five-
ure 4. All of the bridging sulfur atoms in 2a and 2b have membered chelate rings found in the case of aet complex 4a.
the R configuration for the ∆ unit and the S configuration It can be concluded that increasing the number of methyl-
for the Λ unit, which corresponds to the results in all of ene groups in the chelate rings influences the stereochemis-
the reported trinuclear structures. Each complex has six six- try of the complexes. Six-membered chelate rings give rise
membered chelate rings in a molecule, and all of the rings to a larger bite angle than five-membered rings, which is
are in the chair conformation.
very clearly observed in the present case. The S–Rh–N bite
angles in 2a [av. 96.0(1)°] and 2b [98.5(3)°] are significantly
larger than those in 4a [av. 87.0(1)°].
Spectroscopic Properties
UV/Visible Spectra
Diffuse reflectance (DR) spectra of 1 and 3 were mea-
sured in the solid state, since the neutral mononuclear com-
plexes are sparingly soluble in water. Both complexes exhi-
3
–1
bit the characteristic intense bands at ca. 40×10 cm .
These bands may be due to charge transfer (CT) transitions
from the sulfur atoms to the Rh ion. This suggests that 1
Figure 3. Crystal structure of 2a.
III
is the apt mononuclear complex fac(S)-[Rh(apt) ] with the
3
same geometry as 3.
UV/Vis absorption (AB), DR, and circular dichroism
(CD) spectra of 2a and 2b are shown in Figure 6. It was
found that 2a and 2b exhibit characteristic AB and CD
spectra of the trinuclear structure just as for complexes 4a
and 4b with some shift towards the higher energy side.[
The observed AB peaks arise from d–d transitions and CT
transitions from the sulfur atoms to the metal ions. The
33]
3
–1
peaks observed at about 40–50×10 cm are due to CT
III
transitions from the sulfur atoms to the Rh ion. DR and
AB spectra show similar patterns, and therefore it is be-
lieved that the symmetry of 2a and 2b is not altered in solu-
Figure 4. Crystal structure of 2b.
The Co···Rh distances in apt complexes 2a and 2b tion. Furthermore, AB did not change with time. This me-
3.0490(4) and 3.063(1) Å] are significantly longer than that ans that 2a and 2b are stable for a long time in solution.
[
1044
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Eur. J. Inorg. Chem. 2006, 1041–1049

S-Bridged Heterotrinuclear Complexes Containing Six-Membered Chelate Rings
FULL PAPER
Table 2. Selected bond lengths [Å] and angles [°] of 2a and 4a.
2a
4a
2a
4a
Rh1–S1
Rh1–S3
Rh1–N2
Co1–S1
Co1–S3
2.316(1)
2.320(1)
2.127(4)
2.291(1)
2.290(1)
2.3121(9)
2.2993(7)
2.123(4)
2.2853(9)
2.2796(7)
Rh1–S2
Rh1–N1
Rh1–N3
Co1–S2
2.330(1)
2.138(5)
2.136(5)
2.294(1)
3.0490(4)
2.3077(9)
2.122(3)
2.120(3)
2.3069(9)
2.9139(2)
Rh1···Co1
Rh1–S1–Co1
Rh1–S3–Co1
S1–Rh1–S3
N1–Rh1–N2
N2–Rh1–N3
S1–Co1–S3
S1–Rh1–N1
S3–Rh1–N3
82.87(4)
82.82(5)
80.77(4)
87.0(2)
89.4(2)
81.94(4)
96.3(1)
96.5(1)
78.66(3)
79.04(2)
84.32(3)
96.0(1)
Rh1–S2–Co1
S1–Rh1–S2
S2–Rh1–S3
N1–Rh1–N3
S1–Co1–S2
S2–Co1–S3
S2–Rh–N2
82.51(4)
80.74(4)
79.83(5)
88.2(2)
81.99(4)
81.20(5)
95.2(1)
78.31(3)
83.29(3)
83.63(3)
96.4(1)
83.90(3)
84.08(3)
87.0(1)
96.2(1)
85.38(3)
87.04(9)
87.06(8)
Table 3. Selected bond lengths [Å] and angles [°] of 2b.
The CD spectrum of 2b, which was optically resolved
with an SP-Sephadex C-25 column, shows bands in the re-
Rh1–S1
Co1–S1
2.327(3)
2.304(3)
Rh1–N1
Rh1···Co1
2.13(1)
3.063(1)
3
–1
gion 15–40×10 cm . These CD bands correspond well to
3
+
the d–d and CT bands for [Co{Rh(apt) } ] in the AB
3
2
S1–Rh1–S1[
S1–Co1–S1
a]
80.5(1)
81.5(1)
Rh1–S1–Co1
N1–Rh1–N1
S1–Rh1–N1
82.82(9)
86.7(5)
98.5(3)
CD
spectra. It seems that (–)412-2b is the ΛΛ isomer and
+)412-2b is the ∆∆ isomer. The CD spectrum of 2b is also
[
a]
[a]
CD
(
in agreement with that of 4b. In the CD spectra, no signifi-
cant changes were observed with time over several hours.
This illustrates that the trinuclear structures are fairly
stable, retaining their oxidation state even under aerobic
conditions.
[a] Symmetry code: 1 – y, x – y, z.
When comparative studies were performed, it was found
that there was no significant difference between the elec-
tronic spectra of the aqueous solutions of 2a, 2b and 4a, IR and Far-IR Spectra
4
b.
This
trend
is
similar
to
that
of
The IR and far-IR spectra of I, II, and aptH·HCl show
all the characteristic bands for the vibration and bending
modes of the NH and CH groups (Figure S1). The overall
3
+ [14,21]
[
Co{Co(aet or apt) } ]
, whereas it is different from
3
2
2
+
that of [Ni{Ni(aet or apt) } ] , in which important differ-
2
2
2
2
ences were observed.[ The AB peaks in 2a and 2b were
15]
IR spectral pattern of 1 is in good agreement with that of
observed at higher energy levels compared with those in
[35]
3.
The IR spectral patterns of 2a(NO ) and 2bBr are
3 3 3
III
II
the corresponding Co and Ni complexes. It is therefore
concluded that the addition of another methylene group to
the chelate ring in octahedral trinuclear complexes does not
cause important modifications in the chromophores, and
the structures are very similar in both cases.
similar to each other, reflecting the similarity between the
isomers (Figure S2). Moreover, these spectral patterns are
typical for linear-type, S-bridged trinuclear complexes in the
–1 [2,3,35–38]
range 4000–400 cm .
The IR spectra of 1,
2
3
a(NO ) , and 2bBr show characteristic bands in the range
500–2800 cm , corresponding to the vibration modes of
3 3 3
–1
the NH and CH groups. The bands for the bending mode
2
2
of the NH and CH2 groups are observed at 1700–
2
–1
1
000 cm . The IR spectra show similar patterns in the
–1
–1
range 3500–2800 cm , but in the range 1700–1000 cm ,
there are small differences between the spectrum of the mo-
nonuclear complex 1 and those of the trinuclear complexes
–1
2
a(NO ) and 2bBr . The bands at ca. 1100 cm in 1 are
3 3 3
shifted to higher energies in 2a(NO ) and 2bBr , which re-
3
3
3
flects the change from mononuclear to trinuclear geometry.
II
II
II
The same trend is observed in the case of Co , Ni , Zn ,
Cd , and Hg complexes with apt.
II
II
[14,15,20,21]
The similarity
between the IR spectral patterns of 1 and those of the trinu-
clear 2a(NO ) and 2bBr shows that the terminal units re-
3
3
3
tain their structure during the formation of S-bridged com-
plexes. The absence of bands in the range 2550–2600 cm–1
(υS–H) is characteristic of coordinated sulfur. The far-IR
spectra of 1, 2a(NO ) , and 2bBr are quite complicated,
but show little difference in the region 500–420 cm be-
Figure 6. UV/Vis AB (log ε), DR (arbitrary scale), and CD (∆ε)
spectra of 2a (–––––) and (–)412-2b (- - - - - -).
3 3
3
CD
–1
Eur. J. Inorg. Chem. 2006, 1041–1049
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1045

N. Amir, M. Motonishi, M. Fujita, Y. Miyashita, K. Fujisawa, K. Okamoto
FULL PAPER
Table 4. H- and 13C NMR spectral data (coupling constants/Hz).[a]
1
NH
NCH
2
CH
2
SCH
2
I
–[c]
4.17 (t, 2 H, 5.7)
3.48 (t, 2 H, 4.1)
3.12 (t, 2 H, 7.6)
2.98 (m, 2 H)
2.07 (2 H, quint, 6.4)
2.18 (2 H, quint, 5.7)
2.10 (2 H, quint, 7.3)
2.15 (d, 1 H, 15.6)
1.83 (dd, 1 H, 11.6, 13.3)
2.18 (d, 1 H, 15.7)
3.15(t, 2 H, 7.2)[d]
3.00 (t, 2 H, 5.9)
2.82 (t, 2 H, 7.1)
2.45 (dd, 1 H, 5.1, 4.9)
2.08 (t, 1 H, 13.5)
2.46 (dd, 1 H, 5.2, 5.1)
1.89 (t, 1 H, 12.5)
2.49 (d, 1 H, 13.2)
1.86 (td, 1 H, 13.5, 3.3)
2.39 (d, 1 H, 11.2)
1.73 (td, 1 H, 13.5, 3.6)
[
b]
II
9.02 (s, 1 H)
[
c]
aptH·HCl
–
[
[
[
[
c]
c]
c]
c]
2
2
4
4
a
b
a
b
4.15
.41
4.14
3
2.98 (dd, 1 H, 5.5, 5.2)
2.92 (dd, 1 H, 10.6, 12.9)
3.15 (d, 1 H, 11.2)
2.73 (dd, 1 H, 22.5, 13.9)
3.16 (d, 1 H, 12.9)
3
–
–
–
–
.33
1.74 (dd, 1 H, 6.0, 12.7)
[
[
[
[
c]
c]
c]
c]
2.73 (dd, 1 H, 23.7, 10.5)
C=S
194.61
NCH
2
CH
2
SCH
2
I
68.92
44.30
40.72
44.04
43.82
49.89
50.11
29.19
20.46
28.60
29.82
30.84
39.61[e]
30.02
36.39
30.72
31.18
34.40
34.62
[
b]
II
aptH·HCl
2
2
4
4
a
b
a
b
[
a] ppm from D
2
O containing DSS. [b] ppm from CHCl
2
3
containing TMS. [c] NH
2
signals were broad or missing due to H–D exchange.
[d] OCH . [e] OCH .
2
tween the mononuclear complex 1 and the two trinuclear in Figure 7. For the already reported complexes of apt with
III
II
II
II
II
complexes 2a(NO3)3 and 2bBr3 (Figure S2). Because the Co , Ni , Zn , Cd , and Hg , there is no information
[
14,15,20,21]
far-IR spectra were complicated, it was difficult to assign about the electrochemical properties.
Therefore, to
the bands for the shifts resulting from the vibrations of the the best of our knowledge, this is the first report on the
Co–S bonds.
electrochemistry of S-bridged complexes containing apt.
Each of the voltammograms displays a quasi-reversible re-
dox couple in the negative potential region. In analogy to
NMR Spectra
3+
The H- and 13C NMR spectra were measured for each
product during the synthesis of ligands 2a and 2b. The li-
gand aptH·HCl as well as I and II show three sharp signals
for the CH protons and three sharp signals for the CH
1
3 2
the characterized electrochemistry of the [Co{M(aet) } ]
III
III
[33,39–41]
(
M = Rh , Co ) system,
signed as the redox couple corresponding to Co
redox couples of the apt complexes 2a (–0.56 V) and
this redox process is as-
III/II
. The
2
2
1
3
1
2
b (–0.57 V) are more negative than those of the aet com-
carbons. The proton signals in the C- H heteronuclear
multiple-bond correlation spectrum (HMBC) of aptH·HCl
show coupling with the corresponding carbon signals (Fig-
[
33,39]
plexes 4a (–0.35 V) and 4b (–0.36 V).
the Co state in apt complexes is more stable than that in
This means that
III
1
1
4a and 4b. A possible reason for this might be the difference
ure S3). Moreover, the proton signals in the H- H corre-
lation spectroscopy (COSY) indicate coupling between the
corresponding proton signals. Both 2a and 2b also exhibit
three sets of sharp proton signals and three carbon signals
resulting from the six apt ligands (Figure S4). This means
that the S or D symmetrical, S-bridged, trinuclear struc-
in nucleophilicity of sulfur or structural differences of the
III
Co ion resulting from the additional methylene group in
apt, which forms six-membered chelates rather than five-
membered ones, as is the case for aet. Since the difference
in reduction potential resulting from the difference in the
configuration of complexes is very slight, the E1/2 value for
the meso isomer 2a is only 0.01 V more positive than that
for the corresponding racemic isomer 2b. A profound differ-
ence was observed when the ligand was changed from
6
3
tures observed in the crystals are retained in aqueous solu-
tion. The details of the NMR spectroscopic data are shown
in Table 4. In 2a and 2b, the chemical resonances in the H
1
NMR spectra show shifts to lower fields for the NCH pro-
2
tons and to higher fields for the SCH protons. Moreover, fac(S)-[Rh(aet) ] to fac(S)-[Rh(apt) ], where 2b is reduced
2
3 3
the splitting pattern for the protons is also different from (0.21 V) more easily than 4b. The redox process of 2b is
that observed in 4a and 4b.[ It is worth noting that the reversible, as with 4a and 4b. However, in the case of 2a,
chemical shifts for the NCH and SCH carbon atoms in the observed peak separation was too broad to establish
35]
2
2
2
4
a and 2b show shifts to higher fields than those for 4a and whether the redox process is reversible. The difference in
b.
electrochemical properties of 2a, 2b and 4a, 4b could be
related to the difference of reactivity explained in the syn-
thetic part, where it was found that, in the case of 2a and
Electrochemical Properties
2
b, the reaction under nitrogen or air gave the trivalent
III
Cyclic voltammetry experiments were performed for 2a Co complexes as compared with the case of 4a and 4b,
and 2b. The cyclic voltammogram obtained for 2b is shown where H O was used for oxidation.
2
2
1046
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 1041–1049

S-Bridged Heterotrinuclear Complexes Containing Six-Membered Chelate Rings
FULL PAPER
an ice bath. Chlorosulfonic acid (116.5 g, 1.0 mol) was slowly
added to the mixture. The reaction mixture was kept overnight,
and carbon tetrachloride was removed in vacuo. The crude solid
3
was crushed with methanol (400 cm ), and isolated by filtration.
A pure white powder of 1-amino-3-propylsulfate was obtained by
recrystallization from water/methanol. Yield: 123.5 g, 79%.
C H NO S (155.17): calcd. C 23.35, H 5.66, N 9.15; found C 22.87,
3 9 4
H 5.57, N 8.88.
Tetrahydro-1,3-thiazine-2-thione (II): To a suspension containing 1-
amino-3-propylsulfate (252.2 g, 1.62 mol) and carbon disulfide
3
(
150.0 g, 1.94 mol) in ethanol (50%, 700 cm ) was added slowly in
3
an ice bath NaOH (141.8 g, 3.56 mol) in ethanol (50%, 300 cm ).
After the reaction mixture was heated to reflux for 30–40 min the
ethanol was removed by evaporation. Colorless crystals of tetra-
hydro-1,3-thiazine-2-thione were obtained by recrystallization from
4 7 2
hot water. Yield: 149.0 g, 70%. C H NS (133.22): calcd. C 36.06,
H 5.30, N 10.51; found C 35.40, H 5.06, N 10.34.
Figure 7. Cyclic voltammogram of 2b.
3-Aminopropanethiol Hydrochloride (aptH·HCl): A suspension of
tetrahydro-1,3-thiazine-2-thione (149.0 g, 1.12 mol) in conc. HCl
3
(
800 cm ) was heated to reflux for 3 weeks. After evaporating until
Conclusions
an oil remained, a white precipitate of aptH·HCl was obtained by
the addition of ethanol/ether. Yield 133.0 g, 95%. C 10ClNS
127.63): calcd. C 28.23, H 7.89, N 10.97; found C 29.05, H 6.67,
3
H
A novel mononuclear complex fac(S)-[Rh(apt) ] (1) was
synthesized and characterized by spectroscopic methods.
The reaction of 1 with CoCl ·6H O in water formed linear-
type, S-bridged trinuclear complexes ∆Λ-[Co{Rh(apt) } ]
3
(
N 10.30.
2
2
Preparation of Complexes
3+
3
2
3
+
fac(S)-[Rh(apt) ] (1): To a solution containing NaOH (0.61 g,
3
(2a) and ∆∆/ΛΛ-[Co{Rh(apt) } ]
(2b), unlike ∆Λ-
3
2
3
3
+
3+
15 mmol) in water (10 cm ) was added RhCl
3
·3H
2
O (0.10 g,
[
Co{Rh(aet) } ] (4a) and ∆∆/ΛΛ-[Co{Rh(aet)3}2] (4b)
3 2
0
.38 mmol). A solution of aptH·HCl (1.10 g, 8.6 mmol) in water
where an oxidizing agent was required. The complexes were
characterized by stereochemical, spectrochemical, and elec-
trochemical techniques. The Co···Rh, Rh–S, and Rh–N dis-
tances in 2a and 2b are longer than those of 4a. The differ-
3
(
40 cm ) was then added to this mixture . The mixture gave a yellow
precipitate after slight heating and was then heated to reflux for a
further 1–1.5 h. The yellow precipitate was collected by filtration
and washed with water, methanol, and acetone. Yield of 1·2H O:
2
ences in bond lengths and angles are due to the presence of 0.075 g, 53%. C H N O RhS (409.42): calcd. C 28.05, H 6.63, N
9
28
3
2
3
six-membered chelate rings in 2a and 2b, rather than the 10.90; found C 28.02, H 6.11, N 10.34. Reflectance maxima (σ/
3
–1
five-membered chelate rings in 4a. The absorption bands in 10 cm ): 13.5, 28.5, 34.1 sh, 40.4.
2
a and 2b are shifted to higher energies than those of 4a. ∆Λ-[Co{Rh(apt) } ](NO )
[2a(NO3)3]
): To a suspension containing 1 (0.20 g,
and
∆∆/ΛΛ-
3
2
3 3
The results of IR and far-IR spectra indicate that the ter- [Co{Rh(apt)
minal units retain their structure during the formation of
S-bridged complexes. NMR spectra of 2a and 2b show that
the chemical shift values in C NMR are shifted to higher
fields as compared to 4a and 4b. In addition, the Co oxi-
dation state in 2a and 2b is more stable than that in 4a and
4
3
}
2
]Br
3
(2bBr
3
3
0.55 mmol) in water (10 cm ) was added a solution containing
3
CoCl
2 2
·6H O (0.65 g, 2.7 mmol) in water (5 cm ). The mixture was
1
3
stirred at room temperature for 30 min and filtered. A saturated
3
III
aqueous solution of NaNO
filtrate, and the resulting dark red crystals [2a(NO
collected by filtration. A saturated aqueous solution of NaBr
3
(5 cm ) was added to the dark brown
3
)
3
·2H O] were
2
b. It can be concluded that the properties of complexes are
3
(5 cm ) was added to the filtrate, and the resulting dark red crystals
2bBr ·3.5H O) were collected by filtration. Crystals suitable for X-
greatly influenced by increasing the number of methylene
groups in the chelate rings.
(
3
2
ray crystallography were obtained by recrystallization of
a(NO ·2H O and 2bBr ·3.5H O from the aqueous solutions
containing NaNO and NaCl. Yield of 2a(NO ·2H O: 0.065 g,
(1027.77): calcd. C 21.04, H 5.10, N
2.27; found C 21.19, H 4.98, N 11.89. Absorption maxima [σ/
2
3
)
3
2
3
2
3
3
)
3
2
1
1
1
9 2 6
2%. C18H52CoN O11Rh S
Experimental Section
Materials
3
–1
–1
3
–1
0 cm (log ε/mol ·dm ·cm )]: 14.5 (2.11), 20.9 (3.49), 24.7
(
4.14), 31.5 (4.08 sh), 38.6 (4.13 sh), 48.7 (4.78). Reflectance max-
The aet complexes fac(S)-[Rh(aet)
4a(NO ], and ∆∆/ΛΛ-[Co{Rh(aet)
by procedures similar to those in the literature.
were purchased from Wako Pure Chemical Ind. Ltd. All chemicals
were of reagent grade and were used without further purification.
3
] (3), ∆Λ-[Co{Rh(aet)
3 2 3 3
} ](NO )
3
–1
ima (σ/10 cm ): 15.3, 19.0, 24.2, 29.6 sh, 41.1. Yield of
2bBr ·3.5H O: 0.045 g, 7.9%. C H Br CoN O Rh S (1100.49):
calcd. C 19.50, H 5.00, N 7.58; found: C 19.73, H 5.08, N 7.96.
Absorption maxima [σ/10 cm (log ε/mol ·dm ·cm )]: 16.7
(
(
[
3
)
3
3
}
2
]Br (4bBr ) were prepared
3
3
[
31–33]
All reagents
3
2
18 55
3
6
3.5
2 6
3
–1
–1
3
–1
3.11), 18.3 (3.14), 24.3 (4.06), 29.7 (4.14 sh), 40.2 (4.35 sh), 51.0
Preparation of Ligand
3
–1
4.80). Reflectance maxima (σ/10 cm ): 16.5, 19.1, 23.4, 29.5 sh,
The ligand was prepared by literature methods with some modifica-
tions as follows.
40.3.
[
22–24]
Column Chromatography
1
-Amino-3-propylsulfate (I): A mixture of 3-amino-1-propanol
Column chromatography was also performed with an SP-Sephadex
C-25 column (Na+ form). When the reddish brown filtrate was
3
(75.1 g, 1.0 mol) and carbon tetrachloride (200 cm ) was cooled in
Eur. J. Inorg. Chem. 2006, 1041–1049
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1047

N. Amir, M. Motonishi, M. Fujita, Y. Miyashita, K. Fujisawa, K. Okamoto
FULL PAPER
eluted with a NaCl solution (0.5 ), two bands were obtained: a
reddish brown band followed by a greenish brown band. The
UV/Vis absorption spectra of the bands showed that the reddish
brown band contains 2a and the greenish brown band contains 2b.
The purity of the isomers that had been obtained by fractional
precipitation, was confirmed by column chromatography [SP-Se-
AM600 NMR spectrometer in D
silapentane-1-sulfonate (DSS) as an internal reference or CDCl
2
O using sodium 4,4-dimethyl-4-
3
using tetramethylsilane (TMS) as an internal reference. The molar
conductance of the complexes was measured with a HORIBA con-
ductivity meter (DS-14). Electrochemical experiments were per-
formed with a CV-50W voltammetry analyzer, Bioanalytical Sys-
tems, Inc. (BAS) with a platinum-working electrode (BAS, Pt). In
the electrochemical experiments an aqueous Ag/AgCl/NaCl
+
phadex C-25 column (Na form)].
Optical Resolution of 2b
–
3
(
3 mol·dm ) (BAS, RE-1B) and platinum wire were used as the
Compound 2b was optically resolved with an SP-Sephadex C-25
column (K+ form). An aqueous solution of 2b was charged onto
the column and adsorbed. The column was first eluted with an
reference and auxiliary electrodes, respectively. All the measure-
ments were carried out at room temperature in an aqueous solu-
tion, which was bubbled with N
2
gas, and contained Na
2 4
SO
aqueous solution of K
2
[Sb
2
(R,R-tartrato)
2
]·5H
2
O (0.15 ), where-
–3
(
0.1 mol·dm ) as a supporting electrolyte.
upon two distinct greenish brown bands were separated. The bands
were finally eluted and collected by an aqueous solution of KCl
X-ray Crystal Structure Determinations
(
0.5 ). The CD spectra of the two bands were measured, which
Single-crystal X-ray data collections were performed with a Rigaku
AFC-7S Mercury CCD area detector with a graphite monochro-
had a positive or negative CD sign at 412 nm. The CD spectra of
two bands were just opposite to each other. The ∆ε values of each
matized Mo-K
gaku) program package. Crystallographic data of II and complexes
a(NO ·2H O, 2bCl , and 4a(NO ·3H O are listed in Table 5.
The positions of Rh, Co, and non-hydrogen atoms were determined
α
(0.71070 Å) radiation using the CrystalClear (Ri-
CD
CD
eluent containing the (+)412 and (–)412-2b isomers were evaluated
on the basis of the absorption spectroscopic data of 2bBr ·3.5H O.
CD extrema [σ/10 cm (∆ε/mol ·dm ·cm )]: 2b (lower) 16.73 (–
1.06), 24.26 (+99.62), 28.62 (–11.27), 31.38 (+10.65), 35.94
+28.10), 42.05 (+10.96); 2b (upper) 16.62 (+38.24), 24.19 (–96.92),
8.80 (+10.45), 31.46 (–11.07), 36.23 (–27.98), 41.87 (–10.12).
3
2
2
3
)
3
2
3
3
)
3
2
3
–1
–1
3
–1
4
(
2
by direct methods (SHELX 97 2a, 4a)[ or (SIR97 II, 2b), and
some remaining atom positions were found by successive difference
Fourier techniques (DIRDIFF-99).[ The structures were refined
by full-matrix least-squares techniques using anisotropic thermal
parameters for non-hydrogen atoms. All hydrogen atoms except for
those of II were included in calculated positions but not refined.
The CrystalStructure (Rigaku) program package was used for the
calculations.[
42]
[43]
44]
Measurements
Elemental analysis (C, H, and N) was performed by the Depart-
ment of Chemistry in the University of Tsukuba. The concentra-
tions of Co and Rh in the complexes were determined with a NIP-
PON Jarrell-Ash ICPA-575 spectrometer. UV/Vis absorption spec-
tra were recorded with a JASCO V-560 spectrophotometer and so-
lid-state diffuse reflectance spectra were recorded with a JASCO V-
45]
CCDC-279990–CCDC-279993 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
5
70 spectrophotometer equipped with an integrating sphere appa-
ratus (JASCO ISN-470) using powder samples diluted with MgO.
IR and far-IR spectra were recorded with a JASCO FT/IR-550
spectrometer using KBr disks in the range 4000–400 cm–1 and Nu-
jol mulls between polyethylene pellets in the range 650–50 cm . H
and C NMR spectra were recorded with a BRUKER AM500 and
Supporting Information (see footnote on the first page of this arti-
cle): IR and far-IR spectra of I, II, and aptH·HCl (Figure S1); IR
–
1 1
1
3
1
1
and far-IR spectra of complexes 1, 2a, and 2b (Figure S2); H- H
Table 5. Crystallographic Data for II, 2a(NO
3
)
3
·2H
2
O, 2bCl
2a(NO
52CoN
3
, and 4a(NO
3
)
3
·3H
2
O.
2bCl
II
3
)
3
·2H
2
O
3
4a(NO
42CoN
961.62
3 3 2
) ·3H O
Empirical formula
Formula weight
Dimensions [mm]
Crystal system
Space group
a [Å]
C
133.23
0.55×0.30×0.10
monoclinic
4
H
7
NS
2
C
18
H
9
O11Rh
2
S
6
C
18
H
48Cl
3
CoN
6
Rh
2
S
6
C
12
H
9 2 6
O12Rh S
1027.77
912.08
0.15×0.13×0.10
hexagonal
P6/mcc (#192)
12.8060(2)
0.27×0.20×0.05
monoclinic
C2/c (#15)
17.2186(7)
9.3370(2)
23.2258(10)
0.25×0.25×0.10
triclinic
¯
P2
1
/n (#14)
P1 (#2)
4.9986(5)
6.2381(7)
19.717(2)
8.8570(1)
8.9760(1)
12.0893(1)
70.854(8)
69.761(8)
77.198(9)
845.52(2)
1
1.888
18.80
13730
3820
b [Å]
c [Å]
26.3105(5)
α [°]
β [°]
γ [°]
Volume [Å ]
93.486(2)
98.1420(5)
3
613.69(11)
4
1.442
7.39
9380
1444
0.020
1113
64
3696.4(2)
4
3736.69(11)
4
Z
D
–3
calcd. [g·cm ]
1.847
17.25
29146
4413
0.030
2701
239
1.621
18.79
31160
1771
0.073
699
–1
µ [cm ]
Total reflections
Unique reflections
R
int
0.016
3482
250
Used [I Ͼ 3σ(I)]
No. Variables
65
Used/ Variables
Final R [I Ͼ 3σ(I)]
Final Rw [I Ͼ 3σ(I)]
Goodness of fit
17.39
0.062
0.194
1.000
11.30
0.036
0.092
1.019
10.75
0.074
0.195
1.002
13.93
0.039
0.126
1.002
1048
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Eur. J. Inorg. Chem. 2006, 1041–1049

S-Bridged Heterotrinuclear Complexes Containing Six-Membered Chelate Rings
FULL PAPER
1
13
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Received: August 4, 2005
Published Online: January 5, 2006
Eur. J. Inorg. Chem. 2006, 1041–1049
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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