Evaluation of the influence of a thioether substituent on the solid state and solution properties of N3S-ligated copper(II) complexes

Article abstract of DOI:10.1039/b304846b

Admixture of a N₃S(thioether) ligand having two internal hydrogen bond donors (pbnpa: N-2-(phenylthio)ethylN,N-bis-((6-neopentylamino-2- pyridyl)methyl)amine; ebnpa: N-2-(ethylthio)ethyl-N,N-bis-((6-neopentylamino-2- pyridyl)methyl)amine) with equimolar amounts of Cu(ClO₄) ₂·6H₂O and NaX (X = Cl^-, NCO ^-, or N₃^-) in CH₃OH/ H₂O yielded the mononuclear Cu(II) derivatives [(pbnpa)Cu-Cl]ClO₄ (1), [(ebnpa)Cu-Cl]ClO₄ (2), [(pbnpa)Cu-NCO]ClO₄ (3), [(ebnpa)Cu-NCO]ClO₄ (4), [(pbnpa)Cu-N₃]ClO₄ (5), and [(ebnpa)Cu-N₃]ClO₄ (6). Each complex was characterized by FTIR, UV-VIS, EPR, and elemental analysis. Complexes 1, 2, 3 and 6 were characterized by X-ray crystallography. The structural studies revealed that [(pbnpa)Cu-X]ClO₄ derivatives (1, 3) exhibit a distorted square pyramidal type geometry, whereas [(ebnpa)Cu-X]ClO₄ complexes (2, 6) may be classified as distorted trigonal bipyramidal. EPR studies in CH₃OH/CH₃CN solution revealed that 1-6 exhibit an axial type spectrum with g_∥ > g_⊥ > 2.0 and A_∥ = 15-17 mT, consistent with a square pyramidal based geometry for the Cu(II) center in each complex. A second species detected in the EPR spectra of 2 and 6 has a smaller A_∥ value, consistent with greater spin delocalization on to sulfur, and likely results from geometric distortion of the [(ebnpa)Cu(II)-X]⁺ ions present in 2 and 6. The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b304846b

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Evaluation of the influence of a thioether substituent on the solid
state and solution properties of N3S-ligated copper(II) complexes†
Kyle J. Tubbs,‡a Amy L. Fuller,‡a Brian Bennett,b Atta M. Arif,c
Magdalena M. Makowska-Grzyskaa and Lisa M. Berreau*‡a
a Department of Chemistry and Biochemistry, Utah State University, Logan, UT, USA.
E-mail: berreau@cc.usu.edu
b Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road,
Milwaukee, WI, USA. E-mail: bbennett@mcw.edu
c Department of Chemistry, University of Utah, Salt Lake City, UT, USA.
E-mail: arif@chemistry.utah.edu
Received 30th April 2003, Accepted 13th June 2003
First published as an Advance Article on the web 30th June 2003
Admixture of a N3S(thioether) ligand having two internal hydrogen bond donors (pbnpa: N-2-(phenylthio)ethyl-
N,N-bis-((6-neopentylamino-2-pyridyl)methyl)amine; ebnpa: N-2-(ethylthio)ethyl-N,N-bis-((6-neopentylamino-2-
pyridyl)methyl)amine) with equimolar amounts of Cu(ClO4)2ؒ6H2O and NaX (X = ClϪ, NCOϪ, or N3Ϫ) in CH3OH/
H2O yielded the mononuclear Cu() derivatives [(pbnpa)Cu–Cl]ClO4 (1), [(ebnpa)Cu–Cl]ClO4 (2), [(pbnpa)Cu–
NCO]ClO4 (3), [(ebnpa)Cu–NCO]ClO4 (4), [(pbnpa)Cu–N3]ClO4 (5), and [(ebnpa)Cu–N3]ClO4 (6). Each complex
was characterized by FTIR, UV-VIS, EPR, and elemental analysis. Complexes 1, 2, 3 and 6 were characterized by
X-ray crystallography. The structural studies revealed that [(pbnpa)Cu–X]ClO4 derivatives (1, 3) exhibit a distorted
square pyramidal type geometry, whereas [(ebnpa)Cu–X]ClO4 complexes (2, 6) may be classified as distorted
trigonal bipyramidal. EPR studies in CH3OH/CH3CN solution revealed that 1–6 exhibit an axial type spectrum
with g|| > g⊥ > 2.0 and A|| = 15–17 mT, consistent with a square pyramidal based geometry for the Cu() center
in each complex. A second species detected in the EPR spectra of 2 and 6 has a smaller A|| value, consistent
with greater spin delocalization on to sulfur, and likely results from geometric distortion of the [(ebnpa)Cu()–X]ϩ
ions present in 2 and 6.
et al. found that their ability to spectroscopically observe a
novel Cu–OOH intermediate was related to the nature of the
thioether substituent present, with a phenyl thioether ligand
Introduction
Within the active sites of the copper-containing enzymes
dopamine β-monooxygenase (DβM) and peptidylglycine
providing a spectroscopically observable CuO2H derivative.
α-amidating enzyme (PAM), substrate oxidation is proposed
Notably, ligands having –SCH3 and –S(i-C3H7) substitutents
to occur at a mononuclear nitrogen/sulfur(thioether)-ligated
were not effective in producing a spectroscopically observable
CuO2H intermediate. A copper() chloride complex of the
2-bis-(6-methyl-2-pyridylmethyl)amino-1-(phenylthio)ethane
copper center.1 The coordination environment of this copper
ion is similar for both enzymes and appears to vary with the
oxidation level of the metal center.2,3 For oxidized DβM, the
ligand was shown to exhibit a distorted square pyramidal
CuB coordination environment has been identified by copper
geometry (τ = 0.39)8 with a long axial Cu–S(thioether) inter-
K-edge EXAFS studies as being comprised of two/three
action (Cu–S 2.6035(3) Å). This distance is slightly shorter than
histidine ligands and one/two water molecules.2a In the oxidized
copper() form of PAM, the primary coordination sphere of
CuM consists of two histidine nitrogens, a water molecule, and
that observed for the CuM–SMet interaction (∼2.7 Å) in the oxi-
dized form of PAM.3 The structures of mononuclear divalent
copper complexes of other N3S ligands involved in the study by
a weakly-coordinated methionine sulfur (Cu–SMet ∼2.7 Å).3 It is
Kodera et al. (e.g. –SCH3, S(i-C3H7) derivatives) were not
generally believed that a similar long Cu–SMet interaction is
reported. Thus, it is unclear whether the phenylthio substituent
present in DβM, but is undetectable by EXAFS. Reduction
of the copper ions in DβM and PAM yields CuB and CuM
was the only supporting chelate ligand in the above outlined
series of ligands to yield a weak Cu–S(thioether) interaction
in copper() derivatives. Another observation regarding the
2-bis-(6-methyl-2-pyridylmethyl)amino-1-(phenylthio)ethane-
ligated copper system of Kodera et al. is that the phenyl
thioether substituent does not undergo sulfur oxidation in
the presence of H2O2. Copper complexes having a –SCH3 and
–S(i-C3H7) substituent in the supporting chelate ligand were
centers that both exhibit strong coordination to a methionine
sulfur (CuB Cu–SMet: 2.25 Å (EXAFS);2a CuM: Cu–SMet: 2.24 Å
(EXAFS)2b,4) as well as two histidine nitrogens.5 These changes
in Cu–SMet interactions in DβM and PAM, as a function of the
oxidation state of the metal, have been suggested to be import-
ant toward tuning the redox potential of the copper center.2b
A recent model study suggests that the influence of thioether
instead observed to readily undergo sulfur oxidation to yield
ligation on the chemistry of divalent copper centers remains to
sulfoxides and sulfones under identical conditions.6e
be fully elucidated.6,7 Specifically, an investigation by Kodera
In the work described herein, we have examined the fund-
amental copper() coordination chemistry of two N3S ligands
having two internal hydrogen bond donors. In the context of
and coworkers suggests that the nature of the thioether substi-
tuent in supporting N3S chelate ligands is important toward
influencing the chemistry of copper() species.6e Using a series
this study, we have addressed an issue that is of relevance
of S-substituted N3S ligands (2-bis-(6-methyl-2-pyridylmethyl)-
amino-1-(R-)ethane, R = –SC6H5, –SCH3, –S(i-C3H7)), Kodera
to the previously reported study by Kodera and coworkers.6e
Specifically, we have directed our studies toward evaluating
how different thioether substituents influence the solid state
and solution properties of mononuclear divalent copper com-
plexes relevant to the CuB and CuM sites in DβM and PAM,
respectively.
† Electronic supplementary information (ESI) available: plot of
A|| vs. g||. See http://www.rsc.org/suppdata/dt/b3/b304846b/
‡ These authors contributed equally to this work.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 3 1 1 1 – 3 1 1 6
3111

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Table 1 Crystal data, data collection, and refinement parameters for 1, 2, 3, and 6a
1
2
3
6
Formula
M
C30H43Cl2CuN5O4S
704.19
C26H43Cl2CuN5O4S
656.15
C31H43ClCuN6O5S
710.76
C26H43ClCuN8O4S
662.73
Crystal system
Space group
Monoclinic
P2(1)/c
Triclinic
P1
Monoclinic
P2(1)/c
Triclinic
P1
¯
¯
a/Å
b/Å
c/Å
α/Њ
11.0077(2)
14.5441(2)
20.7276(5)
8.4860(1)
13.8394(2)
14.3749(3)
101.7717(6)
91.7414(6)
106.5561(11)
1577.11(4)
2
0.967
150(1)
11542
7142
7.2979(2)
34.5443(14)
13.0965(5)
8.5866(2)
13.7903(3)
14.6773(4)
78.9526(9)
89.4294(9)
73.8704(16)
1636.89(7)
2
0.856
150(1)
11484
7415
β/Њ
97.4909(7)
91.517(3)
γ/Њ
V/Å3
3290.11(11)
4
0.932
200(1)
13782
7509
3300.5(2)
4
0.855
150(1)
10159
6643
Z
µ/mmϪ1
T/K
Reflns measured
Unique reflns obs.
R1
wR2
0.0462
0.1027
0.0321
0.0723
0.0499
0.0911
0.0405
0.0969
a All structures determined using Mo Kα radiation, refinements based on F 2. For I>2σ(I ), R1 =Σ||Fo|Ϫ|Fc||/Σ|Fo|, and wR2 =[Σ[w(Fo2 ϪFc2)2/
Σ[(Fo )2]]1/2, where w=1/[σ2(Fo )ϩ(aP)2 ϩbP].
2
2
Scheme 1
[(L2)Cu–Br]ClO4: Cu–S(1) 2.762(3) Å, τ = 0.19).8,10 Significant
Results and discussion
solid-state structural perturbation is found when the phenyl
thioether moiety in 1 is replaced by an ethyl thioether substi-
tuent. In the X-ray crystal structure of [(ebnpa)Cu–Cl]ClO4 (2),
the geometry of the copper() ion is distorted trigonal bipyr-
amidal (τ = 0.63),8 with the Cu(1)–S(1) bond length (2.3681(5)
Å) being ∼0.29 Å shorter than that observed for 1. This Cu()–
S(thioether) distance is only slightly longer than that observed
for a distorted square pyramidal (τ = 0.15)8 copper() complex
of the N3S ligand N-2-(methylthio)ethyl-N,N-bis-(2-pyridyl-
ethyl)amine (2.335(2) Å), wherein a pyridyl nitrogen is found in
the axial position (Cu–N 2.199(4) Å).6c The Cu–Npy distances
in 2 are elongated by ∼0.07–0.11 Å as compared to those found
in 1, with the longest being Cu(1)–N(1) (2.1744(14) Å).
On the basis of comparison of R and U(B) values for
structure solutions for 3 as [(pbnpa)Cu–NCO]ClO4 or [(pbnpa)-
Cu–OCN]ClO4, we have concluded that the cyanate ligand
exhibits N-coordination. Overall, as in 1, the copper() center
of 3 exhibits a slightly distorted square pyramidal geometry
(τ = 0.08).8 The Cu(1)–S(1) distance (2.7143(9) Å) is ∼0.05 Å
longer than for the chloride derivative. The Cu–N distances
involving the chelate ligand for 1 and 3 are identical within
experimental error. The Cu(1)–N(6) distance (1.943(3) Å) is at
the long end of the range (∼1.89–1.96 Å) of Cu–N(NCO)
equatorial bond lengths reported in the literature.11 The Cu(1)–
N(6)–C(31) angle (140.1(3)Њ) is acute when compared to other
complexes having terminal cyanate coordination to a copper()
center. (∼138–170Њ) and thus suggests a major contribution of
resonance form A (below) in the cyanate bonding in 3.11 This
notion is supported by the observation of identical N(6)–C(31)
Syntheses and structures
Treatment of a N3S ligand having two internal hydrogen bond
donors (pbnpa or ebnpa9) with equimolar amounts of
Cu(ClO4)2ؒ6H2O and NaX (X = Cl, NCO, N3) in methanol,
followed by crystallization from methanol/water/acetone,
yielded a series of crystalline solids (1–6, Scheme 1) following
partial evaporation of the solutions at ambient temperature.
Each solid was carefully dried under vacuum and characterized
by FTIR, UV-VIS, EPR, and elemental analysis.
Crystals suitable for single crystal X-ray crystallographic
analysis were obtained for complexes 1, 2, 3, and 6. Details
of the data collection and structure refinement are given in
Table 1. Structural drawings of the complexes are shown
in Fig. 1 and 2. Selected bond distances and angles are given in
Table 2.
The structural features of [(pbnpa)Cu–Cl]ClO4 (1) are gener-
ally similar to the chloride complex reported by Kodera and
coworkers supported by the 2-bis-(6-methyl-2-pyridylmethyl)-
amino-1-(phenylthio)ethane chelate ligand (L1).6e However,
subtle differences are present, including a slightly longer Cu–
SPh interaction (1: Cu(1)–S(1) 2.6605(8) Å; [(L1)CuCl]ClO4:
Cu–S 2.6035(3) Å) a more square pyramidal Cu() center (1: τ =
0.25; [(L1)CuCl]ClO4: τ = 0.39),8 and a slightly longer Cu–Cl
bond (1: Cu(1)–Cl(1) 2.2548(8) Å; [(L1)CuCl]ClO4: Cu–Cl(1)
2.2159(3) Å). Notably, the Cu–S(1) distance of 1 is ∼0.1 Å
shorter than that observed for a mononuclear N3S-ligated
copper() bromide complex of the methyl thioether ligand
N-2-(methylthio)ethyl-N,N-bis-(2-pyridylmethyl)amine
(L2,
D a l t o n T r a n s . , 2 0 0 3 , 3 1 1 1 – 3 1 1 6
3112

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Table 2 Selected bond distances (Å) and angles (Њ) for the X-ray
structures of 1, 2, 3, and 6a
1
2
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–Cl(1)
2.025(2)
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–Cl(1)
2.1744(14)
2.0374(15)
2.0897(14)
2.2740(5)
2.3681(5)
105.84(4)
171.75(4)
101.48(4)
86.614(17)
109.59(6)
111.45(4)
133.97(4)
80.35(6)
2.043(2)
2.014(2)
2.2548(8)
2.6605(8)
98.26(7)
149.82(7)
95.59(7)
123.37(3)
165.08(9)
81.25(7)
95.76(7)
82.46(9)
82.78(9)
86.68(7)
Cu(1)–S(1)
Cu(1)–S(1)
Cl(1)–Cu(1)–N(1)
Cl(1)–Cu(1)–N(3)
Cl(1)–Cu(1)–N(4)
Cl(1)–Cu(1)–S(1)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–S(1)
N(4)–Cu(1)–S(1)
N(3)–Cu(1)–N(1)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)–S(1)
Cl(1)–Cu(1)–N(1)
Cl(1)–Cu(1)–N(3)
Cl(1)–Cu(1)–N(4)
Cl(1)–Cu(1)–S(1)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–S(1)
N(4)–Cu(1)–S(1)
N(3)–Cu(1)–N(1)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)–S(1)
81.12(6)
86.01(4)
3
6
Cu(1)–N(1)
Cu(1)–N(3)
Cu(1)–N(4)
Cu(1)–N(6)
2.017(3)
2.040(3)
2.029(3)
1.943(3)
2.7143(9)
97.34(11)
160.69(12)
96.16(10)
113.76(9)
165.70(10)
86.37(7)
92.48(7)
82.61(10)
83.09(10)
85.54(7)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–N(4)
Cu(1)–N(6)
2.0214(18)
2.0950(17)
2.1474(19)
1.9652(19)
2.4015(6)
178.33(7)
99.60(7)
Cu(1)–S(1)
Cu(1)–S(1)
N(6)–Cu(1)–N(1)
N(6)–Cu(1)–N(3)
N(6)–Cu(1)–N(4)
N(6)–Cu(1)–S(1)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–S(1)
N(4)–Cu(1)–S(1)
N(3)–Cu(1)–N(1)
N(3)–Cu(1)–N(4)
N(3)–Cu(1)–S(1)
N(1)–Cu(1)–N(6)
N(2)–Cu(1)–N(6)
S(1)–Cu(1)–N(6)
N(2)–Cu(1)–N(4)
N(2)–Cu(1)–S(1)
N(4)–Cu(1)–S(1)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–N(4)
N(1)–Cu(1)–S(1)
N(4)–Cu(1)–N(6)
91.85(5)
112.24(7)
128.59(5)
115.04(5)
81.66(7)
81.31(7)
86.50(5)
Fig. 1 Representations of the cationic portions of the X-ray crystal
structures of 1 (top) and 2 (bottom). All ellipsoids are shown at the
50% probability level (all hydrogen atoms except secondary amine
hydrogens not shown for clarity).
99.18(8)
a Estimated standard deviations are indicated in parentheses.
and C(31)–O(1) bond lengths for 3 within experimental error
(1.189(4) and 1.199(4) Å, respectively), and a N(6)–C(31)–O(1)
bond angle of 176.5(4)Њ.
Azide anion is an inhibitor of DβM and has been used in
kinetic, EPR, and paramagnetic NMR studies of the enzyme.12
For this reason, we have comprehensively characterized
copper() azide derivatives of the pbnpa and ebnpa ligands (5
and 6). Comparison of the X-ray crystallographically determined
metrical parameters of 6 with those of [Cu(Hbppa)(N3)]ClO4, a
mononuclear Cu() azide complex of a structurally related
ligand (Hbppa = N-(2-pyridylmethyl)-N,N-bis(6-pivaloylamido-
2-pyridylmethyl)amine)13 that has previously been reported in the
literature, reveals interesting perturbations due to substitution of
a thioether for a pyridyl donor in the supporting chelate ligand.
Specifically, the copper() ion in 6 exhibits a more trigonal bi-
pyramidal geometry (τ = 0.83; [Cu(Hbppa)(N3)]ClO4 τ = 0.65),8 a
slightly elongated Cu–N(tertiary amine) distance (6: Cu(1)–N(1)
2.0214(18) Å; [Cu(Hbppa)(N3)]ClO4 1.987(7) Å), and a signifi-
cantly longer bonding interaction with the thioether sulfur
(6: Cu(1)–S(1) 2.4015(6) Å) than is observed with the pyridyl
nitrogen in [Cu(Hbppa)(N3)]ClO4 (2.056(7) Å). The Cu–N(azide)
distances are similar for the two complexes (6: 1.9652 (19) Å;
[Cu(Hbppa)(N3)]ClO4 1.937(7) Å). Finally, the bond distances
(N(6)–N(7) 1.212(3) Å, N(7)–N(8) 1.145(3) Å) and angles
(Cu(1)–N(6)–N(7) 121.00(15)Њ, N(6)–N(7)–N(8) 178.1(2)Њ)
involving the azide ligand in 6 are typical of transition metal
azide ligation. Specifically, the longer N–N distance, due to con-
tributions from the canonical form A (below), is found between
the metal-bound nitrogen and the middle nitrogen, and the M–N3
bond angle is ∼117–132Њ.14
Fig. 2 Representations of the cationic portions of the X-ray crystal
structures of 3 (top) and 6 (bottom). All ellipsoids are shown at the
50% probability level (all hydrogen atoms except secondary amine
hydrogens not shown for clarity).
D a l t o n T r a n s . , 2 0 0 3 , 3 1 1 1 – 3 1 1 6
3113

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Table 3 EPR parameters for 1–6
Complex
g||
g⊥
A||/mT
A⊥/mT
a
a
a
1
2.245
2.223
2.192
2.250
2.248
2.248
2.243
2.167
2.049
2.032
2.054
2.047
2.052
2.050
2.054
15.4
16.6
12.0
15.9
16.8
15.7
15.6
5.6
Evidence for hydrogen-bonding interactions between the
neopentyl amine moieties of the pbnpa/ebnpa ligands and the
bound anions (ClϪ, NCOϪ, and N3Ϫ) may be derived from
the solid state structures of 1–3 and 6. For the chloride deriv-
atives, the observed heteroatom distances (1: N(1) ؒ ؒ ؒ Cl(1)
3.17 Å, N(5) ؒ ؒ ؒ Cl(1) 3.17 Å; 2: N(1) ؒ ؒ ؒ Cl(1) 3.21 Å,
N(5) ؒ ؒ ؒ Cl(1) 3.20 Å) indicate that hydrogen-bonding
interactions are likely present.15 The same can be inferred for
the cyanate and azide derivatives 3 (N(2) ؒ ؒ ؒ N(6) 2.93 Å,
2b
3
1.1
1.3
1.2
4
5
6b
1.1
c
a
–
a None detected. b Two major species were identified by difference.
c g⊥ could not be determined.
N(5) ؒ ؒ ؒ N(6) 2.89 Å) and
6 (N(2) ؒ ؒ ؒ N(6) 2.91 Å,
N(5) ؒ ؒ ؒ N(6) 2.88 Å), albeit based on the bond distances/
angles of these bound psuedohalides, only approximately one
lone pair is available on the metal-bound nitrogen atom of
either 3 or 6 to participate in secondary hydrogen bonding
interactions.
bound anion were observed only for the azide derivatives
(5: 388 nm (2200 MϪ1 cmϪ1); 6: 398 nm (2050 MϪ1 cmϪ1)).
EPR spectra collected on 0.4 mM solutions (9 : 1 CH3OH :
CH3CN) of 1–6 yielded spectra as shown in Fig. 4. These
spectra show species with clear g(z) > g(x,y) and A(z) coupling
for all of the complexes, consistent with the presence of a
dx Ϫy ground state and a square pyramidal-based geometry in
solution. Complexes 2 and 6 exhibit more complicated spectra,
with two species present in each sample. Values for g||, g⊥, A||,
and A⊥ for 1–6, derived from spectral simulation,18 are given in
Table 3.
FTIR, UV-VIS, and EPR spectroscopy
2
2
The νa(NCO) vibrations for 3 and 4 are found at 2191 and 2187
cmϪ1, respectively. A νs vibration, which is typically found in the
range of 1100–1400 cmϪ1, is not readily identifiable in these
systems due to overlap with ligand-based vibrations.
For the azide derivatives 5 and 6, the νa(N3) vibrations are
found at 2051 and 2061 cmϪ1, respectively. These values
compare well with the same vibration observed for Cu(Et4dien)-
Br(N3) (2053 cmϪ1), a complex that possesses a terminal azide
anion with symmetric N–N distances.16 A νs(N3) vibration was
not identifiable (typically ∼1300 cmϪ1) upon comparison of
the solid state FTIR spectra for chloride (1 and 2) and azide
derivatives (5 and 6).
The region of 3400–3200 cmϪ1 in the solid state FTIR spectra
for this family of complexes is complicated by the appearance
of either two distinct bands, or one broad band that looks to be
the overlap of two features. Small differences detected in the
hydrogen-bonding interactions involving the bound halides/
pseudohalides in 1–6 by X-ray crystallography may provide a
rationale for the observation of two bands. However, as the
heteroatom distances of these interactions differ by <0.05 Å, an
alternative explanation could be that the band at lower
frequency is an overtone of the N–H bending vibration (found
in the region 1618–1624 cmϪ1 for 1–6) which is intensified by
Fermi resonance.17
Fig. 4 Low temperature EPR spectra of complexes in frozen solution
(0.4 mM in 9 : 1 CH3OH : CH3CN). Spectra are labelled according to
compound number (1–6). Each trace (except 2a) was recorded at 115 K,
2 mW microwave power, 9.32 GHz. Trace 2a was recorded at 115 K,
159 mW microwave power. All traces are presented with principal
g-values aligned to a magnetic field scale corresponding to a microwave
frequency of 9.64 GHz.
In CH3CN solution (∼2–3 mM), the pbnpa-ligated complexes
(1, 3, and 5) generally exhibit d–d transitions at higher energies,
and with lower extinction coefficients, than the ebnpa-ligated
analogs (2, 4, and 6; Fig. 3). LMCT features involving the
Using an analysis of g(z) and A(z) values developed by
Peisach and Blumberg,19 we have determined that complexes 1
and 3–5 possess predominantly mixed nitrogen/oxygen ligation
(Fig. S1, supplementary information†). Notably, this does not
rule out the presence of a long Cu–S interaction in these
systems, akin to that observed in the solid state structure of 1.
One component present in the EPR spectra of 2 and 6 may be
classified in a similar manner. However, an additional species
present in these samples has a smaller A|| value, consistent with
greater spin delocalization on to sulfur.19 These additional
species likely result from geometric distortion of the Cu()
cations present in 2 and 6, and may be present only in the
ebnpa-ligated systems (–SEt) due to an enhanced donor ability
for the alkyl- versus an aryl-substituted thioether sulfur in the
supporting chelate ligand.
Fig. 3 UV-vis spectral features of 1–6 in d–d transition region.
Complexes having pbnpa as the supporting chelate ligand are shown in
solid lines (1 (square), 3 (circle), 5 (diamond)); ebnpa-ligated systems
are shown in dashed lines (2 (square), 4 (circle), and 6 (diamond)).
Conclusions
In this study, we have examined the structural and solution
properties of a new family of divalent copper complexes
D a l t o n T r a n s . , 2 0 0 3 , 3 1 1 1 – 3 1 1 6
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supported by two N3S(thioether) chelate ligands, each having
two internal hydrogen bond donors. The N3S ligands differ in
the nature of the –SR substituent (R = Ph (pbnpa) or Et
(ebnpa)). Single crystal X-ray crystallographic analysis of
copper() chloride, cyanate, and azide derivatives revealed that
–SPh ligated systems tend to produce copper() derivatives
having a more square pyramidal structure and a long Cu–S
interaction (∼2.7 Å), whereas –SEt ligated systems exhibit a
distorted trigonal bipyramidal geometry in the solid state.
Solution EPR studies revealed that the species present for both
–SPh and –SEt supported copper() complexes have a square
pyramidal based geometry. Interestingly, only –SEt (ebnpa)
derivatives have a second species present that exhibits an A||
value consistent with enhanced spin delocalization on sulfur.
The subtle differences in solution behaviour between the –SPh
and –SEt ligated systems may explain why the presence of a
specific thioether substitutent has been observed to influence
the chemistry of divalent copper complexes relevant to DβM
and PAM.6e
νmax/cmϪ1 (KBr) 3420 (N–H); νmax/cmϪ1 (CH2Cl2, 100 mM)
3427; 1H NMR (CD3CN, 270 MHz): δ 7.32 (t, J = 7.2 Hz, 2H),
7.22–7.16 (m, 4H), 7.15–7.06 (m, 1H), 6.69 (d, J = 7.2 Hz, 2H),
6.32 (d, J = 8.2 Hz, 2H), 5.02 (br, 2H, N–H ), 3.62 (s, 4H), 3.13
(d, J = 6.3 Hz, 4H), 3.14–3.06 (m, 2H), 2.82–2.72 (m, 2H), 0.92
(s, 18H). 13C{1H} NMR (CD3CN, 67.9 MHz) δ 160.2, 158.6,
138.2, 137.9, 130.0, 128.9, 126.3, 111.8, 106.4, 61.0, 52.9, 53.5,
32.9, 31.3, 27.9 (15 signals expected and observed); m/z 506
([M ϩ H]ϩ, 100%).
Caution! Perchlorate salts of metal complexes with organic
ligands are potentially explosive. Only small amounts of
material should be prepared and these should be handled with
great care.23
General procedure for preparation of copper(II) complexes
A methanol solution (∼1 mL) of the chelate ligand (pbnpa or
ebnpa, ∼40–60 mg) was treated with an equimolar amount of
Cu(ClO4)2ؒ6H2O dissolved in methanol (∼1 mL). After stirring
the resulting solution for ∼10 min, a methanol slurry of
NaX (X = Cl, NCO, N3) was added. To this heterogeneous
mixture was added water (∼6 mL) and acetone (∼3 mL) until a
homogeneous solution was obtained. This solution was then
allowed to evaporate at ambient temperature, which led to the
deposition of 1–6 as crystalline solids.
Experimental
General
All reagents and solvents were obtained from commercial
sources and were used as received unless otherwise noted.
Solvent used in the preparation of the pbnpa ligand were dried
according to literature procedures and were distilled under
nitrogen prior to use.20 The ligand ebnpa (N-2-(ethylthio)ethyl-
N,N-bis-(6-neopentylamino-2-pyridymethyl)amine) and the
ligand precursor 2-(phenylthio)ethylamine hydrochloride were
[(pbnpa)Cu–Cl]ClO4 (1)
Yield: 71%. Found: C, 51.04; H, 6.13; N, 9.88. C30H43N5-
O4SCl2Cu requires C, 51.27; H, 6.17; N, 9.97%; λmax/nm
(CH3CN) 325 (ε/MϪ1 cmϪ1 12 400), 670 (sh, 170), 765 (190);
νmax/cmϪ1 (KBr) 3321 (N–H), 1089 (ClO4), 623 (ClO4); m/z 603
([M–ClO4]ϩ, 100%).
1
prepared according to literature procedures.9,21 FTIR and H
and 13C{1H} NMR spectra were collected under conditions
identical to those previously reported.22 EPR spectra were
recorded using Bruker Elexsys E500 spectrometers equipped
with either (1) a 9.64 GHz ER 4116DM cavity and an Oxford
Instruments ESR-900 helium flow cryostat or, (2) a 9.32 GHz
ER 4123SHQE cavity and an ER 4131VT nitrogen flow
temperature control system. Magnetic fields and microwave
frequencies were recorded and spectra are all presented on a
field scale corresponding to 9.64 GHz. Spin Hamiltonian
parameters were derived from data prior to field adjustment.18
Elemental analyses were performed by Atlantic Microlabs of
Norcross, GA.
[(ebnpa)Cu–Cl]ClO4 (2)
Yield: 90%. Found: C, 47.51; H, 6.58; N, 10.51. C26H43N5-
O4SCl2Cu requires C, 47.69; H, 6.62; N, 10.70%; λmax/nm
(CH3CN) 323 (ε/MϪ1 cmϪ1 12 100), 740 (sh, 250), 837 (280);
νmax/cmϪ1 (KBr) 3298 (N–H), 1087 (ClO4), 623 (ClO4); m/z 555
([M–ClO4]ϩ, 100%).
[(pbnpa)Cu–NCO]ClO4 (3)
Yield: 86%. Found: C, 51.60; H, 6.03; N, 11.55. C31H43N6-
O5SClCu requires C, 52.45; H, 6.11; N, 11.85%; λmax/nm
(CH3CN) 324 (ε/MϪ1 cmϪ1 12 300), 628 (180), 719 (190); νmax
/
cmϪ1 (KBr) 3352 (N–H), 2191 (NCO), 1088 (ClO4), 622 (νClO );
Preparation of N-2-(phenylthio)ethyl-N,N-bis-((6-pivalolyl-
amido-2-pyridyl)methyl)amine (pbppa)
4
m/z 610 ([M–ClO4]ϩ, 55%).
Prepared in a similar manner to N-2-(ethylthio)ethyl-N,N-bis-
((6-pivalolylamido-2-pyridyl)methyl)amine (ebppa), in this case
using 2-(phenylthio)ethylamine hydrochloride.9 Purified by
column chromatography on 200–400 mesh silica gel (1 : 1 ethyl
acetate: hexane; Rf = 0.40). Yield: 80%. Found: C, 67.61, H,
7.35, N, 13.04. C30H39N5SO2 requires C, 67.51, H, 7.37, N,
13.13%; νmax/cmϪ1 3436 (N–H), 1684 (C᎐O); 1H NMR (CD CN,
270 MHz): δ 8.20 (br, 2H), 7.99 (d, J = 8.2 Hz, 4H), 7.67 (t,
J = 7.6 Hz, 2H), 7.26 (m, 4H), 3.71 (s, 4H), 3.14–3.05 (m, 2H),
2.80–2.70 (m, 2H), 1.25 (s, 18H). 13C{1H} NMR (CD3CN, 67.9
MHz) δ 178.0, 159.2, 152.2, 139.6, 137.5, 130.0, 129.0, 126.5,
119.6, 112.7, 61.0, 53.9, 40.5, 31.1, 27.6 (15 signals expected and
observed); m/z 534 ([M ϩ H]ϩ, 100%).
[(ebnpa)Cu–NCO]ClO4 (4)
Yield: 81%. Found: C, 49.02; H, 6.50; N, 12.51. C27H43N6-
O5SClCu requires C, 49.00; N, 6.55; H, 12.71%; λmax/nm
(CH3CN) 322 (ε/MϪ1 cmϪ1 12 200), 723 (270), 804 (300). νmax
/
cmϪ1 (KBr) 3306 (N–H), 2187 (NCO), 1090 (ClO4), 623 (ν );
ClO4
m/z 562 ([M–ClO4]ϩ, 59%).
᎐
3
[(pbnpa)Cu–N3]ClO4 (5)
Yield: 69%. Found: C, 50.48; H, 6.06; N, 15.66. C30H43N8O4-
SClCu requires C, 50.76; H, 6.11; N, 15.80%; λmax/nm (CH3CN)
325 (ε/MϪ1 cmϪ1 13 200), 388 (2200), 646 (320), 825 (245); νmax
cmϪ1 (KBr) 3300 (N–H), 2051 (N3), 1095 (ClO4), 624 (ClO4).
/
Preparation of N-2-(phenylthio)ethyl-N,N-bis-((6-neopentyl-
amino-2-pyridyl)methyl)amine (pbnpa)
[(ebnpa)Cu–N3]ClO4 (6)
Prepared in a manner similar to N-2-(ethylthio)ethyl-N,N-bis-
((6-neopenylamino-2-pyridyl)methyl)amine (ebnpa).9 Purified
by column chromatography on 200–400 mesh silica gel (Rf ∼
0.55 broad, trailing band). Yield: 55%. Found: C, 70.45, H,
8.67, N, 13.52. C30H43N5S requires C, 71.24, H, 8.58, N, 13.86%;
Yield: 91%. Found: C, 47.43; H, 6.45; N, 16.65. C26H43N8-
O4SClCu requires C, 47.19; H, 6.55; N, 16.94%; λmax/nm
(CH3CN) 325 (ε/MϪ1 cmϪ1 12 700), 398 (2050), 666 (450), 837
(420); νmax/cmϪ1 (KBr) 3266 (N–H), 2061 (N3), 1090 (ClO4), 624
(ClO4); m/z (relative intensity): 562 ([M–ClO4]ϩ, 12%).
D a l t o n T r a n s . , 2 0 0 3 , 3 1 1 1 – 3 1 1 6
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wherein significant changes in copper coordination environment
have been identified (ref. 2b).
5 A weakly coordinated solvent molecule may also be bound to CuM
in the reduced form of PAM (ref. 2b).
X-ray crystal structure determinations
Crystal data, data collection, and refinement parameters
for 1, 2, 3, and 6 are given in Table 1. The CCDC references
are 209457–209460; see http://www.rsc.org/suppdata/dt/b3/
b304846b/ for crystallographic data in CIF format.
6 Several structural/functional models for the CuB and CuM centers in
DβM and PAM supported by mixed nitrogen/sulfur chelate ligands
have been reported: (a) B. K. Santra, P. A. N. Reddy, M. Nethaji and
A. R. Chakravarty, Inorg. Chem., 2002, 41, 1328; (b) B. K. Santra,
P. A. N. Reddy, M. Nethaji and A. R. Chakravarty, Dalton Trans.,
2001, 3553; (c) F. Champloy, N. Benali-Cherif, P. Bruno, I. Blain,
M. Pierrot, M. Reglier and A. Michalowicz, Inorg. Chem., 1998, 37,
3910; (d ) T. Ohta, T. Tachiyama, K. Yoshizawa, T. Yamabe,
T. Uchida and T. Kitagawa, Inorg. Chem., 2000, 39, 4358; (e)
M. Kodera, T. Kita, I. Miura, N. Nakayama, T. Kawata, K. Kano
and S. Hirota, J. Am. Chem. Soc., 2001, 123, 7715; ( f ) L. Casella,
M. Gullotti, M. Bartosek, G. Pallanza and E. Laurenti, J. Chem.
Soc., Chem. Commun., 1991, 1235.
7 Structural/functional models for DβM/PAM supported by non-
sulfur-containing chelate ligands have also been reported: (a)
A. Wada, M. Harata, K. Hasegawa, K. Jitsukawa, H. Masuda,
M. Mukai, T. Kitagawa and H. Einega, Angew. Chem., Int. Ed.
Engl., 1998, 37, 798; (b) S. Itoh, T. Kondo, M. Komatsu, Y. Ohshiro,
C. M. Li, N. Kanehisa, Y. Kai and S. Fukuzumi, J. Am. Chem. Soc.,
1995, 117, 4714; (c) S. Itoh, H. Nakao, L. M. Berreau, T. Kondo,
M. Komatsu and S. Fukuzumi, J. Am. Chem. Soc., 1998, 120, 2890;
(d ) I. Blain, M. Pierrot, M. Giorgi and M. Reglier, C. R. Acad.
Sci., Ser. IIc: Chim., 2001, 4, 1; (e) I. Blain, M. Giorgi, I. De Riggi
and M. Reglier, Eur. J. Inorg. Chem., 2001, 205; ( f ) I. Blain,
P. Bruno, M. Giorgi, E. Lojou, D. Lexa and M. Reglier, Eur. J. Inorg.
Chem., 1998, 1297; (g) P. A. N. Reddy, M. Nethaji and
A. R. Chakravarty, Inorg. Chim. Acta, 2002, 337, 450; (h) P. A. N.
Reddy, R. Datta and A. R. Chakravarty, Inorg. Chem. Commun.,
2000, 3, 322.
8 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and
G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349.
9 D. K. Garner, S. B. Fitch, L. H. McAlexander, L. M. Bezold,
A. M. Arif and L. M. Berreau, J. Am. Chem. Soc., 2002, 124, 9970.
10 Y. Nishida and K. Takahashi, Inorg. Chem., 1988, 27, 1406.
11 See for example: (a) O. P. Anderson and J. C. Marshall, Inorg.
Chem., 1978, 17, 1258; (b) M. Julve, M. Verdaguer, G. De Munno,
J. A. Real and G. Bruno, Inorg. Chem., 1993, 32, 795; (c) J. Cheng,
F.-L. Liao, T.-H. Lu, P. S. Mukherjee, T. K. Maji and N. R.
Chaudhuri, Acta Crystallogr., Sect. E, 2001, 57, m263; (d ) S. Fox,
R. T. Stibrany, J. A. Potenza, S. Knapp and H. J. Schugar,
Inorg. Chem., 2000, 39, 4950; (e) M. Kabesová, V. Jorík and
M. Dunaj-Jurco, Acta Crystallogr., Sect. C, 1993, 49, 1120; ( f )
F. Valach and M. Dunaj-Jurco, Acta Crystallogr., Sect. B, 1982, 38,
2145; (g) T. Rojo, A. Garcia, J. L. Mesa, M. I. Arriortua, J. L.
Pizarro and A. Fuertes, Polyhedron, 1989, 8, 97; (h) T. Otieno, S. J.
Rettig, R. C. Thompson and J. Trotter, Inorg. Chem., 1993, 32, 4384.
12 (a) N. J. Blackburn, D. Collison, J. Sutton and F. E. Mabbs,
Biochem. J., 1984, 220, 447; (b) N. J. Blackburn, M. Concannon,
S. K. Shahiyan, F. E. Mabbs and D. Collison, Biochemistry, 1988,
27, 6001.
A crystal of each compound 1, 2, 3, and 6 was mounted on
a glass fiber with traces of viscous oil and then transferred to a
Nonius KappaCCD diffractometer with Mo Kα radiation (λ =
0.71073 Å) for data collection at 150(1) K (2, 3, and 6) or 200(1)
K (1). For each compound, an initial set of cell constants was
obtained from ten frames of data that were collected with an
oscillation range of 1Њ frameϪ1 and an exposure time of 20 s
frameϪ1. Indexing and unit cell refinement based on observed
reflections from those ten frames indicated monoclinic P lattices
for 1 and 3, and triclinic P lattices for 2 and 6. Final cell con-
stants for each complex were determined from a set of strong
reflections from the actual data collection. For each data set,
reflections were indexed, integrated, and corrected for Lorentz
polarization and absorption effects using DENZO-SMN and
SCALEPAC.24 The structures were solved by a combination of
direct methods and heavy atom using SIR 97 (Release 1.02).25
All of the non-hydrogen atoms were refined with anisotropic
displacement coefficients. Unless otherwise stated, hydrogen
atoms were assigned isotropic displacement coefficients U(H) =
1.2U(C) or 1.5U(Cmethyl), and their coordinates were allowed
to ride on their respective carbons using SHELXL-97.26
Crystals of 1 were determined to belong to the monoclinic
crystal system. Systematic absences in the data were consistent
with the space group P21/c. All hydrogen atoms were located
and refined independently. Two oxygen atoms of the per-
chlorate anion were found to be disordered over two positions
(0.81 : 0.19 occupancy ratio), whereas the fourth oxygen
was best fit over three positions (0.40: 0.40: 0.20). Complex 2
¯
crystallizes in the space group P1. All hydrogen atoms were
located and refined independently. The cyanate derivative 3
crystallizes in the space group P21/c. All hydrogen atoms were
located and refined independently. The azide complex 6 crystal-
¯
lizes in the space group P1. Hydrogen atoms were located and
refined independently except those on C(14) and C(24), which
were assigned isotropic displacement coefficients and their
coordinates were allowed to ride on their respective carbons.
Acknowledgements
We acknowledge the support of the donors of the Petroleum
Research Fund (ACS-PRF 36394-G3 to LMB), administered
by the American Chemical Society, the National Science
Foundation (CAREER Award CHE-0094066 to LMB), the
Medical College of Wisconsin (BB), and the National Institutes
of Health (RR01008 to National Biomedical EPR Center,
Department of Biophysics, Medical College of Wisconsin).
KJT and ALF thank the Utah State University Vice-President
for Research for funding through the Undergraduate Research
& Creative Opportunities (URCO) program.
13 M. Harata, K. Hasegawa, K. Jitsukawa, H. Masuda and H. Einaga,
Bull. Chem. Soc. Jpn., 1998, 71, 1031.
14 Z. Dori and R. F. Ziolo, Chem. Rev., 1973, 73, 247.
15 (a) A. Allerhand and P. V. R. Schleyer, J. Am. Chem. Soc., 1963, 85,
1233; (b) T. Steiner, Acta Crystallogr., Sect. B, 1998, 54, 456.
16 R. F. Ziolo, M. Allen, D. D. Titus, H. B. Gray and Z. Dori, Inorg.
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17 R. M. Silverstein and F. X. Webster, Spectrometric Identification of
Organic Compounds, Wiley, New York, 1998.
18 Methods of EPR spectra simulation employed: (a) B. Bennett,
W. E. Antholine, V. M. D’souza, G. J. Chen, L. Ustinyuk and
R. C. Holz, J. Am. Chem. Soc., 2002, 124, 13025; (b) D. M. Wang
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4 X-ray crystallography has been used to characterize both the
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