The structural chemistry of copper(II) hinokitiol and its adducts

Article abstract of DOI:10.1016/S0277-5387(02)01064-1

The structure of copper(II) hinokitiol has been determined. Two modifications are possible, one containing only isolated, four- coordinate, square-planar complexes, while a second modification contains both monomers, along with eclipsed and staggered dimers generated through intermolecular O→Cu interactions. Five-coordinate copper is also present in the adduct Cu(hino)₂· pyridine, whose structure has also been determined for comparison.

Full text of DOI:10.1016/S0277-5387(02)01064-1

Polyhedron 21 (2002) 1761ꢀ1766
/
www.elsevier.com/locate/poly
The structural chemistry of copper(II) hinokitiol and its adducts
a
Marie C. Barret , Mary F. Mahon , Kieran C. Molloy , Philip Wright , J.E. Creeth
a
a
a
b
a
Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK
b
Unilever Research, Port Sunlight Laboratories, Bebbington, Wirral, L63 3SW, UK
Received 25 March 2002; accepted 15 May 2002
Abstract
The structure of copper(II) hinokitiol has been determined. Two modifications are possible, one containing only isolated, four-
coordinate, square-planar complexes, while a second modification contains both monomers, along with eclipsed and staggered
dimers generated through intermolecular O0
/
Cu interactions. Five-coordinate copper is also present in the adduct Cu(hino)2×
/
pyridine, whose structure has also been determined for comparison. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Copper; Hinokitiol; X-ray; Adduct
metal ions (M ꢁ, M3ꢁ and M4ꢁ) [8ꢀ
2
/13]. Hinokitiol
1
. Introduction
(Hhino) is isolated from the wood of the Chamacyparis
There is both biological and medicinal interest in
compounds which have ketone and hydroxyl functional
groups adjacent to one another and which exhibit anti-
taiwanesis tree, and since its discovery in 1936 [14] it has
been reported to exhibit anti-microbial effects [7] and
also to stimulate plant growth. However, in contrast to
metal tropolonates, analogous metal derivatives of
hinokitiol remain largely unexplored, though we have
bacterial or -fungal properties [1ꢀ
which fit into this category are 2-hydroxy-2,4,6-cyclo-
heptatrien- -one (tropolone I) and 6-isopropyltropolone
II), commonly called hinokitiol [7].
/6]. Two compounds
recently reported the structures of X Sn(hino) (XꢂF,
/
1
2
2
Cl) [15] and Zn(hino)2×/EtOH [16]. The structure of
In(hino) has also been determined [17].
Our general interest in this area lies in the inorganic
(
3
chemistry of M(II) (MꢂCu, Zn, Sn) derivatives of
/
orally viable a-hydroxyketones e.g. maltol, ethylmaltol
as well as hinokitiol [15,16], which have relevance to
novel dental formulations [18]. In this paper, we report
on the unusual structural chemistry of Cu(II) hinokitiol
and its adduct chemistry.
Tropolone is a representative of a family of non-
2. Experimental
benzenoid aromatic compounds and has been studied in
depth over the last 40 years. The functional groups of
tropolone allow complexation of a number of different
Infrared spectra (cmꢃ1) were recorded as Nujol mulls
between NaCl plates using a Nicolet 510P FT-IR
spectrophotometer, and elemental analyses were per-
formed using an CarloꢀErba Strumentazione E.A.
/
model 1106 microanalyser operating at 500 8C. Starting
materials were commercially obtained and used without
further purification.
*
Corresponding author. Tel.: ꢁ
26-231
E-mail address: chskem@bath.ac.uk (K.C. Molloy).
/
44-1225-826-382; fax: ꢁ44-1225-
/
8
0
277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 0 6 4 - 1

1762
M.C. Barret et al. / Polyhedron 21 (2002) 1761ꢀ1766
/
2
.1. Synthesis of Cu(II) hinokitiol (1)
(54 148 reflections) were corrected for Lp, extinction
and absorption (max. and min. transmission factors:
1.030 and 0.974, respectively). The asymmetric unit
consisted of 2.5 independent molecules. The two full
molecules are located proximate to inversion centres and
hence dimerise with nearby lattice neighbours. The
central copper atom [Cu(3)] in the remaining indepen-
dent half-molecule is seated on an inversion centre
which serves to generate the full molecule in this case.
Disorder in one of the isopropyl groups [C(39)/C(40)]
was successfully modelled as a 55:45 occupancy ratio. In
the final least-squares cycles, all atoms were allowed to
vibrate anisotropically and hydrogen atoms were in-
cluded at calculated positions throughout.
Hinokitiol (0.30 g, 1.83 mmol) was dissolved in aq.
EtOH (50:50, 50 ml) with stirring. Once dissolved, a
solution of copper acetate (0.19 g, 0.95 mmol) was
added and the stirring continued. After stirring and
gentle heating for 2 h, the green/blue solution was
allowed to stand for 1 week after which time the product
crystallised from solution as green/blue plate-like crys-
tals. Anal. Found (Calc. for C H CuO ): C, 61.6
2
0
22
4
(
61.6); H, 5.64 (5.69)%. Selected IR data (cmꢃ1): 1600,
1
574 n(Cꢀ
/
O); 1512 n(Cꢀ
/
C); 1286ꢀ
/
1228 n(Cꢁ
/
O).
2
.2. Synthesis of (hinokitiol) Cu×
/
(pyridine) (2)
2
Crystallographic measurements for 2 were made at
293(2) K on a CAD4 automatic four-circle diffract-
Pyridine (5 ml) was added to a solution of 1 (0.30 g, 0.77
mmol) in C H CH (30 ml). After stirring for 20 min, the
ometer in the range 2.248B
/
u B24.988. Data (4337
/
6
5
3
solution was cooled to ꢃ
/
15 8C whereupon a green solid
reflections) were corrected for Lp but not for absorp-
tion. In the final least-squares cycles, all atoms were
allowed to vibrate anisotropically. Hydrogen atoms
appeared (0.06 g; 17%). Some crystals suitable for X-ray
crystallography were obtained from the filtrate. Anal.
Found (Calc. for C H CuNO ): C, 63.7 (64.0); H, 5.79
were included at calculated positions where relevant.
In all three cases, refinement was based on F .
2
5
27
4
5.76); N, 2.85 (2.98)%. Selected IR data (cmꢃ1): 1583,
2
o
(
1
569, 1496 n(Cꢀ
/
O) and n(Cꢀ
/
C); 1261, 1231 n(Cꢁ
/O).
Software used: SHELXS-86 [19], SHELXL-97 [20], ORTEX
[
21]. The asymmetric units of 1 (two modifications) and
2
.3. Synthesis of (hinokitiol) Cu×
/
(bipyridine) (3)
2 are displayed in Figs. 1ꢀ3 along with the atomic
/
2
numbering scheme. Selected metric data for modifica-
tion 1 of 1 and 2 are given in the figure captions, while
that for modification 2 of 1 are given in Table 2.
Bipyridine (1.00 g, 6.25 mmol) was dissolved in
C H CH (30 ml) and then added to a solution of 1
6
5
3
(
0.40 g, 1.03 mmol) in C H CH (50 ml). The mixture was
6 5 3
stirred for 20 min and then left at room temperature for
few days, yielding a brown solid (0.44 g, 78%). Anal.
Found (Calc. for C H CuN O ): C, 65.5 (65.9); H, 5.48
3
. Results and discussion
3
0
30
2
4
(
5.49); N, 5.83 (5.13)%. Selected IR data (cmꢃ1): 1594,
Cu(II) hinokitiol (1) was synthesised using the method
1
554, 1511 n(Cꢀ
/
O) and n(Cꢀ
/
C); 1278, 1199 n(Cꢁ
/O).
detailed in Eq. (1). After 1 week, a large number of blue
plate-like crystals had formed in the solution. Micro-
analysis of these crystals showed the complex to be
anhydrous.
2
.4. Crystallography
Suitable crystals of 1 were obtained either from EtOH
modification 1) or from C H CH in the presence of
urea (modification 2). Crystals of 2 were obtained from
(
6
5
3
a dilute solution in C H CH (Table 1).
5
6
3
For modification 1 of 1, crystallographic measure-
ments were made at 293(2) K on a CAD4 automatic
four-circle diffractometer in the range 2.408B
/
u B
/
2
3.928. Data (1685 reflections) were corrected for Lp
and 10% decay of the crystal in the X-ray beam. An
absorption correction was not applied. In the final least-
squares cycles all atoms were allowed to vibrate
anisotropically. Hydrogen atoms were included at
calculated positions where relevant except for H3, H4,
H5 and H7 which were easily located in the penultimate
difference Fourier map and refined at a distance of 0.93
˚
A from the carbon atoms to which they are attached.
For modification 2 of 1, crystallographic measure-
ments were made at 150 K on a Nonius Kappa CCD
ð1Þ
We have previously noted that copper derivatives of
a-hydroxyketones (maltol, hinokitiol etc.) in which the
copper is four-coordinate, square-planar geometry are
notably anti-bacterially and/or -microbially active,
whereas the analogous zinc species, in which the zinc
is either five- or six-coordinate, are markedly less so [18].
diffractometer in the range 3.808B
/
u B27.488. Data
/

M.C. Barret et al. / Polyhedron 21 (2002) 1761ꢀ
/1766
1763
Table 1
Crystallographic data for 1 and 2
1
(modification 1)
22CuO
1 (modification 2)
22CuO
2
Empirical formula
Formula weight
Temperature (K)
l (Mo Ka) ( A˚ )
Crystal system
Space group
C H
389.92
20
4
C
389.92
20
H
4
C
469.02
25 4
H27CuNO
293(2)
0.71069
monoclinic
150(2)
0.71069
monoclinic
293(2)
0.71069
monoclinic
1
P2 /c
P2
1
/n
1
P2 /n
˚
a (A)
9.254(2)
9.997(2)
11.124(3)
113.86(2)
941.2(4)
2
16.7420(2)
15.5370(2)
18.3010(3)
99.4000(6)
4696.54(11)
10
8.616(2)
26.848(4)
9.910(2)
102.56(2)
2237.5(8)
4
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
Z
r
calc (Mg mꢃ3)
1.376
1.180
1.379
1.183
1.392
1.007
ꢃ1
m (mm
Crystal size (mm)
)
0.3ꢄ0.3ꢄ0.5
2.40ꢀ23.92
1685
1475 [Rintꢂ0.0396]
0.25ꢄ0.10ꢄ0.10
3.80ꢀ27.48
54 148
0.25ꢄ0.20ꢄ0.20
2.24ꢀ24.98
4337
3928 [Rintꢂ0.0326]
u Range (8)
/
/
/
Reflections collected
Independent reflections
Final R indices [I ꢀ2s(I)]
R indices (all data)
10 712 [Rintꢂ0.0471]
R
1
ꢂ0.0430, wR
ꢂ0.1066, wR
2
ꢂ0.0704
ꢂ0.0921
R
1
ꢂ0.0384, wR
ꢂ0.0558, wR
2
ꢂ0.1000
ꢂ0.1139
R
1
ꢂ0.0441, wR
ꢂ0.1271, wR
2
ꢂ0.1232
ꢂ0.1681
R
1
2
R
1
2
R
1
2
In order to assess the importance of metal coordination
number on activity, we have prepared complexes of 1 by
reaction with N-donor Lewis bases (Eq. (2)). 1:1 adducts
with pyridine (2) and 2,2?-bipyridine (3) have been
isolated, which presumably contain five- or six-coordi-
nate copper, respectively.
3.1. The structure of Cu(II) hinokitiol (1)
Cu(II) hinokitiol, prepared as in Eq. (1), was recrys-
tallised from aqueous ethanol, yielding a crystal of
approximate dimensions 0.3ꢄ
/
0.3ꢄ0.5 mm which was
/
used for data collection. Selected structural data are
included in the caption to Fig. 1. This structure will be
discussed as modification 1. An attempt to prepare an
adduct of 1 with urea in toluene failed, and green
crystals of 1 were recovered but whose cell parameters
˚
[
aꢂ
/
16.7420(2); bꢂ
/
15.5370(2); cꢂ
/
18.3010(3) A; bꢂ
/
9
9.4000(6)8] were different to those of modification 1
˚
[
aꢂ
/
9.254(2); bꢂ
/
9.997(2); cꢂ
/
11.124(3) A; bꢂ
/
ð2Þ
113.86(2)8]. This second crystal structure will be dis-
Fig. 1. The asymmetric unit of modification 1 of compound 1 showing the labelling scheme used in the text. Thermal ellipsoids are at the 30%
˚
probability level. Selected metrical data: Cu(1)ꢁ
80.0, O(2)ꢁCu(1)ꢁO(2?) 180.0, O(1)ꢁCu(1)ꢁO(2) 83.84(13), O(1)ꢁ
Symmetry related atoms are generated using ꢃx, ꢃy, ꢃz.
/
O(1) 1.904(3), Cu(1)ꢁ
/
O(2) 1.900(2), O(1)ꢁ
/
C(2) 1.293(5), O(2)ꢁ
/
C(1) 1.296(5) A; O(1)ꢁ
/
Cu(1)ꢁ
/
O(1?)
1
/
/
/
/
/
Cu(1)ꢁ
/
O(2?) 96.16(13), C(2)ꢁ
/
O(1)ꢁCu(1) 113.5(3), C(1)ꢁ
/
/
O(2)ꢁCu(1) 113.5(3)8.
/
/
/
/

1764
M.C. Barret et al. / Polyhedron 21 (2002) 1761ꢀ1766
/
cussed as modification 2. Both forms adopt monoclinic
P2 /c (or P2 /n) symmetries.
single bond. For comparison, the p-electron system in
hinokitiol is also partially delocalised, though the formal
1
1
In modification 1 (Fig. 1), the asymmetric unit
comprises half of a molecule, the remaining portion
being generated via an inversion centre at the origin on
which the copper is sited. The Cu(II) is four-coordinate
and in a square-planar environment. The molecule as a
double bonds [C(1)ꢁ
/
C(7), C(6)ꢁ
/
C(5) and C(4)ꢁ
/
C(3);
1.367, 1.355 and 1.364 A˚ , respectively] are more clearly
distinguishable from the formal single bonds [C(7)ꢁ
C(6), C(5)ꢁC(4) and C(3)ꢁC(2); 1.422, 1.413 and 1.413
A, respectively] than in 1. The C(1)ꢁC(2) bond in the
ligand (1.469 A) is, however, significantly longer than
the other carbonꢁcarbon bonds and is comparable with
that in 1 [23].
/
/
/
˚
/
whole is essentially planar [maximum deviation from
˚
˚
mean plane: 0.029 A for O(2)]. The Cuꢁ
/
O bonds are
/
˚
equivalent [Cuꢁ
and the BO(1)ꢁ
CuꢁO bond lengths are in agreement with other Cu(II)
complexes, e.g. Cu(II) erythritol [Cuꢁ
/
O(1), 1.904(3); Cuꢁ
/
O(2), 1.900(2) A]
/
/
CuꢁO(2) bond angle is 83.8(1)8. The
/
In modification 2 of 1, obtained from toluene in an
attempt to prepare a urea adduct, there are two and half
molecules in the asymmetric unit; two molecules are in
general positions, while half molecule has the copper
atom seated on an inversion centre (Fig. 2), as with
modification 1. For each molecule, the copper is
nominally four-coordinate and in a square-planar en-
vironment. The molecule generated by the inversion
centre [molecule A, containing Cu(3)] has the isopropyl
groups adopting a trans configuration and this is also
the case for one of the two other molecules [molecule B
containing Cu(2)]; in this respect, both molecules
replicate the structure of modification 1. However, in
the remaining molecule [molecule C containing Cu(1)]
the isopropyl groups are cis to each other. This is
unusual, as for previous structures of a-hydroxyketones,
/
/
O: 1.912(4),
˚
1
.922(4) A] [22]. Both of the Cꢁ
/
O bond lengths in 1
compare well with those found in a number of other
˚
metal tropolonates, i.e. 1.27ꢀ
/
1.30 A and Zn(II) hinoki-
1.306(2) A] [16]. Furthermore, upon
coordination to the Cu(II) the CꢁO bond lengths
˚
tiol [1.277(2)ꢀ
/
/
˚
become equal [1.293(5), 1.296(3) A], indicating a similar
bond order in both. This is a more symmetric arrange-
ment than the equivalent bonds in hinokitiol itself (Cꢁ
/
˚
O: 1.349; Cꢀ
/
O: 1.261 A) [23]. The lengths of the Cꢁ
/C
bonds in the hinokitiol ring of 1 are approximately equal
˚
(
approximately 1.38 A) with one notable exception. The
C(2) bond is significantly longer than the others in
the ring, indicating that it is not involved to the same
C(1)ꢁ
/
extent in the p-electron delocalisation within the C unit.
7
˚
the alkyl groups are trans to each other e.g. Zn(hino)
2
×
/
The value of 1.464(6) A observed for the C(1)ꢁ
/
C(2)
3
C(sp )
3
EtOH [16], Zn(maltol) [24], and 2 (see below).
2
bond in 1 is closer to that expected for a C(sp )ꢁ
/
Fig. 2. The asymmetric unit of modification 2 of compound 1 showing the labelling scheme used in the text. Thermal ellipsoids are at the 30%
probability level.

M.C. Barret et al. / Polyhedron 21 (2002) 1761ꢀ
/1766
1765
Fig. 3. The asymmetric unit of 2 showing the labelling scheme used in the text. Thermal ellipsoids are at the 30% probability level. Selected metrical
data: Cu(1)ꢁO(1) 1.940(3), Cu(1)ꢁO(2) 1.945(3), Cu(1)ꢁO(3) 1.965(3), Cu(1)ꢁO(4) 1.933(3), Cu(1)ꢁN(1) 2.311(5), O(1)ꢁC(1) 1.287(5), O(2)ꢁC(2)
.278(6), O(3)ꢁC(8) 1.287(5), O(4)ꢁC(9) 1.277(6) A; O(1)ꢁCu(1)ꢁO(2) 82.73(14), O(1)ꢁCu(1)ꢁO(3) 97.28(14), O(1)ꢁCu(1)ꢁO(4) 172.2(2), O(2)ꢁ
Cu(1)ꢁO(3) 155.2(2), O(2)ꢁCu(1)ꢁO(4) 94.3(2), O(3)ꢁCu(1)ꢁO(4) 82.34(14), O(1)ꢁCu(1)ꢁN(1) 92.3(2), O(2)ꢁCu(1)ꢁN(1) 99.0(2), O(3)ꢁCu(1)ꢁ
N(1) 105.8(2), O(4)ꢁCu(1)ꢁN(1) 95.3(2)8.
/
/
/
/
/
/
/
˚
1
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
The two full molecules in modification 2 (B and C) are
proximate to inversion centres and hence dimerise with
nearby lattice neighbours (Fig. 2). In the dimer based on
B, the isopropyl groups sit above each other (eclipsed
conformation), while in the dimer of C, they are on
opposite sides of the stacked seven-membered rings
(staggered conformation). Thus, molecule B minimises
Table 2
repulsions between isopropyl groups within the mono-
mer but maximises it between molecules on dimer
formation, while the reverse is true for molecule C.
a
˚
Selected bond lengths (A) and angles (8) for modification 2 of 1
Molecule A
Molecule B
Molecule C
In the non-dimerised molecule A, the Cuꢁ
/
O bond
lengths [1.901(2), 1.909(2) A] are similar than those
Bond lengths
trans-Monomer
Cu(3)ꢁO(9)
˚
˚
observed in modification 1 [1.900(2), 1.904(3) A]. For
1.910(2)
1.901(2)
dimers based on molecules B and C, the intramolecular
˚
O bond lengths [1.915(2)ꢀ1.939(2) A] are longer
Cu(3)ꢁO(10)
Cuꢁ
/
/
trans-Dimer
Cu(1)ꢁO(1)
Cu(1)ꢁO(2)
Cu(1)ꢁO(3)
Cu(1)ꢁO(4)
than those in modification 1 and thus the effect of the
dimerisation is similar to the effect of the pyridine
coordination, as in 2 (see below). The intermolecular
1.919(2)
1.920(2)
1.932(2)
1.933(2)
interactions [Cu(1)ꢁ
/
O(4): 2.476(2); Cu(2)ꢁ
/O(8):
˚
cis-Dimer
2.511(2) A] are clearly longer and weaker than the
analogous intramolecular bonds, with the eclipsed
dimerisation in molecule B manifesting itself in the
longer of these two contacts. The intermolecular inter-
actions in both cases do, however, generate almost
Cu(2)ꢁO(5)
Cu(2)ꢁO(6)
Cu(2)ꢁO(7)
Cu(2)ꢁO(8)
1.915(2)
1.921(2)
1.939(2)
1.922(2)
Intermolecular
Cu(1)ꢀ ꢀ ꢀO(4?)
Cu (2)ꢀ ꢀ ꢀO(8?)
perfect
3.09(6)8; B
of each dimer.
Cu O
squares
[B
/
Cu(1)ꢁ
/
O(4)ꢁCu(1?):
/
2
2
2.476(2)
9
/
Cu(2)ꢁ
/
O(8)ꢁCu(2?): 94.80(6)8] at the heart
/
2.511(2)
b
Bond angles
The coordination chemistry of 1 is thus exceedingly
flexible, as both cis and trans ligand arrangements are
possible, as are both monomers and dimers.
O(1)ꢁCu(1)ꢁO(2)
O(1)ꢁCu(1)ꢁO(3)
O(1)ꢁCu(1)ꢁO(4)
O(2)ꢁCu(1)ꢁO(3)
O(2)ꢁCu(1)ꢁO(4)
O(3)ꢁCu(1)ꢁO(4)
84.53(8)
95.47(8)
180.0
84.27(7)
97.95(7)
174.64(7)
166.88(7)
93.36(7)
83.29(7)
83.86(7)
99.15(7)
177.40(7)
165.00(8)
93.55(7)
83.26(7)
180.0
95.47(8)
84.53(8)
3.2. The structure of Cu(II) hinokitiol×
/
pyridine adduct 2
a
Symmetry transformation used to generate equivalent atoms:
Compound 2 crystallises in the monoclinic space
group P2 /n. The copper adopts a square pyramidal
geometry with the pyridine in the axial position (Fig. 3),
ꢃx, ꢃy, ꢃz.
b
Atomic labels refer to molecule C; for molecules A [Cu(3)] and B
Cu(2)], oxygens are O(9, 10) and O(5ꢀ8), respectively.
1
[
/

1766
M.C. Barret et al. / Polyhedron 21 (2002) 1761ꢀ1766
/
˚
[5] Y. Inamori, Y. Sakagami, Y. Morita, M. Shibata, M. Sugiura, Y.
Kumeda, T. Okabe, H. Tsujibo, N. Ishida, Biol. Pharmacol. Bull.
the copper lies 0.125 A above the plane of the four
oxygen atoms. The CuꢁO bond lengths [1.940(3),
.933(3), 1.945(3), 1.985(3) A] are longer than those
observed in isolated molecules of 1 [1.900(2)ꢀ1.909(2)
A]. The structure is similar to the one obtained for
pyridine (Hacrp: 4-hydroxy-6-methyl-3-[3-di-
/
2
3 (2000) 995.
˚
1
[
6] E. Matsumura, Y. Morita, T. Date, H. Tsujibo, M. Yasuda, T.
Okabe, N. Ishida, Y. Inamori, Biol. Pharmacol. Bull. 24 (2001)
299.
/
˚
[
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˚
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/
[
˚
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The electronic spectra of Ni(II) and Cu(II) species
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[
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8
M(hino)(diamine)]ꢁ have been studied [26,27] and
(
[
[
6
2
[
[
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4
. Supplementary material
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
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pounds 1 (two modifications) and 2. Copies of this
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ccdc.cam.uk or www: http://www.ccdc.cam.ac.uk).
EZ, UK (fax: ꢁ44-1223-336033; e-mail: deposit@
/
1
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[
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