Synthesis, solid-state characterization and antimicrobial activities of three different polymorphs of a copper(II) complex with 4-isopropyltropolone (hinokitiol)

Article abstract of DOI:10.1016/j.ica.2003.10.003

There exist at least three different polymorphs in the copper(II) complex [Cu(hino)₂] with a hinokitiol ligand (Hhino; 4- isopropyltropolone¹). In addition to deep-green plate crystals 1a and deep-green rod crystals 1b, whose crystal structures have been recently reported, novel green needle crystals 1c of [Cu(hino)₂] were found, the crystal structure of which was here determined by single-crystal X-ray analysis. Since only one crystal structure has been reported for the copper(II) complex [Cu(trop)₂] with a tropolone ligand (Htrop), the polymorphism found in the crystals of [Cu(hino)₂] would be due to the presence of the isopropyl group on the tropolone ring. The synthetic conditions giving the three polymorphs in good yields were found and the crystals were characterized with elemental analysis, FT-IR, TG/DTA and X-ray powder diffraction (XPD) measurements, as well as solution molecular weight measurements for 1a. The solid-state magnetic behaviors or the temperature-dependent magnetic susceptibilities were measured with Superconductivity Quantum Interference Devices (SQUID): 1a showed a weak ferromagnetic interaction, 1b showed a paramagnetic nature with S = 1/2, while 1c showed a weak antiferromagnetic interaction. The antimicrobial activities for selected bacteria, yeasts and molds were also measured in the water-suspension system: 1a and 1b showed no activity, while 1c showed modest activities, and these activities were compared with those of the neutral Hino and the anionic hino^- ligands.

Full text of DOI:10.1016/j.ica.2003.10.003

Inorganica Chimica Acta 357 (2004) 1168–1176
www.elsevier.com/locate/ica
Synthesis, solid-state characterization and antimicrobial activities
of three different polymorphs of a copper(II) complex with
4-isopropyltropolone (hinokitiol) q
*
Kenji Nomiya , Akira Yoshizawa, Noriko C. Kasuga,
Hironari Yokoyama, Shoko Hirakawa
Department of Materials Science, Faculty of Science, Kanagawa University, Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan
Received 8 July 2003; accepted 4 October 2003
Abstract
There exist at least three different polymorphs in the copper(II) complex [Cu(hino)2] with a hinokitiol ligand (Hhino; 4-iso-
1
propyltropolone ). In addition to deep-green plate crystals 1a and deep-green rod crystals 1b, whose crystal structures have been
recently reported, novel green needle crystals 1c of [Cu(hino)2] were found, the crystal structure of which was here determined by
single-crystal X-ray analysis. Since only one crystal structure has been reported for the copper(II) complex [Cu(trop)2] with a
tropolone ligand (Htrop), the polymorphism found in the crystals of [Cu(hino)2] would be due to the presence of the isopropyl group
on the tropolone ring. The synthetic conditions giving the three polymorphs in good yields were found and the crystals were
characterized with elemental analysis, FT-IR, TG/DTA and X-ray powder diffraction (XPD) measurements, as well as solution
molecular weight measurements for 1a. The solid-state magnetic behaviors or the temperature-dependent magnetic susceptibilities
were measured with Superconductivity Quantum Interference Devices (SQUID): 1a showed a weak ferromagnetic interaction, 1b
showed a paramagnetic nature with S ¼ 1=2, while 1c showed a weak antiferromagnetic interaction. The antimicrobial activities for
selected bacteria, yeasts and molds were also measured in the water-suspension system: 1a and 1b showed no activity, while 1c
showed modest activities, and these activities were compared with those of the neutral Hino and the anionic hinoꢀ ligands.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Copper(II) complex with hinokitiol; Crystal and molecular structures; Polymorphism; X-ray powder diffraction; Temperature-dependent
magnetic susceptibilities; Antimicrobial activities
1. Introduction
and it is effective as a plant growth stimulator [8]. Of
particular note is the fact that Hhino does not develop
microorganisms-resistance [9,10], in contrast to many
antibiotics. Other biological effects have been also ob-
served, such as insecticidal activities [10], cytotoxic effect
on the growth of mammalian cells and on blastogenesis
of mouse splenic T cells [11], phytogrowth-inhibitory
activities [12,13] and a function preventing discoloration
in fresh animal and plant food [14]. Possibilities of the
mode of action and mechanisms of hinokitiol have been
proposed such as effective inhibitors of catechol-O-me-
thyl transferase (COMT) [15] and effective scavenging
activities against active oxygen species [16].
The wide range of biological activities of hinokitiol
(Hhino; C10H12O2) [1], which is a 4-isopropyl substitu-
tion of tropolone (Htrop) and is also called b-thuja-
plicin [2], is noteworthy; in fact, it shows a wide
spectrum of antimicrobial activities against Gram-
positive and -negative bacteria, yeasts and molds [3–7],
1
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2003.10.003.
* Corresponding author. Tel.: +81-463-59-4111; fax: +81-463-58-
9684.
E-mail address: nomiya@chem.kanagawa-u.ac.jp (K. Nomiya).
The systematic names for tropolone and 4-isopropyltropolone are
The monoanion of Hhino forms various metal-
chelate complexes [M(hino)n] through two unequivalent
oxygen donor atoms [17], and it has been reported that
1
2-hydroxycyclohepta-2,4,6-trienone and 2-hydroxy-4-isopropylcyclo-
hepta-2,4,6-trienone, respectively.
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.10.003

K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
1169
their antimicrobial activities, in particular those of sil-
ver(I), iron(III) and copper(II) complexes, are signifi-
cantly changed from that of Hhino [18]. We are
interested in the structure–activity correlation in the
antimicrobial activity of metal complexes with Hhino.
However, X-ray structure analysis is so far limited to the
several examples, i.e. of the ‘‘free’’ ligand Hhino [19],
[SnX2(hino)2] (X ¼ F, Cl) [20], [In(hino)3] [21], [Zn-
(hino)2(EtOH)]2 [22], [Cu(hino)2] (Note: two polymor-
phs, 1a and 1b, have been structurally characterized
[23]), and the very recently determined, dimeric silver(I)
complex [Ag(hino)]2, a dimeric cobalt(II) complex
[Co(hino)2(EtOH)]2 and a monomeric aluminium(III)
complex [Al(hino)3] ꢁ MeOH [24], whereas there are
considerable structural data of tropolonato-metal com-
plexes [21,25–39], e.g. [In(trop)3] [21], [Na(trop)] [25,26],
[Th(trop)4(DMF)] [27], [SnCl(trop)3] and [Sn(OH)-
(trop)3] [28], [Fe(trop)3] [29], [Cu(trop)2] [30–36],
[Al(trop)3] [37], dimeric [Co(4-Metrop)2H2O]2 plus mo-
nomeric [Co(4-Metrop)2] ꢁ 2H2O [38], and [M(trop)4]
(M ¼ Si, Ge, Sn)] [39].
inhibitory concentration (MIC; lg mLꢀ1). Interestingly,
these complexes in a water-suspension system showed
different antimicrobial activities against selected bacte-
ria, yeasts and molds.
2. Experimental
2.1. Reagents and methods
The following were reagent grade and used as re-
ceived: CuSO4 ꢁ 5H2O, EtOH (Wako). The ‘‘free’’ ligand
Hhino was supplied by Asahi Kasei Co., Japan.
CHN analyses were performed using a Perkin Elmer
PE2400 series II CHNS/O Analyzer (Kanagawa Uni-
versity). Infrared spectra were recorded on a JASCO
FT-IR 300 spectrometer as KBr disks at room tem-
perature. Thermogravimetric (TG) and differential
thermal analyses (DTA) were acquired using a Rigaku
TG 8101D and TAS 300 data-processing system. TG/
DTA measurements were run under air with a tem-
perature ramp of 4 °C minꢀ1 between 20 and 500 °C.
The UV–Vis spectra were obtained using a JASCO V-
560 spectrometer.
In a separate account, the molecular structure of the
coordinating hinoꢀ ligand is also interesting in com-
parison with that of the previously reported ‘‘free’’
Hhino ligand with the seven-membered 6p-conjugate
system and without aromaticity [19,24].
X-ray powder diffraction (XPD) data were collected
on a Bruker M18XHF22 diffractometer (Cu Ka radia-
tion) at room temperature. Intensity data were collected
by the step-counting methods (step 0.01° and sampling
time 1.0 s) in the range 2h ¼ 5–60°.
In this work, we found the presence of novel green
needle crystals 1c of [Cu(hino)2] and determined the
crystal structure by single-crystal X-ray analysis, in ad-
dition to the recently reported two polymorphs (deep-
green plate crystals 1a and deep-green rod crystals 1b)
[23]. The molecular structure of 1a is comprised of a
mixture of dimeric trans-, monomeric trans- and dimeric
cis-forms, where the dimer/monomer is based on an
intermolecular interaction through Cuꢁ ꢁ ꢁO interaction
and the cis/trans is based on the relative position of the
isopropyl groups (in 1a, total ratio of the trans- and cis-
forms is 3:2), and the molecular structure of 1b consisted
of only monomeric trans-form. Hence, there exist at
least three different polymorphs in [Cu(hino)2], whereas
only one crystal structure has been reported for
[Cu(trop)2]. Complexes 1a and 1b were quantitatively
obtained by 2 h-refluxing of Hhino and CuSO4 ꢁ 5H2O in
different volumes of a mixed EtOH/water solvent.
Complex 1c was prepared using once isolated complexes
1a or 1b in the mixed EtOH/water solvent. The molec-
ular structure of 1c consisted of only monomeric trans-
form, but the packing system was different from that of
1b. These complexes showed different X-ray powder
diffraction (XPD) patterns and different magnetic be-
haviors (temperature-dependent magnetic susceptibili-
ties measurements with SQUID). Herein, we report full
details of the synthesis, solid-state characterization of
three different polymorphs (1a–1c), and the crystal and
molecular structures of 1c. Also reported are the anti-
microbial activities for 1a–1c, evaluated with minimum
The solid-state magnetic susceptibility measurement
was performed in a quantum design SQUID suscep-
tometer MPMS-55 in the temperature range 3–300 K
with an applied field of 1 T. The data were corrected for
the sample holder contribution and the diamagnetic
contribution estimated through PascalÕs constants.
Molecular weight measurements in solution based on
the vaporimetric method (vapor pressure osmotic
method) using vapor pressure osmometer were per-
formed by Mikroanalytishes Labor Pascher (Remagen,
Germany) and evaluated for 13.65 mg of the complex 1a
dissolved in 1.4905 g of chloroform.
ESR spectra at 297 K were obtained with a JEOL
JES-RE2X X-band spectrometer. A chloroform solu-
tion of complex 1a (10 mM) was placed in a Pyrex-
quartz ESR tube with 5-mm inner diameter, degassed
under 10ꢀ3 Torr, sealed, and used for measurement. X-
Band ESR spectra at liquid nitrogen temperature (77 K)
were also obtained with a JEOL JES-TE200. The g
values were calibrated with Mn(II) marker used as a
reference.
2.2. Synthesis of [Cu(hino)2]
2.2.1. Deep-green plate crystals 1a
To a colorless solution of 0.201 g (1.22 mmol) of
Hhino dissolved in 30 mL of mixed EtOH and water

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K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
(1:1) solvent was added 0.155 g (0.62 mmol) of
CuSO4 ꢁ 5H2O, and the solution was refluxed for 2 h.
The deep-green solution was passed through a folded
filter paper (Whatman #2). The filtrate was evaporated
slowly at room temperature. After a few days deep-
green plate crystals were grown. They were collected on
a membrane filter, washed with H2O (50 mL ꢂ 3) and
dried in vacuo. Deep-green plate crystals, insoluble in
water and soluble in most organic solvents, were ob-
tained in 70.7% (0.171 g scale) yield. Anal. Found: C,
61.71; H, 5.75. Calc. for C20H22O4Cu or [Cu(hino)2]: C,
61.60; H, 5.69%. TG/DTA data: no weight loss was
observed before decomposition. Decomposition began
around 236 °C with an endothermic peak at 178 °C due
to melting and an exothermic peak at 318 °C. Prominent
IR bands (KBr disk): 2960vs, 2926s, 2865m, 1653m,
1635m, 1589vs (m(C@O)), 1506vs (m(C@C)), 1424vs,
1351vs, 1294s, 1238s (m(C–O)), 1186m (m(C–O)), 1130m,
1099w, 1075w, 1039m, 1020w, 958s, 937m, 915s, 894m,
877w, 817s, 776m, 740m, 666m, 580m, 511w, 429m
cmꢀ1. The UV–Vis of 1a (EtOH): kmax 675 (e 67) (d–d
transition), 372, 338, 333 and 255 nm (broad and intense
bands, which are probably due to p–pꢃ transition of the
ligand).
364 and 386 °C. Prominent IR bands (KBr disk):
2955vs, 2930s, 2866m, 1636m, 1589vs(m(C@O)), 1577vs
(m(C@O)), 1505vs(m(C@C)), 1425vs, 1368vs, 1352vs,
1308m, 1274m, 1235s(m(C–O)), 1186m(m(C–O)), 1132w,
1076w, 1040w, 1021w, 957m, 912m, 887w, 808m, 781m,
745m, 666m, 582m, 511w, 433m cmꢀ1
.
2.3. X-ray crystallography of green needle crystals 1c
The intensity data were collected on a Bruker
SMART APEX CCD diffractometer with Mo Ka ra-
diation at 90 K using x-scan. The structures were solved
by direct methods followed by subsequent difference
Fourier calculation and refined by a full-matrix least-
squares procedure using program package SHELXTL
[40]. All non-hydrogen atoms were refined anisotropi-
cally and hydrogen atoms isotropically. Crystal data for
1c: C20H22CuO4, Mr 389.92, triclinic, space group
ꢀ
ꢀ
P1(No. 1), a ¼ 5:0855ð12Þ A, b ¼ 6:9667ð17Þ A,
ꢀ
c ¼ 13:681ð3Þ A, a ¼ 77:626ð3Þ°; b ¼ 84:588ð3Þ°; c ¼
3
ꢀ
70:266ð3Þ°; V ¼ 445:52ð19Þ A , Z ¼ 1; Dcalcd ¼ 1:45
Mg mꢀ3, 3164 reflections measured, 2190 (½I > 2rðIÞꢄ)
used in the refinement on F 2; R ¼ 0:0487; wR ¼ 0:1162.
2.4. Antimicrobial activity
2.2.2. Deep-green rod crystals 1b
Synthesis of 1b was different from that of 1a only in
the volume of the solvent; crystals 1b was obtained from
the reaction in 20 mL of mixed EtOH and water (1:1)
solvent. Deep-green rod crystals, insoluble in water and
soluble in most organic solvents, were obtained in 76.5%
(0.185 g scale) yield. Anal. Found: C, 61.77; H, 5.72.
Calc. for C20H22O4Cu or [Cu(hino)2]: C, 61.60; H,
5.69%. TG/DTA data: no weight loss was observed be-
fore decomposition. Decomposition began around 220
°C with an endothermic peak at 179 °C due to melting
and exothermic peaks at 353, 369 and 398 °C. Promi-
nent IR bands (KBr disk): 2959vs, 2925m, 2864m,
1636m, 1590vs (m(C@O)), 1577vs (m(C@O)), 1509vs
(m(C@C)), 1462s, 1421vs, 1353vs, 1293s, 1237s (m(C–O)),
1188m (m(C–O)), 1140m, 1099w, 1074w, 1041m, 957s,
917s, 898m, 877w, 816s, 781m, 755m, 744s, 669m, 607m,
Antimicrobial activities of the ‘‘free’’ ligand and the
three polymorphs 1a–1c in water-suspension system
were evaluated by the MIC (lg mLꢀ1) as described
elsewhere [41–46].
3. Results and discussion
3.1. Synthesis, compositional characterization and prop-
erties of three polymorphs of [Cu(hino)2]
The two polymorphs of [Cu(hino)2] have been pre-
pared as deep-green plate crystals 1a, comprised of di-
meric trans-, monomeric trans- and dimeric cis-forms in
the solid-state, and rod crystals 1b, comprised of mo-
nomeric trans-forms in the solid-state [23]. In this work,
complexes 1a and 1b were obtained in 71% and 75%
yields, respectively, by 2:1 molar-ratio reaction of Hhino
with CuSO4 ꢁ 5H2O under 2 h-refluxing conditions in
mixed EtOH and water (1:1) solvent using 30 and
20 mL, respectively. On the other hand, novel green
needle crystals 1c, comprised of only monomeric trans-
form in the solid-state, were obtained in 65–76% yield by
2 h-refluxing of crystals 1a or 1b (2.5 mmol) redissolved
in 20 mL of mixed EtOH/water (1:1) solvent, followed
by standing in a refrigerator at 0 °C. The three poly-
morphs of [Cu(hino)2] with m.p. 179 °C, were insoluble
in water, but soluble in most organic solvents, and de-
composed at around 233 °C. Complex 1c showed a
tendency to change to 1b after one month or more
581m, 513w, 433m, 412w cmꢀ1
.
2.2.3. Green needle crystals 1c
Crystals of 1a or 1b (2.5 mmol) were redissolved in
20 mL of mixed EtOH/water (1:1) solvent, followed by 2
h-refluxing. The solution was concentrated to 15 mL
using a rotary evaporator at 30–40 °C. After filtration
through a folded filter paper (Whatman #2), the filtrate
was allowed to stand in a refrigerator at 0 °C to give
green needle crystals 1c (65–76% yield). Anal. Found: C,
61.60; H, 5.75%. Calc. for C20H22O4Cu or [Cu(hino)2]:
C, 61.60; H, 5.69%. TG/DTA: no weight loss was ob-
served below 220 °C. Endothermic peaks were observed
at 178 (m.p.) and 336 °C, and exothermic peaks at 350,

K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
1171
standing at room temperature in the solid-state. XPD
patterns were used to confirm the structure of 1a–1c
because the XPD patterns of 1a–1c were markedly dif-
ferent from each other (see Section 3.2).
The molecular formulas of 1a–1c with Cu2þ
:
hinoꢀ ¼ 1:2 composition and without any solvated
molecules were consistent with elemental analysis and
TG/DTA measurements. Molecular weight measure-
ment of 1a in CHCl3 solution at room temperature,
based on the vapor pressure osmotic method, showed
382 (Calcd value for [Cu(hino)2] was 389.9). This indi-
cates that the dimeric structures contained in 1a in the
solid-state are dissociated and all complexes are present
as a monomeric species in CHCl3 solution, showing that
both monomeric cis- and trans-forms probably exist in
2:3 molar ratio in solution.
The FT-IR spectra of 1a–1c showed several charac-
teristic bands due to the isopropyl group at 2960, 2928,
2866 cmꢀ1, m(C@O) at 1589 and 1576 cmꢀ1, m(C@C) at
1505 cmꢀ1 and m(C–O) at 1239 and 1187 cmꢀ1, which
can be compared with those of Hhino, [Na(hino)] ꢁ 2H2O
[24], [Zn(hino)2] [22], [Sn(hino)2] and [Zn(trop)2] [22].
The UV–Vis absorption spectrum of 1a in EtOH, con-
sisting of the 675 nm band (e 67) due to d–d transition
and the broad and intense bands at 372, 338, 333 and
255 nm probably due to p–pꢃ transition of the ligand,
was very similar to that of [Cu(trop)2] in EtOH [678,
377, 329, 246.3 nm] [30].
Fig. 1. ORTEP view of molecular structure of 1c with the numbering
scheme.
3.2. Crystal and molecular structures of 1c, and X-ray
powder diffraction patterns of 1a–1c
Fig. 2. Packing diagram of 1c (symmetry operations i; x þ 1; y; z, ii;
x ꢀ 1; y; z).
During a few daysÕ standing of the mixed EtOH and
water (1:1) solution in a refrigerator at 0 °C, crystals of
1c with sufficient quality suitable for single-crystal X-ray
diffraction studies were grown. The molecular and
crystal structures of 1c, with the atom numbering
schemes, are depicted in Figs. 1 and 2. Selected bond
distances and angles with their standard deviations are
given in Table 1.
X-ray structure analysis of 1c revealed that the crystal
structure was composed of monomeric trans-form of the
planar CuO4 core with regard to the isopropyl groups
(the sum of four angles around the Cu1 atom was 360°).
The molecular structure of 1c was very similar to that of
1b (Fig. 1), but different from that of 1a consisting of
dimeric trans-, monomeric trans- and dimeric cis-forms.
The Cu1 atom was sandwiched between two intermo-
lecular tropolone rings (C1i–C7i and C11ii–C17ii;
symmetry operations i; x þ 1, y; z, ii; x ꢀ 1; y; z) as a
ladder-type stacking and the distance between Cu1 and
Table 1
ꢀ
Selected bond distances (A) and bond angles (°) for 1c
Cu1–O1 1.885(12)
Cu1–O2 1.928(12)
Cu1–O3 1.952(11)
Cu1–O4 1.881(13)
C1–O1 1.29(2)
C6–C7 1.31(2)
C1–C7 1.48(2)
C11–O3 1.32(2)
C12–O4 1.290(19)
C12–C11 1.479(18)
C12–C13 1.48(2)
C13–C14 1.39(2)
C14–C15 1.43(2)
C15–C16 1.279(19)
C16–C17 1.48(2)
C11–C17 1.32(2)
C2–O2 1.308(19)
C2–C1 1.466(17)
C2–C3 1.33(2)
C3–C4 1.41(2)
C4–C5 1.37(2)
C5–C6 1.496(17)
O4–Cu1–O1 97.1(5)
O1–Cu1–O2 83.3(5)
O2–Cu1–O3 94.9(5)
O4–Cu1–O3 84.7(5)
ꢀ
one ring plane was 3.36 A (Fig. 2). Such an intermolec-
rings of 1c, the C1–C2 and C11–C12 bonds were essen-
tially single bonds, and partial delocalization on the at-
oms of the ring was observed (the mean distance for the
C3–C4, C5–C6, C7–C1, C12–C13, C14–C15 and C16–
ular interaction is not observed in 1b. These aspects are
in contrast to that of [Cu(trop)2] with a transoid struc-
ture, which exists as a sandwich-type dimer by face-
ꢀ
ꢀ
to-face stacking (3.3–3.8 A) [30]. Within the tropolone
C17: 1.46 A and for C2–C3, C4–C5, C6–C7, C13–C14,

1172
K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
ꢀ
C15–C16 and C17–C11: 1.33 A). The distances of C1–
O1, C2–O2, C11–O3 and C12–O4 (the mean distance:
character [19,47,48]. The present work also rules out
aromaticity of the coordinating hinoꢀ ligand in 1a–1c.
X-ray power diffraction (XPD) patterns observed for
1a–1c were markedly different from each other as shown
in Fig. 3, and they were, therefore, useful for convenient
determination of the three different crystal structures.
The simulation of the powder pattern obtained by sin-
gle-crystal X-ray analysis suggested the presence of
ꢀ
1.30 A) were almost the same, and these values are
ꢀ
compared with an ordinal C@O distance (1.21 A) and an
ꢀ
ordinal C–O distance (1.36 A). The two methyl groups of
the isopropyl group were vertical to the ring plane in 1c
(Fig. 2). It has been concluded that neither Htrop nor
Hhino possesses any appreciable degree of aromatic
Fig. 3. The observed XPD patterns (above) and simulated patterns (below) derived from single-crystal X-ray diffraction data, in each set of pair of
figures for plate crystals 1a, rod crystals 1b and needle crystals 1c.

K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
1173
strong peaks 2h at 6.68°, 7.82°, 9.69° for 1a, 10.55,
12.44° for 1b, and 6.62°, 13.88°, 19.48° for 1c, respec-
tively. The observed peaks 2h were found at 6.49°, 7.66°,
9.60° for 1a, 10.39°, 12.36° for 1b, in which the peak
intensities below 10° were small, and 6.43°, 13.91° and
19.50° for 1c. Thus, the observed XPD patterns of 1a–1c
were in accord with the simulation patterns (Fig. 3)
derived from the single-crystal X-ray diffraction data.
These XPD patterns also indicate that the single crystals
are representative of the bulk samples.
frozen CHCl3 solution at 77 K, are compared with those
of the previously reported data (g ¼ 2:036; g
?
==
¼ 2:264; A ¼ ꢅ29 ꢂ 10ꢀ4 cmꢀ1
,
A== ¼ ꢅ146 ꢂ 10ꢀ4
?
cmꢀ1) for the square planar bis(acetylacetonato)cop-
per(II) complex, [Cu(acac)2] [52,53]. The differences in g
and A values in the two copper(II) complexes may be
attributed to the different geometries around the cop-
per(II) centers, i.e. the rectangular CuO4 core of 1a
versus the almost complete square planar CuO4 core of
[Cu(acac)2] [54], and also to the different chelate-ring
sizes based on the extended p-conjugate systems, i.e. 10-
membered ring of 1a (through O1–C1–C7–C6–C5–C4–
C3–C2–O2 bond of hinoꢀ ligand) versus 6-membered
ring of [Cu(acac)2] (through O–C–C–C–O bond of
acacꢀ ligand).
3.3. Magnetic susceptibility measurements of 1a–1c and
ESR spectra of 1a
Temperature-dependent magnetic susceptibilities (vA)
for 1a–1c were measured with SQUID as plots of the
observed values of vA and/or 1=vA, and leff (or lB),
versus temperature in the range of 3–300 K (Fig. 4). The
magnetic behaviors were different from each other: 1a
showed a weak ferromagnetic interaction, 1b showed
a paramagnetic nature with S ¼ 1=2, while 1c showed a
weak antiferromagnetic interaction [49–51].
3.4. Antimicrobial activities
Antimicrobial activities of complexes 1a–1c prepared
here, together with the ‘‘free’’ Hhino ligand and the
sodium salt [Na(hino)] ꢁ 2H2O, are listed in Table 2, as
estimated by the minimum inhibitory concentration
(MIC; lg mLꢀ1).
The ESR parameters (g ¼ 2:049; g ¼ 2:295; A
?
?
==
¼ ꢅ38 ꢂ 10ꢀ4 cmꢀ1, A== ¼ ꢅ178 ꢂ 10ꢀ4 cmꢀ1), evalu-
Hhino showed a wide range of effective activities
against bacteria, yeasts and molds, except for one
ated from four-line ESR spectrum of 1a measured in
Fig. 4. Temperature-dependent magnetic susceptibility measurements (SQUID) of 1a–1c.

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K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
Table 2
Antimicrobial activities evaluated by MIC (lg mLꢀ1
)
Test organism
Hhino
[Na(hino)] ꢁ 2H2O
CuSO4 ꢁ 5H2O
1a
1b
1ca
(1)
(2)
Escherichia coli
250
125
62.5
31.3
>1000
>1000
>1000
>1000
>1000
>1000
>1000
>1000
>1000
>1000
1000
500
500
250
500
500
Bacillus subtilis
1000
1000
Staphylococcus aureus
Pseudomonas aeruginosa
Candida albicans
250
>1000
>1000
7.9
62.5
1000
62.5
62.5
62.5
62.5
>1000
>1000
>1000
>1000
>1000
>1000
1000
500
>1000
1000
1000
1000
1000
Saccharomyces cerevisiae
Aspergillus niger
Penicillium citrinum
7.9
15.7
500
250
15.7
a Results of repeat trials by 1c with two different lot-numbers.
Gram-negative bacterium (Pseudomonas aeruginosa).
The sodium salt [Na(hino)] ꢁ 2H2O, actually acting as an
anionic hinoꢀspecies [24], also showed a wide spectrum
of antimicrobial activities, but a more subtle variety; it
showed enhanced activities against two bacteria (Esch-
erichia coli and Bacillus subtilis), two yeasts (Candida
albicans and Saccharomyces cerevisiae) and two molds
(Aspergillus niger and Penicillium citrinum), but it
showed depressed activities against two bacteria
(Staphylococcus aureus and P. aeruginosa). Thus, we can
say that both neutral Hhino and anionic hinoꢀ mole-
cules show noteworthy antimicrobial activities. The re-
sults are consistent with the reported data for other
Gram-negative and Gram-positive bacteria [18]. The
target of inhibition, the mechanism and mode of action
have not been so far clarified, although several possi-
bilities have been proposed [15,16].
Complexes 1a and 1b showed no activity against the
same microbes, while complex 1c showed a wide spec-
trum of modest activities against selected bacteria,
yeasts and molds. The repeat trials for antimicrobial test
by 1c with two different lot-numbers exhibited the
modest activities, showing the reproducibility. These
results would be a first example of the antimicrobial
activities that the crystal structure influences.
Here, it should be noted that the present results are
different from the literature [18] that has reported higher
activities of the copper(II) complex against several
Gram-positive bacteria (S. aureus and Enterococcus
faecium) and Gram-negative bacteria (P. aeruginosa)
than Hhino and the sodium salt. The literature does not
describe if the copper(II) complex used for the test is the
crystals or the powder. One reason for the controversial
results will be attributed to the purity of the complex
used in the literature. In fact, the analytical data of the
report showed the composition of Cu2þ: hinoꢀ ¼ 1:1.77
or 1.13:2 [18], suggesting that it is contaminated with a
‘‘free’’ copper(II) ion.
protein, and a formation of a radical species such as ÅOH
generated by Fenton mechanism on the Cu2þ-bound
biopolymer [55]. On the other hand, antimicrobial ac-
tivities by copper(II) complexes have been scarcely
studied and the mechanisms have not been reported.
The antimicrobial activities and solid-state properties
show significant features. (1) Complexes 1a–1c are an
inert complex or stronger metal-oxygen bonding com-
plex, and it is not dissociated in solution under evalua-
tion of an antimicrobial test. If the complex is
dissociated in solution, the activities by the ‘‘free’’ cop-
per(II) ion and ‘‘free’’ hinoꢀ ion will appear. A forma-
tion of the CuO4 core inhibits an interaction of oxygen
atoms linked to C1 and C2 atoms with microorganisms/
protein. (2) Depending on the solid-state packing man-
ner, the hinokitiol–metal complex can show activities for
selected microorganisms. An interaction of oxygen at-
oms linked to C1 and C2 atoms with microorganisms/
protein may not be only a factor of antimicrobial ac-
tivities.
4. Conclusions
Three different polymorphs 1a–1c of [Cu(hino)2] have
been prepared in good yields and characterized by XPD,
FT-IR, TG/DTA and elemental analysis. The novel
crystal structure of 1c was determined by single-crystal
X-ray analysis: 1c was composed of a monomeric trans-
form of the planar CuO4 core with regard to the iso-
propyl groups. The molecular structure of 1c was very
similar to that of 1b, but 1c revealed a ladder-type
stacking, which was not seen in the crystal of 1b. Within
the seven-membered ring with 6p-conjugate system, the
ꢀ
C1–C2 bond was essentially a single bond (1.461(6) A)
and the p-electron system was completely delocalized on
the atoms of the ring except the C1–C2 bond. Thus, the
aromaticity of the coordinating hinoꢀ ligand was ruled
out. Molecular weight measurements in CHCl3 showed
that the complex of 1a was present as a monomer in
solution, which probably contains 2:3-ratio of cis- and
trans-forms.
The aqueous copper(II) ion, i.e. [Cu(H2O)n]2þ ion has
shown antimicrobial activities, and there are proposed
many mechanisms; most are concerned with interactions
of copper(II) and/or copper(I) ions with DNA and

K. Nomiya et al. / Inorganica Chimica Acta 357 (2004) 1168–1176
1175
[8] A. Kafuku, Japan Kokai (1976) 7622819 [Chem. Abstr. 85 (1976)
15349z].
As anticipated, the three polymorphs showed differ-
ent magnetic properties; 1a showed a weak ferromag-
netic interaction, 1b showed a paramagnetic nature,
while 1c showed a weak antiferromagnetic interaction.
Complexes 1a and 1b showed no antimicrobial activities
against selected microorganisms, but only 1c showed a
wide spectrum of antimicrobial activities. The antimi-
crobial test was performed in water suspension solution,
but not in homogeneous solution, and these results
would be a first example of the antimicrobial activities
that the crystal structure influences. The presence of the
4-isopropyl group in the tropolone ring significantly
influences the crystal structures of [Cu(hino)2], resulting
in different effects on XPD, SQUID and antimicrobial
activities. Thus, the polymorphism of crystals of other
metal complexes with the hinoꢀ ligand will be also of
interest. Studies in this direction are in progress and the
data will be reported in due course.
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Financial support by a Grant-in-Aid for Scientific
Research (C) No. 10640552 and by a High-tech Re-
search Center Project, both from the Ministry of Edu-
cation, Culture, Sports, Science and Technology, Japan,
is acknowledged. Financial support and a supply of
Hhino by Asahi Kasei Co., Japan, are acknowledged.
We thank Dr. K. Yoza, Bruker AXS Japan, for the
structure analysis, Prof. W. Mori (Kanagawa Univer-
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