Hydrogen-bonding interactions, geometrical selectivity and spectroscopic properties of cobalt(III) complexes with unsymmetrical tridentate amine-amidato-phenolato type ligands

Article abstract of DOI:10.1016/j.ica.2013.01.011

Four cobalt(III) complexes with the formula of [Co(Ln)₂] ^- bearing tridentate amine-amidato-phenolato-type ligands (Ln: n = 1-4) were synthesized. All of the complexes were characterized by ¹H NMR spectroscopy and X-ray an

Full text of DOI:10.1016/j.ica.2013.01.011

Inorganica Chimica Acta 399 (2013) 131–137
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Hydrogen-bonding interactions, geometrical selectivity and spectroscopic
properties of cobalt(III) complexes with unsymmetrical tridentate
amine-amidato-phenolato type ligands
⇑
⇑
Ryoji Mitsuhashi , Takayoshi Suzuki , Yukinari Sunatsuki, Masaaki Kojima
Department of Chemistry, Graduate School of Natural Science and Technology, Okayama University, Tsushima-naka 3-1-1, Okayama 700-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Four cobalt(III) complexes with the formula of [Co(Ln)2]ꢀ bearing tridentate amine-amidato-phenolato-
type ligands (Ln: n = 1–4) were synthesized. All of the complexes were characterized by 1H NMR spectros-
copy and X-ray analysis. The geometrical selectivity was found to depend on the flexibility of the amine-
amidato chelate in combination with the planar 2-oxybenzamido 6-membered chelate; that is, the
amine-amidato 5-membered chelate took the mer-type geometry, and the 6-membered chelate took
the fac-type geometry. In most of the mer-type complexes, intermolecular double hydrogen bonds via
amidato(O) and amino group were selectively formed between their enantiomeric pairs of mononuclear
complexes. In the case of two chiral ligands {L22– = 2-amino-1-(2-oxybenzamido)propane; L32ꢀ = trans-
1-amino-2-(2-oxybenzamido)cyclohexane}, [Co(L3)2]ꢀ showed diastereoselectivity while [Co(L2)2]ꢀ did
not. Furthermore, PPh4[Co(L1)2] (L12ꢀ = 2-amino-1-(2-oxybenzamido)-2-methylpropane) showed an
apparent solvatochromic behavior in several solvents. Although the molecular structures of [Co(L2 or
L3)2]ꢀ are quite similar to that of [Co(L1)2]ꢀ, these complexes did not exhibit such a solvatochromic
behavior.
Article history:
Received 6 September 2012
Received in revised form 28 December 2012
Accepted 4 January 2013
Available online 25 January 2013
Keywords:
Double hydrogen bonds
Amine-amidato type ligand
Geometrical isomers
Diastereoselectivity
Solvatochromism
Ó 2013 Elsevier B.V. All rights reserved.
ꢀ
1. Introduction
(hereafter, abbreviated as [n]ꢀ), and have determined their
molecular and crystal structures including the stereoselective mul-
Hydrogen-bonding interactions play critical roles not only in
biological systems [1] but also in construction of modern func-
tional materials [2,3]. In particular, multiple hydrogen bonds are
designed for highly specific molecular recognition including stere-
oselectivity [2] and are programmed into supramolecular assembly
leading to their characteristic functionalities [3]. In order to
achieve these concepts, the precise design of hydrogen-bonding
donor(s) and acceptor(s) in a molecule is crucial. Metal complexes
tiple hydrogen bonds. Among these unsymmetrical tridentate li-
gands, L12ꢀ L22ꢀ and L32ꢀ form an amine-amidato five-
,
membered chelate together with a rigid 2-oxybenzamido six-
membered chelate, whereas L42ꢀ forms a flexible six-membered
amine-amidato chelate. It was revealed that the difference in flex-
ibility of the amine-amidato chelate ring gave a severe influence on
the molecular structures of the resulting cobalt(III) complexes. A
characteristic solvatochromic behavior of one of the complex salts,
PPh4[1], is also reported.
of a nitrogen-ligating amidato (RC(O)NR0-
jN) ligand having an
amino and a phenolato groups at both terminals are suitable can-
didates for intra- and intermolecular multiple hydrogen bonds, be-
cause the coordinated amino group can act as a hydrogen-bonding
donor while the phenolato-O and amidato-O atoms are possible
hydrogen-bonding acceptors. However, synthetic and structural
studies of such metal complexes have been limited so far [4], pre-
sumably due to some difficulty in preparation of the unsymmetri-
cal tridentate amine-amidato-phenolato type ligands. In this study,
we have successfully prepared the ligand precursors: H2Ln (n = 1,
2, 3 and 4: Scheme 1) and their cobalt(III) complexes: [CoIII(Ln)2]-
2. Results and discussion
2.1. Synthesis and structures
All ligand precursors of H2Ln (n = 1–4) were readily obtained by
a reaction of phenyl salicylate and the appropriate diamines (1,2-
diamino-2-methylpropane, 1,2-diaminopropane, trans-1,2-diami-
nocyclohexane and 1,3-diaminopropane, respectively) in 2-propa-
nol. Different synthetic procedures were reported for H2L3 and
H2L4, but our methods were rather simple and gave higher yields
[1a,5,6]. Owing to low solubility of N-(aminoalkyl)salicylamides
in 2-propanol, the desired compounds were readily isolated with-
⇑
Corresponding authors. Tel./fax: +81 862517900.
E-mail addresses: mitsuhashi@s.okayama-u.ac.jp (R. Mitsuhashi), suzuki@
okayama-u.ac.jp (T. Suzuki).
0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.011

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R. Mitsuhashi et al. / Inorganica Chimica Acta 399 (2013) 131–137
Scheme 1. The amine-amido-phenol ligand precursors (H2Ln: n = 1, 2, 3 or 4) used
in this study.
out further reaction to give symmetrical tetradentate diamides.
When unsymmetrical diamines were used for the preparation of
H2L1 and H2L2, only the amino group at 2-position was reacted [5].
The reaction of CoCl2ꢁ6H2O or Co(OAc)2ꢁ4H2O and H2Ln (n = 1, 2,
3 or 4) in 1:2 molar ratio with a stoichiometric amount of KOtBu in
air resulted in the formation of [CoIII(Ln)2]ꢀ ([n]ꢀ). All of the com-
plexes were crystallized as the K+ salt by vapor diffusion of diethyl
ether into a methanol solution. The tetraphenylphosphonium
(PPh4+) salts of [1]ꢀ and [3]ꢀ were also obtained by cation ex-
change and recrystallization from acetonitrile. For such [M(Ln)2]-
type transition-metal complexes with unsymmetrical A–B–C-type
tridentate ligands, many isomers are possible as shown in
Scheme 2[7]. It is worthwhile to note that the geometrical selectiv-
ity upon coordination is largely dependent on the molecular struc-
tures of the ligands.
The crystal structures of K[1]ꢁCH3OH and PPh4[1]ꢁ1.5CH3-
CNꢁ2H2O were determined by X-ray analysis. Since the conforma-
tion of L12ꢀ is restricted by the combination of a rigid 2-
oxybenzamido O–N six-membered chelate and an amine-amidato
five-membered chelate, [1]ꢀ has the mer-configuration in both
complex salts (Fig. 1). In the crystal of K[1]ꢁCH3OH, the K+ ion is lo-
cated close to [1]ꢀ anion (Coꢁ ꢁ ꢁK separation is 3.52 Å), and it inter-
acted with 2-oxybenzamido moieties of [1]ꢀ and the methanol
molecule of crystallization (see: Supplementary data, Fig. S1a). In
addition, intermolecular hydrogen bonds were observed; one of
the coordinating amino groups acts as a hydrogen-bonding donor,
and one of the noncoordinating amidato-O atoms acts as a hydro-
gen-bonding acceptor. These intermolecular hydrogen bonds were
formed between a pair of enantiomers, C-[1]ꢀ and A-[1]ꢀ (C = clock-
Fig. 1. ORTEP of the anionic complex part (50% probability level, H-atoms omitted)
in the crystal of K[1]ꢁCH3OH.
wise, A = anticlockwise, see Scheme 2), resulting in an infinite zigzag
chain structure (Fig. S1b). Intermolecular hydrogen bonds were
also observed in PPh4[1]ꢁ1.5CH3CNꢁ2H2O. In this crystal, however,
such hydrogen bonds formed a dimeric structure presumably be-
cause of the bulky counter cation (Fig. S2). In this dimer, complex
anions discriminate the chirality of the opposite via double hydro-
gen bonds.
The ligand L22ꢀ, having an asymmetric carbon atom, was de-
signed to examine the diastereoselectivity upon coordination.
Since the molecular structure of ligand L22ꢀ is very similar to that
of L12ꢀ, the bis(L2)-type complex of [2]ꢀ is expected to take the
mer configuration. When a racemic mixture of H2L2 is used, three
diastereomers (C-[Co(R-L2)2]ꢀ, C-[Co(R-L2)(S-L2)]ꢀ, C-[Co(S-L2)2]ꢀ
and their enantiomers) are possible for mer-[2]ꢀ. The X-ray analy-
sis revealed that [2]ꢀ took the mer geometry in K[2]ꢁ0.5CH3-
OHꢁ4.5H2O, as shown in Fig. 2. The intermolecular hydrogen
bonds were doubly formed between two adjacent complex anions,
constructing an infinite chain along the b axis, as shown in Fig. S3.
In this crystal, positional disorders were observed at the C atom
next to the amino groups. This indicates that all of the possible dia-
stereomers, C-[Co(R-L2)2]ꢀ, C-[Co(R-L2)(S-L2)]ꢀ and C-[Co(S-L2)2]ꢀ,
Fig. 2. ORTEP of anionic part (50% probability level, H-atoms omitted) in
K[2]ꢁ0.5CH3OHꢁ4.5H2O. Positional disorders were observed at C9 and C19 atoms,
but only one of the possible structures ([A-Co(R-L2)2]ꢀ) is shown.
Scheme 2. Possible stereoisomers for the bis(unsymmetrical tridentate)-type
complex, [M(A–B–C)2] [7b].

R. Mitsuhashi et al. / Inorganica Chimica Acta 399 (2013) 131–137
133
are mixed in the crystal. Similarly, the 1H NMR spectrum of K[2] in
CD3OD showed a complicated spectrum consisting of signals from
more than two diastereomers (Fig. S4). When optically pure R-H2L2
was used, the 1H NMR spectrum of the product became rather sim-
ple, because only two diastereomers, A-[Co(R-L2)2]ꢀ and C-[Co(R-
L2)2]ꢀ, could be formed (Fig. S4c). These results indicate that there
is no diastereoselectivity upon coordination or crystallization for
[2]ꢀ.
ligand-exchange reactions because of the inertness of CoIII ion
and the chelate effect of the tridentate ligand. On the other hand,
when 1H NMR measurement was carried out in dimethyl sulfoxide,
such spectral change was not observed. Therefore, it is suggested
that the ligand-exchange reaction observed for K[3] and PPh4[3]
is accelerated by the reductive nature of methanol. The DFT calcu-
lations supported that [Co(RR-L3)(SS-L3)]ꢀ is not the most stable
isomer, and suggested that C-[Co(SS-L3)2]ꢀ (and its enantiomer)
is 3.31 kcal/mol more stable than [Co(RR-L3)(SS-L3)]ꢀ in their
ground states (Table S1). This conversion reaction accelerated by
heating to 60 °C, and most of [Co(RR-L3)(SS-L3)]ꢀ was converted
to one of the two C2-symmetric diastereomers within 4 h. When
recrystallization of the complex was attempted from this solution
containing thermodynamically stable C2-symmetric diastereomer,
reddish violet and pale violet microcrystals were obtained.
Although the pale violet microcrystals were not suitable for X-
ray analysis, we confirmed that the reddish violet crystal consisted
of the C1-symmetric [Co(RR-L3)(SS-L3)]ꢀ by X-ray analysis. It was
also shown that the pale violet microcrystals are of the C2-symmet-
ric diastereomer by 1H NMR spectroscopy (Fig. S6). These results
indicate that the thermodynamically stable diastereomer was con-
verted back to [Co(RR-L3)(SS-L3)]ꢀ upon crystallization. The above-
mentioned intermolecular double hydrogen bonds would give a
primary contribution for the preferable crystallization. In contrast,
these hydrogen bonds became ineffective in solution, and conse-
quently [Co(RR-L3)(SS-L3)]ꢀ was gradually converted to the most
thermodynamically stable diastereomer.
The ligand L32ꢀ was also designed to investigate the diastere-
oselectivity. This ligand is also assumed to take the mer-configura-
tion in a bis-type complex owing to its structural similarity to L12ꢀ
and L22ꢀ. While the ligands L12ꢀ and L22ꢀ have a conformationally
flexible ethylene bridge, the trans-cyclohexylene moiety in L32ꢀ is
rather rigid. From the reaction using pure RR-H2L3, 1H NMR spec-
troscopy indicated that a single product with C2 symmetry was ob-
tained, although two diastereomers, C-[Co(RR-L3)2]ꢀ and A-[Co(RR-
L3)2]ꢀ, are possible. This fact suggests that L32ꢀ shows diastereose-
lectivity upon coordination. When the racemic mixture of H2L3
was used, on the other hand, the 1H NMR spectra of crude products
of K[3] and PPh4[3] showed the existence of a C1-symmetric diaste-
reomer in addition to a C2-symmetric diastereomer (Fig. 3a).
Recrystallization of these products afforded K[3]ꢁ3CH3OH and
PPh4[3]ꢁ0.5CH3CN, respectively. The X-ray analysis of these crystals
revealed that the anionic complex was the C1-symmetric [Co(RR-
L3)(SS-L3)]ꢀ, and characteristic intermolecular double hydrogen
bonds were observed between C-[Co(RR-L3)(SS-L3)]ꢀ and A-
[Co(RR-L3)(SS-L3)]ꢀ in both crystals (Fig. 4). Furthermore, it is
worth noting that the intermolecular double hydrogen bonds are
formed between ligands having the same chirality, namely ORR-L3-
The ligand L42ꢀ is assumed to form a N–N six-membered che-
late ring, which is more flexible in its coordination mode, and
would show a different tendency to stabilize a specific geometri-
cal isomer. In contrast to the other H2Ln (n = 1–3), the reaction of
Co(OAc)2ꢁ4H2O and H2L4 in 1:2 molar ratio with a stoichiometric
amount of KOtBu in methanol afforded a green solution. The 1H
NMR spectrum of this reaction mixture indicated that this solu-
tion contained at least two products (Fig. S7). When this green
solution was allowed to stand for two weeks at room tempera-
ture or it was refluxed for 7 h, the solution gradually turned
brown. The 1H NMR spectrum of the brown solution showed
two doublets and two triplets in the aromatic region, indicating
the formation of a single product with Ci or C2 symmetry. Slow
evaporation of the solvent afforded brown prismatic crystals of
K[4]ꢁ5H2O and the crystal structure was determined by X-ray dif-
fraction. In the asymmetric unit, there are two halves of complex
anions that have similar molecular structures to each other. As
shown in Fig. 5, both complex anions take a fac-configuration
with Ci symmetry. This suggests that the amine-amidato 6-mem-
bered chelate is flexible enough to form a stable chair-like confor-
ꢁ ꢁ ꢁHN -L3 and OSS-L3ꢁ ꢁ ꢁHNSS-L3. In other words, each ligand discrim-
RR
inates the chirality of its own and its opposite in the other complex
anion to form double hydrogen bonds. In the case of K[3]ꢁ3CH3OH,
the K+ ion was located close to the [3]ꢀ anion because of a
cation-
(Fig. S5).
p
interaction between K+ and the 2-oxybenzamido moiety
As mentioned above, the 1H NMR spectrum of K[3] measured
immediately after dissolving indicated that the crystals consisted
not only of [Co(RR-L3)(SS-L3)]ꢀ but also of one of the C2-symmetric
diastereomers (Fig. 3). On standing this solution at room tempera-
ture, a set of resonances with C2 symmetry grew gradually, and the
resonances of [Co(RR-L3)(SS-L3)]ꢀ almost disappeared. A similar
spectral change was also observed with PPh4[3]. These results sug-
gest that [Co(RR-L3)(SS-L3)]ꢀ is not the most thermodynamically
stable isomer in solution, and ligand exchange reaction to a more
stable isomer took place. It should be noted that such bis(triden-
tate)cobalt(III) complexes typically have difficulty in undergoing
mation. This conformation, together with
a
planar 2-
oxybenzamido 6-membered chelate, enables the complex to take
the fac-type configuration.
To obtain theoretical support for the geometrical selectivity of
[4]ꢀ, we performed DFT calculations for all possible isomers of
[4]ꢀ and compared their formation energies. The structural models
and the calculation results for all of the isomers are shown in
Fig. S8 and Table S2, respectively. It is found that the most stable
isomer is the fac-all trans isomer, as observed in the crystal of
K[4]ꢁ5H2O, and the second most stable isomer is the fac-
cis,cis,trans(NH2) isomer which is 4.29 kcal/mol higher in energy.
The others are much more unstable (more than 10 kcal/mol higher
in energy than the fac-all trans isomer). Formation of the fac-
cis,cis,trans(NH2) isomer is favored, presumably because the li-
gands’ negative charges are distributed over the equatorial plane.
From these calculations, it is assumed that the green reaction mix-
ture contains a mixture of fac-all trans and fac-cis,cis,trans(NH2)
isomers, and the latter is gradually converted to the former ther-
modynamically more stable fac-all trans isomer.
Fig. 3. Time-dependent 1H NMR spectra of K[3] in CD3OD at 22 °C. (a) Immediately
after dissolving, (b) after 1 day, (c) after 3 days, and (d) after 5 days. Black circle
indicates signals due to C1-symmetric [Co(RR-L3)(SS-L3)]ꢀ and open circle indicates
those due to one of two C2-symmetric diastereomers.

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R. Mitsuhashi et al. / Inorganica Chimica Acta 399 (2013) 131–137
Fig. 4. (a) ORTEP (50% probability level, H-atoms omitted) of anionic part in K[3]ꢁ3CH3OH. (b) A perspective view of the heterochiral double hydrogen-bonds between
C-[Co(RR-L3)(SS-L3)]ꢀ and A-[Co(RR-L3)(SS-L3)]ꢀ.
Fig. 5. ORTEPs (50% probability level, H-atoms omitted) of two anionic complexes in K[4]ꢁ5H2O.
2.2. Spectroscopic properties
The UV–Vis spectra of PPh4[1] in several solvents (Fig. 7) gave a
broad absorption band in the region of 450–700 nm. This band
When PPh4[1] was dissolved in several solvents (acetonitrile,
dichloromethane, chloroform, 2-propanol, ethanol, methanol and
water), it showed different colors, as shown in Fig. 6. A number
of solvatochromic CoIII complexes are known [8]; however, most
of them are accompanied with a structural change of the coordina-
tion environment, such as ligand exchange or additional coordina-
tion of solvent molecules. To investigate the solvatochromic
behavior of PPh4[1] in detail, 1H NMR and UV–Vis spectral mea-
surements were carried out in the above-mentioned solvents
(NMR measurements were carried out in CD3CN, CD2Cl2, CDCl3,
CD3OD and D2O). As the 1H NMR spectra of PPh4[1] showed similar
spectral patterns in all solvents, it is reasonable to assume that
complex [1]ꢀ retains its coordination structure in these solvents
(Fig. S9). The small changes in the chemical shifts are indicative
of the interaction of [1]ꢀ with solvent molecules in the second
coordination sphere.
could be assigned as the splitting components (1A2g
,
1Eg 1A1g
:
holohedralized D4h) of the first d–d (1T1g 1A1g: Oh) transition
band. In the region of 350–450 nm there were two absorption
shoulders, which would be originated from the LMCT transitions
(otherwise, they might be assigned as the splitting components
of the second d–d (1T2g 1A1g: Oh) transition band). In addition,
another intense band due to the intraligand (p–
p⁄) transition
was observed at ꢂ330 nm. Therefore, assuming five absorption
components in the region of 330–700 nm, the spectra in Fig. 7 were
analyzed by the Gaussian curve fitting using Gnuplot program [9],
and the resulting parameters are summarized in Table S3. This
analysis indicated that the transition energies (rmax) of all absorp-
tion bands were little shifted by the solvents, although the color
changes of the solutions were apparent. On the other hand, the
absorption coefficient (emax) and the full width at half maximum
(FWHM) of each band were largely dependent on the kind of sol-
vents. The interaction from solvent molecules in the second coor-
dination sphere (or to the ligand moieties) may give a little
influence on the donor ability of the ligand [10], but it would give
a certain effect to the oscillator strength of the transitions due to
the symmetry breaking of the complex. Thus, it is reasonably as-
sumed that the formation of hydrogen bonds between the complex
anion [1]ꢀ and solvent molecules causes the solvatochromic
behavior. However, because the related complexes of [K(18-
crown-6)][2] and PPh4[3] did not show a similar solvatochromism
(Fig. S10), the origin of this interesting phenomenon is still unclear,
and the research to unveil the reason behind it is in progress.
Fig. 6. The solvatochromic behavior of PPh4[1] (1.0 ꢃ 10–3 M).

R. Mitsuhashi et al. / Inorganica Chimica Acta 399 (2013) 131–137
135
Fig. 7. The absorption spectra of PPh4[1] (a) in acetonitrile, dichloromethane and chloroform and (b) 2-propanol, ethanol, methanol and water.
4.2.2. 2-Amino-1-(2-hydroxybenzamide)propane (H2L2)
3. Conclusion
This compound was prepared by a similar method to the above
using phenyl salicylate (2.11 g, 9.8 mmol) and 1,2-diaminopropane
(0.77 g, 10.4 mmol). Yield: 1.34 g (76%). 1H NMR (CD3OD, 22 °C): d
1.21 (d, J = 6.5 Hz, 3H, –CH3), 3.26 (m, 1H, –CH), 3.43 (m, 2H, –CH2–),
6.74 (t, J = 7.5 Hz, 1H, aryl-H), 6.82 (d, J = 8.3 Hz, 1H, aryl-H), 7.28
(t, J = 7.9 Hz, 1H, aryl-H), 7.79 (d, J = 8.0 Hz, 1H, aryl-H).
We have synthesized [CoIII(Ln)2]ꢀ-type complexes with a series
of unsymmetrical tridentate amine-amidato-phenolato ligands. X-
ray analysis and 1H NMR spectroscopy indicated that the combina-
tion of a 2-oxybenzamido six-membered chelate ring and an
amine-amidate five-membered ring preferred mer-type coordina-
tion geometry both in solution and in the solid states, whereas a
similar ligand with an amine-amidato six-membered ring afforded
the fac-all trans isomer. Characteristic intermolecular heterochiral
double hydrogen bonds were observed in the crystals of mer-type
complexes, except for K[1]ꢁCH3OH. In the preparation of [2]ꢀ, dia-
stereoselectivity was not observed when a racemic mixture of L22ꢀ
was employed. In contrast, the reaction of racemic L32ꢀ and Co2+
ion resulted in a single product with C2 symmetry among three
possible diastereomers in solution. However, the product was con-
verted to [Co(RR-L3)(SS-L3)]ꢀ upon crystallization to form a char-
acteristic dimeric structure by heterochiral double hydrogen
bonds.
4.2.3. (R)-2-Amino-1-(2-hydroxybenzamide)propane (R-H2L2)
This compound was prepared by a similar method to the above
using phenyl salicylate (2.16 g, 10.1 mmol) and (R)-1,2-diamino-
propane (0.94 g, 12.6 mmol). The solvent was removed by evapora-
tion, and a colorless oily residue was obtained. This ligand was
used for the preparation of K[Co(R-L2)2] without purification.
4.2.4. trans-1-Amino-2-(2-hydroxybenzamide)cyclohexane (H2L3)
This compound was prepared by a similar method to the above
using phenyl salicylate (2.14 g, 10.0 mmol) and trans-1-,2-diami-
nocyclohexane (1.20 g, 10.5 mmol). Yield: 1.41 g (60%). 1H NMR
(CD3OD, 22 °C): d 1.40 (d, J = 8.2 Hz, 4H, –CH2–), 1.81 (m, 2H, –
CH2–), 2.02 (m, 2H, –CH2–), 2.77 (td, J = 10.4 and 4.1 Hz, 1H, –
CH–), 3.80 (td, J = 10.5 and 4.2 Hz, 1H, –CH–), 6.72 (t, J = 7.5 Hz,
1H, aryl-H), 6.81 (d, J = 7.9 Hz, 1H, aryl-H), 7.28 (t, J = 7.7 Hz, 1H,
aryl-H), 7.80 (d, J = 8.0 Hz, 1H, aryl-H).
4. Experimental
4.1. General considerations
4.2.5. (1R,2R)-trans-1-Amino-2-(2-hydroxybenzamide)cyclohexane
(RR-H2L3)
All reagents were used as received. Proton NMR measurements
were carried out at 22 °C using Varian NMR System 600 and Varian
Mercury 300 spectrometers. Chemical shifts are referenced to the
solvent residual peak [11]. The UV–Vis absorption spectra were re-
corded at room temperature on a Jasco V-550 spectrophotometer.
All ligands were synthesized by a modified procedure based on a
previously reported method [5,6,12].
This compound was prepared by a similar method to the above
using phenyl salicylate (2.15 g, 10.1 mmol) and (1R,2R)-trans-1-,2-
diaminocyclohexane (1.17 g, 10.2 mmol). The solvent was removed
by evaporation, and a colorless oily residue was obtained. This li-
gand was used for the preparation of K[Co(RR-L3)2] without
purification.
4.2.6. 1-Amino-3-(2-hydroxybenzamide)propane (H2L4)
This compound was prepared by a similar method to the above
using phenyl salicylate (2.15 g, 10.1 mmol) and 1,3-diaminopro-
pane (1.00 g, 13.5 mmol). Yield: 1.72 g (87%). 1H NMR (CD3OD,
22 °C): d 1.85 (quin, J = 6.8 Hz, 2H, –CH2–), 2.85 (t, J = 7.0 Hz, 2H,
–CH2–), 3.49 (t, J = 6.6 Hz, 2H, –CH2–), 6.62 (t, J = 7.5 Hz, 1H, aryl-
H), 6.78 (d, J = 8.3 Hz, 1H, aryl-H), 7.24 (t, J = 7.7 Hz, 1H, aryl-H),
7.78 (d, J = 7.9 Hz, 1H, aryl-H).
4.2. Preparation of ligand
4.2.1. 2-Amino-1-(2-hydroxybenzamide)-2-methylpropane (H2L1)
A solution of phenyl salicylate (2.13 g, 9.9 mmol) in 2-propanol
(30 mL) was added to a 2-propanol solution (10 mL) containing
1,2-diamino-2-methylpropane (0.93 g, 10.6 mmol) dropwise with
stirring. The mixture was stirred overnight at room temperature.
The resulting white precipitate was collected by filtration, washed
with 2-propanol and diethyl ether, and dried in vacuo. Yield: 1.54 g
(76%). 1H NMR (CD3OD, 22 °C): d 1.27 (s, 6H, –CH3), 3.46 (s, 2H, –
CH2–), 6.70 (ddd, J = 1.1, 7.1, and 8.0 Hz, 1H, aryl-H), 6.81 (dd,
J = 8.3 and 0.8 Hz, 1H, aryl-H), 7.27 (ddd, J = 8.5, 7.0, and 1.8 Hz,
1H, aryl-H), 7.82 (dd, J = 7.8 and 1.8 Hz, 1H, aryl-H).
4.3. Preparation of complexes
4.3.1. K[Co(L1)2]ꢁCH3OH (K[1]ꢁCH3OH)
A methanol solution (10 mL) of KOtBu (0.22 g, 2.0 mmol) was
added with stirring to a methanol solution (20 mL) containing

136
R. Mitsuhashi et al. / Inorganica Chimica Acta 399 (2013) 131–137
H2L1 (0.21 g, 1.0 mmol) and CoCl2ꢁ6H2O (0.13 g, 0.55 mmol). After
stirring for 2 h at room temperature in air, the reaction mixture
was concentrated to ca. 5 mL under reduced pressure, and the
resulting white precipitate was filtered off. Diethyl ether vapor
was diffused into the filtered solution, affording violet block crys-
tals. Yeild: 0.25 g (92%). Anal. Calc. for C23H32CoKN4O5: C, 50.92;
H, 5.94; N, 10.33. Found: C, 50.53; H, 5.66; N, 9.91%. 1H NMR (CD3-
OD, 22 °C): d 1.08 (s, 6H, –CH3), 1.14 (s, 6H, –CH3), 2.55 (d,
J = 12.1 Hz, 2H, –NH2), 2.94 (d, J = 11.9 Hz, 2H, –NH2), 3.49 (d,
J = 12.9 Hz, 2H, –CH2–), 4.12 (d, J = 12.9 Hz, 2H, –CH2–), 6.61
(ddd, J = 7.9, 6.9 and 1.2 Hz, 2H, aryl-H), 6.78 (dd, J = 8.2 and
1.1 Hz, 2H, aryl-H), 7.02 (ddd, J = 8.4, 6.8 and 1.9 Hz, 2H, aryl-H),
7.98 (dd, J = 7.9 and 1.8 Hz, 2H, aryl-H).
4.3.6. K[Co(L3)2]ꢁ3CH3OH (K[3]ꢁ3CH3OH)
A methanol solution (5 mL) of KOtBu (0.11 g, 1.0 mmol) was
added with stirring to a methanol solution(5 mL) containing H2L3
(0.117 g, 0.60 mmol) and CoCl2ꢁ6H2O (0.059 g, 0.25 mmol). After
stirring for 2 h at room temperature in air, a white precipitate
was removed by filtration followed by evaporation of the solvent.
The violet solid was dissolved in methanol (15 mL), and the insol-
uble white precipitate was filtered off. Vapor diffusion of diethyl
ether into the solution resulted in deposition of violet platelet crys-
tals. Yield: 0.052 g (32%). Anal. Calc. for C29H44KCoN4O7: C, 52.88;
H, 6.73; N, 8.51. Found: C, 52.56; H, 6.48; N, 8.44%. 1H NMR (CD3-
OD, 22 °C): d 1.21–1.42 (m, 9H, –CH2–), 1.66–1.74 (m, 7H, –CH2–, –
NH2), 2.55 (d, J = 8.2 Hz, 2H –NH2), 2.82 (q, J = 11.8 Hz, 2H, –CH2–),
3.27 (dt, J = 10.4 Hz, J = 2.9 Hz, 2H, –CH2–), 3.47 (d, J = 11.7 Hz, 2H,
–CH–), 6.50 (t, J = 7.4, 2H, aryl-H), 6.91(d, J = 8.2 Hz, 2H, aryl-H),
7.01 (ddd, J = 8.3, 6.9 and 1.6 Hz, 2H, aryl-H), 8.03 (dd, J = 7.0, and
1.8 Hz, 2H, aryl-H).
4.3.2. PPh4[Co(L1)2]ꢁ1.5CH3CNꢁ2H2O (PPh4[1]ꢁ1.5CH3CNꢁ2H2O)
A methanol solution (10 mL) of KOtBu (0.22 g, 2.0 mmol) was
added with stirring to a methanol solution (20 mL) containing
H2L1 (0.20 g, 1.0 mmol) and CoCl2ꢁ6H2O (0.14 g, 0.59 mmol). After
stirring for 2 h at room temperature in air, PPh4Br (0.42 g,
1.0 mmol) was added to the reaction mixture, and the solvent
was evaporated off under reduced pressure. The brown oily resi-
due was dissolved in dichloromethane (15 mL), and the undis-
solved white precipitate was filtered off. The filtrate was
evaporated to dryness, again, and the residue was dissolved in
acetonitrile. Diethyl ether vapor was diffused into the solution,
depositing dark brown platelet crystals. Yield: 0.61 g (68%). Anal.
Calc. for PPh4[1]ꢁ0.5CH3CNꢁH2O = C47H51.5CoN4.5O5P: C, 66.46;
H, 6.11; N, 7.42. Found: C, 66.42; H, 5.98; N, 7.74%. 1H NMR
(CDCl3, 22 °C): d 1.08 (s, 6H, –CH3), 1.16 (s, 6H, –CH3), 1.70 (d,
J = 10.6 Hz, 2H, –NH2), 2.59 (d, J = 11.1 Hz, 2H, –NH2), 3.71 (d,
J = 12.9 Hz, 2H, –CH2–), 4.10 (d, J = 12.8 Hz, 2H, –CH2–), 6.61
(ddd, J = 7.8, 6.6 and 1.3 Hz, 2H, aryl-H), 6.48 (dd, J = 8.2 and
1.3 Hz, 2H, aryl-H), 6.56 (ddd, J = 8.3, 6.6 and 1.9 Hz, 2H, aryl-H),
8.02 (dd, J = 7.8 and 1.8 Hz, 2H, aryl-H).
4.3.7. PPh4[Co(L3)2]ꢁ0.5CH3CN (PPh4[3]ꢁ0.5CH3CN)
A methanol solution (10 mL) of KOtBu (0.45 g, 4.0 mmol) was
added with stirring to a methanol solution (25 mL) of H2L3
(0.24 g, 1.0 mmol) and Co(OAc)2ꢁ4H2O (0.12 g, 0.53 mmol). After
stirring for 2 h at room temperature in air, PPh4Br (0.84 g,
2.0 mmol) was added to the reaction mixture, and the solvent
was evaporated off under reduced pressure. The violet oily residue
was dissolved in dichloromethane (15 mL) and the undissolved
white precipitate was filtered off. Acetonitrile (60 mL) was added
to the filtrate, and the mixture was allowed to stand at room tem-
perature for a week, depositing violet block crystals. Yield: 0.27 g
(63%). Anal. Calc. for C51H53.5CoN4.5O4P: C, 69.34; H, 6.10; N, 7.13.
Found: C, 68.87; H, 5.98; N, 6.99%.
4.3.8. K[Co(RR-L3)2]
This compound was prepared by a similar method to the prep-
aration of K[Co(R-L2)2] using RR-L3, CoCl2ꢁ6H2O and KOtBu, and
was directly used for the 1H NMR measurements.
4.3.3. K[Co(L2)2]ꢁ0.5CH3OHꢁ4.5H2O (K[2]ꢁ0.5CH3OHꢁ4.5H2O)
A methanol solution (10 mL) of KOtBu (0.48 g, 2.0 mmol) was
added with stirring to a methanol solution (25 mL) containing
H2L2 (0.37 g, 1.9 mmol) and Co(OAc)2ꢁ4H2O (0.24 g, 1.0 mmol).
After stirring for 2 h at room temperature in air, the mixture was
concentrated (to ca. 10 mL) under reduced pressure. Vapor diffu-
sion of diethyl ether into the concentrate resulted in deposition
of violet block crystals. Yield: 0.34 g (64%). Anal. Calc. for K[2]ꢁH2-
OꢁCH3OH = C21H30CoKN4O6: C, 47.36; H, 5.68; N, 10.52. Found: C,
47.25; H, 5.57; N, 10.35%.
4.3.9. K[Co(L4)2]ꢁ5H2O (K[4]ꢁ5H2O)
A methanol solution (10 mL) of KOtBu (0.22 g, 2.0 mmol) was
added to a methanol solution (25 mL) of H2L4 (0.19 g, 1.0 mmol)
and Co(OAc)2ꢁ4H2O (0.12 g, 0.53 mmol). The resulting green mix-
ture was refluxed overnight in air, turning the reaction mixture
brown. The solution was concentrated (to ca. 10 mL) under re-
duced pressure. Vapor diffusion of diethyl ether into the concen-
trate gave brown needle crystals. Yield: 0.17 g (63%). Anal. Calc.
for C20H34CoKN4O9: C, 41.96; H, 5.99; N, 9.79. Found: C, 41.53; H,
5.68; N, 9.34%.
4.3.4. K[Co(R-L2)2]
All of the colorless residue of R-H2L2 obtained above was dis-
solved in 30 mL methanol, and 100 mL methanol solution of
Co(OAc)2ꢁ4H2O (1.01 g, 4.1 mmol) and KOtBu (1.17 g, 10.4 mmol)
was added. The mixture was stirred overnight at room tempera-
ture. The resulting solution was chromatographed over Sephadex
LH-20 with methanol followed by evaporation of the solvent. The
resulting violet residue was dissolved in water (20 mL). This solu-
tion was transferred to a separatory funnel and washed with
dichloromethane (3 ꢃ 50 mL). The aqueous layer was collected
and evaporated to dryness affording a deep violet residue. This
product was directly used for the 1H NMR measurements.
4.4. X-ray crystallography
The X-ray diffraction data were obtained at ꢀ80(2) °C using a
Rigaku R-axis rapid imaging plate detector with graphite-mono-
chromated Mo K
a radiation (k = 0.71073 Å). A suitable crystal
was mounted with a cryoloop and flash cooled using a cold nitro-
gen gas stream. The data were processed using the Process-Auto
software package [13], and the absorption corrections were ap-
plied using either empirical or numerical methods [14]. The struc-
tures were solved using the direct method employing the SIR2004
or SIR2008 software package [15] or heavy atom method employ-
ing DIRDIF99, and refined on F2 (with all independent reflections)
using the SHELXL97 software package [16]. All of the calculations
were carried out using the CrystalStructure software package
[17]. All the compounds crystallized in cetrosymmetric space
groups. In the X-ray analysis for K[2]0.5CH3OHꢁ4.5H2O, high elec-
tron densities were observed at the other possible site for C9 and
C19 suggesting the existence of the positional disorders. However,
4.3.5. [K(18-crown-6)][2]
A methanol solution (3 mL) of 18-crown-6 (0.054 g, 0.20 mmol)
was added to
a methanol solution (5 mL) of K[2] (0.099 g,
0.21 mmol), followed by stirring for 10 min. The solvent was evap-
orated to dryness. The resulting violet powder was washed with
diethyl ether. Yield: 0.133 g (85%).

R. Mitsuhashi et al. / Inorganica Chimica Acta 399 (2013) 131–137
137
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a
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Crystal data are collected in Table S4.
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The molecular structure of each isomer was energetically min-
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Acknowledgements
This work was partly supported by a Grant-in-Aid for Challeng-
ing Exploratory Research No. 23655052 from the Ministry of Edu-
cation, Culture, Sports, Science, and Technology, Japan.
Appendix A. Supplementary material
Crystal structures of K[1]ꢁCH3OH, PPh4[1] and K[2]ꢁ0.5CH3-
OHꢁ4.5H2O; 1H NMR spectra of PPh4[1], K[2], PPh4[3] and K[4];
UV–Vis absorption spectra of [K(18-crown-6)][2] and PPh4[3];
DFT optimized structures and calculation results for [3]ꢀ and
[4]ꢀ; and X-ray crystallographic information for all of the com-
pounds analyzed in this study are in PDF format. CCDC 822937,
822938, 822940, 822941, 886578 and 886579 contains the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.ica.2013.01.011.
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