Halides of macrocyclic silver(II) complexes: Crystal structures with hydrogen bond network and reaction kinetics of the decomposition

Article abstract of DOI:10.1016/j.ica.2021.120431

A series of silver(II) complexes of 5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) have been synthesized and characterized by X-ray crystallographic analysis and UV–vis absorption spectra. The crystal structure of [AgL(ClO₄)₂] (1), [AgL(NO₃)₂]·CH₃OH (2), [AgL(H₂O)₂]Cl₂ (3), and [AgL(H₂O)₂]Br₂ (4) showed the macrocyclic ligand L to be in the stable trans-III structure with C-methyl groups at equatorial positions. To our knowledge, this is the first report on the single crystal X-ray structural analysis of halides of silver(II) complex. Usually, silver ions form insoluble inorganic halides, but the stabilization of divalent silver ion by L, enabled characterization of the complex both in the solutions and in crystals. UV–vis analysis revealed that all complexes were in the form of [AgL(H₂O)₂]²⁺ in aqueous solution. These complexes in aqueous solution were found to decompose gradually and lose orange color. The decomposition rate constants of these complexes were evaluated as 0.1012, 0.0971, 0.0981, and 0.2104 h^?1 for complexes 1–4, respectively. The decomposition was accelerated by Br^? and I^? anions.

Full text of DOI:10.1016/j.ica.2021.120431

Inorganica Chimica Acta 524 (2021) 120431
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Research paper
Halides of macrocyclic silver(II) complexes: Crystal structures with
hydrogen bond network and reaction kinetics of the decomposition
a
,
*
a
a
b
a
Akinori Honda , Shunta Kakihara , Shuhei Ichimura , Kazuaki Tomono , Mina Matsushita ,
a
a
a
a,*
Rie Yamamoto , Emi Kikuta , Yoshinori Tamaki , Kazuo Miyamura
a
Department of Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
Applied Chemistry Course, Faculty of Science and Engineering, Kanto-gakuin University, 1-50-1 Mutsuura Higashi Kanazawa-ku, Yokohama City, Kanagawa 236-
037, Japan
b
0
A R T I C L E I N F O
A B S T R A C T
Keywords:
A series of silver(II) complexes of 5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetradecane (L) have
been synthesized and characterized by X-ray crystallographic analysis and UV–vis absorption spectra. The crystal
Silver(II)
Tetraaza macrocycle
Crystal structure
Spectroscopic analysis
Coordination chemistry
structure of [AgL(ClO
4
)
2
] (1), [AgL(NO
3
)
2
]⋅CH
3 2 2 2 2 2 2
OH (2), [AgL(H O) ]Cl (3), and [AgL(H O) ]Br (4) showed the
macrocyclic ligand L to be in the stable trans-III structure with C-methyl groups at equatorial positions. To our
knowledge, this is the first report on the single crystal X-ray structural analysis of halides of silver(II) complex.
Usually, silver ions form insoluble inorganic halides, but the stabilization of divalent silver ion by L, enabled
characterization of the complex both in the solutions and in crystals. UV–vis analysis revealed that all complexes
2
+
in aqueous solution. These complexes in aqueous solution were found to
were in the form of [AgL(H
O)
2 2
]
decompose gradually and lose orange color. The decomposition rate constants of these complexes were evaluated
ꢀ 1
as 0.1012, 0.0971, 0.0981, and 0.2104 h for complexes 1–4, respectively. The decomposition was accelerated
ꢀ
ꢀ
by Br and I anions.
1
. Introduction
Transition-metal complexes with synthetic macrocyclic ligands have
when silver(I) salts are mixed with the macrocyclic amines (L) [17].
2
Ag(I) + L ↔ AgL(II) + Ag(0)
been of great interest in recent years [1–5]. There are numerous reports
concerned with the coordination chemistry of substituted derivative of
tetraazamacrocycles, such as the 14-membered cyclam (1,4,8,11-tet-
raazacyclotetradecane) [6–11]. These macrocyclic ligands provide ideal
coordination sites and form stable complexes with various metal ions. In
addition, high oxidation states such as copper(III) [12], gold(III) [13],
ruthenium(IV) [14] are reported to exist more stably by the macrocyclic
effect.
This process occurs when the “bonding cavity” available for a metal
ion in the ligand molecule is large enough for the incorporation of Ag(II),
but too small to form a complex with four Ag(I)–N bonds [18]. In fact, Ag
(I) ion tends to form linear di-coordinated complex. Clarck and Har-
rowfield [19] have examined the disproportionation behavior and
concluded that it is irreversible in acetone and methanol, irreversible to
a great extent in DMF, and practically absent in DMSO and acetonitrile.
This silver(II) complex was isolated and crystallized as [Ag(cyclam)
(ClO ) ] [20], [Ag(tmc)(ClO ) ] (tmc = 1,4,8,11-tetramethyl-1,4,8,11-
One example of stabilization of unusual oxidation states with
macrocyclic ligands is found with silver(II) [15]. Di- and trivalent silver
ions are rather unstable due to the powerful oxidizing nature of these
ions in solution. Although the kinetics and mechanism of the oxidation
of 2-mercaptopyrimidine by square planar macrocyclic tetraaza silver
4
2
4 2
tetraazacyclotetradecane; N-tetramethyl-cyclam) [21], [Ag(tet b)
(ClO ) ] (tet b = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacy-
4
2
clotetradecane) [22]. These complexes are exceptionally stable
compared to silver(II) complexes with nitrogen heterocycles and related
ligands, which are often quite stable in the solid state, but in solution
they are powerful oxidants with little stability.
(
II) complex as an oxidizing agent have been reported [16], the chem-
istry of silver(II) complex of cyclam is still under investigation. Among
such investigations, an interesting reaction, disproportionation occurs
Most of the reported silver(II) macrocyclic complex salts have
*
Corresponding authors.
E-mail addresses: honda-akinori@rs.tus.ac.jp (A. Honda), miyamura@rs.kagu.tus.ac.jp (K. Miyamura).
https://doi.org/10.1016/j.ica.2021.120431
Received 17 March 2021; Received in revised form 26 April 2021; Accepted 26 April 2021
Available online 30 April 2021
0
020-1693/© 2021 Elsevier B.V. All rights reserved.

A. Honda et al.
Inorganica Chimica Acta 524 (2021) 120431
perchlorate as counter anion. Conversely, the complex salts with halides
are hardly formed. Halides are known to react strongly with silver(I),
therefore, silver ions are usually omitted from the complex forming re-
action due to the disproportionation. In this paper, we report the syn-
thesis of four silver(II) (5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-
tetraazacyclotetradecane; L) complex salts with various counter anions,
X-ray diffraction were obtained by slow-evaporation method of aqueous
solution. Calc. for C14
Found: C, 35.59; H, 7.65; N, 11.56%. IR spectrum (KBr pellet, cm ):
3419 (O H, s), 3089 (N H, s), 2962, 2888, 1461 (s), 1419 (s), 1112 (s),
2 4 2
H36AgCl N O : C, 35.68; H, 7.70; N, 11.89%.
ꢀ 1
–
–
ꢀ
1
ꢀ 1
1028 (s), 762 (m). UV–vis measurement: λmax/nm 354 (
ε
/L mol cm
3
9.12 × 10 ).
ꢀ ꢀ ꢀ ꢀ
including halides (ClO , NO , Cl and Br ). Furthermore, we investi-
4 3
gated the characteristic of these complex salts in crystal structure and
the influence of counter anions on decomposition reaction in aqueous
solution. We have reported the synthesis of L and its nickel(II) complex
by non-template reaction [23]. Additionally, L has two C-methyl groups
and two N-methyl groups so that this ligand L can be regarded as an
intermediate of cyclam (no N-methyl) and tmc (four N-methyl groups).
Therefore, the variations in structural and spectral data depending on
the central metal ions or ligands were investigated.
2.1.4. Diaqua(5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-
2 2 2
tetraazacyclotetradecane)silver(II) dibromide [AgL(H O) ]Br (4)
Complex 4 was synthesized by a similar procedure to 3 using bro-
mide form of AG3-X4A. Crude yield was 4.7% for complexes 4. Calc. for
C
14
H
36AgBr
6.56; N, 10.27%. IR spectrum (KBr pellet, cm ): 3389 (O
(N H, s), 2963 (m), 2875 (m), 1459 (m), 1419 (m), 1110 (m), 1024 (m),
2 4 2
N O : C, 30.02; H, 6.48; N, 10.00%. Found: C, 30.06; H,
ꢀ
1
–
H, s), 3101
–
ꢀ
1
ꢀ 1
763 (w). UV–vis measurement: λmax/nm 354 (
ε/L mol cm 8.37 ×
3
1
0 ).
2
. Experimental
2
.2. Measurement
All chemicals were of reagent grade and used without further puri-
fication. Macrocyclic tetramine L and its precursor, diaminodi-imine L′
IR spectra were measured with a JASCO FT/IR-410 spectropho-
(
L′ = 1,5,8,12-tetramethyl-1,4,8,11-tetraazacyclotetrdeca-4,11-diene)
tometer. Elemental analyses were performed by a Perkin-Elmer 2400II
were synthesized according to the literature, and used as ligands [24].
Perchlorates are potentially explosive in general, and the experiments
should be conducted in a small scale.
Analyzer. UV–vis-NIR spectra were recorded with a JASCO V-570 UV/
ꢀ
4
VIS/NIR spectrophotometer, with sample concentration of 1.0 × 10
ꢀ
1
mol L (aqueous solution). In the case of 3 and 4, single crystal suitable
for X-ray analysis could only be obtained by first crystallization. Usual
re-crystallization procedure led to partial decomposition of Ag(II)
complex.
2
2
.1. Reagents and chemicals
.1.1. (5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-
tetraazacyclotetradecane)silver(II) diperchlorate [AgL(ClO
4
)
2
] (1)
2.3. X-ray crystallography
Silver(I) perchlorate (1.617 g, 7.8 mmol) and ligand L (0.974 g, 3.8
mmol) were stirred in water (10 mL) for 2–3 h. Silver metal gradually
deposited on flask surface and at the same time the solution changed
into orange color. This mixture 1 was filtered in order to remove the
precipitated metallic silver and the filtrate was cooled in a refrigerator.
The orange precipitates thus formed were collected by filtration. The
crude product of 1 was purified by recrystallization from acetonitrile
and ethanol to give crystal suitable for X-ray crystallographic analysis.
Single crystal was mounted on a glass capillary. Intensity data were
collected by a Bruker AXS SMART diffractometer equipped with CCD
area detector and MoKα (λ = 0.71073 Å) radiation. The structures of 1–4
were solved and refined with the SHELX-97 [25] and SHELXL-2016 [26]
using direct method and expanded using Fourier techniques. All non-
hydrogen atoms were refined anisotropically by the full-matrix least-
square method. Hydrogen atoms bound to oxygen or nitrogen atoms
were found in a difference Fourier map, and their position and isotropic
thermal parameters were refined. All H atoms bound to carbon atoms
were placed at idealized positions and refined using a riding model.
Selected crystallographic data are summarized in Table 1. Crystallo-
graphic data have been deposited on Cambridge Crystallographic Data
Centre: Deposit numbers CCDC-763972–763975 for compounds 1–4,
respectively. Copies of the data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cambridge, CB2
1EZ, UK; FAX: +44 1223 336033; mail: deposit@ccdc.cam.ac.uk).
2 4 8
Yields: 0.182 g, 8.5%. Calc. for C14H32AgCl N O : C, 29.86; H, 5.73; N,
9
.95%. Found: C, 30.01; H, 5.64; N, 9.89%. IR spectrum (KBr pellet,
ꢀ
1
cm ): 3236 (N
–
H, s), 2979 (w), 2818 (w), 1467 (m), 1417 (m), 1086
ꢀ 1
ꢀ 1
(
s), 625 (s). UV–vis measurement: λmax/nm 354 (
ε/L mol cm 1.04 ×
4
1
0 ).
2
.1.2. (5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-
tetraazacyclotetradecane)silver(II) dinitrate methanol monosolvate [AgL
NO OH (2)
]⋅CH
Silver(I) nitrate (1.308 g, 7.7 mmol) and ligand L (0.974 g, 3.8 mmol)
(
3
)
2
3
were stirred in water (10 mL) for 2–3 h. This mixture was filtered in
order to remove the precipitated metallic silver, and the solvent of
filtrate was removed under reduced pressure. The crude orange pre-
cipitate of 2 was purified by recrystallization from hot methanol and to
give crystal suitable for X-ray crystallographic analysis. Yields: 0.154 g
3. Results and discussion
3.1. Synthesis and structural analysis
7
.8%. Calc. for C15
4.92; H, 6.77; N, 16.13%. IR spectrum (KBr pellet, cm ): 3447 (O
H, s), 2973 (s), 2874 (w), 2372 (w), 1749 (w), 1630 (s),
H
36AgN
6
O
7
: C, 34.62; H, 6.97; N, 16.15%. Found: C,
In our previous paper [23], we have reported convenient and se-
lective synthetic paths to obtain isomers of nickel(II) complex of L with
either C-equatorial and C-axial configurations. By the reduction of
diamino-di-imine after complexation led to C-equatorial isomer, while
reducing diamino-di-imine ligand before complexation gave C-axial
isomer. According to our papers [23,24,27], nickel(II) complex of L with
C-equatorial configuration adopted six-coordinated octahedral geome-
try with two water molecules occupying two apical sites, while the
apical sites of nickel(II) complex of L with C-axial configuration were
vacant resulting in four coordinate square-planar geometry. Further-
more, copper(II) complex of L with C-axial configuration adopted five
coordinated square-pyramidal geometry with one water molecule
occupying one of two apical sites. In the silver complexes, only C-
equatorial isomer was obtained even the complexation was carried out
ꢀ 1
3
–
H,
s), 3128 (N
–
ꢀ
1
ꢀ 1
1
459 (s). UV–vis measurement: λmax/nm 354 (ε/L mol cm 8.04 ×
3
1
0 ).
2
.1.3. Diaqua(5RS,12SR-1,5,8,12-tetramethyl-1,4,8,11-
2 2
O) ]Cl (3)
tetraazacyclotetradecane)silver(II) dichloride [AgL(H
2
Orange complex salt 3 was obtained by the exchanging counter
anion of 1. Counter anion was exchanged from perchlorate to chloride
ion by anion-exchange resin (AG3-X4A). Crude yield was 5.2% for
complexes 3. As noted below, single crystals of 3 and 4 for X-ray analysis
were difficult to be recrystallized because of the degradation of com-
plexes ending up with silver deposition. The single crystals suitable for
2

A. Honda et al.
Inorganica Chimica Acta 524 (2021) 120431
Table 1
Crystallographic data for 1–4.
Complexes
1
2
3
4
Formula
C
14
H
32AgCl
N
2 4
O
8
C
15
H
36AgN
O
6 7
C
14
H
36AgCl
2
4
N O
2
C
14
H
36AgBr
2 4 2
N O
Formula weight
Crystal Size (mm)
Temperature (K)
Crystal System
Space Group
a (Å)
563.21
520.37
471.24
560.16
0.14 × 0.13 × 0.10
297(1)
0.40 × 0.25 × 0.10
297(1)
0.11 × 0.11 × 0.07
297(1)
0.25 × 0.24 × 0.12
297(1)
Triclinic
P-1
Monoclinic
P2(1)/n
Monoclinic
P2(1)/n
Monoclinic
P2(1)/n
8.326(2)
8.725(2)
8.796(2)
76.118(4)
70.144(4)
69.486(4)
557.6(2)
1
11.127(2)
15.175(3)
13.013(2)
9.1318(13)
11.8882(16)
9.6286(13)
9.3559(8)
b (Å)
12.1708(11)
9.7373(9)
c (Å)
◦
α
( )
◦
β ( )
94.159(2)
107.454(2)
107.7800(10)
◦
γ ( )
3
Volume (Å )
2191.5(7)
4
997.2(2)
2
1055.82(16)
2
Z
ꢀ
3
D
c
(Mg/m
)
1.677
1.577
0.967
1.042
0.0570
0.1475
1.569
1.292
0.989
0.0353
0.0841
1.762
ꢀ
1
µ (mm
GOF
R1
)
1.190
4.752
1.171
0.959
0.0527
0.0239
0.0543
wR2
0.1483
after the reduction. The obtained silver complexes were relatively stable
in the solid state.
donor atoms occupied the planar coordination sites. The configuration
of the cyclam moiety of L was stable trans-III where all four chelate rings
were in the stable skew (five-membered ring) or chair (six-membered
ring) conformations. Note that two C-methyl groups adopted equatorial
configuration and two N-methyl groups adopted axial configuration.
Silver(II) ion was coordinated by four nitrogen atoms of L, and two
molecules occupied the apical sites to adopt six coordinated distorted
Fig. 1 shows the ORTEP [28] drawings with atom numbering scheme
of 1–4. These structures included solvent molecules except for 1. The
ꢀ
complex salt with I was not obtained because formulation of AgI is
faster than stabilization of complex salt. Macrocyclic tetramine L coor-
dinated to silver(II) as a quadridentate ligand, and its four nitrogen-
Fig. 1. ORTEP views of (a) 1, (b) 2, (c) 3, and (d) 4 showing 30% probability ellipsoids with atom numbering scheme. H atoms were omitted for clarity.
3

A. Honda et al.
Inorganica Chimica Acta 524 (2021) 120431
octahedral geometry as a whole. Selected bond lengths and bond angles
are listed in Table 2. The bond length Ag–O in 1 was shorter than that in
the complexes 2–4. Ag–N(1) (N(1) = secondary amino groups) bond
length tended to be shorter than Ag–N(2) (N(2) = tertiary amino groups)
in all complex (1–4).
In complex 1, silver atom on the inversion center was coordinated by
four nitrogen atoms of L in planar form, and two perchlorate ions were
weakly coordinated to two apical sites. The crystal packing is shown in
Fig. 2a. Amine hydrogen atoms are found to form hydrogen bond with
perchlorate ions, as shown in Fig. 3a, and related parameters are tabu-
lated in Table 3. N
–
H⋯O hydrogen bonds and O–Ag–O bonds linked
the Ag(II) complexes in 1-D strand (see Figs. 3a and 2a). The average of
Ag–N bond lengths was 2.161(3) Å, which was in good agreement but
was almost intermediate to the average values of 2.158(2) Å in [Ag(II)
(
4 2 4 2
cyclam)](ClO ) [20] and 2.195(3) Å in [Ag(II)(tmc)](ClO ) [21].
Substitution by N-methyl group seemed to elongate the Ag–N distance.
Ag–O(1) bond length 2.728(5) Å for coordinated perchlorate ion was
slightly shorter than the corresponding distances in [Ag(cyclam)
Fig. 2. Crystal structures of (a) 1 and (b) 2. The dashed lines indicate weak
coordination of apical ligands to silver. All H atoms are omitted for clarity.
(
4 2 4 2
ClO ) ] 2.788(2) Å [20] and [Ag(tmc)(ClO ) ] 2.889(4) Å [21], indi-
cating stronger coordination of perchlorate in complex 1 than that in
other complexes.
In complex 2, on the other hand, the asymmetric unit contained one
crystallographically independent [AgL]2 cation, two nitrate anions and
one methanol as crystal solvent. X-ray analysis has revealed that the
crystal structure of 2 consists of 1-D zigzag chains (see Fig. 2b) of
+
2
+
ꢀ
[
AgL] bridged by one of the two NO . Ag(II) ion was six-coordinate,
3
Table 2
Selected bond lengths [Å] and angles [ ].
◦
[
AgL(ClO ] (1)
4 2
)
Bond lengths
Ag1–N1
Ag1–O1
2.138(5)
2.728(5)
Ag1–N2
2.182(5)
Fig. 3. Hydrogen bonded network of (a) 1 and (b) 2 between complexes and
ꢀ
ꢀ
counter anions (ClO
hydrogen bonds.
4
or non-coordinated NO
3
). The dashed lines indicate N⋯O
Bond angles
N1–Ag1–N2
Ag1–N2–C5
N2–Ag1–O1
i
94.3(2)
115.8(4)
91.9(2)
N1–Ag1–N2
85.7(2)
84.5(2)
N1–Ag1–O1
Table 3
[
AgL(NO
3
2 3
) ]⋅CH OH (2)
Hydrogen bonding parameters for [AgL(ClO
4
)
2
] (1), [AgL(NO
3
)
2
3
]⋅CH OH (2),
Bond lengths
Ag1–N1
Ag1–N3
Ag1–O1
[AgL(H
2
O)
2
]Cl
2 2 2 2
(3), and [AgL(H O) ]Br (4).
2.162(4)
2.166(4)
2.917(5)
Ag1–N2
Ag1–N4
2.168(3)
2.169(3)
2.964(4)
D–H⋯A
H⋯A [Å]
D⋯A [Å]
D–H⋯A [◦]
ii
i
Ag1–O3
1
2
N1–H1⋯O2i
N1–H1⋯O4
2.56(8)
2.37(8)
3.209(8)
3.168(9)
134
158
Bond angles
N1–Ag1–N2
Ag1–N2–C5
N2–Ag1–O1
ii
N1–H1⋯O4
N3–H3⋯O5
N3–H3⋯O6
O7–H7⋯O1
O7–H7⋯O3
2.13(5)
2.42(5)
2.33(5)
2.41(3)
2.30(3)
2.863(6)
3.261(7)
3.010(6)
3.175(9)
3.038(8)
150
164
136
155
150
95.06(15)
114.7(3)
90.06(14)
N2–Ag1–N3
N1–Ag1–O1
85.35(14)
98.16(17)
[
2 2 2
AgL(H O) ]Cl (3)
Bond lengths
Ag1–N1
3
4
N1–H1⋯Cl1
O1–H2⋯Cl1
O1–H3⋯Cl1
2.29
3.265(3)
3.182(3)
3.222(4)
177
160
165
2.164(3)
2.938(3)
Ag1–N2
2.181(3)
2.41(3)
2.41(2)
iii
Ag1–O1
N1–H1⋯Br1
O1–H2⋯Br1
O1–H3⋯Br1
2.43
3.411(19)
3.292(3)
3.331(3)
177
157
173
Bond angles
N1–Ag1–N2
Ag1–N2–C5
N2–Ag1–O1
2.51(2)
2.49(19)
iii
95.14(10)
114.9 (2)
94.50(10)
N1–Ag1–N2
N1–Ag1–O1
84.86(10)
90.76(10)
iv
Symmetry codes: [i] 1 ꢀ x, 2 ꢀ y, 1 ꢀ z; [ii] 3/2 ꢀ x, 1/2 + y, 3/2 ꢀ z; [iii] ꢀ 1/2
x, 3/2 ꢀ y, ꢀ 1/2 + z; [iv] 1/2 + x, 3/2 ꢀ y, 1/2 + z.
+
[
2 2 2
AgL(H O) ]Br (4)
Bond lengths
Ag1–N1
complexed with four nitrogen atoms of L and two different oxygen
atoms (O(1) and O(3)) of nitrate anions at two apical positions. Four
Ag–N bond lengths of 2 were almost the same distance in the range of
2.162–2.169 Å. Ag–N(1) bond length tended to be shorter than Ag–N(2)
in all complex (1–4). However, the elongation by N-methyl substitution
in 2 was small compared with other salts. In this crystal, one of the two
nitrate anions was not coordinated directly to Ag(II). The closest dis-
tance between oxygen atom (O(5)) of non-coordinated nitrate and silver
2.159(2)
2.984(2)
Ag1–N2
2.184(17)
Ag1–O1
Bond angles
N1–Ag1–N2
Ag1–N2–C5
N2–Ag1–O1
iv
95.52(7)
114.40(14)
95.70(7)
N1–Ag1–N2
N1–Ag1–O1
84.48(7)
89.83(7)
Symmetry codes: (i) ꢀ x, 2 ꢀ y, 1 ꢀ z; (ii) 3/2 ꢀ x, ꢀ 1/2 + y, 3/2 ꢀ z; (iii) 1 ꢀ x,
ꢀ y, 1 ꢀ z; (iv) 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
1
4

A. Honda et al.
Inorganica Chimica Acta 524 (2021) 120431
ꢀ
ꢀ
was 4.394 Å. Three N
–
H⋯O hydrogen bonds between amino hydrogen
Cl or Br ) hydrogen bonds of 3 and 4 are tabulated in Table 3. The
parameters of N
H⋯Cl hydrogen bonds were almost the same between
3, Cu(II) ([CuL(H O) ]Cl ) [27,31], and Ni(II) ([NiL(H O) ]Cl ) [24],
although the IR peak of each v(N H) were found to be different. The v
(N H) bands in IR spectra of Ag(II), Cu(II), and Ni(II) complexes were
3089, 3090, and 3137 cm respectively. Conversely, both the average
O⋯Cl distance and v(O H) band in the IR spectra were different be-
tween [AgL(H O) ]Cl 3, [CuL(H O) ]Cl , and [NiL(H O) ]Cl : 3.202 Å
of L and non-coordinated nitrate ion evidenced by IR spectra were
–
2
ꢀ
1
observed (Fig. 3b). For 2, v(N
–
H) appeared at about 3128 cm , which
2
2
2
2
2
ꢀ 1
ꢀ 1
was about 100 cm lower than 3236 cm observed for 1. Additionally,
–
O
–
H⋯O hydrogen bonds were observed between non-coordinate ni-
–
ꢀ
1
trate and methanol of crystal solvent. Thus, we concluded that the small
deviation of Ag–N bond lengths in 2 was brought about by the presence
of the three strong hydrogen bond networks between silver complex and
counter anion or the effect of packing structure including the hydrogen
bond networks. In contrast, Ag–O bond lengths 2.917(5) and 2.964(4) Å
–
2
2
2
2
ꢀ 1
2
2
2
2
2
ꢀ
1
ꢀ 1
(3419 cm ), 3.174 Å (3355 cm ), and 3.188 Å (3301 cm ), respec-
ꢀ
tively. These results indicate that Cl is bound strongly to N
–
than to O H in silver(II) complex.
–
H rather
for coordinated nitrate ions were much longer than 1. In the case of 2,
ꢀ
apical sites NO
3
were also stabilized by hydrogen bond between
ꢀ
methanol and NO
3
, causing the longer Ag–O length. In fact, the corre-
sponding distance in [Ag(tet a)(NO
3
.2. UV–vis investigation
The kinetic stability of Ag(II) complex was studied in aqueous solu-
3
)
2
] (tet a = meso-5,5,7,12,12,14-
hexamethyl-1,4,8,11-tetraazacyclotetradecane) [29], which is not
include crystal solvent, is 2.807(4) Å, shorter than that in 2.
tion by monitoring the absorbance change at wavelength of 250–500
nm. UV–vis spectral change of 1 and 4 in water (1.0 × 10 mol L ) are
shown in Fig. 6a and b. The spectra of 2 and 3 were similar to that of 1
Crystals of 3 and 4 were found to be almost isomorphous. Silver(II)
ion was surrounded by four nitrogen atoms of L and two oxygen atoms of
the two water molecules to adopt six-coordinated octahedral geometry
ꢀ 4
ꢀ 1
(
Fig. S1a and b). One strong peak at ca. 354 nm and a shoulder peak at
as a whole. Furthermore, Jahn-Teller distortion due to the weak coor-
dination to axial position, a characteristic of d9 system, was observed.
ca. 280 nm were observed. Note that the UV–vis spectra of these com-
plexes were almost the same at 0 h, and the absorption maxima did not
depend on the counter anion. This implies that all complexes are in the
Ag–O(1) bond length (2.938(3) Å in chloride salt (3) and 2.984(2) Å in
bromide one (4)) for coordinated water molecules were shorter than
2
+
form of [AgL(H
2
2
O) ]
in aqueous solution. Estimating from the value of
3
.24 Å, the sum of van der Waals radii. It was interesting to note that
3
ꢀ 1
ꢀ 1
ε
(order of 10 L mol cm ), the absorption peaks were assigned as CT
there were no particular interactions between silver and halide ions. The
closest distances between silver and halide ions were 4.379 Å in chloride
salt and 4.500 Å in bromide one. Similar situation was reported in
transition. These aqueous solutions of Ag(II) complex were found to
decolorate gradually. The color of the solution was yellow initially, but
disappeared after a couple of days. The free Ag metals were deposited in
[
Ag
2
6
(TSCZ) ]Cl
2
[TSCZ = thiosemicarbazide; SC(NH
2
)NHNH
2
] complex
9
ꢀ
the reaction vessel. This means that colored d Ag(II) turned into
where silver ion was monovalent [30]. In [Ag
2
(TSCZ)
6
]Cl
2
, Cl ion did
colorless d10 Ag(I) species, and then to metallic Ag(0). Macrocyclic
ligand L was probably oxidized [17].
not interact directly with the central silver but rather formed N
–
H⋯Cl
hydrogen bonds with TSCZ ligands [30]. Apical coordination of water
molecule was weak in 3, and the Ag–O bond distances were clearly
longer than those of the perchlorate ion (2.728(5) Å) in 1. As shown in
our previous report [23,24,27], the use of nickel(II) as central metal ion
resulted in opposite result. The Ni–O bond length of chloride salt (2.210
Å) [24] was shorter than that of perchlorate salt (2.887 Å) [23]. How-
ever, in the case of copper(II) complexes, Cu–O bond length of chloride
salt (2.692 Å) [27] was almost the same to that of the perchlorate salt
Fig. 7 shows the spectral change of complexes 1–4 at the maximum
absorption wavelength (354 nm) with respect to time. The measurement
was finished when the value of absorbance stopped changing. Assuming
that this decay reaction is the first order reaction, the rate constant k is
represented as follows:
(
)
C
ln
= ꢀ kt
C
0
(
2.696 Å) [31].
Regarding the intermolecular interaction, two complexes 3 and 4
where C is the concentration at time t and C is the concentration at 0 h,
0
ꢀ
ꢀ
together with halide ions (Cl or Br ) and water were found to construct
a network of hydrogen bonds. The crystal packing and hydrogen bond
network of 3 and 4 are shown in Figs. 4 and 5. Two hydrogen atoms of a
water molecule were involved in hydrogen bonding, where one atom is
and k is the first-order rate constant. Fig. 7 shows that 1–3 decomposes
by first-order reaction but the decomposition behavior of 4 changes after
◦
6 h. The rate constants k for the decay reaction at 25 C were estimated
ꢀ 1
to be 0.1012, 0.0971, and 0.0981 h for complexes 1–3, respectively.
Since the decomposition rate is almost the same for 1–3, anions are not
involved in the decomposition of the Ag(II) complex. However, the rate
of decomposition of 4 was significantly accelerated, and the solution lost
color in only 12 h. In addition, the precipitation other than black Ag(0)
particles was often observed. The precipitation is considered to be AgBr.
As will be described later, silver halides are very insoluble in water,
ꢀ
ꢀ
bound to the halide ion (Cl or Br ), and another one to the symmetry
related halide ion. Amino hydrogen atoms were also hydrogen bound to
the halide ion. The parameters related to N
H⋯X and O H⋯X (X =
– –
ꢀ 4
owing to their lower solubility (AgCl; 1.92 × 10 g/100 mL and AgBr;
ꢀ 5
1
.32 × 10 g/100 mL) than that (525 g/100 mL and 216 g/100 mL) of
AgClO and AgNO . The estimated rate constants can be correlated with
the solubilities.
4
3
The reason for the remarkably fast decomposition rate of 4 can be
explained as follows. First, Ag(II)L is decomposed into Ag(I) ion and L in
aqueous solution by irradiation of UV–vis light in the UV–vis measure-
ment. The ligand L may be subject to oxidation. Then, the oxidized
macrocyclic ligand reacts with Ag(I) to reform Ag(II) complex together
0
with Ag by disproportionation. In the case of 4, AgBr easily precipitated
and removed from the solution due to the low solubility to water,
resulting in the decrease in Ag(I) ion and preventing the dispropor-
tionation. According to the study on the decomposition of silver halide,
the stability of AgCl is lower than that of AgBr and AgI [32]. Thus, the
regeneration of Ag(II) complex tends to be occurred in 3, but depressed
Fig. 4. Crystal structures of (a) 3 and (b) 4. The dashed lines indicate weak
coordination of water molecules to silver at apical position. H atoms were
omitted for clarity.
ꢀ
ꢀ
ꢀ
in 4. UV–vis spectra of 1 with NaX (X = Cl , Br , I ) were recorded to
5

A. Honda et al.
Inorganica Chimica Acta 524 (2021) 120431
ꢀ
ꢀ
Fig. 5. Hydrogen bonded network of (a) 3 and (b) 4 among complexes, waters, and counter anions (Cl or Br ). Orange dashed lines indicate N
–
H⋯halide hydrogen
–
bonds, and Blue ones indicate O H⋯halide hydrogen bonds.
Fig. 7. Plots of ln(C/C
0
) versus t taken for the decay reaction of 1–4 at 25 ◦C.
Fig. 6. Time dependent change in UV–vis spectra of (a) [AgL(ClO
b) [AgL(H O) ]Br (4). Spectra are taken at an interval of 3 h until change in
the spectra disappeared.
4 2
) ] (1) and
(
2
2
2
investigate the effect of halogens to decomposition of Ag(II)L complex
ꢀ 4
ꢀ 1
ꢀ
ꢀ
ꢀ
(
Fig. 8). The concentration of 1 and NaX was 1.0 × 10 mol L
.
Fig. 8. Decomposition rate of 1 with NaX (X = Cl , Br , I ).
Decomposition rate of 1 and NaX mixed solution depended on halogens
ꢀ
ꢀ
ꢀ
(
I
> Br > Cl ). This may be relative to HSAB rule. Similarly to the case
CH
3
OH (2), [AgL(H O) ]Cl (3), and [AgL(H O) ]Br (4) adopted the
2
2
2
2
2
2
of 4, AgI can inhibit the regeneration of Ag(II)L. These results are also
stable trans-III structure, and C-methyl groups of L adopted equatorial
configuration. The single crystals of halides of silver(II) complex were
obtained due to the stabilization by macrocyclic effect. Additionally,
hydrogen bond network between the complexes and counter anions
stabilized the crystal structures. In addition to the crystal structural
analysis, the characteristic of the complexes in solution was investi-
gated. The UV–vis spectra revealed that all complexes 1–4 were in the
ꢀ
supported by standard oxidation-reduction potential. In the case of Br
ꢀ
ꢀ
and I , Ag(II)L gets electron from Br
Ag(II)L receives electron from H
2
or I
2
. However, in the case of Cl ,
ꢀ
2
O because Cl
2
/Cl + 1.3595 V > O
2
/
H
2
O + 1.229 V. In summary, the decomposition rate depends on the
stability of AgX precipitation and the concentration of Ag(I) cation and
ꢀ
halide anion (X ) in the solution.
2
+
in aqueous solution, but the decomposition rate
form of [AgL(H
2
O)
2
]
4
. Conclusion
depended on the counter anions. Especially, bromide and iodide ions
accelerated the decomposition owing to the lower solubility of AgBr and
AgI.
The single crystal structures of silver(II) macrocyclic complexes were
investigated. The macrocyclic ligand of [AgL(ClO
4
)
2
] (1), [AgL(NO
3
)
2
]⋅
6

A. Honda et al.
Inorganica Chimica Acta 524 (2021) 120431
CRediT authorship contribution statement
[6] A. Zhanaidarova, C.E. Moore, M. Gembicky, C.P. Kubiak, Chem. Commun. 54
(
2018) 4116–4119.
[
7] M. Paúrov a´ , T. David, I. Císarov a´ , P. Lubal, P. Hermann, J. Kotek, New J. Chem. 42
Akinori Honda: Formal analysis, Investigation, Writing - original
draft, Visualization. Shunta Kakihara: Formal analysis, Investigation,
Visualization. Shuhei Ichimura: Validation, Investigation. Kazuaki
Tomono: Validation, Investigation. Mina Matsushita: Validation,
Investigation. Rie Yamamoto: Investigation. Emi Kikuta: Investiga-
tion. Yoshinori Tamaki: Investigation. Kazuo Miyamura: Conceptu-
alization, Resources, Supervision.
(
2018) (1929) 11908–11911.
[8] T.J. Hubin, A.N. Walker, D.J. Davilla, T.N.C. Freeman, B.M. Epley, T.R. Hasley, P.
N.A. Amoyaw, S. Jain, S.J. Archibald, T.J. Prior, J.A. Krause, A.G. Oliver, B.
L. Tekwani, M.O.F. Khan, Polyhedron 163 (2019) 42–53.
[
9] S.F. Robey, B.L. Mash, T. Jiang, M. Zeller, T. Ren, Polyhedron 170 (2019) 471–475.
[10] E.V. Basiuk, C.C.O. Bravo, V.G. Vidales, M. Kakazey, V.A. Basiuk, J. Mater. Sci. 55
(
2020) 5364–5377.
[
11] S.M. Abozeid, D. Asik, G.E. Sokolow, J.F. Lovell, A.Y. Nazarenko, J.R. Morrow,
Angew. Chem. Int. Ed. 59 (2020) 12093–12097.
[
[
12] D.C. Olson, J. Vasilevskis, Inorg. Chem. 10 (1971) 463–470.
13] E. Kimura, Y. Kurogi, T. Koike, M. Shionoya, Y. Iitaka, J. Coord. Chem. 28 (1993)
33–49.
Declaration of Competing Interest
[
[
14] Chi-Ming Che, Kwok-Yin Wong, Chung-Kwong Poon, Inorg. Chem. 25 (1986)
1
809–1813.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
15] E.K. Barefield, M.T. Mocella, Inorg. Chem. 12 (1973) 2829–2832.
[16] R. Trismitro, H.N. Po, J. Coord. Chem. 17 (1988) 1–14.
[
[
17] M.O. Kestner, A.L. Allred, J. Am. Chem. Soc. 94 (1972) 7189–7190.
18] B. Olejniczak, J. Dziegiee, A. Grzejdziak, Monatshefte für Chemie 128 (1997)
1
3–21.
Appendix A. Supplementary data
[19] I.J. Clark, J.M. Harrowfield, Inorg. Chem. 23 (1984) 3740–3745.
[
[
[
20] T. Ito, H. Ito, K. Toriumi, Chem. Lett. 10 (1981) 1101–1104.
21] H.N. Po, E. Brinkman, Acta Crystllogr. C 47 (1991) 2310–2312.
22] H.N. Po, Shu-Chin Shen, Acta Crystallogr. C 49 (1993) 1914–1916.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120431.
[23] K. Miyamura, M. Kohzuki, R. Narushima, M. Saburi, Y. Gohshi, J. Chem. Soc.,
Dalton Trans. 12 (1987) 3093–3098.
[
24] H. Kawamura, K. Ono, K. Tomono, K. Miyamura, Inorg. Chim. Acta 362 (2009)
References
4
804–4808.
[
25] G.M. Sheldrick, Acta Crystalogr., A 64 (2008) 112–122.
[
[
1] H. Shi, J. Xie, W.W.Y. Lam, W.-L. Man, C.-K. Mak, S.-M. Yiu, H.K. Lee, T.-C. Lau,
Chem. Eur. J. 25 (2019) 12895–12899.
[26] G.M. Sheldrick, Acta Crystallogr., C 71 (2015) 3–8.
[27] K. Tomono, E. Otani, R. Ikwda, Y. Sonwta, N. Saita, K. Miyamura, J. Incl. Phenom.
Macrocycl. Chem. 70 (2011) 241–247.
2] V. Pirovano, A. Caselli, A. Colombo, C. Dragonetti, M. Giannangeli, E. Rossi,
E. Brambilla, ChemCatChem 12 (2020) 5250–5255.
[28] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[
[
3] S. Ghosh, S. Selvamani, S. Mehta, A. Mondal, Dalton Trans. 49 (2020) 9208–9212.
4] N.D. Savi ´c , B.B. Petkovi ´c , S. Vojnovic, M. Mojicevic, H. Wadepohl, K. Olaifa,
E. Marsili, J.N. Runic, M.I. Djuran, B.Đ. Gli ˇs i ´c , Dalton Trans. 49 (2020)
[29] K.B. Mertes, Inorg. Chem. 17 (1978) 49–52.
[30] A.C. Bonamartini, G.F. Gasparri, M.F. Belicchi, M. Nardelli, Acta. Crystallogr. C 43
(1987) 407–413.
1
0880–10894.
[31] T. Lu, S. Lin, H. Aneetha, K. Panneerselvam, C. Chung, J. Chem. Soc., Dalton Trans.
19 (1999) 3385–3391.
[
5] P.G. Barros, D. Moonshiram, M.G. Sepulcre, P. Pelosin, C.G. Suri n˜ ach, J.
B. Buchholz, A. Llobet, J. Am. Chem. Soc. 142 (2020) 17434–17446.
[32] D. Hayes, K.H. Schmidt, D. Meisel, J. Phys. Chem. 93 (1989) 6100–6109.
7