Covalent and ionic Cu(II) complexes with cyclam and substituted benzoato ligands: Structural, thermal, redox and mesomorphic properties

Article abstract of DOI:10.1080/00958972.2016.1147032

A covalent mononuclear complex, [Cu(p-HOC₆H₄COO)₂(cyclam)] (1), and two ionic mononuclear complexes, [Cu(cyclam)(H₂O)₂](p-CH₃OC₆H₄COO)₂ (2) and [Cu(cyclam)(

Full text of DOI:10.1080/00958972.2016.1147032

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Covalent and ionic Cu(II) complexes with cyclam
and substituted benzoato ligands: structural,
thermal, redox and mesomorphic properties
Norbani Abdullah, Zainudin Arifin, Edward R. T. Tiekink, Naima Sharmin, Nur
Syamimi Ahmad Tajidi & Siti Amira Mat Hussin
To cite this article: Norbani Abdullah, Zainudin Arifin, Edward R. T. Tiekink, Naima Sharmin,
Nur Syamimi Ahmad Tajidi & Siti Amira Mat Hussin (2016): Covalent and ionic Cu(II) complexes
with cyclam and substituted benzoato ligands: structural, thermal, redox and mesomorphic
properties, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2016.1147032
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1147032
Published online: 29 Feb 2016.
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Date: 03 March 2016, At: 13:51

Journal of Coordination Chemistry, 2016
ꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958972.2016.1147032
ꢀ
Covalent and ionic Cu(II) complexes with cyclam and substituted
benzoato ligands: structural, thermal, redox and mesomorphic
properties
Norbani Abdullah, Zainudin Arifin, Edward R. T. Tiekink, Naima Sharmin, Nur Syamimi
Ahmad Tajidi and Siti Amira Mat Hussin
scꢄꢆꢇcꢆ fꢈcꢉꢊꢁꢋ, Cꢀꢆꢌꢄꢍꢁꢅꢋ dꢆpꢈꢅꢁꢌꢆꢇꢁ, uꢇꢄvꢆꢅꢍꢄꢁꢄ mꢈꢊꢈꢋꢈ, Kꢉꢈꢊꢈ lꢉꢌpꢉꢅ, mꢈꢊꢈꢋꢍꢄꢈ
ABSTRACT
ARTICLE HISTORY
rꢆcꢆꢄvꢆꢂ 6 mꢈꢅcꢀ 2015
accꢆpꢁꢆꢂ 31 dꢆcꢆꢌbꢆꢅ 2015
A covalent mononuclear complex, [Cu(p–HOC H COO) (cyclam)] (1), and
6
4
2
two ionic mononuclear complexes, [Cu(cyclam)(H O) ](p–CH OC H COO)
2
2
3
6
4
2
(
2) and [Cu(cyclam)(H O) ](p–CH (CH ) OC H COO) ·H O (3), were
2 2 3 2 15 6 4 2 2
KEYWORDS
formed from reaction of cyclam with [Cu (p–HOC H COO) (H O) ], [Cu (p–
2
6
4
4
2
2
2
Cꢉ(ii); cꢋcꢊꢈꢌ; ꢍꢉbꢍꢁꢄꢁꢉꢁꢆꢂ
bꢆꢇzꢃꢈꢁꢆꢍ; cꢅꢋꢍꢁꢈꢊꢍ; ꢅꢆꢂꢃx;
ꢁꢀꢆꢅꢌꢈꢊ; ꢌꢆꢍꢃꢌꢃꢅpꢀꢄꢍꢌ
CH OC H COO) (H O) ]
and
[Cu (p-CH (CH ) OC H COO) (H O) ],
3
6
4
4
2
2
2 3 2 15 6 4 4 2 2
respectively. These complexes were isolated as purple crystals with molecular
structures showing distorted octahedral N O geometry. Complexes 1 and 2
4
2
were irreversibly reduced to Cu(I) and oxidized to Cu(III), while 3 was redox
inactive. Complex 2 reacted with N-(hexadecyl)isonicotinamide (L) to form
[
Cu(cyclam)(L) ](p–CH OC H COO) (4). These complexes were thermally
2 3 6 4 2
stable (Tdec > 200 °C for 1–3 and 174 °C for 4). Complexes 3 and 4 behaved
as ionic liquids (melting temperatures lower than 100 °C) and exhibited
mesomorphism.
CONTACT nꢃꢅbꢈꢇꢄ abꢂꢉꢊꢊꢈꢀ
ꢇꢃꢅbꢈꢇꢄꢈ@ꢉꢌ.ꢆꢂꢉ.ꢌꢋ
©
2016 tꢈꢋꢊꢃꢅ & fꢅꢈꢇcꢄꢍ

2
N. AꢀꢁꢂLLAH ET AL.
1. Introduction
Most Cu(II) carboxylates are dimeric with a paddle-wheel structure [1–16]. In the absence of solvent
molecules at the axial positions, the dimers are linked into a one-dimensional oligomeric chain in the
solid state [17] and remain intact in solution [18, 19]. The two Cu(II) ions in the dimer are separated by
about 2.61 Å [20], and experience a strong antiferromagnetic interaction (-2 J about 300 cm− [5, 21]),
postulated to occur indirectly through the bridging carboxylato ligands (the super-exchange pathway)
1
[5]. Previous research on these complexes was focused on their potential as molecular sieves, molecular
magnets, and redox catalysts [22–24], and less on their chemical properties, even though both Cu(II)
ions in the dimeric structure are readily accessible for attack by Lewis bases.
Cyclam (1,4,8,11-tetraazacyclotetradecane) is a macrocyclic N -donor with the ability to form kineti-
4
cally and thermodynamically stable complexes with many transition metal ions [25-27]. These complexes
are of interest as redox catalysts [28–34], sensors [35], and as pharmaceutical materials [36]. Structurally,
most of these complexes are mononuclear with cyclam occupying the four basal sites of the metal ion,
while the two axial sites are occupied by other ligands [37].
We noted that [Cu (4-XC H COO) ] (X = H [37], tert-butyl [37], and Cl [38]) reacted with cyclam to
2
6
4
4
form ionic complexes, [Cu(cyclam)(H O) ](4-XC H COO) . In these complexes, the axial sites were weakly
2
2
6
4
2
coordinated by H O molecules, resulting in an elongated octahedral N O geometry at Cu(II).
2
4
2
This article reports the synthesis, structures, thermal, and redox properties of a covalent complex,
[
Cu(p–HOC H COO) (cyclam)] (1), and two ionic complexes, [Cu(cyclam)(H O) ](p–CH OC H COO) (2)
6
4
2
2
2
3
6
4
2
and [Cu(cyclam)(H O) ](p–CH (CH ) OC H COO) ·H O (3), formed from reactions of the correspond-
2
2
3
2 15
6
4
2
2
ing Cu(II) substituted benzoates with cyclam. Also reported is an ionic complex, [Cu(cyclam)(L) ](p–
2
CH OC H COO) (4), formed from the reaction of 2 with N-(hexadecyl)isonicotinamide (L). L was chosen
3
6
4
2
as it was a monodentate, N-donor expected to form complexes with mesomorphic properties, lower
melting temperatures, and higher solubility in non-polar organic solvents (lipophilic cyclam complexes
were found to possess good anti-tumor activity [39]). The synthetic steps for these complexes are
shown in scheme 1. Complexes 1–3 were isolated as purple crystals and their molecular structures were
determined by X-ray crystallography. 1 is the first example of a molecular Cu(II) complex reported from
such reaction, while the ionic structures of 2 and 3 are similar to those reported [37]. Finally, this article
reports the mesomorphic properties of 3 and 4.
(
a)
(
b)
Scheme 1. (ꢈ) sꢁꢅꢉcꢁꢉꢅꢈꢊ ꢎꢃꢅꢌꢉꢊꢈ ꢃꢎ N-(ꢀꢆxꢈꢂꢆcꢋꢊ)ꢄꢍꢃꢇꢄcꢃꢁꢄꢇꢈꢌꢄꢂꢆ (l); (b) ꢍꢋꢇꢁꢀꢆꢍꢆꢍ ꢃꢎ 1–4.

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
3
2. Experimental
2
.1. Materials and measurements
All chemicals were analaR grade and used without purification. Elemental analyses were carried out on
1
a Thermo Finnigan Flash EA 1112. H NMR spectra were recorded on a JEOL FT-NMR lambda 400 MHz
spectrometer. FTIR spectra were recorded from 4000 to 450 cm−1 on either a Perkin Elmer Spectrum
4
00 spectrophotometer or Perkin Elmer Frontier FTIR spectrophotometer equipped with a diamond
attenuated total reflectance attachment. Electronic spectra were recorded on a Shimadzu ꢂV-vis-NIR
600 spectrophotometer. Magnetic susceptibilities of solid samples were measured at room tempera-
3
ture on a Sherwood automagnetic susceptibility balance by the Gouy method, using Hg[Co(NCS) ] as
4
the calibrant. Molar susceptibility values were corrected for the diamagnetism of the constituent atoms
using Pascal’s constants. Thermogravimetry (TG) was done on a Perkin Elmer Pyris ꢁiamond TG/ꢁTA
3
−1
instrument under N at a flow rate of 10 cm min . The temperature range was 50–900 °C and the scan
2
−
1
rate was 20 °C min . ꢁifferential scanning calorimetry (ꢁSC), was done on a Mettler Toledo ꢁSC 822
3
−1
−1
calorimeter under N at a flow rate of 20 cm min and scan rate of 10 °C min . The onset temperatures
2
were quoted for all peaks observed. The photomicrographs were captured on an Olympus polarizing
optical microscopy (POM) equipped with a Mettler Toledo FP90 central processor and a Linkam THMS
6
00 hot stage. The samples were finely ground and any moisture absorbed from the atmosphere was
removed prior to analysis by heating in an oven at 60 °C overnight in order to obtain clear photomicro-
−1
graphs of the optical textures. The heating and cooling rates were 10 and 2 °C min , respectively, and
the magnification was 50x. Cyclic voltammetry (CV) was performed on a Gamry Potentiostat/Galvanostat
6
00 instrument at 25 °C. A standard three-electrode set up (glassy carbon working electrode, Ag/AgCl
reference electrode, and platinum wire counter electrode) was used. For 1 and 2, the solvent was H O,
2
and the supporting electrolyte was Na SO . For 3, the solvent was CHCl , and the supporting electrolyte
2
4
3
was tetrabutylammonium tetrafluoroborate. The molarities of complexes were 1 mM, while those of
−1
the electrolytes were 0.5 M. The scan rate was 100 mV s , and the quoted E values were versus Ag/
AgCl. The solutions were bubbled with N prior to measurements.
2
2
.2. Synthesis of [Cu (p–HOC H COO) (H O) ]
2 6 4 4 2 2
[
Cu (CH COO) (H O) ] (12.5 mmol, 4.99 g) was added portionwise to an ethanolic solution of p-HOC H-
2
3
4
2
2
6
4COOH (50.0 mmol, 6.91 g) at 60 °C, and the reaction mixture was further heated at this temperature
for 30 min. The blue powder formed was filtered from the hot reaction mixture, washed with distilled
−1
water, and dried in a warm oven (60 °C). ꢃield: 7.18 g (80.7%). IR (Kꢀr disk, cm ): 3446 (br), 3210 (br),
1
609 (vs), 1580 (s), 1548 (s), 1406 (vs), 1237 (s). Anal. Calcd for C H Cu O (%): C, 47.3; H, 3.4. Found:
28 24 2 14
C, 46.9; H, 3.3.
2
.3. Synthesis of [Cu (p–CH OC H COO) (H O) ]
2 3 6 4 4 2 2
The procedure was the same as for [Cu (p–HOC H COO) (H O) ], using [Cu (CH COO) (H O) ] (12.5 mmol,
2
6
4
4
2
2
2
3
4
2
2
4
.99 g) and p–CH OC H COOH (50.0 mmol, 7.61 g). The product was a greenish blue powder. ꢃield: 8.4 g
3 6 4
−1
(87.5%). IR (Kꢀr, disk, cm ): 3603 (vw), 2953 (vw), 2829 (vw), 1595 (s), 1544 (vs), 1428 (s), 1403 (s), 1251
vs). Anal. Calcd for C H Cu O (%): C, 50.1; H, 4.2. Found: C, 49.5; H, 4.0.
(
32
32
2
14
2
.4. Synthesis of [Cu (p–CH (CH ) OC H COO) (H O) ]
2 3 2 15 6 4 4 2 2
CH (CH ) ꢀr (50.0 mmol, 15.27 g) was added dropwise to a mixture of p–HOC H COOC H (50.1 mmol,
3
2 15
6
4
2
5
8
.33 g), K CO (100.0 mmol, 13.84 g), and a catalytic amount of KI in ꢁMF at room temperature. The
2 3
reaction mixture was then refluxed for 24 h and cooled to room temperature. The white powder (p–
CH (CH ) OC H COOC H ) obtained was washed several times with distilled water and recrystallized
3
2 15
6
4
2
5
1
from hot CH CH OH. ꢃield: 9.55 g (48.9%). H NMR (400 MHz, CꢁCl , ppm): δ = 0.83 (t, 3 H, CH (CH ) O),
3
2
3
3
2 15

4
N. AꢀꢁꢂLLAH ET AL.
1
.2–1.3 (m, 30 H, CH (CH ) O), 3.9 (t, 3 H, COOCH CH ), 4.3 (q, 2 H, COOCH CH ), 6.8 (d, 2 H, C H ), 7.9
3
2 15
2
3
2
3
6
4
-
1
(
d, 2 H, C H ). IR (neat, cm ): 2915 (vs), 2848 (s), 1712 (vs), 1606 (m), 1509 (m), 1470 (s), 1314 (m), 1248
6 4
(
vs), 768 (s), 696 (m).
An aqueous solution of KOH was added in excess to a hot ethanolic solution of p-CH (CH ) OC H-
3
2 15
6
COOC H (14.3 mmol, 5.6 g). The mixture was refluxed for 4 h and then cooled to room temperature.
4
2
5
The white powder (p–CH (CH ) OC H COOK) obtained was filtered, washed thoroughly with distilled
3
2 15
6
4
−1
water, and dried in an oven. ꢃield: 4.15 g (72.4%). IR (neat, cm ): 2917 (vs), 2848 (s), 1601 (m), 1541 (m),
393 (s), 1252 (s), 791 (s), 651 (m). Anal. Calcd for C H KO (%): C, 68.9; H, 9.3. Found: C, 69.4; H, 10.1.
1
23
37
3
CuSO ·5H O (5.0 mmol, 1.26 g) was added to a warm ethanolic solution of p-CH (CH ) OC H COOK
4
2
3
2 15
6
4
(
10.0 mmol, 4.02 g). The reaction mixture was stirred for 30 min, and the blue powder formed was fil-
−1
tered, washed with distilled water, and dried in a warm oven. ꢃield: 3.0 g (74.6%). IR (neat, cm ): 3400
br), 2916 (vs), 2849 (s), 1609 (m), 1593 (m), 1499 (s), 1435 (vs), 1256 (s), 785 (s), 664 (m). Anal. Calcd for
C H Cu O (%): C, 68.7; H, 9.5. Found: C, 68.1; H, 9.2.
(
92
152
2
14
2
.5. Synthesis of [Cu(p–HOC H COO) (cyclam)] (1)
6 4 2
An ethanolic solution of cyclam (0.89 mmol, 0.18 g) was added portionwise to an ethanolic suspension
of [Cu (p–HOC H COO) (H O) ] (0.42 mmol, 0.30 g). The purple solution formed was heated at 60 °C for
2
6
4
4
2
2
1
h and filtered hot. ꢁark-purple prismatic crystals were deposited after 2 days at room temperature.
−1
ꢃield: 0.40 g (78.4%). IR (neat, cm ): 3239 (m), 3122 (m), 2933 (m), 2870 (m), 1605 (m), 1585 (s), 1539
vs), 1351 (vs), 1272 (vs), 789 (vs), 617 (s).
(
2
.6. Synthesis of [Cu(cyclam)(H O) ](p–CH OC H COO) (2)
2 2 3 6 4 2
The procedure was the same as for 1, using cyclam (2.5 mmol, 0.50 g) and [Cu (p-CH OC H COO) (H O) ]
2
3
6
4
4
2
2
−
1
(
1.19 mmol, 0.91 g). The product was isolated as purple needles. ꢃield: 0.87 g (60.8%). IR (neat, cm ):
3
133 (m), 2934 (m), 1599 (s), 1549 (s), 1382 (s), 1255 (s), 791 (vs).
2
.7. Synthesis of [Cu(cyclam)(H O) ](p-CH (CH ) OC H COO) ·H O (3)
2 2 3 2 15 6 4 2 2
The procedure was the same as for 1, using cyclam (0.05 mmol, 0.01 g) and [Cu (p-
2
CH (CH ) OC H COO) (H O) ] (0.11 mmol, 0.17 g). The product was isolated as purple crystals. ꢃield:
3
2 15
6
4
4
2
2
−
1
0
.046 g (88.4%). IR (neat, cm ): 3193 (br), 2917 (s), 2851 (m), 1604 (s), 1583 (s), 1546 (s), 1472 (m), 1376
(
vs), 1241 (s), 788 (s), 647 (s).
2
.8. Synthesis of N-(hexadecyl)isonicotinamide (L)
A solution of isonicotinic acid (51.6 mmol, 6.35 g) and CH (CH ) NH (50.5 mmol, 12.2 g) in CHCl
3
3
2 15
2
3
(
100 cm ) was refluxed in the presence of anhydrous MgSO for 3 h. The hot reaction mixture was
4
filtered, and a pale yellow powder was obtained from the filtrate on cooling. It was recrystallized from
1
hot CH CH OH. ꢃield: 12.3 g (70.3%). H NMR (400 MHz, CꢁCl , ppm): δ = 0.83 (t, 3 H, CH ), 1.1–1.2
3
2
3
3
(
m, 26 H, CH (CH ) CH ), 1.6 (m, 2 H, CH CH (CH ) CH ), 2.8 (m, 2 H, CH CH (CH ) CH ), 3.4 (b, 1 H,
2 2 13 3 2 2 2 13 3 2 2 2 13 3
−1
NHCH CH (CH ) CH ), 7.7 (d, 2 H, C H ), 8.6 (d, 2 H, C H ). IR (Kꢀr disk, cm ): 2918 (s), 2853 (s), 1636
2
2
2 13
3
6
4
6
4
(
m), 1529 (s).
2
.9. Synthesis of [Cu(cyclam)(L) ](p–CH OC H COO) (4)
2 3 6 4 2
A mixture of 2 (0.39 mmol, 0.26 g) and L (0.87 mmol, 0.30 g) in CH CH OH–CHCl (1 : 1) was stirred at
3
2
3
room temperature for 30 min. The purple powder formed was isolated by filtration and washed with
CH OH. ꢃield: 0.28 g (65.7%). Anal. Calcd for C H CuN O (%): C, 66.77; H, 9.12; N, 8.90. Found: C, 66.35;
3
70 114
8
8

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
5
Table 1. Cꢅꢋꢍꢁꢈꢊ ꢂꢈꢁꢈ ꢈꢇꢂ ꢍꢁꢅꢉcꢁꢉꢅꢆ ꢅꢆfiꢇꢆꢌꢆꢇꢁ ꢎꢃꢅ 1–3.
Complex
1
2
3
Cꢀꢆꢌꢄcꢈꢊ ꢎꢃꢅꢌꢉꢊꢈ
fꢃꢅꢌꢉꢊꢈ ꢌꢈꢍꢍ (g ꢌꢃꢊ )
t (K)
C h Cꢉn o
C h Cꢉn o
C56h104Cꢉn4o9
1040.97
173(2)
2
4
34
4
6
26 42
4 8
−1
538.1
100(2)
602.19
100(2)
Cꢅꢋꢍꢁꢈꢊ ꢍꢋꢍꢁꢆꢌ
spꢈcꢆ gꢅꢃꢉp
a (Å)
b (Å)
c (Å)
α (°)
β (°)
mꢃꢇꢃcꢊꢄꢇꢄc
oꢅꢁꢀꢃꢅꢀꢃꢌbꢄc
Pbca
15.5810(6)
7.0534(2)
25.8128(9)
90
tꢅꢄcꢊꢄꢇꢄc
P¯1
P2 /c
1
8.2488(1)
13.2976(2)
11.1659(2)
90
102.725(1)
90
1194.70(3)
2
1.496
9.1310(11)
14.3849(16)
22.192(3)
89.533(2)
88.267(2)
82.150(2)
2886.2(6)
2
90
90
γ (°)
Vꢃꢊꢉꢌꢆ (Å )
3
2836.80(17)
4
1.41
1276
0.824
Z
−3
DCalcd (g cꢌ )
F(0 0 0)
1.198
1138
0.434
566
0.963
−1
μ (mꢃ Kα) (ꢌꢌ )
mꢆꢈꢍꢉꢅꢆꢂ ꢂꢈꢁꢈ
uꢇꢄqꢉꢆ ꢂꢈꢁꢈ
12,947
2751
15,747
2501
37,551
13,243
obꢍꢆꢅvꢆꢂ ꢂꢈꢁꢈ (I ≥ 2.0σ(I))
R, ꢃbꢍ. ꢂꢈꢁꢈ; ꢈꢊꢊ ꢂꢈꢁꢈ
a, b ꢄꢇ wꢆꢄgꢀꢁꢄꢇg ꢍcꢀꢆꢌꢆ
Rw, ꢃbꢍ. ꢂꢈꢁꢈ; ꢈꢊꢊ ꢂꢈꢁꢈ
2481
1842
8642
0.024; 0.065
0.033, 0.636
0.028; 0.067
0.035; 0.079
0.046, 0.726
0.057; 0.089
0.049, 0.091
0.064, 0.222
0.116, 0.137
Table 2. sꢆꢊꢆcꢁꢆꢂ bꢃꢇꢂ ꢊꢆꢇgꢁꢀꢍ (Å) ꢎꢃꢅ 1–3.
Complex
1
2
3
Cꢉ–n1
Cꢉ–n2
Cꢉ2–n3
Cꢉ2–n4
Cꢉ–o1
2.0235(11)
2.0168(11)
2.0095(19)
2.0187(19)
2.0176(19)
2.035(2)
2.017(2)
2.0140(19)
–
–
–
–
–
2.3830(10)
2.5355(17)
Cꢉ⋯o2
Cꢉ1–o1w
Cꢉ2–o2w
3.6304(11)
–
–
–
–
–
–
2.4800(18)
2.4587(18)
−1
H, 9.05; N, 8.01. IR (neat, cm ): 2917 (vs), 2851 (vs), 1636 (s), 1599 (vs), 1543 (vs), 1473 (m), 1382 (vs),
250 (s), 961 (s), 792 (s), 615 (m).
1
2
.10. Crystallographic data collection and structural determination
Intensity data for 1–3 were collected at reduced temperature on a ꢀruker SMART APEX II CCꢁ fitted with
Mo Kα radiation. Each data set was corrected for absorption based on multiple scans [40] and reduced
using standard methods [41]. The structures were solved by direct methods with SHELXS97 [42] and
2
refined by a full-matrix least-squares procedure on F using SHELXL97 with anisotropic displacement
2
2
2
parameters for non-hydrogen atoms and a weighting scheme of the form w = 1/[σ (F ) + aP + bP],
o
2
2
where P = (Fo + 2F )/3). All hydrogens in 1 were included in the final refinement in their calculated
c
positions. For 2 and 3, C-bound hydrogens were treated similarly but the O- and N-bound hydrogens
were located from a difference map and refined with distance restraints O–H = 0.84 ± 0.01 Å and
N–H = 0.88 ± 0.01 Å; for 3, N–H was fixed at 0.88 Å. Crystal data and refinement details are given in
table 1, selected bond lengths and angles are given in table 2, and hydrogen bonding data are given
in table 3. Figures 1, 3 and 5, showing the atom labeling schemes, were drawn with 50% displacement
ellipsoids using ORTEP-3 for Windows [43], and the packing diagrams were drawn with ꢁIAMONꢁ [44].
Crystallographic data for the structural analyses have been deposited at the Cambridge Crystallographic
ꢁata Center.

6
N. AꢀꢁꢂLLAH ET AL.
Table 3. sꢉꢌꢌꢈꢅꢋ ꢃꢎ ꢍꢆꢊꢆcꢁꢆꢂ ꢄꢇꢁꢆꢅꢌꢃꢊꢆcꢉꢊꢈꢅ ꢄꢇꢁꢆꢅꢈcꢁꢄꢃꢇꢍ (d–h⋯a; Å, °) ꢃpꢆꢅꢈꢁꢄꢇg ꢄꢇ ꢁꢀꢆ cꢅꢋꢍꢁꢈꢊ ꢍꢁꢅꢉcꢁꢉꢅꢆꢍ ꢃꢎ 1–3.
ꢁ
–H⋯A
d(ꢁ–H)
d(H⋯A)
d(ꢁ⋯A)
<(ꢁHA)
Symmetry operation
Cꢃꢌpꢊꢆx 1
n1–h1ꢇ⋯o2
o3–h30⋯o2
Cꢃꢌpꢊꢆx 2
0.930(1)
0.840(1)
2.076(1)
1.7789(9)
2.950(2)
2.618(1)
155.83(7)
176.45(8)
1−x, 1−y, −z
−x, ½+y, ½−z
o1w–h2w⋯o2
n1–h1ꢇ⋯o1
o1w–h1w⋯o1
n2–h2ꢇ⋯o2
Cꢃꢌpꢊꢆx 3
0.83(2)
0.87(1)
0.84(2)
0.87(1)
2.02(2)
2.04(1)
1.92(2)
2.10(1)
2.848(2)
2.864(3)
2.757(2)
2.921(3)
174(2)
156(2)
171(2)
157(2)
x, y, z
1−x, −y, −z
1−x, 1−y, −z
x, 1+y, z
o1w–h1w1⋯o1
o1w–h1w2⋯o4
o2w–h2w1⋯o1
o2w–h2w2⋯o5
o3w–h3w1⋯o2
o3w–h3w2⋯o4
n1–h1ꢇ⋯o2
n2–h2ꢇ⋯o4
n3–h3ꢇ⋯o3w
n4–h4ꢇ⋯o5
0.84(2)
0.84(2)
0.84(2)
0.83(2)
0.84(2)
0.83(2)
0.930(2)
0.930(2)
0.930(2)
0.930(2)
1.93(2)
2.00(2)
1.93(2)
1.92(2)
1.96(2)
2.07(2)
2.134(2)
2.079(2)
2.045(2)
1.961(2)
2.767(2)
2.797(3)
2.772(2)
2.735(3)
2.796(3)
2.900(2)
2.978(3)
2.987(3)
2.959(3)
2.888(2)
175(2)
158(2)
172(2)
165(2)
174(2)
174(2)
150.4(1)
165(1)
167.2(1)
174.6(1)
x, y, z
x, y, z
x, y, z
x, y, z
x, y, z
x, y, z
x, y, z
1−x, −y, 1−z
−x, 1−y, 1−z
x, y, z
Figure 1. Cꢃꢃꢅꢂꢄꢇꢈꢁꢄꢃꢇ ꢆꢇvꢄꢅꢃꢇꢌꢆꢇꢁ ꢃꢎ Cꢉ(ii) ꢄꢇ 1. tꢀꢆ ꢈꢁꢃꢌꢍ cꢃꢌpꢅꢄꢍꢄꢇg ꢁꢀꢆ ꢈꢍꢋꢌꢌꢆꢁꢅꢄc ꢉꢇꢄꢁ ꢈꢅꢆ ꢊꢈbꢆꢊꢆꢂ. tꢀꢆ ꢉꢇꢊꢈbꢆꢊꢆꢂ ꢈꢁꢃꢌꢍ ꢈꢅꢆ
ꢅꢆꢊꢈꢁꢆꢂ bꢋ ꢁꢀꢆ ꢍꢋꢌꢌꢆꢁꢅꢋ ꢃpꢆꢅꢈꢁꢄꢃꢇ i: 1−x, 1−y, −z.

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
7
Table 4. iꢇꢍꢁꢅꢉꢌꢆꢇꢁꢈꢊ ꢂꢈꢁꢈ ꢎꢃꢅ cꢃꢌpꢊꢆxꢆꢍ ꢃꢎ cꢃppꢆꢅ(ii) wꢄꢁꢀ ꢍꢉbꢍꢁꢄꢁꢉꢁꢆꢂ bꢆꢇzꢃꢈꢁꢆꢍ ꢄꢇ cꢃꢌpꢈꢅꢄꢍꢃꢇ wꢄꢁꢀ pꢉbꢊꢄꢍꢀꢆꢂ cꢅꢋꢍꢁꢈꢊꢍ ꢃꢎ ꢂꢄꢌꢆꢅꢄc
pꢈꢂꢂꢊꢆ-wꢀꢆꢆꢊ, ꢁꢅꢄꢇꢉcꢊꢆꢈꢅ ꢈꢇꢂ ꢀꢆxꢈꢇꢉcꢊꢆꢈꢅ cꢃꢌpꢊꢆxꢆꢍ.
a
−1
λ/nm (ε/M−1 cm−1)
Complex
Cꢉ (r1) (h o) ]
∆ (cm )
μeff /ꢀM
Reference
b
[
174
141
158
144
206
173
177
162
715 (65)
2.2
2.8
2.9
na
2.1
1.6
2.5
10.2
tꢀꢄꢍ wꢃꢅk
tꢀꢄꢍ wꢃꢅk
tꢀꢄꢍ wꢃꢅk
[7]
[10]
[15]
2
4
2
2
[
Cꢉ (r2) (h o) ]
677 (431)c
2
4
2
2
c
[Cꢉ (r3) (h o) ]
682 (388)
694
2
4
2
2
ꢂ
Cꢉ (r4) (eꢁoh) ]
2
4
2
704ꢂ
671 (375)c
na
2
4
2
2
[
Cꢉ (Ch (Ch ) Coo) ]
2
3
2 5
4
[Cꢉ (r6) ]
[48]
[49]
3
6
[
Cꢉ (r7) ]
685 (505)c
6
12
ꢈ
∆
= ῡ Coo – ῡ Coo.
ꢈꢍ
ꢍ
b
c
iꢇ dmso.
iꢇ ChCꢊ3.
ꢂ
rꢆflꢆcꢁꢈꢇcꢆ.
R1 = p–hoC h Coo; R2 = p–Ch oC h Coo; R3 = p–Ch (Ch ) oC h Coo; R4 = 1-pꢀꢆꢇꢋꢊcꢋcꢊꢃpꢅꢃpꢈꢇꢆ-1-cꢈꢅbꢃxꢋꢊꢈꢁꢃ;
6
4
3
6
4
3
2 15
6 4
R5 = 2,6-(Ch o) ꢇꢄcꢃꢁꢄꢇꢈꢁꢃ; R6 = 2,4,6-ꢁꢅꢄꢄꢍꢃpꢅꢃpꢋꢊbꢆꢇzꢃꢈꢁꢃ; R7 = 3,4,5-ꢁꢅꢄꢆꢁꢀꢃxꢋbꢆꢇzꢃꢈꢁꢃ; na = ꢇꢃꢁ ꢈvꢈꢄꢊꢈbꢊꢆ.
3
2
3. Results and discussion
3
.1. Syntheses and structures of [Cu (p–ROC H COO) (H O) ] (R=H, CH , CH (CH ) )
2
6
4
4
2
2
3
3
2 15
Three Cu(II) carboxylates, [Cu(p–ROC H COO) (H O)] (R=H, CH , CH (CH ) ), were synthesized accord-
6
4
2
2
3
3
2 15
ing to published methods [1–16]. In order to deduce their structural formulas, we compared their IR,
ꢂV-vis, and magnetic data with crystals of dimeric [7, 10, 15], a trinuclear [45] and a hexanuclear [46]
copper(II) carboxylates (table 4). ꢀased on these data and the following arguments, we inferred that
our complexes were likely dinuclear ([Cu (p–ROC H COO) (H O) ]) adopting the paddle-wheel struc-
2
6
4
4
2
2
ture: (a) the difference in values of the COO(asym) and COO(sym) vibrations of the carboxylate ligands
Δ = ʋCOO,asym – ʋCOO,sym) from IR spectra have been extensively used by many authors to probe
(
−1
the binding modes of carboxylate ligands [47]. The Δ value for [Cu(p–HOC H COO) (H O)] (174 cm )
was similar to the dimeric paddle-wheel [Cu (CH (CH ) COO) ] (173 cm ) [15], while the lower values
for [Cu(p–ROC H COO) (H O)] (141 cm for R=CH ; 158 cm for R=CH (CH ) ) can be indicative of a
6
4
2
2
−
1
2
3
2 5
4
−1
−1
6
4
2
2
3
3
2 15
bridging bidentate coordination geometry, very likely of the paddle-wheel type, (b) the similar λmax
value (685 nm) from the ꢂV-vis spectrum of the hexanuclear complex with our complexes (682–715 nm)
may arise from the dissociation of the former complex in solution, (c) the trinuclear and hexanuclear
complexes were formed from trisubstituted benzoato ligands and their colors were dark green, while
our complexes were formed from monosubstituted benzoato ligands and their colors were blue, and
(
d) the hexanuclear complex was sparingly soluble in both polar and nonpolar solvents, while our
complexes were quite soluble in solvents such as hot ethanol, ꢁMSO, and THF.
The value for the effective magnetic moment (μ ) for [Cu (p–HOC H COO) (H O) ] (2.2 ꢀM) was
eff
2
6
4
4
2
2
in agreement with most dinuclear Cu(II) complexes adopting paddle-wheel structures [1.6–2.1
M [10, 15]). However, the values obtained for [Cu (p-CH OC H COO) (H O) ] (2.8 ꢀM) and [Cu (p-
ꢀ
2
3
6
4
4
2
2
2
CH (CH ) OC H COO) (H O) ] (2.9 ꢀM) were slightly higher and cannot be currently rationalized in
3
2 15
6
4
4
2
2
the absence of variable-temperature magnetic data.
3
.2. Reactions of cyclam with [Cu (p–ROC H COO) (H O) ] (R=H, CH , CH (CH ) )
2
6
4
4
2
2
3
3
2 15
Cyclam reacted with [Cu (p–ROC H COO) (H O) ] (R=H, CH , CH (CH ) ) (mole ratio = 2 : 1) to form a mon-
2
6
4
4
2
2
3
3
2 15
onuclear covalent complex, [Cu(p–HOC H COO) (cyclam)] (1), and two mononuclear ionic complexes,
6
4
2
[
Cu(cyclam)(H O) ](p–CH OC H COO) (2) and [Cu(cyclam)(H O) ](p–CH (CH ) OC H COO) ·H O (3),
2 2 3 6 4 2 2 2 3 2 15 6 4 2 2
respectively. Complexes 1–3 were purple crystals and their molecular structures were determined by
X-ray crystallography. In the presence of cyclam, the dimeric structure of [Cu (p–ROC H COO) (H O) ]
2
6
4
4
2
2
dissociated in hot ethanol, and the‘free’ions formed, self-assembled to form the monomeric complexes,
though the concept of an‘assembly effect’proposed by Lindoy et al. [37] may also apply, especially for 1.

8
N. AꢀꢁꢂLLAH ET AL.
Figure 2. sꢉpꢅꢈꢌꢃꢊꢆcꢉꢊꢈꢅ ꢈꢍꢍꢃcꢄꢈꢁꢄꢃꢇ ꢃpꢆꢅꢈꢁꢄꢇg ꢄꢇ 1. tꢀꢆ o–h⋯o ꢀꢋꢂꢅꢃgꢆꢇ bꢃꢇꢂꢄꢇg (ꢃꢅꢈꢇgꢆ ꢂꢈꢍꢀꢆꢂ ꢊꢄꢇꢆꢍ) ꢊꢆꢈꢂꢍ ꢁꢃ cꢀꢈꢄꢇꢍ ꢈꢊꢃꢇg
ꢀꢆ b-ꢈxꢄꢍ. iꢇꢁꢅꢈꢌꢃꢊꢆcꢉꢊꢈꢅ n–h⋯o ꢀꢋꢂꢅꢃgꢆꢇ bꢃꢇꢂꢍ ꢈꢅꢆ ꢍꢀꢃwꢇ ꢈꢍ bꢊꢉꢆ ꢂꢈꢍꢀꢆꢂ ꢊꢄꢇꢆꢍ. Cꢃꢊꢃꢅ cꢃꢂꢆ: Cꢉ, ꢃꢅꢈꢇgꢆ; o, ꢅꢆꢂ; n, bꢊꢉꢆ; C, gꢅꢈꢋ;
ꢈꢇꢂ h, gꢅꢆꢆꢇ (ꢍꢆꢆ ꢀꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958972.2016.1147032 ꢎꢃꢅ cꢃꢊꢃꢅ vꢆꢅꢍꢄꢃꢇ).
ꢁ
3
.3. Structures of 1–3
The molecular structure of 1 (figure 1) shows a Cu(II) located on a crystallographic center of inversion
which exists within a trans-N O donor set, being four-coordinate by the four N atoms of cyclam and
4
2
two carboxylate-O1 atoms. The resulting coordination geometry was based on a tetragonally distorted
i
octahedron (table 2). O2 was aligned over the Cu–N1 bond but was oriented away from the Cu ion to
allow for formation of an intramolecular N1–H⋯O hydrogen bond. As a result, the Cu⋯O2 separation
was 3.6304(11) Å, a distance too long to be considered as significant bonding interaction. There was a
small twist of the COO group out of the plane of the aromatic ring to which it was connected (O1/C1/
C2/C3 torsion angle = -167.24(12)°). The p-HOC H COO ligand was folded towards the plane through
6
4
the four N atoms with the dihedral angle formed between the CuN and C planes being 49.11(5)°
4
6
(
p–HOC H COO adopted an orthogonal disposition to the CuN plane).
6
4
4
The crystal packing in 1 was dominated by O–H⋯O hydrogen bonds (table 3). The hydroxyl–O3–H
forms a hydrogen bond to the carbonyl-O2 so that the latter, which also participates in an N–H⋯O inter-
action, is bifurcated. The O–H⋯O hydrogen bonds link the p-HOC H COO ligand into a supramolecular
6
4
chain along the b-axis. Successive chains were interspersed by [Cu(cyclam)] units via the coordinate
Cu–O bonds and N–H⋯O hydrogen bonds. The resulting layers, which have a flattened topology, lie

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
9
−
Figure 3. Cꢃꢃꢅꢂꢄꢇꢈꢁꢄꢃꢇ ꢆꢇvꢄꢅꢃꢇꢌꢆꢇꢁ ꢃꢎ Cꢉ(ii) ꢄꢇ 2 ꢆxꢁꢆꢇꢂꢆꢂ ꢁꢃ ꢄꢇcꢊꢉꢂꢆ ꢁꢀꢆ ꢀꢋꢂꢅꢃgꢆꢇ-bꢃꢇꢂꢆꢂ p-Ch oC h Coo ꢄꢃꢇꢍ. tꢀꢆ ꢈꢁꢃꢌꢍ
3
6 4
cꢃꢌpꢅꢄꢍꢄꢇg ꢁꢀꢆ ꢈꢍꢋꢌꢌꢆꢁꢅꢄc ꢉꢇꢄꢁ ꢈꢅꢆ ꢊꢈbꢆꢊꢆꢂ. tꢀꢆ ꢉꢇꢊꢈbꢆꢊꢆꢂ ꢈꢁꢃꢌꢍ ꢈꢅꢆ ꢅꢆꢊꢈꢁꢆꢂ bꢋ ꢁꢀꢆ ꢍꢋꢌꢌꢆꢁꢅꢋ ꢃpꢆꢅꢈꢁꢄꢃꢇ i: 1−x, 1−y, −z.
parallel to the (102) plane (figure 2). The hydroxyl–OH...O(carboxylate) hydrogen bonding results in the
formation of rather large 40-membered {⋯OCOCuOC OH⋯OC OH⋯} synthons which are stabilized
5
5
2
by two internal six-membered {⋯HNCuOCO} synthons. The supramolecular layers stack in a ⋯AꢀA⋯
fashion with the primary contacts between the layers being of the type C–H⋯O.
For 2, a similar centrosymmetric and octahedral trans-N O donor set (table 2) is observed, but in
4
2
−
this case the trans-oxygens are derived from coordinating water (figure 3). The p-CH OC H COO ions
3
6
4
2+
−
are associated with [Cu(cyclam((H O) ] by aqua-OH⋯O2 hydrogen bonds. The p–CH OC H COO ions
2
2
3
6
4
form an intramolecular N1–H⋯O1 hydrogen bond, and so in a sense, the structure of 2 differs from 1
−
by the insertion of two H O molecules between Cu(II) and p–CH OC H COO . As for 1, the COO group
2
3
6
4
−
of p–CH OC H COO is twisted out of the plane of the aromatic ring to which it is connected [O1/C1/
3
6
4
C2/C3 torsion angle = 8.0(3)°].
Significant hydrogen bonding is also apparent in the crystal structure of 2 (table 3). Thus, the second
aqua-H1w is hydrogen bonded to the carboxylate-O1, and the amine-N2-H is hydrogen bonded to
2
+
carboxylate-O2, so that each carboxylate oxygen is bifurcated. As a result, each [Cu(cyclam((H O) ]
2
2
−
is surrounded by four p–CH OC H COO ions, with each of these associations stabilized by an
3
6
4
eight-membered {⋯HNCuOH⋯OCO} synthon. A supramolecular chain along the b-axis occurs as
2
+
[
Cu(cyclam((H O) ] ions are bridged by centrosymmetric 12-membered {...OHO...OCO} synthons
2
2
2
−
involving p–CH OC H COO ions and coordinated H O molecules (figure 4). The chains are connected
3
6
4
2
into layers in the ab-plane via C–H⋯O interactions occurring between the CH O groups, and the layers
3
interdigitated along the c-axis with no specific interactions between them.
2
+
For 3, the crystallographic asymmetric unit is made up of two half [Cu(cyclam)(H O) ] ions (each ion is
2
2
−
disposed about a center of inversion), two p–CH (CH ) OC H COO ions and a lattice H O (figure 5). Each
3
2 15
6
4
2
−
Cu(II) is located within a trans-N O donor set (table 2). The alkyl chains in p–CH (CH ) OC H COO adopt
4
2
3
2 15
6 4

10
N. AꢀꢁꢂLLAH ET AL.
Figure 4. sꢉpꢅꢈꢌꢃꢊꢆcꢉꢊꢈꢅ ꢈꢍꢍꢃcꢄꢈꢁꢄꢃꢇ ꢄꢇ 2. tꢀꢆ o–h⋯o ꢈꢇꢂ n–h⋯o ꢀꢋꢂꢅꢃgꢆꢇ bꢃꢇꢂꢄꢇg (ꢃꢅꢈꢇgꢆ ꢈꢇꢂ bꢊꢉꢆ ꢂꢈꢍꢀꢆꢂ ꢊꢄꢇꢆꢍ, ꢅꢆꢍpꢆcꢁꢄvꢆꢊꢋ)
ꢊꢆꢈꢂ ꢁꢃ ꢈ cꢀꢈꢄꢇ ꢈꢊꢃꢇg ꢁꢀꢆ b-ꢈxꢄꢍ. Cꢃꢊꢃꢅ cꢃꢂꢆ: Cꢉ, ꢃꢅꢈꢇgꢆ; o, ꢅꢆꢂ; n, bꢊꢉꢆ; C, gꢅꢈꢋ; ꢈꢇꢂ h, gꢅꢆꢆꢇ (ꢍꢆꢆ ꢀꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958
972.2016.1147032 ꢎꢃꢅ cꢃꢊꢃꢅ vꢆꢅꢍꢄꢃꢇ).
Figure 5. (ꢈ), (b) tꢀꢆ cꢃꢃꢅꢂꢄꢇꢈꢁꢄꢃꢇ ꢆꢇvꢄꢅꢃꢇꢌꢆꢇꢁꢍ ꢃꢎ Cꢉ(ii) ꢄꢇ ꢁꢀꢆ ꢁwꢃ ꢄꢇꢂꢆpꢆꢇꢂꢆꢇꢁ cꢈꢁꢄꢃꢇꢍ ꢄꢇ 3. tꢀꢆ ꢈꢁꢃꢌꢍ cꢃꢌpꢅꢄꢍꢄꢇg ꢁꢀꢆ ꢈꢍꢋꢌꢌꢆꢁꢅꢄc
ꢉꢇꢄꢁ ꢈꢅꢆ ꢊꢈbꢆꢊꢆꢂ. tꢀꢆ ꢉꢇꢊꢈbꢆꢊꢆꢂ ꢈꢁꢃꢌꢍ ꢈꢅꢆ ꢅꢆꢊꢈꢁꢆꢂ bꢋ ꢁꢀꢆ ꢍꢋꢌꢌꢆꢁꢅꢋ ꢃpꢆꢅꢈꢁꢄꢃꢇꢍ: 1−x, −y, 1−z ꢄꢇ (ꢈ) ꢈꢇꢂ −x, 1−y, 1−z ꢄꢇ (b); (c), (ꢂ) tꢀꢆ
ꢁ
wꢃ ꢄꢇꢂꢆpꢆꢇꢂꢆꢇꢁ cꢈꢅbꢃxꢋꢊꢈꢁꢆ ꢈꢇꢄꢃꢇꢍ ꢀꢄgꢀꢊꢄgꢀꢁꢄꢇg ꢁꢀꢆ ꢆxꢁꢆꢇꢂꢆꢂ cꢃꢇꢎꢃꢅꢌꢈꢁꢄꢃꢇꢍ ꢃꢎ ꢁꢀꢆ ꢈꢊkꢋꢊ cꢀꢈꢄꢇꢍ.
an extended, all-trans conformation. The major difference between the ions is the relative orienta-
tions of the COO group with respect to the C H ring, being either twisted (O1–C11–C12–C13 torsion
6
4
angle = 17.3(3)°) or co-planar (O4–C34–C35–C36 = −3.5(3)°).
The components of the crystallographic asymmetric unit in 3 (figure 6) are connected via O–H⋯O
hydrogen bonds (table 3), whereby coordinated and lattice H O molecules bridge the carboxylate-O.
2

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
11
Figure 6. sꢉpꢅꢈꢌꢃꢊꢆcꢉꢊꢈꢅ ꢈꢍꢍꢃcꢄꢈꢁꢄꢃꢇ ꢄꢇ 3. (ꢈ) o–h⋯o ꢈꢇꢂ n–h⋯o ꢀꢋꢂꢅꢃgꢆꢇ bꢃꢇꢂꢍ bꢆꢁwꢆꢆꢇ ꢁꢀꢆ cꢃꢌpꢃꢇꢆꢇꢁꢍ ꢃꢎ ꢁꢀꢆ ꢈꢍꢋꢌꢌꢆꢁꢅꢄc
ꢉꢇꢄꢁ, (b) ꢍꢉpꢅꢈꢌꢃꢊꢆcꢉꢊꢈꢅ cꢀꢈꢄꢇ ꢈꢊꢃꢇg [1 −1 0] (ꢌꢃꢍꢁ ꢃꢎ ꢁꢀꢆ ꢈꢊkꢋꢊ cꢀꢈꢄꢇꢍ ꢈꢇꢂ ꢈꢊꢊ ꢇꢃꢇ-ꢈcꢄꢂꢄc ꢀꢋꢂꢅꢃgꢆꢇꢍ wꢆꢅꢆ ꢅꢆꢌꢃvꢆꢂ ꢎꢃꢅ cꢊꢈꢅꢄꢁꢋ) ꢈꢇꢂ
(
c) ꢈ vꢄꢆw ꢄꢇ pꢅꢃjꢆcꢁꢄꢃꢇ ꢂꢃwꢇ ꢁꢀꢆ b-ꢈxꢄꢍ ꢃꢎ ꢁꢀꢆ ꢉꢇꢄꢁ cꢆꢊꢊ cꢃꢇꢁꢆꢇꢁꢍ. tꢀꢆ o–h⋯o ꢈꢇꢂ n–h⋯o ꢀꢋꢂꢅꢃgꢆꢇ bꢃꢇꢂꢍ (ꢍꢀꢃwꢇ ꢈꢍ ꢃꢅꢈꢇgꢆ ꢈꢇꢂ
bꢊꢉꢆ ꢂꢈꢍꢀꢆꢂ ꢊꢄꢇꢆꢍ, ꢅꢆꢍpꢆcꢁꢄvꢆꢊꢋ) ꢊꢆꢂ ꢁꢃ ꢈ cꢀꢈꢄꢇ. Cꢃꢊꢃꢅ cꢃꢂꢆ: Cꢉ, ꢃꢅꢈꢇgꢆ; o, ꢅꢆꢂ; n, bꢊꢉꢆ; C, gꢅꢈꢋ; ꢈꢇꢂ h, gꢅꢆꢆꢇ (ꢍꢆꢆ ꢀꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/
0.1080/00958972.2016.1147032 ꢎꢃꢅ cꢃꢊꢃꢅ vꢆꢅꢍꢄꢃꢇ).
1
Each N–H forms a N–H⋯O hydrogen bond to a carboxylate-O, with the result that three of the car-
2
+
boxylate-O atoms are bifurcated and the other trifurcated (figure 6(a)). As each [Cu(cyclam)(H O) ]
2
2
ion lies on a center of inversion, similar hydrogen bonds are formed on the other side of each CuN4
plane, leading to a supramolecular chain with base vector [1 −1 0] (figure 6(b)). The chains align in the
ab-plane, with the carboxylate substituents lying to either side (figure 6(c)). The only notable contact
between chains is of the type C–H⋯π.
Liu et al. found that, for Cu(II) complexes of a 22-membered symmetric macrocyclic ligand, the smaller
NO − is coordinated to Cu(II) while the bigger ClO4− is not coordinated, and related the differences to
3
anion size [48]. However, the size effect may not account for the difference in the structures of 1 and 2,
−
−
since similar complexes reported by Lindoy et al., show that C H COO (smaller than p–HOC H COO in
6
5
6
4

12
N. AꢀꢁꢂLLAH ET AL.
1) was not coordinated to Cu(II) [37]. The difference was actually surprising given the analogous crystal-
lization conditions employed (see Experimental) and similar pK values for the parent carboxylic acids
a
(
pK = 4.55 for p-HOC H COOH and 4.47 for p–CH OC H COOH). Even more perplexing is the fact that,
a 6 4 3 6 4
when these are compared with two closely related complexes available in the Cambridge Structural
atabase (CSꢁ) [49]: [Cu(en) (H O) ](p–HOC H COO) ·2H O (en = ethylene-1,2-diamine) [50] (an analog
ꢁ
2
2
2
6
4
2
2
of 1) is similar to 2, and [Cu(pn) (p–CH OC H COO) ] (pn = 1,3-propanediamine) [51] (an analog of 2) is
2
3
6
4
2
similar to 1. Clearly, the observed molecular structures for 1 and 2 arose as a result of the subtle inter-
play of chemical composition and supramolecular aggregation patterns, in particular the ability of the
–
OH in 1 to form hydrogen bonds to the carboxylate, a feature absent in 2. We are currently collecting
theoretical data to further rationalize the difference. We note that there were no Cu(II) complexes in
the CSꢁ [49] with similar structure as 3 for comparison.
Finally, based on the crystal structures of 1 and 2, and on the fact that Cu(II) has a preference for
N-donor ligands than O-donor ligands, we decided to treat these complexes with N-(hexadecyl)ison-
icotinamide (L) to form magnetic complexes with liquid crystal properties. We found that under sim-
ilar conditions, 1 hardly reacted with L, but 2 reacted to form a purple powder (4) in good yield. The
chemical formula of 4, [Cu(cyclam)(L) ](p–CH OC H COO) , was deduced from elemental analyses (see
2
3
6
4
2
Experimental) and comparison of its spectroscopic data with 1–3 (table 5). ꢁue to solubility differences,
the ꢂV-vis spectra for 1–4 were recorded in different solvents: 1 in H O (slightly soluble), 2 in CH CH OH,
2
3
2
and 3 and 4 in CHCl3.
IR spectra for these complexes show peaks for coordinated H O and N–H(cyclam) at 3200–3700 cm ,
−
1
2
−
1
−1
−1
C–C(aromatic) at 1600 cm , COO(asym) at 1585 cm (for 1) and 1545 cm (for 2–4), N–H(cyclam) at
−1
−1
−1
1
540 cm , and COO(sym) at 1531 cm (for 1) and 1380 cm (for 2-4). In addition, there are strong peaks
−1
−1
−1
for CH (asym) at 2922 cm and CH (sym) at 2850 cm for 3 and 4, and for C=O(amide) at 1636 cm
2
2
for 4. The ∆ values for 1–3 are in agreement with the carboxylate binding modes as revealed from their
−
1
−1
−1
crystal structures (∆ = 234 cm for monodentate in 1; 167 cm for ionic in 2, and 170 cm for ionic in 3).
−1
−
For 4, the ∆ value is 161 cm , from which we infer that p-CH OC H COO ion is not coordinated to Cu(II).
3
6
4
The ꢂV-vis spectrum for 1 shows a broad d–d band at 505 nm (εmax = 155 M− cm ), suggesting a
1
−1
trans III square planar geometry [52, 53]. For 2–4, the bands are at lower energies (λ = 528–546 nm;
max
εmax = 30–119 M− cm ), suggesting a trans III octahedral geometry [53–55]. The geometries for 2–4 were
1
−1
expected based on their structures, but the geometry for 1 was unexpected as this means that both
−
coordinated p–HOC H COO ligands dissociated in aqueous solution. However, the result for 1 is actually
6
4
2
−1
supported by its molar conductance value of 137 S cm mol in H O, indicating a 1 : 2 electrolyte [56].
2
3
.4. Magnetic properties of 1–3
The μeff values for 1–3 were determined at room temperature by the Gouy method. The values for 1
(
(
1.72 ꢀM) and 2 (1.67 ꢀM) are lower than the values reported for several Cu(II) octahedral complexes
1.9–2.2 ꢀM) [57–62]. The results suggest weak antiferromagnetic interactions between the Cu(II) ions
in both molecules, which are linked by H-bonds. A similar suggestion was proposed by ꢀhargavi et al.,
for Mn(acphpn)(H O)NCS]·2H O (acphpn = N,N′-bis(2-hydroxyacetophenone)-1,3-diaminopropane [63].
2
2
However, the value for 3 (2.15 ꢀM) is in agreement with the reported values. From these, we infer that
the magnetic properties of these complexes are independent of the different coordination modes of
the carboxylate ions and the alkyl chain length.
Table 5. Cꢀꢈꢅꢈcꢁꢆꢅꢄzꢈꢁꢄꢃꢇ ꢂꢈꢁꢈ ꢎꢃꢅ 1–4.
−
1
ꢂV-vis λmax (nm) (εmax/M−1 cm−1)
TG Tdec/oC
ꢁSC Tonset (oC) (∆H/kJ mol−1)
Complex
IR ∆ (cm )
μeff (ꢀM)
1
234
505 (155)
1.72
262
58.9 (+22.9), 120.3 (+9.1)
241.8 (+22.2)
2
3
167
170
536 (119)
546 (85)
1.67
2.15
249
210
53.2 (+77.7), 101.8 (+5.2)
58.2 (+56.4), 86.5 (+34.7)
00.5 (+19.8), 137.8 (+30.7)
72.8 (+37.9), 86.7 (1.8)
1
4
161
528 (30)
-
174

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
13
(
a)
(b)
Figure 7. CV ꢃꢎ ꢈꢇ ꢈqꢉꢆꢃꢉꢍ ꢍꢃꢊꢉꢁꢄꢃꢇ ꢃꢎ (ꢈ) 1 ꢈꢇꢂ (b) 2.
3
.5. Redox properties of 1–3
Cyclam is structurally flexible. Hence, it is able to stabilize unusual oxidation states of metal ions, resulting
in their uses as homogeneous redox catalysts. Examples include electrocatalytic reduction of carbonyl
groups [34] and oxidation of alkenes [28–33]. An important parameter for such applications is the redox
potential of the complex, which may be determined by CV.
For 1, its CV scan in H O (figure 7(a)) shows a weak cathodic peak (E ) at −0.25 V and a strong anodic
2
pc
2+
+
peak (E ) at + 0.89 V. The cathodic peak is assigned to the reduction of [Cu(cyclam)] to [Cu(cyclam)] as
pa
its value is in the region normally observed for most mononuclear copper(II) complexes (about −0.13 V)
2+
3+
[
64]. The anodic peak is assigned to the oxidation of [Cu(cyclam)] –[Cu(cyclam)] as the value is similar
to that reported by Zhang et al. for the Cu(II) complex of 1,4,8,11-tetraazacyclotetradecane-5,7-dione in
aqueous solution (+0.83 V) [65]. The stronger anodic peak suggests a more facile oxidation compared
to the reduction process, but both redox processes were irrreversible. ꢂnder similar conditions, the CV
scan for 2 (figure 7(a)) shows a weak cathodic peak at −0.2 V and two strong anodic peaks at + 0.18 V
and + 1.0 V. The first anodic peak may be due to oxidation of cyclam, while the other two peaks may
be similarly assigned as for 1. There were no cathodic or anodic peaks in the CV scan for 3 in CHCl3,
which is ascribed to the presence of insulating long alkyl chains [15]. In CHCl , the long alkyl chains
3
were expected to result in the formation of micelle-like structures, with the hydrophobic part on the
2
+
outside and the hydrophilic part ([Cu(cyclam)(H O) ] ) on the inside. In this structure, the electrons
2
2
from the electrode were unable to reach the ‘insulated’Cu(II) ions to reduce them, and electrons from
the ‘insulated’ Cu(II) ions were unable to reach the electrode to oxidize it. According to these results,
these complexes were unsuitable as homogeneous catalysts.
3
.6. Thermal and mesomorphic properties of 1–4
The thermal properties of 1–4 (table 5) were studied by TG, while the mesomorphic properties of 3
and 4 were studied by ꢁSC and POM, as the latter complexes were expected to be liquid crystals due
to their anisotropic molecular shapes and the presence of long alkyl chains.
For 1, the TG trace showed an initial mass loss of 83.9% (Calcd 88.2%) from 262 °C to about 500 °C
−
due to decomposition of p–HOC H COO and cyclam. Its ꢁSC scan showed three endothermic peaks at
5
6
4
−1
−1
−1
8.9 °C (ΔH = + 22.9 kJ mol ), 120.3 °C (ΔH = + 9.1 kJ mol ), and 241.8 °C (ΔH = + 22.2 kJ mol ), assigned
to breaking of p–HOC H COO–Cu and both inter- and intramolecular hydrogen bonds, respectively.
6
4
For 2, the TG trace showed an initial mass loss of 6.8% (Calcd 6.0%) from 104 °C to 195 °C due to
evaporation of coordinated H O, followed by 82.4% (Calcd 83.5%) from 249 °C to about 600 °C due
2
−
to decomposition of p–CH OC H COO and cyclam. Its ꢁSC scan showed two endothermic peaks at
3
6
4
−1
−1
5
3.2 °C (ΔH = + 77.7 kJ mol ) and 101.8 °C (ΔH = + 5.2 kJ mol ), assigned to breaking of both inter-
and intramolecular hydrogen bonds and dissociation of coordinated H O molecules, respectively. The
2
significantly higher enthalpy change for 2 compared to 1 suggests stronger hydrogen bonds in the

14
N. AꢀꢁꢂLLAH ET AL.
(a)
(b)
(c)
(d)
Figure 8. Pꢀꢃꢁꢃꢌꢄcꢅꢃgꢅꢈpꢀꢍ ꢃꢎ (ꢈ) 3 ꢃꢇ cꢃꢃꢊꢄꢇg ꢈꢁ 141 °C, (b) l ꢃꢇ cꢃꢃꢊꢄꢇg ꢈꢁ 98.0 °C, (c) 4 ꢃꢇ ꢀꢆꢈꢁꢄꢇg ꢈꢁ 84.3 °C, ꢈꢇꢂ (ꢂ) 4 ꢃꢇ cꢃꢃꢊꢄꢇg
ꢈꢁ 74.2 °C.
−
former complex, which is to be expected since these bonds involved free p–CH OC H COO , coordinated
3
6 4
H O and cyclam–NH in 2, but only coordinated p–HOC H COO and cyclam–NH in 1.
2
6
4
The TG trace for 3 showed an initial mass loss of 2.3% (Calcd 1.7%) from 67 °C to about 100 °C due
to evaporation of lattice H O, followed by 87.4% (Calcd 92.2%) from 210 °C to about 500 °C due to
2
−
evaporation of coordinated H O and decomposition of p-CH (CH ) OC H COO and cyclam. Its ꢁSC
scan showed four endothermic peaks at 58.2 °C (ΔH = + 56.4 kJ mol ), 86.5 °C (ΔH = + 34.7 kJ mol ),
00.5 °C (ΔH = + 19.8 kJ mol ) and 137.8 °C (ΔH = + 30.7 kJ mol ). These are assigned to the breaking
2
3
2 15
6
4
−
1
−1
−1
-1
1
of hydrogen bonds and van der Waals forces, dissociation of coordinated H O molecules, and crys-
2
tal-to-mesophase transition, respectively. ꢂnder POM, dendritic textures (figure 8(a)) were observed
at 141 °C on cooling from its isotropic liquid phase (145 °C). This mesophase then coalesced on further
cooling until it crystallized at 89.9 °C.
Finally, the TG trace for 4 showed an initial mass loss of 96.4% (calcd. 95.0%) from 174 °C to 568 °C
−
due to decomposition of L, p–CH OC H COO and cyclam. Its ꢁSC scan showed two endothermic peaks
3
6
4
−1
−1
at 72.8 °C (ΔH = + 37.9 kJ mol ) and 86.7 °C (ΔH = + 1.8 kJ mol ). ꢂnder POM the sample started to
melt at 74.3 °C, forming a needle-like texture (figure 8(c)) similar to L (figure 8(b)) on further heating
at 93.2 °C, but did not clear to the isotropic liquid, even on heating to near its decomposition temper-
ature (174 °C). We repeated the POM experiment and found that when the fluid phase at 100 °C was
cooled, a brush-like texture (figure 8(d)), consistent with mesomorphic ionic liquids [66], rapidly formed

JOꢂRNAL OF COORꢁINATION CHEMISTRꢃ
15
at 78.9 °C. Combining the ꢁSC and POM data, it seems that the complex melted at 72.8 °C, and then
the axially coordinated L ligands dissociated at 86.7 °C. On cooling, its components reassembled to a
mesophase at 78.9 °C. A similar dissociation of N-donor ligands (pyridine, pyrazine and 4,4′-bipyridine)
coordinated at the axial positions of Cu(II) alkylcarboxylates was suggested by Attard and Cullum [67].
The amount of residue found at 600 °C for these complexes (16.1% for 1, 10.8% for 2, 10.3% for 3,
and 3.6% for 4) were in agreement with the calculated values, assuming pure CuO [68, 69].
ꢀased on the above data, the thermal stability of these complexes follows the order: 1 > 2 > 3 > 4.
Hence, it may be inferred that the molecular complex is thermally more stable than the ionic complexes.
Also, 3 and 4 exhibit mesomorphisms as expected for ionic complexes.
4. Conclusion
Three dimeric complexes, [Cu (p–ROC H COO) (H O) ] (R=H, CH , CH (CH ) ), were formed from reac-
2
6
4
4
2
2
3
3
2 15
tions of Cu(II) with the corresponding carboxylate. In the reaction with cyclam, these complexes formed
a mononuclear covalent complex, [Cu(p–HOC H COO) (cyclam)] (1), and two mononuclear ionic com-
6
4
2
plexes, [Cu(cyclam)(H O) ](p–CH OC H COO) (2) and [Cu(cyclam)(H O) ](p–CH (CH ) OC H COO) ·H O
2
2
3
6
4
2
2
2
3
2 15
6
4
2
2
(
3), respectively. Complexes 1–3 show differences in supramolecular association due to extensive
hydrogen bonding interactions. The Cu(II) ions in 1 and 2 are irreversibly reduced to Cu(I) and oxidized
to Cu(III), while 3 is redox inactive due to the insulating long alkyl chains. Complex 2 reacted with
N-(hexadecyl)isonicotinamide (L) to form [Cu(cyclam)(L) ](p–CH OC H COO) (4). These complexes have
2
3
6
4
2
high decomposition temperatures (>200 °C for 1–3, and 174 °C for 4); the covalent 1 is the most ther-
mally stable, while the lower thermal stability of 4 arose from the presence of N-donor ligands at the
axial sites of Cu(II). Complexes 3 and 4 have melting temperatures lower than 100 °C, defining them as
ionic liquids, and both exhibit mesomorphism characteristics of ionic liquid crystals.
Supplementary material
CCꢁC-765498 (1), 912696 (2) and 985198 (3) contain the supplementary crystallographic data. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic ꢁata Center,
1
2 ꢂnion Road, Cambridge Cꢀ2 1EZ, ꢂK; Fax: (+44) 1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the Malaysia Ministry of Education for High Impact Research [grant number ꢂM.C/625/1/HIR/
MOHE/05 and ꢂM.C/HIR/MOHE/SC/03]; ꢂniversity of Malaya for postgraduate research grants [grant number PV056–2012A
and PG023–2013A].
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