Synthesis, crystal structure, thermal decomposition, and XPS studies of homo and heterotrinuclear Cu(II)–Cu(II)–Cu(II) and Cu(II)–Ni(II)–Cu(II) complexes obtained from salpn type ligands

Article abstract of DOI:10.1134/S1070328417070028

In this study, a mononuclear CuL complex was prepared by the use of bis-N,N′-(salicylidene)-1, 3-propanediamine (LH₂) and Cu²⁺ ion. NiCl₂ and NiBr₂ salt were treated with this complex in dioxanewater medium and two new complexes [(CuL)₂NiCl₂(H₂O)₂] and [(CuL)₂NiBr₂(H₂O)₂)] with Cu(II)–Ni(II)–Cu(II) nucleus structure were obtained. In addition to this bis-N,N′-(2-hydroxybenzyl)-1,3-diaminopropane (L^HH₂) was prepared by the reduction of LH₂ with NaBH₄ in MeOH medium. The treatment of this reduced complex with Cu²⁺ ion resulted a complex [(CuL^H)₂CuCl₂] with a structure of Cu(II)–Cu(II)–Cu(II). The complexes prepared were characterized by the use of elemental analysis, IR spectroscopy, thermogravimetric and X-ray diffraction methods. The crystal structures of [(CuL)₂NiBr₂(H₂O)₂] (СIF file CCDC 1448402) and [(CuL^H)₂CuCl₂] (СIF file CCDC 1448401) complexes were elucidated. It was found that halogen ions are coordinated to terminal Cu²⁺ ions which are in a distorted square pyramid coordination sphere. It was determined that the central Cu(II), which joins terminal square pyramidal Cu(II), was coordinated only by the phenolic oxygens of the ligand while the central Ni(II) was coordinated by two phenolic oxygens of the organic ligand and two water molecules. These complexes were investigated by XPS and it was found that the terminal and central Cu²⁺ ions were different in Cu(II)–Cu(II)–Cu(II) complex. Also, the thermal degradation of the CuLH complex unit was observed to exothermic in contrast to the expectations.

Full text of DOI:10.1134/S1070328417070028

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2017, Vol. 43, No. 7, pp. 463–472. © Pleiades Publishing, Ltd., 2017.
Synthesis, Crystal Structure, Thermal Decomposition, and XPS
Studies of Homo and Heterotrinuclear Cu(II)–Cu(II)–Cu(II)
and Cu(II)–Ni(II)–Cu(II) Complexes Obtained
from Salpn Type Ligands1
N. Acara, O. Atakola, F. N. Dinçer Kayab, I. Svobodac, M. Yazıcıoğlua, and S. Özd, *
aAnkara University, Faculty of Science, Department of Chemistry, Ankara, 06100 Turkey
bMersin University, Faculty of Pharmacy Department of Analytical Chemistry, Yenisehir Campus, Mersin, 33169 Turkey
cStrukturforschung, FB Materialwissenschaft, TU-Darmstadt, Petersenstrasse 23, D-12 Darmstadt, 64287 Germany
dAhi Evran University, Faculty of Science and Arts, Department of Chemistry, Kırşehir, 40100 Turkey
*e-mail: sevioz@hotmail.com
Received February 25, 2016
Abstract⎯In this study, a mononuclear CuL complex was prepared by the use of bis-N,N'-(salicylidene)-1,
3-propanediamine (LH2) and Cu2+ ion. NiCl2 and NiBr2 salt were treated with this complex in dioxane-
water medium and two new complexes [(CuL)2NiCl2(H2O)2] and [(CuL)2NiBr2(H2O)2)] with Cu(II)–
Ni(II)–Cu(II) nucleus structure were obtained. In addition to this bis-N,N'-(2-hydroxybenzyl)-1,3-diami-
nopropane (LHH2) was prepared by the reduction of LH2 with NaBH4 in MeOH medium. The treatment of
this reduced complex with Cu2+ ion resulted a complex [(CuLH)2CuCl2] with a structure of Cu(II)–Cu(II)–
Cu(II). The complexes prepared were characterized by the use of elemental analysis, IR spectroscopy, ther-
mogravimetric and X-ray diffraction methods. The crystal structures of [(CuL)2NiBr2(H2O)2] (СIF file
CCDC 1448402) and [(CuLH)2CuCl2] (СIF file CCDC 1448401) complexes were elucidated. It was found
that halogen ions are coordinated to terminal Cu2+ ions which are in a distorted square pyramid coordination
sphere. It was determined that the central Cu(II), which joins terminal square pyramidal Cu(II), was coordi-
nated only by the phenolic oxygens of the ligand while the central Ni(II) was coordinated by two phenolic
oxygens of the organic ligand and two water molecules. These complexes were investigated by XPS and it was
found that the terminal and central Cu2+ ions were different in Cu(II)–Cu(II)–Cu(II) complex. Also, the
thermal degradation of the CuLH complex unit was observed to exothermic in contrast to the expectations.
Keywords: salpn type Schiff base, reduced Schiff base, heterotrinuclear complex, binding energy, XPS study
DOI: 10.1134/S1070328417070028
INTRODUCTION
ligands [20]. The reduced state of LH2 ligand is very
prone to the formation of polynuclear complexes in a
similar manner [13, 21–23]. However, the nuclear
structure of these trinuclear complexes is either
Bis-N,N'(salicylidene)-1,3-propanediamine (LH2) is
a ligand which has a great tendency to give polynuclear
homo and heteronuclear complexes. The first dinu-
clear and trinuclear complexes were reported by the
use of this ligand were reported in 1976 and in 1990
respectively [1, 2]. There have been so many trinuclear
complexes of this tetradentate ligand prepared by the
us since 1990 [3–18]. The Ni(II) and Cu(II) salts give
NiL and CuL mononuclear complexes with LH2 in
weakly basic alcoholic or other organic solvents. The
molecular models of these compounds have been
known since 1985 [19]. It is also known that the Schiff
bases could easily be converted into phenyl amines
with NaBH4 in alcoholic media LH2 ligands were
reduced like that and used as the reduced Shiff base
mononuclear
(Ni(II)–Ni(II)–Ni(II),
Cu(II)–
Cu(II)–Cu(II), Co(II)–Co(II)–Co(II), Co(III)–
Co(II)–Co(III)) or dinuclear (Ni(II)–M(II)–Ni(II),
M = Fe(II), Cu(II), Co(II), Mn(II), Zn(II), Cd(II),
Hg(II), Pb(II)). The number of trinuclear complexes
where the terminal metal ions are Cu2+ is highly lim-
ited. The trinuclear complex of Cu(II)–Ni(II)–
Cu(II) has been reported [24, 25].
This study was related to the formation of Cu(II)–
Ni(II)–Cu(II) complexes with the use of LH2 and its
reduced state bis-N,N'-(2-hydroxybenzyl)-1,3-diamino-
propane (LHH2). In this line the original plan of this
study is first the formation of mononuclear CuL and
1
The article is published in the original.
463

464
ACAR et al.
CuLH complexes with the reaction of LH2 or LHH2 using
Cu(II) salts and then preparation of [CuLNi-
Cl2CuL(H2O)2] (I) and [CuLNiBr2CuL(H2O)2] (II)
complexes by the reaction of these mononuclear com-
plexes with NiCl2, NiBr2, and Ni(AcO)2 salts. The over-
all reaction is depicted in Scheme:
X
H
OH2
H
H
C N
O
N C
Cu
Ni
Cu
H
H
C N
O
N C
O
O
O
in MeOH/H2O
H2O
+ NiX2
Cu
O
C N
X
N C
H
However, this has only worked between CuL and analysis were completed by a GBC Avanta PM Model
flame atomic absorption device. The related complex
(2–3 mg) was dissolved in a mixture of HNO3 (63%)
and 1 mL H2O2 (30%) with heating, diluted to
100 mL, and placed into a nebulizer of the atomic
absorpion device for the metal analysis. The NMR
spectra of the ligands were recorded with a Varian
brand Mercury model 400 MHz NMR spectropho-
tometer.
X-ray structure determination. A single crystal of
[CuLNiBr2CuL(H2O)2] (II) and [CuLHCuCl2CuLH]
(III) complexes were analyzed on an Oxford Diffrac-
tion Xcalibur Single Crystal X-ray Diffractometer with
a sapphire CCD detector using MoKα radiation (λ =
0.71073 Å) operating in ω/2θ scan mode. The unit cell
parameters were determined and refined by using the
angular settings of 25 automatically centered reflec-
tions in 3.28° ≤ θ ≤ 26.36° range for III and 2.96° ≤ θ ≤
26.02° for II complex. The data of II and III were col-
lected at 293(2) and 100(2) K, respectively. The
empirical absorption corrections were applied by the
semi-empirical method via the Crys Alis CCD soft-
ware [29]. The molecular models were obtained from
the results of the cell refinement and the data reduc-
tions were carried out using the solution software
SHELXL-97 [30]. The structures of complexes were
solved by direct methods using the SHELXS-97 soft-
ware implemented in the WinGX package [31].
NiCl2 and NiBr2. CuL and Ni(AcO)2 did not give a
complex like this. When Ni(AcO)2 was used, it was
observed that the Cu(II) in the mononuclear CuL
complex was replaced with Ni(II) resulting the forma-
tion of [SNi(L)Cu(AcO)2Ni(L)S] (S is a solvent such
as dioxane or MF) type complexes given in the litera-
ture. Similarly, it was not possible to obtain the related
complex with the use of the reduced ligand. However,
sample with trinuclear stochimetry of [CuLHCu-
Cl2CuLH] (III) similar to the literature with the use of
reduced ligand a CuCl2 [26–28].
The three complexes obtained were first character-
ized by the help of elemental analysis and IR spectros-
copy and their thermal decomposition products were
analyzed by the use of thermogravimetric (TG) meth-
ods. The complexes II and III, obtained in crystals
with suitable sizes were enlightened with X-ray dif-
fraction (XRD) method. Finally, all three-complex
synthesized were subjected to XPS (X-ray photoelec-
tron spectroscopy) study and the apparent XPS signals
of Cu, O, and N atoms were investigated.
EXPERIMENTAL
Apparatus and methods. The TG-DTA studies were
carried out using a Shimadzu DTG-60H apparatus.
The thermogravimetric analyses were carried out in Pt
pans at a rate of 10 K/min under nitrogen atmosphere.
The temperature and heat calibrations of both devices
were carried out using In and Pb metals. The IR spec-
tra of the ligands and complexes were carried out by
the use of Shimadzu brand Infinity model FTIR appa-
ratus equipped with three reflection ATR unit and all
IR spectra were recorded at a resolution of 4 cm–1. The
mass spectra were obtained by the use of a direct inlet
(DI) unit of a Shimadzu 2010 Plus GCMS apparatus.
Crystallographic data and structural refinements
for compounds II, III are summarized in Table 1, and
selected bond lengths and angles are listed in Table 2.
Supplementary material for structures II and III
has been deposited with the Cambridge Crystallo-
graphic Data Centre (CCDC 1448402 (II), 1448401
(III); deposit@ccdc.cam.ac.uk or http://www.ccdc.
cam.ac.uk).
Synthesis of LH2. This Schiff base was prepared via
C, H, and N analyses were carried out using an condensation reaction in EtOH under hydrothermal
Eurovector 3018 CHNS analyzer while Ni and Cu conditions using 2-hydroxy-benzaldehyde and 1,3-
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SYNTHESIS, CRYSTAL STRUCTURE, THERMAL DECOMPOSITION, AND XPS STUDIES
465
Table 1. Crystallographic data and structure refinement of complex II and III
Value
Parameter
II
III
Formula weight
T, K
1138.41
293(2)
830.22
100(3)
Crystal size, mm
Crystal system
Space group
0.16 × 0.16 × 0.14
Monoclinic
P21/n
0.36 × 0.22 × 0.14
Monoclinic
P21/n
a, Å
b, Å
c, Å
β
10.6618(4)
15.4516(6)
15.0511(5)
91.240(3)
11.0189(7)
15.3861(8)
10.3441(8)
106.959(7)
1742.32(19)
V, Å3
2478.97(16)
Z
2
2
calcd, g cm–3
1.616
1.583
ρ
µ, mm–1
0.2902
0.2011
F(000)
1232
850
Tmax/Tmin
θ Range, deg
Index ranges
0.6868–0.6539
2.96–26.02
–13 ≤ h ≤ 12,
–18 ≤ k ≤ 19,
–18 ≤ l ≤ 14
0.7660–0.5313
3.28–26.36
–13 ≤ h ≤ 13,
–18 ≤ k ≤ 18,
–7 ≤ l ≤ 13
Reflections collected
Rreflections unique
R1, wR2 (I > 2σ(I))
R1, wR2 (all)
4871
3306
0.0494–0.1079
0.0878–0.1240
4871/310
1.045
3489
2977
0.0285–0.0729
0.0363–0.0755
3489/220
1.102
Data/parameters
GOOF of F2
Largest difference peak/hole, e Å–3
0.771/–0.483
0.564/–0.311
2.01 (p. –CH2–). 13C NMR (CH3COCH3-d6; δ,
ppm): 166.6, 161.1, 132.7, 132.1, 119.1, 118.9 (CAr),
116.9 (–C=N), 58.5 (N–CH2–), 31.9 (–CH2–). MS
(m/z): 282 [M]+, 161 [HO–C6H4–CH=N–CH2–
CH2–CH2]+, 148 [HO–C6H4–CH=N–CH2–CH2]+
(BP = base peak), 134 [HO–C6H4–CH=N–CH2]+,
120 [HO–C6H4–CH=N]+, 107 [HO–C6H4–CH2]+,
77 [C6H5]+.
diaminopropane. 2-Hydroxy-benzaldehyde (0.1 mol,
12.20 g) was dissolved in 120 mL of warm EtOH, then
0.05 mol (3.70 g) of 1,3-diaminopropane was added to
this solution and heated up to the boiling point. After
cooling, yellow crystals were filtered and dried in air.
Yield, 90–95%, mp 58°C (determined by TG).
For C17H18N2O2
anal. calcd., %: C, 72.32;
Found, %: C, 71.95;
H, 6.43;
H, 6.33;
N, 9.92.
N, 10.09.
Synthesis of LHH2. 3.0 g of LH2 was dissolved in
70.0 mL of MeOH by stirring and heating. This solu-
tion was heated up to 50°C and to this solution solid
NaBH4 in small portions was added until colorless
under strong mixing [32–35]. After 10 min of stirring,
300 mL of ice water was added to it. The final mixture
was left to stand for 24 h. After filtration, the white
IR data (ν, cm–1): 2627 ν(O–H), 3021–3019 ν(C–
HAr), 2929–2862 ν(C–HAliph), 1629 ν(C=N), 1608
ν(C=Cring), 1274–1151 ν(C–OPhenol), 762 δ(C–HAr).
λ
max, nm (ε, L mol–1 cm–1): 243 (7045) in DMSO; 242
(7865) in MeOH. 1H NMR data: (CH3COCH3-d6; δ,
ppm): 13.51 (s. O–H), 8.60 (s. –CH=), 7.43 (d. HAr),
7.32 (t. HAr), 6.88 (t. HAr), 3.68 (t. N–CH2–), precipitate was air-dried. The product LHH2 was
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Table 2. Selected bond distances (Å) and angles (deg) for II and III
Bond
d, Å
Bond
d, Å
II
N(1)–Cu(1)
1.972(4)
1.978(4)
1.968(3)
2.087(3)
1.967(3)
2.080(3)
2.025(3)
O(3)–H(3A)
0.86(2)
N(2)–Cu(1)
O(1)–Cu(1)
O(1)–Ni(1)
O(2)–Cu(1)
O(2)–Ni(1)
O(3)–Ni(1)
O(3)–H(3B)
Ni(1)–O(3)
Ni(1)–O(2)
Ni(1)–O(1)
Cu(1)–Br(1)
0.81(2)
2.025(3)
2.080(3)
2.087(3)
2.8242(8)
III
O(2)–Cu(2)
N(1)–Cu(1)
N(1)–H(1A)
N(2)–Cu(1)
N(2)–H(2A)
O(1)–Cu(2)
O(1)–Cu(1)
1.994(2)
0.82(3)
1.9108(16)
1.9632(16)
2.5091(7)
2.9138(3)
O(2)–Cu(1)
Cu(1)–Cl(1)
Cu(1)–Cu(2)
1.995(2)
0.86(3)
1.919(15)
1.9823(16)
Angle
ω, deg
Angle
ω, deg
II
O(3)Ni(1)O(3)
O(3)Ni(1)O(2)
O(2)Ni(1)O(2)
O(3)Ni(1)O(1)
O(2)Ni(1)O(1)
O(1)Ni(1)O(1)
O(2)Cu(1)O(1)
O(2)Cu(1)N(1)
O(1)Cu(1)N(1)
180.0(3)
O(2)Cu(1)N(2)
O(1)Cu(1)N(2)
N(1)Cu(1)N(2)
O(2)Cu(1)Br(1)
O(1)Cu(1)Br(1)
N(1)Cu(1)Br(1)
N(2)Cu(1)Br(1)
91.57(15)
165.35(16)
94.11(18)
100.95(9)
102.14(9)
91.40(13)
91.18(12)
89.65(13)
180.0(2)
91.19(13)
105.21(11)
180.0(16)
80.04(12)
166.30(15)
91.66(15)
III
N(1)Cu(1)Cl(1)
O(2)Cu(1)O(1)
O(2)Cu(1)N(1)
O(1)Cu(1)N(1)
O(2)Cu(1)N(2)
O(1)Cu(1)N(2)
N(1)Cu(1)N(2)
O(2)Cu(1)Cl(1)
O(1)Cu(1)Cl(1)
78.09(7)
164.01(8)
92.91(7)
93.17(7)
168.75(8)
93.88(8)
89.93(5)
88.09(5)
103.10(6)
99.08(6)
40.55(5)
40.86(4)
133.48(6)
132.53(6)
76.179(16)
180.0(10)
N(2)Cu(1)Cl(1)
O(2)Cu(1)Cu(2)
O(1)Cu(1)Cu(2)
N(1)Cu(1)Cu(2)
N(2)Cu(1)Cu(2)
Cl(1)Cu(1)Cu(2)
O(2)Cu(2)O(2)
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recrystallized from hot EtOH–H2O (2 : 1, v/v). Yield, melting point and decomposes above 260°C. Yield,
60–80%.
55–60%, mp = 107°C.
For C17H16N2O2Cu
For C17H22N2O2
anal. calcd., %: C, 59.38; H, 4.68; N, 8.14; Cu, 18.48.
anal. calcd., %:
Found, %:
C, 71.30;
C, 70.86;
H, 7.74;
H, 6.69;
N, 8.01.
N, 8.37.
Found, %:
C, 58.82; H, 4.37; N, 7.92; Cu, 17.56.
IR data (ν, cm–1): 3048–3018 ν(C–HAr), 2954–
2869 ν(C–HAliph), 1618 ν(C=N), 1599 ν(C=Cring),
1317–1149 ν(C–OPhenol), 756 δ(C–HAr).
Second stage preparation of trinuclear complex.
0.687 g (0.002 mol) CuL 60 mL was dissolved in hot
dioxane heated at its boiling point. A solution of
0.238 g (0.001 mol) NiCl2 · 6H2O in 40 mL of
MeOH–H2O (1 : 1, v/v) was added to it. The solution
was kept at the bench for 2–3 days and precipitated
crystals were filtered off and dried in air. Yield, 27%.
For C42H52N4O10Cl2Cu2Ni (I)
IR data (ν, cm–1): 3307 ν(N–H), 3055–3023
ν(C–HAr), 2967–2823 ν(C–HAliph), 1606–595
ν(C=Cring), 1253–1099 ν(C–OPhenol), 752 δ(C–HAr).
1H NMR data (CH3COCH3-d6; δ, ppm): 13.22 s.,
7.12 m., 6.67 m., 4.73 br., 3.80 m., 2.56 m., 1.15 m.
13C NMR (CH3COCH3-d6; δ, ppm): 155.41, 151.23,
143.27, 126.92, 128.56, 124.85, 65.43, 61.17, 18.62. MS
(m/z): 286 (molecular peak), 179 [HO–C6H4–CH2–
NH–CH2–CH2–CH2–NH]+, 163 [HO–C6H4–
CH2–NH–CH2–CH2–CH2]+, 150 [HO–C6H4–
CH2–NH–CH2–CH2]+, 134 [HO–C6H4–CH2–N–
CH2]+, 122 [HO–C6H4–CH2–NH]+, 107 [H–
C6H4–CH2]+ (base peak), 90 [C6H4–CH2]+, 77
[C6H5]+.
anal.
calcd., %: 49.03; 5.09; 5.63; 6.89; 12.35; 5.70.
Found, %: C, H, N, Cl, Cu, Ni,
C,
H,
N,
Cl,
Cu,
Ni,
48.81; 4.49; 5.63; 7.12; 12.30; 5.88.
IR data (ν, cm–1): 2627 ν(O–H), 3021–3019 ν(C–
HAr), 2929–2862 ν(C–HAliph), 1629 ν(C=N), 1608
ν(C=Cring), 1274–1151 ν(C–OPhenol), 762 δ(C–HAr).
Synthesis of II was carried out in two stages as men-
tioned above and the second stage was the synthesis of
complex II by using CuL (0.687 g) and NiBr2 (0.219 g,
Synthesis of I. First stage preparation of CuL. 1.410 g
(0.005 mol) LH2 was dissolved in 50 mL EtOH;
1.0 mL Et3N and 0.850 g CuCl2 · 2H2O solution in
20 mL hot water were added to it. The resulting mix-
ture was kept on the bench for 5–6 h and the dark
green crystals were filtered off. It has no definite 0.001 mol).
For C42H52N4O10Br2Cu2Ni
anal. calcd., %:
Found, %:
C, 45.14;
C, 44.67;
H, 4.68;
H, 5.43;
N, 5.01;
N, 4.91;
Br, 14.30;
Br, 14.94;
Cu, 11.32;
Cu, 11.32;
Ni, 5.25.
Ni, 4.96.
IR data (ν, cm–1): 3023–3010 ν(C–HAr), 2941–
by heating up to 70°C. Et3N (0.5 mL) and a solution of
2854 ν(C–HAliph), 1631–1624 ν(C=N), 1610 CuCl2 · 2H2O (0.510 g, 20 mL) in hot MeOH–H2O
ν(C=Cring), 1278–1159 ν(C–OPhenol), 752 δ(C–HAr).
(1 : 1, v/v) were added to this mixture. The resulting
Synthesis of III. Reduced Schiff base LHH2 mixture was kept on the bench for 48 h; the crystalized
(0.572 g, 0.002 mol) was dissolved in 40 mL of dioxane green complex was filtered off and dried in air.
For C34H40N4O4Cl2Cu3
anal. calcd., %:
Found, %:
C, 49.19;
C, 49.03;
H, 4.85;
H, 4.71;
N, 6.75;
N, 7.16;
Cl, 8.54;
Cl, 8.40;
Cu, 22.96.
Cu, 22.14.
IR data (ν, cm–1): 3170 ν(N–H), 3033–3012 ν(C–
HAr), 2947–2872 ν(C–HAliph), 1595 ν(C=Cring),
1275–1076 ν(C–OPhenol), 748 δ(C–HAr).
RESULTS AND DISCUSSION
The X-ray diffraction images of [CuLNi-
Br2CuL(H2O)2] (II) and [CuLHCuCl2CuLH] (III)
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ACAR et al.
(a)
C(9a)
C(10a)
C(8a)
N(2a)
C(11a)
C(13a)
C(12a)
O(5)
C(19)
N(1a)
C(22b)
C(17a)
C(23)
Br(1a)
C(20)
C(21)
Cu(1a)
C(7a)
C(16a)
C(15a)
C(18)
C(4a)
C(6a)
O(2a)
O(1a)
Ni(1)
O(6)
O(4)
C(5a)
O(6b)
C(23b)
C(3)
C(4)
O(3a)
C(1a)
C(2)
C(6)
C(22)
O(3)
C(3a)
C(2a)
O(1)
O(2)
C(16)
C(15)
C(1)
C(5)
Cu(1)
Br(1)
C(17)
C(7)
C(8)
N(1)
N(2)
C(12)
C(14)
C(13)
C(11)
C(10)
C(9)
(b)
C(14)
C(13)
C(12)
C(11)
C(4a)
C(5a)
C(7a)
C(3a)
C(15)
C(16)
C(17)
C(6a)
C(2a)
C(1a)
C(8a)
N(1a)
N(2)
O(1a)
C(10)
Cu(1)
O(2)
Cl(1a)
Cu(2)
Cu(1a)
Cl(1)
C(9a)
C(10a)
C(9)
O(2a)
C(17a)
C(16a)
C(15a)
O(1)
C(1)
N(1)
C(7)
C(8)
N(2a)
C(11a)
C(2)
C(12a)
C(13a)
C(14a)
C(6)
C(3)
C(4)
C(5)
Fig. 1. Ortep picture of complexes II (a) and III (b).
ion. Central Ni2+ ion is coordinated by four phenolic
oxygens and two water molecules in an octahedral
coordination sphere O(6).
complexes drawn with Ortep program are given in
Fig. 1 [31].
Complex II contains two additional dioxane mole-
cules. The coordination of the both complexes are
similar in both CuL and CuLH units of terminal Cu
complexes. Both have distorted square pyramidal
In the complex III which contains reduced ligands,
the terminal Cu2+ ion is in a similar coordination
sphere but coordinated only four phenolic oxygens. A
structure. The terminal Cu2+ ions are coordinated by five-member square pyramidal coordination is very
two phenolic oxygens of two iminic and one chloride common for Cu(II) complexes [26–28]. Similarly, a
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SYNTHESIS, CRYSTAL STRUCTURE, THERMAL DECOMPOSITION, AND XPS STUDIES
469
four-member coordination is also very common for
Cu(II) complexes, but Cu2+ ions make sometime a
distorted square-planar coordination [26, 27]. In our
study, Cu(II) seems to be in a square planar coordina-
tion since programs solve the molecules on symmetry
basis. The octahedral coordination is an expected sit-
uation for central Ni2+ ion. The central Ni(II) in these
type trinuclear complexes was always found to be in
octahedral coordination in the literature [2, 13, 14, 16,
17]. There is some difference in chelate rings formed in
the complex. Looking at the data listed in Table 2 the
chelate rings formed by the terminal Cu(II) are differ-
ent. The six membered Cu–N(1)–C(8)–C(9)–
C(10)–N(2) chelate is in chair conformation for both
compounds. However, the chair confirmation formed
by the reduced ligand is more ideal. The angles
between these chelate planes can easily be determined
by the use of the Parst program [36]. In complex III,
the angle between the C(8)–C(9)–C(10) and N(1)–
C(8)–C(10)–N(2) planes was 56.63(0.22)° and the
angle between the N(1)–C(8)–C(10)–N(2) and
N(1)–Cu–N(2) planes was determined to be
47.00(0.09)°. Two angles are very close to each other.
However, the ligand in complex II is a Schiff base and
the same angles in complex II were 59.74(0.07)°
and 28.14(0.01)°, respectively. The chelate ring in
complex III is in a much-stressed form. This is obvi-
ously due to the imine bonds in Schiff base. The imine
bond is a double bond between C and N and this
makes the torsion angles of C(8)C(9)N(1)Cu and
C(9)C(10)N(2)Cu smaller. These torsion angles
were 61.9(2)° and –60.7(2)° in reduced ligand or com-
plex III while it reduces to 52.0(6)° and –52.4(6)o in
complex II.
(a)
13
12
11
10
9
8
7
6
5
II
III
I
4
3
0
100 200 300 400 500 600 700
T, °C
(b)
40
30
20
10
0
–10
–20
–30
–40
–50
–60
III
I
II
0
100 200 300 400 500 600 700
T, °C
There is a different situation when the square pyra-
midal structures of terminal Cu2+ ions are compared.
The following equation, which shows that the five-
membered coordination are in square pyramid or
trigonal pyramid structures undifferently how dis-
torted they are, is frequently used [37].
Fig. 2. The comparative TG (a) and DTA (b) curves of
complexes I–III.
One of the most effective methods to determine the
complex stoichiometry is thermogravimetry [15]. Fig-
ure 2a shows the thermogravimetric curves for all
three complexes in a comparative manner. It is clear
that the first process is the decomposition of water
from complexes I and II. Figure 2b shows the DTA
curves for the thermal reactions given in a comparative
manner. The first thermal reaction in complex I and II
is endothermic.
Τ = (α–β)/60.
Here, α and β are two largest angles around Cu2+
ion. As τ value approaches to zero the coordination
sphere is closer to the square pyramidal structure.
Similarly, if this value goes to unity then the coordina-
tion is most likely to be trigonal bipyramid. Figure 1
clearly reveals that the coordination spheres obtained
in this study were square pyramid. The τ value for
The central Ni2+ ions in complex I and II are coor-
complex III and II are observed to be 0.0158 and dinated with two H2O molecules as well as two pheno-
0.079, respectively (Table 2). In summary, the coordi-
nation of the complexes obtained by the use of Schiff
base is much closer to the ideal structure. On the other
hand, the chelate rings are much more distorted from
the ideal structure. In these types of complexes, it is
highly difficult to determine the coordinated H2O
lic oxygens. The XRD data show that in complex II the
coordination includes two oxygen molecules as well
water molecules. The molecular model of complex II
cannot be presented since it was not possible to grow
its crystals to the appropriate dimensions. However,
the thermo gravimetric results show that two water
molecules since elemental analysis do not give definite molecules are present in the molecule as a coordinated
information about it. solvent. The first thermal reaction is most probably is
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470
ACAR et al.
Table 3. The thermoanalytical data of complexes I–III
Thermal reaction
loss of H2O
or H2O + dioxane (1)
loss of dioxane
or H2O + dioxane (2)
(3)
weight loss, %
weight loss, %
weight
loss,
range, °C % (found)
Complex
temperature
range, °C
temperature
range, °C
temperature
exptd
11.55
found
exptd
found
(CuL)2NiCl2(H2O)2 68–102
DTA peak:
90.72 (endo)
(CuL)2NiBr2(H2O)2 67–93
11.77 0.22 114–147
DTA peak:
11.55 12.31 0.40 266–287
6.85
6.26
DTA peak:
273
(C4H8O2)2 (I)
130.07 (endo)
3.50
3.73 0.11 126–173
DTA peak:
15.75 14.99 0.30 265–289
DTA peak:
86.62 (endo)
DTA peak:
273
(C4H8O2)2 (II)
163.04 (endo)
(CuLH)2CuCl2 (III)
230–247
DTA peak: trinuclear
Most probably 8.04 0.38
246 (exo)
complex
decomposes
the removal of H2O molecules from the structure. The coordinated by four phenolic oxygens. As seen from
Fig. 2b, no weight loss is observed at the hydrothermal
temperature range because a water or dioxane mole-
cule was not coordinated on the complex molecule.
weight loss which takes place between 68–102°C
belonging to removal of two H2O from complex I do
not match the expected value, while the weight loss in
complex II which takes place at 67–93°C corresponds
to the removal of two H2O molecules (found 3.73
0.11%; exptd 3.50%). Table 3 lists the thermodynamic
data related to these complexes. The thermal reaction
(2) took place in complex II corresponds to the loss of
two dioxane molecules. The weight loss in the thermal
reaction (1) of complex I was found to be 11.77
0.22%. This value is much higher than the value
expected for the removal of two H2O molecules. How-
ever, if one thinks that the structure contains two diox-
ane molecules it can be concluded that there were one
H2O and one dioxane molecule removed from the
structure (exptd 11.55%; found 11.77 0.22%). Again,
the weight loss found in the second thermal weight loss
of the complex I also matches the removal of one H2O
and one dioxane molecules from the structure (exptd
11.55%; found 12.31 0.40%). TG and DTA curves of
complex I and II are in the same form. The thermal
reaction (3) observed starts at 260°C. It is probable
that after the removal of the coordinated H2O mole-
cules the trinuclear complex completely decomposes
into terminal CuL and central Ni(II) units. After this
temperature, thermal decomposition of CuL complex
takes place. In the literature, it was reported that the
CuL and NiL complexes starts to decompose at tem-
perature with a similar TG curve [15, 34]. The TG and
DTA curves of complex III are entirely different. This
complex was obtained by the template synthesis using
the reduced ligand and CuCl2. It was not possible to
obtain mononuclear complexes by template synthesis.
It is most probably due to the fact that terminal
CuLH units are not stable, and for this reason the
mononuclear CuLH unit could not be obtained in a
stable form. At the template synthesis, the CuLH units
are formed and trimerised by central Cu2+ ion. During
the thermal analysis when the temperature reaches to
240°C complex III decomposes into terminal CuLH
and central Cu(II). The instable CuLH units begin to
decomposition in an exothermic manner at this tem-
perature. The exothermic peak observed in DTA curve
of complex III in Fig. 2c corresponds to this decom-
position process. At this temperature, the trinuclear
complex decomposes with a small weight loss. If this is
the case, then the electron densities of Cu2+ ions must
be very different. The XPS scanning data of Cu2+ ions
and O and N atoms are comparatively listed in Fig. 3.
When Fig. 3a is examined it is easily seen that com-
plexes I and II give a signal maximum at 397 eV. This
value was observed to shift 0.5 V higher potential in
complex III. In complexes I and II, there is only one
type N atom since all N atoms have the same chemical
environment. That is why only a single signal was
observed. However, in complex III the nitrogen atoms
are in secondary amine form and they are supposed to
be rich in electrons. Therefore, the binding energy
must decrease. However, a completely reverse case is
observed here. In complex II there needed more
energy to snatch an electron from the N atom in
complex II. In that case, the electrons on the N
The XRD data show that the central Cu2+ ion is only atoms are largely transferred to terminal Cu(II)
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SYNTHESIS, CRYSTAL STRUCTURE, THERMAL DECOMPOSITION, AND XPS STUDIES
471
Figure 3b shows the situation of the O atoms in
three complexes. There are three types of oxygen
atoms, namely oxygen of water, phenolic oxygen, and
oxygen of dioxane (C4H8O2). The H2O molecules
form a coordination bond. Therefore, there must be a
small difference between these three different types of
oxygens. When we focus on curves of complexes I and
II there is a shoulder at 531 eV in addition to the signal
observed at 529 eV which is absent in the curve of com-
plex III.
(a)
3400
3200
3000
2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
III
I
II
The most surprising result in XPS studies was
observed for the 2p electrons of Cu atoms. As known
the electrons of Cu atom which give distinctive signals
are the p electrons and this situation is entirely specific
to Cu atoms. The 2p1/2 and 2p3/2 electrons give XPS
signals about 930 and 950 eV, respectively, and both
these signals are observed in the presence of Cu atoms
[38]. There are two signals expected from complexes I
and II coming from 2p1/2 and 2p3/2 electrons since they
contain only one type of Cu atom. This is the situation
in Fig. 3c which contains two signals at 930 and 950 eV.
However, the situation is entirely different for
complex III. Here there are two different Cu atoms
with different chemical environments. The chemical
surroundings of the terminal and central Cu atoms are
different. Also, the chemical environment of the ter-
minal Cu(II) atoms in complex III differs from those
in complexes I and II. This is also clearly apparent in
Fig. 3b. The signals of complex III show a slight shift
towards the higher energy. The central Cu(II) is differ-
ent. There are two weak signals at 942 and 961 eV in
Fig. 3b. This is most probably due to the central Cu(II)
atom. These sorts of great differences are not very
common in XPS studies. However, it is the case here.
These findings show that the central Cu atoms joining
to CuLH units resulting a much stretched complex. It
is most probable that the strong exothermic signals
observed at 240°C are due to this highly stretched
structure. However, there is not a cogent explanation
of this situation.
390
395
400
405
410
415
Binding energy, eV
(b)
4500
4000
3500
3000
2500
2000
1500
1000
500
III
I
II
540
520
525
530
535
545
Binding energy, eV
(c)
12000
10000
8000
6000
4000
2000
III
I
II
920 930 940 950 960 970 980
Binding energy, eV
ACKNOWLEDGMENTS
This work was supported by the Scientific Research
Fund of the University of Ankara (project
no. 13L4240018) and Scientific Research Fund of the
Ahi Evran University (grant no. 4001.12.014).
Fig. 3. XPS scanning curves of 1s electrons of N (a), O (b),
Cu (c) atoms in the complexes I–III.
atoms. This situation is clearly apparent in IR spectra.
The ν(N–H) vibrations are observed at 3307 cm–1 in
when the reduced ligand is in its free state and shifts to
3170 cm–1. There is a shift of approximately 137 cm–1
to lower energy. The fact that the vibrational frequency
of the donor atoms shifts to the lower energy values
after they make coordination bond has been known for
a long time. However, the shift here is higher than the
normal value. The IR data also show that there is an
extensive electron transfer from N atom to the reduced
ligand.
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