Hexanuclear [Cu4IILn2III] compounds incorporating N,O-donor ligands – Synthesis, crystal structures and physicochemical properties

Article abstract of DOI:10.1016/j.ica.2017.06.002

The reaction between N₂O₄-donor ligand N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane (H₄L?=?C₁₇H₁₈N₂O₄) and different salts leads to the formation of novel hexanuclear clusters [Cu₄Sm₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·9H₂O (1) and [Cu₄Eu₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·3H₂O·CH₃COOH·CH₃OH (2) that crystallize in the triclinic system, space group P-1. The structures of 1 and 2 show two heterotrinuclear [Cu₂Ln] moieties that are linked by a nitrato bridge between two copper(II) ions. The [CuH₂L] fragments coordinated to the lanthanide(III) ion are not coplanar. Results of thermal analysis show that compounds 1 and 2 are stable at room temperature. The FTIR spectra of the gas phase products indicate that the decomposition of the title complexes is mainly connected with the release molecules of water, carbon dioxide, carbon monoxide, nitric oxides and ammonia. The solid residues obtained during the thermal decomposition of 1 and 2 in air atmosphere are the mixture of CuO and CuLn₂O₄.

Full text of DOI:10.1016/j.ica.2017.06.002

Inorganica Chimica Acta 466 (2017) 160–165
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Research paper
Hexanuclear [CuI4ILnI2II] compounds incorporating N,O-donor ligands –
Synthesis, crystal structures and physicochemical properties
Beata Cristóvão a, , Barbara Miroslaw b, Agata Bartyzel a
⇑
a Department of General and Coordination Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 2, 20-031 Lublin, Poland
b Department of Crystallography, Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
a r t i c l e i n f o
a b s t r a c t
The reaction between N2O4-donor ligand N,N0-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane
(H4L = C17H18N2O4) and different salts leads to the formation of novel hexanuclear clusters
[Cu4Sm2(H2L)4(NO3)4(H2O)3](NO3)2ꢀ9H2O (1) and [Cu4Eu2(H2L)4(NO3)4(H2O)3](NO3)2ꢀ3H2OꢀCH3COOHꢀ
CH3OH (2) that crystallize in the triclinic system, space group P-1. The structures of 1 and 2 show two
heterotrinuclear [Cu2Ln] moieties that are linked by a nitrato bridge between two copper(II) ions. The
[CuH2L] fragments coordinated to the lanthanide(III) ion are not coplanar. Results of thermal analysis
show that compounds 1 and 2 are stable at room temperature. The FTIR spectra of the gas phase products
indicate that the decomposition of the title complexes is mainly connected with the release molecules of
water, carbon dioxide, carbon monoxide, nitric oxides and ammonia. The solid residues obtained during
the thermal decomposition of 1 and 2 in air atmosphere are the mixture of CuO and CuLn2O4.
Ó 2017 Elsevier B.V. All rights reserved.
Article history:
Received 21 December 2016
Received in revised form 20 April 2017
Accepted 1 June 2017
Available online 3 June 2017
Keywords:
Schiff base
N,O-donor ligand
Hexanuclear complexes
Phenoxo bridge
3d-4f compounds
1. Introduction
units which are linked by a bis-chelating oxalate bridge between
the Nd3+ ions (the first complex) and by a nitrato group bridging
The heteronuclear 3d–4f complexes are of great interest in the
coordination chemistry for their interesting structures and func-
tional properties as magnetic, catalytic, optical and electronic
materials [1–24]. As indicated by many examples N2O4-donor
ligands tend to form heteronuclear LnIII–MII compounds which is
the result of the fact that their inner, smaller pocket N2O2 indicates
the preference for transition metal ions whereas the outer one O4
shows preference for lanthanide ions [1–24]. Recently, several
3d–4f compounds, obtained by connecting heterodi- or heterotrin-
uclear cationic complexes with nitrato or polycarboxylato ions as
linkers were reported [1,3,22]. Im et al. synthesized tetranucelar
two Pr3+ ions (the second complex), respectively [3]. Gheorghe
et al. reported also [{(LCuII)2SmIII}2fum2](OH)2 complex (where
fum = fumarate dianion). The X-ray diffraction studies of this com-
pound revealed its structure to be [CuII–SmIII–CuII] moieties linked
through carboxylato groups of two fum2- ions acting as bridges
between the Cu2+ and Sm3+ ions [22]. The hexadentate Schiff
base N,N0-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane, H4-
L = C17H18N2O4 (Scheme 1) as a bicompartmental ligand possesses
an inner smaller compartment with two N- and two O-donor
chelating centers suitable for the coordination of metal ions, radii
0.60–0.75 Å e.g. copper, nickel or zinc ions and an outer bigger
coordination site with four O-donor atoms being able to incorpo-
rate larger metal ions, radii 0.85–1.06 Å e.g. rare earth ions. In com-
parison to other N,O-donor ligands the unique feature of this
compound is presence in its structure the additional OH groups
that remain protonated upon complex formation.
We report herein novel heterohexanuclear cationic complexes
[Cu4Sm2(H2L)4(NO3)4(H2O)3](NO3)2ꢀ9H2O (1) and [Cu4Eu2(H2L)4
(NO3)4(H2O)3](NO3)2ꢀ3H2OꢀCH3COOHꢀCH3OH (2) which were
obtained in the reaction of H4L with the respective salts of Ln3+
and Cu2+, their syntheses, unique structural features, spectroscopic
and thermal characterization. These compounds are the example of
3d-4f complexes in which the hexanuclear compartment species
complex [NiNd(L)(NO3)2(l-NO3)(H2O)(CH3CN)]2(H2O)2 (where
H2L = 1,3-bis((3-methoxysalicylidene)aminopropane)) and its
crystal structure can be described as being constructed from dinu-
clear [NiII–NdIII] entities which are connected by two nitrato
bridges
hexanuclear salen type compounds [{(LCu(ONO2))(LCu(H2O))
l
-NOꢁ3 between Nd3+ and Ni2+ metal ions [1]. Two 3d–4f
Nd}2-(
l
-C2O4)](NO3)2ꢀ6H2O
and
[{(LNi(H2O))(N(CN)2)}2Pr}2
(ONO2)](OH)ꢀ2H2Oꢀ3CH3CN (where L is the dianion of N,N0-bis(2-
hydroxy-3-methoxybenzylidene)-1,3-diaminopropane) obtained
by Gheorghe et al. are constructed from trinuclear [MII–LnIII–MII]
⇑
Corresponding author.
E-mail address: beata.cristovao@poczta.umcs.lublin.pl (B. Cristóvão).
http://dx.doi.org/10.1016/j.ica.2017.06.002
0020-1693/Ó 2017 Elsevier B.V. All rights reserved.

B. Cristóvão et al. / Inorganica Chimica Acta 466 (2017) 160–165
161
and 2 and the Schiff base ligand (H4L) were carried out by the ther-
mogravimetric (TG) and differential scanning calorimetry (DSC)
methods using the SETSYS 16/18 analyser (Setaram). The experi-
ments were carried out under air flow in the temperature range
of 20–1000 °C (compounds) and 20–700 °C (ligand) at a heating
rate of 10 °Cꢀminꢁ1. The samples (7.27 mg (1), 7.80 mg (2) and
7.10 mg (ligand)) were heated in Al2O3 crucibles. The TG–FTIR of
the title compounds was recorded using the TGA Q5000 analyzer
TA Instruments, New Castle, Delaware, USA, interfaced to the Nico-
let 6700 FTIR spectrophotometer (Thermo Scientific). The complex
samples were put in an open platinum crucible and heated from
ambient temperature to 700/1000 °C. The analysis was carried
out at a heating rate of 20 °C minꢁ1 under nitrogen at flow rate
of 20 mL minꢁ1. To reduce the possibility of gasses condensing
along the transferline, the temperature in the gas cell and transfer
line was set to 250 and 240 °C, respectively. Gas analysis was per-
formed by matching the spectra against those from the spectrum
library Nicolet TGA Vapor Phase of the software Ominic together
with the literature sources. The X-ray powder diffraction patterns
of the products of decomposition process were collected at room
temperature on an Empyrean PANanalytical automated powder
Scheme 1. Schematic diagram of the Schiff base ligand.
have been formed without the addition of an external linking
ligand.
2. Experimental
2.1. Materials
The chemicals: 2,3-dihydroxybenzaldehyde, 1,3-diamino-
propane, Cu(CH3COO)2ꢀH2O, Sm(NO3)3ꢀ6H2O, Eu(NO3)3ꢀ5H2O, as
well as the solvent (methanol) were of analytical reagent grade.
They were purchased from commercial sources and used as
received without further purification.
diffractometer with CuK radiation (k = 1.54187 Å) over the scat-
a
tering angular range 2h = 20–120°.
2.2. Synthesis of N,N0-bis(2,3-dihydroxybenzylidene)-1,3-
diaminopropane H4L
2.5. X-ray crystal structure determination
The H4L ligand (C17H18N2O4) was synthesized by a condensation
reaction between 2,3-dihydroxybenzaldehyde (1.38 g, 10 mmol)
and 1,3-diaminopropane (0.37 g, 5 mmol) in methanol (50 ml)
according to the reported procedure [25]. The compound was sep-
arated as yellow needles and recrystallized twice from methanol.
The X-ray diffraction intensities for 1 and 2 were collected at
100 K on Oxford Diffraction Xcalibur CCD diffractometer with the
graphite-monochromatized MoK radiation (k = 0.71073 Å). All
a
data were collected using the
x scan technique, with an angular
scan width of 1.0°. The programs CrysAlis CCD, CrysAlis Red and
CrysAlisPro [26,27] were used for data collection, cell refinement
and data reduction. The structures were solved with the olex2.-
solve structure solution program using Charge Flipping and refined
with the olex2.refine refinement package using Gauss-Newton
2.3. Synthesis of complexes [Cu4Sm2(H2L)4(NO3)4(H2O)3](NO3)2ꢀ9H2O
(1) and [Cu4Eu2(H2L)4(NO3)4(H2O)3] (NO3)2ꢀ3H2OꢀCH3COOHꢀCH3OH
(2)
The hexanuclear complexes 1 and 2 were prepared as follows:
the solution of Cu(OAc)2ꢀH2O (0.4 mmol, 0.0799 g) in methanol
(10 mL) was added dropwise to the stirred solution of N,N0-bis
(2,3-dihydroxybenzylidene)-1,3-diaminopropane, H4L (0.4 mmol,
0.1248 g) in methanol (30 mL) to produce a green coloured mix-
ture. The reaction mixture was stirred for 30 min at 45 °C. Next,
the freshly prepared methanol solution (5 mL) of Sm(NO3)3ꢀ6H2O
(0.2 mmol, 0.0889 g) or Eu(NO3)3ꢀ5H2O (0.2 mmol, 0.0856 g) was
added slowly to the solution with constant stirring and the result-
ing deep green mixture was stirred for another 30 min. A small
amount of precipitate that appeared was filtered off. Green single
crystals suitable for X-ray diffraction analysis were formed at
4 °C (in a refrigerator) after three weeks.
Yield 21% 1. Anal. C68H88N14O46Cu4Sm2 2393.38 (%): C, 34.11; H,
2.68; N, 8.19; Cu, 10.63; Sm, 12.57. Found: C, 34.40; H, 2.90; N,
7.80; Cu, 10.20; Sm, 12.20.
Yield 23% 2. Anal. C71H86N14O43Cu4Eu2 2381.62 (%): C, 35.77; H,
3.61; N, 8.23; Cu, 10.67; Eu, 12.76. Found: C, 35.80; H, 3.15; N,
8.00; Cu, 10.10; Eu, 12.40.
Table 1
Selected spectroscopic data of the Schiff ligand (N,N0-bis(2,3-dihydroxybenzylidene)-
1,3-diaminopropane), CuI2ISm4III (1), Cu2IIEuI4II (2).
Ligand
CuI2ISmI4II
CuI2IEuI4II
Proposed assignments
–
–
–
3456 m
–
–
3432 m
2920 w
2860 w
–
1620 vs
1568 m
1468 s
1384 w
–
m
m
m
m
m
m
m
(OAH) +
(CH3)as
(CH3)s
(OAH) M
(C@N)
m(CAH)
3200 m, br
1640 vs
1544 m
1460 s
1396 m
1356 m
–
–
m(NAH)
1620 vs
1568 m
1468 s
1384 w
–
(C@C)
(C@C) +
m
(NAO)comp.
sc(CAH) +
d(OAH)
m(CCC))
1308 s
1252 s
1220 s
1172 w
1088 w
1072 w
972 w
–
864 m
784 w
740 s
640 w
612 w
560 w
524 w
500 w
412 w
1300 s
1256 s
12120 s
1168 w
1088 w
1072 w
972 w
–
864 m
784 w
740 s
640 w
616 w
556 w
524 w
500 w
412 w
m
m
(CAN) +
(CAO)
x(CAH) + m(NAO)
–
1236 vs
1164 w
–
1064 m
–
900 w
868 w
788 w
748 vs
–
mm(CAO) + d(OAH)
(CAC) + tw(CAH)
m
d (CAH) + m(NAO)
skeletal
q
(CAH) + CH2 + d(CCC)
(OAH)
d(C–N@C)
c
2.4. Methods
c
c
(CAH) +
(CAH)
m(NAO)
d(C@C) + ring deform.
ring deform.
The contents of carbon, hydrogen and nitrogen in the com-
pounds were determined by elemental analysis using a CHN
2400 Perkin Elmer analyser. The contents of copper and lan-
thanides were established using ED XRF spectrophotometer (Can-
berraꢁPackard). The FTIR spectra of compounds were recorded
over the range of 4000–400 cmꢁ1 using M–80 spectrophotometer
(Carl Zeiss Jena). Sample for FTIR spectra measurements was pre-
pared as KBr discs (Table 1). Thermal analyses of complexes 1
–
–
m(MAO)
c(CAH)
c(CAH)
m(MAN)
504 w
–
vs – very strong, s – strong, m – medium, w – weak, br – broad,
deformation in plane, sc – scissoring, – waggining, tw – twisting,
deformation out of plane, as – asymmetric, sym – symmetric,
m
– stretching, d –
x
q
– rocking, c –

162
B. Cristóvão et al. / Inorganica Chimica Acta 466 (2017) 160–165
minimization [28]. Compound 1 crystallizes as a non merohedral
twin. Although the model of crystal structure was found without
difficulties, the refinement was not satisfactory. Finally the struc-
ture was refined as a two-component twin with the ratio of the
twin components being of 0.46:0.54. The BASF parameter was
0.267(3). The R1 value decreased from 0.160 to 0.070 for the twin
refinement. One of the nitrate groups in 2 is disordered over two
positions with occupancy of 0.58(2) for the major part. Due to
low quality of crystals some of the C, N and O atoms were refined
isotropically. The H atoms of water molecules were not found in
the difference Fourier maps and were omitted from the model.
The C-bonded H atoms were positioned geometrically and the ‘rid-
ing’ model for the CAH bonds was used in the refinement with
Uiso(H) = 1.5 Ueq(C/O) for methyl groups and Uiso(H) = 1.2 Ueq(C)
for the rest. The O-bonded H atoms of the Schiff base ligand were
located in the difference Fourier maps and refined isotropically
with restraints. The summary of experimental details and the crys-
tal structure refinement parameters are given in Table 2. The
molecular plots were drawn with Mercury CSD [29].
The metal-nitrogen coordination bond is also confirmed by the
new band presented at ca. 416 cmꢁ1 that may be assigned to the
m
lic
(Cu–N) vibration [35,36]. The strong peak characteristic of pheno-
m
(CAO) stretching vibration band observed at 1236 cmꢁ1 for the
free N,O-donor ligand is shifted to lower wavenumber in the FTIR
spectra of complexes 1 and 2 and occurs at 1220 cmꢁ1, indicating
the involvement of the phenolic oxygen atoms in the metal-ligand
bonding [33,37]. The metal-oxygen coordination bond is confirmed
by the new band presented at ca. 560 cmꢁ1 that can be attributed
to m(MAO) vibration [35,36]. In the FTIR spectra of the analyzed
compounds the characteristic frequencies of nitrate groups acting
as mono- and bidentate ligands overlap and occur at about
1468 cmꢁ1, 1308 cmꢁ1, 1088 cmꢁ1 and 784 cmꢁ1 [38]. The weak
bands at around 2920 cmꢁ1 and 2860 cmꢁ1 presented only in the
spectrum of 2 may be attributed to asymmetric and symmetric
stretching vibrations of the methyl group, m(CH3) [39]. A medium
band characteristic of m(OAH) stretching vibrations has its maxi-
mum at around 3430 cmꢁ1 (caused by methanol and crystal water
as well as the protonated hydroxyl groups of the Schiff base)
[34,35,39,40].
3. Result and discussion
3.2. Crystal and molecular structure
3.1. Infrared spectra
Single-crystal X-ray studies revealed that [Cu4Sm2(H2L)4(-
NO3)4(H2O)3](NO3)2ꢀ9H2O (1) and [Cu4Eu2(H2L)4(NO3)4(H2O)3]
(NO3)2ꢀ3H2OꢀCH3COOHꢀCH3OH (2) (where H2L = C17H16N2O4 is a
The infrared spectra of compounds 1 and 2 have some common
features as expected for their structural similarities. In order to get
some information about binding mode of the N2O4-donor ligand
(H4L) to 3d and 4f metal ions the FTIR spectra of the obtained com-
plexes were compared with the spectrum of the free Schiff base
(Table 1). N,O-donor ligands are able to form coordinate bonds
with various metal ions through azomethine as well as phenolic
dianion
of
N,N0-bis(2,3-dihydroxybenzylidene)-1,3-diamino-
propane) crystallize in the triclinic space group P-1. The 1 and 2
consist of a hexanuclear complex cation [Cu4Ln2(H2L)4(NO3)4(H2-
O)3]2+, two nitrate ions, crystal water and in the case of 2 methanol
as well as acetic acid molecules. Details for the structure solution
and refinement are summarized in Table 2, and selected bond dis-
tances and angles are listed in Table 3. A perspective view of the
molecular structures of 1 and 2 is presented in Figs. 1 and 2 and
the schematic diagram of the coordination unit is given in
groups. The band characteristic of the azomethine group m(C@N)
of the free ligand H4L appeared at 1640 cmꢁ1 while in the analyzed
complexes 1 and 2 this band is shifted to lower frequency and is
observed at around 1620 cmꢁ1 indicating a decrease in the C@N
bond order due to the coordinate bond formation between the CuII
ion and the imine nitrogen lone pair of the organic ligand [30–34].
Fig. S1. In the molecules 1 and 2 one l2-NO3 anion plays the role
of connecting two CuII ions to generate a structure coupling two
CuII-LnIII-CuII units. The separation between two copper ions linked
by the nitrate bridge is ca. 6.15 Å. In each heterotrinuclear unit CuII
and LnIII ions are located in the inner, smaller N2O2 pocket and
outer, bigger O4 one of H2L2- ligand, respectively and linked by
two phenol oxygen atoms from the Schiff base ligand. The
intramolecular Cuꢀ ꢀ ꢀLn and Cuꢀ ꢀ ꢀCu separations are ca. 3.5 and
7.0 Å, respectively. In the crystals 1 and 2 the CuII ions are five-
(Cu2 and Cu3) and six-coordinate (Cu1 and Cu4) with distorted
square pyramidal and distorted octahedral geometry, respectively
(Fig. S2). The average CuANimine and CuAOphenoxo distances are in
the typical ranges 1.97–2.01 Å and 1.93–1.97 Å, respectively
[41,42,3,43,44].
Table 2
Crystal data and structure refinement for 1 and 2.
Identification code
1
2
Empirical formula
Formula weight
Crystal system
Space group
a/Å
C
68H88N14O46Cu4Sm2
C71H86N14O43Cu4Eu2
2381.62
triclinic
2392.38
triclinic
P-1
P-1
13.2934(12)
17.5990(10)
19.9453(10)
85.892(5)
89.181(5)
68.016(7)
4315.4(5)
2
13.2178(9)
17.3653(13)
20.1010(14)
93.004(6)
90.324(5)
110.313(7)
4319.5(5)
2
b/Å
c/Å
a
/°
b/°
/°
The nine-coordinate sphere of LnIII is formed by eight oxygen
atoms from the two N2O4-donor ligands and one oxygen atom
from the water molecule giving a tricapped trigonal prismatic
geometry (Fig. S2). The distances LnAO vary in the range 2.36–
2.55 Å, the shortest ones being LnAOphenoxo and the longest
LnAOhydroxyl bonds (Table 2). In the crystals 1 and 2 the three
metallic centers of a trinuclear subunit [Cu2Ln] are almost collinear
with the value of the CuII-LnIII-CuII angle being ca. 170°. It should be
noted that two [CuH2L] fragments coordinated to the lanthanide(III)
ion are not coplanar. In the complexes 1 and 2 one CuO2Ln frag-
c
Volume/Å3
Z
q
l
calcg/cm3
1.841
2.416
2404.0
1.831
2.503
2392.0
/mmꢁ1
F(000)
Crystal size/mm3
Reflections collected
Independent
reflections
0.4 ꢂ 0.2 ꢂ 0.1
0.2 ꢂ 0.15 ꢂ 0.05
29476
21206
15551 [Rint = 0.0629,
Rsigma = 0.1588]
–
21206
[Rsigma = 0.1613]
0.267(3)
BASF
Data/restraints/
parameters
15551/37/1047
21206/31/1087
ment of the trinuclear unit is nearly planar with
of 3–8°, whereas the second half of the molecule is significantly
twisted ( values are 15–20°). The separation between two Ln
a values being
Goodness-of-fit on F2
Final R indexes
0.955
0.973
a
R1 = 0.0699, wR2 = 0.1536
R1 = 0.0880,
wR2 = 0.2188
2.87/-3.67
[I > = 2r (I)]
(III) ions is ca. 8.96 Å. In the crystals 1 and 2 there are many intra-
as well as intermolecular hydrogen bonds. The adjacent molecules
are bridged by hydrogen bonds through protonated hydroxyl
group, nitrate ions, acetic acid (2), methanol (2) and water
Largest diff. peak/hole
1.71/-1.15
1517282
/ e Åꢁ3
CCDC No.
1517281

B. Cristóvão et al. / Inorganica Chimica Acta 466 (2017) 160–165
163
Table 3
Intramolecular geometry for 1 and 2 [Å].
Distance
1
2
Distance
1
2
Cu1–N1
Cu1–N2
Cu1–O1
1.98(1)
1.976(8)
1.971(9)
1.932(7)
1.960(7)
2.470(1)
2.520(7)
1.980(1)
1.972(9)
1.935(7)
1.948(7)
3.310(1)
2.455(9)
1.960(1)
2.010(1)
1.938(7)
1.953(8)
2.550(7)
1.982(9)
1.968(9)
1.947(7)
1.966(7)
2.430(1)
2.430(1)
O1–Ln1
O2–Ln1
O3–Ln1
O4–Ln1
O5–Ln1
O6–Ln1
O7–Ln1
O8–Ln1
2.381(8)
2.436(6)
2.509(7)
2.554(7)
2.402(7)
2.363(7)
2.470(7)
2.526(7)
2.462(9)
2.402(7)
2.387(8)
2.470(6)
2.516(7)
2.407(7)
2.350(1)
2.486(7)
2.521(8)
2.470(9)
3.527(1)
3.528(1)
3.543(2)
3.497(2)
8.731(1)
2.370(7)
2.395(7)
2.466(7)
2.512(7)
2.414(7)
2.357(7)
2.476(7)
2.498(7)
2.440(8)
2.395(7)
2.370(8)
2.455(7)
2.496(8)
2.404(7)
2.338(7)
2.465(7)
2.486(7)
2.479(8)
3.513(1)
3.521(1)
3.514(2)
3.483(1)
8.960(1)
1.982(9)
1.959(6)
1.936(8)
2.570(2)
2.504(9)
1.970(1)
1.990(1)
1.941(8)
1.955(7)
2.500(1)
2.455(9)
1.980(1)
1.990(1)
1.936(8)
1.934(8)
2.543(8)
1.982(9)
1.960(1)
1.942(9)
1.969(8)
2.610(1)
2.400(2)
Cu1–O2
Cu1–O19
Cu1–O22
Cu2–N3
Cu2–N4
Cu2–O5
O17–Ln1
O9–Ln2
Cu2–O6
Cu2–O35
Cu2–O40
Cu3–N5
Cu3–N6
Cu3–O9
Cu3–O10
Cu3–O23
Cu4–N7
Cu4–N8
Cu4–O13
Cu4–O14
Cu4–O28
Cu4–O34/O25*
O10–Ln2
O11–Ln2
O12–Ln2
O13–Ln2
O14–Ln2
O15–Ln2
O16–Ln2
O18–Ln2
Cu1–Ln1
Cu2–Ln1
Cu3–Ln2
Cu4–Ln2
Ln1. . .Ln2i
*
i
bonds Cu4–O34 for 1 and Cu4–O25 for 2, Ln = Sm for 1 and Eu for 2. Symmetry code x–1, y–1, z.
molecules. The hydroxyl groups of the ligand molecules remain
protonated in the complex. This conclusion was drawn basing on
the analysis of the intra- and intermolecular environment of each
hydroxyl groups in the crystal (Fig. S3). The observed interatomic
distances and the directional nature of the interactions correspond
well with the expected hydrogen bond network. In both crystals
the hydroxyl O8 and O16 atoms form hydrogen bonds with the
central bridging NOꢁ3 anion, stabilizing the hexanuclear coordina-
tion unit. Atoms O3, O4, O7 and O11 link through hydrogen bonds
to O-nitro atoms, whereas atoms O12 and O15 act as hydrogen
bond donors to solvent molecules (to water in 1 and to methanol
and acetic acid molecules in 2). The geometry of chosen hydrogen
bonds has been listed in the Table S1.
In the Table S2 there is comparison of some structural parame-
ters (Cu–N (Å), CuAOphen (Å), LnAOphen (Å), LnAOmethoxy (Å),
Cuꢀ ꢀ ꢀLn (Å)) of chosen CuII-LnIII compounds prepared with
o-vanillin (or its derivatives). As shown in this table all compounds
consist of diphenoxo-bridged heterometallic cores in which
CuII metal ion is placed in N2O2 compartment of the Schiff-base
ligand, while the LnIII ion is present in the larger and open
O2O2 [O(phenoxo)2O(methoxy)2] one. The Cu–N and Cu–O bond dis-
tances are similar and range from 1.9 to 2.0 Å. The LnꢁO distances
from the phenolato oxygen atoms are much shorter than those
from the methoxy oxygens. The intramolecular separation CuꢀꢀꢀLn
is about 3.4–3.5 Å. Three types of lanthanide counterions NOꢁ3 ,
Clꢁ and different carboxylic acid ions (e.g. acetate, fumarate, oxa-
late, hexafluoroacetylacetonato) are mainly used in the synthesis
of salen type 3d-4f compounds. It is worth mentioning that the
structure of CuII-LnIII complexes depends on several factors: the
nature of the donor atoms of the linkers, the oxophilicity of the
lanthanides, the preference of the Cu(II) ion for nitrogen atoms,
the degree of deprotonation of the ligands, the stoichiometry of
the used reagents and kind of used solvents. According to the lit-
erature (Table S2) in complexes nitrato anions contributing to the
electroneutrality and also to the completion of the coordination
sphere of the 4f ions (as chelating nitrato group) whereas the
organic counterions act also as linkers i.e. carboxylato group
works as a bridge between the lanthanide(III)/copper(II) and lan-
thanide(III) ions. In contrast to compounds presented in the
Table S2, in the structures of complexes 1 and 2 two heterotrin-
Fig. 1. Molecular structure with atom numbering scheme of CuI4I–Sm2III (1). The outer
coordination sphere solvent molecules were omitted for clarity.
Fig. 2. Molecular structure with atom numbering scheme of CuI4I–Eu2III (2). The outer
coordination sphere solvent molecules were omitted for clarity.

164
B. Cristóvão et al. / Inorganica Chimica Acta 466 (2017) 160–165
uclear [Cu2Ln] moieties are linked by a nitrato group acting as a
bridge between two copper(II) ions.
(27.88% (1), 28.14% (2)). These results are in accordance with those
presented by other researches [46].
3.3. Thermal properties
4. Conclusion
The CuI4ILnI2II complexes can be considered as resulting from the
assembly of two [CuI2ILnIII] building blocks. In the each heterotrinu-
clear unit, CuII and LnIII ions are located in the inner N2O2 and outer
O4 pockets of the Schiff base ligand, respectively. The 3d and 4f metal
ions are bridged by two phenoxo oxygen atoms belonging to the N,
O-donor ligand. The coordination number of lanthanide(III) ion is
equal to nine whereas the copper(II) ions are five- and six-coordi-
nated. The destruction and combustion of the Schiff base ligand is
mainly connected with the release molecules of NH3, CO2, CO, N2O,
NO. The compounds are stable at room temperature and their
decomposition processes proceed in the similar way. Heating of
complexes leads at first to the desolvation and next to decomposi-
tion processes. The final solid products of the complex decomposi-
tion are CuO and Ln2CuO4.
In order to examine the thermal behaviour and the stability of
the Schiff base ligand and analyzed complexes 1 and 2 the TG,
DTG and DSC curves were recorded. During heating in air the Schiff
base ligand is stable up to 167 °C (Fig. S4) and next at the beginning
of its thermal decomposition on the DSC curve an endothermic
effect is observed. This effect is connected with the negligible mass
loss, which is characteristic of the melting process. It should be
noticed that DSC peak is sharp which indicates that the ligand is
a crystalline, pure substance. The melting point observed on the
DSC curve is about 170 °C and the enthalpy of fusion equals
25.93 kJmolꢁ1. As shown in Figs. S5 and S6 the compounds 1 and
2 are stable at room temperature. The TG curves of 1 and 2 display
practically the same weight-loss patterns. Heating the samples up
to ca. 130 °C in air atmosphere leads to the weight loss of 6.00%
(calculated 6.77%) (1) and 4.70% (calculated 4.03%) (2) consistent
with the lose solvent molecules (water (1), methanol and water
(2)). This process is accompanied with small endothermic effect
seen on the DSC curves with the maximum at ꢃ90 °C. The values
of the enthalpy of the desolvation processes are 149.86 kJ molꢁ1
(1) and 371.49 kJmolꢁ1 (2), respectively. These results are also con-
firmed by the TG-FTIR analysis (Figs. S7–S12). The recorded FTIR
spectra of evolved gas phase for the analyzed compounds show
that water and methanol are the main products released during
this stage. The characteristic vibration bands in the wavenumber
ranges 4000–3400 cmꢁ1 and 2060–1260 cmꢁ1 correspond to
stretching and deforming vibrations of H2O molecules [39],
whereas the bands associated with the presence of CH3OH are
observed at 3368 cmꢁ1, 1307 cmꢁ1 and 1095 cmꢁ1, respectively
[33]. The second mass weight in the temperature range of 140–
275 °C (1) and 145–280 °C (2) may be due to the lose nitrate and
coordinated water molecules in the case of the compound 1 (calcu-
lated 17.81%, found 18.10%) and nitrate, acetic acid and coordi-
nated water molecules in the case of the complex 2 (calculated
20.41%, found 20.20%), respectively. The FTIR spectra recorded dur-
ing this stage show the presence of bands characteristic of the N2O
(double peaks at 2250–2150 cmꢁ1 and 1250–1000 cmꢁ1), H2O
Appendix A. Supplementary data
Crystallographic data for 1 and 2 have been deposited with the
Cambridge Crystallographic Data Centre: CCDC 1517282 and
1517281, respectively. This data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_re-
quest@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.ica.2017.06.002.
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