Di- and tetracarboxylic aromatic acids with silane spacers and their copper complexes: Synthesis, structural characterization and properties evaluation

Article abstract of DOI:10.1016/j.jorganchem.2014.10.006

Two polycarboxylic acids, bis(p-carboxyphenyl)diphenylsilane and bis(3,4-dicarboxyphenyl)dimethylsilane, were prepared according to published procedures and characterized, besides elemental and spectral analysis, for the first time by X-ray single crystal

Full text of DOI:10.1016/j.jorganchem.2014.10.006

Journal of Organometallic Chemistry 774 (2014) 70e78
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Di- and tetracarboxylic aromatic acids with silane spacers and their
copper complexes: Synthesis, structural characterization and
properties evaluation
,
Maria Cazacu a *, Angelica Vlad a, Mirela-Fernanda Zaltariov a, Sergiu Shova a,
, c, d
Ghenadie Novitchi b, Cyrille Train b
a “Petru Poni” Institute of Macromolecular Chemistry, Aleea Gr. Ghica Voda 41A, 700487 Iasi, Romania
Laboratoire National des Champs Magnetiques Intenses, CNRS UPR 3228, 25 Rue des Martyrs, 38042 Grenoble, France
b
ꢀ
c
ꢀ
Universite Joseph Fourier, F-38041 Grenoble, France
d Institut Universitaire de France (IUF), 103, bd Saint-Michel, F-75005 Paris, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Two polycarboxylic acids, bis(p-carboxyphenyl)diphenylsilane and bis(3,4-dicarboxyphenyl)dimethylsi-
lane, were prepared according to published procedures and characterized, besides elemental and
spectral analysis, for the first time by X-ray single crystal diffraction. Their copper(II) complexes were
obtained in the presence of 1,10-phenantroline as co-ligand, the crystallographic data revealing the
formation of 2D structures through hydrogen bonds. The hydrogen bond dynamics of the copper com-
plexes was studied by FTIR-ATR spectrometry. The thermal stability of the acids and derived copper
complexes was evaluated by thermogravimetrical analysis. The moisture uptake capacity and porosity of
the complexes were estimated on the basis of the water vapour sorption measurements in dynamic
regime. Magnetic measurements performed on the two metal complexes correspond to not interacting
copper(II) with S ¼ 1/2 and g factor equal to 2.14 and 2.19 being consistent with pentacoordinated Cu(II)
paramagnetic centres.
Received 10 July 2014
Received in revised form
28 September 2014
Accepted 2 October 2014
Available online 13 October 2014
Keywords:
Copper complexes
Dicarboxylic acids
Tetracarboxylic acids
Phenantroline
2D structures
Hydrogen bonds
© 2014 Elsevier B.V. All rights reserved.
Introduction
ligands to extend the architecture to 1D chains, 2D layer and 3D
network [5]. The formation and stability of polynuclear carbox-
Polycarboxylic acids are among the most attractive building
blocks for the metal-organic frameworks, due to their versatile
binding features [1] as well as their robustness and thermal sta-
bility [2]. The carboxylate anions which are characterized by an
increased electron density on the oxygen atoms, high proton af-
finity, and low ionization energies are widely used as bridging li-
gands in polynuclear complexes of d elements [3]. The multiple
oxygen donors can adopt different coordination modes permitting
the formation of the networks with various topologies [4]. The
coordination modes of carboxylate ligands are diverse: synesyn,
syneanti or antieanti [3]. Carboxylic acids themselves are able to
coordinate the metal ions monodentate, preserving the nonionized
carboxy group and thus creating conditions for intermolecular
hydrogen bonding that leads to supramolecular systems [3]. Thus,
carboxylate ligands may act as both counteranions and bridging
ylate complexes, their chemical and physical properties, as well as
the tendency to formation of supramolecular systems are in
dependence on the acid strength and the donoreacceptor power of
the carboxylate ion. These characteristics are affected by the nature
of organic group at which the carboxyl group is attached [3]. There
are many reports in literature on the using dicarboxylate, tri-
carboxylate, and tetracarboxylate ligands, which are inter-bridged
by mono- or multi-nuclear metal nodes, leading to stable metal-
organic frameworks (MOFs) with permanent porosity [1]. Thus,
porous structures were built by metal and carboxylate-type li-
gands, such as phthalate, biphenylcarboxylate, benzenetricarbox-
ylate, and adamantanedicarboxylate or more rigid multicarboxy
late ligand such as anthraquinone-1,4,5,8-tetracarboxylic acid
[4,6,7]. MOFs with variable dimensionality and different coordi-
nation styles have been designed and synthesized in the last time
[6e8]. MOFs constructed from tetracarboxylates with rigid spacer
groups such as poly(phenylene) or 4,40-bipyridyl units are also well
documented in the literature [1]. Lately, some investigations have
been focused on flexible multidentate ligands (malonate [9], 1,4-
* Corresponding author.
E-mail address: mcazacu@icmpp.ro (M. Cazacu).
http://dx.doi.org/10.1016/j.jorganchem.2014.10.006
0022-328X/© 2014 Elsevier B.V. All rights reserved.

M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
71
cyclohexanedicarboxylic acid [10], 1,2,3,4,5,6-cyclohexanehexa
carboxylic acid [11], tetrahydrofuran tercarboxylic acid [12], and
cyclohexane-1,2,4,5-tetracarboxylic acid [6]), as they are able to
form diversified coordination networks with different metal ions
[13]. Bis(oxy)isophthalic acid ligands with CH2e and (CH2)2e
spacers, which impart features of flexibility to the tetracarboxylic
acid moiety were successfully utilized in the construction of two-
and three-dimensional coordination polymers by reacting them
with a variety of the oxophilic lanthanoid metal ions [1,2].
The electronic absorption spectra were measured with an An-
alytic Jena SPECORD 200 spectrophotometer in 10 mm optical path
quartz cells fitted with polytetrafluoroethylene stoppers.
The thermogravimetric (TG)edifferential thermogravimetric
(DTG) analysis was performed on a STA 449F1 Jupiter NETZSCH
equipment. The measurements were made in the temperature
20e700 ꢁC range under a nitrogen flow (50 mL/min) using a
heating rate of 10 ꢁC/min. Alumina crucible was used as sample
holder.
In search for new metal-organic framework, in this paper we
prepared two polycarboxylic carbosilane acids according to already
reported procedures [14e19] but for the first time used as ligands
for copper besides 1,10-phenantroline as co-ligand. All involved
intermediates and final compounds were structurally character-
ized. Thermal stability in the solid state and in solution, the mois-
ture behaviour and magnetic properties were evaluated.
Dynamic water vapour sorption (DVS) capacity of the samples
was determined in the relative humidity (RH) range 0e90 % by
using the fully automated gravimetric analyzer IGAsorp produced
by Hiden Analytical, Warrington (UK). The sample was dried at
25 ꢁC in flowing nitrogen (250 mL/min) until it reaches a constant
weight at RH < 1%. Then, the relative humidity (RH) was gradually
increased from 0 to 90 %, in 10% humidity steps, each step having a
pre-established equilibrium time between 5 and 10 min so as the
sorption equilibrium to be achieved every time. When RH
decreased, the desorption curves were recorded. The drying of the
samples before sorption measurements was carried out at 25 ꢁC,
35 ꢁC and 55 ꢁC respectively in flowing nitrogen (250 mL/min) until
the weight of the sample was in equilibrium at RH < 1%.
Magnetic measurements were carried out on microcrystalline
samples of 5 and 6 with a Quantum Design SQUID magnetometer
(MPMS-XL). Variable-temperature (1.8e300 K) direct current (dc)
magnetic susceptibility was measured under an applied magnetic
field of 0.1 T. All data were corrected for the contribution of the
sample holder and diamagnetism of the samples estimated from
Pascal's constants [20,21].
Experimental
Materials
Diphenyldichlorosilane
(C12H10SiCl2)
97%,
dimethyldi-
chlorosilane (CH3)2SiCl2) 98%, 4-bromotoluene (C7H7Br) 98%,
metallic lithium 99%, chromium trioxide (CrO3) 99.9%, 4-bromo-o-
xylene (C8H9Br) 99%, acetic anhydride ((CH3CO)2O) 98%, 1,10-
phenantroline (C12H8N2) 99%, glacial acetic acid (C2H4O2) 99.7%,
pyridyne 99%, copper(II) perchlorate hexahydrate, Cu(ClO4)2$6H2O,
copper(II) sulphate pentahydrate, CuSO4$5H2O, anhydrous diethyl
ether, N,N-dimethylformamide were purchased from Sigma-
eAldrich and used as such. Potassium permanganate (KMnO4),
hydrochloric acid (HCl) 35% and sulphuric acid (H2SO4) 96%,
ethanol, methanol were received from Chemical Company.
Bis(p-tolyl)diphenylsilane (1), (p-carboxyphenyl)diphenylsi-
lane, H2L1, (2), bis(3,4-dimethylphenyl)dimethylsilane (3) and (3,4-
dicarboxyphenyl)dimethylsilane, H4L2 (4) were obtained as
described in Supporting information (ESI), according to Refs.
[14e19].
Crystallographic measurements for compounds 1, 2, 3, 5, and 6
were carried out with an Oxford-Diffraction XCALIBUR E CCD
diffractometer equipped with graphite-monochromated Mo-K
a
radiation. The crystals were placed 40 mm from the CCD detector.
The unit cell determination and data integration were carried out
using the CrysAlis package of Oxford Diffraction [22]. All the
structures were solved by direct methods using Olex2 [23] software
with the SHELXS structure solution program and refined by full-
2
matrix least-squares on F0 with SHELXL-97 [24]. Atomic dis-
placements for non-hydrogen, non-disordered atoms were refined
using an anisotropic model. The positional parameters of the ClO4ꢀ
anion and solvate DMF molecules for structures 2, 4 and 5 have
been refined as disordered models in combination with the avail-
able tools (PART, DFIX, and SADI) of SHELXL97, using anisotropic/
isotropic refinement for non-H atoms. The carbon H atoms were
placed in fixed, idealized positions and refined as rigidly bonded to
the corresponding atom. Hydrogen atoms for OH groups have been
placed by Fourier Difference accounting for the hybridation of the
supporting atoms and the hydrogen bonds parameters. The mo-
lecular plots were obtained using the Olex2 program [23]. The main
crystallographic data together with refinement details are sum-
marized in Table 1.
Measurements
Infrared spectra were recorded using a Bruker Vertex 70 FTIR
spectrometer in the transmission mode (KBr pellets) between 4000
and 400 cmꢀ1 at room temperature with a resolution of 2 cmꢀ1 and
accumulation of 32 scans.
The temperature-dependent ATR-FTIR spectra were recorded in
both heating and cooling runs on the Bruker Vertex 70 FT-IR In-
strument equipped with a Golden Gate single reflection ATR
accessory and a temperature controller. The solid samples were
added on the ATR crystal surface and sealed with a cap to avoid the
solvent evaporation. The temperature varied between 22 and 52 ꢁC
being increased with 5 ꢁC at each registration. After the tempera-
ture was changed, the sample was maintained 2 min before the
acquisition of the spectrum. The registrations were performed in
ATR mode in the 600-4000 cmꢀ1 spectral range with 64 scans at
2 cmꢀ1 resolution.
ATR-FTIR spectra in solution were registered using a Bruker
Vertex 70 FTIR spectrometer equipped with a ZnSe crystal. The
measurements were performed in ATR (Attenuated Total Reflec-
tance) mode in the 600e4000 cmꢀ1 range at room temperature
with a resolution of 4 cmꢀ1 and accumulation of 32 scans.
The NMR spectra were recorded on a Bruker Avance DRX
400 MHz Spectrometer equipped with a 5 mm QNP direct detection
probe and z-gradients. Spectra were recorded in CDCl3, at room
Procedure
Preparation of the copper complex [Cu(Bpy)2(HL1)]ClO4·DMF·H2O, 5
In a 50 mL round bottom flask equipped with magnetic stirrer,
and reflux condenser was introduced 0.1000 g (0.24 mmol) bis(p-
carboxyphenyl)diphenylsilane, 2, and 5 ml DMF and the mixture
was stirred until dissolved. A solution consisting in 0.1698 g
(0.94 mmol) 1,10-phenantroline and 5 mL DMF was dropped over
this and the resulted mixture was stirred at room temperature for
3 h. After that, another solution formed from 0.1747 g (0.47 mmol)
copper perchlorate and 5 mL methanol was added and the stirring
continued for 2 h at 60 ꢁC. A crystalline product (5) was formed
within about two weeks. Yield: 0.079 g (79%).
temperature. The chemical shifts are reported as
d values (ppm).

72
M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
Table 1
Crystallographic data, details of data collection and structure refinement parameters for 1e3, 5 and 6.
1
2
3
5
6
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
C26H24Si
364.54
293
Monoclinic
C2/c
18.479(5)
7.191(5)
16.359(5)
90
100.842(5)
90
2135.0(17)
4
1.134
0.117
C32H34N2O6Si
570.70
293
Monoclinic
C2/c
16.5947(11)
7.5485(5)
25.2409(14)
90
95.041(6)
90
3149.6(3)
4
1.204
0.119
C18H24Si
268.46
200
Orthorhombic
Cmc21
21.9562(12)
12.4173(7)
5.8118(4)
90
C53H44ClCuN5O10Si
1038.01
200
Triclinic
P-1
10.270(5)
13.941(5)
17.906(5)
97.419(5)
90.825(5)
93.897(5)
2535.6(17)
2
C48H52.5CuN6O14.25Si
1033.09
150
Triclinic
P-1
13.619(2)
14.309(2)
15.720(2)
96.512(5)
109.869(5)
117.951(5)
2403.9(6)
2
b/Å
c/Å
ꢁ
ꢁ
a
/
b
/
90
90
ꢁ
g
/
V/Å3
1584.51(17)
4
1.125
Z
Dcalc/mg/mm3
1.360
0.570
0.10 ꢂ 0.10 ꢂ 0.20
5.12e52
30,413
1.427
0.554
m
/mmꢀ1
0.134
Crystal size/mm3
0.05 ꢂ 0.05 ꢂ 0.2
5.08e52
4746
0.05 ꢂ 0.05 ꢂ 0.10
4.92e51.98
6375
0.10 ꢂ 0.01 ꢂ 0.20
6.46e52
3738
0.20 ꢂ 0.10 ꢂ 0.05
q
min,
q
max (ꢁ)
4.88e52
Reflections collected
24,060
Independent reflections
2092 [Rint ¼ 0.0346]
2092/0/124
0.0672
0.1498
1.018
3098 [Rint ¼ 0.0685]
3098/0/195
0.0709
0.1486
0.966
1203 [Rint ¼ 0.0515]
1203/1/104
0.0673
0.1772
1.048
9946 [Rint ¼ 0.0541]
9946/23/636
0.0645
0.1709
1.044
9417 [Rint ¼ 0.0461]
9417/11/630
0.0512
0.1321
1.041
Data/restraints/parameters
a
R1 (I > 2
s(I))
wR2b (all data)
GOFc
Drmax and Drmin/e/Å3
0.22/ꢀ0.14
0.19/ꢀ0.18
0.60/ꢀ0.29
0.83/ꢀ0.66
1.06/ꢀ0.72
a
R1 ¼ SjjFoj ꢀ jFcjj/SjFoj.
b
wR2 ¼ {S[w (F2o ꢀ F2c)2]/S[w(Fo2)2]}1/2
.
c
GOF ¼ {S[w(F2o ꢀ Fc2)2]/(n ꢀ p)}1/2, where n is the number of reflections and p is the total number of parameters refined.
Elem. anal., wt%: Found 60.96; H 4.49; N 6.35. Calcd. for
Results and discussion
C
53H44ClCuN5O10Si (M ¼ 1038.01 g/mol): C 61.27; H 4.24; N 6.74.
IR, nmax (KBr), cmꢀ1: 391w, 406w, 430w, 470m, 509m, 532m,
Two silicon-containing polycarboxylic acids, bis(p-carbox-
yphenyl)diphenylsilane, 2, and bis(3,4-dicarboxyphenyl)dime-
thylsilane, 4, were prepared according to already published
multisteps procedures [14e19] (ESI) but for the first time, the main
intermediates, 1 and 3, and finally products 2 and 4, were struc-
turally characterized by X-ray crystallography, besides common
elemental and spectral methods. The carboxylic acids were pre-
pared in view of their use as organic building units for metal-
organic frameworks on the assumption that the presence in their
structures of the relative flexible spacer, CeSieC, would facilitate
the self-assembling in supramolecular architectures, decrease
phase-transition temperatures, and improve solubility. In addition,
the phenyl rings can freely rotate around the CeSieC single bond
according to the small change in the coordination environment in
order to minimize the steric hindrance [25]. The carboxylic groups
can be partially or completely deprotonated, leading to various
coordination modes; they can be involved in hydrogen bonds both
as an acceptor or a donor while the aromatic ring can stabilize the
543m, 622s, 649m, 663m, 676m, 702s, 725vs, 761w, 771w, 792w,
802w, 846s, 914w, 968w, 997m, 1016m, 1091vs, 1149m, 1184w,
1253m, 1265m, 1313m, 1344m, 1386s, 1429s, 1454w, 1460w, 1517s,
1537s, 1552w, 1583s, 1670s, 1718s, 1940vw, 2003vw, 2611vw,
2775vw, 2854w, 2925w, 3022w, 3068w, 3415s, 3653vw (Fig. 1Sc).
UVeVIS (DMF): lmax ¼ 330 nm (ε ¼ 486 molꢀ1 cmꢀ1);
lmax
¼
344 nm (ε
¼
248 molꢀ1 cmꢀ1); lmax
¼
443 nm
(ε ¼ 126 molꢀ1 cmꢀ1) (Fig. 7S).
Preparation of the copper complex [Cu(Bpy)2(H2L2)]2DMF·4.25
H2O, 6
0.1287 g (0.51 mmol) copper sulphate pentahydrate was dis-
solved in 3 mL DMF in a 50 mL round bottom flask equipped with
magnetic stirrer. Then,
a solution consisting in 0.1000 g
(0.25 mmol) bis(3,4-dicarboxyphenyl)dimethylsilane, 4, dissolved
in 5 mL DMF and 1 mL distilled water was added over this from a
dropping funnel, and the mixture was stirred for two hours.
Thereafter, another solution consisting in 0.1855 g (1.030 mmol)
1,10-phenantroline dissolved in 5 ml DMF was dropped. The
mixture was stirred 72 h at room temperature after that was
filtered. Blue crystals separated from the filtrate after about one
month. Yield: 0.089 g (89%). The product is insoluble in THF, CH2Cl2
CHCl3 but it is soluble in DMF.
crystal structure via
pep stacking interactions. These structural
properties are essential in the design of high dimensional frame-
works [26]. Thus, the two carboxylic acids, 2 and 4, were reacted
with copper(II) salt in presence of 1,10-phenantroline as co-ligand
when green crystalline complexes, 5 and 6, respectively were
formed (Scheme 1).
FTIR analysis
Elem. anal., wt%: Found 59.5; H 4.82; N 8.47. Calcd. for
C
48H44CuN6O10Si (M 956.59 g/mol): C 60.21; H 4.60; N 8.78.
In FTIR spectrum of the complex 5, the absorption band assigned
to deprotonated carboxyl group involved in cooper coordination at
1659 and protonated group at 1715 cmꢀ1 are present. The bands at
424 and 617 cmꢀ1 are assigned to nMeN and nCueO, respectively
[27,28]. Similar, in the compound 6, deprotonated and protonated
carboxyl groups are manifested by the presence in IR spectrum of
the absorption bands at 1670 and 1719 cmꢀ1 while the bands
IR, nmax (KBr), cmꢀ1: 424m, 489w, 541w, 617s, 682w, 723vs,
769vs, 806s, 827s, 854vs, 1068s, 1105s, 1139m, 1182m, 1224w,
1255m, 1288w, 1313s, 1377vs, 1425vs, 1488m, 1517s, 1585s, 1608vs,
1658vs, 1714s, 2925w, 2958vw, 3060w, 3415s (Fig. 4Sc).
UVeVIS (DMF): lmax ¼ 330 nm (ε ¼ 4930 molꢀ1 cmꢀ1);
lmax ¼ 346 nm (ε ¼ 2420 molꢀ1 cmꢀ1); lmax ¼ 443 nm
(ε ¼ 85 molꢀ1 cmꢀ1) (Fig. 8S).
assigned to nMeN and nCueO, can be identified at 407 and 623 cmꢀ1
.

M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
73
Fig. 2. X-ray molecular structure of compound 3. Thermal ellipsoids are drawn at 30%
probability level. Symmetry code for equivalent atoms: ꢀx, y, z.
consisting from bis(p-carboxyphenyl)diphenylsilane and DMF as
solvate molecules in 1:2 ratio. Si atom in the H2L1 unit is located on
two fold axis which imposed the own C2 symmetry of the bis(p-
carboxyphenyl)diphenylsilane molecule. The main crystal structure
motif results from the packing of isolated molecular associates
formed via OeH/O and CeH/O hydrogen bonds between
carboxylate groups of bis(p-carboxyphenyl)diphenylsilane and
solvate DMF (Fig. 3). The asymmetric part of the unit cell in the
Scheme 1. Complexation of copper(II) with dicarboxylic/tetracarboxylic acids 2 and 4
in presence of 1,10-phenantroline leading to compounds 5 and 6.
Crystallography
crystal structure
5
is depicted in Fig. 4. It comprises
[Cu(Bpy)2(HL1)]þ coordination cation, ClOꢀ4 counter anion and
DMF and H2O as solvate molecules. The Cu atom exhibits a slightly
distorted square-pyramidal N4O coordination environment pro-
vided by two bidentate Bpy and monodeprotonated bis(p-carbox-
yphenyl)diphenylsilane ligands. The second carboxylate group is
non-deprotonated and does not participate into the coordination
to copper atom so that the charge balance is in agreement with the
formation of species [Cu(Bpy)2(HL1)]ꢀ. The coordination cations
are associated in the crystal through OeH/O hydrogen bonds into
X-ray single-crystal study has revealed that the starting com-
pounds 1 and 3 used to design polycarboxylate ligands exhibit
molecular crystal structure built from neutral entities depicted in
Figs. 1 and 2, respectively. The Si1 atom in the crystal structure 1
occupies the special position on twofold axis. Because the Si1, C9
and C10 atoms in the crystal structure 3 are located on mirror plane,
the molecular structure of 1 and 3 compounds is characterized by
imposed C2 and Cs symmetry, respectively. According to X-ray
crystallography, H2L1$2DMF (2) has
a molecular structure
Fig. 3. X-ray structure of H2L1 (2). Non-relevant H-atoms are omitted for clarity.
Thermal ellipsoids are drawn at 50% probability level. Symmetry code: 1 ꢀ x, y, 3/2 ꢀ z.
H-bonds parameters: O1eH/O3 [O1eH 0.82 Å, H/O3 1.69 Å, O1/O3 2.510(7) Å,
O1eH/O3 170.5ꢁ], C14eH/O2 [C14eH 0.93 Å, H/O2 2.57 Å, C14/O2 3.247(7) Å,
C14eH/O2 129.6ꢁ.
Fig. 1. X-ray molecular structure of compound 1. Thermal ellipsoids are drawn at 30%
probability level. Symmetry code for equivalent atoms: 1 ꢀ x, y, 1/2 ꢀ z.

74
M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
The molecular structure of [Cu(Bpy)2(H2L2)] (6) (Fig. 7) re-
sembles in the main the structure of [Cu(Bpy)2(HL1)]þ complex
cation (5). In both complexes, the copper atom has a similar coor-
dination polyhedra, where the average CueN bond lengths
(2.055(2) Å) along with the CueO distances (1.986(2) Å) are com-
parable to those found in earlier studied copper complexes [29]. In
contrast to the bis(p-carboxyphenyl)diphenylsilane in compound 5,
bis(3,4-dicarboxyphenyl)dimethylsilane, in compound 6, contains
four carboxylate groups, two of them being in deprotonated form.
Nevertheless, both carboxylate ligands (HL1 and H2L2) behave as
monodentate ligands. As the result, compound 6 has a molecular
structure composed from neutral [Cu(Bpy)2(H2L2)] complexes and
DMF and water as solvate molecules in 1:2:4.25 ratio. In the crystal,
all the components of the structure are assembled by multiple
OeH/O hydrogen bonds (Table 2) into two dimensional supra-
molecular layers, as it is shown in Fig. 8.
Hydrogen bond dynamics
The hydrogen bond dynamics of the compounds 5 and 6 have
been emphasized by using a FTIR-ATR spectrometer equipped with
a temperature controller. The spectra have been recorded from five
to five temperature degrees for the both samples during heating
until 60 ꢁC. In the spectra of the compounds 5 (Fig. 9Sb) and 6
(Fig. 10Sb) recorded during the heating procedure appear the
specific broad bands of the OH stretching vibrations at 3731 cmꢀ1
due to dissolution of the hydrogen bonds present in the structure
between C]O from acid and water molecules, as it is shown in the
molecular structures of the complexes. An important feature of the
compounds 5 and 6 is that the structural changes that occur as a
result of increasing temperature are reversible. By cooling with the
same rate, the initial spectra of the complexes are obtained, indi-
cating that the specific structural hydrogen bonds between car-
boxylic OH groups and water molecules were reformed.
Fig. 4. View of the independent part of the unit cell in the crystal structure 5. Some H-
atoms are omitted. Thermal ellipsoids are drawn at 40% probability level. Selected
bond lengths (Å) and angles (ꢁ): Cu1eO1 1.953(2), Cu1eN1 2.033(3), Cu1eN2 2.003(3),
Cu1eN3 2.205(3), Cu1eN4 2.018(3); O1Cu1N4 91.7(1), O1Cu1N2 91.2(1), O1Cu1N3
96.6(1), N4Cu1N3 79.6(1), N4Cu1N1 95.4(1), N2CuN3 100.7(1), N2Cu1N1 81.7(1),
N1Cu1N3 101.5(1), O1Cu1N1 161.4(1), N2Cu1N4 177.1(1).
supramolecular centrosymmetric dimers, as shown in Fig. 5. Due to
the presence of different fragments which are potential proton
donors or proton acceptors, the further extension of the crystal
structure occurs via a complex network of OeH/O hydrogen
In order to explain the solubility of the copper complexes, 5 and
6, a FTIR study was performed in solution (2 mg sample in 0.5 mL
DMF) by using ATR-FTIR technique. The solutions containing Cu(II)
complexes 5 and 6 were applied on the ZnSe crystal surface and the
bonds and
pep stacking interactions. As the results, the crystal
structure 5 is characterized as a 2D supramolecular architecture,
the fragment of which is shown in Fig. 6.
Fig. 5. View of H-bonded dimer in crystal structure 5. Two intramolecular H-bonds O3eH/O1w [O3eH 0.82 Å, H/O1w (ꢀx þ 1, ꢀy þ 1, ꢀz) 1.85 Å, O3/O1w 2.648(5) Å,
O3eH/O1w 163.5ꢁ] and O1weH/O2 [O1weH 0.83 Å, H/O2 1.92 Å, O1w/O2 2.741(4) Å, O1weH/O2 173.7ꢁ] are also shown.

M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
75
Fig. 7. View of the asymmetric part of the unit cell in the crystal structure
[Cu(Bpy)2(H2L2)]$2DMF$4.25H2O, 6. Selected bond lengths (Å) and angles (ꢁ): Cu1eO1
1.986(2), Cu1eN1 2.010(2), Cu1eN2 2.048(2), Cu1eN3 2.194(2), Cu1eN4 2.019(2):
O1CuN1 92.08(8), O1CuN2 152.79(9), O1CuN3 98.75(8), O1CuN4 93.43(9), O1CuN2
81.43(9), N1CuN3 95.90(9), N1CuN4 173.4(1), N2CuN3 108.15(9), N4CuN2 95.21(9),
N4CuN3 79.72(9).
can be explained by their increased content of aromatic compo-
nent. The metal complexes proved to be less stable as compared
with the corresponding acids. It is possible as the metal to catalyse
the decomposition of the complexes [30e32]. This is supported by
the less residue amounts in the case of the complexes as compared
with carboxylic acids although it would have been expected to be
reversed due to the metal presence. However, in all cases, the
amount of residue is higher than predicted based on silica and
metal content possibly due to formation of the ceramic materials
(see ESI).
In the crystal structures 5 and 6, there are free spaces in the form
of 1D channels, the corresponding views of these in desolvated
forms being showed in Figs. 18Se20S. These spaces would accom-
modate different small molecules such as the water that can affect
the stability or behaviour of the compounds as environmental
moisture changes. Therefore, the moisture sorption/desorption iso-
therms were registered in relative humidity range 0e90 %. These
are showed in Fig. 10, and some data estimated on their basis are
centralized in Table 4. It can notice high differences between the
shape of the sorption isotherms and maximum sorption capacities
of the two complexes. Thus, the sample 6 shows high hysteresis and
increased maximum sorption capacity as compared with sample 5
(i.e., maximum sorption capacity 3.4% for sample 5 and 9.7% for
sample 6 at room temperature). Both complexes adsorb more
moisture than the acids from which they originate (Fig. 15S) and
retain some water (0.5 and 0.6 wt%, respectively) after desorption.
Fig. 6. View of 2D supramolecular layer in the crystal structure 5.
spectra were registered every 5 min until the solvent evaporated,
by using repeating measurement experiments at room tempera-
ture. Initial, in the FTIR spectra are present the specific bands of
DMF (2934 cmꢀ1 and 2866 cmꢀ1 for methyl groups stretching vi-
brations, 1655 cmꢀ1 carbonyl-C]O band, 1256, 1094 and 660 cmꢀ1
other specific bands). During the evaporation of DMF, all charac-
teristic bands of the compounds 5 (Figs.11S) and 6 (Fig. 12S) appear,
analogous with the spectra registered in solid state, indicating that
the starting structures are reformed.
Table 2
H-bonds parameters for compound 6.
DeH/A
Distance, Å
Angle
DeH/A, deg
Symmetry code
Thermal and moisture behaviour
DeH H/A D/A
TG (Fig. 9) and DTG (Fig. 13S) curves were registered for the
polycarboxylic acids and their copper complexes in nitrogen at-
mosphere. Some characteristics extracted from these curves are
presented in Table 3. By analysing the thermal data, it can be seen
that the decomposition of the dicarboxylic acid, 2, and derived
copper complex, 5, occurs in four steps while the tetracarboxylic
acid, 4, and its metal complex, 6, decompose mainly in three steps,
the last taking place generally at temperatures greater than dicar-
boxylates. The higher thermal stability of the compounds 4 and 6
O1weH/O2w 0.86
O1weH/O2 0.87
O2weH/O3w 0.87
1.99
1.99
1.96
1.99
1.79
2.05
1.82
1.66
2.07
2.04
2.821(4) 161.6
x, y, z
x, y, z
x, y, z
x, y, z
2.825(3) 167.9
2.794(4) 162.0
2.836(8) 149.5
2.660(3) 173.1
2.864(3) 170.1
2.63(1) 169.1
2.376(3) 142.6
2.864(4) 153.3
2.829(4) 155.0
O2weH/O10
OeH/O5
O3weH/O8
0.85
0.82
0.82
1 þ x, 1 þ y, 1 þ z
x, y, z
O4weH/O5w 0.82
x, y, z
x, y, z
O5eH/O7
O5weH/O6
O5weH/O9
0.84
0.85
0.85
2 ꢀ x, 1 ꢀ y, 1 ꢀ z
2 ꢀ x, 1 ꢀ y, 1 ꢀ z

76
M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
Fig. 8. Two-dimensional supramolecular layer in the crystal structure 6.
The BrunauereEmmetteTeller (BET) method [33] was used to
summarizing the voxels that are at 1.2 Å away from the network
substrate was used in this aim. The obtained values are presented in
Table 4. It can be seen the higher value of the void volume in the
case of sample 6 as compared with 5.
evaluate the surface area based on the water vapour sorption data
registered in the conditions presented in Experimental section. The
sorption values for water activities between 0.05 and 0.35 were
considered where BET equation is applicable with good results. The
model of Barett, Joyner and Halenda (BJF model) was applied in
order to estimate the average pore size, considering pores to be
cylindrical [34]. The method uses the desorption branch of the
isotherm. As expected, sample 5 that shows smaller water sorption
capacity has larger pores. The results are in agreement with the
data estimated on the basis of crystallographic data. The solvent
accessible volume determined on the basis of the solvent accessible
surface (mapped out by the centre of probe spheres) was calculated
based on the structure from which any solvate (H2O and DMF)
molecules were excluded. The technique available in Olex2 [23] by
The differences between maximum sorption values of the two
samples determined on the basis of isotherms and their void vol-
umes calculated from crystallographic data are originated probably
in the presence of the solvate molecules within the networks that
are not completely removed during the drying the sample at 25 ꢁC
in nitrogen stream before isotherms registration. In fact, as can be
seen from the thermogravimetric data (Fig. 9, Table 3), even by
heating up to around 200 ꢁC, the samples did not lose entirely
solvent molecules (i.e., DMF) contained within lattice (i.e. samples
5 and 6 loss 5.51 and 10.48 wt% towards a solvate content of 8.78
and 21.55 wt%, respectively as determined by structural analysis).
Table 3
The main parameters of the thermograms.
Compound
Peak,
step
T (ꢁC)
The mass
loss, %
The rest, %
45.37
Ton
Tmax.
Tof
130.47
2
I
86.92
187.33
342.62
~500
158.73
308.9
~450
74.74
147.15
275.73
321.54
80.86
102.56
222.94
454.17
581.57
184.11
390.33
465.05
96.27
201.11
289.23
351.95
104.6
1.21
2.30
37.64
13.19
7.11
26.93
11.17
1.49
II
III
IV
I
II
III
I
II
III
IV
I
237.49
472.40
618.17
194.19
406.45
493.43
104.39
208.37
308.48
386.52
~200
4
5
53.53
41.67
4.02
16.14
36.25
10.86
6
31.65
157.76
238.18
338.46
II
III
221.10
308.02
268.63
386.31
31.23
25.65
Fig. 9. TGA curves for the carboxylic ligands, 2 and 4, and metal complexes, 5 and 6.

M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
77
Fig. 10. The shape of the moisture sorptionedesorption isotherms for copper com-
plexes 5 and 6 at room temperature.
The sorption values increase as temperature rises; in the same time,
the isotherms become more reversible by decreasing the hysteresis
loop and water retained after desorption (Figs. 16S and 17S,
Table 4).
Fig. 11. cMT versus T plot data for 5 and 6. Insert figure corresponds to best fits of
magnetisation data for 5 and 6 at 2.0 K using Brillouin function.
and 1,10-phenantroline as co-ligands. The crystallographic data
revealed the formation of 2D structures through hydrogen bonds,
that are destroyed in a reversible way in a polar solvent (DMF) or by
heating as FTIR-ATR spectrometry study revealed.
Magnetic properties
Thermal evolution of cMT product of 5 and 6, is presented in
Fig. 11. At room temperature, the cMT product is worth 0.42 for 5
and 0.45 for 6 cm3 K molꢀ1 which close to the expected cMT value
(0.375 cm3 K molꢀ1) for one isolated CuII ions (d9, g ¼ 2.0, S ¼ 1/2)
[21]. With decreasing temperature, the cMT product for both
compounds remains constant in limit of errors of measurements
suggesting absence of any important magnetic interaction. The
slightly higher values of cMT should be associated to big g factor
(2.12 for 5 and 2.18 for 6) of distorted pentacoordinated Cu(II) ions.
The temperature measurements of magnetic susceptibility are
consistent with low temperature magnetisation measurements
(Fig. 11). Fits using the Brillouin function with S ¼ 1/2 at 2.0 K
indicate g ¼ 2.19(1) for 6 and 2.14(1) for 5, which are similar with
values obtained from temperature measurements and correspond
to non-interacted Cu(II) ion.
The dicarboxylic acid and derived copper complex, proved to be
more thermally stable than tetracarboxylate while the metal
complexes were less stable as compared with the corresponding
acids. As expected, the tetracarboxylic acid is more hydrophilic than
dicarboxylic acid, while the copper complexes absorb more mois-
ture than acids from which they were formed. The moisture sorp-
tion capacity increases as temperature rises. The results of the
magnetic measurements performed for the two metal complexes
correspond to not interacting copper(II) metal centres with S ¼ 1/2
and g factor equal to 2.14 for 5 and 2.19 for 6, respectively being
consistent with pentacoordinated Cu(II) paramagnetic centers.
Acknowledgements
This work was supported by a grant of the Ministry of National
Education, CNCS e UEFISCDI, project number PN-II-ID-PCE-2012-4-
0261. The authors acknowledge to Dr. Olivier Leynaud from Insti-
tute NEEL CNRS/UJF UPR2940, Grenoble for powder diffraction X-
ray experiments.
Conclusions
Two new soluble copper(II) complexes were obtained by the
reaction of copper salt with well-characterized bis(p-carbox-
yphenyl)diphenylsilane or bis(3,4-dicarboxyphenyl)dimethylsilane
Appendix A. Supplementary material
Table 4
The sorption and morphological parameters estimated on the basis of water vapour
sorption isotherms and crystallographic data.
CCDC 950973, 950974, 950976, 950977 and 950975 contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Sample
Weighta (%d.b.) at
Average pore
sizea (nm)
ABET
Water
a
(m2/g)
accessible
volumesb
25
35
4.2
55
6.2
V (Å)
V (%)
Appendix B. Supplementary data
5
6
3.4
9.7
4.41
1.75
20.6
110.9
493
834
20.1
34.7
12.4
17.1
a
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.10.006.
Calculated on the basis of the sorption isotherms.
Estimated based on crystallographic data by using Olex2 technique [23].
b

78
M. Cazacu et al. / Journal of Organometallic Chemistry 774 (2014) 70e78
[13] (a) M.C. Hong, Y.J. Zhao, W.P. Su, R. Cao, M. Fujita, Z.Y. Zhou, A.S.C. Chan, J. Am.
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