Copper(II)-phenylmalonate complexes with the bifunctional ligands nicotinamide and isonicotinamide

Article abstract of DOI:10.1016/j.poly.2011.06.006

The use as coligands of the nicotinamide (nia) and isonicotinamide (inia) molecules in the complex formation between copper(II) and phenylmalonate [Phmal = dianion of phenylmalonic acid] yielded the compounds of formula [Cu(inia)(Phmal)(H₂O)] (

Full text of DOI:10.1016/j.poly.2011.06.006

Polyhedron 30 (2011) 2451–2458
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Copper(II)-phenylmalonate complexes with the bifunctional ligands
nicotinamide and isonicotinamide
Jorge Pasán a, Joaquín Sanchiz b, Francesc Lloret c, Miguel Julve c, Catalina Ruiz-Pérez a,
⇑
a Laboratorio de Rayos X y Materiales Moleculares, Departamento de Física Fundamental II, Facultad de Física, Universidad de La Laguna, Av. Astrofísico Francisco
Sánchez s/n, 38206 La Laguna (Tenerife), Spain
b Departamento de Química Inorgánica, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, 38206 La Laguna (Tenerife), Spain
c ICMol/Departament de Química Inorgánica de la Universitat de València, Polígono La Coma s/n, 46980 Paterna (València), Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The use as coligands of the nicotinamide (nia) and isonicotinamide (inia) molecules in the complex forma-
tion between copper(II) and phenylmalonate [Phmal = dianion of phenylmalonic acid] yielded the com-
pounds of formula [Cu(inia)(Phmal)(H2O)] (1) and [Cu(inia)(Phmal)(H2O)]n (2). Although single crystals
of 1 of appropriate size were grown, their unresolved twinning and space group ambiguity prevented a
satisfactory X-ray structure determination. The crystal structure 2 consists of corrugated layers of cop-
per(II) ions with intralayer carboxylate–phenylmalonate bridges in the anti-syn (equatorial-apical) coor-
dination mode. A water molecule and the isonicotinamide group are coordinated to the copper atom in
trans position being located above and below each layer. The Phmal ligand adopts the bidentate/monoden-
tate coordination mode with the bidentate coordination involving one equatorial and one apical bonds, a
feature which is unprecedented for the copper(II) complexes with alkyl(aryl)substituted-malonate deriv-
Received 22 April 2011
Accepted 14 June 2011
Available online 23 July 2011
Keywords:
Copper(II)
Coordination polymer
Phenylmalonate ligand
Magnetic properties
Crystal engineering
atives. Intra- and interlayer H-bonds together with intralayer p–p type interactions between the phenyl
and inia aromatic groups contribute to the stabilization of the three-dimensional supramolecular struc-
ture. Magnetic susceptibility measurements of complexes 1 and 2 in the temperature range 1.9–300 K
are quasi identical and they correspond to a very weak ferromagnetic interaction between the copper(II)
ions [J = +0.091(2) cmꢀ1 (1) and +0.097(2) cmꢀ1 (2) through the spin Hamiltonian for an isotropic square
grid of interacting spin doublets which is defined as H = ꢀJRiSi ꢁ Si+1]. The strong similarity in the magnetic
properties of 1 and 2 allow us to conclude that although they are not isostructural species, their structures
have to be very close.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
hydrogen bonds and p–p type interactions). Their subtle interplay
makes difficult the prediction of the final structure.
The design of coordination polymers lies at the interface of coor-
dination and supramolecular chemistry, and it is a part of crystal
engineering, whose ultimate goal is to obtain solids with technolog-
ically useful functionalities (molecular magnetic materials, con-
ducting solids, zeolite-like materials, catalysts, luminescent
materials, etc.) [1]. The metal ions plays both structural (directing
and sustaining the solid-state architecture) and functional roles
(spin carrier, optical or redox properties, etc.). An important point
concerning the general architecture of crystals containing coordi-
nation polymers is their packing which is the result of the hierar-
chic organization determined by the primary (metal–ligand bonds
which generate the coordination polymer) and the secondary struc-
tures (a concert of electrostatic and non-covalent forces such as
Among the metal ions used to build molecule-based magnetic
materials, copper(II) has played a prominent role both from exper-
imental and theoretical points of view [2]. However, looking at the
structural aspects, the plasticity of the coordination sphere of the
copper(II) ion, which accounts for the richness and variety of its
coordination chemistry, is at the origin of the diversity of the topol-
ogies and connectivities occurring in the extended assemblies con-
taining this metal ion.
In contrast with the rigidity of the aromatic dicarboxylate spac-
ers, the aliphatic dicarboxylate ligands exhibit a greater conforma-
tional freedom and then, a greater coordination versatility being
considered as highly flexible connectors. Under mild conditions,
the self-assembly of metal ions with
a,x-dicarboxylate ligands,
such as the malonate (dianion of propanedioic acid, H2mal) [3],
afforded a variety of supramolecular motifs where the discrete
metal–oxygen polyhedra could be interconnected by organic link-
ers into polymeric chains, layers and 3D frameworks. Focusing on
the malonate-bridged copper(II) complexes, it has been shown that
⇑
Corresponding author. Tel.: +34 922318236; fax: +34 922318320.
E-mail addresses: caruiz@ull.es, caruizperez@gmail.com (C. Ruiz-Pérez).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.06.006

2452
J. Pasán et al. / Polyhedron 30 (2011) 2451–2458
the carboxylate–malonate bridge is able to mediate significant fer-
romagnetic interactions between the copper(II) ions [3k,3o]. More
recently, we have started a systematic study on the copper(II) com-
plexation by substituted malonate ligands such as phenylmalonate
(dianion of phenylmalonic acid, H2Phmal) [4] and methylmalonate
(dianion of methylmalonic acid, H2Memal) [5]. One of the aims of
this study is to analyze the influence that factors such as the steric
hindrance, the rigidity and the possibility of specific attractive
interactions between phenyl rings can exert on the structure and
magnetic coupling of copper(II) complexes with aryl(alkyl)-substi-
tuted malonate derivatives.
In the present work, we have explored the magneto-structural
effects caused by the presence of the bifunctional ligands nicotin-
amide (nia) and isonicotinamide (inia) in the copper(II)-phenylmal-
onate system. Two compounds of formula [Cu(inia)(Phmal)(H2O)]
(1) and [Cu(inia)(Phmal)(H2O)]n (2) were prepared, the crystal of
2 determined and the variable-temperature magnetic properties
of 1 and 2 investigated. Our aim in this work has been to combine
the well established molecular inorganic chemistry with well
established aspects of supramolecular organic chemistry. Hydrogen
bonds combine the most favorable aspects of directionality and
strength among intermolecular interactions and in spite of being
weaker than the metal–ligand covalent bonds, they offer a greater
flexibility and there are well developed principles for fostering mu-
tual recognition by functional groups through hydrogen bonding
[6]. The choice of the nia and inia as coligands was made for two
reasons: (i) firstly, the higher affinity of the copper(II) ion for the
nitrogen-donors, which ensures its coordination to the nia and inia
pyridyl-nitrogen atom, the amide fragment remaining uncoordi-
nated; (ii) and secondly, amide moieties have a well established
propensity to be engaged in complementary hydrogen bonds
resulting either in ribbons (through head-to-head interactions), or
in chains via equivalent N–Hꢁ ꢁ ꢁO type contacts [amide–amide
interactions in organic molecular solids typically involve ‘‘head-
to-head’’ R22(8) or catemer C11(4) hydrogen bonds] [7]. In the case
of 2, the latter motif is observed and its structure contains quasi lin-
ear N–Hꢁ ꢁ ꢁO hydrogen bonds that connect neighboring amide
moieties.
refinement. Nevertheless, this is an important observation as it is
indicative of the difficulty in predicting the overall structural
arrangement. Yield ca. 80%. Anal. Calc. for C15H14O6N2Cu (1): C,
47.18; H, 3.70; N, 7.34. Found: C, 47.12; H, 3.57; N, 7.27%. Main IR
peaks (values in cmꢀ1/KBr pellets): 1696s, 1668s, 1640s, 1605vs,
1420m, 1384s, 1298m, 1284m; 726m, 700m.
2.2.2. Synthesis of [Cu(inia)(Phmal)(H2O)]n (2)
Complex 2 was synthesized following the same procedure than
that described for 1, but using isonicotinamide (0.5 mmol, 61 mg)
instead of nicotinamide. X-ray quality crystals of 2 as thin blue
plates appeared in the H-shaped tube on standing at room temper-
ature after three weeks. Yield ca. 82%. Anal. Calc. for C15H14O6N2Cu
(2): C, 47.18; H, 3.70; N, 7.34. Found: C, 47.15; H, 3.59; N, 7.27%.
Main IR peaks (values in cmꢀ1/KBr pellets): 1674s, 1616s, 1595vs;
1550s, 1449m, 1398s, 1380s, 1284m, 1220m, 845m, 818m, 722m.
2.3. Physical techniques
The IR spectra (450–4000 cmꢀ1) of 1 and 2 were recorded on a
Bruker IF S55 spectrophotometer with samples prepared as KBr pel-
lets. Magnetic susceptibility measurements on polycrystalline sam-
ples of 1 and 2 were performed with a Quantum Design SQUID
magnetometer in the temperature range 1.9–300 K operating at
1 T (T P 50 K) and 1000 G (T > 50 K). Diamagnetic corrections for
the constituent atoms were estimated from Pascal’s constants as
155.8 ꢂ 10ꢀ6 cm3 molꢀ1 per mol of copper(II) for 1 and 2 [8]. Exper-
imental magnetic susceptibilities were also corrected for the tem-
perature independent paramagnetism (60 ꢂ 10ꢀ6 cm3 molꢀ1 per
copper(II) ion) and the magnetization of the sample holder.
2.4. X-ray crystallography
A single crystal of 2 was mounted on a Bruker-Nonius KappaCCD
diffractometer and the diffraction data were collected at 293(2) K
using graphite-monochromated Mo K
The data collection was carried out with
a
radiation (k = 0.71073 Å).
scans in the 6.43–
u–x
30.0° h range. Data were collected with the COLLECT [9] program
and indexed, integrated and scaled with EVALCCD [10]. SADABS absorp-
tion correction was applied to these data [11]. The crystal structure
of 2 was solved by direct methods and refined with the full-matrix
least-squares technique on F2 using the SHELXS-97 and SHEXL-97 pro-
grams [12] included in the WINGX software package [13]. All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms
of 2 were located from Fourier differences and refined isotropically.
The absolute configuration of the chiral crystal could be reliably
solved with a Flack parameter of 0.018(11). Measurements on dif-
ferent crystals yielded a racemic mixture of the two enantiomeric
forms. The final geometrical calculations and the graphical manip-
ulations were carried out with PARST95 [14] and DIAMOND [15] pro-
grams. A summary of the crystallographic data and structure
refinement for 2 is given in Table 1 while main bond lengths and an-
gles and hydrogen bonds are listed in Tables 2 and 3.
2. Experimental
2.1. Materials and methods
Reagents and solvents used in all the syntheses were purchased
from commercial sources and used without further purification.
{[Cu(H2O)3][Cu(Phmal)]}n was prepared as previously reported
[4a]. Elemental analyses (C, H, N) were performed on an EA 1108
CHNS-O microanalytical analyzer.
2.2. Preparation of the complexes
2.2.1. Synthesis of [Cu(inia)(Phmal)(H2O)] (1)
An aqueous solution (3 cm3) of {[Cu(H2O)3][Cu(Phmal)]}n
(0.125 mmol, 134 mg) was introduced into one arm of an H-shape
tube while a 50:50 (v/v) water/methanol solution (1 cm3) of nico-
tinamide (0.5 mmol, 61 mg) was added in the other arm. Water
was added dropwise to fill the H-tube and the tubes were covered
with parafilm. Pale blue single crystals of 1 as extremely thin plates
were grown in the H-shaped tube on standing after one month at
room temperature. Although single crystals of 1 of adequate size
were synthesized in several attempts, they always exhibit twin
growth. The thinnest plates of 1 exhibit the characteristic differen-
tiation in color areas when they are looked through polarized light
(Fig. S1). Unfortunately, to date all data sets exhibit unresolved
twinning and have space group ambiguity preventing satisfactory
3. Results and discussion
3.1. Description of the crystal structure of 2
The structure of
2 consists of a quasi square grid of
trans-aqua(isonicotinamide)copper(II) units linked through phe-
nylmalonate-carboxylate bridges running parallel to the ab plane
(Figs. 1 and 2), similar to that of the compound of formula [Cu
(pym)(Phmal)]n (pym = pyrimidine) [4d]. The corrugated layers
are stacked along the crystallographic c axis being linked through
hydrogen bonds involving the amide group of the isonicotinamide

J. Pasán et al. / Polyhedron 30 (2011) 2451–2458
2453
Table 1
interactions between the phenyl (Phmal) and pyridyl (inia) rings
contribute to the stabilization of the three-dimensional supramo-
lecular structure. The shortest centroid–centroid separation and
off-set angle are 4.773(2) Å and 29.9(3)° respectively, values which
are somewhat longer than those previously reported for this type
of interactions [16].
Each copper atom exhibits a distorted octahedral environment
with the parameters s/h and / being 1.32° and 56.5°, respectively
(values to be compared with those for an ideal octahedron: s/
h = 1.22 and / = 60°) [17]. Two oxygen atoms from two different
phenylmalonate ligands [O(4) and O(1a); (a) = ꢀx, y + 1/2, ꢀz + 1],
a isonicotinamide nitrogen atom [N(1)] and a water molecule
[O(1w)] build the basal plane (mean value of the equatorial bond
lengths being 2.0016(19) Å; see Table 2), while two phenylmalo-
nate oxygen atoms [O(2) and O(3b)] occupy the axial positions
Crystallographic data for complex 2.
2
Formula
Formula weight
Crystal system
Space group
a (Å)
C
15H14O6N2Cu
381.82
monoclinic
P21
7.3012(10)
7.2406(12)
14.852(4)
104.020(11)
761.8(3)
2
14.69
293(2)
1.665
0.71073
ꢀ10 6 h 6 3,
ꢀ10 6 k 6 7,
ꢀ16 6 l 6 20
3445 (0.0182)
3039
b (Å)
c (Å)
b (°)
V (Å3)
Z
l(Mo K
a
) (cmꢀ1
)
T (K)
qcalc (g cmꢀ3
k (Å)
)
Index ranges
Independent reflections (Rint
Obs. reflections [I > 2
)
r(I)]
Parameters
273
Flack parameter
Goodness-of-fit
0.018(11)
0.899
R [I > 2r(I)]
0.0260
Rw [I > 2
r(I)]
0.0523
R (all data)
0.0337
Rw (all data)
0.0543
Table 2
Selected bond lengths (Å) and bond angles (°) for compound 2.a,b
Cu(1)–O(2)
Cu(1)–O(4)
Cu(1)–O(1a)
Cu(1)–O(3b)
Cu(1)–N(1)
Cu(1)–O(1w)
O(2)–Cu(1)–O(4)
O(2)–Cu(1)–O(1a)
O(2)–Cu(1)–O(3b)
O(2)–Cu(1)–N(1)
O(2)–Cu(1)–O(1w)
2.2154(17)
1.9729(16)
1.9740(16)
2.3651(18)
2.0360(19)
2.0235(17)
85.92(7)
88.27(7)
179.23(7)
94.42(8)
O(4)–Cu(1)–O(1a)
O(4)–Cu(1)–O(3b)
O(4)–Cu(1)–N(1)
O(4)–Cu(1)–O(1w)
O(1a)–Cu(1)–O(3b)
O(1a)–Cu(1)–N(1)
O(1a)–Cu(1)–O(1w)
O(3b)–Cu(1)–N(1)
O(3b)–Cu(1)–O(1w)
N(1)–Cu(1)–O(1w)
173.38(8)
93.65(7)
90.43(8)
89.22(7)
92.13(7)
86.87(7)
94.28(7)
84.94(7)
87.16(7)
172.05(8)
93.47(8)
a
Estimated standard deviations in the last significant digits are given in
parentheses.
b
Symmetry code: (a) ꢀx, y + 1/2, ꢀz + 1; (b) ꢀx ꢀ 1, y + 1/2, ꢀz + 1.
Table 3
Hydrogen bonds in 2.
D–HꢁꢁꢁAa
Interlayer
N(2)–Hꢁ ꢁ ꢁO(5)
D–H (Å)
0.67(2)
Hꢁ ꢁ ꢁA (Å)
D–Hꢁ ꢁ ꢁA (°)
Dꢁ ꢁ ꢁA (Å)
2.28(2)
172.4(8)
2.946(4)
Intralayer
O(1w)–Hꢁ ꢁ ꢁO(2)
0.79(3)
0.82(3)
1.84(2)
1.88(2)
164.7(9)
178.1(9)
2.616(3)
2.703(3)
O(1w)–Hꢁ ꢁ ꢁO(4)
a
D and A stand for donor and acceptor, respectively.
ligand (see Table 3 and Fig. 2) affording a supramolecular three-
dimensional network. The inia and Phmal ligands located in
trans-position respect to the copper atom and inversely located re-
spect to the adjacent [Cu(inia)(Phmal)(H2O)] units, these bulky
groups being located in an hydrophobic area which separates the
layers as occur in the previously reported [Cu(pym)(Phmal)]n com-
plex (the shortest interlayer copper–copper separation being
13.390(3) Å (see Fig. 2)). Intralayer hydrogen bonds between the
water molecule O(1w) and the coordinated phenylmalonate-oxy-
Fig. 1. A view of the asymmetric unit of 2 along with the numbering scheme.
gens O(2) and O(4) occur (see Table 3). Weak intralayer
p-type

2454
J. Pasán et al. / Polyhedron 30 (2011) 2451–2458
Fig. 2. A perspective view of the crystal packing of 2 along the a axis (left). Views of the square grid of carboxylate-bridged copper(II) ions (top, right) and the hydrogen
bonding scheme involving the isonicotinamide ligands of adjacent layers (bottom, right).
(average Cu–O(ax) bond distance being 2.2902(18) Å; (b) = ꢀx ꢀ 1,
y + 1/2, ꢀz + 1).
the pyridyl ring is 27.9(2)°. This unprecedented behavior of the inia
molecule illustrates the potential of combining coordination chem-
istry and hydrogen bonding aiming at designing and controlling
new crystalline materials. Coordination chemistry is able to pro-
vide a good prediction of the coordinating behavior of a given
ligand which can be used to direct its ability in hydrogen bonding
through suitable substituents. Nowadays, hydrogen bonding
arrangements exhibit a high degree of predictability, but their
inherent weakness leaves open different structural possibilities
with similar energy values [20].
A survey on the Cambridge Structural Database [21] was carried
out in order to compare the functionality of the inia ligand in 2
with other related systems. A total of twenty-two inia-containing
copper(II) complexes has been found [22]. Although the inia ligand
establishes intermolecular hydrogen bonds with neighboring units
in most of them, compound 2 is revealed as the first example
where the inia group is used with the final purpose of act as a pillar
for a two-dimensional coordination polymer. The amide groups
recognize each other forming interlayer hydrogen bonds. The same
structural survey performed for the case of the nia ligand reveals
that this pillar functionality was neither reported.
The phenylmalonate ligand adopts simultaneously the bidentate
(through O(2) and O(4) toward Cu(1), the angle subtended at the
copper atom being 85.92(7)°) and bis-monodentate (across O(1)
and O(3) toward Cu(1c) and Cu(1d), respectively; (c) = ꢀx, y ꢀ 1/2,
ꢀz + 1; (d) = ꢀx ꢀ 1, y ꢀ 1/2, ꢀz + 1) coordination modes. The
bidentate coordination of the Phmal ligand involves one equatorial
[O(4)] and one axial [O(2)] bonds (see Scheme 1). This structural
feature which has been scarcely observed in copper(II) complexes
with alkyl(aryl)-substituted malonate ligands [3h,4c,18], although
it is not uncommon for copper(II)–oxalate complexes [19]. Two dif-
ferent anti-syn carboxylate bridges are present in the structure of 2
(namely O(1)–C(1)–O(2) and O(3)–C(3)–O(4)) with values for the
copper–copper separation of 5.3362(6) and 5.3856(6) Å, respec-
tively. Both carboxylate bridges connect an equatorial [O(1) and
O(4)] with one axial position [O(2) and O(3)] at the copper environ-
ments. The shortest interlayer copper–copper separation is
13.390(3) Å.
The inia ligand acts as a monodentate ligand [through N(1)], the
amide group participating in interlayer hydrogen bonds (Table 3).
The dihedral angle between the plane of the amide group and
3.2. Structural remarks
The copper atom in 2 exhibits an octahedral environment with
the inia and water ligands occupying equatorial positions. This fea-
ture makes the phenylmalonate ligand to chelate the copper atom
through one equatorial and one axial positions, the remaining
coordination sites being filled by oxygen atoms from adjacent
Phmal ligands (Fig. 3). Considering an ideal octahedral metal
environment, such a situation is achiral. However, due to the
Jahn–Teller effect, the ideal Oh symmetry is lowered and the result-
ing environment becomes chiral. The
K and D conformations are
shown in Fig. 3. An identical situation was found in the complex
[Cu(2,40-bpy)(Phmal)(H2O)]n [4c] (2,40-bpy = 2,40-bipyridine) but
Scheme 1. Coordination mode of the Phmal ligand in 2.

J. Pasán et al. / Polyhedron 30 (2011) 2451–2458
2455
Fig. 3. Views of the
D (left) and K (right) conformations of the copper(II)
environment in 2. The arrows indicate the direction of the pseudo-Jahn–Teller
elongation. The aromatic rings of the Phmal and inia ligands are omitted for clarity.
exhibiting a static Jahn–Teller disorder within the crystal. The 2,40-
bpy and water ligands which occupy the equatorial positions are
unaffected by the J–T disorder.
Also looking in the previously reported copper(II) complex
[Cu(4,40-bpy)(Phmal)]nꢁ2nH2O [4c] (4,40-bpy = 4,40-bipyridine), the
square pyramidal environment at the copper atom is built by two
4,40-bpy nitrogen atoms occupying equatorial positions, two oxy-
gen atoms from a bidentate Phmal ligand in one equatorial and api-
cal positions and another oxygen atom from an adjacent Phmal
group in the remaining equatorial position. The equatorial-apical
bidentate coordination and the fact that the Phmal ligand has two
different substituents (a phenyl ring and a hydrogen atom) in the
central carbon atom of the malonate skeleton account for the chi-
rality of the copper environment. The superposition of the metal
environment with its inversion related one shows that the unique
difference is the relative situation of the substituents of the meth-
ylene carbon atom of the malonate ligand.
Let us finish with an important point: the structure of 2 shows
that all complexes exhibiting the equatorial-axial bidentate
coordination of the phenylmalonate ligand will lead to chiral envi-
ronments, a situation which was not observed in the related cop-
per(II)–malonate complexes.
3.3. Magnetic properties of 1 and 2
The magnetic properties of 1 and 2 under the form of a
vMT ver-
sus T plot ( M is the magnetic susceptibility per copper(II) ion) are
v
shown in Fig. 4 (top (1) and middle (2)]. At room temperature, vMT
is equal to 0.44 cm3 molꢀ1 K for 1 and 2, a value which is as ex-
pected for a magnetically isolated spin doublet. Upon cooling,
Fig. 4.
v
MT vs. T plots for 1 (top) and 2 (middle): (s) experimental data; (—) best-fit
vMT remains almost constant down to 50 K, and further increases
to reach values of 0.50 (1) and 0.51 cm3 molꢀ1 K for (2) at 2.0 K. This
behavior is indicative of the existence of a very weak ferromagnetic
interaction between the copper(II) ions. The magnetization (M) ver-
sus H plot for 1 and 2 at 2.0 K (Fig. 4, bottom) confirms this behav-
ior: the magnetization data for both compounds are slightly above
the Brillouin curve (dashed line) for a magnetically isolated spin
doublet.
curve through Eq. (1) (see text). The inset shows a detail of the low temperature
region. M vs. H plot (bottom) for 1 (triangles) and 2 (circles) together with the
Brillouin function for a magnetically isolated spin doublet with g = 2.0 (dashed line).
temperature expansion series for the isotropic ferromagnetic qua-
dratic lattice with local spin doublets (Eq. (1)) [23].
!"
#
10
Nb2g2
3kT
xn
X
Although 1 and 2 are not isostructural species, the similarity of
their magnetic properties strongly supports a close structure for
them. Having in mind this similarity from a magnetic point of view
and the fact that the structure of 2 consists of a quasi square grid of
copper(II) ions linked by anti-syn carboxylate bridges, the magnetic
data of 1 and 2 have been analyzed by means of the derived high-
vM
¼
SðS þ 1Þ 1 þ
an
ð1Þ
2n
n¼1
In this expression, N, g, b and kB have their usual meanings, x =
J/kT, J is the intralayer magnetic coupling, an are coefficients which
run up to n = 10 with the spin Hamiltonian being defined as

2456
J. Pasán et al. / Polyhedron 30 (2011) 2451–2458
Table 4
Selected magneto-structural data for some equatorial-apical carboxylate-bridged malonato- and phenylmalonato-containing copper(II) complexes.
Compounda
Cuꢁ ꢁ ꢁCu (Å)
Cuꢁ ꢁ ꢁO(ap) (Å)
Cuꢁ ꢁ ꢁO(eq) (Å)
s
Cu1/Cu2b
Jc (cmꢀ1
)
Ref.
[Cu(H2O)4][Cu(mal)2(H2O)2]
{[Cu(H2O)4]2[Cu(mal)2(H2O)]}
{[Cu(H2O)3][Cu(mal)2(H2O)]}n
[Cu(Im)2(mal)]n
5.781(1)
5.857(2)
4.640(1)
6.036(2)
6.099(2)
4.8831(10)
4.6853(7)
5.014(3)
5.081
2.393(4)
2.381(3)
2.185(2)
2.394(2)
2.270(4)
2.6107(14)
2.262(3)
2.314(2)
2.705(2)
1.948(3)
1.941(2)
1.930(2)
1.962(2)
1.961(3)
1.9314(11)
1.900(3)
1.934(2)
1.928(2)
Oh/0.05
Oh/0.12
0.24/0.28
0.016
0.18
Oh
0.08
0.10
Oh
+1.8
+1.2
+1.9
+1.6(1)
+0.4(1)
+0.049(1)
+0.10(1)
+0.31(1)
+0.6
+0.3(2)
+0.091(2)
+0.097(2)
[3a]
[3a]
[3a]
[3g]
[3g]
[3h]
[4b]
[4b]
[26]
[27]
–
[Cu(2-MeIm)2(mal)]n
{(H2bpe)[Cu(mal)2]}nꢁ4nH2O
[{Cu(2,20-bpym)(Phmal)}]n
[{Cu(phen)(Phmal)}]nꢁ3nH2O
{(H2ade)2[Cu(
l
-mal)2]ꢁ2H2O}n
{[Cu(mal)2](Hpic)2ꢁ2H2O}n
6.0910(2)
–
5.3362(6) 5.3856(6)
2.6143(10)
–
2.2154(17) 2.3651(18)
1.9458(9)
–
1.9740(16) 1.9729(16)
Oh
–
Oh
1
2
–
a
Abbreviations used: H2mal = malonic acid, Im = imidazole, 2-MeIm = 2-methylimidazole, bpe = 1,2-bis(4-pyridyl)ethylene, H2Phmal = phenylmalonic acid, 2,2’-
bpym = 2,20-bipyrimidine, phen = 1,10-phenanthroline, ade = adenine, pic = 2-amino-4-picoline.
b
Distortion of the five-coordinated copper environment (
Values of the magnetic coupling.
s = 1 for trigonal bipyramidal and 0 for square pyramidal); Oh stands for octahedral.
c
Scheme 2. Magnetic coupling between the copper(II) ions through the carboxylate bridge in the anti-syn conformation.
H = ꢀJRiSi ꢁ Si+1. Least-squares best-fit parameters in the tempera-
but most likely ferromagnetic. The computed magnetic interac-
tions in 1 and 2 are within the range observed for this kind of
bridge in other related copper(II)–malonate complexes as shown
in Table 4.
ture range 1.9–300 K are J = +0.092(2) cmꢀ1
,
g = 2.10(2) and
R = 1.1 ꢂ 10ꢀ4 for
1 ; g = 2.10(2) and
and J = +0.099(2) cmꢀ1
R = 1.3 ꢂ 10ꢀ4 for
2
(R is the agreement factor defined as
P
P
i[(
v
MT)obs(i) ꢀ (
v
MT)calc(i)]2/ i[(
v
MT)calc(i)]2). The calculated
The magnitude of the ferromagnetic behavior observed in 1 and
2 is significantly weaker than that observed for copper(II) complex
of formula [Cu(pym)(Phmal)]n [J = +5.6(1) cmꢀ1] [4d], the three
compounds exhibiting the same carboxylate-bridged (anti-syn
conformation) square-grid of copper(II) ions. The fact that the
nicotinamide (1) and the isonicotinamide (2) ligands occupy equa-
torial positions at the metal environment causes one of the oxygen
atoms from the phenylmalonate ligand to fill an apical position,
and then the carboxylate-bridge becomes of the equatorial-apical
type. This situation alters completely the magnetic behavior since
this kind of carboxylate-bridge is much less efficient than the
equatorial-equatorial exchange pathway which occurs in
[Cu(pym)(Phmal)]n (see Scheme 2).
curves (solid lines in Fig. 4 (top and middle) match very well the
experimental data in the whole temperature range.
The weak magnetic interactions in 1 and 2 are as expected for
anti-syn carboxylate-bridges which connect equatorial with apical
positions of adjacent copper(II) ions. The magnetic orbital (that is
the unpaired electron) of the copper(II) ion with elongated octahe-
dral surrounding is of the dx2
character (the x and y axes being
ꢀy2
roughly defined by the equatorial bonds) with some admixture of
the dz2 (the z axis corresponding to the axial bonds). According to
the Kahn’s model [24], the magnetic orbital dx2
interacts with
ꢀy2
the dz2 across the equatorial-axial exchange pathway provided by
the carboxylate bridge. The weak spin density, which is predicted
for the axial position together with the poor overlap (S) between
these two magnetic orbitals [25], would lead to a very weak mag-
netic interaction. As the antiferromagnetic contribution in a dicop-
per(II) unit is proportional to the square of the overlap integral (S2)
between the magnetic orbitals and given that it is minimized in the
case of 1 and 2, the resulting magnetic coupling is certainly weak
4. Conclusions
The structure of the complexes 1 and 2 consists of carboxylate-
bridged copper(II) layers which are linked through hydrogen bonds

J. Pasán et al. / Polyhedron 30 (2011) 2451–2458
2457
(m) F.S. Delgado, C. Ruiz-Pérez, J. Sanchiz, F. Lloret, M. Julve, CrystEngComm
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involving the amide groups of the nia (1) or inia (2) ligands. This sit-
uation is as expected for their use as coligands, analogously to the
case of the complex [Cu(pym)(Phmal)]n. However, the weakness
of the intralayer ferromagnetic coupling between the copper(II)
ions across the carboxylate bridge in 1 and 2 when compared to that
in [Cu(pym)(Phmal)]n is due to the occurrence of equatorial-axial
(former compounds) versus equatorial–equatorial (latter com-
pound) exchange pathways involved. The equatorial-axial connec-
tion through the carboxylate-bridge in 1 and 2 appears as a
consequence of the equatorial coordination at the copper atom of
the nia and inia ligands. Moreover, a water molecule is also present
in the coordination sphere of the copper(II) ion in 1 and 2 while this
is not the case for the pym-containing copper(II) compound. Sum-
marizing, the present work shows that the subtle but predictable
structural changes which are associated to the introduction of the
amide group of the coligand in the Phmal-containing copper(II)
system are relevant for a magnetic point of view and consequently,
the investigation about how different magnetic properties could
arise from similar structures remains an open subject.
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