Octanuclear [NiII4LnIII4] complexes. Synthesis, crystal structures and magnetocaloric properties

Article abstract of DOI:10.1039/c4dt00515e

Two original heterooctanuclear [Ni^II₄Ln ^III₄] complexes (Ln^III = Sm^III, Gd^III) have been obtained starting from the [Ni^II(valpn) (H₂O)₂] mononucl

Full text of DOI:10.1039/c4dt00515e

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Octanuclear [NiII LnIII ] complexes. Synthesis,
4
4
crystal structures and magnetocaloric properties†‡
Cite this: Dalton Trans., 2014, 43,
9136
Traian D. Pasatoiu,a Alberto Ghirri,b Augustin M. Madalan,a Marco Affronte*b and
Marius Andruh*a
Two original heterooctanuclear [NiII4LnIII4] complexes (LnIII = SmIII, GdIII) have been obtained starting from
the [NiII(valpn)(H2O)2] mononuclear precursor [H2valpn
6-methoxy-phenol)] and the corresponding lanthanide nitrates, in the presence of azide anions, through
slow capture of atmospheric CO2. Three weak and competitive exchange interactions, JGdGd, JGdNi, JNiNi
= 1,3-propanediylbis(2-iminomethylene-
Received 18th February 2014,
Accepted 20th March 2014
,
make the ground state of this magnetic system degenerate at cryogenic temperature and zero field. This,
along with the high spin of GdIII, lead to a significant magnetocaloric effect spread in the temperature
range 1 to 20 K (ΔSm[0–7 T, 3.5 K] = 19 J kg−1 K−1).
DOI: 10.1039/c4dt00515e
www.rsc.org/dalton
netic material and is related to the change of the magnetic
entropy, −ΔSm, once it is exposed to a magnetic field. When
Introduction
An important research topic in molecular magnetism is rep- the magnetic field is switched off, if the demagnetization
resented by the synthesis of heterometallic complexes contain- process occurs without any heat flow from the environment, a
ing both paramagnetic 3d and 4f ions. The interaction drop (ΔTad) of the temperature of the system is observed. This
between d and f spin carriers within the same molecular entity behaviour can be exploited for magnetic refrigeration.5 A pre-
leads to interesting magnetic properties. Moreover, 3d–4f com- requisite for achieving a large MCE is a highly degenerate mag-
plexes have been intensively studied in order to reveal the netic ground state and an easy lift of this degeneration by the
factors governing the nature and magnitude of the exchange application of an external magnetic field which, in turns,
interaction between lanthanides and various 3d metal ions.1 induces a large variation of the entropy.6 Although attention of
The interest for 3d–4f heteronuclear complexes grew rapidly chemists was mostly oriented towards lanthanide compounds
after Gatteschi’s report on the ferromagnetic interaction and alloys, due to their large magnetic entropy changes,5
between adjacent CuII and GdIII ions in trinuclear CuIIGdIIICuII heterometallic 3d–4f polynuclear complexes were also shown
complexes.2 Nowadays, the revival of 3d–4f combined chem- to exhibit a magnetic refrigerant behaviour.7
istry arises from to the discovery of molecular nanomagnets
In previous papers we have shown that binuclear [NiII-
(single-molecule magnets, SMMs, and single-chain magnets, (valpn)LnIII] complexes, apart from their interest for the inves-
SCMs),1a,b,3 and from their significant magnetocaloric effect tigation of the NiII–LnIII exchange interactions,8 can be
(MCE).4 On one hand, the design of 3d–4f molecular nano- employed as precursors for obtaining high-nuclearity clusters
magnets requires the use of lanthanide ions exhibiting a high and coordination polymers with interesting magnetic pro-
anisotropy, the best candidates being TbIII, DyIII, and HoIII perties (valpn2− is a Schiff-base compartmental ligand resulted
ions.3 On the other hand, in order to generate molecular com- from the condensation of o-vanillin with 1,3-propanedi-
pounds with a large magnetocaloric effect,4 ions with high amine).9 Herein we present two novel octanuclear clusters,
spin and low magnetic anisotropy are necessary, such as the [NiII4LnIII4], which are obtained by reacting the binuclear
isotropic GdIII ion. MCE is an intrinsic property to any mag- [NiIILnIII] precursors with sodium azide and through the
simultaneous fixation of atmospheric CO2 (Ln = Sm, Gd). The
magnetothermal properties of the gadolinium derivative
have been investigated. The reaction between coordination
aInorganic Chemistry Laboratory, Faculty of Chemistry, University of Bucharest, Str.
Dumbrava Rosie nr. 23, 020464-Bucharest, Romania. E-mail: marius.andruh@dnt.ro
bC.N.R. – Institute of NanoSciences S3 and Dipartimento di Scienze Fisiche,
compounds and atmospheric CO2 was first observed with
several transition metal complexes,10 resulting in carbonato-
bridged complexes. More recently, several 4f,11 and 3d–4f
complexes12 have been shown to be able to capture atmos-
pheric CO2, resulting in a quite rich variety of carbonato-
complexes.
Informatiche e Matematiche, Università di Modena e Reggio Emilia, Via G. Campi
213/A, 41100 Modena, Italy. E-mail: marco.affronte@unimore.it
†Dedicated to Professor Francesc Lloret on the occasion of his 60th birthday.
‡Electronic supplementary information (ESI) available. CCDC 986980 and
986981. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4dt00515e
9136 | Dalton Trans., 2014, 43, 9136–9142
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 1 Crystallographic data, details of data collection and structure
refinement parameters for compounds 1 and 2
Experimental
Materials
Compound
1
2
The chemicals used, o-vanillin, 1,3-diaminopropane, sodium
azide, Sm(NO3)·6H2O, Gd(NO3)3·6H2O, as well as all the
solvents were purchased from commercial sources. The mono-
nuclear complex, [Ni(valpn)], was prepared as follows:
10 mmol 1,3-propylenediamine and 20 mmol triethylamine
were added under stirring to 50 mL THF solution containing
20 mmol o-vanillin. After 30 minutes, an aqueous solution
(50 mL) containing 10 mmol Ni(NO3)·6H2O is added. The
resulting mixture is stirred for an hour, then 500 mL H2O were
added to facilitate the precipitation of the mononuclear
complex. The light green solid obtained is filtered and dried.
In order to synthesize [NiIILnIII] (LnIII = Sm, Gd), the method
Chemical formula
C
78H130N33O47Ni4Sm4 C80H129N33O45Ni4Gd4
M (g mol−1
)
3104.38
293
0.71073
Monoclinic
P21/n
13.1410(4)
23.4741(8)
19.0068(5)
90.00
91.216(2)
90.00
3136.83
293
0.71073
Monoclinic
P21/n
13.1507(7)
23.5171(14)
18.9619(10)
90.00
91.06
90.00
5863.3(6)
2
1.764
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
5861.8(3)
2
1.759
Dc (g cm−3
)
we have previously described8a was used:
4 mmol of
μ (mm−1
F(000)
)
2.696
2.953
3116
3092
Ln(NO3)3·6H2O are added to a suspension containing 4 mmol
[Ni(valpn)] in 20 mL acetonitrile. The reaction mixture is
stirred for about 20 minutes and then let to slowly evaporate at
room temperature.
Refinement on
Goodness-of-fit
Final R1, wR2
[I > nσ(I)]
F2
F2
1.068
0.0600, 0.1490
0.850
0.0521, 0.0893
R1, wR2 (all data)
0.0768, 0.1589
0.1134, 0.1023
1.482, −0.775
[[(N3)1.5(H2O)0.5Ni(valpn)Sm(H2O)3(μ-CO3)Sm(H2O)3(valpn)-
Largest diff. peak and 2.448, −1.883
hole (e Å−3
)
Ni(N3)(μ1,3-N3)0.5]2] (N3)2·12H2O
1 and [[(N3)1.5(H2O)0.5Ni-
(valpn)Gd(H2O)3(μ-CO3)Gd(H2O)3(valpn)Ni(N3)(μ1,3-N3)0.5]2]-
(N3)2·10H2O·CH3CN 2 were prepared as follows: a solution con-
taining 0.1 mmol NaN3 dissolved in 10 mL H2O was added
to a solution containing 0.1 mmol of the corresponding [NiII-
(valpn)LnIII] (LnIII = Sm, Gd) heterodinuclear complex dis-
solved in 20 mL acetonitrile. The reaction mixture was stirred
for 30 minutes and then filtered. Several days later, the slow
vaporization of the solvent yielded green crystals of the octa-
nuclear complexes. Yields: 20% for 1, and 22% for 2. Calcd:
30.05 C; 4.20 H; 14.82% N. Found: 30.1 C; 4.1 H; 14.8% N for
1. Calcd: 30.64 C; 4.14 H; 14.73% N. Found: 30.4 C; 3.9
H; 14.5% N for 2.
3
means of a Quantum Design He refrigerator, using the relax-
ation method and two-tau fitting. In this case, microcrystalline
samples were pressed in thin pellets having a mass of about
2 mg.
Results and discussion
The aim of this work is to check whether our strategy for
designing high-nuclearity clusters and coordination polymers,
starting from heterodimetallic complexes, can be applied in
X-Ray structure determination
Single crystals suitable for X-ray diffraction studies were order to organize binuclear high spin [NiIILnIII] species into
obtained by slow vaporization, as described above. Data were complexes with an important magnetocaloric effect. The self-
collected at 293 K on a STOE IPDS II diffractometer using assembly processes between preformed [NiIILnIII] complexes
graphite-monochromated Mo Kα radiation (λ = 0.71073Å). The (Ln = Sm, Gd) and the azide anion, in the presence of carbo-
structures were solved by direct methods and refined by full- nate anions (resulted from the fixation of atmospheric CO2),
matrix least squares techniques based on F2. The non-H atoms afforded two novel octanuclear clusters [[(N3)1.5(H2O)0.5Ni-
were refined with anisotropic displacement parameters. The (valpn)Sm(H2O)3(μ-CO3)Sm(H2O)3(valpn)Ni(N3)(μ1,3-N3)0.5]2]-
crystallographic data are collected in Table 1. CCDC reference (N3)2·12H2O 1 and [[(N3)1.5(H2O)0.5Ni(valpn)Gd(H2O)3(μ-CO3)-
number: 986980, 986981.
Gd(H2O)3(valpn)Ni(N3)(μ1,3-N3)0.5]2](N3)2·10H2O·CH3CN 2. The
carbonato ligand is formed during the slow crystallization
process, a phenomenon observed with other 3d–4f complexes
Physical measurements
The IR spectra were recorded on KBr pellets on a JASCO FTIR as well.12 The infrared spectrum of 2 (Fig. S1‡) gives some
4100 spectrophotometer in the 4000–400 cm−1 range.
useful information. First of all, we notice characteristic bands
The magnetic characterization was performed on microcrys- of the carbonato ligand at 1467 and 1074 cm−1; the absorption
talline powders of 2 by means of a Quantum Design PPMS-7 band at 1528 cm−1 is assigned to the ν(C–O) stretching
T. Susceptibility measurements were performed with an ac vibrations, while the π(C–O) out-of-plane bending vibration
excitation field of 10 Oe and frequency 90, 1730 and 9300 Hz. appears as a weak absorption band at 852 cm−1 13
The intense
.
Magnetization measurements were carried out with a 7 T band located at 2033 cm−1 is due to the azido ligands. We also
superconducting coil and dc extraction technique. Heat mention that the characteristic bands of the nitrato ligands
capacity was measured in the temperature range of 0.3–20 K by are no more observed and this confirms that the nitrato
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9136–9142 | 9137

View Article Online
Paper
Dalton Transactions
groups from the binuclear precursors have been replaced by restrained in the crystal structure refinement to occupy the
the azido and carbonato ligands.
same crystallographic position with site occupancies factors of
0.5 each]. The equatorial coordination sites are occupied by
four atoms of the valpn2− Schiff-base ligand [Ni2–N3 =
2.024(9), Ni2–N4 = 2.006(10), Ni2–O6 = 2.032(7), Ni2–O7 =
Description of the structures
X-ray diffraction measurements indicated the two complexes 2.031(6) Å]. The two Ni2 ions within the octanuclear unit are
are isomorphous and crystallize in a monoclinic space group placed at a distance of 24.459 Å.
(Table 1). Their structure consists of octanuclear cationic units
The gadolinium ions are located in the outer compartment
(Fig. 1), uncoordinated azide anions, and solvent molecules of the valpn2− ligand and are nine-coordinated by oxygen
(H2O in crystal 1, respectively H2O and CH3CN in crystal 2). atoms. The Gd1 ions are surrounded by four oxygen atoms of
The gadolinium derivative is particularly interesting from the the Schiff-base ligand [Gd1–O1 = 2.544(6), Gd1–O2 = 2.360(6),
magnetic point of view, while the first compound was syn- Gd1–O3 = 2.389(6), Gd1–O4 = 2.556(6) Å], three oxygen atoms
thesized in order illustrate that the absorption of the CO2 from belonging to aqua ligands [Gd1–O12 = 2.439(8), Gd1–O13 =
the air is a general reaction within this system. They have 2.467(8), Gd1–O14 = 2.460(7) Å], and two oxygen atoms coming
the following compositions: [[(N3)1.5(H2O)0.5Ni(valpn)Sm- from a carbonato bridge [Gd1–O9 = 2.486(7), Gd1–O10 =
(H2O)3(μ-CO3)Sm(H2O)3(valpn)Ni(N3)(μ1,3-N3)0.5]2](N3)2·12H2O 2.415(7) Å].
1
and [[(N3)1.5(H2O)0.5Ni(valpn)Gd(H2O)3(μ-CO3)Gd(H2O)3-
The Gd2 ion is coordinated to four oxygen atoms of the
(valpn)Ni(N3)(μ1,3-N3)0.5]2](N3)2·10H2O·CH3CN 2. Since the two valpn2− ligand [Gd2–O5 = 2.560(7), Gd2–O6 = 2.370(6), Gd2–
structures are very similar, only the one of the gadolinium O7 = 2.398(7), Gd2–O8 = 2.545(7) Å], three aqua ligands [Gd2–
derivative, 2, will be discussed here.
O15 = 2.424(8), Gd2–O16 = 2.432(8), Gd2–O17 = 2.461(7) Å],
The construction of the centrosymmetric octanuclear and two oxygen atoms from the bridging carbonato ligand
complex can be described as resulting by connecting two which displays a two-(η3 chelation) [Gd2–O9 = 2.465(7), Gd2–
{Ni2Gd2} moieties through the 1,3-azido bridge that links the O11 = 2.456(6) Å]. The separation between the carbonato-
nickel ions; each tetranuclear moiety is constructed from two bridged GdIII ions is Gd1⋯Gd2 = 4.942 Å. The distances
binuclear {Ni(valpn)Gd} entities bridged by
a carbonato between the metal ions within the binuclear {NiGd} units are:
ligand, which interacts solely with the gadolinium ions. Ni1⋯Gd1 = 3.538 and Ni2⋯Gd2 = 3.523 Å. The intramolecular
Within the octanuclear unit, there are two types of NiII ions, Gd1⋯Gd1′ and Gd2⋯Gd2′ (′ = −x, 2 − y, 1 − z) separations, are
Ni1 and Ni2, both being hexacoordinated. The equatorial 10.016 and 19.610 Å, respectively. Selected bond distances and
plane of the Ni1 ion is occupied by donor atoms of the valpn angles for 1 and 2 are given in Tables 2 and 3, respectively.
ligand [Ni1–N1 = 2.027(7), Ni1–N2 = 2.023(9), Ni1–O2 =
2.043(6), Ni1–O3 = 2.050(6) Å], while two azido ligands are co-
ordinated into the axial positions. One of them behaves like a
Magnetic properties
terminal ligand [Ni1–N6 = 2.093(10) Å], while the second one The ac susceptibility of 2 have been measured between 2 and
forms a μ1,3-N3 bridge between two Ni1 ions [Ni1–N9 = 2.211(9) 300 K (Fig. 2). The room temperature value of the χMT product,
Å]. The intermetallic Ni1⋯Ni1′ separation has a value of 36.8 cm3 mol−1 K, corresponds to the one expected for the
6.007 Å (′ = −x, 2 − y, 1 − z). The axial positions of Ni2 ions are eight non-interacting ions (four NiII and four GdIII): 36.3 cm3
occupied by one nitrogen atom coming from a terminal azido mol−1 K, assuming gNi = 2.2 and gGd = 2. The χMT product is
ligand [Ni2–N12 = 2.220(9)] and by one nitrogen atoms coming constant down to 50 K, then it increases, reaching ∼37.5 cm3
from another terminal azido ligand or the oxygen atom of one mol−1 K at 8 K. Below this temperature, χMT decreases abruptly
aqua ligand [Ni2–N15/O32 = 2.191(9) Å, the N15 and O32 were reaching ∼33 cm3 mol−1 K at 1.8 K. The spin Hamiltonian for
Fig. 1 View of the octanuclear cationic species [[(N3)1.5(H2O)0.5Ni(valpn)Gd(H2O)3(μ-CO3)Gd(H2O)3(valpn)Ni(N3)(μ1,3-N3)0.5]2]+ in 2 (’ = −x, 2 − y,
1 − z).
9138 | Dalton Trans., 2014, 43, 9136–9142
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 2 Selected bond distances and angles for compound 1
Ni1–N1
Ni1–N2
Ni1–N6
Ni1–N9
Ni1–O2
Ni1–O3
Ni2–N3
Ni2–N4
2.016(5)
2.032(6)
2.111(6)
2.190(6)
2.059(4)
2.049(4)
2.014(7)
2.020(6)
2.196(6)
2.206(7)
2.042(5)
2.025(5)
2.206(7)
2.556(5)
2.382(4)
2.398(4)
2.562(5)
2.500(5)
2.445(5)
2.435(6)
2.455(5)
2.477(5)
2.570(5)
2.381(5)
2.414(4)
2.560(6)
2.476(5)
2.462(5)
2.445(6)
2.424(6)
2.467(6)
N2–Ni1–N1
N2–Ni1–O2
N1–Ni1–O2
N2–Ni1–O3
N1–Ni1–O3
O2–Ni1–O3
N2–Ni1–N6
N1–Ni1–N6
O2–Ni1–N6
O3–Ni1–N6
N2–Ni1–N9
N1–Ni1–N9
O2–Ni1–N9
O3–Ni1–N9
N6–Ni1–N9
N4–Ni2–N3
N4–Ni2–O6
N3–Ni2–O6
N4–Ni2–O7
N3–Ni2–O7
O6–Ni2–O7
N4–Ni2–O32
N3–Ni2–O32
O6–Ni2–O32
O7–Ni2–O32
N4–Ni2–N12
N3–Ni2–N12
O6–Ni2–N12
O7–Ni2–N12
O32–Ni2–N12
Ni1–O2–Sm1
Ni1–O3–Sm1
Ni2–O6–Sm2
Ni2–O7–Sm2
97.0(3)
170.0(2)
91.2(2)
O2–Sm1–O3
O2–Sm1–O10
O3–Sm1–O10
O2–Sm1–O12
O3–Sm1–O12
O10–Sm1–O12
O2–Sm1–O14
O3–Sm1–O14
O10–Sm1–O14
O12–Sm1–O14
O2–Sm1–O13
O3–Sm1–O13
O10–Sm1–O13
O12–Sm1–O13
O14–Sm1–O13
O2–Sm1–O9
O3–Sm1–O9
O10–Sm1–O9
O12–Sm1–O9
O14–Sm1–O9
O13–Sm1–O9
O2–Sm1–O1
O3–Sm1–O1
O10–Sm1–O1
O12–Sm1–O1
O14–Sm1–O1
O13–Sm1–O1
O9–Sm1–O1
O2–Sm1–O4
O3–Sm1–O4
O10–Sm1–O4
O12–Sm1–O4
O14–Sm1–O4
O13–Sm1–O4
O9–Sm1–O4
O1–Sm1–O4
67.34(15)
109.20(17)
148.35(18)
72.4(2)
73.9(2)
75.2(2)
76.91(16)
73.52(16)
137.76(18)
141.70(19)
131.49(18)
130.76(18)
76.4(2)
O6–Sm2–O7
O6–Sm2–O15
O7–Sm2–O15
O6–Sm2–O16
O7–Sm2–O16
O15–Sm2–O16
O6–Sm2–O11
O7–Sm2–O11
O15–Sm2–O11
O16–Sm2–O11
O6–Sm2–O17
O7–Sm2–O17
O15–Sm2–O17
O16–Sm2–O17
O11–Sm2–O17
O6–Sm2–O9
O7–Sm2–O9
O15–Sm2–O9
O16–Sm2–O9
O11–Sm2–O9
O17–Sm2–O9
O6–Sm2–O8
O7–Sm2–O8
O15–Sm2–O8
O16–Sm2–O8
O11–Sm2–O8
O17–Sm2–O8
O9–Sm2–O8
O6–Sm2–O5
O7–Sm2–O5
O15–Sm2–O5
O16–Sm2–O5
O11–Sm2–O5
O17–Sm2–O5
O9–Sm2–O5
O8–Sm2–O5
67.26(16)
133.7(2)
129.4(2)
79.0(2)
70.07(19)
144.4(2)
146.07(18)
114.76(16)
73.4(2)
91.3(2)
171.4(2)
80.34(18)
92.0(3)
92.0(3)
93.4(2)
90.1(2)
89.6(3)
88.7(2)
84.9(2)
88.9(2)
178.2(3)
97.7(3)
171.0(3)
91.1(3)
89.6(2)
172.6(2)
81.52(19)
92.2(3)
86.8(3)
90.1(2)
Ni2–N12
Ni2–N15
Ni2–O6
71.1(2)
76.49(19)
74.10(17)
70.6(2)
142.22(19)
137.4(2)
104.72(16)
144.95(16)
81.8(2)
74.92(19)
52.66(16)
139.26(17)
127.75(17)
62.73(17)
74.5(2)
97.1(2)
72.76(17)
76.4(2)
124.73(17)
62.86(17)
125.49(17)
77.3(2)
118.2(2)
118.67(17)
74.3(2)
Ni2–O7
Ni2–O32
Sm1–O1
Sm1–O2
Sm1–O3
Sm1–O4
Sm1–O9
Sm1–O10
Sm1–O12
Sm1–O13
Sm1–O14
Sm2–O5
Sm2–O6
Sm2–O7
Sm2–O8
Sm2–O9
Sm2–O11
Sm2–O15
Sm2–O16
Sm2–O17
148.2(2)
70.08(17)
143.12(16)
109.95(15)
52.73(16)
71.8(2)
139.30(17)
79.73(18)
62.88(15)
126.65(15)
69.59(17)
107.0(3)
77.73(19)
75.87(19)
121.05(16)
127.99(16)
63.05(15)
121.01(17)
106.8(3)
75.18(18)
76.26(19)
71.53(16)
146.27(19)
93.7(2)
89.0(2)
92.2(3)
88.9(2)
87.2(2)
178.5(3)
106.20(19)
105.95(19)
105.9(2)
105.23(19)
70.80(17)
144.6(2)
this system should include three exchange parameters (JNiGd
,
low temperature M(H) tends to reach a value of ∼35NAμB
JGdGd, JNiNi) and this, together with the high spin value of Gd, although saturation is not completely achieved at 7 T. This is
leads to the huge dimension of the matrix and does not make compatible with the 4 spins S = 7/2 of GdIII and 4 spins S = 1
possible to solve the problem numerically. However, the mag- of NiII per formula unit and indicates that the magnetic field
netic behaviour of 2, depicted in Fig. 2, can be understood, overcomes the weak (anti-)ferromagnetic interactions.
having in mind that: (i) the exchange interaction between
phenoxo-bridged NIII and GdIII ions is in most cases weak heat C(T,H) at low temperature in different applied magnetic
ferromagnetic, with J values ranging from 0.2 to ∼5 cm−1 8a,14
field (Fig. 4). The C(T) curve in zero field shows a Schottky
To get more insight we have also measured the specific
;
(ii) the exchange interaction between the carbonato-bridged anomaly with a maximum at 1 K. This anomaly reflects the
GdIII ions, if any, is very weak;12d (iii) the magnetic coupling degeneracy of the ground state due to both the small – but
between NiII ions connected by 1,3-azido bridges is, in finite – anisotropy of the single NiII and GdIII ions and to the
most cases, antiferromagnetic, with J values as large as weak and competitive interactions. The Schottky anomaly is
−114.5 cm−1 15 rarely, it was showed to be ferromagnetic.16 In progressively shifted towards higher temperatures with the
;
case of complex 2, the values for Ni1–N9–N10, Ni1′–N9′–N10, application of magnetic field of increasing strength. For
and τ dihedral angles are 121.53, 121.53, and 0°, respectively, highest fields (i.e. 5, 7 T) the maximum disappears but at 15 K
which suggests
a moderate antiferromagnetic coupling the specific heat is higher than in zero field, indicating that a
between NiII ions.15c,d Consequently, the increase of the χMT significant amount of magnetic entropy is present at that
product below 50 K is probably due to dominant ferromagnetic temperature.
interactions (characteristic for the NiII–GdIII pair); below 10 K,
Starting from the specific heat, the change of entropy in
a superposition of the antiferromagnetic interactions men- magnetic field is evaluated by using the relation: S(T)B
=
Ð
tioned above with the zero field splitting effect associated to
(C/T)B)dT + S0, where S0 is an additive constant that accounts
the NiII ions is likely to occur as shown by the drop of the χMT for the specific heat curve for T < 0.3 K. According to the
product in Fig. 2.
Maxwell equation, the entropy variation can also be estimated
Ð
The field dependence of magnetization M(H) was measured using the magnetization data: ΔSm(T)ΔB
at different temperatures as shown in Fig. 3. At high field and In Fig. 5, the ΔSm values obtained with the two different
=
(∂M(T,B)/∂B)B dB.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9136–9142 | 9139

View Article Online
Paper
Dalton Transactions
Table 3 Selected bond distances and angles for compound 2
Ni1–N1
Ni1–N2
Ni1–N6
Ni1–N9
Ni1–O2
Ni1–O3
Ni2–N3
Ni2–N4
2.028(7)
2.023(8)
2.093(10)
2.213(9)
2.043(6)
2.051(6)
2.025(9)
2.004(9)
2.221(9)
2.191(9)
2.032(7)
2.032(6)
2.191(9)
2.545(6)
2.360(6)
2.389(6)
2.557(6)
2.485(7)
2.414(7)
2.440(8)
2.469(8)
2.461(7)
2.561(7)
2.370(6)
2.399(6)
2.545(7)
2.466(6)
2.456(6)
2.425(7)
2.432(8)
2.461(7)
N2–Ni1–N1
N2–Ni1–O2
N1–Ni1–O2
N2–Ni1–O3
N1–Ni1–O3
O2–Ni1–O3
N2–Ni1–N6
N1–Ni1–N6
O2–Ni1–N6
O3–Ni1–N6
N2–Ni1–N9
N1–Ni1–N9
O2–Ni1–N9
O3–Ni1–N9
N6–Ni1–N9
N4–Ni2–N3
N4–Ni2–O6
N3–Ni2–O6
N4–Ni2–O7
N3–Ni2–O7
O6–Ni2–O7
N4–Ni2–O32
N3–Ni2–O32
O6–Ni2–O32
O7–Ni2–O32
N4–Ni2–N12
N3–Ni2–N12
O6–Ni2–N12
O7–Ni2–N12
O32–Ni2–N12
Ni1–O2–Gd1
Ni1–O3–Gd1
Ni2–O6–Gd2
Ni2–O7–Gd2
96.7(3)
169.8(3)
91.5(3)
91.4(3)
171.7(3)
80.3(2)
92.9(4)
93.1(4)
92.7(3)
88.6(3)
89.1(3)
88.7(3)
85.1(3)
89.3(3)
177.2(4)
97.7(4)
170.5(3)
91.6(3)
89.3(3)
172.9(3)
81.3(3)
91.6(4)
87.5(4)
90.5(3)
93.2(3)
89.3(3)
91.5(3)
88.8(3)
87.7(3)
178.8(4)
106.7(2)
105.4(2)
106.1(3)
105.0(3)
O2–Gd1–O3
O2–Gd1–O10
O3–Gd1–O10
O2–Gd1–O12
O3–Gd1–O12
O10–Gd1–O12
O2–Gd1–O14
O3–Gd1–O14
O10–Gd1–O14
O12–Gd1–O14
O2–Gd1–O13
O3–Gd1–O13
O10–Gd1–O13
O12–Gd1–O13
O14–Gd1–O13
O2–Gd1–O9
O3–Gd1–O9
O10–Gd1–O9
O12–Gd1–O9
O14–Gd1–O9
O13–Gd1–O9
O2–Gd1–O1
O3–Gd1–O1
O10–Gd1–O1
O12–Gd1–O1
O14–Gd1–O1
O13–Gd1–O1
O9–Gd1–O1
O2–Gd1–O4
O3–Gd1–O4
O10–Gd1–O4
O12–Gd1–O4
O14–Gd1–O4
O13–Gd1–O4
O9–Gd1–O4
O1–Gd1–O4
67.49(18)
108.8(2)
147.4(3)
72.1(2)
73.6(3)
74.5(3)
77.1(2)
74.0(2)
138.2(2)
141.8(2)
132.1(2)
130.5(2)
77.4(3)
148.2(3)
70.0(2)
142.5(2)
108.8(2)
53.2(2)
71.2(2)
139.5(2)
80.2(2)
63.4(2)
127.3(2)
69.7(2)
107.2(3)
77.6(2)
76.0(2)
121.5(2)
128.4(2)
63.6(2)
121.0(2)
107.7(3)
74.8(2)
74.8(2)
71.4(2)
145.2(2)
O6–Gd2–O7
67.5(2)
133.1(2)
129.2(3)
78.1(2)
70.2(2)
145.7(2)
145.3(2)
114.0(2)
74.9(2)
70.9(2)
76.5(2)
73.9(2)
70.2(2)
141.8(2)
138.2(2)
104.4(2)
145.2(2)
82.0(2)
75.0(3)
53.2(2)
139.1(2)
127.9(2)
62.7(2)
74.6(3)
98.2(3)
72.8(2)
76.2(2)
125.1(2)
63.2(2)
125.9(2)
76.5(3)
117.6(3)
118.9(2)
74.4(2)
70.2(2)
144.2(3)
O6–Gd2–O15
O7–Gd2–O15
O6–Gd2–O16
O7–Gd2–O16
O15–Gd2–O16
O6–Gd2–O11
O7–Gd2–O11
O15–Gd2–O11
O16–Gd2–O11
O6–Gd2–O17
O7–Gd2–O17
O15–Gd2–O17
O16–Gd2–O17
O11–Gd2–O17
O6–Gd2–O9
O7–Gd2–O9
O15–Gd2–O9
O16–Gd2–O9
O11–Gd2–O9
O17–Gd2–O9
O6–Gd2–O8
O7–Gd2–O8
O15–Gd2–O8
O16–Gd2–O8
O11–Gd2–O8
O17–Gd2–O8
O9–Gd2–O8
O6–Gd2–O5
O7–Gd2–O5
O15–Gd2–O5
O16–Gd2–O5
O11–Gd2–O5
O17–Gd2–O5
O9–Gd2–O5
O8–Gd2–O5
Ni2–N12
Ni2–N15
Ni2–O6
Ni2–O7
Ni2–O32
Gd1–O1
Gd1–O2
Gd1–O3
Gd1–O4
Gd1–O9
Gd1–O10
Gd1–O12
Gd1–O13
Gd1–O14
Gd2–O5
Gd2–O6
Gd2–O7
Gd2–O8
Gd2–O9
Gd2–O11
Gd2–O15
Gd2–O16
Gd2–O17
Fig. 2 Temperature dependence of the χMT product for 2.
Fig. 3 Isothermal magnetization curves for 2 from 0 to 7 T.
methods compare very well one to another. The peak of (>5 J kg−1 K−1) at 20 K. Thus while ΔSm value is comparable to
ΔSm(T) is found at about 3.5 K with a maximum value of those reported for other molecular GdIII complexes,4 it turns
ΔSm[0–7 T] = 19 J kg−1 K−1. This peak results not particularly out that the process of entropy removal is spread over a wider
pronounced but the entropy variation ΔSm[0–7 T] is still large temperature range (1–20 K) in this complex.
9140 | Dalton Trans., 2014, 43, 9136–9142
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Acknowledgements
Financial
support
from
the
UEFISCDI
(grant
PNII-ID-PCCE-2011–2-0050) is gratefully acknowledged.
References
1 (a) M. Andruh, J.-P. Costes, C. Diaz and S. Gao, Inorg.
Chem., 2009, 48, 3342; (b) R. Sessoli and A. K. Powell,
Coord. Chem. Rev., 2009, 253, 2328; (c) M. Sakamoto,
K. Manseki and H. Okawa, Coord. Chem. Rev., 2001,
219–221, 379; (d) J. S. Miller and D. Gatteschi, Chem. Soc.
Rev., 2011, 40, 3065.
2 A. Bencini, C. Benelli, A. Caneschi, R. L. Carlin, A. Dei and
D. Gatteschi, J. Am. Chem. Soc., 1985, 107, 8128.
3 D. Gatteschi, R. Sessoli and J. Villain, Molecular Nanomag-
nets, Oxford University Press, New York, 2006.
Fig. 4 Temperature dependence of specific heat measured at different
applied magnetic fields. The Schottky anomaly at zero field has a
maximum at 1 K and it is spread towards higher temperature with
increasing magnetic field.
4 (a) M. Evangelisti, in Molecular Magnets, Physics and Appli-
cations, ed. J. Bartolomè, F. Luis and J. F. Fernandez,
Springer Verlag, 2014, ISSN 1434-4904, pp. 365–387;
(b) R. Sessoli, Angew. Chem., Int. Ed., 2011, 50, 2;
(c) M. Evangelisti and E. K. Brechin, Dalton Trans., 2010,
39, 4672; (d) A. S. Dinca, A. Ghirri, A. M. Madalan,
M. Affronte and M. Andruh, Inorg. Chem., 2012, 51, 3935.
5 (a) C. Zimm, A. Jastrab, A. Sternberg, V. K. Pecharsky,
K. A. Gschneidner Jr., M. Osborne and I. Anderson, Adv.
Cryog. Eng., 1998, 43, 1759; (b) V. K. Pecharsky and
K. A. Gschneidner Jr., J. Magn. Magn. Mater., 1999, 200, 44;
(c) K. A. Gschneidner Jr., A. O. Pecharsky and
V. K. Pecharsky, in: Cryocoolers II, ed. R. S. Ross Jr., Kluwer
Academic/Plenum Press, New York, 2001, p. 433.
6 (a) M. Manoli, R. D. L. Johnstone, S. Parsons, M. Murrie,
M. Affronte, M. Evangelisti and E. K. Brechin, Angew.
Chem., Int. Ed., 2007, 46, 4456; (b) M. Evangelisti,
A. Candini, A. Ghirri, M. Affronte, E. K. Brechin and
E. J. L. McInnes, Appl. Phys. Lett., 2005, 87, 072504;
(c) Y.-Z. Zheng, M. Evangelisti, F. Tuna and
R. E. P. Winpenny, J. Am. Chem. Soc., 2012, 134, 1057;
(d) F.-S. Guo, J.-D. Leng, J.-L. Liu, Z.-S. Meng and
M.-L. Tong, Inorg. Chem., 2012, 51, 405; (e) M. Evangelisti,
O. Roubeau, E. Palacios, A. Camón, T. Hooper,
E. K. Brechin and J. J. Alonso, Angew. Chem., Int. Ed., 2011,
50, 6606; (f) Y.-Z. Zheng, M. Evanghelisti and
R. E. P. Winpenny, Angew. Chem., Int. Ed., 2011, 50, 3692;
(g) S. K. Langley, N. F. Chilton, B. Moubaraki, T. Hooper,
E. K. Brechin, M. Evanghelisti and K. S. Murray, Chem. Sci.,
2011, 2, 1166; (h) J.-B. Peng, Q.-C. Zhang, X.-J. Kong,
Y.-P. Ren, L.-S. Long, R.-B. Huang, L.-S. Zheng and
Z. Zheng, Angew. Chem., Int. Ed., 2011, 50, 1; (i) F.-S. Guo,
Y.-C. Chen, J.-L. Liu, J.-D. Leng, Z.-S. Meng, P. Vrábel,
M. Orendáč and M.-L. Tong, Chem. Commun., 2012, 48,
12219.
Fig. 5 Entropy variation between 0 T and 7 T calculated from magneti-
zation (markers) and specific heat (lines) data.
Conclusions
In conclusion, we have obtained two novel octanuclear [NiII
-
4
LnIII4] [Ln = Sm, Gd] molecular clusters through fixation of
atmospheric CO2. The eight metal ions are held together by
three different types of bridge: phenoxo, carbonato and azido.
The increasing number of such complexes shows that
slow crystallization processes in the presence of a basic
reagent (e.g. triethylamine) favor the absorption of the CO2,
with the formation of carbonato bridged species. The investi-
gation of the magnetic properties of the [NiII4GdIII4] complex
reveals a significant magnetocaloric effect (ΔSm[0–7 T] =
19 J kg−1 K−1).
7 (a) R. D. McMichael, R. D. Shull, L. J. Swartzendruber,
L. H. Bennett and R. E. Watson, J. Magn. Magn. Mater.,
1992, 111, 29; (b) L. H. Bennett, R. D. McMichael,
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 9136–9142 | 9141

View Article Online
Paper
Dalton Transactions
H. C. Tang and R. E. Watson, J. Appl. Phys., 1994, 75, 5493;
F. Lloret and E. Colacio, Inorg. Chem., 2013, 52, 9620;
(d) S. Sakamoto, T. Fujinami, K. Nishi, N. Matsumoto,
N. Mochida, T. Ishida, Y. Sunatsuki and N. Re, Inorg.
Chem., 2013, 52, 7218.
(c) M. Evangelisti, A. Candini, A. Ghirri, M. Affronte,
S. Piligkos, E. K. Brechin and E. J. L. McInnes, Polyhedron,
2005, 24, 2573; (d) R. Shaw, R. Laye, L. Jones, D. Low,
C. Talbot-Eeckelaers, Q. Wei, C. Milios, S. Teat, 13 K. Nakamoto, Infrared and Raman Infrared and Raman
M. Helliwell, J. Raftery, M. Evangelisti, M. Affronte,
D. Collison, E. K. Brechin and E. J. L. McInnes, Inorg.
Chem., 2007, 46, 4968.
Spectra of Inorganic and Coordination Compounds, Part B,
Applications in Coordination, Organometallic, and Bio-
inorganic Chemistry, John Wiley & Sons, Inc., Hoboken, New
Jersey, 6th edn, 2009.
8 (a) T. D. Pasatoiu, J. P. Sutter, A. M. Madalan,
F. Z. C. Fellah, C. Duhayon and M. Andruh, Inorg. Chem., 14 (a) J.-P. Costes, F. Dahan, A. Dupuis and J. P. Laurent,
2011, 50, 5890; (b) T. D. Pasatoiu, C. Tiseanu,
A. M. Madalan, B. Jurca, C. Duhayon, J. P. Sutter and
M. Andruh, Inorg. Chem., 2011, 50, 5879.
9 (a) T. D. Pasatoiu, M. Etienne, A. M. Madalan, M. Andruh
and R. Sessoli, Dalton Trans., 2010, 39, 4802;
(b) T. D. Pasatoiu, M. Etienne, A. M. Madalan, R. Sessoli
and M. Andruh, Rev. Roum. Chim., 2012, 57, 507.
10 (a) N. Kitajima, K. Fujisawa, T. Koda, S. Hikichi and
Y. Moro-oka, J. Chem. Soc., Chem. Commun., 1990, 1357;
(b) T. Tanase, S. Nitta, S. Yoshikawa, K. Kobayashi,
T. Sakurai and S. Yano, Inorg. Chem., 1992, 31, 1058;
(c) M. M. El-Hendawy, N. J. English and D. A. Mooney,
Inorg. Chem., 2012, 51, 5282; (d) M. Ito and Y. Takita, Chem.
Lett., 1996, 929; (e) M. Fondo, N. Ocampo, A. M. García-
Deibe, R. Vicente, M. Corbella, M. R. Bermejo and
J. Sanmartín, Inorg. Chem., 2006, 45, 255.
Inorg. Chem., 1997, 36, 4284; (b) J.-P. Costes, T. Yamaguchi,
M. Kojima and L. M. Vendier, Inorg. Chem., 2009, 48, 5555;
(c) J.-P. Sutter, S. Dhers, R. Rajamani, S. Ramasesha,
J.-P. Costes, C. Duhayon and L. Vendier, Inorg. Chem., 2009,
48, 5820; (d) P. Khuntia, M. Mariani, A. V. Mahajan,
A. Lascialfari, F. Borsa, T. D. Pasatoiu and M. Andruh, Phys.
Rev. B: Condens. Matter Mater. Phys., 2011, 84, 184439;
(e) V. Chandrasekhar, B. M. Pandian, R. Boomishankar,
A. Steiner, J. J. Vittal, A. Houri and R. Clérac, Inorg. Chem.,
2008, 47, 4918; (f) N. Bridonneau, L.-M. Chamoreau,
P. P. Lainé, W. Wernsdorfer and V. Marvaud, Chem.
Commun., 2013, 49, 9476; (g) T. Shiga, N. Ito, A. Hidaka,
H. Okawa, S. Kitagawa and M. Ohba, Inorg. Chem., 2007,
46, 3492; (h) M.-G. Alexandru, D. Visinescu, S. Shova,
F. Lloret and M. Andruh, Inorg. Chem., 2013, 52,
11627.
11 (a) S. K. Langley, B. Moubaraki and K. S. Murray, Inorg. 15 (a) J. Ribas, M. Monfort, C. Diaz, C. Bastos and X. Solans,
Chem., 2012, 51, 3947; (b) H. Tian, L. Zhao, Y. N. Guo,
Y. Guo, J. Tang and Z. Liu, Chem. Commun., 2012, 48, 708;
(c) A. K. Ghosh, M. Pait, M. Shatruk, V. Bertolasic and
D. Ray, Dalton Trans., 2014, 43, 1970; (d) J. Vallejo, J. Cano,
I. Castro, M. Julve, F. Lloret, O. Fabelo, L. Cañadillas-
Delgado and E. Pardo, Chem. Commun., 2012, 48, 7726.
12 (a) S. Sakamoto, S. Yamauchi, H. Hagiwara, N. Matsumoto,
Inorg. Chem., 1993, 32, 3557; (b) J. Ribas, A. Escuer,
M. Monfort, R. Vicente, R. Cortés, L. Lezama and T. Rojo,
Coord. Chem. Rev., 1999, 193–195, 1027; (c) S. S. Massoud,
F. A. Mautner, R. Vicente, A. A. Gallo and E. Ducasse,
Eur. J. Inorg. Chem., 2007, 1091; (d) R. Cortes, K. Urtiaga,
L. Lezama, J. L. Pizarro, A. Goñi, M. I. Arriortua and
T. Rojo, Inorg. Chem., 1994, 33, 4009.
Y. Sunatsuki and N. Re, Inorg. Chem. Commun., 2012, 26, 16 (a) P. S. Mukherjee, S. Dalai, E. Zangrando, F. Lloret and
20; (b) B. Zhang, X. Zheng, H. Su, Y. Zhu, C. Du and
M. Song, Dalton Trans., 2013, 42, 8571; (c) S. Titos-Padilla,
J. Ruiz, J. M. Herrera, E. K. Brechin, W. Wersndorfer,
N. R. Chaudhuri, Chem. Commun., 2001, 1444;
(b) A. Escuer, C. J. Harding, Y. Dussart, J. Nelson, V. McKee
and R. Vicente, J. Chem. Soc., Dalton Trans., 1999, 223.
9142 | Dalton Trans., 2014, 43, 9136–9142
This journal is © The Royal Society of Chemistry 2014