Preparation, First Structure Analysis, and Magnetism of the Long-Known Nickel Benzoate Trihydrate - A Linear Ni···Ni···Ni Polymer and Its Parallels with the Active Site of Urease

Article abstract of DOI:10.1002/ejic.201501255

Nickel benzoate trihydrate (1) has been prepared in single-crystalline form by the reaction of nickel carbonate with benzoic acid in boiling aqueous solution. Its crystal structure comprises positively charged [Ni(Bz)(H₂O)₂]_nⁿ⁺ chains, benzoate anions, and one independent water molecule of solvation. The hexacoordinate Ni^II centers in the chains are triply bridged by one syn-syn carboxylato and two aqua bridges, and adjacent chains are linked by O-H···O hydrogen bonds [O···O distances are in the range 2.647(3)-2.684(3) ?] through solvate water molecules and benzoate anions. Thermal analysis revealed that 1 is stable up to 100 °C; further heating led to full dehydration accompanied by an additional decomposition reaction, as characterized by IR analysis of the intermediates. The geometrical features of the Ni centers have been compared with similar features at the active sites of urease. The effective magnetic moment per formula unit μ_eff has a value of 3.17μ_B at room temperature and upon cooling reaches a maximum value of 12.39μ_B at T = 4.6 K, which indicates ferromagnetic coupling between the nearest Ni^II atoms [3.0671(1) ?] within the chains; at lower temperatures this is counteracted by zero-field splitting.

Full text of DOI:10.1002/ejic.201501255

DOI: 10.1002/ejic.201501255
Full Paper
Chain Compounds
Preparation, First Structure Analysis, and Magnetism of the
Long-Known Nickel Benzoate Trihydrate – A Linear Ni···Ni···Ni
Polymer and Its Parallels with the Active Site of Urease
[
a]
[b]
[c]
[d]
[d]
Anna Vráblová, Larry R. Falvello, Javier Campo, Jozef Miklovič, Roman Boča,
[
a]
[e]
Juraj Černák* and Milagros Tomás
Abstract: Nickel benzoate trihydrate (1) has been prepared in accompanied by an additional decomposition reaction, as char-
single-crystalline form by the reaction of nickel carbonate with acterized by IR analysis of the intermediates. The geometrical
benzoic acid in boiling aqueous solution. Its crystal structure features of the Ni centers have been compared with similar
n+
comprises positively charged [Ni(Bz)(H O) ]
chains, benzoate features at the active sites of urease. The effective magnetic
2
2 n
anions, and one independent water molecule of solvation. The moment per formula unit μeff has a value of 3.17μ at room
B
II
hexacoordinate Ni centers in the chains are triply bridged by temperature and upon cooling reaches a maximum value of
one syn-syn carboxylato and two aqua bridges, and adjacent 12.39μ at T = 4.6 K, which indicates ferromagnetic coupling
B
II
chains are linked by O–H···O hydrogen bonds [O···O distances between the nearest Ni atoms [3.0671(1) Å] within the chains;
are in the range 2.647(3)–2.684(3) Å] through solvate water mol- at lower temperatures this is counteracted by zero-field split-
ecules and benzoate anions. Thermal analysis revealed that 1 ting.
is stable up to 100 °C; further heating led to full dehydration
Introduction
formed fortuitously under solvothermal conditions beginning
with nickel(II) nitrate, sodium benzoate, and 2,2′-bipyridine, has
If chemical simplicity could be conflated reliably with ease of
preparation and characterization, then various forms of nickel
benzoate, the trihydrate of which is the subject of this report,
would have been characterized many decades ago. The tri-
hydrate has long been known, its preparation reported by
[6]
been reported. However, a structure analysis of the title trihy-
drate by diffraction methods, the present-day sine qua non
standard for characterizing new coordination compounds, has
remained elusive.
As one of the simpler and more easily handled carboxylates,
benzoate has been used in studies of more complex systems in
[
1]
[2]
Ephraim and Pfister in 1925 and by Pfeiffer and Müllenheim
in 1933. From that time several partial studies of different forms
of nickel benzoate (trihydrate, tetrahydrate, anhydrous) have
[
7]
which carboxylates are common, such as MOFs and magnetic
[
8]
solids. The ubiquity of carboxylates in natural compounds is
[
3–5]
been reported.
More recently, the crystal structure of the
[
9]
well known, including in enzymes in which, inter alia, they
participate at the active sites of biocatalytic processes.
dinuclear “paddle-wheel”-type complex [Ni (μ -Bz) (HBz) ],
2
2
4
2
The different manners in which a carboxylate function such
as that of benzoate can coordinate metal centers, namely as a
terminal, chelating, or bridging ligand, permit a wide variability
in the processes and structures in which this group is involved.
As a bridge, carboxylate participates in discrete molecules and
extended nets, and possesses a special capacity for drawing
metal centers closer together than do, for example, cyanide or
azide bridges. This property propitiates magnetic interactions
and can activate metal centers for catalytic applications.
[
a] Department of Inorganic Chemistry,
P. J. Šafárik University in Košice,
Moyzesova 11, 04154 Košice, Slovakia
E-mail: juraj.cernak@upjs.sk
www.upjs.sk
[
[
b] Departamento de Química Inorgánica,
Instituto de Ciencia de Materiales de Aragón (ICMA),
University of Zaragoza-CSIC,
Pedro Cerbuna 12, 50009 Zaragoza, Spain
c] Departamento de Física de la Materia Condensada,
University of Zaragoza-CSIC,
Among the metals that have been studied in carboxylate
complexes, nickel(II), when six-coordinate, that is, in an octahe-
dral coordination or in a distorted shape derived from the octa-
Pedro Cerbuna 12, 50009 Zaragoza, Spain
[
[
d] Department of Chemistry, FPV, University of SS Cyril and Methodius,
1701 Trnava, Slovakia
9
e] Departamento de Química Inorgánica,
hedron, is expected to be paramagnetic with S = 1. Nickel also
Instituto de Síntesis Química y Catálisis Homogénea (ISQCH),
University of Zaragoza-CSIC,
Pedro Cerbuna 12, 50009 Zaragoza, Spain
Supporting information and ORCID(s) from the author(s) for this article
are available on the WWW under http://dx.doi.org/10.1002/ejic.201501255.
[10]
appears at the active sites of numerous enzymes,
including
urease, in which two nickel atoms bridged by one carboxylate
[
11]
and one water molecule are present at the active sites; com-
pounds with two nickel atoms bridged by two carboxylate
Eur. J. Inorg. Chem. 2016, 928–934
928
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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–1
groups and one water molecule have been used as model sys- rated by the sharp absorption band observed at 1593 cm ,
[
12,13]
tems for understanding the workings of urease.
which can be attributed to the C –C in-ring stretching vibra-
ar ar
II
Ni complexes with one-dimensional (1D) polymeric struc- tion. The most characteristic absorption bands are the ones due
tures and with S = 1 have been the subject of many experimen- to the asymmetric (1547, 1494 cm ) and symmetric (1424,
tal and theoretical studies associated with magnetic phenom- 1384 cm ) stretching modes of the COO groups. We note that
The synthesis of 1D Ni coordination polymers is usu- Pavkovic reported similar values of 1553, 1500, 1440, and
ally mediated by suitable bridging ligands linking Ni central 1392 cm for the trihydrate.
–1
–1
–
ena.[
14–19]
II
II
–1
[3]
atoms, for example, pyrazine (pyr) in {[Ni(pyr)(H O) ](NO ) ·
2
4
3 2
[
20]
2
H O} ,
bromide anions in [Ni(Br) (tz)2]n (tz = 1,3-thi-
2
n
[
2
21]
azole),
3
or azido anions in [Ni(3,5-dmpy) (N ) ] (3,5-dmpy =
2
3 2 n
,5-dimethylpyridine).[ Using the complex anion [Ni(CN)4]
22]
2–
as a bridging unit, we have previously synthesized several
[
23]
chain-like structures, for example, [Ni(en) Ni(CN) ]
and
2
4
[
Ni(dien)(mea)Ni(CN) ] (dien = diethylenetriamine, mea = 2-
4
[
24]
aminoethanol).
The disadvantage of these cyanide com-
plexes as regards their magnetism is the large distance between
II
the paramagnetic Ni atoms (approximately 10 Å), which results
in very weak intrachain exchange interactions. Recently, in our
II
II
quest for 1D Ni systems with shorter separations between Ni
centers, we prepared a microcrystalline sample of the Haldane
gap system [Ni(bpy)(ox)] (bpy = 2,2-bipyridine, ox = oxalate) in
n
II
which the Ni atoms are bridged in bis-chelating fashion by
Figure 1. Comparison of the IR spectra of samples 1 (blue trace), 1-120 (sam-
ple heated at 120 °C, red), and 1-230 (sample heated at 230 °C, green).
[
25]
oxalate.
II
As a continuation of our studies on 1D Ni coordination poly-
mers, we report herein the preparation of {[Ni(Bz)(H O) ]·
2
2
To study the thermal stability as well as the dehydration of
, its thermal curves were recorded (Figure 2). As can be seen
Bz·H O} (1; HBz = benzoic acid) in single-crystal form, its mag-
2
n
1
netism, and its crystal structure analysis, which reveals a geo-
metrically linear Ni···Ni···Ni polymeric structure with a small
Ni···Ni separation of 3.0671(1) Å. Within the chain, pairs of nickel
centers are triply bridged by a carboxylate and two water mol-
ecules. The triple bridge presents interesting similarities to the
active site of urease, including its hydrogen-bonding interac-
tions with uncoordinated water molecules.
from the TG curve in Figure 2, complex 1 is stable up to 100 °C.
Over the broad temperature range 100–330 °C, a total weight
loss of 21.3 % occurs, which can be seen (Figure 2) to comprise
at least two successive processes. The first occurs in the temper-
ature range 100–160 °C and corresponds to a rapid endother-
mic weight loss of 14.0 %, and the second part, over the larger
temperature range of 160–330 °C, manifests itself by a much
slower weight loss amounting in the end to 7.3 %. We note that
the calculated weight loss for the total dehydration of 1 is
Results and Discussion
1
5.2 %, which suggests that, besides dehydration, another reac-
We have prepared complex 1 in single-crystal form by the reac- tion(s) is taking place. To obtain more insight into the observed
tion of nickel(II) carbonate with a slight excess of benzoic acid processes, samples of 1 were heated in an oven at 120 and
in boiling water. The product as isolated contained benzoic acid 230 °C for 30 min (samples 1-120 and 1-230, respectively). The
as an impurity, but this could be removed by rinsing with eth- IR spectrum of 1-120 (Figure 1) indicates the absence of water
anol. The purity and identity of the product were checked by molecules in the sample; in addition, substantial changes in the
chemical analysis. In addition, the powder X-ray diffraction pat- shape and positions of the absorption bands of the asymmetric
–
tern was recorded to confirm that the phase identity of the bulk and symmetric modes of COO can be observed. The IR spec-
sample was the same phase characterized in the single-crystal trum of 1-230 is similar to that of 1-120 with a decrease in the
X-ray study (see Figure S1 in the Supporting Information).
intensities of all bands. It is interesting to note the presence of
–1
The IR spectrum of 1 is rich in content (Figure 1), but some a weak absorption near 3600 cm , which may correspond to
characteristic absorption bands can be identified. A broad ab- an O–H stretching vibration in the absence of hydrogen bond-
sorption band of medium intensity centered at around ing. These results suggest that the thermal decomposition of 1
–
1
2
965 cm can be attributed to ν(OH) stretching vibrations of starts with dehydration, as was reported for the similar tetra-
[
27]
the solvate water molecules and aqua ligands. The observed hydrate
shift of this band to lower wave numbers can be explained by benzoate of Ni .
and the analogous hydrate of the 2-chloro-4-nitro-
II [28]
As to the further, much slower decomposi-
the participation of the water molecules in medium-to-strong tion process, several scenarios are possible; among these is par-
hydrogen bonds (HBs; see below). This band has a shoulder, a tial decarboxylation. We note that it has been reported that
very weak absorption at 3054 cm– attributable to a C –H benzoic acid can be transformed into phenol by oxidative de-
1
ar
[
26]
[29a]
stretching vibration, as indicated by Nakamoto;
spectrum of benzoic acid this vibration is positioned at water over NiO
in the IR carboxylation
(the Dow Phenol Process) in the presence of
or by using copper benzoate as catalyst.
[
29b]
[30]
–
1
3
070 cm . The presence of the aromatic rings is also corrobo- The calculated weight loss for such a combination of processes
929
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(
3 × H O and 1 × CO with one oxygen atom coming from the
2 2
atmosphere) is 23.1 %, which is comparable to the observed
weight loss of 21.3 %.
Figure 3. One segment of the structure of 1 with the atom numbering
scheme. Displacement ellipsoids are drawn at the 50 % probability level. Sym-
metry codes: i: 1.5 – x, y, 1 – z; ii: 1 + x, y, z; iii: 0.5 + x, 1 – y, z; iv: 1 – x,
1
– y, 1 – z; v: 0.5 – x, y, 1 – z; vi: 0.5 – x, y, –z.
Figure 2. TGA curves of 1.
Further heating of 1 in the temperature range 320–530 °C
leads to a strong exothermic decomposition of its organic com-
ponent. The residual mass of 20.7 % is in good agreement with
the calculated residual mass for NiO (21.0 %); the formation of
NiO was also reported in the case of the thermal decomposition
II
[31]
of the anhydrous Ni benzoate in air.
As expected, anhydrous Ni(Bz) displayed enhanced thermal
2
stability (230 °C) and upon the observed mass loss the forma-
[
4]
tion of NiO as a solid residue was reported. On the other
hand, the tetrahydrate Ni(Bz) ·4H O is stable only up to 100 °C
2
2
(
as was observed for 1) and the formation of metallic nickel
[
5]
was reported at the end of the thermal decomposition.
Figure 4. Polymeric structure of 1.
The crystal structure of 1 is composed of positively charged
n+
[
Ni(Bz)(H O) ]
chains, benzoate anions, and solvate water
2
2 n
Table 1. Selected bond lengths [Å] and angles [°] for 1.
molecules (Figure 3 and Figure 4). The chains are built up of
triply bridged pairs of Ni atoms; two bridges are formed by μ -
aqua ligands and the third by a syn-syn-benzoate ligand. Al-
though the Ni···Ni···Ni chains are strictly linear, running parallel
to the crystallographic a axis, the axial coordination directions
II
Ni1–O1
Ni1–O1W
Ni1–O1W
O1–Ni1–O1W
O1–Ni1–O1W
O1W–Ni1–O1W
1.9654(18)
2.1270(18)
2.0979(19)
87.16(7)
90.61(8)
83.39(8)
C1–O1
C11–O11
1.270(2)
1.261(3)
2
v
v
Ni1–O1W–Ni1
O1–C1–O1
O11–C11–O11
93.09(7)
125.3(3)
124.2(4)
v
v
v
vi
II
at the Ni atoms, that is, the Ni1···O1 and symmetry related
bonds, are tilted by 12.34(7)° with respect to the b axis.
Symmetry codes: v: 0.5 – x, y, 1 – z; vi: 0.5 – x, y, –z.
II
The Ni center (–1 site) is hexacoordinate (donor set O O )
2
4
in the form of a compressed bipyramid (Figure 3). The axial bridge in compound 1 coincides with a Ni···Ni separation of
Ni1–O1 bond lengths [1.9654(18) Å; 2 ×] are shorter than those 3.0671(1) Å, and the extended chain has Ni···Ni···Ni angles of
II
II
II
in the equatorial plane, 2.0979(19) and 2.1270(18) Å (Table 1). 180°. Very few linear Ni ···Ni ···Ni 1D polymers, that is, with
The observed compression of the octahedron can be expressed angles of 170–180° and distances between Ni atoms of less
by the ratio κ = (Ni–O) /<(Ni–O) > = 0.93. A similar compres- than 4 Å, have been reported in metal–organic crystals. In the
ax
eq
II
sion of the octahedral coordination of Ni was found in known examples, the bridges are mainly chlorine or bromine
Ni(H O) ][Zn(H O) (phen) ] ·2btc·H O (phen 1,10-phen- atoms, although some structures with S (benzenethiolato:
[
=
2
6
2
2
2 2
2
[
32]
[34]
anthroline; btc = 1,3,5-benzenetricarboxylate) with the value Ni···Ni distance = 3.173 Å)
or pyrazolate bridges (Ni···Ni dis-
κ = 0.95; a similar value of κ = 0.94 was found in tance = 3.471 Å)[ have been reported. The Ni···Ni distances
[Ni(cbab)(H O) ]·H O} [cbab = 4-(4-carboxybenzoylamino)- in the 1D polymers with halogen bridges depend on the num-
35]
{
2
2
2
n
[
27]
benzoate] bearing the μ -bridging aqua ligand.
O(H )–Ni angle in 1 is 93.09(7)°.
The Ni– ber of bridges (two or three) and the nature of the halogen,
the shortest being those with triple chlorine bridges (for in-
2
2
Reports of Ni compounds in which the Ni atoms are triply stance, with an Ni···Ni distance of 3.063 or 3.060 Å)[36] with
bridged by a carboxylate and two water molecules are scarce, Ni···Ni separations similar to those in compound 1.
comprising just a single family of hexanickel(II) complexes with
Binuclear nickel compounds with carboxylate and water
[
33]
Ni···Ni distances between 3.105 and 3.111 Å.
The triple bridges are of interest as models for the active centers of en-
Eur. J. Inorg. Chem. 2016, 928–934
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zymes.[10,11] Although the number of nickel compounds with a
carboxylate and two aqua bridges, as in compound 1, is very
small, nickel compounds with one aqua and two carboxylate
bridges are more common. Some of these compounds have
been used as models for the active site of the enzyme
[
12]
urease,
because the active site contains two nickel atoms
bridged by a single carboxylate and a single water molecule
with a terminal water molecule at each of the nickel centers
(
Figure 5a). It is not clear whether all of the sites identified as
water in urease are indeed water or whether some are hydrox-
ide. Neither is it clear yet how the urease catalyzes the hydroly-
sis of urea into two ammonia molecules and carbonic acid; but
the common first step in all of the proposed mechanisms is the
binding of urea to one of the nickel atoms, displacing the termi-
nal water. In Figure 5 we can see that a similar result would be
obtained if urea were to coordinate to one of the nickel centers
in compound 1, breaking one of the water bridges. That would
leave one terminal and one bridging water in addition to the
newly bound terminal urea. Therefore, compound 1 is of poten-
tial interest as a model for studying the mechanism of urease
activity, or as a precursor for other, related compounds.
Figure 6. Hydrogen-bonding scheme in 1. Symmtery codes: iii: 0.5 + x, 1 – y,
z; vi: 0.5 – x, y, –z; vii: –x, 1 – y, –z.
the IR spectrum (all hydrogen atoms are involved in hydrogen
bonding) as well as the observed shift of its position to
–1
2
965 cm . The hydrogen-bonding system connects covalent
chains into supramolecular layers perpendicular to the b axis
Figure 6). The active site of urease also contains one external
(
water molecule that forms strong hydrogen bonds with the co-
ordinated water molecules.
For both benzoate fragments the delocalization of π elec-
trons between the aromatic ring and the carboxylate group is
hindered, as the dihedral angles between the ring and COO–
are 15.17(9)° (benzoate containing C1) and 14.4(3)° (C11). The
twist is likely a result of weak C–H···π interactions between
neighboring phenyl rings (Figure 7, Table 3). Evidence of π delo-
calization was observed in the structure of [Ni (μ -Bz) (HBz) ],
2
2
4
2
in which the dihedral angle between the aromatic ring and the
plane defined by the carboxylate group has values of 1.2, 12.7,
[
6]
and 7.7° for the three independent benzoato ligands.
Figure 5. First step in the previously proposed mechanism of urease activity
[
(a) → (b)] and the hypothetical parallel reactivity of compound 1 [(c) → (b)].
The water molecules and carboxylate oxygen atoms in 1 are
involved in O–H···O hydrogen bonds of considerable strength,
as indicated by the short O···O distances in the range 2.647(3)–
2
.684(3) Å and O–H···O angles close to linearity (Table 2, Fig-
Figure 7. Weak C–H···π interactions between the phenyl rings in the crystal
structure of 1. Symmetry code: vi: 0.5 – x, y, –z.
ure 6).
Table 2. Hydrogen bonds [Å, °] for 1.
Table 3. Possible weak hydrogen-bonding interactions for 1.
D–H···A
D–H [Å]
H···A [Å]
D···A [Å]
D–H···A [°]
C–H···Cg
C–H [Å]
0.96(4)
H···Cg [Å]
C···Cg [Å]
C–H···Cg [°]
O1W–H1A···O11
O1W–H1B···O2W
O2W–H2A···O11
0.76(3)
0.81(3)
0.82(3)
1.90(3)
1.88(3)
1.86(3)
2.647(3)
2.684(3)
2.679(2)
169(3)
172(3)
172(3)
C4–H4···Cg2ii
2.93(3)
3.458(4)
116(3)
vii
Symmetry code: ii: 1 + x, y, z
Symmetry codes: vii: –x, 1 – y, –z
The structure of compound 1 is similar to that of
[
37]
Some of the hydrogen bonds are formed between the bridg- [Cu(H O) (Bz)]·HBz·H O;
however, in 1, the bridging water
2
2
2
ing water molecules and the free benzoate groups, O1W– molecules are essentially symmetrically bonded to the nickel
H1A···O11, which further polarizes the water O···H bond, favor- atoms [2.0979(19) and 2.1270(18) Å, O···Ni···O angle 83.39(8)°],
–
ing a putative deprotonation to give HO groups in compound whereas they are quite different in the copper compound
1
, in a further possible analogy to the active site of urease.
One consequence of the formation of strong hydrogen this is the origin of the large difference in the unit-cell ꢀ angles
bonds is the shape of the observed ν(OH) absorption band in for the two structures [95.331(3)° in compound 1 and 90.0° in
(1.972 and 2.504 Å, angle 88.6°) due to the Jahn–Teller effect;
Eur. J. Inorg. Chem. 2016, 928–934
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the copper analogue]. This is also the origin of the differences in line with the presence of a compressed octahedron in 1.
[
3]
in their X-ray powder patterns, as noted by Pavkovic.
The evolution of the magnetic properties of 1 (molar mag- D is negative. [Dstr is calculated as Δ
netic susceptibility, effective magnetic moment, magnetization
= d – <d >, with the average <d > taken over all three ligand
Thus, one could expect that the zero-field splitting parameter
– (Δ + Δ )/2, in which
z
y
x
Δ
i
i
i
i
per formula unit) is shown in Figure 8. The effective magnetic pairs.] Nevertheless, the quality of the fit with D < 0 is much
moment μeff is 3.17μ at room temperature, in accord with the worse than with D > 0.
B
II
II
presence of Ni (S = 1) centers. Upon lowering the temperature,
Ferromagnetic interactions between Ni centers are not as
the effective magnetic moment increases slowly at first, and common as their antiferromagnetic counterparts; examples of
II
then rapidly below 15 K, reaching a maximum of 12.39μB at ferromagnetically coupled Ni atoms within chain-like arrange-
T = 4.6 K. This is a fingerprint of the ferromagnetic exchange ments have been reported, for example, in chiral [Ni(L/D-
interaction (J > 0). The decrease in μeff at lower temperatures is mand)(4-MePy) ] ·n(ClO ) (Hmand = mandelic acid, 4-MePy = 4-
3 n
32]
4
[
due to single-ion anisotropy, expressed in terms of the zero- methylpyridine)
and [Ni(1-tza) ] (1-Htza = tetrazole-1-acetic
2
n
[
39]
field splitting parameter D.
acid).
Conclusions
The successful preparation and crystallization of nickel benzo-
ate trihydrate, with formula Ni(BzO) (H O) , has permitted a
2
2
3
thorough characterization of this substance, including of its
crystal structure, some 90 years after its solubility properties
[
1]
were first reported by Ephraim and Pfister. The 1D polymer
described by the structure analysis, with a rigorously linear
Ni···Ni···Ni chain, short intermetal distances, and axially com-
pressed octahedral coordination at the Ni centers, correlates
well with its magnetic properties, which reveal ferromagnetic
intrachain coupling between the metal atoms and zero-field
splitting, possibly alongside interchain antiferromagnetic inter-
actions, which takes precedence below T = 4.6 K. In the crystal,
with the Ni···Ni···Ni chain parallel to the a axis, supramolecular
aggregation mediated by hydrogen bonds extends the struc-
ture along the ac plane, and C···H···π interactions add a third
dimension by extending along [101].
Figure 8. Magnetic functions for 1: Left: Effective magnetic moment with
detail (inset upper right) of the low-temperature range. Inset lower left: molar
magnetic susceptibility. Right: Magnetization per formula unit. Solid lines rep-
resent the fitting.
When fitting the magnetic data it must be remembered that
analytical formulae for the magnetic susceptibility in the case
of J > 0 countermanded by D do not exist. The usual device for
dealing with such a case is a finite ring approximation with the
spin Hamiltonian given by Equation (1).
Experimental Section
CHN analyses were performed with a Perkin–Elmer 2400 Series II
CHNS/O analyzer. IR spectra were recorded with a Perkin–Elmer
Spectrum 100 CsI DTGS FTIR spectrometer with a UATR 1 bounce-
(1)
–
1
in which the first summation is restricted to the nearest neigh- KRS-5 in the range 4000–300 cm (UATR = universal attenuated
bors for the directions α = x, z.
total reflectance accessory; KRS-5 = thallium bromoiodide). The X-
ray powder diffraction pattern of 1 (see Figure S1 in the Supporting
Information) was recorded with a RIGAKU D-Max/2500 diffractome-
ter with a rotating anode and RINT2000 vertical goniometer in the
For N = 4, the fitting procedure converges to the following
–1
set of magnetic parameters: J/hc = +12.1 cm , g = 2.29, D/hc =
–
1
+
9.6 cm . The fit is very good for the higher-temperature tail of
2θ range 2.5–40° using Cu-Kα1 radiation (λ = 1.5406 Å) and a step
the magnetic susceptibility, thereby confirming that the Curie–
Weiss law holds true in this region. Also, the molar magnetiza-
tion is well reproduced for higher fields, which confirms the
value (and also the sign) of the D parameter. However, the low-
size of 0.03°; the model powder diffraction pattern was calculated
[40]
by using the Mercury program.
TG and DTG curves were re-
corded with a Netzch STA 409 PC/PG instrument under the follow-
ing conditions: sample weight = 36.906 mg, heating rate =
–
1
temperature region of the magnetic susceptibility and the low 10 K min , dynamic artificial air atmosphere, temperature range
magnetic field of the magnetization are not reproduced well, 300–1174 K, aluminum oxide crucible.
which indicates that the magnetic interactions are more com-
Compound 1
plex than the simple model of a finite ring. Note that the dis-
A mixture of solid NiCO (1.0 g; 7.7 mmol) and solid benzoic acid
II
3
tance between the two neighboring Ni atoms within the chain
(2.0 g, 16.2 mmol) was slowly dissolved in water (250 mL) under
is much shorter [3.0671(1) Å] than the shortest distance be-
heating and stirring to yield a green solution. Slow boiling was
continued until cessation of gas liberation (approx. 45 min; the gas
II
tween the Ni atoms in neighboring chains [6.9793(2) Å] such
that a putative interchain interaction would be weak.
is likely CO ). The loss of water was continuously compensated by
2
Based on the Ni–O bond lengths (Table 1), the structural the addition of boiling water. The hot solution was filtered and the
[
38]
parameter Dstr was calculated to be negative (Dstr = –0.147), filtrate was left aside for crystallization at room temperature. Within
Eur. J. Inorg. Chem. 2016, 928–934
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932 © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
a few days light-green crystals separated (product 1) along with a
few colorless crystals of benzoic acid, which were removed by wash-
ing the product in a Buchner funnel with ethanol. The light-green
crystalline product was dried in air. Yield of 1 based on the metal:
CCDC 1408434 (for 1) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre.
7
2 %. IR (UATR): ν˜ = 3054 (vw), 2965 (br), 1593 (m), 1547 (s), 1494
Acknowledgments
(s), 1424 (s), 1384 (s), 1301 (m), 1070 (m), 1020 (m), 935 (m),
7
2
4
10 (s), 683 (s), 668 (s), 618 (s), 504 (s), 424 (m), 386 (m), 291 (s);
This work was supported by the Slovak Grant Agencies (VEGA
–1
70 (s) cm . C H NiO (354.98): calcd. C 47.36, H 4.55; found C
14
16
7
1
/0075/13, APVV-14-0078, and APVV-14-0073) and a European
6.85, H 4.68.
Regional Development Fund of the European Union (ERDF EU)
The magnetic properties of 1 were investigated using a commercial grant (contract no. ITMS26220120047). Funding from the Minis-
Quantum Design SQUID magnetometer in the temperature range
–300 K at 0.1 T. A powder specimen of 62.130 mg was used. The
try of Science and Innovation (Spain) (grants MAT2011-27233-
C02-01 and MAT2011-27233-C02-02), the Diputación General de
Aragón and the European Union Regional Development Fund is
gratefully acknowledged. A. V. thanks the National Scholarship
2
data were corrected for the diamagnetic contribution with Pascal′s
constants using the MATRA program.[
41]
Single-crystal X-ray data were collected at 295(2) K with an Oxford Programme of the Slovak Republic for financial support of her
Diffraction Xcalibur diffractometer equipped with a Sapphire3 CCD
detector and a graphite monochromator utilizing Mo-Kα radiation
study stay at the University of Zaragoza (Spain). Dr. Rocío
González Álvarez prepared Figure 5.
(
λ = 0.71073 Å). The unit cell was chosen in accord with the recom-
mendations of the International Union of Crystallography Commis-
sion on Crystallographic Data, using the shortest two axes in the Keywords: Nickel · Carboxylate ligands · X-ray diffraction ·
(
monoclinic) ac plane as unit-cell axes. In this case that gave a space
Magnetic properties · Thermal properties
[42]
group of I2/a.
scan technique and were performed using ABSPACK.
Absorption corrections were based on the multi-
[
43]
The struc-
[44]
2
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354.98
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I2/a
[
6.1341(2)
34.1797(13)
6.9793(2)
95.331(3)
1456.96(9)
4
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[°]
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V [Å ]
Z
D
calcd. [Mg/m–3
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1.618
[
T [K]
295(2)
1.364
μ [mm–1
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4.182–27.474
6276
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Received: October 31, 2015
Published Online: January 15, 2016
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934
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim