First structural and magnetic studies of Ni clusters containing 2,6-diacetylpyridine-dioxime as a ligand

Article abstract of DOI:10.1021/ic9020965

In the present work, coordination possibilities of the system dapdoH ₂/Ni²⁺, being dapdoH₂ = 2,6-diacetylpyridine dioxime, have been explored, offering as a result a number of unprecedented clusters with a variety of topologies and magnetic behaviors. Depending on the precursors and reaction conditions, several compounds named [Ni ₂(dapdo)₂] (1), [Ni₃(OH)(B₂O) ₃(dapdo)(dapdoH₂)(H₂O)]-1.25H₂O (2), [Ni₃(AcO)₄(dapdoH)²(H₂O) ₂]-H₂O (3), and [Ni₄(AcO)₃(dapdo) (dapdoH)₂(H₂O)₃], (AcO), 3H₂O (4) were achieved and structurally well-characterized. Dc magnetic measurements were carried out in the 2-300 K range revealing antiferromagnetic interactions for (2-4) compounds and diamagnetic response for the square planar coordinated complex (1).

Full text of DOI:10.1021/ic9020965

Inorg. Chem. 2010, 49, 2259–2266 2259
DOI: 10.1021/ic9020965
First Structural and Magnetic Studies of Ni Clusters Containing
2,6-Diacetylpyridine-dioxime as a Ligand
,†
†
‡
§
§
^
ꢀ
ꢀ
Albert Escuer,* Jordi Esteban, Nuria Aliaga-Alcalde, Merce Font-Bardia, Teresa Calvet, Olivier Roubeau,
and Simon J. Teat#
†
´
ꢁ
ꢁ
Departament de Quımica Inorganica and Institut de Nanociencia i Nanotecnologia de la Universitat de
‡
´
ꢀ
ꢁ
Barcelona (IN2UB), Martı I Franques 1-11, 08028 Barcelona, Spain, ICREA (Institut Catala de Recerca i
´
ꢁ
´
ꢀ
Estudis Avanc-ants) & Departament de Quımica Inorganica de la Universitat de Barcelona, Martı I Franques
§
´
1-11, 08028 Barcelona, Spain, Departament de Mineralogia I Crystalografia, Universitat de Barcelona, Martı
^
ꢀ
ꢀ
Franques s/n, 08028 Barcelona, Spain, Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de
Zaragoza, Pl. San Francisco s/n, 50009 Zaragoza, Spain, and #Advanced Light Source, Lawrence Berkeley
National Laboratory, 1 Cyclotron road, Berkeley, California 94720
Received October 23, 2009
In the present work, coordination possibilities of the system dapdoH2/Ni2þ, being dapdoH2 = 2,6-diacetylpyridine
dioxime, have been explored, offering as a result a number of unprecedented clusters with a variety of topologies and
magnetic behaviors. Depending on the precursors and reaction conditions, several compounds named [Ni2(dapdo)2]
(1), [Ni3(OH)(BzO)3(dapdo)(dapdoH2)(H2O)] 1.25H2O (2), [Ni3(AcO)4(dapdoH)2(H2O)2] H2O (3), and [Ni4-
3
3
(AcO)3(dapdo)(dapdoH)2(H2O)3] (AcO) 3H2O (4) were achieved and structurally well-characterized. Dc magnetic
measurements were carried out in the 2-300 K range revealing antiferromagnetic interactions for (2-4) compounds
and diamagnetic response for the square planar coordinated complex (1).
3
3
Introduction
amount of high nuclearity clusters, as for example: Ni7,2 Ni9,3
Ni10,4 Ni12 or Ni14,5 Fe12,6 and Mn8,7 Mn9,8 Mn10,9 and
Mn12,10 exhibiting in some cases SMM response.7,10
One of the crucial synthetic points in the search of high
nuclearity systems is the design of ligands to increase such
nuclearity and/or generate new topologies. Regarding this
matter, pyridyl dioximato ligands (LH2, with R=various),
Scheme 1, appear as excellent candidates for the achievement
of polynuclear clusters in the bottom-up approach: they
contain a good N-donor unit (pyridinic ring) and two
meta-oximato groups capable of binding four metal centers,
M in Scheme 2.
At present, research of oximes in coordination chemistry is
a growing field. 2-pyridyl oximes are well-known ligands in
this area because of their ability to generate stable first-row
transition coordination compounds with a large range of
nuclearities.1 These molecules are very versatile, able to act as
bidentate ligands in their neutral state or to link up to three
metallic centers in their deprotonated anionic form. Self-
assembly of metal-oximato fragments have yielded a large
*To whom correspondence should be addressed. E-mail: albert.escuer@
ub.edu.
(1) Milios, C. J.; Stamatatos, T. C.; Perlepes, S. P. Polyhedron 2006, 25,
134.
(2) Stamatatos, T. C.; Diamantopoulou, E.; Raptopoulou, C. P.;
Psycharis, V.; Escuer, A.; Perlepes, S. P. Inorg. Chem. 2007, 46, 2350.
(3) (a) Khanra, S.; Weyhermuller, T.; Rentschler, E.; Chaudhuri, P. Inorg.
Chem. 2005, 44, 8176. (b) Stamatatos, T. C.; Diamantopoulou, E.; Tasiopoulos,
A.; Psycharis, V.; Vicente, R.; Raptopoulou, C. P.; Nastopoulos, V.; Escuer, A.;
Perlepes, S. P. Inorg. Chim. Acta 2006, 359, 4149. (c) Stamatatos, T. C.;
Papatriantafyllopoulou, C.; Katsoulakou, E.; Raptopoulou, C. P.; Perlepes, S. P.
Polyhedron 2007, 26, 1830.
(4) Psomas, G.; Dendrinou-Samara, C.; Alexiou, M.; Tsohos, A.;
Raptopoulou, C. P.; Terzis, A.; Kessissoglou, D. P. Inorg. Chem. 1998, 37, 6556.
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Dalton Trans. 2007, 3861. (b) Papatriantafyllopoulou, C.; Jones, L. F.; Nguyen,
T. D.; Matamoros-Salvador, N.; Cunha-Silva, L.; Paz, F. A. A.; Rocha, J.;
Evangelisti, M.; Brechin, E. K.; Perlepes, S. P. Dalton Trans. 2008, 3153. (c)
Stamatatos, T. C.; Escuer, A.; Abboud, K. A.; Raptopoulou, C. P.; Perlepes, S. P.;
Christou, G. Inorg. Chem. 2008, 47, 11825.
(6) Murugesu, M.; Abbout, K. A.; Christou, G. Polyhedron 2004, 23,
2779.
(7) (a) Milios, C. J.; Kefalloniti, E.; Raptopoulou, C. P.; Terzis, A.;
Vicente, R.; Lalioti, N.; Escuer, A.; Perlepes, S. P. Chem.Commun. 2003, 819.
(b) Milios, C. J.; Stamatatos, T. C.; Kyritsis, P.; Terzis, A.; Raptopoulou, C. P.;
Vicente, R.; Escuer, A.; Perlepes, S. P. Eur. J. Inorg. Chem. 2004, 2885. (c)
Stoumpos, C. C.; Stamatatos, T. C.; Psycharis, V.; Raptopoulou, C. P.; Christou,
G.; Perlepes, S. P. Polyhedron 2008, 27, 3703. (d) Stoumpos, C. C.; Stamatatos,
T. C.; Sartzi, H.; Roubeau, O.; Tasiopoulos, A. J.; Nastopoulos, V.; Teat, S. J.;
Christou, G.; Perlepes, S. P. Dalton Trans. 2009, 1004.
(8) Roubeau, O.; Lecren, L.; Li, Y. G.; Le Goff, X. F.; Clerac, R. Inorg.
Chem. Commun. 2005, 8, 314.
(9) Papatriantafyllopoulou, C.; Raptopoulou, C. P.; Escuer, A.; MIlios,
C. J. Inorg. Chim. Acta 2007, 360, 61.
(10) Dendrinou-Samara, C.; Zaleski, C. M.; Evagorou, A.; Kampf, J. W.;
Pecoraro, V. L.; Kessissoglou, D. P. Chem.Commun. 2003, 2668.
r
2010 American Chemical Society
Published on Web 01/26/2010
pubs.acs.org/IC

2260 Inorganic Chemistry, Vol. 49, No. 5, 2010
Escuer et al.
Scheme 1. LH2 Dioxime Ligands (R=H, Me, NH2); DapdoH2 Refers
to the Ligand in Which R=Me
addition, several mononuclear complexes containing one
dapdoH2 ligand in the 1.00111 coordination mode along
with anions or solvent molecules linked in the remainder
positions of the coordination sphere of metal have been
found with Cu2þ 18 Zn2þ 18a In3þ 19 and Ru2þ 20
, , . Besides,
,
some of these coordinated anions may also bind neighboring
centers giving as a result 1D systems in which dapdoH2 acts
exclusively as a tridentate ligand (e.g., [Cu(pdamoH2)(μ-
12
SO4)]n and [Mn(dapdoH2)(μ-Cl)2]n).21 Recent reports
show similar coordination properties for certain trinuclear
systems, [Mn3(dapdoH2)2(R-COO)6] (R=H, Me, Ph).22
Nevertheless, it should be emphasized the existence of
some polynuclear clusters generated after deprotonation of
dapdoH2; where now, the resulting anionic species (dapdoH-
and/or dapdo2-) play a primary role. This group of com-
pounds comprises a dinuclear copper system that contains a
double oximato bridge and two dapdoH- ligands in 2.10111
coordination modes, which general formula is [Cu2(dapdo-
H)2](BF4)2;23 a mixed valence trinuclear Fe system in which
one {FeII(dapdoH)2} subunit is linked to two Fe3þ cations,
described as [FeII(dapdoH)2FeIIICl4(O)];13 an heterometallic
copper-chromium compound in which {Cu(dapdo)} sub-
units bind chromium triazacyclononane groups in a 3.11111
Scheme 2. Coordination Modes for dapdoH2, dapdoH-, or dapdo2-
Ligandsa
coordination mode;24 a family of MnII2MnIII hexanuclear
4
anionic species expressed as [Mn6O2(MeO)2(dapdo)2(dapdo-
H)4]2þ 25 a mixed valence [MnII2MnIII6O4(OH)4(MeO)2-
;
(N3)2(dapdo)2(dapdoH)2(H2O)]25a complex and finally an
heterometallic Mn/Gd trinuclear system.26
Here, we introduce the first polynuclear clusters achieved
by reacting dapdoH2 with different nickel salts in basic
conditions. This approach has led to the formation of unique
structures, Ni2 (1), Ni3 (2, 3), and Ni4 (4), that include the
organic unit or its deprotonated forms exhibiting a variety of
coordination modes. Syntheses, structures, and magnetic
behaviors of these compounds are described in the following
sections.
a A large number of unprecedented possibilities as the novel coordi-
nation mode 3.20111 reported in this work for dapdoH- are still
possible.
Within this family of linkers, 2,6-diacetylpyridine dioxime
(dapdoH2) is the most well-studied and only a few examples
using related ligands like 2,6-pyridine dioxime (pdoH2) or
pyridine-2,6-diamidoxime (pdamoH2) have been reported to
date.1
On the other hand, the putative capacity of dapdoH2 for
the development of high nuclearity systems differs from
current results in the literature, where the majority of com-
pounds happen to be mononuclear. Thus, a number of
systems with general formula [MII(LH2)2]X2 (M = Cu,11
Ni,12 Fe,13 Mn11a), including one [NiII(pdamoH)2]14 and
two [MIV(dapdo)2] (MIV=Ni,15 Co16) have been described.
In all of them, the six coordination sites of the metallic centers
are shielded by two LH2, LH-, or L2- ligands in 1.00111
coordination modes (Harris notation),17 respectively. In
Experimental Section
Syntheses. 2,6-Diacetylpyridine, Ni(AcO)2 4H2O and Ni-
3
(acac)2 (acac = acetylacetonate) were purchased from Sigma-
Aldrich Inc. and Flucka AG and used without further purifica-
tion. Ni(BzO)2 3H2O was synthesized dissolving equimolar
3
quantities (40 mmol) of benzoic acid and NaOH in 40 mL of
(18) (a) Nicholson, G. A.; Petersen, J. L.; McCormick, B. J. Inorg. Chem.
1982, 21, 3274. (b) Vasilevsky, I. V.; Stenkamp, R. E.; Lingafelter, E. C.;
Schomaker, V.; Willett, R. D.; Rose, N. J. Inorg. Chem. 1989, 28, 2619. (c)
Abboud, K. A.; Palenik, R. C.; Palenik, G. J. Acta Crystallogr., Sect. C 1994,
C50, 525.
(19) (a) Abram, S.; Maichle-Mossmer, C.; Abram, U. Polyhedron 1997,
16, 2183. (b) Abram, S.; Maichle-Mossmer, C.; Abram, U. Polyhedron 1997, 16,
2291.
€
€
(20) Singh, S. K.; Sharma, S.; Dwivedi, S. D.; Zou, R.-Q.; Xu, Q.; Pandey,
D. S. Inorg. Chem. 2008, 47, 11942.
(21) (a) Unni Nair, B. C.; Sheats, J. E.; Ponteciello, R.; Van Engen, D.;
Petrouleas, V.; Dismukes, G. C. Inorg. Chem. 1989, 28, 1582. (b) Marsh, R. E.
Inorg. Chem. 1990, 29, 572.
(22) Escuer, A.; Cordero, B.; Solans, X.; Font-Bardia, M.; Calvet, T. Eur.
J. Inorg. Chem. 2008, 5082.
(11) (a) Glynn, C. W.; Turnbull, M. M. Transition Met. Chem. 2002, 27,
822. (b) Halcrow, M. A.; Kilner, C. A.; Wolowska, J.; McInnes, E. J. L.;
Bridgeman, A. J. New J. Chem. 2004, 28, 228.
(12) Bovenzi, B. A.; Pearse, G. A., Jr. J. Chem. Soc., Dalton Trans. 1997,
2793.
(13) Vasilevsky, I. V.; Stenkamp, R. E.; Lingafelter, E. C.; Rose, N. J.
J. Coord. Chem. 1988, 19, 171.
(14) Salonen, M.; Saarinen, H.; Mutikainen, I. J. Coord. Chem. 2008, 61,
1462.
(23) Nicholson, G. A.; Petersen, J. L.; McCormick, B. J. Inorg. Chem.
1980, 19, 195.
€
(24) Khanra, S.; Weyhermuller, T.; Chaudhuri, P. Dalton Trans. 2007,
4675.
(25) (a) Stamatatos, T. C.; Luisi, B. S.; Moulton, B.; Christou, G. Inorg.
Chem. 2008, 47, 1134. (b) Khanra, S.; Weyherm€uller, T.; Chaudhuri, P. Dalton
Trans. 2008, 4885.
(15) Sproul, G.; Stucky, G. D. Inorg. Chem. 1973, 12, 2898.
(16) Namli, H.; Azaz, A. D.; Karabulut, S.; C-elen, S.; Kurtaran, R.;
Kazak, C. Transition Met. Chem. 2007, 32, 266.
(17) Coxall, R. A.; Harris, S. G.; Henderson, D. K.; Parsons, S.; Tasker,
P. A.; Winpenny, R. E. P. J. Chem. Soc., Dalton Trans. 2000, 2349.
(26) Lampropoulos, C.; Stamatatos, T. C.; Abboud, K. A.; Christou, G.
Inorg. Chem. 2009, 48, 429.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2261
H2O, filtering and mixing the final solution with a commercial
source of Ni(NO3)2 6H2O (20 mmol) in 20 mL of water. The
resulting nickel salt was obtained in good yield (>80%).
DapdoH2 was prepared following C.W. Glynn and M.M. Turn-
bull method.11a
matrix were unsuccessful. Twinning was thus taken into account
with TWIN/BASF instructions in shelxl. All non-hydrogens
were refined anisotropically, although displacement parameters
restrains were used for a number of carbon atoms and the lattice
water oxygens. Hydroxyl hydrogens were found in difference
Fourier maps and refined with distance restrains. The rest of
hydrogens were placed geometrically on their riding atom. At
the end of the refinement, large voids remained in the structure
containing only diffuse electron density that could not be
modeled satisfactorily. These voids were thus analyzed and
taken into account by PLATON/SQUEEZE,29 that recovered
a total of 276 electrons per cell in voids occupying a total of 1476
3
[Ni2(dapdo)2] (1). DapdoH2 (0.193 g, 1 mmol) and Ni(acac)2
(0.514 g, 2 mmol) were dissolved in 20 mL of MeOH together
with NEt3 (0.202 g, 2 mmol). The mixture was stirred for 2 h and
then filtered. Crystals were obtained by layering the final
solution with 10 mL of diethyl ether. Anal. Calcd for
C18H18N6Ni2O4 (1): C, 43.26; H, 3.63, N, 16.82%. Found: C,
43.1; H, 3.7, N, 16.6%. Relevant IR bands (cm-1): 3421(b),
1559(w), 1512 (w), 1399(s), 1299(m), 1273(m), 1196(s), 1151(m),
1118(m), 1087(s), 788(m), 559(m).
3
˚
cubic angstroms (main voids volumes are 200 and 125 A ),
resulting in a significant improvement both in R1 and wR2
factors. The derived figures (electrons/volume) would reason-
ably account for a number of diffuse small solvent molecules,
e.g. water or methanol.
A red prismatic crystal of (3) was selected and mounted on a
MAR345 diffractometer with an image plate detector. Unit-cell
parameters were determined from 6640 reflections (3 < θ <
31ꢀ) and refined by least-squares method. Lorentz-polarization
and absorption corrections were made.
The structure was solved by direct methods, using SHELXS
computer program30 and refined by full-matrix least-squares
method with SHELX97 computer program.31 All H atoms were
computed and refined, using a riding model, with an isotropic
temperature factor equal to 1.2 time the equivalent temperature
factor of the atom which are linked.
(4) Data collection of the data was made on a APEX2
(BRUKER AXS, 2005) diffractometer. Unit-cell parameters
were determined from 1896 reflections (2.3 < θ < 23.4ꢀ) and
refined by least-squares method. The structure was solved using
SIR9732 and refined with SHELX97.31
[Ni3(OH)(BzO)3(dapdo)(dapdoH2)(H2O)] 1.25H2O
(2).
DapdoH2 (0.194 g, 1.0 mmol) and Ni(BzO)2 3H2O (0.602 g, 2
3
3
mmol) were dissolved in 40 mL of distilled MeOH and then
NEt3 (0.202 g, 2 mmol) was added. The solution was stirred for 2
h, filtered and crystallized layering with diethyl ether. Anal.
Calcd for C39H38N6Ni3O12 1.25 H2O (2): C, 47.73; H, 4.16, N,
3
8.56%. Found: C, 47.8; H, 4.0, N, 8.8%. Relevant IR bands
(cm-1): 3436(b), 1599(s), 1340(s), 1214(w), 1121(w), 1087(w),
1044(w), 802(w), 721(m).
[Ni3(AcO)4(dapdoH)2(H2O)2] H2O (3). A slurry of dapdoH2
3
(0.193 g, 1 mmol) was dissolved in 20 mL of distilled MeOH and
NEt3 (0.202 g, 2 mmol) together with Ni(AcO)2 4H2O (0.494 g,
3
2 mmol). The solution was stirred for a couple of hours, filtered
and crystallized layering with diethyl ether. Anal. Calcd for
C26H36N6Ni3O14 H2O (3): C, 36.70; H, 4.50, N, 9.88%. Found:
3
C, 35.3; H, 4.6, N, 9.5%. Relevant IR bands (cm-1): 3400(b),
1577(s), 1410(s), 1213(m), 1167(m), 1058(m), 809 (m), 661(m).
[Ni4(AcO)3(dapdo)(dapdoH)2(H2O)3](AcO) 3H2O (4). Dap-
3
doH2 (0.193 g, 1 mmol) and Ni(AcO)2 4H2O (0.494 g, 2 mmol)
3
Unit-cell parameters, structure, and refinement data are listed
in Table 1.
Plots for publication were generated with ORTEP3 for
were added to 20 mL of CH2Cl2 together with NEt3 (0.202 g,
2 mmol). The solution was stirred and after a couple of
hours, filtered and layered using hexane. Anal. Calcd for
Windows and plotted with Pov-Ray programs.33
C35H47N9Ni4O17 3H2O (4); C, 36.41; H, 4.63, N, 10.92%.
3
Found: C, 35.2; H, 4.8, N, 10.5%. Relevant IR bands (cm-1):
3396(b), 1572(s), 1517 (m), 1489(m), 1193 (m), 1167 (m), 1085
(m), 1060 (m), 811 (w), 715 (w), 669 (w).
Results and Discussion
Syntheses. There are several resemblances in the syn-
thetic preparation of compounds 1-4; however, the
chemistry behind suggests a more complex picture than
one may anticipate. This way, it was found that reactions
using Ni(acac)2 or Ni(tfacac)2 (tfacac = trifluoroacetyl-
acetonato) together with dapdoH2 always yielded com-
pound 1, even if different reagent ratios, pH, or solvents
were used. Basically, no examples of octahedral Ni com-
pounds were achieved using acac or derivative ligands as
starting materials. In contrast, compounds 2-4 could be
easily obtained with Ni(BzO)2 or Ni(AcO)2 salts, corres-
pondingly. Nevertheless, we may stress that all three
Physical Measurements. Magnetic susceptibility measure-
ments were carried out on polycrystalline samples with a
DSM5 Quantum Design susceptometer working in the range
30-300 K under magnetic fields of 0.3 T and under a field of
0.03T in the 30-2 K range to avoid saturation effects. Diamag-
netic corrections were estimated from Pascal Tables. Infrared
spectra (4000-400 cm-1) were recorded from KBr pellets on a
Bruker IFS-125 FT-IR spectrophotometer.
X-ray Crystallography. Data for compound 1 were collected
on a red block using a single-axis HUBER diffractometer on
station BM16 of the European Synchrotron Radiation Facility,
Grenoble, France. Cell refinement, data reduction and absorp-
tion corrections were done with HKL-2000 suite.27 The struc-
ture was solved by direct methods and the refinement and all
further calculations were carried out using SHELX-TL suite.28
All non-hydrogens were refined anisotropically. Hydrogens
were found in difference Fourier maps, placed geometrically
on their riding atom and refined with a riding model.
Data for compound 2 were collected on an orange plate on a
Bruker APEX II CCD diffractometer on Advanced Light
Source beamline 11.3.1 at Lawrence Berkeley National Labora-
tory, from a silicon 111 monochromator . The structure was
solved by direct methods and refined on F2.28 The crystal was
found to be twinned, although attempts at finding a twinning
ꢀ
complexes exhibit great dependency on other reactions
variables. Hence, compound 2 was obtained using MeOH
or 96% EtOH as solvents, and a small amount of H2O
in solution was mandatory. No compounds were iso-
lated using dry solvents. Also, of particular interest it is
the necessity of H2O molecules that do not react or
(29) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.
(30) Sheldrick, G. M., SHELXS-A Computer Program for Determination
€
€
of Crystal Structures; University of Gottingen: Gottingen, Germany, 1997.
(31) Sheldrick, G. M., SHELX97-A Computer Program for Determina-
tion of Crystal Structures; University of Gottingen: Germany, 1997.
€
(32) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(33) Ortep-3 for Windows: Farrugia, L. J. J. Appl. Crystallogr. 1997, 30,
565.
(27) Otwinowski, Z.; Minor, W. Methods in Enzymology: Macromole-
cular Crystallography, Part A; Carter, C.W., Jr., Sweet, R. M., Eds.; Academic
press: New York, 1997; Vol. 276, pp 307-326.
(28) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.

2262 Inorganic Chemistry, Vol. 49, No. 5, 2010
Escuer et al.
Table 1. Crystal Data and Structure Refinement for Compounds 1-4
(1)
(2)
(3)
(4)
formula
FW
space group
C18H18 N6Ni2O4
499.76
P21/c
8.319(2)
14.755(3)
7.123(2)
90
92.28(3)
90
873.6(4)
2
150
0.75150
1.900
2.780
0.0344
0.0958
C156H154 N24Ni12O53
3917.55
P212121
13.1697(9)
29.501(2)
44.867(3)
90
90
90
17432(2)
4
150
0.77490
1.489
1.355
0.0661
0.1537
C26H38 N6Ni3O16
846.72
Pca21
13.663(6)
14.994(4)
18.343(6)
90
90
90
3758(2)
4
C35H53 N9Ni4O20
1154.63
C2/c
17.9677(6)
17.4069(7)
35.032(1)
90
95.115(2)
90
10912.9(7)
8
100
0.71070
1.407
1.433
0.0496
0.1299
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
ss (deg)
γ (deg)
3
˚
V (A )
Z
T (K)
293(2)
0.71073
˚
λ(MoKR) (A)
F
calcd (g cm-3
)
μ(MoKR), mm-1
1.558
0.0746
0.2076
R
ωR2
deprotonated, but complete the octahedral coordination
of some of the metal ions of the clusters (2-4). Even more,
intramolecular hydrogen bonds between water molecules
among each other or with the rest of ligands in the
structure are responsible for the closure and stability of
the final compounds (see structural section). The nature
of the solvent is critical too, becoming evident if one
compares compounds 3 and 4. These two complexes were
obtained using identical reagents and ratios. However,
compound 3 was accomplished using a polar solvent,
MeOH, with some drops of H2O, whereas reactions in
CH2Cl2 led always to big crystals of compound 4.
Finally, experiments using sodium azide together with
H2dapdo were carried out in a further attempt to achieve
advance architectures. In contrast, the presence of azido
anions in solution under aerobic conditions gave system-
atically dark crystals of the already reported mono-
nuclear Ni(IV) complex containing two deprotonated
dapdo2- ligands, [Ni(dapdo)2].15
In this sense, it is remarkable the coordination behavior
of the deprotonated form dapdo2- bonded to Ni2þ
atoms. NiIV complexes derived from oximato anions are
well-known (e.g., [Ni(dapdo)2] and [Ni(dmg)3]2-, where
dmg2- stands for dimetylglioximato) and the stabiliza-
tion of their high oxidation state has been related to
strong spherical crystal fields, provided by the oximato
groups themselves.34 However, complexes 2-4 indicate
that coordination of only one dapdo2- ligand is not
enough to favor the oxidation of Ni2þ to Ni4þ while
always stabilizing the square planar environment around
the metallic centers.
Figure 1. Labeled Pov-Ray plot of complex 1. H atoms omitted for
clarity.
˚
Table 2. Selected Interatomic Distances (A) and Angles (deg) for Vompound 1
Ni(1)-N(1)
1.912(2)
1.817(2)
1.282(2)
82.47(7)
164.58(7)
90.58(7)
82.12(7)
173.02(7)
Ni(1)-N(3)
1.927(2)
1.832(1)
1.339(2)
104.84(7)
124.4(1)
129.6(1)
125.5(1)
Ni(1)-N(2)
Ni(1)-O(2a)
N(1)-O(1)
N(3)-O(2)
N(1)-Ni(1)-N(2)
N(1)-Ni(1)-N(3)
N(1)-Ni(1)-O(2a)
N(2)-Ni(1)-N(3)
N(2)-Ni(1)-O(2a)
N(3)-Ni(1)-O(2a)
Ni(1)-N(1)-O(1)
Ni(1)-N(3)-O(2)
Ni(1a)-O(2)-N(3)
dapdo2- ligand, being N(1)-Ni(1)-N(2) and N(2)-Ni-
(1)-N(3) (82.47(7)ꢀ and 82.12(7)ꢀ, respectively), lower
than the bond angles involving the oxygen atom
O(2a)-Ni1-N(1) and O(2a)-Ni1-N(3) (90.58(7) and
104.84(7)ꢀ, respectively).
Both dapdo2- ligands are totally deprotonated and sur-
prisingly, the noncoordinated oximato groups are neither
involved in coordination nor hydrogen bonding. The mole-
cule is practically planar with a slight distortion in the
Ni(1)-N(3)-O(2)-Ni(1a) torsion angle of 1.9(2)ꢀ. A sin-
gle weak intermolecular interaction is observed correspond-
ing to a π-π stacking of the pyridinic rings of neighboring
˚
molecules, with a distance between centroids of 3.721 A.
Description of the Structures. [Ni2(dapdo)2] (1). A
labeled plot of the neutral centrosymmetric dinuclear
units present in compound 1 is shown in Figure 1. Selected
bond parameters are listed in Table 2. The dinuclear units
consist of two nickel atoms linked by two oximato bridges
from two 2.10111 dapdo2- ligands. Each nickel atom
(Ni2þ, d8), is coordinated by three N atoms from one of
the dapdo2- ligands and one O-oximato atom from the
second dapdo2- ligand, providing a distorted square
planar environment. Bond distances lies in the 1.972(2)-
[Ni3(OH)(BzO)3(dapdo)(dapdoH2)(H2O)] 1.25H2O
3
(2). The asymmetric unit of compound 2 contains four
nonequivalent trinuclear units with similar core and bond
parameters. A labeled plot of one of these neutral tri-
nuclear units is shown in Figure 2. Selected bond para-
meters for this unit are also listed in Table 3. This
trinuclear compound combines one tetracoordinated
nickel atom Ni(2), in a distorted square-planar geometry,
with two hexacoordinated nickel atoms, Ni(1) and Ni(3),
connected together by a central μ3-OH group. Coordi-
nation sphere of Ni(2) is formed by the three N-atoms
from a 3.11111 dapdo2- ligand and the central hydroxo
ligand. Each oximato group of this deprotonated dapdo2-
links a second Ni2þ ion giving Ni(2)-N(5)-(O4)-Ni(1)
˚
1.817(2) A range and the bond angles around the nickel
atoms deviates from 90ꢀ due to the low bit angle of the
(34) Baucom, E. I.; Drago, R. S. J. Am. Chem. Soc. 1971, 93, 6469.

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2263
Figure 3. Labeled Pov-Ray plot of complex 3.
˚
Table 4. Selected Interatomic Distances (A) and Angles (deg) for Compound 3
Ni(1)-N(4)
1.996(8)
2.056(8)
2.201(8)
2.075(6)
2.084(6)
2.159(6)
1.998(8)
2.004(8)
2.197(9)
1.335(10)
1.295(11)
124.8(5)
126.1(5)
103.5(3)
Ni(1)-O(8)
2.053(6)
2.058(6)
2.127(6)
2.087(6)
2.182(6)
2.075(6)
2.017(6)
2.061(6)
2.152(6)
1.362(13)
1.316(11)
112.3(4)
111.5(4)
105.1(3)
Ni(1)-N(5)
Ni(1)-O(9)
Ni(1)-N(6)
Ni(1)-O(14)
Ni(2)-O(7)
Ni(2)-O(9)
Ni(2)-O(11)
Ni(3)-O(3)
Ni(3)-O(5)
Ni(3)-O(13)
N(3)-O(2)
N(6)-O(12)
Ni(2)-O(11)-N(5)
Ni(2)-O(1)-N(2)
Ni(2)-O(5)-Ni(3)
Figure 2. Labeled Pov-Ray plot of complex2. Ni atoms in octahedral or
square planar environment are plotted in green and orange color in that
order. Aromatic rings of the benzoate ligands and protons other than the
NOH groups are omitted for clarity.
Ni(2)-O(1)
Ni(2)-O(4)
Ni(2)-O(5)
Ni(3)-N(1)
Ni(3)-N(2)
˚
Table 3. Selected Interatomic Distances (A) and Angles (deg) for Compound 2
Ni(3)-N(3)
N(2)-O(1)
Ni(1)-N(1)
1.993(6)
2.141(6)
2.184(5)
1.779(6)
1.868(6)
2.064(5)
2.111(5)
2.037(5)
1.391(7)
1.320(7)
114.0(4)
108.7(4)
113.7(2)
123.6(2)
105.4(2)
Ni(1)-O(1)
2.001(5)
2.091(5)
2.042(5)
1.862(6)
1.859(5)
2.043(4)
2.108(4)
2.099(5)
1.394(8)
1.319(8)
122.7(4)
122.0(4)
N(5)-O(11)
Ni(1)-N(5)-O(11)
Ni(3)-N(2)-O(1)
Ni(1)-O(9)-Ni(2)
Ni(1)-N(2)
Ni(1)-O(4)
Ni(1)-N(3)
Ni(1)-O(6)
Ni(2)-N(4)
Ni(2)-N(6)
Ni(2)-O(1)
Ni(2)-N(5)
Ni(3)-O(1)
Ni(3)-O(8)
Ni(3)-O(5)
Ni(3)-O(10)
Ni(3)-O(12)
N(3)-O(3)
˚
of the terminal benzoates, >3.90 A, may be pointed as
Ni(3)-O(7)
weak π-π stacking.
Ni3(AcO)4(dapdoH)2(H2O)2] H2O (3). A labeled plot
N(2)-O(2)
N(5)-O(4)
N(6)-O(5)
Ni(2)-N(5)-O(4)
Ni(2)-N(6)-O(5)
3
Ni(1)-O(4)-N(5)
Ni(3)-O(5)-N(6)
Ni(1)-O(1)-Ni(2)
Ni(1)-O(1)-Ni(3)
Ni(2)-O(1)-Ni(3)
of the neutral trinuclear unit of 3 is depicted in Figure 3
and selected bond parameters are listed in Table 4. This
linear compound contains three hexacoordinated nickel
atoms, bounded to a total of two 2.10111 dapdoH-
molecules, four bridging acetate anions, and two water
molecules.
and Ni(2)-N(6)-(O5)-Ni(3) bridges with torsion angles
of 15.5 and 27.1ꢀ, respectively.
The core of 2 is highly asymmetrical, because of the two
hexacoordinated Ni2þ atoms organize differently: coor-
dination sphere of Ni(1) is completed with three N-atoms
from one 1.00111 dapdoH2 and one O-atom from one
DapdoH- molecules act as terminal ligands, capping
terminal Ni(1) and Ni(3) centers by binding them through
their three nitrogen atoms, respectively. The central
nickel atom is coordinated to one deprotonated O-
oximato of each dapdoH-. At the same time, two brid-
ging acetate anions, in η1,μ-AcO and η2,μ-AcO modes,
connect Ni(2) with each Ni(1) and Ni(3) metallic centers.
Finally, there are two water molecules that complete the
coordination sphere of Ni(1) and Ni(3), respectively.
syn-syn benzoate ligand (with a Ni(1)-O(6) O(7)-
3 3 3
Ni(3) torsion angle of 46.8ꢀ); meanwhile, Ni(3) coordi-
nates two additional monocoordinated benzoate groups
and completes the octahedral environment with a mole-
cule of water. N-M-N bond angles for dapdo2- and
dapdoH2 ligands are strongly modified by deprotonation
and O-coordination: N(4)-Ni(2)-N(5) and N(4)-Ni-
(2)-N(6) (83.4(3) and 83.4(3)ꢀ, respectively) are consid-
erably higher than N(1)-Ni(1)-N(2) and N(1)-Ni-
(1)-N(3) (76.1(2) and 76.3(2)ꢀ, in that order). Bond
angles involving the hydroxo ligand are also highly
asymmetric: (Ni(1)-O(1)-Ni(2), Ni(2)-O(1)-Ni(3) Ni-
(1)-O(1)-Ni(3) bond angles are 113.7(2), 105.4(2), and
123.6(2)ꢀ) giving an irregular triangle which distances:
Ni(1) Ni(2), Ni(2) Ni(3), and Ni(1) Ni(3) are
˚
Four Ni-N distances close to 2 A corresponds to the
bonds with the pyridinic rings (N(4)-Ni(1) and N(1)-
Ni(3)) and the deprotonated oximato group (N(5)-Ni(1)
and N(2)-Ni(3)) whereas two larger bond distances close
˚
to 2.2 A involve the links with the protonated oxime
groups (N(6)-Ni(1) and N(3)-Ni(3)). Ni-O distances
˚
range between 2.017 and 2.182 A. N-Ni-N bond angles
ranged between 74.7 and 80.8ꢀ because of the low bite
of the dapdoH- ligands. At last, N-O-Ni angles
are 112.1(4)ꢀ for N(5)-O(11)-Ni(2) and 111.77(4)ꢀ
for N(2)-O(1)-Ni(2). The molecule deviates from pla-
narity, with the Ni(1)-N(5)-O(11)-Ni(2) and Ni(3)-
N(2)-O(1)-Ni(2) torsion angles being slightly greater
than 20ꢀ.
3 3 3
3 3 3
3 3 3
3.232, 3.124, and 3.583, respectively. Overall, Ni-N
2-
˚
distances lie in a 1.779(6)-1.868(6) A range for dapdo
whereas they remain between 1.993(5) and 2.184(5) A in
,
˚
the case of dapdoH2. Ni-O distances lies in a shorter
range comprised between 2.001 and 2.111 A.
The orientation and distance between the centroids of
[Ni4(AcO)3(dapdo)(dapdoH)2(H2O)3](AcO) 3H2O (4).
3
˚
Figure 4 shows the labeled plot of the cationic tetra-
nuclear structure of this compound. Selected bond para-
meters are listed in Table 5. The core of 4 consists of one
the pyridinic ring of dapdo2- and the benzylic ring of one

2264 Inorganic Chemistry, Vol. 49, No. 5, 2010
Escuer et al.
It is remarkable that the fragment Ni(2)/Ni(4) in which
the two metallic ions are linked by one syn-syn and one
monocoordinated carboxylates (together with one oxi-
mato bridge from the dapdoH- ligand coordinated to
Ni(4)) is identical to the Ni(2)/Ni(1) or Ni(2)/Ni(3) frag-
ments in compound 3, with bonds parameters very similar
too, more details in Tables 4 and 5.
H-Bond Role. Structurally, two aspects make
complexes 2 - 4 unanticipated: locally, the variety of
ligands attached to each octahedral Ni2þ ion and, in a
more global sense, the noteworthy, high asymmetry
of the final structures. All three compounds present as
common traits protonated oxime groups from dapdoH2
and/or dapdoH- ligands, coordinated H2O molecules
and noncoordinated O-atoms from monodentate carboxy-
lato groups. Detailed analysis of these fragments reveals
their noninnocent role, where the arrangement of such
units is led by sets of strong, intramolecular H-bonds
that contribute to stabilize the structures. Thus, the
necessity of water in the reaction media to obtain the
reported complexes can be now understood. Besides,
additional crystallization water molecules provide a
number of intermolecular H-bonds among the clusters
generating extended networks in the crystals. Intramo-
lecular H-bonds for compounds 2-4 are summarized
in Table S1 in the Supporting Information (includ-
ing one relevant crystallization water molecule for
3 and the carboxylate anion in 4). A view of these H
bonds within the core of these compounds is shown in
Figure 5.
Figure 4. Labeled Pov-Ray plot of complex 4. Ni atoms in octahedral
and square planar environments are plotted in green and orange colors,
respectively.
˚
Table 5. Selected Interatomic Distances (A) and Angles (deg) for Compound 4
Ni(1)-N(5)
1.819(3)
1.885(3)
2.023(3)
2.115(3)
2.012(3)
1.984(3)
2.085(3)
2.048(3)
1.985(4)
2.038(3)
2.117(4)
1.314(4)
1.367(4)
1.333(4)
124.3(2)
127.9(2)
124.9(2)
Ni(1)-N(7)
1.931(3)
1.869(3)
2.052(3)
2.088(3)
2.052(3)
2.069(3)
2.018(3)
2.144(3)
2.044(3)
2.110(3)
2.045(3)
1.348(4)
1.387(4)
1.394(6)
114.2(2)
110.2(2)
113.2(2)
115.9(2)
124.3(2)
104.2(1)
Ni(1)-N(6)
Ni(1)-O(52)
Ni(2)-O(51)
Ni(2)-O(52)
Ni(2)-O(54)
Ni(3)-N(8)
Ni(2)-O(57)
Ni(2)-O(61)
Ni(2)-O(68)
Ni(3)-O(50)
Ni(3)-N(9)
Ni(3)-O(59)
Ni(3)-N(10)
Ni(4)-N(11)
Ni(4)-N(12)
Ni(4)-N(13)
N(6)-O(51)
Ni(3)-O(69)
Ni(4)-O(56)
Ni(4)-O(58)
Ni(4)-O(61)
N(7)-O(50)
N(9)-O(53)
N(10)-O(52)
In compound 2 (Figure 5, top), H atoms from the
protonated dapdoH2 ligand, the central OH- group and
the coordinated molecule of water form a set of H-bonds
with O-atoms from the monocoordinated benzoate li-
gands. This way, benzoate O(9) atom interacts with
protonated O(1)-hydroxo and O(3)-oxime atoms, O(10)-
benzoate interacts with O(2)-oxime atom, and finally
O(12) from the coordinated water molecule interact with
O(11)-benzoate atom.
N(12)-O(54)
Ni(1)-N(6)-O(51)
Ni(1)-N(7)-O(50)
Ni(3)-N(10)-O(52)
N(13)-O(55)
Ni(2)-O(51)-N(6)
Ni(3)-O(50)-N(7)
Ni(1)-O(52)-N(10)
Ni(2)-O(52)-N(10)
Ni(4)-N(12)-O(54)
Ni(2)-O(61)-Ni(4)
Ni(2)-O(54)-N(12)
Ni(1)-O(52)-Ni(2)
110.6(2)
110.3(1)
tetracoordinated nickel atom, Ni(1), and three hexacoor-
dinated nickel centers, Ni(2)-Ni(4). Ni(1) environment
consist of three N-atoms from one 3.11111 dapdo2-
ligand and one O-oximate bridging atom from one ex-
hibiting a distorted square-planar geometry. The depro-
tonated oximato groups connect Ni(1) with Ni(2) and
Ni(3) in a similar fashion of Ni(2) in complex 3. Ni(3) is
bounded to the three N-atoms of one dapdoH- ligand
that displays the novel 3.20111 coordination mode
(unprecedented until now), one bridging O-oximato
atom, one monocoordinated acetate group, and one
water molecule, giving octahedral environment. This
dapdoH- ligand assist as a link among Ni(1), Ni(2) and
Ni(3). A second dapdoH- ligand exhibiting a 2.10111
coordination mode, is found to be coordinated to Ni(4)
by their three N-atoms. Again, the deprotonated O-
oximato attaches Ni(2) and Ni(4) and the octahedral
environment of both metals is completed by the coordi-
nation of two AcO- ligands in a η1,μ-AcO and η2,μ-AcO
way and two molecules of water, correspondingly.
Similarly, in compound 3 (Figure 5, middle), H-atoms
from the protonated oximato groups form strong intra-
molecular H-bonds with the noncoordinated O-atoms of
the η1,μ-AcO ligands (O(2) O(6) and O(10) O(12)
3 3 3
3 3 3
interactions). In addition, crystallization water molecules
are placed between the O-carboxylato atoms coordinated
to Ni(2) and coordinated water molecules providing
further H-bonds, O(13) O1w O(7) and O(14)
3 3 3
3 3 3
3 3 3
O2w O(4).
3 3 3
In the case of compound 4, H-atoms from the proto-
nated oximato groups and coordinated water molecules
form a set of intramolecular H-bonds that involve the
O-atoms from coordinated and anionic carboxylates.
Here, the protonated oximato groups form H-bonds with
the noncoordinated O-atoms of the η1,μ-AcO ligands
(O(55) O(62) and O(53) O(60), respectively). Also,
3 3 3
3 3 3
one of the coordinated water molecules interacts in a
similar way with the O-atom from the carboxylato co-
ordinated to Ni(3), O(59) O(68). The three coordi-
˚
Ni-N and Ni-O distances lie in the 1.819-2.144 A
3 3 3
range, where the shortest correspond to the square planar
Ni(1). As it was found in previous compounds, N-Ni-N
angles are clearly lower than 90ꢀ lying between
75.3-82.4ꢀ, corresponding to the largest observed with
deprotonated dapdo2- ligand.
nated water molecules form strong H-bonds with the
anionic acetate molecule, O(63) O(58), O(63) O-
(68), and O(64) O(69), folding the molecule. One of
3 3 3
3 3 3
3 3 3
the crystallization water molecules joins one deproto-
nated oximato groups and one monodentate carboxylato

Article
Inorganic Chemistry, Vol. 49, No. 5, 2010 2265
in square planar environment, is diamagnetic. Com-
pound 2 behaves magnetically as a dinuclear system and
therefore the fitting of the experimental data was per-
formed by means of the conventional equation derived
from the Hamiltonian
H ¼ -JðS1S3Þ
for two local S=1 spin centers including an intermole-
cular interaction parameter zJ0. The subindexes of the
local Sn spins along this section refer to the numbers of the
corresponding structures. Best fit parameters were J =
þ2.16(7) cm-1, zJ0 = -0.87(1) K, and g = 2.141(2). In
good agreement with the above results, magnetization
experiments show a magnetization plot that reaches a
nonsaturated value 3.3 electrons under an external field of
5 T with an increase versus field lower than the expected
for the Brillouin plot for two isolated S=1 centers.
Compound 3 exhibits a room temperature value of 3.43
cm3 K mol-1 which decreases down to 0.82 at 2 K. The
χMT plot shows a plateau around 1.15 cm3 K mol-1 and
between 5 and 13 K. Analysis of the magnetic data of
compound 3 was performed by means of analytical
expression derived from the Hamiltonian
H ¼ -JðS1S2 þ S2S3Þ
which corresponds to a symmetric linear arrangement of
three paramagnetic centers where the interaction between
the terminal spin carriers have been neglected. Best fit
parameters were J=-18.8(2) cm-1, zJ0=-0.90(3) cm-1
,
Figure 5. From top to bottom, partially labeled plots of the intramole-
cular H-bonds for compounds 2-4, in that order. H-atoms not involved
in H-bonds, Me groups, aromatic benzoate rings, and parentheses of the
labels has been omitted for clarity.
and g=2.233(3). Magnetization plot shows a Brillouin
shape behavior supporting the idea of having two elec-
trons as can be expected for a well isolated S=1 ground
state.
Tetranuclear compound 4 contains one square planar
nickel atom and therefore can be analyzed as a trinuclear
system. Room temperature χMT value is 3.41 cm3 K
mol-1, which decreases gradually upon cooling, reaching
0.73 cm3 K mol-1 at 2 K. As it occurred in the previous
compound, a change in the slope of χMT plot at values
slightly greater than the expected for an S=1 ground state
was observed.
In this case, structural data reveals different kind of
bridges between the paramagnetic centers of com-
pound 4 and then the experimental χMT plot was
analyzed by means CLUMAG program35 on the two-J
Hamiltonian
Figure 6. Plot of the χMT product vs T for compounds 2 (squares), 3
(diamonds), and 4 (dot centered circles).
H ¼ -J1ðS2S4Þ -J2ðS2S3Þ
ligand as well, giving as a result weaker interactions,
O(67) O(51) and O(67) O(57).
Best-fit parameters were J1=-16.7 cm-1, J2=1.16 cm-1
,
3 3 3
3 3 3
and g=2.17. As described above, the Ni(2)/Ni(4) frag-
ment of compound 4 is structurally similar to the one
found in 3. Therefore, J1 could be related to the exchange
parameter of 18.8 cm-1 found for 3 and be assigned to the
Ni(2)-Ni(4) interaction, whereas the weak interaction J2
could be related to the single, high torsioned, oximato
bridge between Ni(2) and Ni(3). Likewise for compound
3, here magnetization at 5 T tends to a nonsaturated value
associated to two electrons.
Magnetic Measurements and Fit Procedure. Diamag-
netic response at room temperature was found for com-
pound 1, in agreement with the expected results for a
cluster containing Ni2þ centers with square planar envir-
onments. χMT product vs T for compounds 2-4 are
plotted in Figure 6. Compound 2 shows a χMT value
nearly constant between 300 and 14 K with a maximum
value of 2.32 cm3 K mol-1 at 30 K. At low temperature,
χMT value decreases down to 1.43 cm3 K mol-1. These
room-temperature values are also consistent with the
structural data that indicate that one of the nickel atoms,
(35) Gatteschi, D.; Pardi, L. Gazz. Chim. Ital. 1993, 123, 231.

2266 Inorganic Chemistry, Vol. 49, No. 5, 2010
Escuer et al.
Conclusions
clusters and new topologies as well as the possibility of
achieving octahedral and square planar coordinations
around the metallic ions with the use of this ligand. This
concept directly affects the magnetic results because square
planar coordination around the Ni decreases the total mag-
netic spin diminishing the superexchange pathways inside the
clusters. From a magnetic point of view, this is indeed a
limitation in the search of Ni clusters with high spin numbers.
Therefore, synthetic strategies should avoid fully deprotona-
tion of the ligand to prevent under aerobic conditions, easy
oxidation to NiIV or square planar coordination.
In the present work, we have reported the results obtained
using ligand dapdoH2 together with different nickel salts as
precursors. Earlier work with pyridyl monooximato ligands,
suggested the possibility of having the neutral ligand,
dapdoH2, or its deprotonated anionic forms, dapdoH- and
dapdo2-, coordinated to Ni centers. The latest, dapdo2-
,
contains two deprotonated oximato groups conferring the
ligand with the capability of increasing the nuclearity and
therefore complexity of the final compounds (fact previously
observed with manganese). Compounds 1-4 are the first
examples that corroborate that this is also possible with Ni.
From all the above, one of the most relevant results in this
preliminary work is the finding of a novel coordination mode
for dapdoH-, 3.20111, which coordinates three Ni2þ units,
arrangement that was unknown in the chemistry of this
dioxime ligand. In addition, another important aspect is
the tendency of dapdo2- to force square planar coordination
around Ni2þ ions, a trait that appears in three of the
four compounds described in this paper: 1, 2, and 4. We
would also like to stress the capacity of dapdoH2/dapdoH-/
dapdo2- to coordinate with Ni, providing high nuclearity
Acknowledgment. This work was supported by the
CICYT Projects CTQ2009-07264. We acknowledge pro-
vision of time at the Advanced Light Source, which is
supported by the Director, Office of Science, Office of
Basic Energy Sciences of the U.S. Department of Energy
under Contract DE-AC02-05CH11231.
Supporting Information Available:
H-bond parameters
(PDF); crystallographic data files for complexes 1-4 (CIF).
This material is available free of charge via the Internet at http://
pubs.acs.org.