Design and synthesis of a new binucleating ligand via cobalt-promoted C-N bond fusion reaction. Ligand isolation and its coordination to nickel, palladium, and platinum

Article abstract of DOI:10.1021/ic034313h

A new polydentate bridging ligand, NH₄C₅N=NC ₆H₄N(H)C₅H₄N (HL²), is synthesized by the cobalt-mediated phenyl ring amination of coordinated NH ₄C₅N=NC₆H₅. The green cobalt complex intermediate [Co(L²)2](ClO₄), [1](ClO ₄), and the free ligand HL² were isolated and characterized. The X-ray structure of [H₂L²](ClO ₄) is reported. The ligand, upon deprotonation, behaves as a bridging ligand. It reacts with NiCl₂·6H₂O and Na₂[PdCl₄] to produce dimetallic complexes, [Ni ₂Cl₂(L²)₂], 2, and [Pd ₂(L²)₂](ClO₄)₂, [3](ClO₄)₂, respectively. X-ray structures of these two dimetallic complexes are reported. The structure of the dinickel complex, in particular, is unique. In this complex, the two deprotonated secondary amine nitrogens of the two [L²]^- ligands bind to two nickel centers simultaneously forming a planar Ni₂N₂ arrangement. The complex [3] (ClO₄)₂ is diamagnetic while the complex 2 is paramagnetic. The results of magnetic measurements on the dinickel complex in the temperature range 1.8-300 K are reported. The system can be described as a single spin S = 2 in the low-temperature range T ? J/k whereas at high temperatures, T ? J/k, it behaves as two independent spins S = 1. The reaction of [L²]^- with K₂[PtCl₄], however, yielded a monometallic platinum complex, [PtCl₃(L ²)], 5, where the pyridyl nitrogen of the aminopyridyl function remained unused. The X-ray structure of the complex 4a is reported. The bond lengths along the ligand backbones in all the complexes indicate extensive π-delocalization. Spectral data of the complexes are reported and compared.

Full text of DOI:10.1021/ic034313h

Inorg. Chem. 2003, 42, 5367−5375
Design and Synthesis of a New Binucleating Ligand via
Cobalt-Promoted C−N Bond Fusion Reaction. Ligand Isolation and Its
Coordination to Nickel, Palladium, and Platinum
Kunal K. Kamar,† Srijit Das,† Chen-Hsiung Hung,‡ Alfonso Castin˜eiras,§ Michael D. Kuz’min,|
,†
Conrado Rillo,| Juan Bartolome´,| and Sreebrata Goswami*
Department of Inorganic Chemistry, Indian Association for the CultiVation of Science,
Kolkata 700 032, India, Department of Chemistry, National Changhua UniVersity of Education,
Changhua, Taiwan 500, Republic of China, Departamento de Qu´ımica Inorga´nica, UniVersidade
de Santiago de Compostela, Campus UniVersitario Sur, E-15782 Santiago de Compostela, Spain,
and Instituto de Ciencia de Materiales de Arago´n, CSICsUniVersidad de Zaragoza,
50009 Zaragoza, Spain
Received March 24, 2003
A new polydentate bridging ligand, NH C NdNC H N(H)C H N (HL2), is synthesized by the cobalt-mediated phenyl
4
5
6
4
5 4
ring amination of coordinated NH C NdNC H . The green cobalt complex intermediate [Co(L2)2](ClO ), [1](ClO ),
4
5
6
5
4
4
and the free ligand HL2 were isolated and characterized. The X-ray structure of [H L2](ClO ) is reported. The
2
4
ligand, upon deprotonation, behaves as a bridging ligand. It reacts with NiCl2‚6H O and Na2[PdCl4] to produce
2
dimetallic complexes, [Ni2Cl2(L2)2], 2, and [Pd2(L2)2](ClO ) , [3](ClO ) , respectively. X-ray structures of these two
4 2
4 2
dimetallic complexes are reported. The structure of the dinickel complex, in particular, is unique. In this complex,
the two deprotonated secondary amine nitrogens of the two [L2]- ligands bind to two nickel centers simultaneously
forming a planar Ni2N arrangement. The complex [3](ClO ) is diamagnetic while the complex 2 is paramagnetic.
2
4 2
The results of magnetic measurements on the dinickel complex in the temperature range 1.8−300 K are reported.
The system can be described as a single spin S ) 2 in the low-temperature range T , J/k whereas at high
temperatures, T . J/k, it behaves as two independent spins S ) 1.The reaction of [L2]- with K [PtCl4], however,
2
yielded a monometallic platinum complex, [PtCl3(L2)], 5, where the pyridyl nitrogen of the aminopyridyl function
remained unused. The X-ray structure of the complex 4a is reported. The bond lengths along the ligand backbones
in all the complexes indicate extensive π-delocalization. Spectral data of the complexes are reported and compared.
Chart 1
Introduction
The ability of the 2-aminopyridine functionality to serve
as a three-atom bridge has long been known.1 This can hold
metal atoms in proximity (Chart 1). Using this binding mode
of 2-aminopyridine many interesting di- and polymetallic
complexes have been synthesized. It is now known that this
type of bridging ligand can hold the metal ions in close
* Corresponding author. E-mail: icsg@mahendra.iacs.res.in. Fax: + 91
33 2473 2805.
proximity with flexible separation, providing a suitable
platform for coordination environments for intermetallic
interactions.
In the recent past we have been working on the coordina-
tion chemistry of a tridentate N,N,N-donor, HL1, which has
some novel features. For example, the conjugate base of HL1
stabilizes2,3 uncommon entities like low-spin states of man-
† Indian Association for the Cultivation of Science.
‡ National Changhua University of Education.
§ Universidade de Santiago de Compostela.
| CSICsUniversidad de Zaragoza.
(1) (a) Chakravarty, A. R.; Cotton, F. A.; Tocher, D. A. Organometallics
1985, 4, 863. (b) Chakravarty, A. R.; Cotton, F. A.; Falvello, L. R.
Inorg. Chem. 1986, 25, 214. (c) Chakravarty, A. R.; Cotton, F. A.
Inorg. Chim. Acta 1986, 113, 19.
10.1021/ic034313h CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/22/2003
Inorganic Chemistry, Vol. 42, No. 17, 2003 5367

Kamar et al.
Chart 2
ganese(II), iron(II), and iron(III) in the complexes. A few
interesting ruthenium, osmium, and rhodium complexes have
also been noted4-6 by us. The compounds of this ligand
system in general display rich spectral and redox properties,
which originate from strong delocalization of electronic
charge along the ligand backbone. In the context of develop-
ing new materials that are suitable for efficient redox
processes, such redox noninnocent ligands often play a
crucial role. In its known complexes, the ligand anion [L1]-
acts as a bis-chelating ligand, which forms monometallic
complexes as shown in Chart 1.
Synthesis of the ligand HL1 was achieved2,7 using cobalt-
mediated amination reaction of coordinated 2-(phenylazo)-
pyridine (pap) ligand. The above transformation is regio-
selective and occurs smoothly in neat amine. With this
background information, we thought it worthwhile to ex-
amine the amination reaction on coordinated pap ligand using
2-aminopyridine as the reagent. It was anticipated that fusion
of the 2-aminopyridine residue to the ortho carbon of the
phenyl ring of pap would produce a new ligand HL2. This
ligand is similar to HL1 in all respects except that it has an
additional pyridine N donor site for coordination. It was
hoped that the additional pyridyl function of HL2 would bind
to a second metal ion. Thus a bimetallic coordination of [L2]-
may be anticipated (Chart 2).
In this paper we report the synthesis of the new bridging
ligand HL2 following amination reaction of coordinated pap
ligand in a cobalt(II) complex. Its conjugate base [L2]- indeed
acts as a bridge across the two metal ions. In addition to its
bridging capability, the ligand also acts as a bis-chelating
tridentate N-donor, which is used to satisfy the coordination
number of the metal ions. Recently we have observed8 that
this ligand forms stable complexes with d10-metal ions, which
absorb at unusually long wavelengths (ca. 600 nm). The
coordination chemistry of the extended ligand [L2]- involving
nickel, palladium, and platinum is compared in this work.
Figure 1. An ORTEP plot and atom-numbering scheme for [H2L2]+ in
[H2L2](ClO4).
molten 2-aminopyridine (H2NPy) on a steam bath to produce
an intense green cobalt(III) complex, [Co(L2)2]+, [1]+, which
was isolated as its perchlorate salt in 60% yield. Reduction
of the cobalt complex by dilute hydrazine followed by
removal of cobalt(II) as CoS produced the orange HL2 in
70% yield. The synthetic reactions are shown in Scheme 1.
Scheme 1
The green diamagnetic cobalt(III) compound is a 1:1
1
electrolyte in acetonitrile and shows a highly resolved H
NMR spectrum. All twelve resonances in its spectrum were
visible (Supporting Information, Figure S1). Notably each
kind of proton in the complex, [1]+, of the anionic ligand
[L2]- gave rise to one signal. Thus the two ligands in it are
magnetically equivalent, indicating the presence of a 2-fold
symmetry axis. Its analytical data are in complete agreement
with its formulation. Selected spectral data are collected in
Table 1. These are similar8 to those of the analogous [Co-
(L1)2]+ complex. The orange ligand HL2 was obtained as a
crystalline solid which melts at 90 °C. Its FAB mass spec-
trum showed an intense peak at m/z 276 confirming its
formulation. The ligand dissociates the amine proton easily
(pKa ) 8.6 ( 0.1). Its acidity is comparable2 to that of HL1.
The ligand HL2, though crystalline, did not produce X-ray
quality crystals. However, the perchlorate salt of its conjugate
acid, [H2L2]+, formed good crystals for its X-ray structure
determination. Figure 1 shows the ORTEP plot of [H2L2]+,
and its bond parameters are collected in Table 2. This indeed
confirms the formation of HL2 from the cobalt-promoted
C-N fusion reaction as shown in Scheme 1. In this
compound only one of the two pyridyl nitrogens, viz., the
aminopyridyl function, is protonated. The N-N distance in
it is 1.246(3) Å, confirming10 its double-bond character. The
rest of the bond lengths are normal.
Results and Discussion
A. Ligand Synthesis and Its Structure. The brown
cationic tris-chelate, [Co(pap)3]2+, reacts9 smoothly with
(2) Saha, A.; Majumdar, P.; Goswami, S. J. Chem. Soc., Dalton Trans.
2000, 1703.
(3) Saha, A.; Majumdar, P.; Peng, S.-M.; Goswami, S. Eur. J. Inorg.
Chem. 2000, 2631.
(4) Das, C.; Ghosh, A. K.; Hung, C.-H.; Lee, G.-H.; Peng, S.-M.;
Goswami, S. Inorg. Chem. 2002, 41, 7125.
(5) Das, C.; Peng, S.-M.; Lee, G.-H.; Goswami, S. New J. Chem. 2002,
26, 222.
B. Dinickel Complex. We recently have reported3 the
synthesis and properties of the monometallic [Ni(L1)2]
(6) Das, C.; Saha. A.; Hung, C.-H.; Lee, G.-H.; Peng, S.-M.; Goswami,
S. Inorg. Chem. 2003, 42, 198.
(7) Saha, A.; Ghosh, A. K.; Majumdar, P.; Mitra, K. N.; Mondal, S.; Rajak,
K. K.; Falvello, L. R.; Goswami, S. Organometallics 1999, 18, 3772.
(8) Das, S.; Hung, C.-H.; Goswami, S. Inorg. Chem., in press.
(9) Mahapatra, A. K. Ph.D. Thesis, Jadavpur University, Calcutta, India,
1986.
(10) Saha, A.; Das, C.; Peng, S.-M.; Goswami, S. Indian J. Chem., Sect.
A 2001, 40A, 198.
5368 Inorganic Chemistry, Vol. 42, No. 17, 2003

A New Binucleating Ligand
Table 1. Optical Spectral Data
c
IR (ν, cm-1
ν(NdN)
1370
)
a
compound
λ
max/nm (ꢀ/ M-1 cm-1
)
ν(CdN)
ν(ClO4)-
[1](ClO4)
860 (8535), 775 (11665), 705 (10965), 655 (8285), 400 (18865),
290b (29580), 240 (49530)
450 (5330), 312 (14550), 275 (19025)
1585
1075, 610
HL2
2
[3](ClO4)2
4a
1595
1605
1599
1606
1450
1385
1384
1377
590 (9855), 350 (25610), 280 (36540), 250 (35930)
905 (7055), 825 (8060), 430b (9235), 330 (28220), 230 (43925)
1065 (3030), 930 (6090), 835 (6105), 740 (3825), 460b (4420),
380b (10260), 350 (17795), 235 (27785)
1087, 627
4b
5
1060 (2420), 930 (4630), 840 (4700), 745 (3040), 455b (3950),
380b (8205), 350 (14040), 235 (22220)
1602
1599
1600
1597
1384
1380
1385
1384
1170 (2015), 1020 (3585), 900 (3135), 810 (1900), 470b (7510),
355 (16875), 280 (19985)
6a
6b
1240 (1430), 1055 (2815), 895 (3425), 795 (3550), 715 (2615),
655 (1505), 470b (6710), 355 (13960), 275 (27540)
1245 (1440), 1060 (2735), 915 (3230), 800 (3255), 725 (2445),
660 (1460), 475b (6275), 355 (13375), 265 (19545)
a Solvent, acetonitrile for the compounds [1](ClO4), HL2, 2, [3](ClO4), and 4 and dimethylformamide for the compounds 5 and 6. b Shoulder. c In
KBr disk.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) of [H2L2](ClO4), 2‚H2O, [3](ClO4)2‚H2O, 4a, and 5
[H2L2](ClO4)
C(6)-C(11)
N(3)-C(11)
N(3)-N(4)
N(1)-C(5)
N(2)-C(5)
N(2)-C(6)
1.335(4)
1.350(4)
1.406(4)
1.400(4)
1.413(4)
1.246(3)
N(4)-C(12)
N(5)-C(12)
1.427(4)
1.336(4)
[Ni2Cl2(L2)2]‚H2O, 2‚H2O
Ni(1)-N(14)
Ni(1)-N(34)
Ni(2)-N(14)
Ni(2)-N(34)
Ni(1)-N(35)
2.094(3)
2.277(3)
2.277(3)
2.103(3)
2.056(3)
Ni(1)-N(11)
Ni(1)-N(13)
Ni(1)-Cl(1)
N(11)-C(15)
N(12)-C(15)
2.099(4)
1.996(3)
2.3482(12)
1.347(5)
1.423(6)
N(12)-N(13)
N(13)-C(16)
N(14)-C(21)
N(14)-C(22)
N(15)-C(22)
1.271(5)
1.404(6)
1.379(5)
1.392(5)
1.343(5)
Ni(1)-N(14)-Ni(2)
93.32(12)
Ni(1)-N(34)-Ni(2)
93.09(12)
[Pd2(L2)2](ClO4)2‚H2O, [3](ClO4)2‚H2O
Pd(1)-N(1)
Pd(1)-N(3)
Pd(1)-N(4)
Pd(1)-N(10)
N(1)-C(5)
N(2)-C(5)
N(2)-N(3)
N(3)-C(6)
1.992(7)
1.916(6)
1.967(6)
2.012(7)
1.363(10)
1.390(9)
1.277(7)
1.379(8)
C(6)-C(11)
N(4)-C(11)
N(4)-C(12)
Pd(2)-N(6)
Pd(2)-N(8)
Pd(2)-N(9)
Pd(2)-N(5)
N(6)-C(21)
1.427(10)
1.343(9)
1.370(10)
2.024(7)
1.919(7)
1.999(7)
2.044(7)
1.364(10)
N(7)-C(21)
N(7)-N(8)
N(8)-C(22)
C(22)-C(27)
N(9)-C(27)
N(9)-C(28)
1.410(9)
1.288(8)
1.396(9)
1.435(11)
1.344(10)
1.366(11)
N(1)-Pd(1)-N(3)
N(8)-Pd(2)-N(9)
78.6(3)
82.9(4)
N(3)-Pd(1)-N(4)
N(6)-Pd(2)-N(8)
81.6(2)
78.8(3)
[PdCl(L1a)], 4a
N(1)-C(11)
C(6)-C(11)
N(2)-C(6)
Pd(1)-N(1)
2.029(3)
1.930(3)
2.029(3)
2.3031(11)
1.338(4)
1.440(4)
1.360(4)
N(2)-N(3)
N(3)-C(5)
N(4)-C(5)
1.305(3)
1.388(4)
1.369(4)
Pd(1)-N(2)
Pd(1)-N(4)
Pd(1)-Cl(1)
N(1)-Pd(1)-N(2)
81.83(13)
N(2)-Pd(1)-N(4)
79.00(13)
[PtCl3(L2)], 5
Pt(1)-N(1)
Pt(1)-N(3)
Pt(1)-N(4)
Pt(1)-Cl(1)
Pt(1)-Cl(2)
2.050(4)
1.967(4)
2.041(4)
2.3196(12)
2.3309(12)
Pt(1)-Cl(3)
N(1)-C(5)
N(2)-C(5)
N(2)-N(3)
N(3)-C(6)
2.3159(12)
1.376(5)
1.408(5)
1.272(5)
1.360(5)
C(6)-C(11)
N(4)-C(11)
N(4)-C(12)
N(5)-C(12)
1.430(6)
1.342(6)
1.416(5)
1.342(6)
N(1)-Pt(1)-N(3)
79.32(14)
N(3)-Pt(1)-N(4)
82.05(14)
complex, which is green in color. The ligand [L1]-, in the
nickel complex, acts as a monoanionic bis-chelating tridentate
donor, two of which satisfy the six coordination number of
the central Ni(II) ion. In contrast, the reaction of hydrated
salt NiCl2‚6H2O with [L2]- in equimolar proportions pro-
duced an intense and bright blue solution. The usual workup
followed by crystallization of the crude mass produced a
molecular dinickel complex, [Ni2Cl2(L2)2], 2, in an excellent
yield (80%). This showed all characteristic IR stretches for
the coordinated ligands. The dinickel complex is soluble in
all common solvents. Its UV-vis spectrum consists of
several charge-transfer transitions, of which the broad band
near 600 nm is responsible for its blue color.
The dinickel complex forms dark blue crystals, whose
single-crystal X-ray structure has been solved. A labeled
ORTEP plot of the complex 2 is shown in Figure 2, and
Inorganic Chemistry, Vol. 42, No. 17, 2003 5369

Kamar et al.
C-N single bond. A similar effect was noted before3 in the
structure of the monometallic complex, [Ni(L1)2]. We also
note that the Ni-N(amide) lengths in the Ni2N2 ring are of
two types; the Ni(1)-N(14) and Ni(2)-N(34) [av 2.099(3)
Å] are smaller than the other two Ni-N bonds [av 2.277(3)
Å], indicating that the bridging amide nitrogens do not
interact equally with the two nickel ions. The separation
between the two nickel ions in this molecule is 3.1818(8)
Å, which does not suggest11b any Ni-Ni bonding.
Magnetic susceptibility of the dinickel complex was
measured at temperatures ranging from 1.8 to 300 K and is
presented in Figure 3 as (3køT/NµB2)1/2 vs T, where ø is the
molar susceptibility, N is Avogadro’s number, and µB is
Bohr’s magneton. Clearly, the quantity plotted in Figure 3
is not a constant, as it would be in a simple paramagnet.
The magnetic behavior of the nickel dimer can be understood
as that of an exchange-coupled pair of spins S ) 1. The
following Hamiltonian describes the system:
Figure 2. An ORTEP plot and atom-numbering scheme for the molecular
complex [Ni2Cl2(L2)2], 2. Hydrogen atoms are omitted for clarity.
selected bond parameters are collected in Table 2. Two nickel
ions in this molecule are in a highly distorted octahedral
geometry with each nickel surrounded by a N5Cl environ-
ment. The two extended ligands satisfy five coordination sites
of each nickel ion and act as bridges across the two nickel
centers. The coordination mode of the anionic [L2]- ligand
in this molecule is unique in many respects. In addition to
the pyridyl nitrogens, viz., N(15) and N(35) of the amino-
pyridyl function, the two deprotonated amine nitrogens, viz.,
N(14) and N(34), bind simultaneously to two nickel ions.
Double-bridged dinuclear complexes with bridging coordina-
tion of a deprotonated secondary amine function and having
a M2(µ-NR2)2 core are scarce11 in the literature. The two
amide nitrogens together with two nickel(II) ions in this
complex form a plane with no atom deviating by more than
0.033 Å. For this, the 2-pyridylamide functions, [N-Py]-,
of each [L2]- form highly strained four-member chelate rings
comprising Ni(1), N(34), C(42), N(35) and Ni(2), N(14),
C(22), N(15). Four-member chelates for dithiocarbamates
are common, and those for carboxylates and nitrates are also
known; however, such strained coordination is not common
for an extended multidentate ligand. Of the five Ni-N bonds
around each nickel ion, the two Ni-N(azo) lengths [e.g.,
Ni(1)-N(13), 1.996(3) Å] are appreciably short compared
to the other Ni-N bonds. This may12,13 be due to the presence
of extensive charge delocalization along the ligand backbone
of the anionic ligand [L2]-. Consequently, the -NdN-
lengths are elongated and the azo nitrogen to phenyl carbon
distances as well as the lengths of deprotonated amide
nitrogen bond to the phenyl group of pap are shorter than a
Hˆ ) -2JSˆ1‚Sˆ2 - D(Sˆ21z + Sˆ22z) + gµBH‚Sˆ
which includes Heisenberg exchange, zero-field splitting, and
interaction with the magnetic field. The exchange integral,
J, is positive, which corresponds to ferromagnetic interaction.
In the low-temperature range, T , J/k, the system can be
described as a single spin S ) 2, whereas at high tempera-
tures, T . J/k, it behaves as two independent spins S ) 1.
Finally, at very low temperatures the effect of zero-field
splitting becomes apparent as the data points plotted in Figure
3 drop sharply below T ∼ 10 K.
For better stability, the determination of the adjustable
parameters was carried out in two stages: (i) At temperatures
to the right of the maximum (T > 20 K), where the zero-
field splitting is irrelevant, the data were fitted to a simplified
formula, which neglected D but included a temperature-
independent Van Vleck term, NR. The best-fit values are
J ) 18.5 cm-1, g ) 2.14, R ) 1.7 × 10-27 cm3. (ii) Using
the formalism14,15 of Ginsberg et al., which allows for a
nonzero D, the entire data set was fitted. At this stage D
was the sole adjustable parameter, while J, g, and R were
kept fixed at the values established previously. In this way
D ) - 9 cm-1 was found. The final calculated curve is
shown in Figure 3. However, the most convincing confirma-
tion of the adopted interpretation of the magnetic susceptibil-
ity data comes from low-temperature magnetization curves,
which are submitted as Supporting Information.
(14) Ginsberg, A. P.; Martin, R. L.; Brookes, R. W.; Sherwood, R. C. Inorg.
Chem. 1972, 11, 2884.
(11) (a) Aullo´n, G.; Lledo´s, A.; Alvarez, S. Inorg. Chem. 2000, 39, 906.
(b) Holland, P. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem.
Soc. 1996, 118, 1092. (c) Hope, H.; Olmstead, M. M.; Murray, B. D.;
Power, P. P. J. Am. Chem. Soc. 1985, 107, 712.
(12) This may also happen due to geometric reason. For a bis-chelating
bidentate ligand, forming two five-member chelate rings, the M-N
bond length for the middle nitrogen is smaller13 than those for the
terminal nitrogens.
(13) (a) Pramanik, N. C.; Pramanik, K.; Ghosh, P.; Bhattacharya, S.
Polyhedron 1998, 17, 1525. (b) Matsumoto, N.; Motoda, Y.; Matsuo,
T.; Nakashima, T.; Re, N.; Dahan, F.; Tuchagues, J.-P. Inorg. Chem.
1999, 38, 1165. (c) Bruin, B. De.; Bill, E.; Bothe, E.; Weyhermuller,
T.; Wieghardt, K. Inorg. Chem. 2000, 39, 2936.
(15) Neglect of the interdimer exchange interaction in the above approach
is justified by the weakness of that interaction. Thus, between
1.8 and 5 K, the susceptibility follows the Curie-Weiss law, ø )
C/(T - θ), with C ) 4.2 K emu/mol and θ ≈ -2 K. The interdimer
exchange integral is then estimated as zJ′ ) θ/4 ≈ -0.5 K, z being
the number of nearest neighbors. On the other hand, D < 0, hence
the ground state of the dimer is a nonmagnetic singlet, therefore the
presence of the small interdimer interaction, z|J′| , |D|, is irrelevant.
Any possibility of a positive zero-field splitting can be ruled out, since
this would have meant a doublet ground state and a Curie-Weiss
behavior with a much smaller Curie constant, C ) 2.3 K emu/mol.
This conclusion holds regardless of the interdimer interaction, which
affects θ but not C.
5370 Inorganic Chemistry, Vol. 42, No. 17, 2003

A New Binucleating Ligand
2
1/2
Figure 3. A plot of (3køT/NµB
)
vs T (K) for [Ni2Cl2(L2)2]‚H2O, 2‚H2O. The line represents the best fit, and the points are experimental data.
Previous studies on the Ni dimers containing Ni2O2 were
reported, where the exchange coupling constant was shown16
to be directly proportional to the Ni-O-Ni bridge angles
or Ni-Ni separation. The bridge bond angle Ni-N-Ni in
our system is ca. 93°, and the two-nickel centers are coupled
ferromagnetically. As far as we are aware no other experi-
mental result on the system containing a Ni2N2 core was
available. The magnetostructural data available for a few
halo-bridged nickel(II) complexes17 are indicative of ferro-
magnetic coupling taking place via 90° Ni-X-Ni (X ) Cl,
Br) interactions. More results are accessible for azido-bridged
nickel(II) complexes. Compounds with end-on bridges are
known to exhibit ferromagnetic exchange while end-to-end
bridge systems give rise to antiferromagnetic interaction.18,19
For several end-on µ2-N3 nickel(II) complexes the reported
J values lie between 20 and 49 cm-1.
Figure 4. 1H NMR spectra of (a) [Pd2(L2)2](ClO4)2, [3](ClO4)2, in DMSO-
d6, and (b) [PdCl(L1a)], 4a, in CDCl3.
coordinated anioinc ligand [L2]- gave rise to one signal. Thus
the two ligands in [3]2+ are magnetically equivalent, indicat-
ing the presence of a 2-fold symmetry axis. Notably, the
-NH resonance in [3]2+ was absent.
C. Palladium Complexes. A dipalladium complex having
the composition [Pd2(L2)2](ClO4)2, [3](ClO4)2, was obtained
in 70% yield from the reaction of deprotonated HL2 and
Na2[PdCl4] in equimolar proportions in methanol at room
temperature. Dilute NEt3 was used for the deprotonation of
HL2. The cationic palladium complex [3]2+ was isolated as
its perchlorate salt. It gave consistent analysis confirming
its formulation. In solution, the complex behaves as a 1:2
The structural analysis of [3](ClO4)2 has indeed authen-
ticated the dimetallic coordination of [L2]-. The 2-(phenyl-
azo)pyridyl part [N(1) and N(3)] along with the deprotonated
amine nitrogen [N(4)] bind to a palladium center, Pd(1) as
a tridentate donor. The pyridyl nitrogen [N(5)] of this cannot
bind to the same metal; instead it coordinates to a second
palladium center [Pd(2)]. The second [L2]- ligand binds in
a similar fashion, as a tridentate donor around Pd(2), and
binds to Pd(1) through its pyridyl [N(10)] nitrogen. The two
ligands thus satisfy four coordination of each palladium. The
complex as a whole is a dication, and there are two per-
chlorate counterions along with two water molecules with
0.5 occupancy on each oxygen atom as crystallization in the
asymmetric unit. Figure 5 shows the ORTEP plot and atom-
numbering scheme for the cationic complex [Pd2(L2)2]2+.
Thus the bridging coordination mode of the ligand [L2]- in
its palladium complex is as anticipated. However, the
bridging coordination mode of the [NAr2]- function was not
observable in the case of the dipalladium system. This is in
electrolyte (ΛM ) 240 Ω-1 cm2 mol-1 in 1 × 10-3
M
acetonitrile). The diamagnetic complex [3]2+ shows the
1
resolved H NMR spectrum (Figure 4). The spectrum is in
agreement with the crystal structure of [Pd2(L2)2](ClO4)2‚
H2O (vide infra). Notably, each kind of proton of the
(16) Nanda, K. K.; Thompson, L. K.; Bridson, J. N.; Nag, K. J. Chem.
Soc., Chem. Commun. 1994, 1337.
(17) (a) Laskowski, E. J.; Felthouse, T. R.; Hendrickson, D. N.; Long, G.
Inorg. Chem. 1976, 15, 2908. (b) Journaux, Y.; Kahan, O. J. Chem.
Soc., Dalton Trans. 1979, 1575.
(18) (a) Ribas, J.; Monfort, M.; Diaz, C.; Bastos, C.; Solans, X. Inorg.
Chem. 1993, 32, 3557. (b) Karmakar T. K.; Chandra, S. K.; Ribas, J.;
Mostafa, G.; Lu, T. H.; Ghosh, B. K. Chem. Commun. 2002, 2364.
(c) Ribas, J.; Monfort, M.; Ghosh, B. K.; Solans, X. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 2087 and references therein.
(19) Mohanta, S.; Nanda, K. K.; Werner, R.; Haase, W.; Mukherjee, A.
K.; Dutta, S. K.; Nag, K. Inorg. Chem. 1997, 36, 4656 and references
therein.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5371

Kamar et al.
Figure 6. An ORTEP plot and atom-numbering scheme for the molecular
complex [PdCl(L1a)], 4a. Hydrogen atoms are omitted for clarity.
Figure 5. An ORTEP plot and atom-numbering scheme for [Pd2(L2)2]2+
in [Pd2(L2)2](ClO4)2, [3](ClO4)2. Hydrogen atoms are omitted for clarity.
Semiempirical EHMO calculations20 on these indicate that
while the HOMOs are the admixture of metal and ligand
orbitals, the LUMOs are predominantly ligand orbitals.
Hence the low-energy transitions may best be ascribed as
π-π* transitions.
contrast to the observation noted before in the dinickel
complex. Selected bond distances of the above dipalladium
complex are collected in Table 2. The two azo nitrogens of
the anionic tridentate ligands approach the metal center
closest with Pd(1)-N(3), 1.916(6) Å, and Pd(2)-N(8),
1.919(7) Å, respectively. Indications of significant backbone
conjugation in each of the coordinated anionic ligands were
noted. Thus the average of the two N-C lengths, viz., N(4)-
C(11) and N(9)-C(27), 1.343(9) Å, is considerably shorter
than a N-C single bond length. The average of N-N
distances of the azo nitrogen also indicates elongation, which
is consistent with the delocalization along the ligand
backbone of the anionic ligand [L2]-.
D. Platinum Complexes. Unlike its palladium congener,
the product of reaction of the platinum salt, K2[PtCl4], and
either of the ligands HL1 and HL2 was not as anticipated.
The above reactions do not proceed at all in methanol. On
prolonged stirring (>2 h) some insoluble precipitate appeared
presumably due to formation of platinum metal. However,
reaction of K2[PtCl4] with the deprotonated ligand, [L2]-,
was observed to occur in boiling acetonitrile in the presence
of air. The reaction mixture became green in about 2 h. The
usual workup followed by crystallization of the above
reaction mixture produced a crystalline molecular complex
of formula [PtCl3(L2)], 5. In this compound the ligand [L2]-
coordinates as a tridentate ligand using one pyridyl, azo, and
deprotonated amine nitrogens. The second pyridyl nitrogen
of amino pyridyl function remained unused (vide infra).
Notably, the metal ion, during this reaction, undergoes two-
step oxidation [Pt(II) f Pt(IV)], which is brought about by
air. A similar Pt(IV) product was isolated from the reaction
of K2[PtCl4] and HL1. Thus the results, in the case of
platinum, are different from that observed in the two former
cases. Differences in redox properties of the reference metal
ions are no doubt responsible for this. Platinum(II) being
more susceptible to redox processes undergoes reduction to
platinum metal in a reducing solvent like methanol. It, on
the otherhand, undergoes oxidation to platinum(IV) by air
in acetonitrile. In its reaction with [L2]- the dimetallic
complex was not observed due to inertness of the resultant
platinum(IV) complex, [PtCl3(L2)], 5, toward substitution.
In contrast, the corresponding palladium(II) complex, the
plausible intermediate, is labile and undergoes dimerization
easily to produce a dimetallic complex. The two types of
reactions of palladium and platinum are compared in Scheme
2. It may relevant to note here that the above platinum(IV)
complex is extremely inert and is unreactive to Ag(I) even
in boiling acetonitrile.
We then thought it worthwhile to scrutinize a similar
reaction of Na2[PdCl4] with [L1]- under an identical condition
for a comparison. We wish to reiterate here that a phenyl
group in [L1]- replaces a 2-pyridyl group of [L2]-. In line
with our strategy Na2[PdCl4] was reacted with HL1 in
methanol in the presence of NEt3 as a base. A brown
molecular compound of composition [PdCl(L1)], 4, was
isolated in almost quantitative yield. This gave a resolved
1H NMR spectrum (Figure 4). The X-ray structure of a
representative [PdCl(L1a)], 4a, was determined. The ORTEP
plot and atom-numbering scheme for 4a are shown in Figure
6. The compound 4a is monometallic. The coordination
sphere involves PdN3Cl. The tridentate ligand [L1]- along
with one chloride completes a distorted square planar
geometry. The bond lengths in this molecule indicate
significant conjugation along the ligand backbone. The
Pd(1)-N(2) is shortest [1.930(3) Å] and is comparable to
those [Pd(1)-N(3) and Pd(2)-N(8)] observed in the dipal-
ladium complex, [3]2+.
The solution colors of the palladium compounds are
brown. Selected spectral characterization data are collected
in Table 1. Multiple and overlapping absorption of moderate
intensities was observed in the near-infrared region. Interest-
ingly, the intensities of transitions for the dipalladium
complex, [3](ClO4)2, are much higher than those for the
monometallic complex, 4. Interligand charge-transfer transi-
tions were noted for both the complexes in the UV region.
(20) Mealli, C.; Proserpio, D. M. J. Chem. Educ. 1990, 67, 399.
5372 Inorganic Chemistry, Vol. 42, No. 17, 2003

A New Binucleating Ligand
Scheme 2
The platinum(IV) complex, [PtCl3(L2)], 5, formed suitable
X-ray quality crystals. A view of the molecular complex is
shown in Figure 7. In this complex, the platinum center is
surrounded by a distorted octahedral coordination environ-
ment by three chloride ligands and the tridentate monoanionic
bis-chelating ligand. One of the two pyridyl nitrogens [N(5)]
remained uncoordinated. The selected bond parameters are
collected in Table 2. Taken together, the lengthening of the
azo -NdN- length in [L2]- and the shortening of the N-C
distances alongside of the azo moiety, with respect to the
corresponding distances in [H2L2]+ (Table 2), indicate
considerable delocalization of π-electron density in [L2]-.
The central Pt-N bond of the anionic ligand, Pt(1)-N(3),
1.967(4) Å, is significantly shorter than the other two similar
Pt-N distances with average 2.045(4) Å.
red shifted considerably compared to the corresponding
palladium(II) complexes.
Conclusion
The successful design and synthesis of a new N-donor
bridging ligand, [2-(2-pyridylamino)phenylazo]pyridine have
been achieved by cobalt-mediated fusion of 2-aminopyridine
on coordinated 2-(phenylazo)pyridine. This acts as a potential
bridging ligand. Two dimetallic complexes of nickel and
palladium have been synthesized. The coordination mode
of the anionic ligand in the dinickel complex is unique and
different from that in the case of the dipalladium complex.
In the former example, the pyridyl and the deprotonated
secondary amine nitrogens act as bridge across the two nickel
centers. It may be relevant to note that such a bridging mode
of a [NR2]- function is not available in the literature. The
two nickel centers in the dinickel complex are ferromag-
netically coupled with J ) 18.5 cm-1. A different type of
reaction was, however, observed in the case of platinum.
Platinum(II), being redox active, undergoes two-step oxida-
tion to result in a platinum(IV) monometallic complex of
[L2]- in air. This monometallic Pt(IV) complex is absolutely
inert toward substitution and cannot dimmerize to produce
a dimetallic complex.
The 1H NMR spectra of the two platinum(IV) complexes
are similar in nature, but they are different from those
observed for the corresponding palladium(II) complexes. The
combination of several high-intensity visible range transitions
in their solution spectra characterizes these platinum com-
plexes. In addition, ligand-based transitions were observed
in the UV region. Semiempirical EHMO calculations20 using
the X-ray structural parameters of [PtCl3(L2)], 5, indicate that
the HOMO is a mixed metal-ligand orbital while the
acceptor orbital LUMO is a combination of ligand orbitals
with only small contributions of the metal orbitals. Notably,
the lowest energy transitions in platinum(IV) complexes are
Experimental Section
Materials. The starting complex [Co(pap)3](ClO4)2 and the HL1
were prepared2 by a reported procedure. The salts PdCl2 and
K2[PtCl4] were obtained form Arora-Matthey, Kolkata. PdCl2 was
converted to Na2[PdCl4] as before.21 Solvents and chemicals used
for synthesis were of analytical grade. CAUTION: Perchlorate salts
of metal complexes can be explosive. Although no detonation
tendencies have been observed, care is advised and handling of
only small quantities recommended.
Physical Measurements. A JASCO V-570 spectrophotometer
was used to record the electronic spectra. The IR spectra were
1
recorded with a Perkin- Elmer 783 spectrophotometer. H NMR
spectra were measured in CDCl3 and DMSO-d6 with a Brucker
(21) (a) Chattopadhyay, P.; Nayak, M. K.; Bhattacharya, S. P.; Sinha, C.
Polyhedron 1997, 16, 1291. (b) Basuli, F.; Chattopadhyay, P.; Sinha,
C. Polyhedron 1996, 15, 2439.
Figure 7. An ORTEP plot and atom-numbering scheme for the molecular
complex [PtCl3(L2)], 5. Hydrogen atoms are omitted for clarity.
Inorganic Chemistry, Vol. 42, No. 17, 2003 5373

Kamar et al.
Avance DPX 300 spectrometer, and SiMe4 was used as the internal
standard. A Perkin-Elmer 240C element analyzer was used to collect
microanalytical data (C, H, N). Electrical conductivity was measured
by using a Systronics direct reading conductometer 304. Melting
points were determined with the help of a capillary fitting Mel.
Temp. II (Laboratory Devices Inc., USA) apparatus.
[PdCl(L1a)], 4a. The ligand HL1a (0.1 g, 0.36 mmol) was
dissolved in methanol (30 mL), and to it were added 1-2 drops of
dilute triethylamine. To the deprotonated ligand solution was added
a methanolic solution of Na2[PdCl4] (0.11 g, 0.37 mmol), and the
mixture was stirred for 30 min at room temperature. The color of
the solution changed from orange yellow to brown. The compound
was precipitated from the solution mixture within this period. The
crude product was collected by filtration and dissolved in dichlo-
romethane. Crystalline 4a was obtained by slow diffusion of a
dichloromehane solution of the compound into hexane. Yield: 80%.
Anal. Calcd for C17H13N4ClPd: C, 49.14; H, 3.13; N, 13.49.
Found: C, 49.20; H, 3.20; N, 13.42.
Magnetic measurements were performed in a commercial SQUID
magnetometer from Quantum Design. First, the ac magnetic
moment was measured as a function of temperature between 1.8
and 300 K. The applied ac field had an amplitude of 4.5 Oe at 10
Hz. From the measured ac magnetic moment, the in-phase magnetic
susceptibility, ø′, and the out-of phase magnetic susceptibility, ø′′,
were calculated. At first glance ø′(T) was paramagnetic in the whole
temperature range, but not a simple paramagnet following a unique
Curie law ø′(T) ) C/T. Confirming the paramagnetic behavior, ø′′
was negligible in the whole temperature range. For a more complete
magnetic study, isothermal magnetization curves M(µ0H) were taken
at T ) 1.8 and 5 K, in the magnetic field range 0 < µ0H < 5 T.
Synthesis of Complexes. [Co(L2)2](ClO4), [1](ClO4). A mixture
of [Co(pap)3](ClO4)2 (0.2 g, 0.25 mmol) and 2-aminopyridine (0.1
g, 1.06 mmol) was heated on a steam bath for 1 h. The initial brown
color gradually changed to intense green. The cooled green mixture
was thoroughly washed with diethyl ether. Crystallization of the
crude green product from a dichloromethane-hexane mixture
yielded crystalline [Co(L2)2](ClO4) in 60% yield.
The complex [PdCl(L1b)], 4b, was synthesized similarly using
HL1b in place of HL1a. Yield: 75%. Calcd for C18H15N4ClPd: C,
50.35; H, 3.50; N, 13.05. Found: C, 50.38; H, 3.47; N, 13.08.
[PtCl3(L2)], 5. The ligand HL2 (0.1 g, 0.36 mmol) was dissolved
in acetonitrile (30 mL), and to it were added 1-2 drops of dilute
triethylamine. To the deprotonated ligand solution was added a
solution of K2[PtCl4] (0.15 g, 0.36 mmol) in acetonitrile (15 mL),
and the mixture was refluxed for 2 h on a steam bath. The color of
the solution changed to green. The resultant mixture was filtered
and concentrated to 15 mL, from which crystalline green 5 was
obtained in 60% yield. Anal. Calcd for C16H12N5Cl3Pt:C, 33.35;
H, 2.08; N, 12.15. Found: C, 33.40; H, 2.02; N, 12.20.
[PtCl3(L1a)], 6a. The ligand HL1a (0.1 g, 0.36 mmol) was
dissolved in acetonitrile (30 mL), and to it were added 1-2 drops
of dilute triethylamine. To the deprotonated ligand solution was
added a solution of K2[PtCl4] (0.15 g, 0.36 mmol) in acetonitrile
(15 mL), and the mixture was refluxed for 2 h on a steam bath.
The color of the solution changed to green. The resultant mixture
was filtered and concentrated to 15 mL, from which crystalline
green 6a was obtained in 65% yield. Anal. Calcd for C17H13N4-
Cl3Pt: C, 35.50; H, 2.26; N, 9.75. Found: C, 35.55; H, 2.28;
N, 9.72.
Anal. Calcd for C32H26N10ClO5Co: C, 53.01; H, 3.58; N, 19.32.
Found: C, 53.06; H, 3.53; N, 19.25.
Isolation of [2-(2-Pyridylamino)phenyl]azopyridine (HL2)
from the Complex [1](ClO4). The cobalt complex [Co(L2)2](ClO4)
(0.15 g, 0.21 mmol) was dissolved in ethanol (30 mL), and to it
were added hydrazine hydrate (5 mL) and yellow ammonium sulfide
(5 mL). The mixture was then stirred for 30 min at room
temperature. The resulting orange-yellow solution was evaporated
under vacuum, then extracted with dichloromethane, and subjected
to a silica gel PTLC technique. An orange-yellow band was eluted
with a toluene-chloroform mixture (1:2), which on evaporation
yielded orange crystals of HL2 in 70% yield. FAB mass (M): 276.
Mp: 90 °C. pKa ) 8.6 ( 0.1. Anal. Calcd for C16H15N5O: C, 65.53;
H, 5.12; N, 23.89. Found: C, 65.55; H, 5.15; N, 23.92.
Similarly the complex [PtCl3(L1b)], 6b, was prepared following
the above procedure using HL1b in place of HL1a. Yield: 60%.
Anal. Calcd for C18H15N4Cl3Pt: C, 36.70; H, 2.54; N, 9.51.
Found: C, 36.75; H, 2.50; N, 9.55.
X-ray Structure Determination. Crystallographic data for the
compounds [H2L2](ClO4), [2]‚H2O, [3](ClO4)2‚H2O, 4a, and 5 are
collected in Table 3.
[Ni2Cl2(L2)2], 2. The ligand HL2 (0.1 g, 0.36 mmol) was
dissolved in methanol (30 mL), and to it were added 1-2 drops of
dilute triethylamine. To the deprotonated ligand solution was added
a methanolic solution of NiCl2‚6H2O (0.086 g, 0.362 mmol) with
constant stirring. The mixture was stirred for 1 h at room
temperature. The color of the solution changed to bright blue. The
resultant mixture was filtered, and the solvent was evaporated under
vacuum. Crystalline [Ni2Cl2(L2)2] was finally obtained by slow
diffusion of a dichloromethane solution of the compound into
hexane. Yield: 80%. Anal. Calcd for C32H26N10Cl2ONi2: C, 50.86;
H, 3.44; N, 18.54. Found: C, 50.82; H, 3.46; N, 18.50.
[Pd2(L2)2](ClO4)2, [3](ClO4)2. The ligand HL2 (0.1 g, 0.36 mmol)
was dissolved in methanol (30 mL), and to it were added 1-2 drops
of dilute triethylamine. To the deprotonated ligand solution was
added a methanolic solution of Na2[PdCl4] (0.11 g, 0.37 mmol),
and the mixture was stirred for 30 min at room temperature. The
color of the mixture gradually became greenish brown. The
compound was precipitated from the solution mixture within this
period. The crude product was collected by filtration. It was
dissolved in acetonitrile. Slow evaporation of acetonitrile solution
of the compound yielded crystalline [3](ClO4)2. Yield: 70%.
ΛM ) 240 Ω-1 cm2 mol-1 (1 × 10-3 M in acetonitrile). Anal.
Calcd for C32H28N10Cl2O10Pd2: C, 38.54; H, 2.81; N, 14.05.
Found: C, 38.58; H, 2.86; N, 14.01.
[H2L2](ClO4). X-ray quality crystals (0.41 × 0.09 × 0.08 mm3)
of [H2L2](ClO4) were obtained by slow diffusion of an acetonitrile
solution of the compound into toluene. The data were collected
(1.97° < θ < 26.43°) at 293(2) K on a Bruker SMART CCD 1000
diffractometer equipped with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). A total of 10588 reflections were
collected, of which 3493 were unique (Rint ) 0.0269). The structure
was solved by direct methods using the Program SHELXS-9722a
and refined by full-matrix least-squares techniques against F2 using
SHELXL-97.23 Positional and anisotropic atomic displacement
parameters were refined for all non-hydrogen atoms.
[Ni2Cl2(L2)2]‚H2O, 2‚H2O. X-ray quality crystals (0.50 ×
0.10 × 0.08 mm3) of 2‚H2O were obtained by slow diffusion of a
dichloromethane solution of the compound into hexane. Data
were collected (2.99° < θ < 24.99°) at 293(2) K on a Stoe
imaging plate diffraction system (IPDS) using Mo KR radiation
(22) (a) Sheldrick, G. M. Acta Crystallogr. 1990, 46A, 467. (b) Sheldrick,
G. M. SHELXS-97, Program for the Solution of Crystal Structures;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(23) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
5374 Inorganic Chemistry, Vol. 42, No. 17, 2003

A New Binucleating Ligand
Table 3. Crystallographic Data
[H2L2](ClO4)
2‚H2O
[3](ClO4)2‚H2Oa
4a
5
empirical formula
molecular mass
temp (K)
cryst syst
space group
a (Å)
C16H14N5ClO4
375.77
293(2)
monoclinic
P21/c (No. 14)
7.3393(19)
18.897(5)
12.505(3)
90
98.172(5)
90
1716.7(8)
4
C32H26N10Cl2ONi2
754.95
293(2)
monoclinic
P21/n (No. 14)
16.3100(18)
11.6605(6)
16.9164(12)
90
97.387(11)
90
3190.5(4)
4
C32H26N10Cl2O9 Pd2
978.33
293(2)
monoclinic
P21/n
12.5546(9)
14.4884(11)
21.2438(15)
90
102.919(2)
90
3766.3(5)
4
C17H13N4ClPd
415.16
293(2)
monoclinic
P21/n
6.7919(5)
16.9123(13)
13.8290(10)
90
91.161(2)
90
1588.2(2)
4
C16H12N5Cl3Pt
575.75
150(2)
monoclinic
P21/n
11.641(3)
8.486(2)
18.402(5)
90
105.817(4)
90
1749.0(7)
4
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
D
calcd (Mg/m3)
1.454
1.572
1.750
1.736
1.750
cryst dimens (mm3)
θ range for data collection (deg)
GOF
0.41 × 0.09 × 0.08
1.97-26.43
1.026
0.50 × 0.10 × 0.08
2.99-24.99
1.064
0.40 × 0.13 × 0.10
1.73-27.56
1.013
0.40 × 0.15 × 0.11
1.90-27.49
0.960
0.40 × 0.13 × 0.10
1.82 -27.50
1.008
wavelengths (Å)
reflns collected
0.71073
10588
0.71073
26943
0.71073
23768
0.71073
9991
0.71073
8411
unique reflns
3493
5470
8654
3621
3920
largest diff between
0.664, -0.411
0.515, -0.265
0.899, -0.427
0.793, -0.417
1.417, -1.740
peak and hole (e Å-3
)
final R indices (I > 2σ(I))
R1 ) 0.0562
wR2 ) 0.1434
R1 ) 0.0408
wR2 ) 0.0719
R1 ) 0.0502
wR2 ) 0.1073
R1 ) 0.0292
wR2 ) 0.0536
R1 ) 0.0254
wR2 ) 0.0510
a There are two water molecules with 0.5 occupancy on each oxygen atom.
(λ ) 0.71073 Å). A total of 26943 reflections were collected, of
which 5470 were unique (Rint ) 0.0811). The structure was solved
by direct methods using the program SHELXS-9722b and refined
by full-matrix least-squares techniques against F2 using SHELXL-
97.23 Positional and anisotropic atomic displacement parameters
were refined for all non-hydrogen atoms.
[Pd2(L2)2](ClO4)2‚H2O, [3](ClO4)2‚H2O. X-ray quality crystals
(0.40 × 0.13 × 0.10 mm3) of [3](ClO4)2‚H2O were obtained by
slow evaporation of an acetonitrile solution of the compound. The
data were collected (1.73° < θ < 27.56°) at 293(2) K on a Bruker
SMART diffractometer equipped with graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å). Data were corrected for Lorentz-
polarization effects. A total of 23768 reflections were collected, of
which 8654 were unique (Rint ) 0.0481). The structure was solved
by employing the SHELXS-9722a program package and refined by
full-matrix least squares based on F2 (SHELXL-97).23
[PdCl(L1a)], 4a. X-ray quality crystals (0.40 × 0.15 × 0.11 mm3)
of 4a were obtained by slow diffusion of a dichlomethane solution
of the compound into hexane. The data were collected (1.90° <
θ < 27.49°) at 293(2) K on a Bruker SMART diffractometer
equipped with graphite-monochromated Mo KR radiation (λ )
0.71073 Å). Data were corrected for Lorentz-polarization effects.
A total of 9991 reflections were collected, of which 3621 were
unique (Rint ) 0.0294). The structure was solved by employing
the SHELXS-9722a program package and refined by full-matrix least
squares based on F2 (SHELXL-97).23
[PtCl3(L2)], 5. X-ray quality crystals (0.40 × 0.13 × 0.10 mm3)
of 5 were obtained by slow evaporation of a concentrated
acetonitrile solution of the compound. The data were collected
(1.82° < θ < 27.50°) at 150(2) K on a Bruker SMART
diffractometer equipped with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Data were corrected for Lorentz-
polarization effects. A total of 8411 reflections were collected, of
which 3920 were unique (Rint ) 0.0370). The structure was solved
by employing the SHELXS-9722a program package and refined by
full-matrix least squares based on F2 (SHELXL-97).23
Acknowledgment. Financial support received from the
Department of Science and Technology, New Delhi, is
gratefully acknowledged. The magnetic work carried out at
ICMA was supported by Grant MAT02/166 from CICYT,
and M.D.K. acknowledges receiving a fellowship from
Ministerio de Educacio´n, Culturay Deporte of Spain, No.
SAB2000-0084.
Supporting Information Available: 1H NMR spectrum of the
complex [1](ClO4) in CDCl3, a plot of magnetic moment vs
magnetic field, results of low-temperature magnetization, and X-ray
crystallographic details in CIF format of the five compounds [H2L2]-
(ClO4), 2‚H2O, [3](ClO4)2‚H2O, 4a, and 5. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC034313H
Inorganic Chemistry, Vol. 42, No. 17, 2003 5375