Synthesis of complexes with the polydentate ligand N,N′-bis(2- hydroxyphenyl)-pyridine-2,6-dicarboxamide

Article abstract of DOI:10.1016/j.poly.2010.10.012

The pentadentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6- dicarboxamide (POPYH₄) has been used to prepare a variety of new complexes [HNEt₃]₂[Zn₄Cl(POPYH)₃] (2), [HNEt₃][PdCl(POPYH

Full text of DOI:10.1016/j.poly.2010.10.012

Polyhedron 30 (2011) 284–292
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Polyhedron
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Synthesis of complexes with the polydentate ligand N,N0-bis(2-hydroxyphenyl)-
pyridine-2,6-dicarboxamide
b
Yolanda Pérez a, Andrew L. Johnson b, , Paul R. Raithby
⇑
a Departamento de Química Inorgánica y Analítica, E.S.C.E.T, Universidad Rey Juan Carlos 28933 Móstoles, Madrid, Spain
b Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
a r t i c l e i n f o
a b s t r a c t
The pentadentate ligand N,N0-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide (POPYH4) has been
used to prepare a variety of new complexes [HNEt3]2[Zn4Cl(POPYH)3] (2), [HNEt3][PdCl(POPYH2)] (3),
[HNEt3][Ni(POPYH)] (4) and K[Ni(POPYH)] (5) which show the versatility of this multidentate ligand.
The complexes have been characterised spectroscopically and their molecular and crystal structures have
been determined by single crystal X-ray diffraction techniques. In these complexes the ligand exhibits
different modes of coordination towards different transition metal ions. The structure of triethylammo-
nium salt of the Zn(II) dianion 2 consists of an unusual tetra-zinc core supported by three POPYH ligands
each one of which links two adjacent zinc centres through two oxygen and two nitrogen donor atoms.
The salt of the square planar Pd(II) anion 3 contains one POPYH2 ligand which coordinates in a tridentate
fashion through the two deprotonated amido groups and by the central pyridine nitrogen donor. The two
Ni(II) salts 4 and 5 contain the same [Ni(POPYH)]ꢀ anion in which the square planar Ni(II) centre is che-
lated by a POPYH ligand through the two deprotonated amido nitrogen atoms, the pyridine nitrogen and
a deprotonated hydroxyl group.
Article history:
Received 26 February 2010
Accepted 21 October 2010
Available online 27 October 2010
Keywords:
Dicarboxamide
Zinc
Nickel
Palladium
Coordination
Crystal structures
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
unusual coordination number of seven for Fe(III). In two other
structurally characterised Fe(III) complexes the ligand is only par-
The interest in metal complexes of ligands that contain amide
moieties stems from their occurrence in metalloproteins and metal
complexes of glycopeptide antibiotics such as bleomycin (BLM) [1].
In addition, the use of ligands pyridine-2,6-dicarboxamide to stabi-
lize high formal oxidation states of metal ions due to the good
tially deprotonated and is coordinated to the iron centre through
the deprotonated phenolate oxygen atoms in a bidentate fashion.
Coordination and reactivity of the POPYH4 ligand towards a range
of M(II) ions (Co, Ni, Cu, Mn, Zn and Cd) [8] and lanthanide ions
(Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Y) [9] have also been de-
scribed, but to date structural elucidation of these structures has
not been reported. We have previously reported the structure of
the potassium complex [POPYH4ꢁKOAcꢁ2NCMe] as part of a wider
study into the use of the POPYH4 ligand system in extended molec-
ular arrays [10]. In this paper we report the synthesis, characterisa-
tion and crystal structures of a series of new complex anions of
zinc, palladium and nickel that contain partially deprotonated
forms of the N,N0-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxam-
ide ligand and which displays a range of coordination modes that
are dependant on the electronic requirements of the metal centres.
r
-donor properties of the deprotonated nitrogen atom has been
well documented [2]. These ligands have been considered as model
compounds for the study of the effect of intramolecular and
intermolecular hydrogen bonding [3]. In addition, pyridine carbox-
amide ligands have found use in asymmetric catalysis, [4] dendri-
mer synthesis [4a] and gold(III) [5] and platinium(II) [6] complexes
with antitumour properties.
Structurally characterised Iron(III) complexes with the N,N0-
bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide ligand (PO-
PYH4), which is based on the pyridine-2,6-dicarboxamide moiety
and contains two additional phenolic groups donors, have been re-
ported previously [7]. Two of these iron complexes contain the
fully deprotonated pentadentate ligand which lies in the equatorial
plane of metal and the coordination environment is completed by
two monodentate ligands which sit the two axial sites to give an
2. Results and discussion
2.1. Structural analysis of the ligand POPYH
The ligand POPYH4 has been synthesised previously [8] by
reacting 2 equiv. of 2-aminophenol with 1 equiv. of 2,6-pyridined-
icarbonyl dichloride in THF. However, since the crystal structure of
⇑
Corresponding author. Fax: +44 1225383183.
E-mail address: a.l.johnson@bath.ac.uk (A.L. Johnson).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.10.012

Y. Pérez et al. / Polyhedron 30 (2011) 284–292
285
Table 1
the compound has not been reported yellow needles of the ligand
Selected bond lengths (Å) and angles (°) for POPYH4
1
suitable for X-ray analysis were grown by vapour diffusion of ethyl
acetate into DMF solution of the ligand and a crystal structure
determination carried out.
Bond lengths (Å)
O(1)–C(6)
N(2)–C(6)
N(2)–C(7)
C(8)–O(3)
1.2256(17)
1.349(2)
1.4102(19)
1.3618(17)
O(2)–C(13)
N(3)–C(13)
N(3)–C(14)
O(4)–C(15)
1.2337(16)
1.3417(18)
1.4056(19)
1.3591(17)
In the crystal the neutral POPYH4 molecule co-crystallises with
a dimethylformamide solvent molecule. The molecular structure of
the POPYH4 ligand (1) is shown in Fig. 1 which also includes the
dimethylformamide molecule, while selected bond lengths and an-
gles are listed in Table 1. The molecular parameters all lie within
the expected ranges and are similar to those reported for both
[POPYH4ꢁKOAcꢁ2NCMe] [10] and N,N0-bis(2-methoxyphenyl)pyri-
dine-2,6-dicarboxamide [11]. The C–Namide [N(2)–C(6) = 1.349(2),
N(3)–C(13) = 1.3417(18) Å] and C@O [O(1)–C(6) = 1.2256(17),
O(2)–C(13) = 1.2337(16) Å] distances are in accord with the dis-
tances found in derivatives of 2,6-pyridinedicarboxamide [C–Na-
mide = 1.317–1.367 and C@O = 1.226–1.247 Å] [12]. The POPYH4
molecule is not planar and the two phenyl rings make angles of
8.9(1) and 18.3(2)° with the central pyridine ring, respectively,
while the dihedral angle between the two phenyl rings is
25.5(2)°. The torsion angles of C(5)–C(6)–N(2)–C(7) 177.1(1)° and
O(1)–C(6)–N(2)–C(7) ꢀ3.6(3)° and C(1)–C(13)–N(3)–C(14) ꢀ173.7(1)
and O(2)–C(13)–N(3)–C(14) 3.8(2)° confirm that the carboxamide
units are essentially planar. In the dimethylformamide molecule
the N(4) atom adopts a planar geometry with a maximum devia-
tion from the N(4)C(20)C(21)C(22) plane of ꢀ0.003(1) Å for N(4).
Overall, the bond parameters for POPYH4 similar to those reported
in the potassium bis-acetonitrile adduct [10].
Bond angles (°)
O(1)–C(6)–C(5)
O(1)–C(6)–N(2)
N(2)–C(6)–C(5)
C(6)–N(2)–C(7)
Hydrogen-bonds (Å)
D–Hꢁ ꢁ ꢁA
120.87 (14)
124.99(14)
114.13(13)
129.17(14)
O(2)–C(13)–C(1)
O(2)–C(13)–N(3)
N(3)–C(13)–C(1)
C(13)–N(3)–C(14)
121.46(13)
123.93(14)
114.57(12)
128.95(12)
d(D–H)
d(Hꢁ ꢁ ꢁA)
2.226(16)
22.49(16)
1.70(2)
d(Dꢁ ꢁ ꢁA)
N(2)–H(2N)ꢁ ꢁ ꢁN(1)
N(3)–H(3N)ꢁ ꢁ ꢁN(1)
O(3)–H(3O)ꢁ ꢁ ꢁO(5)
O(4)–H(4O)ꢁ ꢁ ꢁO(2A)
0.903(17)
0.882(16)
0.94(2)
2.6783(17)
2.6992(18)
2.6340(17)
2.6584(14)
0.92(2)
1.74(2)
Symmetry codes used to generate equivalent atoms (A): x + 1, y, z.
the level of deprotonation of the ligand in the complexes obtained,
reactions between 1 and the metal salts, ZnCl2, PdCl2 and NiCl2, in
the presence of a base (Scheme 1) have been explored. In each
reaction a solution of the ligand 1 in hot CH3CN was treated with
an excess of NEt3 to facilitate the removal of the protons that could
be dissociated and 1 equiv. of the ZnCl2, PdCl2 or NiCl2ꢁ6H2O were
added to obtain the complexes 2, 3 and 4, respectively. The com-
plex 5 was synthesised by reaction of ligand 1 dissolved in hot
methanol with 2 equiv. of NiCl2ꢁ6H2O and KOH as the base.
The 1H NMR spectrum of 3 shows only one set of the signals
indicating that the two phenolic rings are magnetically equivalent
in solution. Nevertheless the spectra 1H NMR spectra of the com-
plexes 2, 4 and 5 display a more complex pattern for the signals
for the phenolic rings suggesting the different coordination of the
ligand to metal. In the 1H NMR spectra of 3, 4 and 5 the absence
of the amide protons confirms that the ligand coordinates in a
deprotonated form. In the 1H NMR spectrum of 2 the disappear-
ance of the OH signal indicates that the coordination of the ligand
is via the deprotonated phenolic oxygen donors. In the case of
complexes 4 and 5, 1H NMR studies showed no indication of ex-
change between the coordinated (de-protonated) and uncoordinated
In the crystal structure of POPYH4.DMF there is a network of
hydrogen bonds linking adjacent molecules. The two hydrogen
atoms of the hydroxyl groups of POPYH4 act as hydrogen bond do-
nors; one, H(4O), to the carbonyl oxygen atom O(2) in an adjacent
POPYH4 molecules and the second, H(3O), to the oxygen of the
dimethylformamide solvent O(5). The parameters associated with
these hydrogen bonds are presented in Table 1.
3. Syntheses of complexes
In order to explore the versatility of POPYH4 (1) with a range of
transition metal halides and to establish the factors that influence
Fig. 1. The structure of POPYH4ꢁDMF showing the atom numbering scheme and the H-bonding netwok. The O(2A), H(4OA), O(4A) atoms are generated by the symmetry
operator x + 1, y, z, and are included to show the H-bonding environment around the POPYH4 molecule. The anisotropic displacement parameters have been drawn at the 50%
probability level.

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Y. Pérez et al. / Polyhedron 30 (2011) 284–292
2-
Cl
O
O
N
H
Zn
N
H
O
O
2 Et3NH
N
N
Zn
Zn
N
N
O
O
O
O
2
(2)
i) ZnCl2
ii) NEt3
K
Et3NH
O
O
i) NiCl2:6H2O
ii) KOH
O
O
O
O
i) PdCl2
ii) NEt3
N
N
N
N
O
N
NH
OH
HN
N
N
Pd
Ni
Cl
HO
HO
OH
HO
5
)
1
(
3
( )
(
)
i) NiCl2:6H2O
ii) NEt3
Et3NH
O
O
N
N
O
N
Ni
HO
(4)
Scheme 1.
(protonated) phenolic groups, a feature which has been observed
in related bis-aminopropane-pyridine-2,6-dicarboxamide com-
plexes [13].
atom and a terminal chloride atom. The bonds length of Zn(3)–
O(4), Zn(4)–O(8) and Zn(2)–O(12) are notably longer than the
other due to the coordination of adjacent carboxamido nitrogen
to the metal. The Zn–Npy distances [Zn(3)–N(1) = 2.213(5), Zn(4)–
N(4) = 2.266(5) and Zn(2)–N(7) = 2.223(5) Å] are longer than those
found in related zinc pyridine complexes [16].
3.1. Molecular structure of [HNEt3]2[Zn4Cl(POPYH)3] (2)
A search of the Cambridge Structural Database [17] reveals that
the structure of the anion is quite unique. While there are over 100
Reaction of ZnCl2 with 1 in a 1:1 stoichiometric ratio, in the
presence of NEt3, resulted in an immediate colour change to the
reaction mixture. After workup and cooling at ꢀ10°C a crop of yel-
low/orange crystals 2 where isolated and characterised. Crystallo-
graphic analysis of a suitable crystal of 2 shows that the complex is
composed of an unusual tetranuclear [Zn4Cl(POPYH)3]2ꢀ anion
with two triethylammonium cations. In the structure one of the
triethylammonium cations was so severely disordered that no
chemically sensible model for it could be refined so that, as a last
resort, it and several part occupancy water molecules were re-
moved from the model and the electron density compensated for
using the SQUEEZE [14] routine in PLATON [15]. Satisfactory
refinement was then achieved and the structural parameters did
not alter significantly between the refinements using the un-
SQUEEZEd and the SQUEEZEd data. Full confidence can be given
to the charge balance in the structure as the remaining amine
hydrogen atom was clearly located in the electron density differ-
ence map (but was refined with an AFIX constraint).
The unusual [Zn4Cl(POPYH)3]2ꢀ unit consist of four zinc centres
linked by three [POPYH]3ꢀ ligands with one zinc atom additionally
coordinated to a chlorine ligand (Fig. 2). Selected bond lengths and
angles are collected in Table 2. If viewed down the Cl1–Zn1 bond
direction the dianion has pseudo-three-fold symmetry. Each zinc
centre is tetra-coordinate adopting the expected tetrahedral geom-
etry. The metals are linked by two deprotonated phenolic oxygen
atoms from two different ligands. Zn(2), Zn(3), Zn(4) are also coor-
dinated by one deprotonated carboxamido nitrogen donor and one
pyridine nitrogen donor from the same ligand, while the coordina-
tion environment of Zn(1) is completed by a third phenolic oxygen
Fig. 2. The structure of the [Zn(POPYH)3Cl]2ꢀ dianion in 2 showing the atom
numbering scheme. Hydrogen atoms have been omitted for clarity.

Y. Pérez et al. / Polyhedron 30 (2011) 284–292
287
expected region for Pd(1)–Namide and Pd(1)–Npy interactions,
respectively [19]. The bite angles N(1)–Pd(1)–N(3) and N(1)–
Pd(1)–N(2) of the ligand are 79.9(3)o and 80.1(3)o, respectively,
while the N(2)–Pd(1)–N(3) angle of 160.0(3)o angle is ca. 20° from
the ideal angle of 180°.
Nevertheless, the N(1)–Pd(1)–Cl(1) angle of 177.88(19)o is close
to linear. The chelate rings show subtle differences upon complex-
ation (ligand 1: C(13)–N(3)–C(14) = 128.94(12)°, C(6)–N(2)–
C(7) = 129.16 (13)° while the equivalent angles in complex 3 are
C(7)–N(3)–C(21) = 117.1(7)°, C(6)–N(2)–C(7) = 118.1(7)°).
In the crystal the salt crystallises in the monoclinic space group
P21/c and the cation and anion are linked by an intermolecular
hydrogen bond [N(4)–H(4)ꢁ ꢁ ꢁO(1): 0.84 Å longer than those found
in related zinc, 1.89 Å, 2.786(9) Å, 162.6°]. There is also an intramo-
lecular hydrogen bond involving the hydroxyl hydrogen atom on
O(2) [O(2)–H(2A)ꢁ ꢁ ꢁO(1): 0.94 Å, 1.95 Å, 2.691(7) Å, 146.9°] and
an intermolecular hydrogen bond involving the other hydroxyl
hydrogen bond [O(4)–H(4A)ꢁ ꢁ ꢁO3 {1ꢀx, ꢀy, 1ꢀz} 0.84 Å, 1.93 Å,
2.733(8) Å, 160.8°].
Fig. 3. The ‘‘Zn4O6’’ core in the structure of the [Zn(POPYH)3Cl]2ꢀ dianion.
examples of Zn4O4 cubic core structures this appears to be the first
example of a Zn4O6 core that can best be described as an adaman-
tane-like structure, as shown in Fig. 3. This structure reflects the
3.3. Molecular structure of [HNEt3][Ni(POPYH)] 1.5H2O (4)
nꢀ
versatility of the [POPYH4–n
]
ligand and the ability to stabilise
polynuclear metal complexes. This is an aspect of its chemistry
which has not been established previously since, in all the structur-
ally characterised examples of complexes that contain this ligand,
the ligand only coordinates to one metal centre [7].
The crystal structure of complex 4 reveals that the asymmetric
unit contains a [Ni(POPYH2)]ꢀ anion with a triethylammonium cat-
ion and one and a half molecules of water. Selected bond lengths
Table 3
Selected bond lengths (Å) and angles (°) for the complex 3
3.2. Molecular structure of [HNEt3][Pd(POPYH2)Cl] (3)
Bond lengths (Å)
Pd(1)–N(1)
Pd(1)–N(3)
O(2)–C(16)
N(2)–C(1)
N(2)–C(11)
C(7)–O(3)
Bond angles (°)
N(2)–Pd(1)–N(3)
N(1)–Pd(1)–N(2)
O(1)–C(1)–C(2)
O(1)–C(1)–N(2)
N(2)–C(1)–C(2)
C(1)–N(2)–C(11)
1.940(6)
2.028(6)
1.387(11)
1.333(10)
1.434(10)
1.246(9)
Pd(1)–Cl(1)
Pd(1)–N(2)
O(1)–C(1)
N(3)–C(7)
N(3)–C(21)
O(4)–C(26)
2.303(2)
2.060(7)
1.270(10)
1.347(10)
1.435(10)
1.372(10)
The X-ray crystallographic study reveals that the salt 3 is com-
posed of [Pd(POPYH2)Cl]ꢀ anion with a triethylammonium cation.
Selected bond lengths and angles are collected in Table 3. The pal-
ladium atom adopts the distorted squared-planar geometry ex-
2ꢀ
pected for four-coordinate Pd(II). The POPYH2 ligand employs
three nitrogen donor atoms (two deprotonated carboxamido nitro-
gen atoms and one pyridine nitrogen atom) to coordinate the pal-
ladium centre, as illustrated in Fig. 4. The fourth coordination site
is occupied by chlorine atom with Pd(1)–Cl(1) distance 2.303(2) Å,
similar to the normal value found for Clꢀ trans to a pyridine ligand
[18]. The Pd(1)–N(3) and Pd(1)–N(1) bond lengths are in the
160.0(3)
80.1(3)
118.2(8)
127.3(8)
114.5(8)
118.1(7)
N(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–N(3)
O(3)–C(7)–C(6)
O(3)–C(7)–N(3)
N(3)–C(7)–C(6)
C(7)–N(3)–C(21)
177.88(19)
79.9(3)
119.0(7)
128.1(8)
112.8(8)
117.1(7)
Table 2
Selected bond lengths (Å) and angles (°) for the complex 2
Bond lengths (Å)
Zn(1)–O(3)
Zn(4)–O(3)
Zn(2)–O(4)
Zn(3)–O(4)
Zn(3)–N(1)
Zn(3)–N(3)
O(1)–C(6)
O(2)–C(13)
1.963(4)
1.990(4)
1.972(4)
2.155(4)
2.213(5)
1.975(5)
1.230(8)
1.235(9)
1.378(7)
1.359(7)
2.189(2)
Zn(1)–O(7)
Zn(2)–O(7)
Zn(3)–O(8)
Zn(4)–O(8)
Zn(4)–N(4)
Zn(4)–N(6)
O(5)–C(25)
O(6)–C(32)
O(7)–C(27)
O(8)–C(34)
1.964(4)
2.031(4)
1.955(4)
2.132(4)
2.266(5)
1.957(5)
1.238(8)
1.256(8)
1.392(7)
1.370(8)
Zn(1)–O(11)
1.957(4)
2.001(4)
2.126(4)
1.973(4)
2.223(5)
1.988(5)
1.246(8)
1.235(8)
1.357(8)
1.354(7)
Zn(3)–O(11)
Zn(2)–O(12)
Zn(4)–O(12)
Zn(2)–N(7)
Zn(2)–N(9)
O(9)–C(44)
O(10)–C(51)
O(11)–C(46)
O(12)–C(53)
O(3)–C(8)
O(4)–C(15)
Zn(1)–Cl(1)
Bond angles (°)
Zn(1)–O(3)–Zn(4)
Zn(2)–O(4)–Zn(3)
O(4)–Zn(3)–N(1)
N(3)–Zn(3)–N(1)
O(1)–C(6)–C(5)
O(2)–C(13)–C(1)
O(1)–C(6)–N(2)
O(2)–C(13)–N(3)
N(2)–C(6)–C(5)
N(3)–C(13)–C(1)
C(6)–N(2)–C(7)
C(13)–N(3)–C(14)
120.1(2)
122.8(2)
158.8(2)
80.2(2)
118.1(7)
117.9(6)
124.6(7)
128.9(7)
117.4(6)
113.2(6)
122.1(6)
125.1(6)
Zn(1)–O(7)–Zn(2)
Zn(3)–O(8)–Zn(4)
O(8)–Zn(4)–N(4)
N(6)–Zn(4)–N(4)
O(5)–C(25)–C(24)
O(6)–C(32)–C(20)
O(5)–C(25)–N(5)
O(6)–C(32)–N(6)
N(5)–C(25)–C(24)
N(6)–C(32)–C(20)
C(25)–N(5)–C(26)
C(32)–N(6)–C(33)
125.9(2)
122.9(2)
159.1(2)
79.7(2)
116.8(6)
116.7(6)
124.4(7)
128.8(7)
118.8(6)
114.6(6)
123.6(6)
125.0(6)
Zn(1)–O(11)–Zn(3)
Zn(4)–O(12)–Zn(2)
O(12)–Zn(2)–N(7)
N(9)–Zn(2)–N(7)
O(9)–C(44)–C(43)
O(10)–C(51)–C(39)
O(9)–C(44)–N(8)
O(10)–C(51)–N(9)
N(8)–C(44)–C(43)
N(9)–C(51)–C(39)
C(44)–N(8)–C(45)
C(51)–N(9)–C(52)
122.3(2)
123.1(2)
158.3(2)
81.0(2)
118.1(6)
117.3(6)
122.2(6)
128.5(6)
119.7(6)
113.2(5)
122.7(6)
124.4(5)

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Y. Pérez et al. / Polyhedron 30 (2011) 284–292
Fig. 4. The structure of the salt [HNEt3][Pd(POPYH2)Cl] 3 showing the intermolecular hydrogen bond between the cation and the anion. The anisotropic displacement
parameters have been drawn at the 50% probability level.
and angles are collected in Table 4. The geometry around the
central nickel atom is close to square planar, with the four donor
atoms consisting of two deprotonated carboxamido nitrogen
atoms, one deprotonated phenolate oxygen atom and one pyridine
nitrogen atom as displayed in Fig. 5. The Ni(1)–Namide distances
[1.8415(17) and 1.9066(17) Å] are similar to those found in other
square-planar Ni complexes with pyridine amide ligands (1.835–
1.932 Å) [20]. Nevertheless, the Ni(1)–Namide distances are shorter,
compared to those in Ni complexes where the pyridine amide li-
Table 4
Selected bond lengths (Å) and angles (°) for the complex 4.
Bond lengths (Å)
Ni(1)–N(1)
Ni(1)–N(2)
C(13)–O(2)
N(3)–C(13)
C(14)–N(3)
O(4)–C(15)
Bond angle (°)
N(2)–Ni(1)–N(3)
N(1)–Ni(1)–N(2)
O(1)–C(6)–C(5)
O(1)–C(6)–N(2)
N(2)–C(6)–C(5)
C(6)–N(2)–C(7)
1.806(2)
1.842(2)
1.247(3)
1.340(3)
1.422(3)
1.359(3)
Ni(1)–O(3)
Ni(1)–N(3)
O(1)–C(6)
N(2)–C(6)
N(2)–C(7)
O(3)–C(8)
1.862(2)
1.907(2)
1.249(2)
1.333(3)
1.408(3)
1.353(3)
gands are coordinated in
a tridentate mode (2.109–2.135 Å)
167.08(8)
83.68(8)
122.58(19)
128.3(2)
109.11(17)
129.24(17)
N(1)–Ni(1)–O(3)
N(1)–Ni(1)–N(3)
O(2)–C(13)–C(1)
O(2)–C(13)–N(3)
N(3)–C(13)–C(1)
C(13)–N(3)–C(14)
171.44(7)
83.42(8)
119.95(19)
128.9(2)
111.11(17)
120.17(17)
[2a,21]. The demands of the ligand bite angles are reflected in
the relatively narrow N(1)–Ni(1)–N(2) = 83.68(8)° and N(1)–Ni(1)–
N(3) = 83.42(8)° angles. The trans N(2)–Ni(1)–N(3) = 167.08(8)°
and N(1)–Ni(1)–O(3) = 171.44(7)° angles also show deviations
from the ideal value of 180°.
Fig. 5. The structure of [HNEt3][Ni(POPYH)] 4 showing the atom numbering scheme. The solvent water molecules have been omitted for clarity. The anisotropic displacement
parameters have been drawn at the 50% probability level.

Y. Pérez et al. / Polyhedron 30 (2011) 284–292
289
Table 5
In the crystal structure the cation and anion are linked through
an intermolecular hydrogen bond from the triethylammonium
proton to carbonyl oxygen atom on the anion [N(4)–
Selected bond lengths and angles for the complex (5)
a
Bond lengths (Å)
Ni(1)–N(1)
Ni(1)–N(2)
C(13)–O(2)
N(3)–C(13)
C(14)–N(3)
O(4)–C(15)
Bond angles (°)
N(2)–Ni(1)–N(3)
N(1)–Ni(1)–N(2)
O(1)–C(6)–C(5)
O(1)–C(6)–N(2)
N(2)–C(6)–C(5)
C(6)–N(2)–C(7)
1.801(3)
1.835(2)
1.239(4)
1.358(4)
1.432(4)
1.372(4)
Ni(1)–O(3)
Ni(1)–N(3)
O(1)–C(6)
N(2)–C(6)
N(2)–C(7)
O(3)–C(8)
1.865(2)
1.909(2)
1.252(4)
1.334(4)
1.404(4)
1.372(4)
H(4)ꢁ ꢁ ꢁO(2) 0.931 Å, 1.85 Å, 2.737(2) Å, 159.8°]. There is also a
hydrogen bond from the hydroxyl group on the anion with a car-
bonyl oxygen atom on an adjacent molecule [O(4)–H(4)ꢁ ꢁ ꢁO(1)
{ꢀx, 1 ꢀ y, ꢀz} 0.87(4) Å, 1.83(4) Å, 2.672(2) Å, 161(3)°] and a
hydrogen bond involving one of the solvent water molecules and
the coordinated hydroxyl oxygen atom on the anion, O(3)
[O(1S)–H(1S)ꢁ ꢁ ꢁO(3) {ꢀx, 1 ꢀ y, ꢀz} 0.827(10) Å, 2.002(15) Å,
2.797(3) Å, 161(4)°].
167.29(12)
83.68(11)
122.0(3)
128.2(3)
109.8(3)
127.9(3)
N(1)–Ni(1)–O(3)
N(1)–Ni(1)–N(3)
O(2)–C(13)–C(1)
O(2)–C(13)–N(3)
N(3)–C(13)–C(1)
C(13)–N(3)–C(14)
170.73(10)
83.60(11)
120.5(3)
128.2(3)
111.3(3)
117.3(2)
3.4. Molecular structure of K[Ni(POPYH)].2MeOH (5)
In the crystal structure of K[Ni(POPYH)]ꢁ2MeOH each asymmet-
ric unit contains one cation, one anion and two molecules of meth-
anol solvent. The [Ni(POPYH)]ꢀ anion is essentially identical to that
found in 4. The molecular structure of the anion 5 is illustrated in
Fig. 6 while selected bond lengths and angles are collected in Table
5. The coordination to nickel is close to square planar, similar to
that for Ni in the complex 4. The hydroxyl hydrogen on the unco-
ordinated oxygen atom, O(4), forms an intermolecular hydrogen
bond to the carbonyl oxygen atom, O(1), on an adjacent anion
[O(4)–H(4O)ꢁ ꢁ ꢁO(1) {ꢀx, 1 ꢀ y, ꢀz} 0.830(10) Å, 1.92(2) Å, 2.649(3)
Å, 147(4)°], a feature that is also observed in the packing of 4. How-
ever, the presence of the potassium ion and the two methanol mol-
ecules are responsible for major differences in the crystal packing
compared to 4. The two methanol solvent molecules hydrogen
bond to the coordinated hydroxyl oxygen atom, O(3), on the
[Ni(POPYH)]ꢀ anion [O(1S)–H(1O)ꢁ ꢁ ꢁO3 0.827(10) Å, 1.900(12) Å,
2.716(3) Å, 169(3)°, and O(2S)–H(2O)ꢁ ꢁ ꢁO3 0.830(10) Å, 1.965
(15) Å, 2.778(3) Å, 166(4)°. The K+ ion interacts with one of the car-
bonyl oxygen atoms, O(1), on one [Ni(POPYH)]ꢀ anion (K(1)ꢁ ꢁ ꢁO(1)
2.731(1) Å), and with the other carbonyl oxygen atom, O(2), on an
adjacent anion related by the symmetry operation 1 ꢀ x, 1 ꢀ y, -z at
a distance of 2.570(2) Å. The cation also interacts with the metha-
nol oxygen atoms O(1S) and O(2S) from two different symmetry
related methanol molecules [K(1)ꢁ ꢁ ꢁO(1S) {x, ꢀy ꢀ 1.5, z ꢀ 0.5}
2.603(2) Å and K(1)ꢁ ꢁ ꢁO(2S) {1 ꢀ x, 1 ꢀ y, ꢀz} 2.570(2) Å], and the
uncoordinated hydroxyl oxygen atom O(4) related by the symme-
try operation –x, 1 ꢀ y, ꢀz at a distance of 2.933(3) Å. The potas-
sium coordination environment is completed by an interaction
with the
p cloud of the C(17)–C(18) bond of the free aromatic ring
[K(1)ꢁ ꢁ ꢁC(17) {x, ꢀy-1.5, z ꢀ 0.5} 3.424(4) and K(1)ꢁ ꢁ ꢁC(18) {x,
ꢀy ꢀ 1.5, z ꢀ 0.5}3.317(4) Å]. This gives the potassium ion a dis-
torted octahedral coordination environment as illustrated in Fig. 7.
4. Conclusion
The series of investigations in this work show that the N,N0-
bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide ligand (PO-
PYH4), under basic conditions, displays a versatile coordination
chemistry in its interactions with a range of transition metal ions.
Previously, only the chemistry with Fe(III) had been explored [9].
In a partially deprotonated form the ligand forms mononuclear
monoanionic salt complexes with nickel(II) and palladium(II), in
complexes 3, 4 and 5, satisfying the requirement of the square pla-
nar coordination geometry for these d8 ions. In the reaction with
Zn(II) salts a unique tetranuclear dianion 2 with an unusual
Fig. 6. The structure of K[Ni(POPYH)].2MeOH 5 showing the interaction of the [Ni(POPYH)]- anion with the K+ cation and the two methanol solvent molecules. The
anisotropic displacement parameters have been drawn at the 50% probability level.

290
Y. Pérez et al. / Polyhedron 30 (2011) 284–292
UV–Vis spectrum in EtOH, kmax nm (e
, Mꢀ1 cmꢀ1): 311 (11560).
Found (calc. for C57H33N9O12ClZn4): C 51.39 (51.36), H 2.47
(2.50), N 9.30 (9.46).
6.3. Synthesis of [HNEt3][PdCl(POPYH2)] (3)
To a stirring solution of POPYH4 (0.66 g, 2 mmol) in CH3CN
(50 mL) at 70 °C was added NEt3 (0.6 mL, 4.3 mmol). The solution
was allowed to stir for 15 min and a solution of PdCl2 (0.36 g,
2 mmol) in hot CH3CN (10 mL) was then added. The mixture was
refluxed for 3 h and then cooled to 25 °C. The brown solution
was filtered and the solvent was removed under vacuum. The
brown solid was dissolved in THF and yellow/orange crystals were
l
obtained. Yield: 0.59 g, 66%. H NMR (300 MHz, DMSO-d6, 25 °C):
d = 1.17 (t, 3H, ꢀHNCH2CH3), 3.06 (q, 2H ꢀHNCH2CH3), 6.62 (m,
2H, C6H4), 6.69 (m, 2H, C6H4), 6.89 (m, 2H, C6H4), 7.03 (m, 2H,
C6H4), 7.78 (d, 1H, J = 7.8 Hz, C5H3N), 8.17 (m, 1H, C5H3N), 8.25 (t,
1H, J = 7.8 Hz, C5H3N), 9.52 (s, 1H, ꢀHNCH2CH3) 10.41 (s, 2H, O–
H). 13C{lH} NMR (75 MHz, DMSO-d6, 25 °C): d = 115.3 (C10, C17),
116.9 (C11, C18), 123.8 (C19, C12), 128.2 (C9, C16), 133.7 (C7,
C14), 139.4 (C–OH), 150.1 (C2, C4), 150.2 (C3), 163.1 (C5, C1),
167.3 (C@O). Selected IR bands (KBr–Nujol, cmꢀ1): 3210 (w, O–
H), 1604 (s, C@O), 1582 (s), 1541 (s) 1457 (vs), 1377 (s), 1229
(w), 1172 (m), 1100 (w), 1035 (m), 761 (m). Found (calc. for
Fig. 7. The coordination environment of the potassium cation in K[Ni(POPYH)].2-
MeOH 5 showing the distorted octahedral environment.
Zn4O6 adamantane core is formed. This represents the first polynu-
nꢀ
clear complex of the [POPYH4–n
]
ligand and provides and impe-
tus for studies of this ligand with early first row transition metals
and the heavier transition metals from the second and third row of
the d block.
C
19H13N3O4PdꢁHNEt3): C 54.32 (54.11), H 5.17 (5.09), N 9.92
5. Experimental section
(10.10).
Ligand synthesis was performed using standard Schlenk tube
technique under an atmosphere of dry nitrogen. Complexation
reactions were conducted under aerobic conditions. All commer-
cial materials and solvents were used as received; Triethylamine
and pyridine were distiled from appropriate drying agents.
6.4. Synthesis of [HNEt3][Ni(POPYH)] (4)
Complex 4 was made using an identical method to that used to
synthesis 3, using NiCl2ꢁ6H2O (0.48 g, 2 mmol). Complex 4 was iso-
lated by filtration following recrystallization from hot acetonitrile
l
to give complex 4 as yellow/orange crystals. Yield: 0.66 g, 66%. H
NMR (300 MHz, DMSO-d6, 25 °C): d = 1.12 (t, 3H, ꢀHNCH2CH3),
3.08 (q, 2H ꢀHNCH2CH = 3), 6.05 (m, 1H, C6H4), 6.18 (m, 1H,
C6H4), 6.45 (m, 1H, C6H = 4), 6.76 (m, 2H, C6H4), 6.94 (m, 1H,
C6H4), 7.20 (m, 1H, C6H4) 7.35 (d, 1H, J = 7.8 Hz, C6H4), 7.52 (d,
1H, J = 7.2 Hz, C5H3N), 7.73 (m, 1H, C5H3N), 8.1 (t, 1H, J = 7.8 Hz,
C5H3N), 10.44 (s, 1H, O–H). 13C{lH} NMR (75 MHz, DMSO-d6,
25 °C): d = 112.9 (C10), 114.4 (C17), 117.6 (C11), 117.9 (C18),
118.6 (C19), 121.1 (C12), 122.3 (C9), 124.3 (C16), 128.0 (C7),
134.3 (C14), 139.4 (C–OH), 140.1 (C–OH), 150.4 (C5), 150.7 (C1),
153.6 (C3), 161.5 (C2, C4), 165.2 (C@O), 166.2 (C@O). Selected IR
bands (KBr–Nujol, cmꢀ1): 3281 (w, O–H), 1617 (s, C@O), 1585
(s), 1464 (vs), 1377 (m), 1290 (m), 1180 (w), 1095 (w), 1031 (w),
6. Preparation of compounds
6.1. Synthesis of N,N0-bis(2-hydroxyphenyl)-pyridine-2,6-
dicarboxamide (POPYH4) (1)
The ligand was prepared following a reported procedure for 2,6-
pyridinedicarbonyldichloride compound [8]. Pale yellow needles of
the ligand suitable for X-ray analysis were grown by vapour diffu-
sion of ethyl acetate into DMF solution of the ligand. Yield: 5.78 g,
92%.
6.2. Synthesis of [HNEt3]2[Zn4Cl(POPYH)3] (2)
731 (m). UV-Vis spectrum in EtOH, kmax nm (e
, Mꢀ1 cmꢀ1): 311
To a stirring solution of POPYH4 (0.33 g, 1 mmol) in CH3CN
(50 mL) at 70 °C was added NEt3 (0.3 mL, 2.15 mmol). The bright
yellow solution was allowed to stir for 15 min and a solution of
ZnCl2 (0.14 g, 1 mmol) in hot CH3CN (10 mL) was then added.
The mixture was heated under reflux for 3 h and cooled to 25 °C.
The solution was filtered and the solvent was removed under vac-
uum. The yellow solid was dissolved in ethanol and pale yellow/or-
ange crystals were obtained. Yield: 0.74 g, 56%. lH NMR (300 MHz,
DMSO-d6, 25 °C): d = 1.19 (t, 3H, ꢀHNCH2CH3), 3.01 (q, 2H
ꢀHNCH2CH3), 6.06 (d, 1H, J = 8.1 Hz, C6H4), 6.23 (m, 2H, C6H4),
6.38 (m, 2H, C6H4), 6.62 (t, 1H, J = 7.8 Hz, C6H4), 7.86 (d, 1H, J =
8.1 Hz, C6H4), 8.30 (t, 1H, J = 7.8 Hz, C6H4), 8.39 (d, 1H, J = 7.8 Hz,
C5H3N), 8.49 (d, 1H, J = 7.5 Hz, C5H3N), 8.66 (d, 1H, J = 8.1 Hz,
C5H3N), 11.43 (s, 1H, N–H). 13C{lH} NMR (75 MHz, DMSO-d6,
25 °C): d = 113.6 (C10), 114.1 (C17), 116.4 (C11), 117.5 (C18),
118.6 (C19), 119.9 (C12), 120.7 (C9), 120.9 (C16), 124.9 (C7),
128.1 (C14), 135.7 (C–OH), 140.1 (C–OH), 150.0 (C5), 151.7 (C1),
152.8 (C3), 152.9 (C2, C4), 160.5 (C@O), 161.4 (C@O). Selected IR
bands (KBr–Nujol, cmꢀ1): 3352 (w, NH), 1654 (s, C@O), 1608 (m),
1575 (s), 1526 (s), 1465 (s), 1316 (w), 1271 (m), 1239 (w).
(11300). Found (calc. for C19H13N3O4NiꢁHNEt3): C 59.46 (59.32),
H 5.29 (5.38), N 11.66 (11.07).
6.5. Synthesis of K[Ni(POPYH)] (5)
Complex 5 was made using an identical method to that used to
synthesis 3, using NiCl2ꢁ6H2O (0.48 g, 2 mmol) and KOH (0.25 g,
4.5 mmol) in place of triethylamine. Complex 5 was isolated by fil-
tration following recrystallization from hot methanol to give com-
plex 5 as yellow/orange crystals. Yield: 0.29 g, 72%. lH NMR
(300 MHz, DMSO-d6, 25 °C): d = 6.06 (m, 1H, C6H4), 6.14 (m, 1H,
C6H4), 6.43 (m, 1H, C6H4), 6.72 (m, 2H, C6H4), 6.93 (m, 1H, C6H4),
7.20 (m, 1H, C6H4) 7.34 (d, 1H, J = 7.8 Hz, C6H4), 7.51 (d, 1H,
J = 7.2 Hz, C5H3N), 7.71 (m, 1H, C5H3N), 7.99 (t, 1H, J = 7.8 Hz,
C5H3N), 10.44 (s, 1H, O–H). 13C lH NMR (75 MHz, DMSO-d6,
25 °C): d = 111.8 (C10), 113.4 (C17), 116.7 (C11), 117.4 (C18),
120.0 (C19), 121.2 (C12), 121.3 (C9), 123.2 (C16), 127.0 (C7),
133.2 (C14), 138.2 (C–OH), 139.0 (C–OH), 149.3 (C5), 149.7 (C1),
152.6 (C3), 161.5 (C2, C4), 164.2 (C@O), 165.2 (C@O). Selected IR
bands (KBr–Nujol, cmꢀ1): 3321 (w, O–H), 1614 (s, C@O), 1573

Y. Pérez et al. / Polyhedron 30 (2011) 284–292
291
Table 6
Crystal data for compounds 1–5
1
2
3
4
5
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
C
19H15N3O4.(C3H7NO)
C69H92ClN11O14Zn4
1596.47
Monoclinic
P21/n
16.5860(5)
15.4580(5)
29.9250(11)
90
C25H29ClN4O4Pd
591.37
Monoclinic
P21/c
10.0390(2)
20.0330(6)
12.9080(4)
90
C25H31N4NiO5.5
534.25
Monoclinic
P21/n
12.1690(2)
10.8170(2)
18.5920(3)
90.00
C21H20KN3NiO6
508.21
Monoclinic
P21/c
7.6550(2)
13.5910(5)
20.7350(8)
90.00
422.44
Monoclinic
P21/n
7.4020(1)
10.8050(2)
26.6320(7)
90
b (Å)
c (Å)
a
(°)
b (°)
97.487(1)
90
2111.83(7)
150(2)
99.877(2)
90
7558.6(4)
150(2)
112.598(1)
90
2396.64(11)
150(2)
92.693(1)
90
2444.60(7)
150(2)
90.876(1)
90
2157.00(13)
150(2)
c
(°)
V (Å3)
T (K)
Z
4
4
4
4
4
Dc (g cmꢀ3
)
1.329
0.096
1.403
1.357
1.639
0.927
1.452
0.840
1.565
1.136
l
(mmꢀ1
)
F(0 0 0)
888
3328
1208
1124
1048
Crystal size (mm)
Tmax/Tmin
h limits (°)
Measured reflection
Unique reflections
Independent reflections Rint
0.30 ꢂ 0.15 ꢂ 0.15
0.994/0.908
3.36–25.02
11760
3651
0.0424
0.15 ꢂ 0.10 ꢂ 0.08
1.000/0.892
2.91–23.35
10719 (after SQUEEZE)
10719
0.20 ꢂ 0.13 ꢂ 0.01
1.000/0.844
3.57–20.86
14537
2489
0.1713
0.20 ꢂ 0.13 ꢂ 0.10
1.000/0.910
3.62–30.50
46658
7280
0.0736
0.15 ꢂ 0.15 ꢂ 0.10
1.000/0.898
3.15–27.49
14015
4691
0.0685
0.000
Observed reflections (I > 2
R1, wR2 (obs data)
r
(I))
2770
7603
1842
4982
3237
0.0364, 0.0850
0.0569, 0.0947
0.162
0.0573, 0.1748
0.0845, 0.1913
0.513
0.0558, 0.0860
0.0907, 0.0952
0.535
0.0445, 0.1129
0.0820, 0.1323
0.702
0.0463, 0.1085
0.0828, 0.1238
0.406
R1, wR2 (all data)
Max residual electron density (e Åꢀ3
)
(s), 1489 (s), 1463 (vs), 1377 (m), 1273 (m), 1144 (w), 1093 (w),
Acknowledgements
1029 (w), 732 (m). UV–Vis spectrum in EtOH, kmax nm
(e,
Mꢀ1ꢁcmꢀ1): 371 (12030). Found (calc. for C19H12N3O4NiꢁK: C
We are grateful to the EPSRC for support and for the award of a
Senior Fellowship (to P. R. R.). Y. C.-P is grateful to the Departamento
de Química Inorgánica y Analítica, E.S.C.E.T, Universidad Rey Juan
Carlos, for study leave and for financial support.
51.48 (51.38), H 2.71 (2.72), N 9.23 (9.46).
7. Crystallography
Appendix A. Supplementary data
X-ray data collection and structure determination: All data col-
lections for 1–5 were carried out on a Bruker KappaCCD diffrac-
tometer, equipped with an Oxford Cryosystems Cryostream
crystal cooling apparatus, using graphite monochromated Mo K
radiation. Structure solution and refinements were performed
using SHELX86 [22] and SHELX97 [23] software, respectively. Full ma-
trix anisotropic refinement on F2 was implemented and refinement
continued until convergence was reached. In the final least-squares
cycles a weighting scheme was introduced that minimised the var-
iance. For 1, all the hydrogen atoms were located from the Fourier
difference map and were freely. For the other structures the hydro-
gen atoms were included at calculated positions and allowed to
ride on the bonded carbon or oxygen atom with the H-atom as-
signed a displacement parameter 1.2 times that of the adjacent
atom (1.5 times for methyl H-atoms), except in 4 and 5 where
the hydroxyl H-atom was allowed to refine freely (4) or DFIXed
(5) and the water H-atoms were dFIXed to the oxygen atom posi-
tion Crystals of 2 small and weakly diffracting, hence the low res-
olution level. In the structure of 2 one of the [HNEt3]+ and several
low occupancy water molecules were so severely disordered that
no chemically sensible, stable refinement model could be found
and, as a last resort, these atoms were removed and the structure
was SQUEEZEd using the SQUEEZE [12] routine in PLATON [13].
This procedure gave a stable refinement for the rest of the struc-
ture (details of the SQUEEZE results are included in the cif file for
2). In the case of complex 3, a poor resolution to the data was ob-
tained because of weakly diffracting crystals, and no observed data
beyond 0.8 Å resolution was collected. A summary of crystal data,
data collection and refinement parameters for the structural anal-
ysis is given in Table 6.
CCDC 747981-747985; contains the supplementary crystallo-
graphic data for compounds 1–5. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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