Synthesis and coordination chemistry of doubly-tridentate tripodal pyridazine and pyrimidine-derived ligands: Structural interplay between M 2L and M2L2 (M = Ni and Pd) complexes and magnetic properties of iron(II) complexes

Article abstract of DOI:10.1071/CH09244

The coordination chemistry of three bridging doubly-tridentate ligands, including the known compound 3,6-bis(di-2-pyridylmethyl)pyridazine (1), which is structurally similar to 1,4-bis(di-2-pyridylmethyl)phthalazine (2), and two pyrimidine-linked compounds 4,6-bis(di-2-pyridylmethyl)pyrimidine (3), and 4,6-bis(di-2-pyridylamino)pyrimidine (4), was investigated with Fe^II, Ni^II, and Pd^II metal salts. Ligands 3 and 4 were synthesized in one-pot reactions from easily obtained starting materials; compound 3 was synthesized from di-2-pyridylmethane and 4,6-diiodopyrimidine in 48% yield, while ligand 4 was prepared by reacting di-2-pyridylamine with 4,6-dichloropyrimidine in 27% yield. During the synthesis of 4, an additional compound, 4-chloro-6-(di-2-pyridylamino)pyrimidine (5), with only one tridentate binding site was obtained in 30% yield. Reactions of 1, 3, and 4 with Fe ^II or Ni^II salts gave two types of complexes, either discrete M₂L or M₂L₂ assemblies. The Pd ^II complexes obtained were also characterized as discrete M ₂L complexes. The compounds were characterized by a combination of NMR and IR spectroscopy, microanalysis and X-ray crystallography. Noticeable differences in the structures obtained for Ni^II coordination complexes with the carbon-linked (3) and nitrogen-linked (4) ligands were observed, whereby the nitrogen linker adopted a trigonal planar geometry and prevented tridentate facial coordination of the octahedral metal centres. The magnetic properties of dinuclear Fe^II complexes of 1 were examined to see if they showed spin-crossover effects, a feature recently observed by others in other dinuclear helicate complexes, but the complexes remained high-spin at all temperatures between 300 and 2 K. CSIRO 2009.

Full text of DOI:10.1071/CH09244

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
Aust. J. Chem. 2009, 62, 1142–1154
www.publish.csiro.au/journals/ajc
Synthesis and Coordination Chemistry of Doubly-Tridentate
Tripodal Pyridazine and Pyrimidine-Derived Ligands:
Structural Interplay Between M L and M L (M = Ni and Pd)
2
2 2
Complexes and Magnetic Properties of Iron(II) Complexes
A,B,D
C
C
Christopher J. Sumby,
Ben A. Leita, Boujemaa Moubaraki,
C
A
Keith S. Murray, and Peter J. Steel
A
Department of Chemistry, College of Science, University of Canterbury, Christchurch, New Zealand.
Current address: School of Chemistry and Physics, University ofAdelaide,Adelaide, SA 5005,Australia.
School of Chemistry, Monash University, Clayton, Vic. 3800, Australia.
B
C
D
Corresponding author. Email: christopher.sumby@adelaide.edu.au
The coordination chemistry of three bridging doubly-tridentate ligands, including the known compound 3,6-bis(di-
-pyridylmethyl)pyridazine (1), which is structurally similar to 1,4-bis(di-2-pyridylmethyl)phthalazine (2), and two
pyrimidine-linked compounds 4,6-bis(di-2-pyridylmethyl)pyrimidine (3), and 4,6-bis(di-2-pyridylamino)pyrimidine (4),
2
II
II
II
was investigated with Fe , Ni , and Pd metal salts. Ligands 3 and 4 were synthesized in one-pot reactions from easily
obtained starting materials; compound 3 was synthesized from di-2-pyridylmethane and 4,6-diiodopyrimidine in 48%
yield, while ligand 4 was prepared by reacting di-2-pyridylamine with 4,6-dichloropyrimidine in 27% yield. During the
synthesis of 4, an additional compound, 4-chloro-6-(di-2-pyridylamino)pyrimidine (5), with only one tridentate binding
II
II
site was obtained in 30% yield. Reactions of 1, 3, and 4 with Fe or Ni salts gave two types of complexes, either
II
discrete M2L or M2L2 assemblies. The Pd complexes obtained were also characterized as discrete M2L complexes. The
compounds were characterized by a combination of NMR and IR spectroscopy, microanalysis and X-ray crystallogra-
II
phy. Noticeable differences in the structures obtained for Ni coordination complexes with the carbon-linked (3) and
nitrogen-linked (4) ligands were observed, whereby the nitrogen linker adopted a trigonal planar geometry and prevented
II
tridentate facial coordination of the octahedral metal centres. The magnetic properties of dinuclear Fe complexes of
1
were examined to see if they showed spin-crossover effects, a feature recently observed by others in other dinuclear
helicate complexes, but the complexes remained high-spin at all temperatures between 300 and 2 K.
Manuscript received: 25 April 2009.
Manuscript accepted: 16 July 2009.
Introduction
multinuclear complexes have been studied. Extension to
ꢀ ꢀ ꢀ
2,2 ,6 ,2 -terpyridine (tpy) chelating motifs as components of
Transition metal complexes of bridging heterocyclic ligands
capable of facilitating strong interactions between multiple coor-
dinated metal centres have continued to attract attention, in
[27]
bridging ligands has also been reported.
A structural variation of the tridentate tpy approach to gener-
ating bridging ligands is to use C3-symmetric tridentate tripodal
ligands, which are capable of facially coordinating to an octahe-
dral metal atom rather than the meridional mode adopted by tpy.
Although there are many examples and studies of simple tripodal
ligands, the extension from tripodal ligands to multitopic tripo-
dal bridging ligands has attracted limited attention. Examples
[
1,2]
[3–7]
particular with regard to their stereochemical,
magnetic,
electrochemical, and photophysical properties.[
8–11]
In regard to
the magnetic properties of multinuclear transition metal com-
plexes, bridging ligands with the potential to chelate at both
metal centres result in complexes with greater stability and
potentially enhanced metal–metal interaction.
ple of such a chelating ligand, 2,2 -bipyrimidine (bpym), has
been the subject of significant investigation and has been shown
[7,12]
An exam-
ꢀ
include the doubly-tripodal hexadentate ligand, 1,2-bis[(6-bis(2-
pyridyl)methyl)-2-pyridyl]ethane[
28–30]
and a series of ligands
[8,13]
[31,32]
to form complexes with short metal–metal distances.
For
incorporating multiple tris(1-pyrazolyl)methane groups
(C. J. Schneider, S. R. Batten, B. Moubaraki, K. S. Murray,
unpubl. data).
II
example, Real’s classic Fe dinuclear spin crossover (SCO)
[
14]
complexes,
[{Fe(bpym)(NCE)2}2-µ-bpym] (E = S, Se) uti-
lize bpym to facilitate spin coupling in this SCO system with
We have undertaken a study of ligands with the schematic
representation shown in Fig. 1a. The ligands have both the
metals coordinated to a planar aromatic heterocycle (N–Y–N)
that should result in complexes displaying strong magnetic or
electronic coupling through the ligand π-system. There are
several potential points of variation within the generalized
short metal–metal separations of ∼5.5 Å.
ꢀ
[15]
Bridging ligands possessing 2,2 -bipyridine (bpy)
and
di-2-pyridylmethane
and di-2-pyridylamine (dpa)[20–26] chelating
motifs for facilitating strong metal–metal interactions within
[
15]
1
,10-phenanthroline units (phen),
[
16–19]
(
dpm),
©
CSIRO 2009
10.1071/CH09244
0004-9425/09/091142

RESEARCH FRONT
Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(ii) Complexes
1143
(
a)
Z
Z
included to bestow further information on the coordination
preferences of 3 and, in particular, 4.
Y
N
N
N
N
N
N
L
L
L
L
M
L
M
L
Results and Discussion
Syntheses of the Ligands
A procedure for the synthesis of ditopic tripodal ligands contain-
ing a carbon linker atom (Z) has been reported previously.
(
b)
[37,38]
Lithiation of di-2-pyridylmethane with n-butyllithium, fol-
lowed by reaction with either 3,6-dichloropyridazine or 1,4-
dichlorophthalazine, gave 1 and 2, respectively, as previously
described. A similar procedure was employed for the synthesis
of 3. In this case, a chloride leaving group did not give usable
yields of product, but this was overcome by using an iodide leav-
ing group. The metathesis reaction was carried out as shown in
Scheme 1; simply stirring a slurry of 4,6-dichloropyrimidine in
N
N
N
N
N
N
N
N
N
N
N
N
1
3
2
4
N
N
hydriodic acid gave the desired 4,6-diiodopyrimidine (6) in 52%
N
N
N
N
N
N
N
N
[47]
N
N
N
yield.
Repeating the synthesis of 1 using 6 gave the desired
N
ligand in 48% yield.
The method of Mosny and Crabtree[48] for the synthesis
of tpa was adapted for the synthesis of 4. Reaction of di-2-
pyridylamine with 4,6-dichloropyrimidine (Scheme 1) in reflux-
ing mesitylene gave a mixture of unreacted starting material,
monosubstituted product, and the desired compound.After chro-
matography and recrystallization, this provided modest yields of
the desired product, 4 (27%) and the intermediate monoadduct,
N
Cl
N
N
N
N
5
5
(30%).
Fig. 1. (a) A schematic representation of the ligands studied in this work;
and (b) the structures of compounds 1–5.
Investigation of the Coordination Chemistry
Complexes of 1
The coordination chemistry of 1 has been investigated pre-
structure schematically represented, with different pendant
heterocyclic donors (N), different linker atoms (Z), and bridg-
ing heterocyclic cores (N–Y–N) possible. Two ligands fitting
this schematic structure, 3,6-bis(di-2-pyridylmethyl)pyridazine
viously. Copper(ii) complexes with both coordinating and non-
have been synthesized for 1 with
a focus on investigating the magnetic properties of such com-
coordinating anions[
33,35,36]
plexes. When 1 was reacted with copper perchlorate, a [2 + 2]
(
1) and 1,4-bis(di-2-pyridylmethyl)phthalazine (2) (Fig. 1b),
dimeric complex was obtained, which was structurally charac-
[33–39]
[33]
have been investigated by several groups,
including
terized by X-ray crystallography.
Subsequently, it was shown
[
40,41]
II
I
[34]
ourselves,
and have been shown to bridge two metals in
that a Cu /Cu mixed-valence complex could be prepared.
the desired manner. In several salient examples, 1 and 2 form
We have previously reported that 1 forms a similar saturated
homotopic double-stranded dinuclear helicate with Ni .
II [41]
saturated double-stranded dinuclear helicates with M(BF4)2
[
41]
[33]
[40]
(
M = Cu, Ni),
Cu(ClO4)2,
and recently, Cu(NO3)2.
We have also investigated further chemistry of 1 with other
Group 10 transition metals and utilized coordinating anions.
Reaction of 1 with palladium chloride gave a complex 7 that
was characterized as [{PdCl2}2(1)]·2H2O by elemental analy-
sis. Based on other results obtained for 4 (see below), it was
proposed that in this complex, the metal centres coordinate only
through the pyridine nitrogen atoms.This could not be confirmed
for 7 as it was insoluble in common NMR solvents. Reaction of
1 with nickel perchlorate and sodium thiocyanate gave com-
plex 8 in 91% yield. The complex was shown by the crystal
structure, microanalysis, and IR spectroscopy to have an Ni2L
compositionwiththeformula[{Ni(NCS)(µ2-NCS)}2(1)]·2H2O
II
I
A structurally similar mixed-valent Cu /Cu system has also
been reported with 1[
34]
and 2.
[39]
Other related dinucleat-
ing pyridazine-linked chelating ligands have been studied by
Thompson et al.[
42–44]
and Brooker et al.
[45]
II
to probe magnetic
II
exchange and SCO effects, the latter in Co and Fe species.
Herein, we report further coordination chemistry of a doubly-
tridentate bridging ligand containing a pyridazine core (1) and
the synthesis and coordination chemistry of related ligands
with a pyrimidine core, 4,6-bis(di-2-pyridylmethyl)pyrimidine
(
3) and 4,6-bis(di-2-pyridylamino)pyrimidine (4). In addition
to structural studies of nickel(ii) and palladium(ii) dinuclear
complexes of ligands 1, 3, and 4 with coordinating and non-
coordinating anions, we report the magnetic properties of iron(ii)
dinuclear complexes of 1, which possesses a short pyridazine
bridge. We were particularly interested to see if these new di-
(Scheme 2). This is very similar to the structure of copper(ii)
complexes of 1 with bridging halide anions[
33,35,36]
and also
copper(ii) and nickel(ii) complexes reported for 2 with coordi-
natinganions.[
37–40,49]
TheIRspectrumof 8revealstheexpected
II
[7]
−1
nuclear Fe compounds displayed SCO. This follows on from
absorbances at 2097 cm for capping N-bound thiocyanate and
1996 cm for µ2-bridging N-bound thiocyanate.
II
−1
a recent report of a two-step SCO transition for Fe coordi-
nation polymers of the analogous N-linked pyrimidine ligand
Complexes 9–11 were synthesized via the method shown in
Scheme 2. For example, a solution of iron tetrafluoroborate in
methanol was added to a solution of ligand 1 in a 1:1 mol ratio
to give, after isolation and drying, [Fe2(1)2](BF4)4 (9) as an
−
−
[46]
4
, containing NCS and NCSe as co-ligands.
complexes of two related model compounds, tri-2-pyridylamine
tpa) and 4-(di-2-pyridylamino)-6-chloropyrimidine (5), are also
Nickel(ii)
(

RESEARCH FRONT
1
144
C. J. Sumby et al.
Di-2-
pyridylmethane,
n-BuLi, THF
Cl
Cl
I
I
HI
N
N
N
N
48%
N
N
52%
N
N
N
N
6
3
Di-2-
pyridylamine,
Cu powder,
Na CO , KBr,
mesitylene
2
3
N
Cl
N
N
N
N
N
N
ꢀ
N
N
N
N
N
N
4, 27%
5, 30%
Scheme 1.
Fe(X) (H O)
6
ꢃ
2
2
ꢃ
(
X ꢂ BF , ClO )
PdCl2
4
4
[
Fe (1) ](X)
[{PdCl } (1)]·2H O
2 2 2
2
2
4
N
N
NH PF6
N
N
N
4
ꢃ
N
7
X ꢂ BF4
9
ꢃ
ClO4 10
1
ꢁ
6
ꢃ
Ni(ClO ) (H O)
4 2 2
FP6 11
NaSCN
N
N
N
N
N
N
N
N
N
N
N
N
N
Ni
N
Ni
N
N
N
N
C
N
C
S
N
N
C
SN
C
S
S
•
2H O
2
M2L helical structure
2
8
Scheme 2.
ꢁ
6
Ni(ClO ) (H O)
4
2
2
N
N
N
N
NaSCN
N
N
N
N
N
N
N
Ni
Ni
N
N
N
C
S
N
N
O
S
C
S
C O
C
3
S
S
S
1
2
Scheme 3.
orange solid in a yield of 82%. The IR spectrum confirmed the
helicates[41] as observed for nickel(ii) with non-coordinating
anions (Scheme 2).
−
1
presence of 1, with characteristic bands at 1544 and 1439 cm
corresponding to the ligand, while the tetrafluoroborate anion
−
1
was established by observation of the B–F stretch at 1059 cm
.
Complexes of 3
In a similar manner, the perchlorate and hexafluorophosphate
analogues, [Fe2(1)2](ClO4)4 (10) and [Fe2(1)2](PF6)4 (11), were
synthesized in 76 and 57% yields, respectively. In all three cases,
the microanalysis data broadly matched the calculated values for
the complexes, although small amounts of impurities or solva-
tion may have been present in 9 and 11. For 10, the IR spectrum
Initial complexation studies for ligand 3 were focussed
on coordinating it to transition metals that preferred an
octahedral geometry, with the aim of forming discrete
[{MX (solvent)} (3)] (X = Cl, Br, SCN) or [M (3) ](X) com-
2
2
2
2
4
plexes (X = ClO , BF ). With this in mind, we set about reacting
4
4
−
1
showed characteristic bands at 1544 and 1439 cm correspond-
ing to the ligand, and that the perchlorate anion was present in
3 with several different transition metal salts. Despite possessing
two distinct pre-organized tridentate binding sites for two transi-
tion metal ions, isolation of crystalline complexes of 3 proved to
be particularly difficult. However, reaction of 3 with nickel per-
chlorate followed by addition of sodium thiocyanate provided
[{Ni(NCS) (DMSO)} (3)]·3.5DMSO·H O (12) (Scheme 3).
−
1
the sample with a ν(Cl–O) band at 1089 cm . The IR spectrum
of 11 showed the presence of 1 with characteristic bands at 1544
−1
and 1441 cm . The anion metathesis from the starting tetraflu-
oroborate to the hexafluorophosphate anion was successful, with
2
2
2
−
1
a ν(P–F) band at 843 cm and no evidence for a ν(B–F) band
The structure was elucidated by X-ray crystallography and sup-
ported by IR spectroscopy and microanalysis on the bulk sample,
in the IR. The structures are proposed to be M2L2 dinuclear

RESEARCH FRONT
Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(ii) Complexes
1145
although the latter indicated the possible presence of a small
amount of impurities. The IR spectrum showed an absorption
at 2100 cm consistent with N-bound SCN, in addition to the
expected peaks for the ligand.
atoms have an octahedral geometry with slight distortions of
the angles of the capped faces caused by the bite angles of 3.
The O-bound DMSO co-ligands coordinate to the nickel atoms
on opposite faces of the pyrimidine ring, which allows the thio-
cyanate groups to be readily accommodated. All the thiocyanate
anions coordinate to the nickel atom through a nitrogen donor,
as expected, rather than through the softer sulfur donors. There
are no unusually short intermolecular interactions between the
dinuclear complexes.
−1
Crystal Structure of [{Ni(NCS)2(DMSO)}2(3)]·
3.5DMSO·H2O, 12
The structure of complex 12 is a discrete M2L dinuclear com-
plex in which, pleasingly, the ligand coordinates in the desired
tripodal fashion to each nickel atom (Fig. 2). The complex crys-
tallizes in the monoclinic space group P21/n, with one molecule
of 3, two nickel atoms, four thiocyanate anions, two coordi-
nated, and four non-coordinated DMSO molecules (one 50%
occupied) and two water molecules (both 50% occupied) in the
asymmetric unit. The ligand acts as a ditopic tripodal donor to
the two nickel atoms, with two N-bound thiocyanate anions and a
coordinated DMSO molecule completing the coordination envi-
ronment of each nickel atom. The metal–metal distance in 12 is
A
defining feature of the ligand conformation in
[{Ni(NCS)2(DMSO)}2(3)] is the geometry of the carbon linker
atom (Z, in the schematic representation shown in Fig. 1). The
carbon atoms have the anticipated tetrahedral geometry with
bond angles to the carbon atoms of the arene rings between
◦
1
07.9(4) and 112.7(4) . This allows all three of the nitrogen
donors that are connected to that carbon atom to coordinate to
the metal centre with the desired tripodal coordination mode.
II
Attempts to make Fe compounds of the helical type,
−
−
[
Fe2(3)2](X)4, X = BF4 and ClO , in a similar manner to the
4
5
.951(2) Å, which is similar to previous bimetallic units bridged
[
50]
preparationofthe complexes ofligand 1 yielded yellowpowders,
reproducibly, on slow diffusion of diethyl ether into methanolic
reaction solutions, but crystals were not forthcoming. However,
the microanalytical data did not agree with the expected formula-
tion and, unlike the complexes 9–11, the C:H:N ratios suggested
that the formation of other types of complex had occurred.
by pyrimidine,
and naturally longer than related complexes
[33,35–41,50]
containing pyridazine or phthalazine cores.
trast, the Fe–Fe distances in the 1D compounds [Fe(4)(NCE)2]n
In con-
[
51]
(
E = S, Se)
are ∼9.2 Å, but these do not have the tripo-
dal chelation in 12 and only have the dpa moieties binding to
adjacent Fe atoms.
The bond lengths for the nickel atoms range from 2.033(5)
to 2.113(4) Å, with the two shortest bonds of 2.033(5) and
Complexes of 4
By contrast to the results obtained for the methane ligand 3,
ligand 4 was found to be significantly more inclined to form
isolatable coordination complexes. However, none of these com-
plexes was shown to adopt the desired doubly-tridentate mode.
Complexes of 4 were prepared with two nickel(ii) salts and two
palladium(ii) salts (Scheme 4), and three of these complexes
were characterized by X-ray crystallography.
Reaction of 4 with nickel tetrafluoroborate in methanol gave
pale blue crystals of [{Ni(CH3OH)2}2(4)2](BF4)2(SiF6) (13).
Reaction of 4 with nickel perchlorate and sodium thiocyanate
in the manner outlined for 1 and 3 gave a complex having a 1:1
metal–ligand ratio. This was an unexpected result for a coordi-
nating anion such as thiocyanate, which had been anticipated to
provide a discrete M2L complex with a very similar structure to
complex 12. Crystals of [{Ni(NCS)2}2(4)2] (14) confirmed the
structure to be a closely related [2 + 2] dimer.
2
.036(5) Å to the thiocyanate nitrogen atoms (N70 and N90),
which are trans to the pyrimidine nitrogen atoms. The nickel
N41
N21
N51
N31
N3
N1
Ni2
Ni1
N70
N80
N60
N90
O110
O100
Fig. 2. A perspective view of the complex [{Ni(NCS)2(DMSO)}2(3)] (12)
showing tripodal coordination at each metal. Hydrogen atoms and non-
coordinated solvent molecules are omitted for clarity. Selected bond lengths
Crystal Structure of
[
{Ni(CH3OH)2}2(4)2](BF4)2(SiF6), 13
[{Ni(CH3OH)2}2(4)2](BF4)2(SiF6) crystallizes in the space
[
Å]: Ni1–N70 2.033(5), Ni1–O110 2.085(4), Ni1–N60 2.086(5), Ni1–N51
.092(4), Ni1–N1 2.100(4), Ni1–N41 2.108(4), Ni2–N90 2.036(5), Ni2–
2
group C2/c, with one ligand molecule, a nickel atom, two coor-
N80 2.067(5), Ni2–N3 2.084(4), Ni2–N31 2.089(4), Ni2–O100 2.103(4),
Ni2–N21 2.113(4).
dinated methanol molecules, one tetrafluoroborate anion, and
[
Ni (4) (CH OH) ](BF ) (SiF )·2H O
[Pd (4)Cl ]·2H O
2
4
2
2
2
3
4
4
2
6
2
PdCl2
Ni(BF4)2
13
15
N
N
N
N
N
N
N
N
Ni(ClO4)2
NaSCN
Pd(OAc)2
4
[
Ni (4) (NCS) ]·3H O
[Pd (4)(OAc) ]
2 4
2
2
4
2
14
16
Scheme 4.

RESEARCH FRONT
1
146
C. J. Sumby et al.
half a hexafluorosilicate anion in the asymmetric unit.The hexa-
fluorosilicate anion present in the crystal structure is likely to
originate from the action of hydrofluoric acid (which is formed
from decomposition of the tetrafluoroborate anion by water)
on the glass container used to crystallize the complex.[ The
molecule, and three non-coordinated DMF solvate molecules in
the asymmetric unit. Each nickel atom is octahedral with coor-
dination by two thiocyanate ligands, two pyridine rings from one
ligand and one pyridine nitrogen, and a pyrimidine nitrogen of
the other ligand molecule. Therefore, as observed before, the
ligand is not using all its possible coordination sites and is hypo-
dentate. An interesting crystallographic feature of this structure
is the presence of a DMF molecule, which is disordered four
ways and lies on a four-fold improper rotation axis.
52]
[
2 + 2] dimeric structure of 13 consists of two nickel centres
bridged by two molecules of 4 (Fig. 3).
In complex 13, the nickel atom has an octahedral geo-
metry with bond lengths in the range 2.064(2)–2.124(3) Å. This
involves coordination by two methanol molecules, two pyridine
nitrogen atoms of one ligand and a pyridine and pyrimidine
donor from a second ligand molecule. The bridging ligand only
utilizes four of its six potential donor atoms in forming this com-
plex, and thus is hypodentate,[ with the two non-coordinated
pyridine rings oriented away from the metal centres. These non-
coordinated pyridine rings cover the open sides of the cavity
formed by the pyrimidine rings to form a box-like structure.
Unexpectedly, a pyrimidine nitrogen donor is coordinated pref-
erentially over a pyridine donor in complex 13.This coordination
mode was exploited in the synthesis of a closely related discrete
The nitrogen linker atoms again have geometry closer to trig-
onal planar than tetrahedral with bond angles between 114.5(5)
◦
and 125.0(6) . This has the effect of holding the pyridine
rings away from the pyrimidine core of the ligand and, thus,
prevents the ligand from acting as a tripodal donor. The metal–
metal distance is 8.044(1) Å and very similar to that in the
previous dinuclear nickel complex formed with 5. There is a
strong π-stacking interaction between the two pyrimidine rings
(centroid–centroid distance 3.33 Å) within this complex. This is
quite a short distance, with a typical distance for this type of
interaction being in the range 3.3–3.8 Å.[
53]
54]
II
[51]
dinuclear Fe complex of 2,5-bis(di-2-pyridylamino).
Ligand 4 was further exploited as a doubly-bidentate donor in
reactions with palladium(ii) salts. Reaction of two equivalents of
palladium chloride with 4 gave a yellow complex that was only
sparingly soluble in DMSO. Using a combination of elemental
The second unanticipated aspect of this structure is that the
tertiary nitrogen-linker atoms of ligand 4 are close to trigonal
◦
planar, with bond angles in the range 113.2(2)–124.1(2) . The
1
metal–metal distance is 7.990(1) Å, considerably longer than in
the nickel(ii) complex 12, reflective of the coordination of each
metal by only one of the pyrimidine nitrogen donor atoms from
analysis and H NMR spectroscopy, the complex was charac-
1
terized as [{PdCl2}2(4)]·2H2O (15). The H NMR spectrum of
the complex revealed several changes in chemical shifts, (coor-
dination induced shifts, CIS), which result from coordination
to the metal ion. These changes originate predominately from
ligand-to-metal σ-donation in this complex. Significant down-
field shifts for the pyridine ring and the symmetry of the complex
by NMR indicate that the ligand forms a symmetrical dinuclear
complex, which coordinates only through the pyridine nitrogen
atoms. No coordination appears to occur through the pyrimi-
dine ring. Subsequent reaction of 4 with palladium acetate gave
[54]
eachligand.Thereisarelativelystrongπ-stackinginteraction
between the two pyrimidine rings (centroid–centroid distance
.41 Å) in this complex, with the pyrimidine rings oriented in
3
opposite directions to favour this stacking arrangement. Non-
coordinated tetrafluoroborate and hexafluorosilicate anions fill
the voids between the [2 + 2] molecular box structures, and with
the coordinated methanol molecules, participate in an intricate
hydrogen-bonding network.
[{Pd(OAc)2}2(4)] (16) as yellow crystals, suitable for X-ray
crystallography, which confirmed the proposed bis-bidentate
coordination mode for palladium complexes of 4.
Crystal Structure of [{Ni(NCS)2}2(4)2]·3DMF·H2O, 14
The structure of complex 14 is also a [2 + 2] molecular box
formed from two equivalents of metal and ligand. It has an
almost identical structure (Fig. 4) to the previously described
nickel complex 13 but with the thiocyanate anions replacing
the coordinated solvate molecules. The complex crystallizes in
the tetragonal space group I41/a, with one ligand molecule, a
nickel atom, two thiocyanate anions, one non-coordinated water
Crystal Structure of [{Pd(OAc) } (4)]·6H O, 16
2
2
2
As proposed, in this structure ligand 4 is hypodentate and no
coordination to the palladium centre occurs through the nitrogen
N41
N51
N61
N1
N51
Ni1
O81
Ni1
N3
N81
N83
O91
N21
N41
Fig. 3.
A
perspective view of the cationic component in
[
{Ni(CH3OH)2}2(4)2](BF4)2(SiF6) (13) showing the [2 + 2] molecu-
Fig. 4. A perspective view of complex [{Ni(NCS)2}2(4)2]·3DMF·H2O
with hydrogen atoms and solvate molecules omitted for clarity. Selected
bond lengths [Å]: Ni1–N83 2.027(6), Ni1–N81 2.028(6), Ni1–N1 2.099(5),
Ni1–N61 2.099(5), Ni1–N41A 2.122(6), Ni1–N51A 2.123(5).
lar box with hydrogen atoms and non-coordinated anions omitted. Selected
bond lengths [Å]: Ni1–N3A 2.065(2), Ni1–O91 2.064(2), Ni1–N21A
2
.082(3), Ni1–O81 2.086(2), Ni1–N51 2.089(2), Ni1–N41 2.124(3).

RESEARCH FRONT
Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(ii) Complexes
1147
model system. A cobalt complex in which three ligands could
be readily displaced by a chelating tripodal ligand is sodium
cobaltinitrite. Facial coordination of octahedral cobalt is exem-
plified by reaction of the tripodal ligand 1,4,7-triazacyclononane
(tacn) with sodium cobaltinitrite.[ Replacement of three of the
nitrite groups resulted in a neutral complex that readily precip-
itated from the water/methanol reaction mixture. Therefore, a
similar reaction was attempted with tpa to test the possibility
of forming the desired dinuclear complexes with ligands 1–4.
Simply mixing a solution of sodium cobaltinitrite in water with
a solution of tpa dissolved in methanol gave a crude orange pre-
cipitate. This suspension was heated for 30 min before being
filtered and the collected precipitate dried under vacuum to give
O40
56]
N11
Pd1
N21
O30
Fig. 5. The palladium acetate complex [{Pd(OAc)2}2(4)]·6H2O (16)
[
Co(NO2)3(tpa)] (17) in 86% yield. Complex 17 was charac-
showing the ligand acting as a tetradentate bridge. Selected bond lengths
1
◦
terized by H NMR spectroscopy as a symmetrical complex
and shown by infrared spectroscopy to have all N-bound nitrite
groups. The proposed tripodal coordination was confirmed by
X-ray crystallography, with the ligand coordinating as a tripo-
dal tridentate donor to the octahedral cobalt atom and three
nitrogen-bound nitrite anions completing the coordination.
The successful formation of a tripodal complex with tpa
prompted us to undertake the same reaction with ligands 3 and 4.
Unfortunately, thesereactionswerenotsuccessfulusingthestan-
dard conditions employed for the equivalent reaction with tpa.
This was attributed to the formation of various combinations
of discrete ML and ML2 complexes, and polymeric species in
the reaction. Reaction of 3 with sodium cobaltinitrite resulted
in a complicated mixture of products. The mononuclear cobalt
complex is only sparingly soluble in water/methanol, and thus
does not further react to give the expected dinuclear complex.
Changing the reaction solvent did not lead to the formation of
the desired dinuclear complex with ligand 3.
[
2
1
Å] and angles [ ]: Pd1–N21 2.010(3), Pd1–N11 2.011(3), Pd1–O40
.024(3), Pd1–O30 2.026(2), N21–Pd1–N11 87.65(11), N21–Pd1–O40
75.88(10), N11–Pd1–O4092.59(11), N21–Pd1–O3091.98(11), N11–Pd1–
O30 176.06(10), O40–Pd1–O30 87.51(10).
atoms on the pyrimidine ring. The complex, shown in Fig. 5,
crystallizes in the C-centred monoclinic space group C2/c, with
a two-fold rotation axis running through the C2 and C5 carbon
atoms of the pyrimidine ring.Thus, the asymmetric unit contains
half the bridging ligand, one palladium atom, two coordinated
acetate anions, and three water solvate molecules. The coordi-
nated acetate anions and the non-coordinated water molecules
are involved in an extensive hydrogen-bonding network that
connects adjacent complexes to form infinite one-dimensional
chains.
The palladium centre is four-coordinate, with coordination
by two monodentate acetate anions and two pyridine nitrogen
atoms.The bond lengths (2.010(3)–2.026(2) Å) and angles of the
palladium atom are typical for such a donor set. The pyrimidine
ring does not bridge the metals in the di-palladium complex and
so the metal–metal distance is longer than the other complexes
of this ligand (9.520(1) Å) but similar to the ∼9.2 Å observed in
An ML2 bis-tripodal coordination motif was also desired
for the formation of complexes with the tripodal ligands. There
are several examples of such complexes with the ligands tris(2-
[55,57]
pyridyl)methane (tpm) and tris(2-pyridyl)amine (tpa).
To
further probe the amine-based system and possible planarization
of the nitrogen atom, tpa was reacted with nickel tetrafluoro-
borate. The anticipated ML2 complex [Ni(tpa)2](BF4)2 (18) was
obtained as pink crystals, in 51% yield.
[
51]
the 1D compounds, [Fe(4)(NCE)2]n (E = S, Se). The coordi-
nation of the ligand is consistent with the CIS values measured
for the palladium chloride complex; the H5 proton of the pyrim-
idine ring is in a position to be shielded slightly by the pyridine
rings of the ligand in the conformation the complex adopts in
the solid state.
Crystal Structure of [Ni(tpa)2](BF4)2, 18
Unlike the nickel tetrafluoroborate complex of 4 described
above, the nickel complex of tpa does indeed have the desired
bis-tripodal coordination of the octahedral nickel centre. A per-
spective view of the complex 18, which crystallizes in the
monoclinic space group P21/n, is shown in Fig. 6. The asym-
metric unit includes one ligand, a half nickel atom, and one
tetrafluoroborate anion. The nickel atom has octahedral geo-
metry with slight distortions of the angles of the capped faces,
as in other complexes of the nitrogen- and carbon-linked ligands,
The crystal structure again highlights the unexpected feature
of the triarylamine nitrogen linker atom (Z) in these tripodal
ligands. The nitrogen atom of 4 has an approximate sp geome-
try and is almost planar. The bond angles for the nitrogen atom
are 121.3(3), 121.8(3), and 116.8(2) . These observations for
2
◦
the three structures of ligand 4 are in contrast to the carbon
3
linker atom of ligands 1–3, which have a tetrahedral sp geo-
metry. Furthermore, particular complexes of tpa,[ including
the examples described in the present work, have tetrahedral
angles at the N atom to allow tridentate coordination of the
coordinated metal. Ligand 4 does not favour the desired tripo-
dal tridentate coordination mode, preferring to be hypodentate,
which has led to predominantly M2L2 dimeric structures, rather
than doubly-tripodal M2L complexes.
55]
caused by the restricted bite angle of the ligand (bond angles of
◦
8
5.90(7)–87.03(8) ). The bond lengths for the nickel–nitrogen
bonds are all very similar, ranging from 2.079(2) to 2.104(2) Å,
which is typical of such complexes, and shorter than complexes
[55]
with monodentate pyridine ligands. A nickel nitrate complex
[
Ni(tpa)2](NO3)2 was characterized by Astley et al. with Ni–N
[58]
bond lengths of 2.069(2) Å.
Complexes of tpa
Complexes of 5
The known tripodal ligand tpa has been demonstrated to bind
[55]
to a large range of transition metal salts.
As part of our
Ligand 5 is potentially a new tripodal tridentate ligand that
is effectively half of ligand 4, but with an extra remote mon-
odentate coordination site on the pyrimidine ring. Following on
investigations into transition metal precursors capable of bind-
ing in the desired manner to ligands 1–4, tpa was studied as a

RESEARCH FRONT
1
148
C. J. Sumby et al.
N31
Ni1
N11
N11ꢁ
N21
N21
N21ꢁ
Ni
N30
N11
N40
Fig. 6. A perspective view of [Ni(tpa)2](BF4)2 (18) with the tetrafluorob-
◦
orate anions omitted for clarity. Selected bond lengths [Å] and angles [ ]:
Ni1–N11 2.079(2), Ni1–N31 2.082(2), Ni1–N21 2.104(2), N11–Ni1–N31
8
7.03(8), N11–Ni1–N21 86.56(8), N31–Ni1–N21 85.90(7).
Fig. 7. The nickel thiocyanate complex of 5, showing the ML2 structure.
Selected bond lengths [Å]: Ni–N40 2.045(7), Ni–N30 2.048(7), Ni–N21
2
from previous success in showing tpa as a tripodal ligand with
some of the metal precursors under study, we chose to investigate
whether 5 would act as a tripodal ligand and coordinate facially
to an octahedral centre. Reaction of the ligand with nickel per-
chlorateandsodiumthiocyanategaveapurplecrystallinesample
of [Ni(SCN)2(5)2]·2H2O (19), which was isolated in a low 33%
yield.
ꢀ ꢀ
.096(6), Ni–N11 2.100(6), Ni–N21 2.121(5), Ni–N11 2.131(6).
Table 1. The average geometries around the linker atom (Z) for
selected complexes of the tripodal ligands reported in this paper and
for complexes of tpm and tpa from the literature
Ligand
Complex
present work)
Z
Average azine–Z
bond length [Å]
Average bond
angle [ ]
◦
(
Crystal Structure of [Ni(SCN)2(5)2]·CH3CN, 19
A
A structure of the nickel complex formed from reaction of 5
with nickel thiocyanate is shown in Fig. 7. The crystals exam-
ined were grown by vapour diffusion of diethyl ether into an
acetonitrile solution of the isolated complex. The complex crys-
tallized in the triclinic space group P-1, and the asymmetric unit
contains two heterocyclic ligands and two thiocyanate anions
bound to the nickel, along with a non-coordinated acetonitrile
molecule. In 19, the nickel atom has an octahedral geometry with
the two molecules of ligand 5 coordinated through the pyridine
donor atoms only, and the two thiocyanate anions coordinated
in a cis-arrangement through their nitrogen donor atoms. Again,
like selected complexes of 5, the pyrimidine nitrogen atoms are
not involved in coordination, meaning the ligand is hypodentate.
The observed coordination mode is consistent with the pyrimi-
dine being a poorer donor than the pyridine nitrogen atoms. The
coordination mode employed by the ligand also demonstrates
tpm
C
C
C
C
N
N
N
N
N
1.538
1.515
1.524
1.525
1.418
1.414
1.421
1.420
1.418
110.2
111.5
111.1
110.7
118.7
120.0
119.5
119.4
120.0
A
1
2
A
3
tpa
4
4
4
5
12
A,B
13
14
16
19
AThe values reported are from a Cambridge Structural Database search on
complexes of each of these ligands where the ligand coordinates in a tripo-
dal mode and are an average of all structures (CSD version 5.29 including
January and August 2008 updates).
B
In the case of tpa, the average value includes complex 18.
complexes of ligands 1 and 2 have similar tetrahedral geome-
tries for the carbon linker atom, as do selected complexes of
tpa, which has a nitrogen linker atom. In contrast, the ligands 4
and 5 with a nitrogen linker atom did not have angles close to
a tetrahedral geometry. This planarization of the nitrogen atom
when bonded to pyrimidine effectively prevents ligands with
a nitrogen linker atom from coordinating tripodally to a metal
centre. This is likely to result from two factors. The first is the
delocalization of the nitrogen lone pair by the diazine ring, forc-
2
the preference the nitrogen-linker atom has for an sp geometry
when bonded to an electron-deficient pyrimidine ring.
Comparison of the Structures
An interesting feature of the nitrogen- and carbon-linked lig-
ands described in this work is the geometry of the linker atom
(Z, see Fig. 1) in complexes of these ligands. Typically, the
2
geometry of the carbon linker atom was closest to tetrahedral,
indicating a preference for tripodal coordination by these ligands
ing a planar sp arrangement of bonding about the bridgehead
nitrogen atom. Second, the poorer donor ability of the pyrim-
idine nitrogens leads to these motifs preferentially acting as
bidentate donors. It is interesting to note that a similar effect
(
Table 1).The bond lengths and angles for the carbon linker atom
of the ligand in complexes reported here are very similar to the
corresponding values for complexes of tpm. Previously reported
2
is not always observed for tpa, although this planar sp -like

RESEARCH FRONT
Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(ii) Complexes
1149
8
7
6
5
4
3
2
confirm the spin states or mixtures of states. Interestingly, the
FeN6 ligand field, per Fe site, is rather like that in the monomeric
2+
compound [Fe(tpm)2] , which structure and magnetism show
to be low-spin.[ The lack of thermal SCO behaviour in these
systems presumably is primarily because of the magnitude of the
ligand field generated at Fe but may also be a consequence of the
tetrahedral C-linker atom in ligands 1, rather than the planarized
57]
2
[46]
sp N-linker of ligand 4.
Conclusion
The present paper has described the synthesis of two bridg-
ing ligands (3 and 4) by reaction of both di-2-pyridylmethane
and di-2-pyridylamine with an appropriately substituted pyrim-
idine precursor. This extends the existing chemistry of such
ligands incorporating pyridazine (1) and phthalazine (2) cores.
An investigation of the coordination chemistry of these lig-
ands was complemented by studies of a known ligand (tpa)
and a by-product of the synthesis of ligand 4, 4-chloro-6-(di-
0
50
100
150
200
250
300
T [K]
Fig. 8. Plot of magnetic moment, per Fe2, versus temperature for complex
1. The solid line is just a guide to the eye.
1
2-pyridylamino)pyrimidine (5). Two common structural types
are observed for complexes of tripodal ligands of this type in
the literature and in the present work: either discrete M2L com-
plexes, or [2 + 2] metal–ligand dimers. The novel compound 3,
prepared in the current work, and ligands 1 and 2 from the litera-
ture, all of which contain a carbon linker atom, formed either of
these structural motifs with octahedral metal atoms. In contrast,
ligand 4 appears to favour the formation of [2 + 2] metal–ligand
dimers. This control over the types of structure appears to be
a consequence of the sp planar tertiary amine linker atom,
which prevents the ligand adopting the conformation required
to facially cap an octahedral metal ion.
Ligand 3 does act in the targeted manner by facially
coordinating to two octahedral metal centres in the complex
nitrogen atom is also observed in complexes of ligands possess-
[20,22,23,59]
ing a di-2-pyridylamine group and an aryl
or triazine
[
23,24,60]
ring.
Presumably, the three pyridine donors of tpa readily
enforce a tetrahedral geometry on coordination.
Magnetism
The magnetic properties of the three pyridazine-linked
iron(ii) complexes, 9–11, described above were studied over
the temperature range 300–2 K. Unfortunately, none of the
complexes underwent thermal SCO in the way recently
2
[
61,62]
4+
observed
in dinuclear tri-helicates of type [Fe2L3] that
also contained FeN6 donor sets. Complex 11 showed high-spin
[{Ni(NCS)2(DMSO)}2(3)] (12). However, the syntheses of
II
Fe magnetic behaviour over the whole temperature range. In
complexes of this type were problematic. Indeed, many attempts
were made to prepare well-defined binuclear complexes with a
wide range of metal precursors without success. Unfortunately,
the amine ligand 4 was not suited to formation of complexes with
the desired coordination motif. Thus, while these systems may
offer the possibility of forming stereochemically well-defined
binuclear complexes, they have their own set of pitfalls. The
magnetic measurements undertaken on the iron(ii) coordination
complexes of ligands 1 revealed that these complexes did not
undergo SCO in the solid state. This is in contrast to a pre-
Fig. 8, it can be seen that the effective magnetic moment (µeff )
values, per Fe2, decrease gradually from 7.24 µB (5.12 µB per
Fe) at 300 K, then a bit more rapidly below 50 K, to reach 5.05 µB
(
3.57 µB per Fe) at 2 K, with no step characteristic of SCO.
Rather similar plots have been observed for other high spin-high
II
[4,6,63]
spin Fe species.
This temperature-dependent behaviour
is due to a combination of spin-orbit and distorted octahedral lig-
5
II
[64]
and fields acting to split the parent T2g Fe states,
perhaps
influenced also by weak antiferromagnetic coupling between the
II
Fe s = 2 spins, across the pyridazine linker, within the dinuclear
II
vious report of an Fe 1-D coordination polymer of 4 that
species.The more rapid decrease in µeff below 50 K is also influ-
underwent a two-step SCO transition, but this possessed other
enced by zero-field splitting of the lowest quintet state on each
[46]
co-ligands in the coordination spheres of the Fe centres. There
II [4,6,65]
Fe .
is scope for further studies of SCO in dinuclear helicate species
or side-by-side [Fe2L2] complexes having FeN6 ligand fields.
Complexes 9 and 10 have much lower µeff values, per Fe2,
at 300 K than is the case for complex 11, viz. 4.09 µB (2.89 µB
per Fe) for 9; 2.76 µB (1.95 µB per Fe) for 10 (see Accessory
Publication). The slopes of the magnetic moment plots are, how-
ever, similar to that for 11. Even allowing for the effects that a
change in anion can have on SCO features, the results for 9
and 10 present us with a dilemma. The microanalytical data
would appear to preclude the presence of significant concentra-
tions of a diamagnetic diluent (e.g. excess ligand), or of Fe(iii)
species, in the samples that would reduce the µeff values from
Experimental
General Experimental
Melting points were recorded on an Electrothermal melting point
apparatus and are uncorrected. The Campbell microanalytical
laboratory at the University of Otago performed elemental anal-
yses. IR spectra were collected on Perkin–Elmer 1600 series
Fourier-transform (FT)-IR spectrometer as KBr disks (range
6
6
−1
−1
the high-spin d values. The low-spin–low-spin (t2g ) situation
can sometimes yield values of ∼1.4 µB (1.0 µB per Fe), with
similar slopes to those seen here, originating from second-order
4000–500 cm , 16 scans, resolution ± 4 cm ) or on Shimadzu
FTIR-8201PC spectrophotometer as Nujol mulls. Intensities are
described by the following abbreviations: s, strong; m, medium;
w, weak; br, broad; and sh, shoulder. Electrospray (ES) mass
spectra were recorded using a Micromass liquid chromatogra-
phytandemtime-of-flightmassspectrometer. NMRspectrawere
[
7]
Zeeman effects, but the present values are higher than this
and we would require further data on crystal structures (Fe–N
distances), NMR spectral shifts, and Mössbauer isomer shifts to

RESEARCH FRONT
1
150
C. J. Sumby et al.
◦
recorded on Varian 300 MHz and Varian 500 MHz spectrome-
solid. Yield 0.86 g (30%). Mp 145–147 C (Found: C 59.32,
H 3.32, N 24.62, Cl 12.28. C15H10N5Cl requires: C 59.27, H
◦
1
ters at 23 C, using a 3-mm probe. H NMR spectra recorded in
CDCl3 were referenced relative to the internal standard Me4Si.
+
3.55, N 24.68, Cl 12.50%.) m/z (ES-MS) 284.1 [(M + 1)] . δH
1
ꢀ
ꢀ
H NMR spectra recorded in [D6]DMSO were referenced to
(CDCl3) 8.54 (s, 1H, H2), 8.53 (d, 2H, H6 ), 7.79 (t, 2H, H4 ),
the solvent peak: 2.5 ppm. 13C NMR spectra were referenced
to their solvent peak: CDCl3, 77.0 ppm; [D6]DMSO, 39.6 ppm.
Unless otherwise stated, reagents were obtained from commer-
cial sources and used as received. THF was dried by standard
literature procedures and freshly distilled as required. Tri-2-
7.23 (m, 4H, H5 , H3 ), 6.99 (s, 1H, H5); δH ([D6]DMSO) 8.65
(s, 1H, H2), 8.55 (d, 2H, H6 ), 7.99 (dd, 2H, H4 ), 7.42 (t, 2H,
H5 ), 7.36 (d, 2H, H3 ), 7.18 (s, 1H, H5). δC (CDCl3) 160.4,
158.2, 155.0, 149.5, 142.4, 138.6, 121.9, 121.1, 108.8.
The second band contained 4 as a pale brown solid that
was collected, washed with cold ethyl acetate and recrystallized
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
[
48]
[33]
[37]
[47]
pyridylamine (tpa),
1,
2,
and 6
were prepared by
◦
literature procedures.
from ethanol/diethyl ether. Yield 1.14 g (27%). Mp 192–194 C
(
Found: C 69.00, H 4.49, N 26.81. C24H18N8 requires: C 68.89,
+
Magnetism
H 4.34, N 26.79%.) m/z (ES-MS) 419.2 [(M + 1)] . δH (CDCl3)
ꢀ
ꢀ
8
4
8
6
1
.51 (s, 1H, H2), 8.41 (dd, 4H, H6 ), 7.70 (t, 4H, H4 ), 7.23 (d,
Magnetic measurements were carried out on a Quantum Design
MPMS 5 SQUID magnetometer calibrated with a standard
palladium sample (Quantum Design) of accurately known mag-
netization or by use of magneto-chemical calibrants such as
CuSO4·5H2O. Susceptibility versus temperature studies in the
linear portion of the magnetization versus field curve was made
using a field of 1T over a temperature range of 2–300 K. Pow-
dered samples (∼30 mg) were contained in calibrated gelatine
capsules held at the centre of a drinking straw fixed to the end
of the sample rod.
ꢀ
ꢀ
H, H3 ), 7.10 (dd, 4H, H5 ), 6.47 (s, 1H, H5); δH ([D6]DMSO)
ꢀ
ꢀ
ꢀ
ꢀ
.43 (m, 5H, H2, H6 ), 7.90 (t, 4H, H4 ), 7.31 (m, 8H, H3 , H5 ),
.32 (s, 1H, H5). δC (CDCl3) 162.5, 158.2, 155.9, 149.0, 138.0,
20.9, 120.7, 99.2.
Complexes of 1
[{PdCl } (1)]·2H O, 7
2
2
2
PdCl2 (17.9 mg, 0.10 mmol) was dissolved in dilute
hydrochloric acid (4 mL) and added dropwise to a solution of
1
(19.7 mg, 0.047 mmol) in methanol (5 mL). An immediate
Syntheses of Ligands
change gave an orange solution, which formed a yellow pre-
cipitate that was collected, washed with cold methanol and dried
under vacuum. Yield 28 mg (74%). Mp >340 C (dec.) (Found:
C 38.56, H 2.57, N 9.99, Cl 17.20. C H N O Pd Cl requires:
C 38.69, H 3.00, N 10.41, Cl 17.57%.)
4,6-Bis(di-2-pyridylmethyl)pyrimidine, 3
◦
Di-2-pyridylmethane (650 mg, 3.82 mmol) was dissolved in
◦
26
24
6
2
2
4
dry THF (5 mL), under argon, and cooled to −78 C in a
dry ice/acetone bath. n-BuLi (2.5 mL, 4.00 mmol) was added
◦
dropwise and the solution stirred for 15 min at −78 C. 4,6-
[
{Ni(NCS)(µ2-NCS)}2(1)]·2H2O, 8
Diiodopyrimidine (634 mg, 1.91 mmol) was dissolved in a fur-
ther 10 mL of THF and added dropwise to the solution of
lithiated di-2-pyridylmethane. Over an hour, the dark red solu-
tion went brown and the solution was left to warm to room
temperature, with constant stirring for 48 h. Water (0.5 mL) was
added slowly and the reaction stirred a further hour.The solvents
were removed under vacuum and the residue extracted into hot
ethanol. The ethanol solution was reduced under vacuum and
the residue triturated with diethyl ether (40 mL) to give 3 as an
A methanolic solution (5 mL) of 1 (20.1 mg, 0.048 mmol)
was added dropwise to a solution of Ni(ClO4)2(H2O)6 (39.6 mg,
0.11 mmol) dissolved in water (5 mL). The resultant green solu-
tion was stirred for 30 min and an excess of NaSCN was
added to give a green precipitate. Recrystallization, by vapour
diffusion of ethanol into a DMSO solution of the complex, pro-
duced crystals suitable for X-ray crystallography. Yield 35 mg
◦
(91%). Mp 310 C (dec.) (Found: C 44.99, H 2.95, N 17.66.
◦
C30H24N10O2S4Ni2 requires: C 44.92, H 3.02, N 17.46%.)
νmax(Nujol)/cm 2097 (N-bound SCN), 1996 (µ2 N-bound
SCN).
orangesolid.Yield379 mg(48%). Mp153–155 C(dec.)(Found:
−
1
C 70.11, H 4.87, N 18.94. C26H20N6·1.5H2O requires: C 70.41,
H 5.23, N 18.95%.) δH (CDCl3) 9.13 (s, 1H, H2), 8.53 (d, 4H,
ꢀ
ꢀ
ꢀ
H6 ), 7.62 (t, 4H, H4 ), 7.37 (s, 1H, H5), 7.34 (d, 4H, H3 ), 7.15
(
ꢀ
[Fe (1) ](BF ) , 9
2
2
4 4
dd, 4H, H5 ), 5.86 (s, 2H, CH); δH ([D6]DMSO) 9.09 (s, 1H,
ꢀ
ꢀ
ꢀ
H2), 8.55 (d, 4H, H6 ), 7.83 (t, 4H, H4 ), 7.38 (m, 9H, H5, H3 ,
A solution of Fe(BF4)2(H2O)6 (33.7 mg, 0.1 mmol) in
methanol (5 mL) was added to a stirred solution of 1 (41.7 mg,
0.1 mmol) in methanol (5 mL). This mixture was stirred for 2 h,
filtered; then diffusion of diethyl ether overnight yielded an
orange precipitate of 9. The precipitate was collected, washed
with diethyl ether, and then dried at the pump.Yield 53 mg (82%)
(Found: C49.38, H3.82, N12.99. C52H40N12B4F16Fe2 requires:
C 48.35, H 3.12, N 13.01%.) νmax(KBr)/cm 3424br, 1737w,
1720w, 1708w, 1666w, 1655w, 1606m, 1544sh, 1525w, 1510w,
1475m, 1439s, 1059s, 771s, 524w.
ꢀ
H5 ), 5.95 (s, 2H, CH). δC (CDCl3) 169.4, 159.5, 158.4, 149.4,
42.5, 136.7, 124.2, 122.1, 63.4.
1
4,6-Bis(di-2-pyridylamino)pyrimidine, 4
4
,6-Dichloropyrimidine(1.51 g, 10 mmol), di-2-pyridylamine
(
3.5 g, 20 mmol), Na2CO3 (2 g), copper powder (0.05 g), KBr
◦
−1
(
5
trace), and mesitylene (5 mL) were heated at 160 C for
days. The mesitylene was removed under vacuum before
the residue was suspended in dichloromethane. The insoluble
component was filtered off, and the filtrate, containing a mix-
ture of starting material and products, taken to dryness under
vacuum. The resulting oil was purified on a silica gel col-
umn (20 × 5 cm) eluting with 1:40 methanol/chloroform solu-
tion. Two bands were collected. The monosubstituted product,
[
Fe2(1)2](ClO4)4, 10
A solution of Fe(ClO4)2(H2O)6 (34.5 mg, 0.1 mmol) in
methanol (5 mL) was added to a stirred solution of 1 (41.7 mg,
0.1 mmol) in methanol (5 mL). This mixture was stirred for 2 h,
filtered; then diffusion of diethyl ether overnight yielded an
orange precipitate of 10. The precipitate was collected, washed
with diethyl ether, and then dried at the pump. Yield 51 mg
4
-chloro-6-(di-2-pyridylamino)pyrimidine (5) co-eluted with
the starting di-2-pyridylamine. Recrystallization from a 3:1 mix-
ture of light petroleum/ethyl acetate gave 5 as a creamy yellow

RESEARCH FRONT
Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(ii) Complexes
1151
(
76%) (Found: C 46.90, H 3.70, N 13.00. C52H40N12Cl4O16Fe2
requires: C 35.80, H 2.25, N 13.92, Cl 17.61%.) δH ([D6]DMSO)
−
1
ꢀ ꢀ
8.93 (d, 4H, H6 ), 8.68 (s, 1H, H2), 8.36 (t, 4H, H4 ), 8.14 (d, 4H,
requires: C 46.52, H 3.00, N 12.52%.) νmax(KBr)/cm 3423br,
ꢀ
ꢀ
1
1
6
775w, 1737w, 1720w, 1703w, 1687w, 1655m, 1638w, 1561w,
544w, 1524w, 1510w, 1476m, 1439s, 1384m, 1089s, 769m,
25m.
H3 ), 7.75 (t, 4H, H5 ), 6.19 (s, 1H, H5).
[{Pd(OAc)2}2(4)], 16
Pd(OAc)2 (24.5 mg, 0.109 mmol) was dissolved in ace-
tone (5 mL) and added dropwise to a solution of 4 (21.3 mg,
.051 mmol), dissolved in methanol (5 mL), to give an orange
[
Fe2(1)2](PF6)4, 11
A solution of Fe(BF4)2(H2O)6 (33.8 mg, 0.1 mmol) in
methanol (5 mL) was added to a stirred solution of 1 (41.7 mg,
.1 mmol) in methanol (5 mL). This mixture was stirred for 1 h,
0
solution. Slow evaporation gave orange crystals, suitable for
X-ray crystallography, which were collected by filtration and
0
◦
then NH4PF6 (32.6 mg, 0.2 mmol) was added, and stirred for
a further hour, followed by filtration; then, diffusion of diethyl
ether overnight yielded an orange precipitate of 11. The precip-
itate was collected, washed with diethyl ether, and then dried at
the pump.Yield 44 mg (57%) (Found: C 41.31, H 3.26, N 12.01.
C52H40N12P4F24Fe2 requires: C 40.97, H 2.64, N 11.06%.)
dried under vacuum. Yield 23 mg (52%). Mp 225 C (dec.)
(
Found: C 44.05, H 3.50, N 12.61. C32H30N8O8Pd2 requires:
C 44.31, H 3.49, N 12.92%.) δH ([D6]DMSO) 8.67 (s, 1H, H2),
ꢀ
ꢀ
ꢀ
ꢀ
8
(
.55 (d, 4H, H6 ), 8.20 (m, 8H, H4 , H3 ), 7.68 (t, 4H, H5 ), 6.20
s, 1H, H2), 1.90 (s, 12H, CH3).
−1
νmax(KBr)/cm
3423br, 3050sh, 1872w, 1848w, 1775w,
Complexes of tpa
1
1
737w, 1667w, 1654w, 1602m, 1544sh, 1510w, 1475m, 1441s,
343w, 1056w, 1021s, 843s, 768m, 674w, 558m, 524w, 425w.
[
Co(NO2)3(tpa)]·CH3OH, 17
Na3[Co(NO2)6] (190 mg, 0.47 mmol) was dissolved in
water (10 mL) and stirred at room temperature. Tpa (103 mg,
Complex of 3
0
.42 mmol) was dissolved in methanol (10 mL) and added drop-
[
{Ni(NCS)2(DMSO)}2(3)]·3.5DMSO·H2O, 12
wise to this solution, resulting in a copious orange precipitate.
Ligand 3 (20 mg, 0.048 mmol) was dissolved in methanol
5 mL) and added to a solution of Ni(ClO4)2(H2O)6 (36 mg,
.98 mmol) dissolved in water (5 mL). After stirring for 30 min,
NaSCN was added to give an orange precipitate that was col-
lected by filtration and washed with methanol. Recrystallization,
by vapour diffusion of acetone into a DMSO solution of the
complex, furnished purple crystals suitable for X-ray crystallog-
raphy.Yield 18 mg (41%). Mp 324 C (dec.) (Found: C 43.81, H
.15, N 16.25. C34H32N10O2S6Ni2 requires: C 44.27, H 3.50, N
5.18% (calculated values are for the desolvated compound).)
◦
This suspension was stirred for 30 min at 70 C, cooled in ice,
(
0
filtered and then washed successively with water, ethanol, and
diethyl ether. Yield 159 mg (86%). Crystals, which appeared
suitable for X-ray crystallography, were obtained from vapour
diffusion of methanol into a DMSO solution of the complex. Mp
◦
1
98–200 C (Found: C 40.36, H 3.09, N 20.74. C16H16N7O7Co
−1
requires: C 40.26, H 3.38, N 20.54%.) νmax(Nujol)/cm 1433b
◦
(
N-bound NO2), 1306s (N-bound NO2), 820s (N-bound NO2).
δH ([D6]DMSO) 8.80 (d, 3H, H6), 8.42 (t, 3H, H4), 8.17 (d, 3H,
H3), 7.87 (t, 3H, H3).
3
1
−1
νmax(Nujol)/cm 2100 (N-bound SCN).
[
Ni(tpa)2](BF4)2, 18
Complexes of 4
Methanol solutions (5 mL each) of Ni(BF4)2 (28.1 mg,
.083 mmol) and tpa (20.3 mg, 0.081 mmol) were combined.
Slow evaporation of the resulting solution gave pink crys-
tals, suitable for X-ray crystallography. Yield 15 mg (51%). Mp
>330 C (Found: C 49.50, H 3.16, N 15.40. C30H24B2N8F8Ni
requires: C 49.44, H 3.32, N 15.37%.)
[
{Ni(CH3OH)2}2(4)2](BF4)2(SiF6)·2H2O, 13
0
Ni(BF4)2 (16.3 mg, 0.048 mmol)and 4(19.9 mg, 0.048 mmol)
were both dissolved in hot methanol (5 mL each) and the solu-
tions combined. On standing, pale blue crystals, suitable for
X-ray crystallography, precipitated, were collected and then
◦
◦
dried under vacuum. Yield 17 mg (44%). Mp >280 C (dec.)
(
Found: C 43.22, H 3.85, N 16.25. C52H56B4N16O6F16Ni2
Complex of 5
requires: C 43.55, H 3.94, N 15.63%.)
[
Ni(NCS)2(5)2]·2H2O, 19
[
{Ni(NCS)2}2(4)2]·3H2O, 14
A methanolic solution (5 mL) of 5 (21.4 mg, 0.075 mmol)
was added dropwise to a solution of nickel perchlorate (27.7 mg,
A methanolic solution (10 mL) of 4 (80.4 mg, 0.192 mmol)
0.076 mmol) dissolved in water (5 mL).After stirring for 30 min,
was added dropwise to a solution of Ni(ClO4)2(H2O)6
NaSCN was added to give a pale purple crystalline precipitate.
The complex was collected by filtration and recrystallized, by
vapour diffusion of diethyl ether into an acetonitrile solution of
the complex, to give crystals suitable for X-ray crystallography.
The crystals were filtered, washed with methanol, then diethyl
ether, and dried under vacuum.Yield 21 mg (33%). Mp >222 C
(dec.) (Found: C 48.28, H 3.11, N 21.91. C30H24N12O2S2Ni
requires: C 48.42, H 3.23, N 21.59%.) νmax(Nujol)/cm 2091
(
141.5 mg, 0.387 mmol) in water (10 mL). After stirring for 2 h,
sodium thiocyanate was added to give a pale purple precipitate.
Yield 155 mg (64%). Recrystallization by diffusion of acetone
into a DMF solution of the complex provided crystals suitable
for X-ray crystallography. Mp >300 C (dec.) (Found: C 50.74,
H 3.20, N 22.46. C52H42N12O3S4Ni2 requires: C 50.34, H 3.41,
◦
◦
−
1
N 22.58%.) νmax(Nujol)/cm 2091 (N-bound SCN).
−
1
[
{PdCl2}2(4)]·2H2O, 15
(N-bound SCN).
PdCl2 (36.9 mg, 0.208 mmol) was dissolved in dilute
hydrochloric acid (4 mL) and added dropwise to a solution of 4
Crystallography
(
41.4 mg, 0.099 mmol) in methanol (5 mL). A yellow precipitate
All measurements were made with a Siemens charge cou-
pled device area detector using graphite monochromatized Mo
Kα (λ = 0.71073 Å) radiation at the temperature indicated in
Table 2. The data reduction was performed using SAINT.[
formed, was collected by filtration, washed with cold methanol,
and dried under vacuum. Yield 71 mg (89%). Mp 310 C (dec.)
(
◦
65]
Found: C 35.99, H 2.47, N 13.82, Cl 17.60. C24H22N8O2Pd2Cl4

RESEARCH FRONT
1
152
C. J. Sumby et al.

RESEARCH FRONT
Structural Interplay Between M2L and M2L2 (M = Ni and Pd) Complexes and Magnetic Properties of Iron(ii) Complexes
1153
The intensities were corrected for Lorentz and polarization
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[
67]
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[
68]
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SIR97
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[69]
In general, all
[
[
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non-hydrogen atoms with occupancies greater than 0.5 were
refined with anisotropic displacement parameters.Aromatic and
aliphatic hydrogen atoms were included in calculated positions
with isotropic displacement parameters 1.2 or 1.5 times the
isotropic equivalent of their carrier carbon atoms, respectively.
CCDC 729361–729366 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Specific Additional Details of Crystallography
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The structure of 12 possesses several disordered DMSO sol-
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isotropically.Two disordered solvate molecules (both disordered
over two sites with ∼50% occupancy) generate a short inter-
molecular contact. Similarly, a water and DMSO molecule are
disordered over another site. Crystals of 14 are weakly diffract-
ing with two poorly behaved DMF solvate molecules (high
isotropic displacement parameters) and a third DMF solvate
molecule lying on a special position. The hydrogen atoms on
the water molecules in complex 16 were not able to be located
in the difference map. Complex 19 was weakly diffracting and
[
[
[
02603590590920578
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