Palladium(II)-palladium(II) bonding in two open clamshell dinuclear complexes

Article abstract of DOI:10.1039/c7nj01604b

Condensing 2-hydrazinopyridine separately with glyoxal and benzil in 2:1 mole ratio, two osazones LH₂ and L′H₂·H₂O (H: dissociable proton) are synthesized. Their reactions with K₂[PdCl₄] afford red [Pd(LH)]₂(Cl)(ClO₄) (1) and [Pd(L′H)]₂(ClO₄)₂ (2). In the X-ray crystal structures, they contain [Pd₂(ligand)₂]²⁺ cations with ligand = LH or L′H. They are open clamshell type, with angles of 58.9° and 40.1° in 1 and 2 respectively. The respective Pd-Pd distances in 1 and 2 are found to be 3.2669(6) and 3.0128(5) ?. While this distance in 1 is almost equal to the sum of the van der Waals' radii of two Pd atoms, it is significantly less in 2. Theoretical calculations and structural factors indicate some sort of interaction between the two Pd(ii) centers though the net bond order from the derived molecular orbitals for the Pd(ii)₂ core is found to be zero. The situation is similar to the crystal field splitting in tetrahedral copper(i) complexes. In 1 and 2, the interactions between the two Pd(ii) centers increase as decreases. This is displayed in the difference in the redox potentials of the Pd^IIIPd^II/Pd^IIPd^II and Pd^IIIPd^III/Pd^IIIPd^II couples in cyclic voltammetry, when compared with the same property in some similar dinuclear Pd(ii) complexes known in the literature.

Full text of DOI:10.1039/c7nj01604b

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Palladium(II)–palladium(II) bonding in two open
clamshell dinuclear complexes†
Cite this:DOI: 10.1039/c7nj01604b
a
Shanti G. Patra,a Nirmal K. Shee,a Michael G. B. Drewb and Dipankar Datta
*
Condensing 2-hydrazinopyridine separately with glyoxal and benzil in 2 : 1 mole ratio, two osazones LH2
and L0H2ꢀH2O (H: dissociable proton) are synthesized. Their reactions with K2[PdCl4] afford red
[Pd(LH)]2(Cl)(ClO4) (1) and [Pd(L0H)]2(ClO4)2 (2). In the X-ray crystal structures, they contain
[Pd2(ligand)2]2+ cations with ligand = LH or L0H. They are open clamshell type, with angles (y) of 58.91
and 40.11 in 1 and 2 respectively. The respective Pd–Pd distances in 1 and 2 are found to be 3.2669(6)
and 3.0128(5) Å. While this distance in 1 is almost equal to the sum of the van der Waals’ radii of two Pd atoms,
it is significantly less in 2. Theoretical calculations and structural factors indicate some sort of interaction
between the two Pd(II) centers though the net bond order from the derived molecular orbitals for the Pd(II)2
core is found to be zero. The situation is similar to the crystal field splitting in tetrahedral copper(I) complexes.
In 1 and 2, the interactions between the two Pd(II) centers increase as y decreases. This is displayed in the
difference in the redox potentials of the PdIIIPdII/PdIIPdII and PdIIIPdIII/PdIIIPdII couples in cyclic voltammetry,
when compared with the same property in some similar dinuclear Pd(II) complexes known in the literature.
Received 10th May 2017,
Accepted 23rd June 2017
DOI: 10.1039/c7nj01604b
rsc.li/njc
forming bonds with the halides. The relative ordering of the
1. Introduction
2
2
m.o.s. in terms of energy is: s o p o d o d* o p* o s*. This
Metal–metal bonding (order Z1) is an interesting aspect of m.o. scheme yields a b.o. of four between the two Re(II) centers
transition metal chemistry.1,2 Pauling perceived it as a genuine in Re2Cl8 as Re(III) is a d4 system. Evidently when this m.o.
2ꢁ
possibility. Still it was only in 1956 that Figgis and co-workers scheme is applied to a pair of Pd(II) centers,9 all the bonding
first explicitly established the metal–metal bond order (b.o.) in and the antibonding orbitals are filled up (since Pd(II) is d8)
chromous acetate as four.3 In the same paper they proposed in leading to a net metal–metal b.o. of zero. Yet some workers9–11
copper acetate a Cu(II)–Cu(II) b.o. of one through a ‘‘delta bond’’. maintain that there does exist some kind of metal–metal
While subsequently a number of dinuclear metal complexes have interactionin clamshell Pd(II) dimers. Such a claim is also made
been discovered or synthesized deliberately4 with metal–metal b.o. in reference to some unsupported Pd(II) dimers12,13 where the
4 1, unfortunately the case of copper acetate is still being argued Pd–Pd bond distances are significantly less than the sum of van
about.5 Here we are concerned with metal–metal bonding between der Waals distance which is 3.26 Å in Bondi’s14 scale. Here we
two Pd(II) atoms.
revisit the situation by scrutinising the electronic structure and
The first dinuclear metal complex having a metal–metal some physicochemical properties of two new dicationic dinuclear
b.o. of four is K2Re2Cl8ꢀ2H2O, characterized by Cotton and Pd(II) complexes having ‘‘open clamshell’’ geometry which were
co-workers6,7 in 1964. When only the five d orbitals of Re(III) prepared while developing the metallo chemistry of the ligands
are considered, for two interacting Re(III) centers, a simple described in Chart 1 below.15
molecular orbital (m.o.) theory4,8 yields four bonding molecular
orbitals (m.o.): s (involving a pair of dz2 orbitals), a doubly
degenerate 2p (arising out of two pairs of dxz and dyz) and d
(formed by two dxy orbitals). The corresponding antibonding
orbitals are s*, 2p* and d*. The dx2 ꢁ y2 orbitals are engaged in
a Department of Inorganic Chemistry, Indian Association for the Cultivation of
Science, Calcutta 700 032, India. E-mail: icdd@iacs.res.in
b Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD,
UK
† CCDC 1547789 and 1547790. For crystallographic data in CIF or other electronic
Chart 1 (a) The ligands used (H: dissociable amino proton) and (b) a
format see DOI: 10.1039/c7nj01604b
fragment of them.
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2. Results and discussion
The ligands are osazones. While LH2 is a 1 : 2 condensate of
glyoxal and 2-hydrazinopyridine, use of benzil in lieu of glyoxal
affords L0H2ꢀH2O. These have been synthesised by following
reported procedures.15,16 Refluxing K2[PdCl4] with the two ligands
separately in equimolar proportions in methanol and subsequently
adding excess of aqueous NaClO4 at room temperature, red
complexes [Pd(LH)]2(Cl)(ClO4) (1) and [Pd(L0H)]2(ClO4)2 (2) are
obtained. The crystal structures of 1 and the diacetonitrile
solvate of 2 have been determined (Fig. 1 and 2; Table 1). They
contain [Pd2(ligand)2]2+ cations with ligand = LH or L0H respectively.
The backbone of the ligands is identical and as a result the cations
have equivalent structures. Dimensions are compared in Table 2.
The bonding of each ligand is asymmetrical with the metals being
bonded to three donor atoms from one ligand and one donor atom
from the other. Thus the ligands in 1 and 2 are tetradentate.
The [Pd2(LH)2]2+ cation in 1 has crystallographic C2 symmetry.
Also in the asymmetric unit are a chloride anion on a two-fold
axis and a perchlorate anion with the chlorine atom also on a two
fold axis. The metal atom has an approximately square planar
four-co-ordinate environment being bonded to four nitrogen
atoms with different bond lengths. Thus Pd(1)–N(18) o Pd(1)–
N(22) o Pd(1)–N(11) o Pd(1)–N(28)* (* = symmetry element
1/2 ꢁ x, 2 ꢁ y, z) with distances of 1.949(3), 1.969(3), 2.016(3),
2.045(3) Å respectively. The Pd(1)ꢀ ꢀ ꢀPd(1)* distance is 3.2669(6) Å.
The N(17)–H(17) bond forms a hydrogen bond to the chloride
anion; the dimensions are given in Table 3.
Fig. 2 A view of the crystal structure of the [Pd2(L0H)2]2+ cation in 2 with
ellipsoids at 50% probability. The perchlorate anions and acetonitrile
solvent molecules are omitted for clarity.
Table 1 Crystal data and refinement parameters for 1 and 2
Complex
1
2
The structure of 2.2CH3CN contains discrete [Pd2(L0H)2]2+
cations, two perchlorate anions and two acetonitrile solvent
molecules. The cation has an approximate C2 symmetry. The
two metal atoms have equivalent environments as demonstrated
by the dimensions in the coordination spheres detailed in
Table 2. The Pd(1)ꢀ ꢀ ꢀPd(2) distance is 3.0128(5) Å significantly
shorter than that found in 1. In 2, as in 1, the two metal atoms are
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C24H22Cl2N12O4Pd2
826.23
Orthorhombic
Pcca
16.2703(6)
10.6913(4)
16.8761(5)
(90)
(90)
(90)
2935.61(18)
4
1.869
C52H44Cl2N14O8Pd2
1276.71
Triclinic
P1
10.5484(16)
11.4088(14)
13.033(2)
66.797(15)
67.828(15)
89.922(11)
1314.8(4)
1
a (deg)
b (deg)
g (deg)
V (Å3)
Z
dcalc (g cmꢁ3
)
1.612
0.855
644
m (Mo Ka) (mmꢁ1
F(000)
)
1.462
1632
Reflections collected
Independent reflns
Reflections [I 4 2s(I)]
R1, wR2 [I 4 2s(I)]
R1,wR2 [all data]
GOF
13 173
4230
2905
0.0432, 0.0790
0.0778, 0.0933
1.019
0.695, ꢁ0.950
9338
7669
7410
0.0258, 0.0589
0.0275, 0.0605
1.026
0.338, ꢁ0.905
Max, min residual
density e Åꢁ3
bonded to three nitrogen atoms from one ligand and one
nitrogen from the other. The Pd–N bond lengths follow a similar
pattern to those in 1, with those to unique nitrogen Pd(1)–N(68),
Pd(2)–N(28) at 2.045(3), 2.055(3) Å being longer than Pd(1)–N(11),
Pd(2)–N(51) at 2.010(3), 2.010(3) Å, no doubt due to some steric
strain. These distances to pyridine nitrogen atoms are longer
than those to internal nitrogen atoms which are also different
with Pd(1)–N(18), Pd(2)–N(58) shorter at 1.949(3), 1.949(3) Å
Fig. 1 A view of the crystal structure of the [Pd2(LH)2]2+ cation in 1
containing crystallo-graphic C2 symmetry with ellipsoids at 50% probability.
The anions are omitted for clarity.
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Table 2 Dimensions (Å, deg) in the metal coordination spheres
1
2
Pd(1)–N(11)
Pd(1)–N(18)
2.032(3)
1.960(3)
1.998(3)
2.060(3)
2.016(3)
1.949(3)
1.969(3)
2.045(3)
Pd(1)–N(22)
Pd(1)–N(28)*a
Pd(2)–N(58)
Pd(2)–N(62)
1.949(3)
1.980(3)
Pd(2)–N(51)
Pd(2)–N(28)
2.010(3)
2.055(3)
Pd(1)ꢀ ꢀ ꢀPd(2)
3.2669(6)
90.30(13)
80.87(13)
171.13(12)
172.46(14)
97.06(12)
91.74(12)
3.0128(5)
90.58(11)
82.00(12)
172.34(11)
175.41(12)
94.00(11)
93.42(11)
90.34(11)
81.66(12)
171.36(11)
175.53(11)
94.11(11)
93.92(11)
N(18)–Pd(1)–N(22)
N(18)–Pd(1)–N(11)
N(22)–Pd(1)–N(11)
N(18)–Pd(1)–N(28)*a
N(22)–Pd(1)–N(28)*a
N(11)–Pd(1)–N(28)*a
N(58)–Pd(2)–N(62)
N(58)–Pd(2)–N(51)
N(62)–Pd(2)–N(51)
N(58)–Pd(2)–N(28)
N(62)–Pd(2)–N(28)
N(51)–Pd(2)–N(28)
Fig. 3 Electronic spectra of 1 (blue) and 2 (black) in acetonitrile.
a
N(28)* in 1 is equivalent to N(68) in 2. * represents symmetry element of dimers. Our complexes are not photoluminescent at room
(0.5 ꢁ x, 2 ꢁ y, ꢁz).
temperature in acetonitrile.
The nature of HOMO in our complexes deserves a few
comments as so far in all related Pd(II) complexes9,10,12 HOMO
Table 3 Hydrogen bonds (distances, Å; angles, deg) in the structures
has been found to be metal based. In these cases, actually the
antibonding combination of the two d22 orbitals appears as the
Donor (D) acceptor (A)
N–H
Hꢀ ꢀ ꢀA
Nꢀ ꢀ ꢀA
N–Hꢀ ꢀ ꢀA
HOMO. The LUMO being ligand based, MMLCT becomes
possible. Our situation being rather unusual, we have performed
M06-2X/LanL2DZ and BP86/LanL2DZ calculations on [(2-
phenylpyridine)Pd(m-OAc)]2 (Bercaw’s complex) to test the reliability
of our DFT methods (Table 4). It is found that at our levels of
calculations also, the HOMO in Bercaw’s complex is the dz2 ꢁ d22
combination (Table 4). While BP86 is a very well tested functional,
elsewhere we have shown that M06-2X is well suited for studying
In 1
N(17)–H(17)ꢀ ꢀ ꢀCl(1)
0.84(2)
2.22(2)
3.052(3)
176(4)
In 2
N(17)–H(17)ꢀ ꢀ ꢀN(1)
0.86(2)
0.84(2)
2.32(4)
2.40(4)
3.077(5)
3.086(5)
147(5)
140(6)
N(57)–H(57)ꢀ ꢀ ꢀO(71)
than Pd(1)–N(22), Pd(2)–N(62) at 1.969(3), 1.980(3) Å. This is weak interactions.17,18 It should be noted that this functional in
presumably due to the different nature of the nitrogen atoms contrast to BP86 shows that the LUMO in Bercaw’s complex involves
and the fact that the adjacent nitrogen atoms to N(18), N(58), p–p interactions (Table 4).
namely N(17), N(57) are protonated while those adjacent to
We now discuss the electronic structures of 1 and 2 in an
N(22), N(62), namely N(21), N(61) are not. These two protonated attempt to ascertain whether there is any Pd–Pd bond in 1 and
nitrogen atoms N(17) and N(57) form hydrogen bonds to a 2. Our DFT calculations yield Fig. 4 where the energy ordering
solvent acetonitrile nitrogen atom N(1) and a perchlorate oxy- of the m.o.s. arising out of the overlap of two sets of 4d orbitals
gen atom O(71) respectively as listed in Table 3.
is shown. The sixteen 4d electrons of the Pd2 units fill up four
As mentioned earlier, colours of our complexes 1 and 2 are bonding m.o. and four anti-bonding m.o.s. resulting in a net
red. They display three charge transfer bands in the UV-Vis b.o. of zero. Still certain observations are worth noting. The two
spectra in acetonitrile (Fig. 3). The band positions are different. atomic dz2 orbitals produce two m.o.s. – bonding and anti-
Respective bands are more intense in 2 than in 1. The absorption bonding in an approximate axial direction. The splitting D
around 450 nm is responsible for their red colour. Our density value in 2 is more than that in 1 by 0.05 eV clearly indicating
functional theory (DFT) calculations using M06-2X and BP86 some sort of interaction between the two Pd atoms along the
functionals with LanL2DZ basis set, reveal that the HOMOs in z axis in 2 (Table 5). The angle y (Fig. 5) between the two arms of
the cations of 1 and 2 are ligand based while the LUMOs are the open clamshell is 58.91 and 40.11 in 1 and 2 respectively. It
centered on the metals (Table 4). Thus the lowest energy band in should be noted that as y - 01, the interaction between the two
1 and 2 is due to ligand to metal–metal charge transfer dz2 would approach its maximum causing much larger split-
(LMMCT). The HOMO–LUMO gap in 2 is less than that in 1 ting. Since y in 2 is less than that in 1, the splitting in 2 is larger.
by 0.40 eV.
Furthermore, the Pdꢀ ꢀ ꢀPd distance in 1 is approximately equal to
Accordingly the LMMCT band in 2 is red shifted compared the sum of the van der Waals’ radii of two Pd atoms (vide supra).
to 1 (Fig. 3). Bercaw et al.9 have pointed out that appearance of But it is significantly less in 2. This factor also works in tandem
the band at 450 nm in related Pd(II) complexes is characteristic with y to increase the value of D. In Bercaw’s complex,9
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Table 4 The frontier orbitals of the cations in 1 and 2 and their energies as obtained from DFT. Results of our calculations on Bercaw’s complex [(2-
phenylpyridine)Pd(m-OAc)]2 are also given for comparisona
Complex
HOMO
LUMO
d (eV)
At M06-2X/LanL2DZ level
1
5.44
2
5.04
Bercaw’s complex
6.10
At BP86/LanL2DZ level
1
1.80
2
1.55
Bercaw’s complex
1.72
a
d is (energy of LUMO) ꢁ (energy of HOMO).
y is 23.21. Indeed the value of D becomes so large (Table 5) that in [(2-phenylpyridine)Pd(m-OAc)]2 of 2.86216(11) Å is also
the six m.o.s. arising out of the interactions between the dxy, dxz shorter than that in 2.
and dyz orbitals are found to have energies intermediate
Thus though there are distinct interactions between the two
between dz2 + dz2 and dz2 ꢁ dz2. However, the Pd–Pd distance Pd(II) centers in 1 and 2, the net b.o. between them is zero. Such
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Table 5 Bonding and antibonding combinations of the dz2 orbitals in 1, 2
and Bercaw’s complex and the energy difference (splitting) between them,
as obtained at the M06-2X/LanL2DZ and BP86/LanL2DZ levels
Complex
dz
2
+ dz
2
dz2
ꢁ dz
2
D (eV)
At M06-2X/LanL2DZ level
1
1.28
2
1.25
Fig. 4 The m.o.s. resulting from the mutual interactions of the metal
d orbitals of the Pd2 moiety in the cation of 1 at BP86/LanL2DZ level. The
dxy ꢁ dxy antibonding m.o. (tentatively shown by a dotted line) could not be
located properly. The relative ordering of the m.o.s. remains similar in the
cation of 2.
Bercaw’s complex
1.80
At BP86/LanL2DZ level
a conclusion has been drawn by some previous workers also.
The phenomenon, in our opinion, is similar to the crystal field
splitting in tetrahedral d10 copper(I) complexes. The situation is
+
exemplified in Cu(NH3)4 (Fig. 6).
1
0.81
At the BP86/6-31+G(d,p) level, 10Dq (Td) of ammonia is
found to be 4154 cmꢁ1. Conventional 10Dq is the splitting
between T2g and Eg orbitals in an octahedral geometry.
So to compare with the literature values of 10Dq of ammonia,
we have multiplied our 10Dq (Td) by 9/4 to obtain 10Dq (Oh) as
9347 cmꢁ1. Earlier Gray and co-workers19 have designated a value
of 100 80 cmꢁ1 as the 10Dq of ammonia with respect to nickel(II).
Hence despite splitting of the d orbitals in a tetrahedral Cu(I)
complex, it does not impart any net crystal field stabilization
energy.
2
0.86
The existence of some kind of interaction between the Pd(II)
centers in at least 2 is also evident from its cyclic voltammetric
behaviour (Fig. 7). Complex 1 shows an irreversible oxidation of
the Clꢁ at 1.09 V vs. NHE. On the other hand, complex 2 shows
two quasi-reversible PdIIIPdII/PdIIPdII and PdIIIPdIII/PdIIIPdII
couples with E1/2 values 1.28 and 1.47 V (vs. NHE) respectively.
If the two Pd centers had no interaction between them, the two
waves would occur at the same potential; the difference in the
redox potentials of the observed two couples increases with the
magnitude of the interactions between the two metals.20 The
difference in the E1/2 of the two couples is 0.32 V in Bercaw’s
Bercaw’s complex
1.11
complex where the Pd–Pd distance is 2.86216(11) Å. These two centers in Bercaw’s complex is much stronger than that in 2.
quantities in our complex 2 are 0.19 V and 3.0128(5) Å. So the We have already reached such a conclusion while discussing
natural conclusion is that the interaction between the Pd the effect of clamshell angle y on D.
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3. Concluding remarks
Our ligands LH2 and L0H2 contain a 2-aminopyridine fragment
(Chart 1). The bite angle of this fragment is such that it gives
rise to dinuclear complexes with metal–metal bonds.21 In our case
also, this particular fragment yields dinuclear Pd(II) complexes –
[Pd(LH)]2(Cl)(ClO4) (1) and [Pd(L0H)]2(ClO4)2 (2). Still, previously
working with butane-2,3-dione bis(20-pyridylhydrazone) i.e. R = Me
in Chart 1 (designated as L00H2), several workers22,23 have reported
mononuclear green Pd(II) complexes of the type [Pd(L00H2)]Cl2 and
PdL00.
The metal–metal bond distances in 1 and 2 are 3.2669(6) and
3.0128(5) Å respectively. While the distance in 1 is approximately
equal to the sum of the van der Waals’ radii of two Pd atoms
(in Bondi’s scale), it is significantly less in 2. Consideration of
theoretical calculations, structural factors and electrochemistry
lead us to ascertain that there is indeed some sort of interaction
between the two Pd(II) centers though the net b.o. from the
ordering of the m.o.s. for the Pd(II)2 core comes out as zero. This
is because Pd(II) has an electronic configuration of d8. We have
pointed out that the situation is similar to the crystal field
splitting in tetrahedral copper(I) complexes. The parallelism lies
Fig. 5 Open clamshell angle (y); angle between the two planes formed by
the coordinating atoms of each metal ions in 1 and 2.
+
in the fact that in Cu(NH3)4 and our Pd(II) dimers, though the
d-orbitals are favorably disposed, a net stabilization due to the
related effects is denied in these cases in terms of m.o. theory.
The observation of PdIIPdII/PdIIPdIII and PdIIPdIII/PdIIIPdIII
couples in 2 deserves a few comments. As soon as an electron is
removed from 2 electrochemically, the b.o. of the resulting Pd2
core no longer remains as zero. It becomes 0.5 and then the
abstraction of the second electron occurs at a different potential.
The difference DE1/2 between the redox potentials for the two
electron transfer processes depends on the extent of interaction
between the metals which in turn is dictated by the clamshell
angle y and the metal–metal distance. Since the values of y and the
Pd–Pd bond distance in 2 are more than those encountered in
Bercaw’s complex, DE1/2 for Bercaw’s compound is larger than
that in 2.
Fig. 6 Crystal field splitting of the five d orbitals of Cu in tetrahedral
Cu(NH3)4 into T2 and E sets. The energy values were obtained by DFT
+
calculations at the BP86/6-31+G(d,p) level.
4. Computational
All the DFT calculations were carried out by using GAUSSIAN09
package.24 Inputs for the Pd complexes were created from the
respective crystal structures. Functionals used here are BP8625–27
and M06-2X.28 LanL2DZ29,30 basis set was employed for the
geometry optimization of the Pd complexes and 6-31+G(d,p) for
+
Cu(NH3)4 . Frequency calculations were performed in all cases to
ensure that true minima are achieved. Pictorial representations
of the various m.o.s. were generated from the respective .chk file
by GaussView 5.0.
5. Experimental
5.1. Materials and physical measurements
Benzil and glyoxal were purchased locally. PdCl2, TEAP,
2-hydrazinopyridine and NaClO4ꢀH2O were purchased from
Sigma-Aldrich. K2[PdCl4] was prepared by reacting PdCl2 with
Fig. 7 Cyclic voltammetry of 1 (blue) and 2 (black) in acetonitrile. Supporting
electrolyte, 0.1 M tetraethylammonium perchlorate (TEAP). Solute concentration,
1 mM. Scan rate, 50 mV sꢁ1
.
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stoichiometric amount of KCl in water. Microanalyses were 321 frames were measured with counting times of 10 s. Data
performed by a Perkin-Elmer 2400II CHNS analyser. Molar analysis was carried out with the CrysAlis program.31 The
conductances were measured in CH3CN by a Syntronics (India) structures were solved using direct methods with the Shelxs97
conductivity meter (model 306). FTIR spectra (KBr) were program.32 The non-hydrogen atoms were refined with anisotropic
recorded on a Shimadzu FTIR-8400S spectrometer and UV-Vis thermal parameters. The hydrogen atoms bonded to carbon were
spectra (in CH3CN) on a Perkin Elmer Lambda 950 spectro- included in geometric positions and given thermal parameters
photometer. 500 MHz NMR spectra were recorded on a Bruker equivalent to 1.2 times those of the atom to which they were
Avance III 500 spectrometer in DMSO-d6 and ESI mass spectra attached. Hydrogen atoms bonded to nitrogen were located in a
(in CH3CN) on a Waters Qtof Micro YA263 spectrometer. Cyclic difference Fourier map and refined with distance constraints.
voltammetry was performed in purified acetonitrile with a Absorption corrections were carried out using the ABSPACK
conventional three-electrode system at room temperature using a program.33 The structures were refined using Shelxl2016-6.32
CHI600E electrochemical analyzer. An Ag/AgCl electrode was used
as the reference. A Pt electrode was used as the working one.
Acknowledgements
5.2. Synthesis of [Pd(LH)]2Cl(ClO4) (1)
S. G. P. thanks the Council of Scientific and Industrial
Research, Government of India, New Delhi for a fellowship.
M. G. B. D. thanks EPSRC and the University of Reading for
funds for the Oxford Instruments X-Calibur system.
A methanolic solution (10 ml) of K2[PdCl4] (0.065 g, 0.2 mmol)
was added to a methanolic (10 ml) solution of LH2 (0.048 g,
0.2 mmol) and refluxed for 6 h. Then it was cooled to room
temperature. Then NaClO4ꢀH2O (0.056 g, 0.4 mmol) dissolved
in water (5 ml) was added to it and stirred for 15 min. The clear
reddish solution was then left in the air for slow evaporation.
When the volume reduced to B5 ml, the deposited reddish
References
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