Vibrational Spectroscopic Characterization and DFT Study of Palladium(II) Complexes with N-Benzyliminodiacetic Acid Derivatives

Article abstract of DOI:10.1071/CH16150

The reactions of N-benzyliminodiacetic acid (BnidaH₂) and its para-substituted derivatives, namely N-(p-chlorobenzyl)iminodiacetic acid (p-ClBnidaH₂), N-(p-nitrobenzyl)iminodiacetic acid (p-NO₂BnidaH₂), and N-(p

Full text of DOI:10.1071/CH16150

CSIRO PUBLISHING
Aust. J. Chem. 2016, 69, 1285–1291
Full Paper
http://dx.doi.org/10.1071/CH16150
Vibrational Spectroscopic Characterization and DFT Study
of Palladium(II) Complexes with N-Benzyliminodiacetic
Acid Derivatives
A B
,
A
A
Neven Smrecˇki,
Igor Roncˇevic´, and Zora Popovic´
A
Department of Chemistry, Faculty of Science, University of Zagreb,
Horvatovac 102a, HR-10000 Zagreb, Croatia.
B
Corresponding author: Email: nsmrecki@chem.pmf.hr
The reactions of N-benzyliminodiacetic acid (BnidaH2) and its para-substituted derivatives, namely N-(p-chlorobenzyl)
iminodiacetic acid (p-ClBnidaH2), N-(p-nitrobenzyl)iminodiacetic acid (p-NO2BnidaH2), and N-(p-methoxybenzyl)
iminodiacetic acid (p-MeOBnidaH2) with sodium tetrachloropalladate(II) were performed in aqueous solutions. Three
new complexes [Pd(p-ClBnidaH)2]ꢀ2H2O (2), [Pd(p-NO2BnidaH)2]ꢀ2H2O (3), and [Pd(p-MeOBnidaH)2] (4) were
prepared and characterized by infrared spectroscopy and thermogravimetric and differential thermal analyses.
The molecular geometry and infrared spectra of these three complexes, together with the previously synthesized
[Pd(BnidaH)2]ꢀ2H2O (1a) and [Pd(BnidaH)2] (1b) were also modelled using density functional theory calculations at
the BP86/6–311þG(d,p) level of theory with SDD pseudopotentials.
Manuscript received: 11 March 2016.
Manuscript accepted: 5 May 2016.
Published online: 10 June 2016.
Introduction
studied by infrared spectroscopy as well as density functional
theory (DFT) analysis. Although many research papers include
combined experimental and theoretical investigations of metal
complexes,[24–28] DFT-based structural and vibrational studies of
iminodiacetato complexes are generally scarce in the literature –
few detailed investigations on such topics can be found.[29–34] To
date, similar studies based on comparisons of experimental and
calculated infrared spectra of palladium(II) complexes with
iminodiacetate ligands have not been reported in literature.
Iminodiacetic acids (RidaH2) are well-known chelating agents,
which form stable complexes with many metal ions.[1–3] The
molecular and crystal structures of numerous first-row transition
metal (CoII, NiII, and CuII) complexes with N-substituted imi-
nodiacetic acids, such as N-benzyliminodiacetic acid and its
derivatives, have been thoroughly investigated.[4–14] However,
iminodiacetato complexes of heavy transition metal ions such as
PdII are less known.[15–20] This is surprising, considering that
palladium(II) complexesare known tobe highly efficient catalysts
in modern synthetic organic chemistry.[21,22] Previously, we
prepared several PdII complexes with N-arylalkyliminodiacetic
acids (N-benzyl, N-(2-phenylethyl), N-(3-phenylprop-1-yl), and
N-(o-chlorobenzyl) derivatives) in order to examine their
catalytic activity towards methoxycarbonylation of iodoben-
zene.[23] It was revealed that the catalytic activity of the
palladium(II) complex in this reaction depends on the structure
of non-coordinating arylalkyl group R.[23] To date, no
palladium(II) complexes with para-substituted derivatives of
N-benzyliminodiacetic acid have been reported.
Results and Discussion
Preparation of the Ligands
N-(p-Chlorobenzyl)iminodiacetic acid and N-(p-nitrobenzyl)
iminodiacetic acid were prepared using a method similar to that
used to prepare N-benzyliminodiacetic acid,[14] however, using
N
N
COOH
COOH
COOH
CI
COOH
To get more insights into the role of non-coordinating
substituents in the chemistry of palladium(II) complexes
with iminodiacetic acids, we prepared three new PdII complexes
with p-substituted N-benzyliminodiacetic acid derivatives,
namely N-(p-chlorobenzyl)iminodiacetic acid (p-ClBnidaH2),
N-(p-nitrobenzyl)iminodiacetic acid (p-NO2BnidaH2), and
N-(p-methoxybenzyl)iminodiacetic acid (p-MeOBnidaH2)
(Chart 1). These complexes, namely [Pd(p-ClBnidaH)2]ꢀ2H2O
(2), [Pd(p-NO2BnidaH)2]ꢀ2H2O (3), and [Pd(p-MeOBnidaH)2]
(4), together with previously synthesized and characterized
[Pd(BnidaH)2]ꢀ2H2O (1a) and [Pd(BnidaH)2] (1b)[23] were
BnidaH2
p-CIBnidaH2
N
N
COOH
COOH
p-MeOBnidaH2
COOH
MeO
O2N
COOH
p-NO2BnidaH2
Chart 1. Structural formulae of N-benzyliminodiacetic acid (BnidaH2),
N-(p-chlorobenzyl)iminodiacetic acid (p-ClBnidaH2), N-(p-nitrobenzyl)
iminodiacetic acid (p-NO2BnidaH2), and N-(p-methoxybenzyl)iminodiacetic
acid (p-MeOBnidaH2).
Journal compilation ꢀ CSIRO 2016
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1286
N. Smrecˇki, I. Roncˇevic´, and Z. Popovic´
1) H2NCH2COOH/NaOH/EtOH/H2O
N
O
COOH
H
(p-MeOBnGlyH)
ϩ
2) NaBH4
3) HCl
H3CO
H3CO
1) ClCH2COOH
2) NaOH/H2O
3) HCl
N
COOH
N
COOH
COOH
(p-MeOBnidaH2)
H3CO
H3CO
OCH3
Scheme 1. Preparation of N-(p-methoxybenzyl)iminodiacetic acid (p-MeOBnidaH2) from N-(p-methoxybenzyl)glycine
(p-MeOBnGlyH).
O
HOOC
N
COOH 1) NaOH/H2O
2) Na2PdCl4/H2O
N
O
O
N
Pd
X
X
COOH
X
COOH
(RidaH2)
O
([Pd(RidaH)2]•nH2O) (1a–4)
Scheme 2. Preparation of palladium(II) complexes with N-benzyliminodiacetic acid derivatives. X ¼ H, n ¼ 2 for
1a; X ¼ H, n ¼ 0 for 1b; X ¼ Cl, n ¼ 2 for 2; X ¼ NO2, n ¼ 2 for 3; X ¼ OCH3, n ¼ 0 for 4.
the corresponding para-substituted benzylamine hydrochlorides.
These precursors were prepared via Reichert–Dornis cleavage of
the corresponding N-benzylhexamethylenetetraminium chlor-
ides,[35] which were prepared by the Dele´pine reaction[36] from
hexamethylenetetramine and p-chlorobenzyl chloride or
p-nitrobenzyl chloride. N-(p-Methoxybenzyl)iminodiacetic acid
was prepared by carboxymethylation of N-(p-methoxybenzyl)
glycine (p-MeOBnGlyH). This precursor was prepared
by reductive alkylation of glycine, using a combination of
p-methoxybenzaldehyde and sodium borohydride in an aqueous
ethanolic solution (Scheme 1). A small amount of N,N-bis
(p-methoxybenzyl)glycine as a by-product was also formed in
this reaction.
1a, 2, and 3. This observation can be explained by the existence
of extensive hydrogen-bonding network, observed in the crystal
structure of 1a.[23] Each co-crystallized water molecule forms
hydrogen bonds with three neighbouring molecules of the
complex in this complex 3D framework.[23] Although the crystal
structures of the other two hydrates 2 and 3 are unknown, it is
likely that a similar stabilization exists in these complexes as
they show thermal behaviours similar to those displayed by 1a.
The other two complexes, 1b and 4, as well as 1a, 2, and 3 after
their dehydration, typically decompose in one step, which corre-
sponds to the loss of both coordinated ligands. The complexes are
stable up to ,2008C, when they start to decompose. This
decomposition usually ends at 450–5008C. Complex 3 with
p-nitrobenzyl ligand shows somewhat greater resistance towards
thermal degradation, whereas complex 4 with p-methoxybenzyl
ligand decomposes completely in a narrow temperature range
(190–2808C) under oxygen atmosphere. Thermal degradation of
the complexes under nitrogen atmosphere results in their carboni-
zation, whereas the non-degraded residue obtained upon heating
in oxygen atmosphere usually corresponds to the calculated mass
of PdO, which can form upon complete oxidation of the sample.
The decomposition of all complexes is endothermic under
nitrogen and exothermic under oxygen atmosphere; however,
the dehydration step is endothermic in both nitrogen and oxy-
gen. Full thermal analysis data are given in the Supplementary
Material.
Preparation and Thermal Properties of the Complexes
The complexes were prepared by the reaction of sodium tetra-
chloropalladate(II) with the corresponding iminodiacetic acids
in slightly acidic aqueous solutions (pH E 5) (Scheme 2).
The time after which the complexes start to precipitate out of
the reaction mixture is inversely related to the molecular mass of
the ligands. Complexes of the type [Pd(RidaH)2] were obtained
with all N-benzyliminodiacetic acid derivatives used in this
work, meaning that the structure of the non-coordinating group
R did not influence the coordination ability of the ligand. The
obtained complexes can be classified as dihydrates (1a, 2, and 3)
and anhydrous complexes (1b and 4). All prepared complexes,
including hydrates, are air-stable substances that are sparingly
soluble in common laboratory solvents except for dimethyl
sulfoxide and dimethylformamide. The hydrates decompose
upon heating in nitrogen or oxygen atmosphere in two steps,
the first of which corresponds to the loss of co-crystallized water
molecules. However, it should be noted that this dehydration
is not accomplished easily because stronger heating conditions
(up to ,1508C) are required than typically used for hydrates
(,1008C) to eliminate both water molecules from the samples
Analysis of Experimentally Obtained Infrared Spectra
All the prepared complexes exhibit similar solid-state infrared
(IR) spectra (Fig. 1). The visual appearance of the IR spectra
depends more on the presence or absence of co-crystallized
water molecules in the samples of the complexes than on the
type of substituent at the aromatic ring. At first sight, it can be
seen that complexes 1a, 2, and 3, which are hydrates, show
mutually very similar spectra. The positions of the bands, of

PdII Complexes with N-Benzyliminodiacetic Acids
1287
X
1b
4
3
2
X
Fig. 2. Modelled unit based on the crystal structure of 1a.[23] X ¼ H for 1a
and 1b; X ¼ Cl for 2; X ¼ NO2 for 3; X ¼ OCH3 for 4.
1a
3500
3000
2500
2000
1500
1000
500
Wavenumber [cmϪ1
]
of anhydrous complexes 1b and 4. The position of this band is
more influenced by the molecular mass of the para-substituent
than its structure i.e. for 1a (X ¼ H), the band was observed at
3585 cmꢁ1, whereas in 2 and 3, the band was observed a lower
wavenumber (a difference of ,30–40 cmꢁ1).
Fig. 1. Experimental IR spectra of the complexes 1a,[23] 1b,[23] 2, 3, and 4.
Broad bands of medium intensity, assigned to the OꢁH
stretching of COOH group, n(OH, COOH), were found at almost
the same position in the spectra of the anhydrous complexes
(3447 cmꢁ1 for 1b and 3446 cmꢁ1 for 4). For the hydrates, the
position of this band depends on the type of substituent at imino-
nitrogen and was found at 3422 cmꢁ1 for 1a, 3202 cmꢁ1 for 2,
3383 cmꢁ1 for 3, and 3446 cmꢁ1 for 4. Finally, the band
assigned to the carbonyl stretching of the non-coordinated
carboxylic group, n(C=O), which was observed in the spectra
of the free ligands, was also present in the spectra of 1a
(1718 cmꢁ1), 1b (1736 cmꢁ1), 2 (1716 cmꢁ1), 3 (1729 cmꢁ1),
and 4 (1740 cmꢁ1).
course, depend on the structure of the ligand (i.e. the substituent
at the aromatic ring). In contrast, the IR spectrum of the anhy-
drous complex 1b looks more like the spectrum of 4 than that of
its solvatomorph 1a. The IR spectra of previously reported
anhydrous palladium(II) complexes with N-(o-chlorobenzyl)
iminodiacetic acid, N-(2-phenylethyl)iminodiacetic acid, and
N-(3-phenylprop-1-yl)iminodiacetic acid[23] are also remark-
ably similar to the spectrum of 1b.
Clearly, two types of spectra, belonging to one of the two
families of the complexes (dihydrates and anhydrous com-
plexes), can be distinguished. In general, these spectra are
characterized by the presence of four (for hydrates) or three
(for anhydrous complexes) main absorption bands as follows.
A very strong band of asymmetric stretching of the carboxy-
late ion, nas(COOꢁ)[37,38] (the strongest band in the spectra) was
present in the spectrum of 1a at 1628 cmꢁ1[23] and was also
observed in the similar spectral region for the other complexes 1b
(1613 cmꢁ1), 2 (1634 cmꢁ1), 3 (1628 cmꢁ1), and 4 (1590 cmꢁ1).
A band of medium intensity, assigned to the symmetric stretching
of the carboxylate ion, ns(COOꢁ), was observed in the 1350–
1360cmꢁ1 region for the hydrates (1359 cmꢁ1 for 1a, 1356 cmꢁ1
for 2, and 1353 cmꢁ1 for 3) and was shifted to somewhat higher
wavenumbers in the spectra of the anhydrous complexes
(1379 cmꢁ1 for 1b and 1367cmꢁ1 for 4). The difference between
nas(COOꢁ) and ns(COOꢁ), D value,[39] is larger than 200 cmꢁ1
for each of the mentioned complexes, indicating the presence of
monodentate coordination mode of the carboxylate ion. It can be
noticed that this width of separation between asymmetric and
symmetric stretching is also a characteristic feature of the family
of the complexes because it is remarkably (30–50 cmꢁ1) larger
for the hydrates (D E 270–275 cmꢁ1) than for the anhydrous
complexes (234 cmꢁ1 for 1b and 223 cmꢁ1 for 4).
The spectrum of 3 is also characterized by the presence of
asymmetric (nas(NO2); 1519 cmꢁ1) and symmetric stretching of
the nitro group (ns(NO2); 1318 cmꢁ1).
Molecular Structure of the Complexes and Comparison
of the Experimental and Calculated Spectra
The molecular structure of 1a is characterized by the usual
square-planar coordination environment around palladium(II)
ion with two N-benzylhydrogeniminodiacetate ligands bound as
bidentate chelators, resulting in the formation of the trans iso-
mer.[23] It can be assumed that other investigated compounds in
this series (1b, 2, 3, 4) have similar molecular structures (Fig. 2).
There are two reasons for this assumption: (1) they all exhibit
similar thermal behaviours and (2) more importantly, the mod-
elled spectra for all compounds, obtained using the molecular
structure of 1a, are in good agreement with the experimentally
obtained infrared spectra.
Of all tested methods, BP86/6–311þG(d,p) with added
Grimme’s D3 corrections showed the best correlation with the
experimental spectral data. Choice of the pseudopotential for the
Pd atom does not have much effect on the calculated spectra –
SDD gave marginally better results, with a mean unsigned differ-
ence of ,1 cmꢁ1 in frequency calculations, when compared with
the significantly faster LANL2DZ. This is not surprising, as the
analyzed vibration modes are not inthe vicinityof the metal centre.
The strongest indication of the presence of co-crystallized
water molecules in the hydrates is, however, the appearance of
a sharp band of medium intensity observed at 3585 cmꢁ1 (1a),
3539 cmꢁ1 (2), and 3528 cmꢁ1 (3); this band was assigned to
OꢁH stretching, n(OH, H2O). The band is absent in the spectra

1288
N. Smrecˇki, I. Roncˇevic´, and Z. Popovic´
In order to meaningfully compare the experimental and
Table 1. Experimental and calculated harmonic wavenumbers for
selected modes of 1a–4
calculated spectra, we analyzed the important vibration modes
discussed in the previous section as well as other intensive
signals in the experimental spectra. In order to assign the
calculated frequencies, we matched them with their cor-
responding experimental values using linear regression.
By analyzing 35 vibrations (Table 1), we were able to obtain
the following relationship between the experimental and
calculated frequencies:
Modes marked with an asterisk (*) were corrected by an additional
101 cmꢁ1; wag, wagging; twi, twisting
Complex
1a
Experimental
Predicted
Mode
3585
3422
1718
1628
1359
1319
3447
2930
1736
1613
1417
1379
1216
3539
3202
1716
1634
1356
1228
3528
3383
1729
1628
1519
1353
1318
3446
2992
1740
1590
1516
1433
1367
1254
1217
3551
3377
1728
1641
1356
1334
3450
2935
1728
1639
1403
1357
1206
3543
3183
1718
1638
1361
1242
3552
3399
1729
1655
1492
1356
1269
3450
3010
1729
1641
1516
1424
1356
1245
1222
n(OH, COOH)
v(OH in H2O)
n(C=O)*
vas(COO)
~nexp ¼ ð0:989 ꢂ 0:005Þ~ncalc ꢁ ð16 ꢂ 11Þcmꢁ1; r2 ¼ 0:9993
vs(COO)
dwag(CH2)
n(OH, COOH)*
vs(CH2)
1b
For most analyzed vibrations, this model was satisfactory in
predicting values of the experimental frequencies. However,
some vibrations, namely the carbonyl stretching of the carbox-
ylic group, and several of the hydroxyl stretching frequencies
were found on a parallel regression line, overestimated by
,100 cmꢁ1, as shown in Fig. 3. In other words, the computa-
tionally predicted values of these vibrational frequencies were
consistently too high. The reason that this bond-weakening was
unaccounted for in silico probably lies in the fact that only
one monomer unit was modelled, which neglects interactions
present in the crystal lattice such as hydrogen bonds. Other
discrepancies between the predicted and experimental spectra
can be attributed to a lack of anharmonic corrections, which
have been shown to improve the agreement between experi-
mental and calculated spectra.[40–43]
n(C=O)*
vas(COO)
dwag(CH2)
vs(COO)
din plane(CH in ring)
n(OH, COOH)
v(OH in H2O)*
n(C=O)
2
3
vas(COO)
vs(COO)
dtwi(CH2)
n(OH, COOH)
v(OH in H2O)
n(C=O)*
vas(COO)
nas(NO2)
vs(COO)
Conclusions
ns(NO2)
n(OH, COOH)*
vs(CH2)
4
Palladium(II) complexes with N-benzyliminodiacetic acid and its
p-substituted derivatives were prepared and characterized by
infrared spectroscopy and thermoanalytical methods (thermo-
gravimetric and differential thermal analyses) withthe aid ofDFT
calculations. Two families of the complexes, i.e. dihydrates of
the formula [Pd(RidaH)2]ꢀ2H2O and anhydrous complexes
[Pd(RidaH)2] were successfully distinguished by the examination
of their infrared spectra.
n(C=O)*
vas(COO)
din plane(CH in ring)
dwag(CH2)
vs(COO)
dtwi(CH2)
v(ring), v(C–OCH3)
Infrared spectroscopy, when combined with DFT calcula-
tions, demonstrated to be a good tool in estimating the structure
of these complexes in cases when crystallographic data are
unknown and under the condition that at least one member of
the series (which serves as a starting point) has been structurally
characterized by X-ray crystallography. The successful assign-
ment of the main experimental vibrational modes using only the
geometry of a single complex along with similar thermal
properties are a strong argument that these complexes display
similar molecular structures. Despite the extensive hydrogen-
bonding networks present in the crystal structures of these
compounds, there is very good agreement (r2 ¼ 0.9993) between
the calculated spectra and the experimental results.
3500
3000
2500
2000
1500
1000
In continuation of our research, we plan to synthesize and
investigate iminodiacetato complexes of other noble metals
such as rhodium and iridium in order to get more insights into
the coordination chemistry of trivalent second- and third-row
transition metals with iminodiacetic acid derivatives.
1000
1500
2000
~
2500
3000
3500
n
calc [cmϪ1
]
Experimental
Reagents and Physical Measurements
~
~
Fig. 3. Correlation between calculated (ncalc) and experimental (nexp
)
vibrational frequencies (in cmꢁ1) for the complexes 1a (blue), 1b (orange),
All chemicals for the syntheses were purchased from commer-
cial sources (Aldrich, Acros, or Alfa Aesar) and used as received
without further purification. The CHN analyses were performed
2 (green), 3 (red), and 4 (purple). The vibrations frequencies represented by
triangles required an additional correction of 101 cmꢁ1
.

PdII Complexes with N-Benzyliminodiacetic Acids
1289
on a PerkinElmer 2400 Series II CHNS analyzer in the Ana-
lytical Services Laboratories of the RuXer Bosˇkovic´ Institute,
Zagreb, Croatia. The Fourier transform infrared spectra were
obtained from KBr pellets in the range 4000–400 cmꢁ1 on a
PerkinElmer Spectrum TwoTM FTIR spectrometer. The ther-
mogravimetric and differential thermal analysis measurements
were performed at a heating rate of 108C minꢁ1 in the temper-
ature range of 25–6008C under a nitrogen or an oxygen flow of
150 mL minꢁ1 on a Mettler-Toledo TG/SDTA 851e instrument.
Approximately 10 mg of sample was placed in a standard alu-
minium crucible (40 mL). The differential scanning calorimetry
measurements were performed at a heating rate of 108C minꢁ1 in
the temperature range of 25–5008C under a nitrogen flow of
180 mL minꢁ1 on a Mettler-Toledo DSC 823e instrument.
Approximately 2–5 mg of sample was placed in a standard
aluminium crucible (40 mL). The NMR spectra of the ligands
were recorded at the NMR Centre of the RuXer Bosˇkovic´
Institute, Zagreb, Croatia, on a Bruker AV 600 spectrometer,
operating at 600 MHz for the 1H nucleus and at 150 MHz for the
13C nucleus. The samples were measured in [D6]DMSO solu-
tions at 298 K, using 5-mm NMR tubes. The chemical shifts in
ppm were referenced to TMS.
nmax (KBr)/cmꢁ1 3450m, br (n(OH)), 1576vs (na(COOꢁ)),
1382vs (ns(COOꢁ)). dH ([D6]DMSO, 600 MHz) 3.20 (2H, s),
3.76 (3H, s), 3.90 (2H, s), 6.91 (2H, d, J 8.5), 7.34 (2H, d, J 8.5).
dC ([D6]DMSO, 150 MHz) 49.26 (CH2), 50.55 (CH2), 55.22
(CH3), 114.13 (CH), 127.73 (C), 130.30 (CH), 159.21 (C),
169.80 (COOH). Anal. Calc. for C10H14NO3.5 (204.22): C
58.81, H 6.91, N 6.86. Found: C 59.07, H 6.98, N 6.65 %.
Note 1. The addition of ethanol is necessary because pure
p-methoxybenzaldehyde, unlike benzaldehyde,[44] does not
react with aqueous solution of sodium glycinate, not even upon
heating (two layers are formed).
Note 2. The by-product is N,N-bis(p-methoxybenzyl)
glycine. nmax (KBr)/cmꢁ1 3435m, br (n(OH)), 1611vs
(na(COOꢁ)), 1380vs (ns(COOꢁ)). dH ([D6]DMSO, 600 MHz)
3.10 (2H, s), 3.66 (4H, s), 3.72 (6H, s), 6.88 (4H, d, J 8.5), 7.25
(4H, d, J 8.5). dC ([D6]DMSO, 150 MHz) 52.96 (CH2), 54.95
(CH3), 56.05 (CH2), 113.60 (CH), 129.82 (CH), 130.58 (C),
158.32 (C), 172.22 (COOH). Anal. Calc. for C18H21NO4
(315.36): C 68.55, H 6.71, N 4.44. Found: C 68.89, H 6.52, N
4.15 %.
Preparation of N-(p-Methoxybenzyl)iminodiacetic Acid
Hemihydrate (p-MeOBnidaH2ꢀ1/2H2O)
Preparation of N-(p-Methoxybenzyl)glycine Hemihydrate
(p-MeOBnGlyHꢀ1/2H2O)
The apparatus for this experiment consists of a hot-plate
magnetic stirrer and a three-neck, round-bottom flask (500 mL)
equipped with a Liebig condenser, dropping funnel, and a
thermometer. p-MeOBnGlyHꢀ1/2H2O (10.0 g, 0.05 mol) and
chloroacetic acid (5.0 g, 0.05 mol) were introduced into the
flask, and the mixture was dissolved in water (50 mL) while
stirring. The obtained clear solution was then cooled in an
ice bath to 58C. Aqueous sodium hydroxide solution (4.0 g,
0.1 mol in 40 mL) was then added dropwise, while maintaining
the temperature of the reaction mixture below 108C. After all
alkali was added, the reaction mixture was heated to 908C using
a boiling water bath and, while maintaining this temperature,
treated dropwise with a second solution of NaOH (2.5 g,
0.06 mol in 40 mL) over a 1 h period. The heating was continued
for 1.5 h after all alkali was added, after which the reaction
mixture was poured into a beaker and acidified to pH E 2 with
diluted hydrochloric acid (18.0 mL, 1 : 1 v/v). The product
(6.2 g), which crystallized upon spontaneous cooling, was left in
a refrigerator and filtered off by suction and washed with a small
volume of ice-cold water. An additional amount (2.0 g) of the
product crystallized after spontaneous evaporation of the
filtrate. Total yield: 64 %; mp: 199.78C. nmax (KBr)/cmꢁ1
3475m (n(OH)), 1695vs (n(C=O)), 1616s (na(COOꢁ)), 1388m
(ns(COOꢁ)). dH ([D6]DMSO, 600 MHz) 3.44 (4H, s), 3.72 (3H,
s), 3.80 (2H, s), 6.87 (2H, d, J 8.6), 7.26 (2H, d, J 8.6). dC ([D6]
DMSO, 150 MHz) 53.65 (CH2), 54.88 (CH2), 56.66 (CH2),
113.60 (CH), 129.67 (C), 130.14(CH), 158.55 (C), 171.97
(COOH). Anal. Calc. for C12H16NO5.5 (262.26): C 54.95,
H 6.15, N 5.34. Found: C 55.21, H 5.98, N, 5.41 %.
Caution! Hydrogen is evolved as a by-product. All flames in the
vicinity must be extinguished during the experiment.
Glycine (15.0 g, 0.2 mol) was dissolved in aqueous NaOH
solution (8.0 g, 0.2 mol in 200 mL), after which p-methoxy-
benzaldehyde (27.5 g, 0.2 mol) and ethanol (75 mL) were added
[Note 1]. From this point to the end of the experiment, the
reaction mixture was stirred using a hot-plate magnetic stirrer.
The clear yellow solution, which formed after a few minutes,
was heated to 608C and then stirred without heating for an
additional 2 h. After cooling to 108C in an ice bath, the solution
was maintained at that temperature and treated with NaBH4
(2.50 g, 0.06 mol), which was added in small portions over a 30-
min period. The stirring was continued for the next 30 min
without cooling, after which a second portion of p-methoxy-
benzaldehyde (13.6 g, 0.1 mol) was added. After cooling to
108C, the mixture was treated portionwise with NaBH4
(1.25 g, 0.03 mol) within 15 min, and stirring was continued
for 30 min. The reaction mixture was again cooled to 108C and
subsequently treated with a third portion of p-methoxybenzal-
dehyde (13.6 g, 0.1 mol) and NaBH4 (1.50 g, 0.04 mol) in the
earlier described manner. Then, the reaction mixture was left to
stand overnight in a refrigerator (,58C). Then, the volume of the
solution was reduced to 200 mL in a fume hood to remove
ethanol and, after cooling, extracted with chloroform (first with
100 mL, then twice with 50 mL). The (upper) aqueous layer was
acidified to pH E 6.5 with diluted hydrochloric acid (60 mL;
1 : 1, v/v) and left to stand for 2 h. The white powder [Note 2] that
had separated was filtered off, and the volume of the filtrate was
reduced to 100 mL, after which the product started to crystallize.
After cooling in an ice bath, the product was filtered off by
suction and quickly washed with ice water (40 mL). Yield:
13.2 g (33 %). The crude product is pure enough for the
preparation of N-(p-methoxybenzyl)iminodiacetic acid. How-
ever, if a purer sample is desired, the crude product (2.0 g) can be
dissolved in boiling water (5 mL). Then, the solution is mixed
with acetone (40 mL) and cooled in a refrigerator. The white
crystals are filtered off by suction and washed with acetone
(10 mL). Recovery after recrystallization is 1.4 g (70 %).
Preparation of the Complexes
The complexes were prepared using a previously reported
method[23] by pouring the aqueous solution of Na2PdCl4ꢀxH2O
(x E 3) (0.18 g, 0.5 mmol in 20 mL) into a hot solution con-
taining the ligand (1 mmol) and NaOH (0.04 g, 1 mmol) in water
(25 mL) (pH of the ligand solution is 5–6). The reaction mixtures
(pH E 5) were left to stand overnight at room temperature.
Then, the resulting yellow microcrystalline products were
filtered off, washed with water, and dried in air.

1290
N. Smrecˇki, I. Roncˇevic´, and Z. Popovic´
[Pd(BnidaH)2]ꢀ2H2O (1a):[23] obtained from N-benzylimi-
Combinations of four functionals (B3LYP, BP86 and M06L, all
with added empirical (D3) dispersion corrections,[45] and M11L)
with the 6–311þG(d,p) basis set and two pseudopotentials for the
Pd atom (SDD and LANL2DZ) were tested. The functionals were
chosen because of their good performance with regards to
structural and vibrational calculations.[46–50] All calculations
were performed using the Gaussian 09 program package.[51]
nodiacetic acid (0.23 g) after a few hours. nmax (KBr)/cmꢁ1 3585
(s), 3422 (m, br), 2932 (w), 2711 (w), 2602 (w), 2515 (w), 2365
(w), 1942 (w, br), 1718 (s), 1628 (vs), 1494 (w), 1459 (w),
1434 (w), 1418 (w), 1359 (m), 1319 (m), 1288 (w), 1231 (m),
1114 (w), 1084 (w), 1065 (w), 994 (w), 964 (w), 949 (w), 921
(m), 898 (w), 871 (w), 779 (w), 751 (w), 709 (w), 669 (w), 636
(w), 598 (w), 571 (w), 573 (w).
[Pd(BnidaH)2] (1b):[23] obtained by dehydration of 1a in a
desiccator over solid KOH. nmax (KBr)/cmꢁ1 3447 (m, br), 2930
(m), 2744 (m), 2674 (m), 2598 (m), 2534 (m), 1736 (vs), 1613
(vs), 1494 (w), 1456 (w), 1417 (m), 1379 (vs), 1326 (m), 1260
(m), 1216 (s), 1112 (m), 1084 (w), 1050 (w), 1026 (m), 964 (m),
932 (m), 892 (m), 872 (m), 748 (m), 698 (m), 636 (w), 588 (w),
588 (w), 558 (w), 524 (w), 502 (w).
[Pd(p-ClBnidaH)2]ꢀ2H2O (2): obtained from N-(p-chloro-
benzyl)iminodiacetic acid (0.26 g) after a few minutes. nmax
(KBr)/cmꢁ1 3539 (m), 3202 (m, br), 3092 (w), 3037 (w), 2936
(w), 2725 (w, br), 2516 (w, br), 1943 (w, br), 1716 (s), 1634 (vs),
1493 (m), 1457 (w), 1431 (m), 1412 (m), 1356 (s), 1317 (m),
1295 (w), 1228 (s), 1120 (w), 1102 (m), 1066 (w), 1018 (m), 988
(w), 958 (w), 950 (w), 921 (m), 908 (w), 879 (w), 848 (w), 827
(m), 807 (w), 768 (w), 702 (w), 668 (w), 618 (w), 589 (w), 566
(w), 532 (w), 526 (w), 464 (w). Anal. Calc. for
C22H26N2O10Cl2Pd (655.77): C 40.29, H 4.00, N 4.27. Found:
C 40.49, H 4.09, N, 4.20 %.
[Pd(p-NO2BnidaH)2]ꢀ2H2O (3): obtained from N-(p-nitro-
benzyl)iminodiacetic acid hemihydrate (0.28 g) after a few
minutes. nmax (KBr)/cmꢁ1 3528 (s), 3383 (m, br), 3127 (w),
3081 (w), 3054 (w), 2986 (w), 2952 (w), 2860 (w), 2732 (w, br),
2610 (w, br), 2538 (w, br), 1922 (w), 1729 (s), 1628 (vs), 1519
(vs), 1459 (w), 1435 (w), 1417 (w), 1353 (vs), 1318 (s), 1274
(w), 1241 (s), 1113 (w), 1097 (w), 1063 (w), 1017 (w), 995 (w),
953 (w), 923 (w), 885 (w), 854 (m), 838 (w), 772 (w), 746 (w),
701 (w), 668 (w), 654 (w), 590 (w), 517 (w), 453 (w). Anal. Calc.
for C22H26N4O14Pd (676.87): C 39.03, H 3.87, N 8.28. Found:
C 38.77, H 3.78, N 8.15 %.
Supplementary Material
Thermal analysis data for complexes 1a–4, differential scanning
calorimetry curves for the ligands, thermograms and differential
thermal analysis curves for the ligands and complexes, XYZ
files containing energies and geometries of the modelled com-
plexes, and a supplementary figure displaying a comparison
between the structure of 1a optimized with constrains imposed
by crystallographic data and the structure optimized without any
constrains are available on the Journal’s website.
Conflicts of interest
The authors declare no conflicts of interest.
Acknowledgements
This research was supported by the Ministry of Science, Education and
Sports of the Republic of Croatia (Grant No. 119–1193079–1332) and the
Croatian Science Foundation (Grant No. 7444). The authors are grateful to
Dr Marijana Vinkovic´ for the recorded NMR spectra.
References
[1] F. P. Dwyer, D. P. Mellor, Chelating Agents and Metal Chelates 1964
(Academic Press: New York, NY).
[2] E. Mu¨ller, O. Bayer, H. Meerwein, K. Ziegler, Methoden der Orga-
nischen Chemie (Houben-Weyl), Band XI/2 – Stickstoffverbindungen
II und III 1958 (Georg Thieme Verlag: Stuttgart).
[3] C. F. Bell, Principles and Applications of Metal Chelation 1977
(Oxford University Press: Oxford).
[4] I. N. Polyakova, A. L. Poznyak, V. S. Sergienko, Crystallogr. Rep.
2000, 45, 762. doi:10.1134/1.1312916
[Pd(p-MeOBnidaH)2](4): obtained from N-(p-methoxybenzyl)
iminodiacetic acid hemihydrate (0.26 g) after a few hours. nmax
(KBr)/cmꢁ1 3446 (w, br), 3104 (w), 2992 (w), 2925 (w), 2843
(w), 2748 (w), 2677 (w), 2607 (w), 2523 (m), 2029 (w), 1921
(w), 1740 (s), 1611 (vs), 1590 (vs), 1516 (s), 1453 (w), 1414 (m),
1433 (m), 1367 (s), 1334 (w), 1323 (m), 1308 (w), 1284 (w),
1272 (m), 1254 (s), 1217 (s), 1185 (s), 1123 (w), 1101 (m), 1052
(w), 1020 (m), 954 (m), 926 (w), 899 (m), 877 (w), 858 (w), 845
(w), 822 (s), 765 (w), 718 (w), 684 (w), 578 (w), 668 (w),
613 (w), 600 (w), 558 (w), 529 (w), 518 (w), 483 (w), 427 (m).
Anal. Calc. for C24H28N2O10Pd (610.88): C 47.18, H 4.62,
N 4.59. Found: C 46.95, H 4.70, N 4.49 %.
[5] D. K. Patel, D. Choquesillo-Lazarte, J. M. Gonza´lez-Perez,
A. Dom´ınguez-Mart´ın, A. Matilla-Hernandez, A. Castin˜eiras,
J. Niclo´s-Gutie´rrez, Polyhedron 2010, 29, 683. doi:10.1016/J.POLY.
2009.09.034
[6] E. Bugella-Altamirano, D. Choquesillo-Lazarte, J. M. Gonza´lez-
Perez, M. J. Sa´nchez-Moreno, R. Mar´ın-Sa´nchez, J. D. Mart´ın-
Ramos, B. Covelo, R. Carballo, A. Castin˜eiras, J. Niclo´s-Gutie´rrez,
Inorg. Chim. Acta 2002, 339, 160. doi:10.1016/S0020-1693(02)
00920-9
[7] M. J. Sa´nchez-Moreno, D. Choquesillo-Lazarte, J. M. Gonza´lez-Perez,
R. Carballo, A. Castin˜eiras, J. Niclo´s-Gutie´rrez, Inorg. Chem. Commun.
2002, 5, 800. doi:10.1016/S1387-7003(02)00559-2
[8] D. Choquesillo-Lazarte, A. Dom´ınguez-Mart´ın, A. Matilla-
Hernandez, C. S. de Medina-Revilla, J. M. Gonza´lez-Perez,
A. Castin˜eiras, J. Niclo´s-Gutie´rrez, Polyhedron 2010, 29, 170.
doi:10.1016/J.POLY.2009.06.054
Computational Details
The starting geometries for all modelled complexes were taken
from available crystallographic data for 1a.[23] The analyzed
geometries contained a single palladium atom coordinated by
two bidentate ligands and a single water molecule in the case of
hydrates (Fig. 1). Unconstrained optimizations yielded signifi-
cantly different final geometries from the starting geometries,
suggesting important solid-state interactions. In order to
preserve the solid-state structure obtained crystallographically,
we carried out constrained optimizations in which only the
hydrogen atoms and para-substituted groups (which are not
present in 1a) were mobile. Optimizations were followed by
frequency calculations carried out at the same level of theory.
[9] A. Dom´ınguez-Mart´ın, D. Choquesillo-Lazarte, J. M. Gonza´lez-Perez,
A. Castin˜eiras, J. Niclo´s-Gutie´rrez, J. Inorg. Biochem. 2011, 105,
1073. doi:10.1016/J.JINORGBIO.2011.05.009
[10] M. J. Sa´nchez-Moreno, D. Choquesillo-Lazarte, J. M. Gonza´lez-Perez,
R. Carballo, J. D. Mart´ın-Ramos, A. Castin˜eiras, J. Niclo´s-Gutie´rrez,
Polyhedron 2003, 22, 1039. doi:10.1016/S0277-5387(03)00089-5
[11] D. K. Patel, D. Choquesillo-Lazarte, A. Dom´ınguez-Mart´ın, M. P.
Brandi-Blanco, J. M. Gonza´lez-Perez, A. Castin˜eiras, J. Niclo´s-
Gutie´rrez, Inorg. Chem. 2011, 50, 10549. doi:10.1021/IC201918Y
[12] A. Dom´ınguez-Mart´ın, D. Choquesillo-Lazarte, J. A. Dobado, I. Vidal,
L. Lezama, J. M. Gonza´lez-Pe´rez, A. Castin˜eiras, J. Niclo´s-Gutie´rrez,
Dalton Trans. 2013, 42, 6119. doi:10.1039/C2DT32191B

PdII Complexes with N-Benzyliminodiacetic Acids
1291
[13] A. Dom´ınguez-Mart´ın, D. Choquesillo-Lazarte, J. A. Dobado,
H. Mart´ınez-Garc´ıa, L. Lezama, J. M. Gonza´lez-Pe´rez, A. Castin˜eiras,
J. Niclo´s-Gutie´rrez, Inorg. Chem. 2013, 52, 1916. doi:10.1021/
IC302147U
[14] N. Smrecˇki, B.-M. Kukovec, M. Ðakovic´, Z. Popovic´, Inorg. Chim.
Acta 2013, 400, 122. doi:10.1016/J.ICA.2013.02.017
[15] J. Chakraborty, M. K. Saha, P. Banerjee, Inorg. Chem. Commun. 2007,
10, 671. doi:10.1016/J.INOCHE.2007.02.028
[16] J. Chakraborty, H. Mayer-Figge, W. S. Sheldrick, P. Banerjee, Poly-
hedron 2005, 24, 771. doi:10.1016/J.POLY.2004.09.033
[17] I. N. Polyakova, T. N. Polynova, M. A. Porai-Koshits, A. M. Grevtsev,
J. Struct. Chem. 1979, 20, 574. doi:10.1007/BF00746832
[18] A. L. Poznyak, A. B. Ilyukhin, V. S. Sergienko, Russ. J. Inorg. Chem.
1997, 42, 1660.
[19] R.-F. Song, C.-Z. Zhang, F. Li, S.-C. Jin, Z.-S. Jin, Chem. Res. Chin.
Univ. 1992, 8, 399.
[20] I. N. Polyakova, A. L. Poznyak, V. S. Sergienko, Crystallogr. Rep.
[35] E. Mu¨ller, O. Bayer, H. Meerwein, K. Ziegler, Methoden der Orga-
nischen Chemie (Houben-Weyl), Band XI/1 – Stickstoffverbindungen II
1957 (Georg Thieme Verlag).
[36] W. A. Jacobs, M. Heidelberger, J. Biol. Chem. 1915, 20, 659.
[37] R. M. Silverstein, F. X. Webster, D. Kiemle, Spectrometric Identifica-
tion of Organic Compounds, seventh ed. 2005 (Wiley: New York, NY).
[38] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordi-
nation Compounds, Part B, sixth ed. 2009 (Wiley: Hoboken).
[39] G. B. Deacon, R. J. Phillips, Coord. Chem. Rev. 1980, 33, 227.
doi:10.1016/S0010-8545(00)80455-5
[40] G. Pirc, J. Stare, J. Mavri, J. Chem. Phys. 2010, 132, 224506.
doi:10.1063/1.3429251
[41] J. Stare, J. Mavri, J. Grdadolnik, J. Zidar, Z. B. Maksic´, R. Vianello,
J. Phys. Chem. B 2011, 115, 5999. doi:10.1021/JP111175E
[42] M. Brela, J. Stare, G. Pirc, M. Sollner-Dolenc, M. J. Wo´jcik, J. Mavri,
J. Phys. Chem. B 2012, 116, 4510. doi:10.1021/JP2094559
[43] M. Z. Brela, M. J. Wo´jcik, M. Boczar, R. Hashim, Chem. Phys. Lett.
2013, 558, 88. doi:10.1016/J.CPLETT.2012.12.035
2003, 48, 278.
[21] J. Clayden, N. Greeves, S. Warren, P. Wothers, Organic Chemistry
2001 (Oxford University Press: Oxford).
[44] G. Rowley, A. L. Greenleaf, G. I. Kenyon, J. Am. Chem. Soc. 1971, 93,
5542. doi:10.1021/JA00750A038
[22] J. Tsuji, Palladium Reagents and Catalysts 2004 (Wiley: Chichester).
[23] N. Smrecˇki, B.-M. Kukovec, J. Jazwinski, Y. Liu, J. Zhang,
A.-M. Mikecin, Z. Popovic´, J. Organomet. Chem. 2014, 760, 224.
doi:10.1016/J.JORGANCHEM.2013.10.010
[45] S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem. Phys. 2010, 132,
154104. doi:10.1063/1.3382344
[46] C. J. Cramer, D. G. Truhlar, Phys. Chem. Chem. Phys. 2009, 11, 10757.
doi:10.1039/B907148B
[24] M. T. Bilkan, S. Yurdakul, Z. Demirciog˘lu, O. Bu¨yu¨kgu¨ngo¨r,
[47] L. Goerigk, S. Grimme, Phys. Chem. Chem. Phys. 2011, 13, 6670.
doi:10.1039/C0CP02984J
[48] A. V. Soldatova, M. Ibrahim, T. G. Spiro, Inorg. Chem. 2013, 52, 7478.
doi:10.1021/IC400364X
-
J. Organomet. Chem. 2016, 805, 108. doi:10.1016/J.JORGANCHEM.
2016.01.014
[25] N. Mhadhbi, S. Sa¨ıd, S. Elleuch, T. Lis, H. Na¨ıli, J. Mol. Struct. 2016,
1105, 16. doi:10.1016/J.MOLSTRUC.2015.10.025
[26] H. L. Singh, J. B. Singh, S. Bhanuka, J. Coord. Chem. 2016, 69, 343.
doi:10.1080/00958972.2015.1115485
[27] R. M. Clarke, K. Hazin, J. R. Thompson, D. Savard, K. E. Prosser,
T. Storr, Inorg. Chem. 2016, 55, 762. doi:10.1021/ACS.INORG
CHEM.5B02231
[49] T. T. Tavares, D. Paschoal, E. V. S. Motta, A. G. Carpanez, M. T. P.
Lopes, E. S. Fontes, H. F. Dos Santos, H. Silva, R. M. Grazul, A. P. S.
Fontes, J. Coord. Chem. 2014, 67, 956. doi:10.1080/00958972.2014.
900664
[50] T. Weymuth, E. P. A. Couzijn, P. Chen, M. Reiher, J. Chem. Theory
Comput. 2014, 10, 3092. doi:10.1021/CT500248H
[28] M. Mirzaei, H. Eshtiagh-Hosseini, M. Bazargan, F. Mehrzad,
M. Shahbazi, J. T. Mague, A. Bauza´, A. Frontera, Inorg. Chim. Acta
2015, 438, 135. doi:10.1016/J.ICA.2015.08.030
[29] B. Trzaskowski, S. G. Stepanian, A. Les´, P. A. Deymier, R. Guzman,
L. Adamowicz, J. Comput. Theor. Nanosci. 2006, 3, 775. doi:10.1166/
JCTN.2006.016
[51] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A.
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F.
Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr, J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam,
M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich,
[30] S. Khatua, D. R. Roy, M. Bhattacharjee, P. K. Chattaraj, J. Comput.
Methods Sci. Eng. 2007, 7, 395.
[31] B. Trzaskowski, R. Guzman, L. Adamowicz, Polyhedron 2007, 26,
2477. doi:10.1016/J.POLY.2006.12.020
[32] A. Bhaskarapillai, S. Chandra, N. V. Sevilimedu, B. Sellergren,
Biosens. Bioelectron. 2009, 25, 558. doi:10.1016/J.BIOS.2009.03.043
[33] A. R. McDonald, Y. Guo, V. V. Vu, E. L. Bominaar, E. Mu¨nck,
L. Que, Jr, Chem. Sci.) 2012, 3, 1680. doi:10.1039/C2SC01044E
[34] M. S. Bukharov, V. G. Shtyrlin, G. V. Mamin, S. Stapf, C. Mattea, A. S.
Mukhtarov, N. Y. Serov, E. M. Gilyazetdinov, Inorg. Chem. 2015, 54,
9777. doi:10.1021/ACS.INORGCHEM.5B01467
¨
A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
D. J. Fox, Gaussian 09, Revision D.01 2009 (Gaussian, Inc.:
Wallingford, CT).