Synthesis, spectral characterization, crystal structures and catalytic activity of a series of lanthanide(III) azepane dithiocarbamate complexes

Article abstract of DOI:10.1016/j.poly.2013.01.056

A series of lanthanide(III) azepane dithiocarbamate (Aze-Dtc) complexes, [Ln(Aze-Dtc)₃(Phen)] where Ln = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III), Dy(III) and Er(III), have been synthesized under mild reaction conditions wi

Full text of DOI:10.1016/j.poly.2013.01.056

Accepted Manuscript
Synthesis, spectral characterization, crystal structures and catalytic activity of a
series of lanthanide(III) azepane dithiocarbamate complexes
Ponnuchamy Pitchaimani, Kong Mun Lo, Kuppanagounder P.Elango
PII:
S0277-5387(13)00104-6
DOI:
http://dx.doi.org/10.1016/j.poly.2013.01.056
POLY 9919
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
26 October 2012
30 January 2013
Please cite this article as: P. Pitchaimani, K.M. Lo, K. P.Elango, Synthesis, spectral characterization, crystal
structures and catalytic activity of a series of lanthanide(III) azepane dithiocarbamate complexes, Polyhedron(2013),
doi: http://dx.doi.org/10.1016/j.poly.2013.01.056
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1
Synthesis, spectral characterization, crystal structures and catalytic activity
‡
of a series of lanthanide(III) azepane dithiocarbamate complexes
a
b
a
Ponnuchamy Pitchaimani , Kong Mun Lo and Kuppanagounder P.Elango *
a
Department of Chemistry, Gandhigram Rural Institute-Deemed University,
Gandhigram 624 302, India
b
Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur,
Malaysia
‡
Dedicated to Prof. G. Karthikeyan
ABSTRACT
A series of lanthanide(III) azepane dithiocarbamate (Aze-Dtc) complexes, [Ln(Aze-
Dtc) (Phen)] where Ln = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III), Dy(III)
3
and Er(III), have been synthesized under mild reaction conditions with excellent yields. The
new complexes have been structurally characterized by analytical (CHNS) and various
1
spectral techniques, such as FT-IR, UV–Vis, CV and H NMR. The coordination mode of the
ligands and the geometry of [Pr(Aze-Dtc) (Phen)], [Nd(Aze-Dtc) (Phen)], [Sm(Aze-
3
3
Dtc) (Phen)] and [Dy(Aze-Dtc) (Phen)] were confirmed by single crystal X-ray studies. In
3
3
these complexes the central Ln(III) atom possess a distorted dodecahedral geometry with six
sulfur atoms of three Aze-Dtc ligands and two nitrogen atoms of a 1,10-phenanthroline
ligand coordinated to it. The utility of these complexes as catalysts in trimethylsilylcyanation
of carbonyl compounds has also been screened. The results indicate that the catalytic activity
shown by these complexes is good to excellent.
Keywords: Lanthanide, dithiocarbamate, 1,10-phenanthroline, silylcyanation

Corresponding author. Tel.:+91 451 245 2371; fax: +91 451 245 4466.
E-mail address: drkpelango@rediffmail.com (K.P.Elango).

2
1
. Introduction
Over the years, the synthesis of lanthanide complexes with a variety of ligands has
received considerable interest because of their potential applications in various fields [1-10].
Hence, the synthesis and characterization of newer lanthanide complexes is an ever green
field of research in inorganic chemistry. Though Jorgensen et al. [11] reported the first
lanthanide-dithiocarbamate complexes during the 1960s, a literature review indicated that the
study of such complexes is relatively less when compared to that their transition metal
analogues. Recently, there has been a renaissance of interest in these complexes for a variety
of uses [12,13] and hence the present study.
Cyanohydrins are well-known natural products and versatile synthetic intermediates
for pharmaceuticals and agrochemicals, and they are also excellent starting materials for the
preparation of several important classes of organic compounds [14]. A review of the literature
revealed that transition metal complexes have been widely used as catalysts in
trimethylsilylcyanation of carbonyl compounds [15-18]. However, the use of lanthanide
complexes in such reactions is relatively less studied in the literature [19,20].
The main objective, therefore, of this endeavor is to synthesize a series of Ln(III)
complexes of azepane dithiocarbamate (Aze-Dtc), as such ligands possess a wide variety of
applications. The complexes were characterized using several analytical and spectral
techniques and crystal structures of four of the complexes were determined. The usefulness of
these complexes as a catalyst in trimethylsilylcyanation of carbonyl compounds is also
demonstrated.
2
. Experimental
2
.1 Materials and methods
All the chemicals were of commercially available high purity grade (Aldrich) and
were used as received. The ligand Aze-Dtc has been synthesized according to the literature

3
procedure, with a slight modification [21]. Elemental analyses (CHNS) were carried out on
an Elementar Vario EL III at the Sophisticated Test and Instrumentation Centre at Cochin
University of Science and Technology, Kochi. FT-IR spectra were recorded on a JASCO,
-1
Japan (460 plus) FT-IR spectrometer with KBr pellets in the range 4000–400 cm .
Electronic spectra of the complexes were recorded on a JASCO, Japan (V-630) double beam
1
spectrophotometer. H NMR spectra were recorded at Madurai Kamaraj University, Madurai
in a Bruker, Switzerland NMR spectrometer (300 MHz, DMSO-d ). HPLC studies were
6
carried out on Shimadzu CLASS-VP Ver. 6.14 SP2 instrument. Electrochemical
experiments were performed with an electrochemical workstation CHI Instrument (643B,
Austin, USA) under dry nitrogen. Tetrabutylammonium perchlorate (0.1 M) was used as the
supporting electrolyte. A three-electrode configuration was employed with a glassy carbon
working electrode, a platinum wire as a reference electrode and a platinum wire as an
auxiliary electrode. Single crystal X-ray diffraction data for the complexes were collected at
the University of Malaya, Kuala Lumpur, Malaysia on a Bruker APEX-II CCD area-detector
with Mo Ka radiation (k = 0.71073 Å) by the w scan mode. All esds (except the esd in the
dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The
cell esds are taken into account individually in the estimation of esds in distances, angles and
torsion angles; correlations between esds in cell parameters are only used when they are
defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for
estimating esds involving l.s. planes. Crystal structure refinements were carried using
SHELXTL Ver. 6.12 W95/98/NT/2000/ME.
2
.2 Synthesis of the ligand (Aze-Dtc)
The ligand was prepared by adopting the following procedure [21]. Sodium hydroxide
(0.05 mol) was dissolved in 3 mL of water in an ice bath and 50 mL of ethanol was added to
it. The solution was stirred vigorously, during which time azepane (0.05 mol) was added,
then carbon disulfide (0.05 mol) was added slowly drop by drop which yielded the

4
precipitation of the dithiocarbamate sodium salt. The mixture was stirred for a further 30
minutes for the reaction to complete. The yellow product was collected by filtration, re-
dissolved in a minimum amount of methanol and the pure white product was precipitated by
adding the required volume of diethyl ether. Anal. Calc. for C H NS Na: C, 42.61; H, 6.13;
7
12
2
-1
N, 7.10; S, 32.50%. Found: C, 42.50; H, 6.20; N, 7.22; S, 32.60%. FT-IR (KBr, cm ): 3378s,
3
1
178m, 2978m, 2934s, 2851s, 2102b, 1623s, 1483s, 1448s, 1409s, 1365s, 1258s, 1187s,
1
095m, 1047s, 975s, 953s, 904m, 850s, 762m, 538m, 454m. H NMR (Fig. S1) (DMSO-d δ
6
,
-1
ppm): 1.43 (t, J = 3Hz, 4H), 1.67 (m, 4H), 4.14 (t, J = 6Hz, 4H). UV-Vis (Chloroform, cm )
(log ): 38500 (3.92), 35300 (3.95). Yield 85%.
2
.3 Preparation of the lanthanum(III) complexes
The [Ln(Aze-Dtc) (Phen)] complexes {where Ln=La(III), Ce(III), Pr(III), Nd(III),
3
Sm(III), Gd(III), Tb(III), Dy(III) and Er(III)} (1-9) were prepared by mixing methanolic
solutions of LnCl .6H O (0.5 mmol) and a mixture of Aze-Dtc (1.5 mmol) and Phen (0.5
3
2
mmol). In each case, on stirring the mixture at room temperature the complex precipitated as
a fine powder. The complex was filtered and washed with methanol, which yielded the pure
product. The complexes are freely soluble in chloroform, dichloromethane, DMF and DMSO.
The analytical and spectral data of the complexes are given below.
2
.3.1 [La(Aze-Dtc) (Phen)] (1)
3
Anal. Calc. for C H LaN S : C, 47.07; H, 5.27; N, 8.32; S, 22.85%. Found: C, 46.93; H,
3
3
44
5 6
-
1
5
1
.00; N, 8.32; S, 22.60%. FT-IR (KBr, cm ): 2922s, 2851m, 2361m, 1482s, 1450, 1416s,
1
362s, 1264s, 1187s, 1096m, 848s, 723s, 453m. H NMR (Fig. S2) (DMSO-d δ ppm): 1.43
6
,
(s, 12H), 1.68 (s, 12H), 4.06-4.11 (m, 12H), 7.81 (s, 2H), 8.02 (s, 2H), 8.52 (d, J = 9Hz, 2H),
-1
9
2
.16 (s, 2H). UV-Vis (Chloroform, cm ) (log ): 43900 (4.00), 37300 (4.15). Yield 80%.
.3.2 [Ce(Aze-Dtc) (Phen)] (2)
3

5
Anal. Calc. for C H CeN S : C, 47.07; H, 5.26; N, 8.31; S, 22.82%. Found: C,
3
3
44
5 6
-
1
4
1
7.12; H, 5.24; N, 8.31; S, 22.80%. FT-IR (KBr, cm ): 2922s, 2851m, 2360m, 1573s,1482s,
447s, 1411s, 1366s, 1287m, 1262s, 1096m, 1047m, 981s, 888m, 844s, 726s, 621w, 436m.
-1
UV-Vis (Chloroform, cm ) (log ): 44100 (3.91), 37700 (3.84). Yield 92%.
2
.3.3 [Pr(Aze-Dtc) (Phen)] (3)
3
Anal. Calc. for C H PrN S : C, 46.96; H, 5.25; N, 8.30; S, 22.79%. Found: C,
33
44
5 6
-
1
4
1
0
6.96; H, 5.24; N, 8.28; S, 22.80%. FT-IR (KBr, cm ): 2920s, 2850m, 2361m, 1481s, 1449,
1
262s, 1186s, 1094m, 980m, 848s, 766s, 627s, 453m. H NMR (Fig. S3) (DMSO-d δ ppm):
6
,
.34 (s, b, 24H), 2.25 (s, 12H), 7.47 (s, b, 2H), 7.74 (s, b 2H), 8.22 (s, b, 2H), 8.78 (s, b, 2H).
-1
UV-Vis (Chloroform, cm ) (log ): 43900 (4.04), 37200 (4.15). Yield 99%.
2
.3.4 [Nd(Aze-Dtc) (Phen)] (4)
3
Anal. Calc. for C H NdN S : C, 46.77; H, 5.23; N, 8.26; S, 22.70%. Found: C,
33
44
5 6
-
1
4
1
6.70; H, 5.24; N, 8.28; S, 22.68%. FT-IR (KBr, cm ): 2922s, 2851m, 2361m, 2336m 1482s,
1
411, 1264s, 1186s, 1097m, 982m, 852s, 775s, 723s, 628s, 451m. H NMR (Fig. S4)
(
DMSO-d δ ppm): 1.05-1.19 (m, 12H), 1.43 (s, 12H), 3.84 (s, 12H), 7.79 (s, 2H), 8.01 (s,
6,
-1
2
3
2
H), 8.51 (d, J = 9Hz, 2H), 9.11 (s, 2H). UV-Vis (Chloroform, cm ) (log ): 43900 (4.10),
7200 (4.23). Yield 95%.
.3.5 [Sm(Aze-Dtc) (Phen)] (5)
3
Anal. Calc. for C H SmN S : C, 46.44; H, 5.20; N, 8.21; S, 22.54%. Found: C,
3
3
44
5 6
-
1
4
1
1
6.23; H, 5.20; N, 8.20; S, 22.58%. FT-IR (KBr, cm ): 2922s, 2851m, 2361m, 1484s, 1412s,
1
264s, 1186s, 1096m, 982m, 852s, 775s, 630s, 464m. H NMR (Fig. S5) (DMSO-d δ ppm):
6
,
.38 (d, J = 3Hz, 12H), 1.63 (s, 12H), 3.95 (s, 12H), 7.86-7.80 (m, 2H), 8.01 (s, 2H), 8.52 (d,
-1
J = 3Hz, 2H), 9.11 (d, J = 3Hz, 2H). UV-Vis (Chloroform, cm ) (log ): 43900 (4.05),
3
7300 (4.15). Yield 98%.
2
.3.6 [Gd(Aze-Dtc) (Phen)] (6)
3

6
Anal. Calc. for C H GdN S : C, 46.07; H, 5.15; N, 8.14; S, 22.36%. Found: C,
3
3
44
5 6
-
1
4
1
4
2
6.00; H, 5.20; N, 8.16; S, 21.96%. FT-IR (KBr, cm ): 2925s, 2852m, 2360m, 1491s, 1441,
-1
267s, 1191s, 1098m, 983m, 849s, 760s, 632s, 464m. UV-Vis (Chloroform, cm ) (log ):
3900 (3.78), 37200 (3.90). Yield 84%.
.3.7 [Tb(Aze-Dtc) (Phen)] (7)
3
Anal. Calc. for C H TbN S : C, 45.98; H, 5.14; N, 8.12; S, 22.32%. Found: C,
33
44
5 6
-
1
4
1
4
2
5.90; H, 5.00; N, 7.98; S, 22.45%. FT-IR (KBr, cm ): 2921s, 2851m, 2361m, 1483s, 1412,
-1
264s, 1186s, 1095m, 984m, 852s, 776s, 628s, 459m. UV-Vis (Chloroform, cm ) (log ):
4100 (3.78), 37000 (3.80). Yield 85%.
.3.8 [Dy(Aze-Dtc) (Phen)] (8)
3
Anal. Calc. for C H DyN S : C, 45.63; H, 5.45; N, 8.06; S, 22.15%. Found: C,
33
44
5 6
-
1
4
1
4
2
5.96; H, 5.20; N, 8.08; S, 22.20%. FT-IR (KBr, cm ): 2924s, 2851m, 2360m, 1479s, 1441,
-1
266s, 1190s, 1098m, 983m, 849s, 781s, 632s, 455w. UV-Vis (Chloroform, cm ) (log ):
3900 (4.08), 37300 (4.25). Yield 86%.
.3.9 [Er(Aze-Dtc) (Phen)] (9)
3
Anal. Calc. for C H ErN S : C, 45.38; H, 5.42; N, 8.02; S, 22.03%. Found: C,
3
3
44
5 6
-
1
4
1
4
2
5.82; H, 5.20; N, 8.20; S, 22.50%. FT-IR (KBr, cm ): 2924s, 2852m, 2360m, 1478s, 1441s,
-1
267s, 1191s, 1098m, 984m, 850s, 781s, 633s, 455w. UV-Vis (Chloroform, cm ) (log ):
4100 (3.97), 37200 (4.08). Yield 99%.
.4 X-ray crystallography
The single crystals of 3, 4, 5 and 8 were prepared by the solvent diffusion method
using chloroform and diethyl ether as the solvents. X-ray single-crystal diffraction data for
these complexes were collected and the crystallographic data and experimental details for the
structural analyses are summarized in Table 1. The most important bond lengths between the
metal and coordinating ligand atoms and their bond angles are listed in Table 2.

7
3
. Results and discussion
The nine [Ln(Aze-Dtc) (Phen)] complexes were synthesized (Scheme 1) and
3
characterized using conventional analytical and spectroscopic techniques, such as FT-IR,
1
UV-Vis and H NMR. The crystal structures of [Pr(Aze-Dtc) (Phen)], [Nd(Aze-Dtc) (Phen)],
3
3
[
Sm(Aze-Dtc) (Phen)] and [Dy(Aze-Dtc) (Phen)] were determined and discussed. The
3 3
catalytic activity of these complexes in the trimethylsilylcyanation of carbonyl compounds
was also screened.
3
.1 Crystal structures
The crystal structure of complexes 3, 4, 5 and 8 are shown in Figures 1 to 4,
respectively, and the crystallographic data are given in Table 1. Selected bond angles and
bond lengths are collected in Table 2. It is evident from these figures that the geometry of the
crystals is distorted dodecahedral around the eight coordinated metal ion. The distortion in
the coordination sphere of the metal ion from the ideal geometry may be due to the structural
constraints imposed by the bulky Phen ligand framework. There are three dithiocarbamate
ligands coordinated through six sulfur atoms, and the Phen ligand is coordinated through two
nitrogen atoms.
o
The obtained results of the bond angles ( ) of the three dithiocarbamate ligands in
these crystals are interesting (Table 2). The S-Ln-S bond angles for the two dithiocarbamate
ligands which are in an equatorial position to the Phen ligand are relatively higher than that of
the third dithiocarbamate ligand, which is present in the axial position to the Phen ligand. The
opposite bite angles of the three dithiocarbamate ligands also exhibit a similar trend i.e. the S-
C-S angles of the two equatorial ligands are higher than that of the axial ligand.
The following general conclusions were drawn from the foregoing results. All the four
compounds investigated crystallized in a triclinic system with the space group P-1. All the
four lanthanide crystals investigated are comparable with their analogues reported in the

8
literature [22-24]. In these four compounds, the average length (Å) of the C-S bond is 1.720
Å, which is significantly shorter than the CS single bond length (1.81 Å) and higher than the
C=S distance (1.69 Å). The observed intermediate value between the CS and C=S bond
distance indicates partial double bond character in these complexes [25].
3
.2 FT-IR study
Since, the FT-IR spectra of all the complexes are similar, the important details of the
FT-IR spectrum of [Pr(Aze-Dtc) (Phen)] is discussed here, as a representative case. The
3
characteristic absorption of the hydroxyl group is not present in the complex, indicating that
the complex does not contain a water molecule. The FT-IR spectrum of the free
-1
dithiocarbamate ligand exhibits a doublet at 975 and 953 cm , corresponding to the C-S
-1
stretching [26]. In the complex, it appears as a singlet at 982 cm , indicating coordination of
the ligand in a bidentate manner with the metal ion [27]. The peak corresponding to the νC-N
-1
stretching in the free Phen ligand appeared at 1455 cm , and this peak experienced a shift to
-1
1
481 cm in the complex, suggesting the coordination of Phen with Pr(III) through the two
nitrogen atoms.
1
3
.3 H NMR study
The proton NMR spectra of Aze-Dtc and complexes 1, 3, 4 and 5 were recorded in
DMSO-d solvent and are given in figures S1-S5 (Supplementary data). The spectral data are
6
collected in the experimental section. In the Aze-Dtc ligand three peaks appeared at 1.43,
1
.67 and 4.14 ppm, corresponding to the twelve aliphatic protons. In the complexes, the
observed broadening of the peaks may be due to significant electron delocalization between
the metal and the ligands [28].
3
.4 Electronic absorption study
Electronic absorption spectra of the ligands (Aze-Dtc and Phen), complexes 3-5 and
the corresponding hydrated metal salts were recorded (Fig. S6-S8), and representative spectra

9
are given in Figure 5. It is evident from Figure S6 that there are two intense peaks appearing
-1
in the UV region, i.e. at 44052 and 37735 cm , for the Phen ligand and two medium intensity
-1
peaks at 38461 and 35335 cm for the Aze-Dtc ligand. In the complexes they appear around
1
4
3859 and 37313 cm , respectively. The first band, at the longer wave number, was assigned
to the   transition of the aromatic ligand and the second very intense band is the result
of the overlapping of absorption peaks of the Phen and the Aze-Dtc ligands [22,29].
In the electronic spectra of the complexes, a number of very weak and narrow peaks
(Fig. 5), which are characteristic of the Laporte forbidden f-f transitions of the Ln(III) ions,
are observed in the visible region [30]. In the present case, the assignments of the peaks were
made by a comparison with the spectra of the Ln(III) aquo ions in dilute acid solution
[
31,32]. As representative cases, the f-f transitions observed for complexes 3-5 are collected
in Table 3. In the spectrum of the Pr(III) complex (Fig. 5), it is interesting to note that a small
3
1
peak that corresponds to the H  I transition is observable, which is absent in the
4
6
spectrum of the Pr(III) aquo ion. This transition is hypersensitive to the environment about
the Pr(III) ion [22,33-35].
A perusal of the results in Table 3 indicate that the electronic spectra of the Ln(III)
complexes show a general red shift of all the f-f spectral bands in comparison with those of
their corresponding aquo ions [36]. These red shifts are due to the nephelauxetic effect which
is a measure of the covalency of the metal-ligand bonding. The spectroscopic covalent
parameters of the metal-ligand bonds in these complexes were calculated and are also
collected in Table 3. A nephelauxetic ratio () of less than one and positive values of Sinha’s
1
/2
parameter (δ) and the bonding parameter (b ) suggest the occurrence of some covalent
character in the metal-ligand bond [35,37]. This may be due to the fact that the presence of
the easily polarizable sulfur atoms allows one to expect covalent character between the soft
ligand and the hard lanthanide ions [38]. The absorption bands in the visible region for

1
0
3
4
6
Pr(III), Nd(III) and Sm(III) are due to the transition from the ground levels H , I and H
4
9/2
5/2
respectively to the excited J level of the 4f configuration [39].
.5 Electrochemical properties
The solution electrochemical behavior of the ligands and a representative complex,
Pr(Aze-Dtc) (Phen)], in 0.1 M [Bu N][ClO ]/CH Cl solution was investigated. The cyclic
3
[
3
4
4
2
2
-1
voltammogram recorded at a scan rate of 20 mV s , using a three electrode system, is shown
in Figure 6. Glassy carbon (GC) was used as the working electrode and Pt wire as reference
and auxiliary electrodes. The GC electrode was polished with an alumina slurry before each
run. The cyclic voltammogram of the Phen ligand exhibited three oxidation peaks, at -0.327,
0
.332 and 1.109 V, and a reduction peak at -0.942 V. The Aze-Dtc ligand also exhibited three
oxidation peaks, at 0.464, 0.730 and 0.930V, and a reduction peak at -0.98 V. The complex
exhibited two oxidation peaks (0.220 and 1.088 V) and a reduction peak (-1.095 V). Since the
oxidation state of the central trivalent lanthanide ion does not change, the electrochemical
behavior observed in the complex is due to successive removal or addition of electrons from
or to the ligand-based orbitals [40]. The observed results indicate that the oxidation potential
of the Aze-Dtc ligand shows a significant shift in the complex, as compared to the free
ligand. The oxidation potential in the complex is more positive than that in the free ligand,
which suggests that the oxidation of the Aze-Dtc ligand in the complex is relatively difficult.
This may be due to the fact that the ligand gives electrons on forming coordinate bonds which
makes the oxidation difficult.
3
.6 Catalytic activity
The usefulness of these complexes as a catalyst in trimethylsilylcyanation of carbonyl
compounds has been investigated in dicholoromethane and tetrahydrofuran solvents. In a
typical experiment, to a stirred solution of 1 mol % [Ln(Aze-Dtc) (Phen)] in a given solvent,
3
0
1
.5 mL of benzaldehyde was added at room temperature under a nitrogen atmosphere. Then
.1 mL of trimethylsilyl cyanide was added to the reaction mixture, followed by stirring for 6

1
1
h under an inert atmosphere. After completion of the reaction, the reaction mixture was
quenched with water and extracted with n-hexane/ethyl acetate 2:8 (v/v). The organic layer
was dried over sodium sulfate and concentrated. The crude material was purified by column
chromatography by using 3-5% ethyl acetate in pet-ether to give the pure product as a
1
colorless liquid. The product was characterized using its H NMR spectrum (Fig. S9). The
overall reaction is shown in Scheme 2 and the percentage yields obtained are collected in
Table 4.
Brunel and Holmes [41] have reviewed the development of chemically catalyzed
asymmetric cyanohydrin syntheses. Many metal [Ti(IV), V(IV), Sn(II), Mg(II), Al(III), etc. ]
and a few lanthanide [La(III), Yb(III), Sm(III)] salts/complexes were found to catalyze the
cyanation of aldehydes and ketones to give cyanohydrins. They concluded that, in the case of
lanthanide catalyzed reactions, catalysts loading of 10 mol% were routinely used and at the
same time lanthanide derived systems are proving to be a very fruitful area of research.
Recently, Vale et al. [20] have reported the use of lanthanide-dithiocarbamate complexes as
catalysts in such a reaction, giving 65-98% yields of the product. However, the time required
was reported to be 6-11 h. In the present study, the results indicate that the good to excellent
yields obtained, with 1 mol% catalyst in 6 h at RT, are comparable with those reported using
transition metal and lanthanide complexes as catalysts [15-20]. The advantages of the present
complexes are the simple preparation method with relatively good yields, anhydrous nature of
the complexes and free solubility of the complexes in common organic solvents.
Appendix A. Supplementary data
CCDC numbers 845968, 871332, 871336 and 845969 contains the supplementary
crystallographic data for the complexes [Pr(Aze-Dtc) (Phen)] (3), [Nd(Aze-Dtc) (Phen)] (4),
3
3
[
Sm(Aze-Dtc) (Phen)] (5) and [Dy(Aze-Dtc) (Phen)] (8) given as CIF files. Figures S1-S9
3 3
contains the supplementary data for this paper. Crystallographic data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge

1
2
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223
36 033; or e-mail: deposit@ccdc.cam.ac.uk.
3
RFERENCES
[
1] M.D. Regulacio, K.Bussmann, B.Lewis, S.L. Stoll, J. Am. Chem. Soc. 128 (2006)
1173-11179.
1
[
[
2] E. Carbonella, R. Rothchild, Spectrosc. Lett. 27 (1994) 861-878.
3] J.C. Chertona, M. Beaufoura, L. Menguya, B. Merellia, Spectrosc. Lett. 35 (2002) 415-
4
37.
[
4] T. Ito, M. Inoue, K. Akamatsu, E. Kusaka, K. Tanabe, S. Nishimoto, Bioorg. Med.
Chem. Lett. 21 (2011) 3515-3518.
[
[
[
5] L.J. Ming, Med. Res. Rev., 23 (2003) 697-762.
6] J.G. Bünzli, S.V. Eliseeva, J. Rare Earths, 28 (2010) 824-842.
7] L.A.D. Williams, R.C. Howell, R. Young, I.A. Kahwa, Comp. Biochem. Physiol. C:
1
28 (2001) 119-125.
8] K. Hashino, M. Ito, K. Ikawa, C. Hosoya, T. Nishioka, K.Matsumoto, Anal. Biochem.
55 (2006) 278-284.
[
3
[
[
9] K. Kumar, M.F. Tweedle, Pure. Appl. Chem. 65 (1993) 515-520.
10] C.M.G.D. Santos, A.J. Harte, S.J. Quinn, T. Gunnlaugsson, Coord. Chem. Rev. 252
(2008) 2512-2527.
[
[
11] C. K.Jørgensen, Mol. Phys. (1962) 271-277.
12] R.S. Selinsky, J.H. Han, E.A.M. Pe´rez, I.A. Guzei, S. Jin, J. Am. Chem. Soc. 132
(2010) 15997-16005.
[
[
13] J.A. Vale, W.M. Faustino, P.H. Menezes, G.F. De Sa, Chem. Comm. (2006) 3340-3342.
14] J. Brussee, E.C. Roos, A.V.D. Gen, Tetrahedron Letts. 29 (1988) 4485-4488.

1
3
[
15] N.H. Khan, R.I. Kureshy, S.H.R. Abdi, S. Agrawal, R.V. Jasra, Coord. Chem. Rev. 252
2008) 593-623.
(
[
[
16] M. Hayashi, Y. Miyamoto, T. Inoue, N. Oguni, J. Org. Chem. 58 (1993) 1515-1522.
17] J. Yaozhong, X.Hu, W. Wu, L. Mi, Aiqiao, Tetrahydron: Assymmetry 6 (1995) 405-
4
08.
18] Y. Jiang, L. Gong, X. Feng, W. Hu, W. Pan, Z. Li, A. Mi, Tetrahedron, 53 (1997)
4327-14338.
[
1
[
[
19] H. C. Aspinall, N. Greeves, P.M. Smith, Tetrahedron Lett. 40 (1999) 1763-1766.
20] J.A. Vale, W.M. Faustino, P.H. Menezes, G.F. De Sa, F. Gilberto, J. Braz. Chem.
Soc. 17 (2006) 829-831.
[
[
21] K.K. Dakiya, N.K. Kaushik, Thermochimica Acta 141 (1989) 69-75.
22] M.D. Regulacio, M.H. Pablico, J.A. Vasquez, P.N. Myers, S. Gentry, M. Prushan,
S.W.T. Chang, S. L. Stoll, Inorg. Chem. 47 (2008) 1512-1523.
[
[
[
23] I.Raya, I. Baba, B.M. Yamin, Malaysia J. Anal. Sci. 10 (2006) 93-98.
24] I. Baba, I.Raya, , B.M. Yamin, Sains Malaysian 38 (2009) 185-190.
25] B. A. Prakasam, K. Ramalingam, M. Saravanan, G. Bocelli, A. Cantoni, Polyhedron 23
(2004) 77–82.
[
[
26] C. Su, N. Tang, M. Tan, W. Liu, X. Gan, K. Yub, J. Coord. Chem. 36 (1995) 41-48.
27] Z. Hailiang, T. Ning, G. Xinmin, Z. Weiguang, T. Minyu, W. Aili, Polyhedron
1
2(1993) 945-948.
[
[
28] M.D. Regulacio, N. Tomson, S.L. Stoll, Chem. Mater. 17 (2005) 3114-3121.
29] C.Y. Su, M.Y. Tan, Z.F. Zhang, N. Tang, L.P.Cai, Q.J. Xue, Synth. React. Inorg. Met.-
Org. Chem., 29 (1999) 35-51.
[
[
[
30] C.Y. Su, M.Y. Tan, N. Tang, X.M.Gan, W. Liu, J. Coord. Chem., 38 (1996) 207-218.
31] W.T. Carnall, P.R. Fields, K.J. Rajnak, J. Chem. Phys., 49 (1968) 4424–4442.
32] G.H. Dieke, Spectra and Energy Levels of Rare Earth Ions in Crystals, Interscience,

1
4
New York, 1968.
[
[
[
[
33] M. Ciampolini, N. Nardi, J. Chem. Soc., Dalton Trans. (1977) 379-384.
34] C. Su, N. Tang, M. Tan, W. Liu, X. Gan, Polyhedron 15 (1996) 73-77.
35] C. Su, N. Tan, M. Tang, K.Yu, Polyhedron 15 (1996) 233-239
36] S. Tabassurn, F. Arjmand, K.S. Siddiqik, S.A.A.Zaidi, Synth. React. Inorg. Met.-Org.
Chem., 23 (1993) 1425-1433.
[
[
37] C. Su, N. Tang, M. Tan, N. X. Gan, L Cai, Synth. Reac. Inorg. Met. Org. Chem.,
2
7 (1997) 291-300.
38] C. Su, M. Tan, N. Tang, X. Gan, Z. Zhang, Q. Xue, K. Yu, Polyhedron 16 (1997)
643-1650.
1
[
[
39] S. Cotton, Lanthanide and Actinide Chemistry, John Wiley & Sons Ltd., (2006).
40] J. Zhang, P.F. Yan, G.M. Li, B.Q. Liu, P. Chen, J. Organometallic Chem. 695 (2010)
1
493-1498.
[
41] J.M.Brunel, I.P.Holmes, Angew. Chem. Int. Ed. 43 (2004) 2752-2778.
Figure captions
Figure 1: Molecular structure of [Pr(Aze-Dtc) (Phen)]  CHCl3
3
Figure 2: Molecular structure of [Nd(Aze-Dtc) (Phen)]  CHCl3
3
Figure 3: Molecular structure of [Sm(Aze-Dtc) (Phen)]  CHCl3
3
Figure 4: Molecular structure of [Dy(Aze-Dtc) (Phen)]  CHCl3
3
Figure 5. Electronic f-f transitions in the visible region of PrCl .6H O (red) and
3
2
[
Pr(Aze-Dtc) (Phen)] (blue)
3
Figure 6. Cyclic voltammagram of a) Phen (red) b) [Pr(Aze-Dtc) (Phen)] (green)
3
-1
c) Aze-Dtc (blue) in 0.1M [Bu N][ClO ]/CH Cl at a scan rate of 20 mV s
4
4
2
2
Scheme 1. Preparation of the [Ln(Aze-Dtc) (Phen)] complexes
3
Scheme 2. Catalytic activity

1
5
Figure 1.
Figure 2.

1
6
Figure 3.
Figure 4.

1
7
Figure 5.
Figure 6.

1
8
Scheme 1.
N
N
N
N
0
. 5 mmol
Methanol
S
S
LnCl .6H O +
S
S
3
2
+
N
0. 5 mmol
Ln
N
N
Stirred at
S
N
room temp.
S
S
+
-S
5
min.
Na
1. 5 mmol
Ln = La(III),Ce(III), Pr(III), Nd(III), Sm(III),
Gd(III), Tb(III), Dy(III), Er(III)
Scheme 2.
Si
N
O
TMSCN
O
THF/DCM
1
mol % (complex)
stirred at room temp.
6
h

1
9
Table 1. Summary of the crystallographic data for the complexes 3-5 and 8
Complex
3
4
5
8
Empirical Formula C H Cl N S Pr C H Cl N S Nd C H Cl N S Sm C H Cl N S Dy
3
4
45
3
5
6
34 45
966.70
Triclinic
3
5
6
34 45
972.81
Triclinic
3
5
6
34 45
985.00
Triclinic
3
5 6
Formula Weight
Crystals system
Space group
a (Å)
963.37
Triclinic
P-1
P-1
P-1
P-1
10.719(3)
13.007(4)
16.970(5)
67.747(6)
80.692(6)
72.524(6)
2085.6(11)
2
10.5907(10)
12.9441(2)
16.6542(2)
67.6950(10)
86.5540(10)
72.8810(10)
2015.22(4)
2
10.5911(10)
12.9490(10)
16.6522(2)
67.70
10.6929(9)
b (Å)
12.8900(11)
16.8326(15)
67.988(2)
80.353(2)
72.987(2)
2052.4(3)
2
c (Å)

(°)
(°)
(°)

86.5630(10)
72.92

3
Volume (Å )
Z
2016.33(3)
2
Wavelength (Å)
0.71073
1.534
0.71073
0.71073
1.602
0.71073
1.555
Density
1.593
3
(
calc) (Mg/m )
Abs Coefficient
1.692
1.830
1.998
2.351
-1
(
mm )
Crystal size (mm ) 0.12x0.10x0.08 0.24x0.15x0.10
3
0.14x0.10x0.08
2.89-28.44
8301
0.10x0.08x0.06
1.31-25.00
7181
θ range (°)
Reflections
Collected
0.998-25.00
7339
1.32-26.50
8293
Independent
Reflections
Data / Restraints /
Parameters
F(000)
6505
7722
7913
6173
6505/0/442
7722/0/422
7913/0/442
6173/0/442
980
982
986
946
R1/wR2
0.0327/0.0820
0.0217/0.0629
0.0208/0.0557
0.0345/0.0766

2
0
Table 2. Selected bond parameters of complexes 3, 4, 5 and 8
3
4
5
8
Bond lengths (Å)
Pr1-S2
Pr1-S4
2.9121(12)
Nd1-S1
Nd1-S2
Nd1-S3
Nd1-S4
Nd1-S5
Nd1-S6
Nd1-N4
Nd1-N5
2.8876(7)
2.8381(7)
2.8939(7)
2.8882(7)
2.9026(7)
2.8745(7)
2.651(2)
Sm1-S1
Sm1-S2
Sm1-S3
Sm1-S4
Sm1-S5
Sm1-S6
Sm1-N4
Sm1-N5
2.8935(6) Dy1-S26
2.8879(6) Dy1-S18
2.9034(6) Dy1-S38
2.8745(6) Dy1-S36
2.8392(6) Dy1-S35
2.8863(6) Dy1-S16
2.6512(19) Dy1-N13
2.6299(19) Dy1-N2
2.8415(12)
2.8381(12)
2.8228(12)
2.8164(13)
2.7594(12)
2.7901(12)
2.594(3)
2.8522(13)
2.9062(12)
2.9030(13)
2.9204(13)
2.8858(12)
2.649(3)
Pr1-S12
Pr1-S14
Pr1-S22
Pr1-S24
Pr1-N32
Pr1-N43
2.681(3)
2.626(2)
2.545(3)
o
Bond angles ( )
S2-Pr1-S4
61.68(3)
S1-Nd1-S2 62.250(19) S1-Sm1-S2 61.657(16) S16-Dy1-S18 63.27(3)
S3-Nd1-S4 61.648(19) S3-Sm1-S4 61.963(16) S26-Dy1-S35 63.40(3)
S5-Nd1-S6 61.965(19) S5-Sm1-S6 62.251(16) S36-Dy1-S38 62.65(4)
S12-Pr1-S14 61.03(3)
S22-Pr1-S24 61.40(4)
N32-Pr1-N43 62.21(9)
N4-Nd1-N5 63.04(7)
N4-Sm1-N5 63.15(6)
N2-Dy1-N13 64.68(11)
Averages
Bond lengths (Å)
Pr-S
Pr-N
C-S
2.8966(12)
2.665(3)
1.7208(4)
Nd-S
Nd-N
C-S
2.8808(7)
2.6385(2)
1.7267(3)
Sm-S
Sm-N
C-S
2.8808(6) Dy-S
2.6405(19) Dy-N
1.7265(2) C-S
2.8114(12)
2.5695(3)
1.720(4)
o
Bond angles ( )
S-Pr-S
S-C-S
61.37(3)
118.3667(14) S-C-S
S-Nd-S
61.9543(19) S-Sm-S
118.373(14) S-C-S
61.957(16) S-Dy-S
118.37(15) S-C-S
63.1067(3)
117.6333(3)

2
1
Table 3. Electronic absorption spectral data and related bonding parameters
Ln(III)
Complex
Red shift Covalent
Complexes
aqua ion
log ε
-1
-1
(
cm )
(cm ) parameter
-
1
(
cm )
[
Pr(Aze-Dtc) (Phen)]
22500
21900
21100
20800
20100
16500
2.67
400
-
 = 0.971
% = 2.99
3
-
1400
0800
7000
2.52
2.53
2.48
2.32
1
/2
2
2
1
400 b = 0.121
700
500
[
Nd(Aze-Dtc) (Phen)]
 = 0.967
3
2
2
1
1
1
1
1
1
1600
0000
9900
7900
6200
4900
3700
2700
21000
19200
18800
16900
15900
14600
13300
12300
2.20
600
2
2
2
2
1
2
2
.16
.18
.31
.91
.85
.25
.34
% = 3.46
800
1
/2
b = 0.127
1100
1000
300
300
400
400
[
Sm(Aze-Dtc) (Phen)]
2.26
 = 0.984
% = 1.68
3
2
2
5000
4100
24000
23400
1000
700
1
1
.90
.43
1
/2
b = 0.095
2
2
1600
0900
21400
20800
200
100
1.36

2
2
Table 4. Percentage yields of the products obtained in the trimethylsilylcyanation
reaction
DCM
THF
Compound
Yield % Yield %
[
[
[
[
[
[
[
[
[
La(Aze-Dtc) (Phen)]
85
77
63
81
66
52
75
67
90
80
68
92
86
50
58
73
85
95
3
Ce(Aze-Dtc) (Phen)]
3
Pr(Aze-Dtc) (Phen)]
3
Nd(Aze-Dtc) (Phen)]
3
Sm(Aze-Dtc) (Phen)]
3
Gd(Aze-Dtc) (Phen)]
3
Tb(Aze-Dtc) (Phen)]
3
Dy(Aze-Dtc) (Phen)]
3
Er(Aze-Dtc) (Phen)]
3
The consumption of benzaldehyde was observed by TLC.
Yields refer to the isolated products.

Synthesis, spectral characterization, crystal structures and catalytic activity of a
series of lanthanide(III) azepane dithiocarbamate complexes
Ponnuchamy Pitchaimani, Kong Mun Lo and Kuppanagounder P.Elango*
[
Pr(Aze-Dtc) (Phen)]
3

Synthesis, spectral characterization, crystal structures and catalytic activity of a
series of lanthanide(III) azepane dithiocarbamate complexes
Ponnuchamy Pitchaimani, Kong Mun Lo and Kuppanagounder P.Elango*
A series of lanthanide(III) azepane dithiocarbamate complexes have been synthesized and
characterized by single crystal X-ray studies, and their catalytic activities in the
trimethylsilylcyanation of carbonyl compounds has been screened.