ORIGINAL PAPER

Synthesis and Structural Characterizationof Dibromidobis(N,N0-dimethylthiourea-jS)cadmium(II)and Diiodidobis(N,N0-dimethylthiourea-jS)cadmium(II)

Saeed Ahmad • Muhammad Altaf • Helen Stoeckli-Evans •

Anvarhusein A. Isab • Muhammam Riaz Malik •

Saqib Ali • Shaukat Shuja

Received: 9 August 2010 / Accepted: 7 March 2011 / Published online: 22 March 2011

� Springer Science+Business Media, LLC 2011

Abstract Cadmium(II) complexes, dibromidobis(N,

N0-dimethylthiourea-S)cadmium(II), [Cd(Dmtu)2Br2] (1)

and diiodidobis(N,N0-dimethylthiourea-S)cadmium(II), [Cd

(Dmtu)2I2] (2), have been prepared and their structures have

been determined by X-ray crystal structure analysis. Com-

pound 1 crystallized in the monoclinic space group C2/c,

and the metal ion is situated on a twofold rotation axis.

Compound 2 also crystallized in a monoclinic space group,

P21/c, but here the molecules have no crystallographic

symmetry. In both compounds the cadmium atom is bonded

to two halide ions and to two dimethylthiourea molecules

through the sulfur atoms in a tetrahedral environment. The

molecules are linked via N–H_Halide hydrogen bonds to

form infinite one-dimensional chains in 1 and infinite two

dimensional networks in 2. The complexes were also

characterized by IR and NMR spectroscopy and the data are

consistent with the structures of the compounds.

Keywords Cadmium bromide � Cadmium iodide �N,N0-Dimethylthiourea � Crystal structures

Introduction

The reaction of zinc(II) and cadmium(II) salts with sulfur

containing ligands often results in the formation of com-

plexes with various nuclearities. Such interactions are of

interest in relation to how the resulting compounds interact

in the active sites of metallothioneins and metalloenzymes

[1–10]. The chemistry of metal complexes of sulfur donor

ligands in general is also of interest in relation to the syn-

thesis of detoxifying agents [10–12]. The crystal structures

of several cadmium(II) complexes of thioamides have been

reported, and it was shown that such complexes possess a

variety of structures ranging from four- to six-coordinate

species with tetrahedral and octahedral geometry, respec-

tively [13–27]. The spectroscopic and structural character-

ization of d10 metal complexes with thiones has been

attempted in order to assess their modes of binding and to

study their physical properties [25–36]. In this regard, we

have recently reported the crystal structures of the cad-

mium(II) complexes of N,N0-dimethylthiourea (Dmtu),

[Cd(Dmtu)2Cl2] [37], and of tetramethylthiourea (Tmtu)

[Cd(Tmtu)2X2] (X = Br, I) [38]. The present report

describes the spectroscopic data and the crystal structures of

two new cadmium(II) complexes of N,N0-dimethylthiourea

(Dmtu), [Cd(Dmtu)2Br2] (1) and [Cd(Dmtu)2I2] (2).

Experimental

Materials

Cadmium bromide (CdBr2�4H2O) and Cadmium iodide

(CdI2) were obtained from Merck Chemical Company,

Germany and N,N0-dimethylthiourea (Dmtu) was pur-

chased from Acros Organics, Belgium.

S. Ahmad (&)

Department of Chemistry, University of Engineering

and Technology, Lahore 54890, Pakistan

e-mail: saeed_a786@hotmail.com

M. Altaf � H. Stoeckli-Evans

Institute of Physics, University of Neuchatel, rue Emile-Argand

11, CH-2009 Neuchatel, Switzerland

A. A. Isab

Department of Chemistry, King Fahd University of Petroleum

and Minerals, Dhahran 31261, Saudi Arabia

M. R. Malik � S. Ali � S. Shuja

Department of Chemistry, Quaid-i-Azam University,

Islamabad, Pakistan

123

J Chem Crystallogr (2011) 41:1099–1104

DOI 10.1007/s10870-011-0052-4

Synthesis of [Cd(Dmtu)2Br2] (1) and [Cd(Dmtu)2I2] (2)

The complexes were prepared by adding 2 mM metha-

nolic solution (15 mL) of Dmtu to an aqueous solution

(5 mL) of cadmium bromide (1.0 mmol, 0.35 g) or Cad-

mium iodide (1.0 mmol, 0.37 g) and stirring the mixture

for 30 min. For the bromido complex, white precipitates

were formed on mixing, while for the iodido complex, a

clear solution was obtained. The colorless solutions were

filtered and the filtrates were kept at room temperature for

crystallization. As a result, white crystalline products were

obtained, that were washed with methanol and dried. The

elemental analyses and melting points of the complexes

are given in Table 1.

IR and NMR Measurements

The IR spectra of the complexes were recorded on Perkin–

Elmer FTIR 180 spectrophotometer using KBr pellets over

the range 4000–400 cm-1. The 1H NMR spectra of the

complexes in DMSO-d6 were obtained on Jeol JNM-LA 500

NMR spectrometer operating at a frequency of 500.00 MHz

at 297 K using 0.10 M solution. The 13C NMR spectra were

obtained at the frequency of 125.65 MHz with 1H broadband

Table 1 Elemental analysis and melting points of cadmium(II) complexes

Complexes Found (calculated) (%) Yield (%) mp (�C)

C H N S

[Cd(Dmtu)2Br2] 14.40 (15.00) 3.48 (3.33) 11.32 (11.66) 11.90 (13.35) 40 186–188

[Cd(Dmtu)2I2] 13.10 (12.54) 2.47 (2.79) 9.63 (9.75) 10.50 (11.16) 70 108–110

Table 2 Crystal data and refinement details for compounds 1 and 2

Formula C6H16S2N4CdBr2 C6H16S2N4CdI2

Formula weight 480.57 574.55

Crystal system Monoclinic Monoclinic

Space group C2/c P21/c

a (A) 13.7233(15) 14.197(2)

b (A) 8.9737(7) 8.1443(8)

c (A) 13.0000(14) 14.74482)

b (�) 108.562(7) 109.566(10)

V (A3) 1517.7(3) 1606.484)

Z 4 4

qcalc (g cm-3) 2.103 2.376

l(Mo Ka) (mm-1) 0.6958 5.444

F(000) 920 1064

Crystal size (mm) 0.45 9 0.23 9 0.20 0.45 9 0.29 9 0.03

Temperature (K) 173(2) 173(2)

kMo Ka (A) 0.71073 0.71073

2h range (�) 2.76–29.49 2.82–25.61

h, k, l limits -17:18, -11:12, -13:22 -17:17, -9:9, -16.16

Reflections; collected/Uniq. 6294/2059 (Rint = 0.053) 8759/1870 (Rint = 0.173)

Reflections: observed [I [ 2r(I)] 1549 1507

Tmin, Tmax 0.3908, 0.7775 0.4236, 2.7648

Nref, Npar 2059, 80 1870, 140

R1a, wR2

b, S [I [ 2r(I)] 0.0308, 0.0591, 0.904 0.0895, 0.2827, 1.162

Largest diff. peak, hole (e A-3) 0.548, -0.813 1.792, -2.088

w = [r2(Fo2) ? (0.0242P)2 ? 1.6454P]-1 where P = (Fo

2 ? 2Fc2)/3; for 1 a = 0.0242, b = 1.6454; for 2 a = 0.1617, b = 45.0978

a R1 =P

||Fo| - |Fc||/P

|Fo|b wR2 = {

P[w(Fo

2 - Fc2)2]/

P[w(Fo

2)2]}1/2

1100 J Chem Crystallogr (2011) 41:1099–1104

123

decoupling at 298 K. The 13C chemical shifts were measured

relative to TMS.

X-Ray Structure Determination

Single crystal data collection for complexes 1 and 2 were

performed at 173 K on a Stoe Mark I-Image Plate Dif-

fraction System [39] equipped with a one-circle goniome-

ter and using Mo Ka graphite monochromated radiation.

Diffraction data were collected image plate distance

70 mm, / rotation scans 0–165�, step Dx = 1.0�, expo-

sures of 2 min per image, 2h range 4.10–52.00� and

dmin - dmax = 17.779–0.716 A. The structures were

solved by Direct methods using the program SHELXS-97

[40]. The refinement and all further calculations were

carried out using SHELXL-97 [40]. The NH H-atoms were

located in a difference electron-density map and freely

refined. The C-bound H-atoms were included in calculated

positions and treated as riding atoms: C–H = 0.98–0.99 A

and Uiso(H) = 1.2Ueq(parent N or C-atom). The non-H

atoms were refined anisotropically, using weighted full-

matrix least-squares on F2. A semi-empirical absorption

correction was applied using the MULscanABS routine in

PLATON [41].

Crystals of compound 2 proved to be twins, with the

twin components related by a 180� rotation about the

a-axis. Twin integration, using the program X-Area [39],

indicated that ca. 40% of the reflections were overlapped.

Using the hklf5 reflection file did not give a satisfactory

result, with a large number of electron density peaks which

made no chemical sense. In the final cycles of least-squares

refinement the reflection (hkl) file used consisted of

reflections related to the lager twin component. Even so

there were a small number of electron density peaks which

make no real chemical sense in the final difference elec-

tron-density map. Crystal data and refinement details are

summarized in Table 2.

Results and Discussion

IR and NMR Studies

The reactions of CdX2 (X = Br, I) with Dmtu in a 1:2

molar ratio resulted in products of empirical composition

[Cd(Dmtu)2X2]. In the IR spectra of complexes, the char-

acteristic bands observed were; m(C=S) at 660 and

650 cm-1, and m(N–H) at 3292 and 3300 cm-1 for (1) and

(2) respectively. For free Dmtu these bands were observed

at 672 and 3281 cm-1 respectively. A low frequency shift

in the m(C=S) band and a high frequency shift in m(N–H)

indicate the existence of thione form of Dmtu in the solid

state.

In the 1H NMR spectra of complexes, a downfield shift

in the N–H resonances was observed compared to

uncomplexed Dmtu. This downfield shift in N–H reso-

nance is related to an increase in p electron density in the

C–N bond upon coordination. In 13C NMR, the [C=S

resonance of Dmtu in the complexes is shifted upfield by

about 3 ppm as compared to the free ligand’s resonance in

accordance with the data observed for other complexes of

cadmium(II) [23–25, 35, 36]. The 1H and 13C NMR

chemical shifts are given in Table 3.

X-Ray Structure of [Cd(Dmtu)2Br2] (1)

and [Cd(Dmtu)2I2] (2)

The molecular structure of compound 1, along with the

numbering scheme, is shown in Fig. 1. Selected bond

distances and bond angles are given in Table 4. In the

crystal structure of 1 the cadmium(II) atom is located on a

twofold symmetry axis. The metal is coordinated to two

Dmtu molecules and two bromide ions in an almost regular

tetrahedral geometry. The bond angles are in the range of

107.73(3)–110.85(2)�. The Dmtu ligand behaves as

S-donor and binds in a terminal mode although the bridg-

ing mode has also been observed in some other Cd-thiourea

systems, for example, in [Cd(Metu)2Cl2]n (Metu =

N-methylthiourea) [16]. The bond distances and angles are

Table 3 1H and 13C chemical shifts (d) in ppm of Dmtu and its CdX2

complexes in DMSO

Species N–H C=S N–C

Dmtu 7.38 182.7 30.7

[Cd(Dmtu)2Cl2]a 7.75 178.5 30.6, 31.8

[Cd(Dmtu)2Br2] 7.60 179.8 30.9b

[Cd(Dmtu)2I2] 7.63 180.6 31.3b

a From Ref. [37]b Broad

Fig. 1 Molecular structure of [Cd(Dmtu)2Br2] (1), with displacement

ellipsoids drawn at the 50% probability level [The intramolecular

N–H_Br hydrogen bonds are shown as dashed lines; symmetry code:

(i) = -x, y, -z ? 1/2]

J Chem Crystallogr (2011) 41:1099–1104 1101

123

in the expected range for cadmium complexes containing

this type of ligand [13–26]. The S=CN2 moiety is essen-

tially planar consistent with the sp2 character of the carbon

atoms. The shorter N–C(S) bond lengths compared to

N–CH3 correspond to a bond order intermediate between

single and double bond. The Dmtu ligand adopts a con-

figuration in which one methyl group is cis to the sulfur

atom whereas the other methyl group is trans. The crystal

structure shows both intra and intermolecular hydrogen

bonding interactions (Table 5). In the molecule intramo-

lecular NH_Br hydrogen bonding interactions are present.

They involve each of the two NH groups and the bromide

ions (Fig. 1). In the crystal the molecules are linked by

intermolecular N–H_Br hydrogen bonds leading to

the formation of one-dimensional chains (see Table 5;

Figs. 2, 3).

The molecular structure of compound 2 is shown in

Fig. 4. Selected bond distances and bond angles are given

in Table 4. Here the cadmium(II) atom lies on a general

position and has a slightly more distorted tetrahedral

geometry than in compound 1. It is coordinated to two

Dmtu molecules through the sulfur atom in a monodentate

terminal mode and to two iodide ions. The bond angles

involving the metal atom range from 105.1(3)� to

113.7(2)�. There is an intramolecular N–H_I hydrogen

bond in the molecule, while in the crystal there are N–H_I

intermolecular hydrogen bonds that lead to the forma-

tion of two-dimensional networks lying parallel to plane

(1,0,-2). The details of hydrogen bonding are given in

Table 5 and Fig. 5.

Compound 1 is isostructural with the cadmium(II)

chloride and the zinc(II) chloride complexes of N,N0-dim-

ethylthiourea (Dmtu), i.e. [Cd(Dmtu)2Cl2] [37] and

[Zn(Dmtu)2Cl2] [42]. All three compounds crystallize in

the monoclinic space group C2/c and each molecule pos-

sesses twofold rotation symmetry. In [Cd(Dmtu)2Cl2] and

compound 1 the geometry of the cadmium atom is almost

perfectly tetrahedral, with the bond angles involving the

metal atoms varying from 108.18(3)� to 110.45(2)� in

Table 4 Selected bond distances (A) and bond angles (�) for (1) and

(2)

Bond distance Bond angles

(1)

Cd(1)–Br(1) 2.5974(6) S(1)–Cd(1)–Br(1) 110.85(2)

S(1)–Cd(1)–Br(1i) 107.73(3)

Cd(1)–S(1) 2.5309(10) S(1)–Cd(1)–S(1i) 109.39(3)

Br(1)–Cd(1)–Br(1i) 110.29(2)

C(1)–S(1) 1.738(4) Cd(1)–S(1)–C(1) 106.36(13)

C(1)–N(1) 1.327(5) N(1)–C(1)–S(1) 120.0(3)

C(2)–N(1) 1.452(5) N(1)–C(1)–N(2) 118.5(3)

(2)

Cd(1)–I(1) 2.745(2) S(1)–Cd(1)–I(1) 113.67(18)

Cd(1)–I(2) 2.809(3) S(1)–Cd(1)–I(2) 107.13(17)

Cd(1)–S(1) 2.533(7) S(2)–Cd(1)–I(1) 105.1(3)

Cd(1)–S(2) 2.560(7) S(2)–Cd(1)–I(2) 105.2(2)

C(1)–S(1) 1.74(3) S(1)–Cd(1)–S(2) 108.1(3)

C(4)–S(2) 1.73(3) I(1)–Cd(1)–I(2) 117.02(8)

C(1)–N(1) 1.31(3) Cd(1)–S(1)–C(1) 110.4(9)

C(2)–N(1) 1.46(3) Cd(1)–S(2)–C(4) 99.5(8)

C(1)–N(2) 1.38(3) N(1)–C(1)–S(1) 121(2)

C(3)–N(2) 1.45(4) N(4)–C(4)–S(2) 119(2)

C(4)–N(4) 1.38(3) N(1)–C(1)–N(2) 118(2)

C(4)–N(6) 1.45(4) N(3)–C(4)–N(4) 120(2)

Symmetry code: (i) = -x, y, -z ? 1/2

Table 5 Geometry of hydrogen bonding sites; distances (A) and

angles (�) for (1) and (2)

Donor–H_Acceptor D–H H_A D_A D–H_A

1

N(1)–H(1)_Br(1)ii 0.93(5) 2.55(5) 3.403(3) 153(4)

N(2)–H(2)_Br(1) 0.82(4) 2.63(4) 3.384(4) 152(3)

2

N(1)–H(1)_I(2)iii 0.88 2.95 3.76(2) 155

N(2)–H(2)_I(1) 0.88 2.68 3.55(2) 169

N(3)–H(3)_I(2)iv 0.88 2.92 3.72(2) 152

Symmetry codes: (ii) x - 1/2, -y ? 3/2, z - 1/2; (iii) -x, -y ? 1,

-z; (iv) -x ? 1, y ? 1/2, -z ? 1/2

Fig. 2 A view along the b-axis of the crystal packing in complex (1),

showing the intra and intermolecular N–H_Br hydrogen bonds

(dashed cyan lines) which lead to the formation of one-dimensional

chains [The C-bound H-atoms have been omitted for clarity]

1102 J Chem Crystallogr (2011) 41:1099–1104

123

[Cd(Dmtu)2Cl2], and 107.7(3)–110.85(2)� in compound 1.

However, in [Zn(Dmtu)2Cl2] [42] the bond angles involv-

ing the metal atom vary from 104.35(2)� to 113.30(2)�,

close to the values observed for compound 2, i.e. 105.1(3)–

113.7(2)�. As expected, the Cd–halide bond length

increases in going from the chlorido to iodido complex

(2.4682(7) A for Cd–Cl [37], 2.5974(6) A for Cd–Br in (1)

and 2.745(2)–2.809(3) A for Cd–I in (2)). In the crystals of

[Cd(Dmtu)2Cl2] [37], [Zn(Dmtu)2Cl2] and compound 1,

the same N–H_halide hydrogen bonds are present and

result in the formation of infinite one-dimensional chains

(cf. Figs. 2, 3).

The present report shows, and confirms a previous report

[37], that the interaction of N,N0-dimethylthiourea (Dmtu)

Fig. 3 A view along the one-

dimensional hydrogen bonded

chains in the crystal structure of

complex 1 [The N–H_Br

hydrogen bonds are shown as

dashed lines; the C-bound

H-atoms have been omitted

for clarity]

Fig. 4 Molecular structure of [Cd(Dmtu)I2] (2), with displacement

ellipsoids drawn at the 50% probability level [The intramolecular

N–H_I hydrogen bond is shown as a dashed line]

Fig. 5 A view along the c-axis

of the crystal packing in

complex (2), showing the intra

and intermolecular N–H_I

hydrogen bonds (dashed lines),

which lead to the formation of

two-dimensional networks lying

parallel to plane (1,0,-2) [The

C-bound H-atoms have been

omitted for clarity]

J Chem Crystallogr (2011) 41:1099–1104 1103

123

with cadmium halides results in the formation of com-

plexes with tetrahedral geometry, in which Dmtu coordi-

nates through the sulfur atom in a monodentate terminal

mode.

Supplementary Data

Crystallographic data for the structures reported in this

paper have been deposited with the Cambridge Crystallo-

graphic Center under CCDC No. 731813(1) and 779866

(2). Copies of the data can be obtained free of charge on

application to CCDS, 12 Union Road, Cambridge CB2

1EZ, UK [Fax: (internat.) ?44-1223/336-033; E-mail:

deposit@ccdc.cam.ac.uk].

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