Indian Journal of Chem ist ry
Vol. 43A. April 2004. pp. 790-792
Synthesis, characterization and
electrochemistry of [Ru(L)(2,2' -bpy )CI 2]:
(L= 4 aryl substituted thiosemicarbazide;
bpy = bipyridine)
Milan Maji*, Pm'ba li Sengupta", & Rupam Dinda"
Depa rtmen t of Chemistry, Reg ional Engineering Co ll ege.
Durgapur 7 13209, Indi a
"Department of Inorganic Chemi stry. Indian Assoc iation for the
Cultivation of Science. Jadavpur, Ca lcu tta 700 032, India
E-mai l: [email protected]
Received 11 Feb nwrv 2003; rel'il'l' t/ 3 1 Decelllber 2003
A seri es of ruth en iul11 (II ) complexc s of general formula
Ru(L)(bipy)C I 2 w ith different thi osemicarbazides (L) which
ligated to th e metal ion in the tlli one form have been synthesized
by reacting Ru(bipy)C I. with the corresponding ligands in
methanol. One bipyridine molecule and two chlori de li gand s
complete th e hexacoordination . The compounds Ilave been
characteri sed by element:!1
analysis, magneti c moment
measurement and by di fferent spec troscopic methods. Th e redox
behaviour of the compou nds has been ex plored by cyc lic
vo ltammctry.
IPC Code: InLCl
7
COIG 55/00
A senes of mi xed liga nd complexes having
Ru(bpY )22+ core co mpli men ted wi th a single
thiosemicarbazide moiety have been reported I. I n this
work we report the sy nthes is and charac terization of
the compounds with the Ru(bpy)2+ core.
x = H (I )
CH3(2)
CI (3)
Br(4 )
OCH 3(5)
Experimental
Com mercia l Ru Ci].xH 20 was obtained fro m A rora
Matthey (Ind ia); Ru (b py)C I4 was prepared by the
publi shed procedure 2. T he li gands 4-phe nylth iosemicarbazide [4-PhTSC], 4-(p- me thylpheny l)thi osem i-
carbazide [4-(P-CH])PhTSC] , 4-(p-methoxyphe nyl )thiosemicarbazide,[4-(p-OCH3)PhTSC],
4-(pchloridephenyl)thiosemicarbazide [4-(p-CI)TSC] and
4-(p-bromophenyl) thiosemicarbazide 4-(P- Br)TSC]
were prepared from the cOlTesponding amines by
sl ight modification of the standard procedure]. All
others reagen ts were obtained from commercia l
sources and were used without pu rification . Solvents
were dried before use.
Elemental analyses were performed on a PerkinElmer 240 CHNS/O analy s..:-r. SolLti o n condu ctance
was measured on a Systronics Direct Readin g
Conducti vi ty Meter (model 304), and room
temperature magnetic mom ents wi th a PAR vibrating
sample magnetometer usi ng Hg [Co(SCN )~] as
calibrant. IR and electronic spectra were recorded on
a Perkin-Elmer 783 spectrophotometer (as KBr Pellet)
and a Shimadzu UV-VIS recording spectrophotometer
respectively. Cyclic voltammetric experiments were
carried out on a Bio-Analytical System (BAS ) 27
electrochemical analyser and a BAS Model X- Y
recorder using a glassy carbon working electrode,
platin um auxiliary electrode and Ag/AgCl reference
electrode.
The appropriate thiosemicarbazide (0.5 mmol ) was
added to the suspension of Ru(bpy)C I4 ( 0.2 g, 0.5
m mol) in metha nol (60 mL) and the mixture was
refl uxed for 7 h. It was then filtered a nd the resid ue
was rejected . Vo lume of the fil trate (P H-5) was then
reduced to 20 mL in a rota-evaporato r, excess of ether
was added and it was kept overn ight in a refrigerator.
A dark red soli d separated o ut, which was fil te red
was hed w ith ether. T he compou nd was fin all y
recrystalli sed fro m meth ano l-ether and dri ed over
anhydrous calci um chl ori de. Y ield 55 %.
Results and discussion
In our prev ious work 3 sy nthes is, characterization
and electroche mical studies of Rum ) compl ex having
two bi pyridi ne li gand s a nd one thiosem icarbazide
liga nd was carried out and the starting material was
Ru(bpyhCh. Here Ru (bpY)2Ci4 was c hosen to prepare
Ru (lJ ) comp lex hav in g o ne b ipyridi ne li gands with
co-ligands.
As
two
thiosemicarbazide
thi osemicarbaz ide li gand has reduci ng c haracter as
well as it can stab ili ze Ru (JI) ox idatio n state 4 -6 , it was
expected th at Ru (lV) starting complex woul d not be a
NOTES
problem and because of the presence of four ch loride
ligands in the starting complex we expected that the
four chloride ligands would be substituted by two
thiosemicarbazide li gands. But in practice Ru(II)
complex having one bipyridine ligand and one
thiosemicarbazide ligand i.e., on ly two chloride
ligands
have
been
substituted
by
one
thiosemicarbazide ligand. The ruthenium (II)
comp lexes reported in this study were prepared from
by
reacting
it
with
different
[Ru(bpy)CI 4 ]
thiosemicarbazides in methanol at pH-5. These
compounds are characterised
by
satisfactory
elemental analysis (Table I), room temperature
magnetic
moment,
solution
conductance
measurements Cfable I), IR spectra, UV -vis spectra
and by cycl ic vol tammetry. Magnetic suscepti bi Iity
measurement shows that the compounds are
diamagnetic which indicates th at the formal oxidation
state of ruthenium in the compounds is +2. Though
we have used [Ru(bpy)CI 4 ] as starting materials we
have got Ru(ll) compound as products because of the
reducing character of ihe thiosemicarbazide ligands.
The compounds have the same general formula
Ru(bpy)(L)CI 2 .CH 30H (Structure I) and same
compounds were obtained irrespective of the
791
metal:ligand rati o I.e., 1:1 , 1:2 or eve n 1: 3. These
compounds were characterized by sati sfactory
elemental analy sis (T able 1), room temperature
conductance
magnetic
moment,
solution
measurements (Table I) , IR spectra UV -vis spectra
and by cyclic volammetry. Magnetic susceptibi lity
measurement shows that the compound s are
diamagnetic which indicates that the formal oxidati on
state of ruthenium in the compounds is +2. Th ough
[Ru(bpy)CI 4] was used as starting materials, Ru (l l)
compound was obtained as products becau se of the
reducing character of the thiosemicarbaz ide li gand s.
The compounds are partly soluble in CH 3CN and
CH 2 Ch but completely soluble in DMF. All the
complexes behave as non-electrolyte in DMF whi ch
suggests that the two chloride ions are attached to the
Ru(JI) centre by direct metal chlorine bond. Presence
of on ly one v(Ru-CI) band around 330 cm- I in the
infrared spectra (Table I) of the compounds indicates
that the two Ru-CI bonds are tran s to each othe r. The
ligands behave in a neutral bidentate manner and bind
to the metal centre in the thione form. Thi s
coordination behaviour is indicated by close
examination of their IR spectra. Two new bands
corresponding to v(Ru-N) and v(Ru-S) are observed
Table I- Analytical and physica l data and important, IR bands (cm- I)of th e complexes
Co mplex
Found (Calcd.)%
C
H
N
Ru(bpy)(PhTSC)CI 2 ·
CH 3 0H (I)
Ru(bpy)(pCH 3 PhTSC)CI 2 ·
CH 30H (2)
Ru(bpy )(p-CI PhTSC)CI 2 .
CH 30H (3)
Ru(bpy )(p-BrPh YSC)CI 2 .
CH 30H (4)
Ru(bpy)(p-OCH 3 )PhTSC)CI 2 •
CH 30H (5)
"In DMF
41.2
(41.1)
42.5
(42.2)
38.7
(38.5)
35.8
(35.7)
4 1.1
(41.1)
3.9
(4.0)
4.2
(4.3)
3.2
(3.6)
3.0
(3.3)
3.9
(4. 1)
Conductance"
(Q- I cm 2 mol - I)
v(NH)
31
3200
3200
3200
3200
3200
13.5
( 13.3)
12.5
( 13.0)
12.4
( 12.5)
11.3
( 11.6)
12.2
(12.6)
14
30
• )
8(NH )+v(CN
1600,
1605,
1600,
1600,
1600,
1545.
1550,
1530.
1530,
1550.
1495
15 I 5
1490
1490
1505
v(CS ) v( Ru-C1 )
775
775
765
765
775
32 5
340
325
325
325
Other ba nds
v( Ru -N) v( Ru-S)
520. 425
520.425
510. 420
510. 420
520.425
26
23
Table 2- Cyclicvoltammetric results,,·h and electronic spectral dala" of the complexes
Complex
El d Y), (flEp/mY )
oxidation
Reduction
Am", ( nm ) (£ / M- Ic m- I)
(I)
0.34(60), 0.85(60)
-0.46, - I. 17
240.2 80, 370(5 h). 470(sh)
(2)
0.30(60),0.82(60)
-0.48, - 1.17
240,280. 375(sh). 480(sh)
(3)
0.36(60), 0.91 (60)
-0.40, - 1.1 2
240.280, 375(s h). 480(sh)
(4 )
0.35(60), 0.90(60)
-0.45. -1.12
243 . 288. 370(s h), 470(sh)
(5 )
0.35(60),0.90(60)
-0.45. - 1.12
236.292 . 370(sh). 470(sh)
a Working electrode: Platinum; Referen ce electrode: Ag/ AgCI; EI 12 = 0.5 (Epa+ Epc), where Epc and Ep" '-Ire cath odi c '-I nd ~lIl odi c pe'-l k
potential s, respecti ve ly; hSupporting electrolyte 0. 1 M TEAP; Solute concentration 10- 3 M: Scan rate 200 mY S- I.
792
INDIAN j CHEM , SEC A, APR1L 2004
in the IR spectra of the complexes around 520 and
425 cm- I of the compounds, which are, absent in IR
spectra} of the ligand.
the negative side two irreversible reduction peaks are
observed. The first reduction peak is due to the entry
of an electron to n* orbital of the th iosemicarbazide
ligand. The second reduction is bipyridine based 1.7.
Electrochemistry
The redox behaviour of the co mpounds was
examined by cyclic voltammetry at glassy carbon
electrode. Relevant data are summarised in the
Table 2. Each of the five compounds undergoes two
successive reversible one electron oxidation. The
reversible nature was indicated by ip./ipc "" 1 and !:J.Ep
(peak ' potential separation) val ues which varied
between 60-70 m V. One electron nature of the
oxidation was confirmed from comparison of peak
heights of the couple with that of equimolecular cisRu(bpy hC I2 .2H 20 so luti o n. The first oxidation
process is Ru (If)IRu(Ill) ox idation and the second
Cyclic
one IS a li gand-based oxidation 1.7.
volrammetry
study
of
Zn(H)
comp lex
of
thiosemicarbazide ligand was done and one oxidation
couple at 0.90 V was obtained. This is ligand centered
oxidation as Zn(H) is inert to oxidation. But for Ru(II)
mi xed ligand co mplexes o ne extra ox idati o n couple
around 0.35 V was obtai ned . So it ca n be concl uded
that the first oxidation is due to Ru (lI )/Ru (IIl) couple
and the next one is li ga nd based ox id ati on. The
seco nd co upl e is not Ru(lIl )/Ru (IV) ox idati o n may
also be co ncl uded from th e fact that th e two
success ive metal (ruthe nium ) centre oxidatio n
generall y separated by 1 vo lt. All the compo unds have
similar co mpos iti on and structure and diffe r onl y with
respect to the li gand mo iety, whi ch in turn diffe r o nly
by the substituents in th e pheny l ring. So, the
vari ati on of the metal centre ox idati o n potenti al can
mainl y be attributed to the presence o f different
substituents on the li gand ; in another way, it may be
sa id th at the ox idati o n potenti al of Ru (l!) centre is
finely tuned by the substitu ents on the phenyl ring. In
Electronic spectra
Electronic spectral data for the compounds are
given in the Tab le 2. All the compounds ex hi bit two
metal-ligand charge transfer transi tions around 375
nm and 475 nm. T hese M LCT transitio n invo lve 12..
orbitals of Ru" and n* orbitals of bipyridi ne and
thiosemicarbazide ligands. Two intraligand n-:Hl: *
transition are also observed in the UV reg ion 7. 10.
Acknowledgement
The authors are gratefu l to Prof. Saktiprosad
G hosh, Department of Inorgan ic Chemistry, Indian
Association for the Cu ltivation of Science, Kolkata
for providi ng us the laboratory facil ities .
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