IJCA 44A(8) 1565

Indi an Journal of Chemi stry
Vol. 44A. August 2005. pp. 1565 - 1570
Synthesis, structure and properties of [Co(L)(NO:;)]Cl0 4 .2H 2 0
(L = tetradentate Schiff bases): Example of chelating nitrate
Habibar Chowdh ury". Sk Hafijur Rahaman", Rajarshi Ghosh". Tian-Huey Lu" & Ba rindra Kumar Ghosh",;,
"Departmcnt or Chemi stry. Th e Universi ty or Burd wa n. BunJ wan 7 13 104 , In dia
"Depanm ent of Ph ys ics. Natro nal T sing Hua U ni vers ity. Hsinchu 300. Taiwan. ROC
Ema il: harin _ 10)yaholl.co.UK
HC'cc il 'ed (j April 2()()5: accC'p /('d I()
.11111 ('
20()5
T he syn th esis and characteri zation o r three mononuclear cohalt ( 11) comp lexes of th e type ICo(L)(NO, l jCI0.j.2 H 20
.N'-(his(pyridin -2-yl )!1le thy lidene)butanc- l.
I L = N .N'-(his(pyrid in -2-yl) formyl idene )hutane- 1,4-dia11line (hpfd). I :
4-dia11linc (bpmd ). 2: and N,N' -(bi s( pyridin -2-yl) henzylidene) butanc- I ,4-dia11linc (bpbd). 31 are descrihed herc . In IR. th e
presencc of v ( '0 3 ) band at - 1380 cm -' with di stinct sp litlings is stron gly suggestive of coordination or nitrate instead of it s
simp le counter anioni c view. X-ray diffraction studi es o r ICo(bpfd )( NO,) ]CI0.j.2 H 20 ( I ), has bee n made for th e exaet
knowledge of its coordination sph ere. Stru ctural anal ys is rc veals cobal t( ll ) ce ntre in a di storted octah edral cnv ironment wi th
a CoN 40 2 chromophore ligat ed by four N atoms of th e tetraden tate SchilT hase along with two 0 atoms of nitrate in a
ehelating ra shion . Th e tetrade nlate chelator is I'o lded in th e hut yleni e pan. Th e mononuc lear units in I arc engaged in
in termu lcc ular C- I-L . O and O-H .. . O hydrogen hond ings lead ing to a 2D sheet. Electrochemical electron tran srer studi es in
McCN so lutions show an oxidat i ve res pon se presumahl y due to coba lt( 11I1-cobalt(ll ) couple. A ll th e comp lexes di splay
intrali gand '(1I-rr*) Iluoresccnce and intraligand -'err- rr*) phosphorescence in glassy so luti ons (M eO H at 77 K ).
IPC Cod e: l ilt CI
7
C07C25 1/02 : C07F ISI06
The des ign a nd synthes is of mo no-. bi- a nd
polynuclear co mpl exes of coba lt in its different
l s
ox id atio n slates throu gh appropriate choice - of
diffe re nt li ga nd s are o f ups urge inte rest in
6 8
coordinati on c he mi stry. Sc hiff bases - are use ful
orga nic blockers because of their preparati o nal
access ibiliti es. structural
va ri et ies and
va ri ed
de nti c iti es. III o ne of our rece nt papers, we have
s how n nitrate'} binding in c he lating (0 ,0) fa shi o n in a
zin c(JI) co mpo und w hi c h pro mpted us to searc h thi s
beha vio ur in other meta l complexes. We have
s ucces sfully pre pared cobalt compounds of type
ICo( L)(NO,)JCl O.,).2H 20
(1-3)
IL = N ,N'(bi s( pyridi n-2-y l)a l kyl idene )butane -l ,4-diamin e] . In
one case, ICo( bpfd)(NO, )lC10.j.2 H 20 (1 ), X-ray
structure has been de termined to define the
coordination sphere. The sy nthes is, structure and
redox behaviour of these new com pl exes are
desc ri bed he re.
Materials and Methods
Hi g h purity pyridine-2-ca rboxa lde hyde (Lancaster,
UK), 2-acety lpyridine (La ncaste r, UK ), 2-be nzoy lpyrid ine
(Lancaster,
UK),
butane-l ,4-d iamin e
(Lancaste r,
UK ),
cobalt
nitra te
tetra hydra te
(E. Merck. Indi a) a nd sodium perc hl orate (A ldri c h,
USA) were used as rece ived . The Schiff bases we re
8
pre pared using as repo n ed and stored ill vnclio for
s ubsequ e nt use. MeCN was purifi ed and s upport in g
e lec tro lyte ClEt 4 NJICl0 4]) was prepared as know n
a lt·ead /o. All other c he mi ca ls a nd so lvents we re A R
grade and used as rece ived . The sy nthe ti c reaction s
a nd work-up were done in open air.
Perc hl orate sa lts of meta l io ns are po te ntiall y
exp los ive espec iall y in presence of o rga ni c li ga nd s.
Only a s mall amount of the mate ri a l sho uld be
prepared and handl ed with care.
E le ment a l analysis (C, Hand N) was performed on
a Perkin-Elmer 2400 C HNS/O e leme nta l analyze r. IR
I
spectra (KB r di scs, 4000-300 c m- ) were recorded
us in g a Perkin-Elme r spectrulll RX I FTrR
spec tromete r. Molar co nductances were mea sured
using a Systronics conductiv ity mete r w he re the ce ll
constant was calibrated with 0.01 M KCI so luti o ns
a nd dry MeCN was used as so lve nt. UV-Vis
(in M eCN ) and re fl ectance spectra were d o ne w ith
Ja sco UV -Vis-NIR mode l V -570 s pec troph otomete r.
Roo m temperature mag ne tic s usceptibilities we re
measured on a PAR
155 vibrating samp le
magnetome te r w ith Hg ICo(SCN)41 as reference.
1566
INDIAN J CHEM. SEC A. AUGUST 2005
Diamagnetic con'ections were made uSlllg Pascal's
constants II .
Ti me-reso lved
fluorescence
meas urements were run using a time-correlated single
photon counting (TCSPC) spectrometer Edinburgh
Instruments. model 199; a hydrogen filled coaxial
flash lamp with a pulse width of J .2 ns at FWHM and
a Philips XP-2020Q Photomultiplier tube were
respectively used as the excitation source and the
fluorescence detector. Electrochemical measurements
were made with a computer controlled EG & G
PARC VersaStat (model 270) e lectrochemical
instrume nt using a platinum di sk-working electrode as
l2
desc ribed elsewhere . The solutions were IRcompensated and the results were collected at 298 K.
The following parameters and relation s were used :
scan rate (v), 50 mV s· l ; formal potential E:' = 0 .5
(Epa + Epc) where Epa and Epc are anodic and cathodic
peak potentials, respectively; /)'Ep is the peak-to-peak
separation. The potentials were referenced to a
saturated ca lomel e lectrode (SCE) and are
uncorrected for junction contributions.
Preparation of complexes (1-3)
All the complexes were prepared using a general
procedure. Yields varied in the range 70-80% .
3
Acetonitri le solutions (5 cm ) of L ( I mmol) were
added dropwise to solutions of Co(N0 3 h 4H 20
(I mmol) in the same so lvent (10 cm' ) with constant
stirring for I h. NaCI0 4 (1 mmol) in H 20 (5 cm 3 ) was
added slow ly to each . The red solutions were fi ltered
and the supernatant liquids were kept in air for slow
eva poration . After a few days. the complexes that
sepa rated out were washed with tolue ne and dried ill
vacuo over silica gel indicator. (Found: C, 36.51 ; H,
4.06; N, 13.25; Calcd. CI6H22Ns0 9C ICo (1): C , 36.76 ;
H, 4.24; N, 13.40%. FGund: C, 39.1I; H , 4.70; N,
12.61; O ilcd. CI SH26Ns09CICo (2) : C, 39.25; H, 4.76;
N, 12.72%. Found: C , 49 .73; H, 4.38; N, 10.22;
Calcd. C28H30Ns0 9C1Co (3): C, 49.85 ; H, 4.48 ; N,
10.38%) .
X-ray crystallographic analysis
Single crystals of 1 suitable for X-ray analysis were
obtained by slow e"aporation of a 3: 1 MeCN-H20
so lution of the reaction mixture at 298 K. Diffraction
data were measured at 293(2) K on a S iemens
SMART CCD diffractometer using graphitemonochromated Mo-Ka radiation (A = 0.7 1073
Crysta ll ographic data and structure refinement
parameters are given in Table 1. Of 11462 collected
reflections. 5067 unique reflections were recorded
A).
Table I -
Crystallographic data for [Co(bpl'd)(N O,) ICIO~.
2H 2 0 (1)
Empirical for mul a
Formula wei ght
Colour
Te mperature (K)
Wavelength (A)
Crys tal system. Space gro up
52277
Red
293
0.7 1073
Tricll ni c. P-I
8.520414)
104283(5)
13 293 6(6)
73.8 520( I 0)
1060 52(9)
{/ (A)
b (A)
c (A)
f3 (0)
V (A')
z
D, (Mg m ')
J1 (mm' ])
F(OOO )
ranges (0)
hl k l l
Reflections collected
Independent rellections
Compl eteness to theta
e
Npar
Data/restraints/parameters
Final R indi ces [/> 20(1)1
R indices (all data)
Larges t peak and hol e (e A-3)
1. 637
0.995
538
1.7. 28. 3
- 11/10; - 13/13 ; -1 7/ 16
11462
5067
28.27
5067
36 1
4257
0 .030
R = 0 .0536. wR2 = 0 . 1492
-0.73.0.8 1
using the (D-scan technique. Data were con'ected for
Lorentz polarization effects and for linear-decay.
Semi-emp iri ca l absorption corrections based on
13
\jf-scans were app li ed . The structure was solved by
the heavy atom method us ing SHELXS-97'~ and
successive difference Fourier syntheses. A ll nonhydroge n atoms were refined anisotropically. The
hydrogen atoms were fixed geo metricall y and refined
using a riding mode l. In the fina l diffe re nce Fourier
map , the, residual maxima and minima were 0 .81 a8c1
3
-0.73 ek . A ll calcu lati ons were carried out usi~g
SHELXL-9i s, ORTEP-3i 6
Results and Discussion
Synthesis and formulation
The reaction of cobalt(II) nitrate , L (L = bpfd/
bpmd/bpbd ) and sodium perchlorate in I: J: I molar
ratio in aqueous acetonitri le at roo m temperature
results haxacoordinated comp lexes rCo(L)(N0 3 ) I
CI0 4 .2H2 0 (1 -3), as shown in Eq.( I ):
MeC N- H2 0
Co(N 0 3 h .4H 2 0 + L +
NaCIO.j -----~
298 K
... ( 1)
CHOWDHURY el al.: STUDIES ON SCHIFF BASE COMPLEXES OF COBALT (II )
Table 2 IR" data em-I
Compd
IS67
Analytical data of the complexes
AM h
~tcfr
UV-Vis'
COl li_COli
v(C=N)
v(NO, )
v(CI04 )
ohm-I em 2 mor l
BM
Arlla:~. onl
E '29R. V (t"t.·r . mV )d
1590
1386, \374
1090.620
120
3.78
5 12.405.325.286
0.32 (S O)
2
1592
1385. 1375
1092.622
130
3.79
5 14. 402.326.288
0.31 (80)
3
1593
1386, 1375
1093, 623
120
3.80
510.402.326,284
033 (80)
"In so lid state at 298 K ; hln McCN so lution at 298 K : ' In McCN so lution at 298 K: dWorkin g electrode is platinu1ll.
I
C8
C14
Fig. I ORTEP diagram of monomeric [Co(bpfd)(N O) ]
CI0 4 ·2H2 0 (/ ) wi th atom labelling scheme and 50% probahility
ellipsoids for all non-hydrogen atoms.
All the three complexes were characterised by
elemental analysis , e lectrical conductivity, mag netic
susceptibility, IR, UV-v is and luminesce nce spectra
and electrochcillical study_ The res ults are consistent
with
the
proposed
mononuclear
dihydrate
formulation. The air-stable moisture-in sensitive
complexes are powders, soluble in a range of common
organic so lve nts s uch as methanol , e thanol ,
dichlorome thane, acetonitrile, but are in so lubl e in
wate r. Roo m-temperature so lid -phase
mag net ic
s usceptibility measurements show that all the
complexes a re three-e lec tron paramagnets with /Jeff
value - 3_80 8M . In MeCN solutions, they behave as
I: 1 electrolytes I ? as reflected in their AM values_
Ti me-depe ndence cond ucti vi t)' meas ureme nts show
constancy of the AM value, which is indicati ve of
strong bindin g of NO,- in coordination zone even in
solution . The increase in AM value, if observed, may
correlate the dissociation of nitrate from coordination
zone. IR spectra of the complexes show asymmetric
nitrate stretches v(NO)) centred at -1380 cm- . The
sp littings in nitrate stretch are indicative of chelation
via the oxygen centres and discard si mpl e co unte r
anionic view (Table 2). v(CIO-l) stretches are seen at
I
I
-1090 cm- and -620 cm- res pectively' 8 showing
ionic nature. The v(C=N) stretching vibrations of the
metal bound Schiff bases are routinely observed at
I
-IS90 cm- . All other characteristic li gand vibrations
I
are see n in the 1600-600 cm- range. In MeCN
so lutions, the red complexes exhibit two bands at
-SIO and -400 nm characteristic of octahedral
cobalt(I1)
e nvironment.
Additionally.
bands
corresponding to charge transfer within the li gand
framework are observable a t hi ghe r energies. The
spectra (1: S12. 404. 32S. 28S nm ; 2 : S14, 40 I, 328,
288 nm ; 3 : S10. 402, 326, 282 nm) in nujol are very
similar to those (Tab le 2) in M eCN so lu tions
reflecting s i mi lar gross structure and electro n ic
llJ
structure in so lid state and in so lution .
X-ray structure of [Co(hpfd)(NO.I)]CI0 4 ·211 20 (1)
An ORTEP view with atom numbering scheme of
the mononucl ea r unit and a perspective view of the
two-dime ns io nal sheet formed in 1 are shown in F igs
I a nd 2, respectively. Selected bond di stances and
bond angles re leva nt to the Co coordination sp he re in
the monomer are given in Table 3, and significant
hydrogen bonding data are set in Table 4. The crystal
lattice consists of ICo(bpfd )(NO ])t cations and C IO-lanions . The metal centre is best desc ribed as a
distorted octahedron with a CoN-l0 2 chromophore.
Two pyridine N atoms [N(t), N(4)1. two imin e
atoms [N (2), N(3)] of the te trade ntate Schiff base in
combination with two 0 atoms l O(SI), 0 (S2) I of
bidentate c he lati ng nitrate complete octahedral
coordination around cobalt(II). The equato ri a l
positions are occupied by the two nitrogen ato ms
[N (2) , N (4) J of the tetrade ntate Iigand and two ox yge n
atoms [O(SI ), 0(S2)] of nitrate ion while other two
re maining nitrogen atoms [N(l), N(3)] of the
tetradentate li ga nd are placed at the ax ial pos iti o ns.
INDIAN J CHEM. SEC A . AUGUST 2005
IS68
Distortion from the ideal octahedral geometry is due
to the asymmetric nature of the bound tetradentate
Schiff base and the dev iations of the refine ang les
(90°/180°) formed at the metal centre (Table 3). The
axial Co-N di stance s are Co-N(l) 1.929(3) A and CoN(3) 1.9 16(3) A. The equatorial Co-N and Co-O
di stances are Co-N(2) 1.926(3) A, Co-N (4) 1.961 (3)
A and Co-O(Sl) 1.907(3) A, Co-0(52) 1.893(2) A,
res pect ive ly. Two of the three N-O distances of nitrate
are very close [0(5 1)-N(5) 1.3IS(4) A, 0 (52)-N(5)
1.316(4) AI and large r than the other N-O di stance
10(S3)-N(5) 1.240(5) AI. Thi s indicat es the
coordination through the 0(51) and 0(52) sites of
nitrate to the Co(IT), which is (0,0) type che lat ion .
Fig. 2 - Packing view of 20 sLipramolecul ar sheet formed by
C- H ... O and O-H ... O H-bonding in 1.
The angles subtended by the li gand around cobalt in
the equatorial plane shows a s ign ificant variation
[69.20(1O)-97 .82(ll)°J from the ideal 90.00°. The
!mHS N(l)-Co-N(3) ang le on the other hand has a
va lue [1 75.07(1 3)oJ very close to the ideal 18(r.O()o
The ang les 0(52)-Co-N(2), N(2)-Co-N(4) and N(4 )Co-0(51) in the equatorial plane with va lues
95.97(1 It, 97 .1 8(1 Lt and 97 .82(11)° res pective ly are
much less than
the 0(51 )-Co-O( 52) ang le
169.20(IOn where 0(5 1),0(52) be long to the two
e nd s of the nitrate. Butylenic part of the Schiff base
N(2)-C(7)-C(8)-C(9)-C( I O)-N(3) is to so me exte nt
puckered (Fig. I ) which ha s signifi cant effect o n
va riation of equatorial ang les. The mon onu c lear units
in 1 are engaged in intermolecular C -H ... O and
O-H ... O hydrogen bondin gs leading to a 2D s hee t
(F ig. 2). One hydrogen of each lattice water form s
hydrogen bond with non-coordinated 0 atom [0(S3) 1
of the chetated nitrate: fH(2IY ... 0(53 ), 1.9118 A; <
0(1)11'_ H(21 t ... 0(S3), 169.1S"j . Additional ly, three
di stinctly diffe rent types of intermol ec ular C-H .. . O
hydroge n bond s are seen: [H( 14) .. .O(S I), 2.46(5) A.
< C(l4)-H ( 14) ... 0(S1), 141(3)°: 1-I (6) ... 0(S3 ),
2.56(4)
A, < C(6)-H(6) ... 0(5 3), 134(3t:
H(lS) ... 0(2), 2.46(S) A, < C(lS ) -H(lS) .. . 0(2 ),
132(St; H( 1l ) ... 0(3), 2.37(4) k
< C(ll )H( II ) .. .0 (3), 14S(3)0] (Ta bl e 4).
Redox properties
Tabl e 3 -
Selected bond lengths (A) and an gles (") for I
liol/d distal/ ces
Co-O(S I )
Co-0(S2)
Co-N( I )
Co-N(2)
Co- (3)
1.907 (3)
I. X93(2)
1.929(3)
1.926(3)
1.916(3)
Co-N(4)
O(:"i l )-N(S)
0 (S2) -N(S)
0 (S3)-N(5)
1.%1 (l)
1.3 15(4)
1.3 1()(4)
1.240(5)
69.20( 10)
92 .62( 11 )
164.68( 11 )
91.51(11)
9782( I I )
8'J.8li( ll )
9S97(II)
94. 11 ( 11)
166.64( 11 )
832S( 12)
N( I )·Co-Nel)
N( I )-Co-N(4)
N(2)-Co-N(3)
N(2)-Co-N(4)
0(51 )-N(S)-0(53)
0(52) -N(5)-0(53)
0(51 )- N(S)-0 (52l
N(3)-Co-N(4)
Co-0(51 )-N(S)
Co-0 (52)-N(S)
17507( 13)
9400( 12)
93.44( 12)
97. 18( 12)
125 4 (3)
124 4 (3)
11 02(3)
827 6( 12)
90.0(2)
90.55( 19)
BOlld allgles
0 (5 1)-Co-0(52)
0(51 loCo-Nt I )
0 (51 )-Co-N(2)
0 (5 1loCo-N t})
O(SI )-Co-N(4 )
0(52)-Co-N( I )
0 (S21-Co-N(2)
0 (S2)-Co-N(3)
O(S2)-Co-N(4)
N( I )-Co-N(2)
Tabl e 4 D-H ... A
O( 1)W_H (2 1)w . . 0 (53 )
C( 14)- H(14) .. . 0 (5 1)
C(6) - H(6) .. . 0 (53)
C( II) - H( II) .0(3)
C(l5)- HCI5) ... O(2)
The e lectroactivity of the complexes was examined
in MeCN solutions usin g cyc li c voltammetry (CV ) at
a platinum working e lec trode. A re prese ntative
vo ltammogram is shown in Fig. 3. A nearly-reversib le
(!:lEI' = 80 mY ) one-e lectron oxidati ve res ponse is
observed pres uma bly due to e lectrode reac tion shown
in Eq.(2):
.(2)
The respon se is reproducible with no trace of
deco mposition after a number of cycles. The formal
potentials li e close to -0.3 V vs SCE. One-electron
nature of the couple was verified with compari son of
standard sample- .
~o
Hydrogen bond di stances (A) and angles ( 0) for I
O- H
H ... A
O ... A
O-H ... A
Sy mmetry code
0.8607
0.96(5)
0.90(4)
0.91 (4)
1.04(8)
1.9118
246(5)
256(4)
2.37(4)
143(8)
2762(6)
3260(4)
3.250(4)
3152(7)
3.216(7)
169. 15
141 (3)
134(3)
145(3)
132(5 )
I+x.y. z
-x. -y, I -z
I -x , -yo -z
-I+x. y. z
I -x. -'/..' I -I.
CHOWDHURY
el
al.: STUDIES ON SCH IFF BASE COM PLEXES OF COBALT (Il l
1569
respectively. In glassy solutions (77 K) , a red shift is
observable (550 nm for 1, 548 nm for 2 and 553 nm
for 3) which is presumably due to '(n-n':' )
, I
phosphorescence- .
Conclusions
I
.
0 .4
0.6
0.2
0 .0
Fig. 3 - Cyclic yoltammogram of 1 in acetonitrile solution at
298 K using platinum disk electrode.
We have prepared three new cobalt(II) compounds
containing nitrate binding in (0.0) chelating fashion
in combination with three tetradentate Schiff bases
with variation of substituents on their framew o rk s.
The nitrate-Schiff base combination stabilizes +2 state
of the metal ion. X-ray study of 3 shows that in
crystalline state, hydrogen bonded superstructure
results . Spectroscopic, electrochemical and other
physicochemical properties show that 2 and 3 have
cognate structure to 1. The complexes are good
examples of luminous materials.
Supplementary Data
Crystallographic data (excluding structure factors)
for CCDC-266690 for [Co(bpfd)(N0 3)]CI04 .2H:,O (1)
have
been
deposited
with
the
Cambridge
Crystallographic Data Centre. Copies of this
information can be obtained, free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
IEZ,
UK
(fax:
+44-1223-336033 ;
Email:
or
www:http://
deposit@ccdc.cam.ac.uk
www.ccdc.cam.ac.uk).
~
~
'2
;:J
..
.Q
..::,
"
~
'<;;
c:OJ
C
".,
440
480
SlO
S60
600
Acknowledgement
640
Wavelength (nm)
Fig. 4 - Fluorescence (--) of 1 in MeOH so lution at 298 K,
phosphorescence (- .... .. ) in MeOH glassy solution at 77 K.
Table 5 -
Photophysical data of the complexes
Compd
1
2
3
The authors are grateful to the Department of
Science and Technology (DST) and Council of
Scientific and Industrial Research (CSIR) New Delhi ,
India for financial support.
Life time
(ns)
Emission (A/nm)
Fluorescence"
Phosphorescence
470
468
472
550
548
553
h
2.33
2.35
2.37
"In MeOH at room temperature (298 K); bin MeOH at 77 K
Luminescence behaviour
The spectroscopic data in MeOH solutions and
glasses are listed in Table 5. The complexes show
emission spectra at -470 nm at 298 K. These are
assignable to intraligand '(n-n*) fluorescence . A
representative pattern for 1 is shown in Fig. 4. The
lifetimes are 2.33 ns 0), 2.35 ns (2) and 2.37 ns (3),
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