Structure of 2:1 cobalt(III) complexes derived from arylazocitrazinic acid

Article abstract of DOI:10.1135/cccc2008192

¹H, ¹³C NMR and MS spectra of the 2:1 cobalt(III) complexes, the azo coupling products of 2-amlnophenol or 2-aminobenzoic acid with the citrazinic acid, were measured and analysed. It was found that the cobalt atom is six-coordinated

Full text of DOI:10.1135/cccc2008192

Structure of 2:1 Cobalt(III) Complexes
535
STRUCTURE OF 2:1 COBALT(III) COMPLEXES DERIVED FROM
ARYLAZOCITRAZINIC ACID
b
c
a2
Jaroslava KOŘÍNKOVÁa1,*, Antonín LYČKA , Aleš CEE , Milan NÁDVORNÍK
,
a3
a4
Robert JIRÁSKO and Radim HRDINA
a
Faculty of Chemical Technology, University of Pardubice, Studentská 95, CZ-532 10 Pardubice,
Czech Republic; e-mail: jaroslava.korinkova@upce.cz, milan.nadvornik@upce.cz,
1
2
3
4
robert.jirasko@upce.cz, radim.hrdina@upce.cz
b
c
Research Institute for Organic Syntheses, Rybitví 296, CZ-533 54 Pardubice 20, Czech Republic,
and Faculty of Education, University of Hradec Králové, Rokitanského 62,
CZ-500 03 Hradec Králové, Czech Republic; e-mail: antonin.lycka@vuos.com
Foerstrova 1688/5, CZ-500 02 Hradec Králové, Czech Republic; e-mail: ales.cee@home-net.cz
Received October 1, 2008
Accepted Jan uary 22, 2009
Publish ed on lin e March 18, 2009
1H, 13C NMR an d MS spectra of th e 2:1 cobalt(III) com plexes, th e azo couplin g products of
2-am in oph en ol or 2-am in oben zoic acid with th e citrazin ic acid, were m easured an d an a-
lysed. It was foun d th at th e cobalt atom is six-coordin ated bein g boun d to two oxygen s (on e
from prim ary an d on e from secon dary com pon en t) an d th e n itrogen of 2-am in oph en ol or
2-am in oben zoic acid. Molar m agn etic susceptibility data proved th e presen ce of Co(III). Di-
azotisation of 2-am in oph en ol or 2-am in oben zoic acid an d subsequen t couplin g reaction
with citrazin ic acid an d com plexation of th e form ed azo product proceeded on stan dard
way.
Keyw ord s: Citrazin ic acid; Com plexation ; Co(III) com plexes; Ch elates; Cobalt; NMR spec-
troscopy; Mass spectrom etry.
Metal-com plex dyes play a very im portan t role in dyestuff tech n ology1–5
.
Th e com plexation con verts relatively ch eap dyes to attractive com m ercial
products h avin g appropriate stability an d sh ade. Th e dyes used in prepara-
tion of m etal-com plex dyes are usually triden tate ligan ds an d th e resultin g
products can h ave differen t con figuration s (fac, mer). It would be ideal to
determ in e th e real structure of th ese dyes usin g X-ray data. Th e n um ber of
existin g X-ray structures is very lim ited (e.g. refs.6,7) because of extrem e dif-
ficulties in growin g sin gle crystals.
X-ray crystallograph y an d NMR spectroscopy are in sam e sen se com ple-
m en tary m eth ods for th e structure determ in ation . NMR spectra provide
in form ation about th e un iform ity of m etal-com plex dyes, dyn am ic beh av-
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 4, pp. 535–544
© 2009 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc2008192

536
Kořínková, Lyčka, Cee, Nádvorník, Jirásko, Hrdina:
iour, position of coordin ation , etc., allowin g, at least partially, to solve th e
structures of m etal-com plex dyes in cases wh ere X-ray data are n ot avail-
able. We h ave successfully studied several types of m etal-com plex dyes
derived from ligan ds h avin g eith er h ydroxy or carboxylic groups by m ulti-
n uclear m agn etic reson an ce8–14
.
An im portan t group of m etal-com plex dyes is derived from citrazin ic acid
as secon dary com pon en t15. Masoud et al.16 proposed th e existen ce of struc-
ture 1 h avin g four-m em bered rin gs as a con sequen ce of coordin ation of
citrazin ic acid n itrogen an d both oxygen atom s.
Th is structure differs con siderably from th ose sh own previously an d also
from oth er structures m en tion ed in ref.16. Sin ce citrazin ic acid an d its deriva-
tives are prom isin g secon dary com pon en ts, we decided to study th is type of
1
com poun ds usin g detailed H, 13C NMR an d MS spectra.
RESULTS AND DISCUSSION
Synthesis of the Dyes
Th e preparation of azo dyes 2a–2c is based on th e diazotisation of prim ary
am in e (2-am in oph en ol, 2-am in oben zoic acid or 2-m eth ylan ilin e) in dilute
aqueous HCl at tem perature 0–5 °C, wh ere th e reaction tim e is about
20–30 m in (Sch em e 1).
SCHEME 1
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 4, pp. 535–544

Structure of 2:1 Cobalt(III) Complexes
537
Th e obtain ed diazon ium salt is coupled with aqueous solution of a m ix-
ture of citrazin ic acid an d its salt at pH ~ 8, at tem perature 0–5 °C; reaction
tim e ca. 3 h (Sch em e 2).
SCHEME 2
Cobalt(III) com plex dyes 3a, 3b are prepared in water by com plexation
reaction of azo dyes 2a, 2b with cobalt(II) sulfate at pH ~ 8–9 an d reaction
tem perature 100 °C (reflux); reaction tim e ca. 3 h (Sch em es 3 an d 4).
SCHEME 3
Th e reaction m ixture is vigorously stirred to facilitate th e oxidation of co-
balt (Co2+ → Co3+) with air oxygen .
Th us, th e com poun d Na33a is a Co(III) com plex with 3-[(2-h ydroxy-
ph en yl)azo]citrazin ic acid, Na33b is a Co(III) com plex with 3-[(2-carboxy-
ph en yl)azo]citrazin ic acid. Th e referen ce an ion 4 is a Co(III) com plex with
2-[(2-h ydroxyph en yl)h ydrazon o]-3-oxo-N-ph en ylbutan am ide8 an d th e ref-
eren ce an ion 5 is a Co(III) com plex with 2-[(2-h ydroxy-1-n aph talen yl)azo]-
ben zoic acid17
.
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538
Kořínková, Lyčka, Cee, Nádvorník, Jirásko, Hrdina:
SCHEME 4
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 4, pp. 535–544

Structure of 2:1 Cobalt(III) Complexes
539
Constitution of Prepared Dyes
1
Th e H an d 13C NMR ch em ical sh ifts of startin g azo dyes 2a an d 2b an d th e
an ion 3a were m easured in DMSO-d6 an d th e obtain ed data are collected in
Table I.
TABLE I
1H an d 13C NMR ch em ical sh ifts of an ion s 2–4 in DMSO-d6
2a
2b
3a
4 (ref.8)
Atom
δ(1H)
δ(13C)
δ(1H)
δ(13C)
δ(1H)
δ(13C)
δ(1H)
δ(13C)
a
b
c
2
–
–
–
3
–
121.8
146.7
–
123.3
152.1
–
114.7
d
4
–
–
–
5
6.25
–
114.1
5.97
–
112.1
5.83
104.2
a
b
c
6
–
–
7
–
166.4
–
–
167.5
–
167.4
NH–N
1′
14.38
–
15.66
–
129.4
146.3
116.2
126.6
120.3
114.7
–
143.5
120.1
131.5
123.9
132.8
115.3
168.7
–
145.8
168.8
117.3
128.9
114.4
114.6
–
–
147.1
167.7
117.5
127.9
114.2
114.9
–
2′
–
–
–
–
3′
7.00
7.04
6.94
7.47
10.82
8.01
7.20
7.56
6.70
7.00
6.70
8.03
–
6.63
6.92
6.67
8.23
–
4′
5′
6′
7.86
d
7′
a
b
c
d
163.9 or 161.1; 164.9 or 160.7; 148.7 or 148.3; n ot observed. Addition al sign als:
2a: δ(1H) = 11.79 (br s, 1 H, acidic proton of NH or OH group); 3a: δ(1H) = 11.74 (br s, 1 H,
acidic proton of NH or OH group).
Th e 1H an d 13C NMR ch em ical sh ifts were assign ed usin g H,H-COSY,
gradien t-selected gs-HMQC an d gs-HMBC 11,12 (optim ised for 1J(13C,H) ca.
150 Hz an d 3J(13C,H) ca. 8 Hz). Correlation of H(3′) with th e carbon of
C-OH or COOH group in HMBC spectra was a key in form ation for th e
assign m en t of h ydrogen an d carbon reson an ce of C1′–C7′.
On ly on e set of appropriate NMR sign als was obtain ed for an ion 3a. Th is
means that both ligands in the complex 3a are equivalent and there is only one
arran gem en t or a very fast exch an ge on th e NMR tim e scale. Th e secon d
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540
Kořínková, Lyčka, Cee, Nádvorník, Jirásko, Hrdina:
possibility can be th eoretically exam in ed from th e m easurem en t at low
tem perature. Sin ce m eltin g poin t of DMSO is +18 °C an d sin ce our com -
plexes are in soluble in oth er solven ts, th is low tem perature tech n ique can -
n ot be used. In addition , both ligan ds are spatially so far th at th e use of
NOE or NOESY is im possible.
1
We com pared th e H an d 13C ch em ical sh ifts m easured for an ion 3a with
th ose for an ion 4 for wh ich we un doubtedly proved8 th at cobalt atom is
six-coordin ated via two oxygen an d n itrogen atom s from startin g 2-am in o-
1
ph en ol. A com parison of H an d 13C ch em ical sh ifts in com plexes 3a an d 4
con vin cin gly sh ows th at th e NMR data for com parable structures in both
m olecules are practically th e sam e. Con sequen tly, th e bon din g arran ge-
m en t aroun d cobalt atom in both com plexes is also quite th e sam e.
To provide ch em ical eviden ce for th e im portan ce of th e h ydroxy group
presen ce in th e ligan d m olecule, we prepared com poun d 2c in wh ich h y-
droxy group was replaced with m eth yl group h avin g sim ilar steric require-
m en t as OH group. In accord with our expectation , n o com plexation of 2c
with cobalt(III) cation was observed.
Moreover, in structure 1, proposed by Masoud et al.16, it could be ex-
pected th at both th e h ydroxy groups an d even th e ph en ylazo substituen t
are n ot of decisive im portan ce for a form ation of cobalt(III) com plex. Th us,
we tested th e com plexation of un substituted citrazin ic acid but, again , n o
com plexation was observed.
Sch etty an d Kuster17 observed th e th ree com pon en ts h avin g con siderably
differen t sh ades in cobalt(III) com plex 5. We proved13 th at all th e an ion s
3a, 3b, 4 an d 5 con tain six-coordin ated cobalt atom an d th e differen ce con -
sists in differen t m utual orien tation of two ligan ds. All th ree com pon en ts,
h owever, are separable, after stan din g of each isom er in DMSO solution ,
wh ich results in th e form ation of th e startin g equilibrium .
We m easured 1H an d 13C NMR spectra of an ion 3b an d observed a m ix-
1
ture of four com pon en ts. Th e H NMR spectrum con sists of a stron gly over-
lapped sign als (δ(1H) 7.25–8.28) an d four separated sign als reson atin g at
6.34, 6.20, 6.14 an d 6.07 ppm , h avin g approxim ately th e sam e in ten sities.
Th e latter 1H NMR reson an ces resem ble th ose for H-3′ proton s13 in th e
com poun d. An attem pt to separate th ese isom ers ch rom atograph ically was
n ot com pletely successful sin ce th e ten den cy to establish an equilibrium
durin g evaporation of solven t is stron ger in 3b th an th at in 5.
Th e fact th at th e ligan d 2b was boun d to cobalt(III) ion (form in g 3b) was
also con vin cin gly proved usin g m ass spectrom etry. Th e value of m/z of 3b
was foun d to be 661 (n egative m ode of electrospray ion isation ) an d 663
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 4, pp. 535–544

Structure of 2:1 Cobalt(III) Complexes
541
(positive m ode of electrospray ion isation ) for each ch rom atograph ic frac-
tion .
We studied the cobalt oxidation state by m easuring specific susceptibility of
com pound Na33a. The experim ental value χg was (0.85 ± 0.02) × 10–8 m 3 kg–1.
Calculatin g m olar m agn etic susceptibility χM = 570 × 10–11 m 3 m ol–1 an d
correctin g th is value for diam agn etic con tribution 358 × 10–11 m 3 m ol–1, we
obtain ed corrected m olar m agn etic susceptibility χM = 928 × 10–11 m 3 m ol–1.
An ion 3a exists predom in an tly as a diam agn etic com plex with Co(III) in
th e low-spin state (t2g6) (h igh -spin state h as been observed so far exclusively
in h exafluorocobaltate(III) com plexes in wh ich th eir m agn etic properties
are determ in ed by four un paired electron s with n on quen ch ed orbital an gu-
lar m om en tum an d observed m agn etic m om en ts 6.5–9.5 BM 19). A sm all
con tribution of a Co(II) im purity in th e h igh -spin state with th e con figura-
2
tion (t2g5)(eg ) h avin g th ree un paired electron s can n ot be excluded takin g
experim en tal data in to accoun t. Com plexes of th is type give m agn etic
m oments µeff in the range from 4.3 to 5.2 BM 19 which correspond to the values
of corrected m olar m agn etic susceptibility in th e ran ge of 9760 × 10–11
–
.
14268 × 10–11 m 3 m ol–1 usin g th e expression µeff = 797.5 × (χM T)1/ 2
Provided th is assum ption is correct, th e Co(II) com plex con ten t could be
estim ated to be 6–9% usin g th e experim en tal value of χM = 876 × 10–11
m 3 m ol–1.
Th e results of electrospray ion isation (ESI) m ass spectrom etry m easure-
m en ts both in th e positive- an d n egative-ion m odes for com poun ds 2a–2c
an d Na+ salts 3a, 3b are sum m arised in Experim en tal an d th ey are in agree-
m en t with th eir m olecular weigh ts an d th e structures. Ion s presen tin g in
th e full-scan positive- an d n egative-ion m ass spectra stron gly depen d on
th e Na+ con cen tration in th e solution wh ich is related to th e ch aracter of
m easured com poun ds. Th e presen ce of carboxylic group of ligan ds is con -
firm ed by th e fragm en t ion s observed in th e full-scan n egative-ion m ass
spectra for com poun ds 2a, 2b, 2c an d Na33b an d tan dem m ass spectra for
com poun d Na33a.
CONCLUSIONS
1H, 13C NMR an d MS data, suitable m odel experim en ts an d takin g in to
accoun t som e data from literature, we proved th at 2:1 cobalt(III) com plexes
3a an d 3b derived from azo couplin g products of 2-am in oph en ol or
2-am in oben zoic acid with citrazin ic acid h ave th e sam e structure as th e
com plexes prepared by couplin g of 2-am in oph en ol or 2-am in oben zoic acid
with oth er secon dary com pon en ts an d subsequen t com plexation . An ion 3a
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 4, pp. 535–544

542
Kořínková, Lyčka, Cee, Nádvorník, Jirásko, Hrdina:
is a less flexible com plex with n ew five- an d six-m em bered rin gs, wh ich are
m ore flexible an d, th us, several isom ers existin g in an equilibrium can be
form ed. Molar m agn etic susceptibility data proved th e existen ce th e Co(III)
oxidation state in th e com plexes.
EXPERIMENTAL
Gen eral
Aceton itrile an d m eth an ol for HPLC were purch ased from Sigm a–Aldrich (Prague, Czech
Republic). Water was purified usin g th e Milli-Q plus water purification system (Millipore,
USA). Am m on ium acetate was purch ased from Lach -Ner (Czech Republic). 1H an d 13C NMR
spectra were recorded on a Bruker Avan ce 500 spectrom eter (500.13 MHz for 1H an d
125.76 MHz for 13C) in DMSO-d6. Th e 1H an d 13C NMR ch em ical sh ifts were referen ced to
in tern al TMS. All 2D experim en ts (gradien t-selected gs-COSY, gs-HMQC, gs-HMBC) were
perform ed usin g m an ufacturer’s software. Magn etic susceptibility was m easured at room
tem perature (25 °C) usin g a Variable Tem perature Gouy Balan ce apparatus (Newport In stru-
m en ts, UK) an d Hg[Co(NCS)4] as calibran t. Th e values of m agn etic m olar susceptibility were
corrected by th e Pascal con stan ts19. Positive- an d n egative-ion electrospray ion isation (ESI)
m ass spectra were m easured on an ion trap an alyser (Esquire 3000, Bruker Dalton ics,
Germ an y). Th e full-scan m ass spectra were m easured in th e ran ge m/z 50–1000. Th e sam ples
were dissolved in a water/aceton itrile (1:1) m ixture an d an alysed by direct in fusion at th e
flow rate 5 µl m in –1. Th e ion source tem perature was 300 °C, th e flow rate an d th e pressure
of n itrogen were 4 l m in –1 an d 10 Pa, respectively.
Diazotisation of 2-Am in oph en ol
2-Am in oph en ol (0.02 m ol, 2.18 g; Aldrich ) was m ixed with water (20 m l) an d con cen trated
HCl (5 m l, 35%). Th e obtain ed fin e suspen sion was extern ally cooled un der in ten sive stir-
rin g to 0–5 °C an d 5 M aqueous NaNO2 (5 m l) was slowly added. Th e coolin g was stopped
an d th e suspen sion was stirred at am bien t tem perature (ca. 22 °C) for 20–30 m in un til a
yellow-brown solution of th e diazon ium com poun d was produced. Th e solution was used
for subsequen t couplin g reaction .
Preparation of 3-[(2-Hydroxyph en yl)azo]citrazin ic Acid (2a)
Citrazin ic acid (0.02 m ol, 3.20 g; Aldrich ) was m ixed with water (15 m l) an d 5 M aqueous
NaOH (13 m l) an d th e tem perature was m ain tain ed at 0–5 °C (extern al coolin g). Th e solu-
tion of th e diazon ium com poun d was gradually added un der in ten sive stirrin g. pH was ad-
justed to ca. 8 by th e addition of 5 M aqueous NaOH. Wh en th e couplin g reaction was
com pleted (after ca. 3 h ), pH was adjusted to 4 by th e addition of con cen trated HCl (35%)
an d th e precipitated m on oazo dye was filtered off an d dried at 90–110 °C. Th e yield of
crude dye 2a was 5.84 g (98%). Th e purity of th e dye was determ in ed by TLC (Alugram SIL
G/UV254, Mach erey–Nagel, Germ an y; m obile ph ase: propan -2-ol/propan -1-ol/eth yl acetate/
water 2:4:1:3 (v/v/v/v)). Accordin g to TLC, 2a was pure (RF 0.8). C12H9N3O5 (275): ESI+, m/z:
320.0 [M + 2 Na – H]+, 100%; 301.9 [M + 2 Na – H – H2O]+; 276.0 [M + H]+. ESI–, m/z: 295.8
[M –2 H + Na]–; 273.8 [M – H]–; 255.8 [M – H – H2O]–; 229.8 [M – H – CO2]–, 100%.
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 4, pp. 535–544

Structure of 2:1 Cobalt(III) Complexes
543
Preparation of 3-[(2-Carboxyph en yl)azo]citrazin ic Acid (2b)
Preparation was an alogous to th e preparation of com poun d 2a. Accordin g to TLC, 2b was
pure (RF 0.75). C13H9N3O6 (303): ESI–, m/z: 301.8 [M – H]–, 100%; 257.8 [M – H – CO2]–;
213.8 [M – H – 2 CO2]–.
Preparation of Com plex Na33a
Th e m on oazo dye 2a (0.02 m ol, 5.94 g) was dissolved in water (50 m l) an d pH was adjusted
to 8–9 by th e addition of 5 M aqueous NaOH. Th en CoSO4·7H2O (2.80 g, 0.01 m ol) was
added an d th e reaction m ixture was vigorously stirred at 100 °C (reflux) for ca. 3 h . Wh en
th e reaction was com pleted, com poun d Na33a was precipitated by addition of NaCl, filtered
off an d dried. Th e yield of com poun d Na33a was ca. 78% (based on 2a). Th e purity of th e
dye Na33a was determ in ed by TLC (Alugram SIL G/UV254, Mach erey–Nagel, Germ an y;
m obile ph ase: propan -2-ol/propan -1-ol/eth yl acetate/water 2:4:1:3 (v/v/v/v)). Accordin g to
TLC, 3a was pure (RF 0.69). Na3[Co(C12H6N3O5)2]; C24H12CoN6Na3O10 (672): ESI+, m/z:
651.0 [M – Na + 2 H]+, 100%. ESI–, m/z: 605.1 [M – 3 Na + 2 H]–, 100%. MS/MS, m/z: 605;
560.9 [M – 3 Na + 2 H – CO2]–; 517.0 [M – 3 Na + 2 H – 2 CO2]–.
Preparation of Com plex Na33b
Preparation was an alogous to th e preparation of com plex Na33a. Accordin g to TLC, 3b was
pure (RF 0.71). Na3[Co(C13H6N3O6)2]; C26H12CoN6Na3O12 (728): ESI+, m/z: 684.9 [M – 2 Na +
3 H]+; 663.0 [M – 3 Na + 4 H]+, 100%. ESI–, m/z: 661.0 [M – 3 Na + 2 H]–, 100%; 616.9 [M –
3 Na + 2 H – CO2]–; 572.9 [M – 3 Na + 2 H – 2 CO2]–.
Preparation of 3-[(2-Meth ylph en yl)azo]citrazin ic Acid (2c)
Preparation was an alogous to th e preparation of com poun d 2a. Accordin g to TLC, 2c was
pure (RF 0.84). C13H11N3O4 (273): ESI–, m/z: 271.8 [M – H]–; 227.8 [M – H – CO2]–, 100%.
The authors thank the Ministry of Education, Youth and Sports of the Czech Republic (Project
MSM 0021627501) for financial support. R. Jirásko and J. Kořínková acknowledge the support of the
the Ministry of Education, Youth and Sports of the Czech Republic (Project MSM 0021627502).
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