Cobalt(II) derivatives of cyclic phosphazenes: Synthesis, characterization and fungicidal behaviour

Article abstract of DOI:10.1515/znb-1998-0917

Chlorine atoms of hexachlorocyclotriphosphazene were substituted with -NH.C₂H₅, -NH.CH₂C₆H₅ and -OC₂H₅ to yield organotriphosphazene ligands. Anhydrous cobalt(II) chloride formed a number of addition complexes with these ligands in different stoichiometric ratios. On the basis of electronic and IR spectra, magnetic moment, conductivity measurements and molecular weight determination, structures of these complexes have been suggested. The complexes were screened for their antifungal activities against Aspergillus flavus and Aspergillus niger.

Full text of DOI:10.1515/znb-1998-0917

Cobalt(II) Derivatives of Cyclic Phosphazenes: Synthesis, Characterization
and Fungicidal Behaviour
B. P. Baranwal*, S. S. Das, Poonam Singh
Chemistry Department, University of Gorakhpur, Gorakhpur - 273009 - India
Z. Naturforsch. 52b, 1039-1042 (1997); received July 7, 1997
Cobalt(II) Derivatives, Cyclic Phosphazenes, IR Spectra
Chlorine atoms of hexachlorocyclotriphosphazene were substituted with -NH.C2H5,
-NH.CH2C6H5 and -O C 2Hs to yield organotriphosphazene ligands. Anhydrous cobalt(II)
chloride formed a number of addition complexes with these ligands in different stoichiomet-
ric ratios. On the basis of electronic and IR spectra, magnetic moment, conductivity meas-
urements and molecular weight determination, structures of these complexes have been sug-
gested. The complexes were screened for their antifungal activities against Aspergillus flavus
and Aspergillus niger.
Introduction
one of the later transition elements, in which co-
balt(II) is lying outside the ring. The complexes
have been characterized by their elemental analy-
ses, infra red and electronic reflectance spectra,
magnetic moment and molecular weight determ in-
ations, and conductivity behaviour. Their fungici-
dal activity has also been studied.
Rapid advances in covalent inorganic polymer
research and technology are taking place in the
field of cyclic phosphazene polymers [1,2]. The cy-
clic phosphazenes constitute one of the largest and
most widely studied groups of heterocycles based
on inorganic skeleton with regard to Tr-bonding,
delocalisation and aromaticity in the rings [3-5].
Extensive studies have been carried out on cyclo-
phosphazenes keeping in view the potential appli-
cations of these derivatives as ultrahigh-capacity
fertilizers [6 ], pesticides [7] and insecticides [8 ].
Due to the presence of electron lone pair on each
nitrogen atom of the skeleton, phosphazenes can
easily bind a proton or complex with electron defi-
cient molecules. Compared to the addition com-
pounds of cyclophosphazenes with electron defi-
cient compounds of non-transition elements (e.g.
Al [9], Si [10], As [11] and Sb [12] etc.), the deriva-
tives with transition elements have received little
attention [2]. Witt et al. have reported the synthe-
sis and structural elucidation of some transition
metal derivatives of open and cyclo-phosphazenes
[13-19]. They took early transition elements to
synthesize these derivatives in which the transition
metal occupies the position in the ring of the
cyclophosphazenes.
Experimental
Materials
Anhydrous CoCl2 was prepared by heating its
hexahydrate (BDH) in a current of dry HC1 gas
and analysed.
Calcd
Co 45.39 Cl 54.61%,
Found Co 45.32 Cl 54.20%.
Ethylamine (BDH) was used as such. Benzyl-
amine was distilled (b.p. 185 °C) before use. PC15
and NH4 C1 used were of analytical grade. PhH and
E tO H were dried by the standard literature pro-
cedures [2 0 ].
Analytical and physical methods
Cobalt was estimated as cobalt anthranilate [21],
chloride as AgCl and nitrogen by the standard
Kjeldahl method.
IR spectra were recorded on a Perkin-Elmer
(model 557) spectrophotometer, electronic spectra
on a Hitachi model U-2000 spectrophotometer.
In the present paper we report the synthesis of
some cyclophosphazene complexes of cobalt(II),
Electrical conductances were measured on
a
Beckman RC-18A conductivity bridge. Magnetic
susceptibility measurements were carried out on a
Gouy balance using analytical grade ferrous am-
* Reprints requests to Dr. B. P. Baranwal.
0932-0776/98/0900-1039 $06.00 © 1998 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com
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1040
B. P. Baranwal et al. • Cobalt(II) Derivatives of Cyclic Phosphazenes
monium sulphate as standard. Molecular weights
of the complexes were determined cryoscopically
in benzene.
dissolved in EtO H (40 cm3). Refluxing ( 1 h) and
removal of excess solvent in vacuo (50 °C/1 mm)
yielded blue sticky solid. This solid was dissolved
in E tO H (15 cm3) and reprecipitated with carbon
tetrachloride (60 cm3) and finally dried in vacuo.
Precautions were taken to exclude moisture
throughout. The same procedure was adopted to
synthesize other complexes and the details are
given in Table I. Characteristic data and molecular
weights of some complexes are also listed in Ta-
ble I.
Synthesis o f phosphazene ligands
Phosphorus pentachloride (10.40 g) and ammo-
nium chloride (2.16 g) were refluxed in PhMe (100
cm3) for 4 h. From the reaction mixture
hexachlorocyclophosphazene was crystallized out
in carbon tetrachloride (75 cm3) as a colourless
solid (m.p. 115 °C). The chlorine atoms of this cyclic
trim er (NPC12 ) 3 were substituted by -N H .E t, -
NH.CH 2 Ph and -O E t by treating it with EtN H 2,
PhCH 2N H 2 or N aO Et respectively in 1:6 molar ra-
tio using PhMe as solvent under reflux (3 h). The
synthesized ligands can be represented as follows:
Results and Discussion
Cyclophosphazene ligands are prepared by the
following reactions:
Ph Me
R\ / R
rcPCl5+rtNH4Cl
(NPCl2)„+4nHCl T
(1)
(where n = 3,4 or 5)
The cyclic trimer is crystallised in CC14.
Cl Cl
R.NH NH.R.
P j- t 6HC11 (2)
Ph Me
reflux
N'
R
+ 6 R.NH.
l N-y4
(Where R - -E t or -C H 2 Ph)
W here R = -N H .C 5H5(L');
-NH.CH2C .H .(L 2) and -0 C ,H .(L 3)
\ / OEt
Cl Cl
OEt
Synthesis o f the complexes
Ph H
-N
+ 6 NaOEt
+N =P
+ 6NaCl | (3)
Cyclophosphazene ligand, L1, (4.54 g) was
added to anhydrous cobalt(II) chloride (1.47 g)
reflux
- n
-
Table I. Reaction products of cobalt(II) chloride with phosphazene ligand.
Reactants*
(g)
Molar
ratio
Product and
colour
Found (Calcd)
Cl (%)
Mol. Wt.
Co (%)
N (%)
Co Cl2
(1.47)
+
+
+
+
+
+
+
+
+
L1
1:1
2:1
3:1
1:1
2:1
3:1
1:1
L1 (Co Cl2. EtOH)
Blue sticky solid
10.13
1 2 .2 0
21.17
561
(4.54)
(10.24)
(12.32)
(21.90)
(575)
772
(751)
Co Cl2
(3.78)
L1
(5.81)
L1 (Co Cl2. EtOH) 2
Blue solid
15.48
(15.69)
18.69
(18.87)
16.46
(16.78)
906
(927)
Co Cl2
(5.61)
L1
(5.78)
L1 (Co Cl2. EtOH) 3
Blue solid
19.12
(19.06)
23.01
(22.94)
13.35
(13.60)
-
-
-
12.93
(13.30)
Co Cl2
(0.82)
L2
(4.88)
L2 (Co Cl2. EtOH)
Light Blue solid
6.15
(6 .2 2 )
7.42
(7.48)
11.08
(1 1 .2 2 )
12.74
(12.62)
Co Cl2
(2 .0 2 )
L2
(6.04)
L2 (Co Cl2. EtOH) 2
Blue solid
10.31
(10.49)
9.81
(9.70)
Co Cl2
(2.32)
L2
(4.60)
L2 (Co Cl2. EtOH) 3
Blue solid
13.46
(13.60)
16.16
(16.37)
574
(581)
7.09
(7.23)
Co Cl2
(1.56)
L3
(4.88)
L3 (Co Cl2. EtOH)
Blue solid
9.97
(10.14)
11.96
(1 2 .2 0 )
-
15.34
(15.57)
Co Cl2
(2.27)
L3
(3.56)
2:1
3:1
L3 (Co Cl2. EtOH) 2
Blue solid
18.41
(18.73)
5.31
(5.55)
-
4.63
(4.50)
Co Cl2
(3.06)
L3
(3.21)
L3 (Co Cl2. EtOH) 3
Dark blue solid
18.63
(18.95)
2 2 .6 8
(22.80)
In refluxing ethanol (EtOH).
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B. P. Baranwal et al. • Cobalt(II) Derivatives of Cyclic Phosphazenes
1041
Addition complexes of cobalt(II) chloride with
above phosphazene ligands were synthesized using
E tO H solvent in different m olar ratios:
M olecular weights of some of the above com-
plexes were determ ined cryoscopically in benzene.
The values reported in Table I suggest that the
complexes are monomeric.
Four complexes were screened for their antifun-
gal activity against Aspergillus flavus and Aspergil-
lus niger at 1 0 0 0 , 1 0 0 and 1 0 ppm concentrations.
The results have been compared with the standard
fungicide D ithane M-45, tested under similar con-
ditions. The percentage inhibition was calculated
by using the formula:
ptOH
x CoCl2 + L “efl"ux"*L. (CoCl2.)x
(W here L is cyclophosphazene ligand and x= l,2
or 3).
The reactions are facile and the products are ob-
tained in quantitative yield as blue solids. The m o-
lar conductance measurements in their benzene
solution show that all the complexes behave as
non-electrolytes (2 m values obtained were less
than 0 . 6 ohm -1 cm2 mol-1).
The appearance of a band in their i.r. spectra at
-3160 cm-1 is due to u(OH) stretching of EtO H
coordinated to cobalt. It is much lower than 3300
cm -1 at which the same band appears in free alco-
hol. The new band observed below 700 cm - 1 is
due to coordination of phosphazene ring nitrogen
to cobalt.
In the electronic spectra of the above complexes
in the region 11000-25000 cm - 1 a single band is
observed at 15000±200 cm-1. This is assigned as
v 3 band of cobalt(II) [4A2—*4T, (P)] in a tetrahe-
dral environment [22]. This band is quite com para-
ble to the band obtained for [CoCl4]2- in which
Co2+ is in tetrahedral environment [23]. The blue
colour of the above cobalt(II) complexes also sup-
ports the above view. This is in contrast to the oc-
tahedral environment around cobalt(II) in CoCl2
and [Co(H2 0 ) 6]2+ [22] where two electronic bands
are found in 11000-25000 cm-1.
% inhibition = (C -T )/C x 100
W here, C=D iam eter of fungus colony (in mm) in
controlled plate and T=D iam eter of fungus (in
mm) in treated plate.
The data given in Table II show the effect of
fungicidal behaviour due to different substituents
on the polyphosphazene ligands. It is clear that the
hexaethoxy triphosphazene complexes have the
maximum inhibition against both the fungi. A. fla-
vus and A. niger. O n the otherhand hexabenzyl-
aminotriphosphozene complex has the least reac-
tivity against these fungi. The data further suggest
that the fungicidal activities of all the synthesized
complexes are not comparable with commercial
fungicide D iathane M-45.
Acknowledgem ents
The financial support from University Grants
Commission, New Delhi is thankfully acknowl-
edged. The authors are also thankful to Prof. R. R.
Yadav, Head, D epartm ent of Chemistry for pro-
viding necessary laboratory facilities.
The magnetic moments of the complexes were
found in the range of 4.6-4.7 B.M. These values
are in accordance with the tetrahedral geometry
around cobalt(II) in the above complexes [23].
Table II. Fungicidal activity of the complexes.
Complex
Percentage
inhibition
after
96 h
against
A. flavus at
A. niger at
1000
ppm
100
ppm
10
ppm
1000
ppm
100
ppm
10
ppm
54
59
47
65
93
L1 (Co Cl2. EtOH)
L1 (Co Cl2. EtOH)3
L2 (Co Cl2. EtOH)2
L3 (Co Cl2. EtOH)2
Dithane M-45
42
48
39
54
89
29
40
34
48
82
52
54
48
63
90
44
46
42
55
80
36
39
36
49
77
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1042
B. P. Baranwal et al. • Cobalt(II) Derivatives of Cyclic Phosphazenes
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