Synthesis, physico-chemical characterization and thermal behavior of new complexes with N4O2 donor set

Article abstract of DOI:10.1007/s10973-014-3809-0

Three new coordinative compounds of the type [Co(en)₂CO₃]·0.75H₂O (1) and [M(en)₂(H₂O)₂]CO₃ ((2) M:Ni, (3) M:Cu; en: ethylenediamine) were synthesized and characterized. The IR a

Full text of DOI:10.1007/s10973-014-3809-0

J Therm Anal Calorim
DOI 10.1007/s10973-014-3809-0
Synthesis, physico-chemical characterization and thermal
behavior of new complexes with N4O2 donor set
•
Rodica Olar Gina Vasile Scaeteanu
•
•
•
Ioana Dorina Vlaicu Luminita Marutescu
Mihaela Badea
Received: 29 November 2013 / Accepted: 31 March 2014
´
´
ꢀ Akademiai Kiado, Budapest, Hungary 2014
Abstract Three new coordinative compounds of the type
[Co(en)2CO3]ꢀ0.75H2O (1) and [M(en)2(H2O)2]CO3 ((2)
M:Ni, (3) M:Cu; en: ethylenediamine) were synthesized
and characterized. The IR and UV–Vis spectral data indi-
cate that ethylenediamine acts as chelate, while carbonate
ions act as bidentate chelate ligand for (1)/counter ion for
(2) and (3) generating complexes with octahedral stereo-
chemistry. The thermal behavior provided confirmation of
the complexes composition, as well as the number and the
nature of water molecules and the intervals of thermal
stability. The biological assays revealed a good activity
against Enterococcus faecium for copper complex.
Introduction
Ethylenediamine (en) is an organic compound with many
applications. In coordination chemistry, it functions usually
as chelate ligand [1–3], seldom bridging ligand [4] or is
involved in condensation reactions with different com-
pounds affording new ligands [5, 6]. An unusual behavior
of ethylenediamine has been reported [7] when it occurred
a Michael reaction with acrylic acid in the presence of
Ni(II) ions, leading to a new ligand, ethylenediamino-N,N-
dipropionate dianion and to its’ corresponding complex.
Ethylenediamine complexes are widely investigated due
to their interesting structures and to their importance in
various areas. For example, three varieties of H-bonding
interactions have been evidenced in the case of [Ni(H2-
O)2(en)2](4-nba)2 (nba = 4-nitrobenzoate) that led to
interesting supramolecular interactions [1].
Keywords Ethylenediamine ꢀ Carbonate ꢀ Complex ꢀ
Thermal behavior
There are studies that describe the investigation of
effects of nickel ethylenediamine complexes on prepara-
tion of some catalysts [8]. Also, copper ethylenediamine
complexes exhibit catalytic activity in autooxidation of
phenols [9]. Cobalt complexes of type [Co(en)2L]3?
(L = bipyridine, 1,10-phenanthroline, pyrazole) possess
high antibacterial and antifungal activity [10]. Investiga-
tion of antitumor properties of platinum compound
[Pt(en)(pyridine)Cl]NO3 indicated significant cytotoxic
activity against HL-60 [11].
R. Olar ꢀ M. Badea (&)
Department of Inorganic Chemistry, Faculty of Chemistry,
University of Bucharest, 90-92 Panduri Str., Sector 5,
050663 Bucharest, Romania
e-mail: e_m_badea@yahoo.com
G. V. Scaeteanu
Department of Soil Sciences, University of Agronomical
˘ ˘
Sciences and Veterinary Medicine, 59 Maras¸ti Str., Sector 1,
011464 Bucharest, Romania
Even if coordination compounds that contain complex
ion [Ni(en)2(H2O)2]2? are reported in literature for a long
time [1, 12, 13], there is lack of information regarding
carbonate ion as counter ion.
I. D. Vlaicu
National Institute of Materials Physics, POB MG-7,
˘
077125 Magurele-Ilfov, Romania
As interest in ethylenediamine complexes is continu-
ously growing, we report herein the synthesis, thermal
decomposition, and biologic activity of three new ethy-
lenediamine complexes: [Co(en)2CO3]ꢀ0.75H2O (1),
L. Marutescu
Department of Microbiology, Faculty of Biology, University of
Bucharest, 1-3 Portocalelor Str., Sector 6, 060101 Bucharest,
Romania
123

R. Olar et al.
diffractometer. The structure was solved by direct methods
and refined by full-matrix least squares techniques based
on F2. The non-H atoms were refined with anisotropic
displacement parameters. Calculations were performed
using SHELX-97 crystallographic software package. A
summary of the crystallographic data and the structure
refinement for crystal [Ni(en)2(H2O)2]CO3 is given in
Table 1. The detailed structural data have been deposited
with CCDC-989475.
Table 1 Crystallographic data, details of data collection and struc-
ture refinement parameters for compound [Ni(en)2(H2O)2]CO3
Chemical formula
C5H20N4NiO5
M/g mol-1
274.93
Temperature/K
298
˚
Wavelength/A
0.71073
Crystal system
Space group
orthorombic
Ccmb(64)
7.0796(6)
24.549(2)
10.6986(12)
1859.39(30)
˚
a/A
In vitro antimicrobial tests were carried out by an
adapted agar-disk diffusion technique using 0.5 McFarland
suspension of bacteria obtained from 24 h cultures. The
antimicrobial activities of the newly synthesized com-
pounds were determined against American Type Culture
Collection (ATCC) reference and clinical microbial strains,
i.e., Gram negative (Escherichia coli ATCC 25922), Gram
positive (Staphylococcus aureus ATCC 6538, Bacillus
subtilis 6683, Enterococcus faecium E5), and fungal strains
(Candida albicans 1760).
˚
b/A
˚
c/A
3
˚
Cell volume/A
Cell ratio
a/b = 0.2884; b/c = 2.2946;
c/a = 1.5112
Z
4
Calculated density/g cm-3
Goodness-of-fit on F2
Final R1, wR2 [I [ 2r(I)]
R1, wR2 (all data)
1.16773
1.035
0.0667; 0.1963
0.0725; 0.2047
The compounds were dissolved in water to a final con-
centration of 1 mg mL-1. A volume of 10 lL of each
tested compounds solution was distributed directly on the
solid medium previously seeded with the microbial
inoculums. The inoculated plates were incubated for 24 h
at 37 ꢁC. Antimicrobial activity was assessed by measuring
the growth inhibition zones diameters [14–16].
[Ni(en)2(H2O)2]CO3 (2), [Cu(en)2(H2O)2]CO3 (3). For
nickel complex (2) is presented X-ray structure also.
The quantitative assay of the minimal inhibitory con-
centration (MIC, lg mL-1) was based on liquid medium
twofold microdilutions. After 24 h incubation at 37 ꢁC, the
bactericidal activity was quantified by measuring the
absorbance of the liquid culture at 620 nm. At the end of
the experiment, the wells were emptied, washed three times
with PBS, fixed with cold methanol and stained with 1 %
violet crystal solution for 30 min. The biofilm formed on
plastic wells was resuspended in 30 % acetic acid. The
intensity of the colored suspensions was assessed by
measuring the absorbance at 490 nm [14–16].
Experimental
Materials and methods
All chemicals were purchased from Sigma-Aldrich, reagent
grade and were used without further purification.
Chemical analysis has been performed using a EuroEA
elemental analyser (for C, N and H) and a Shimadzu AA
6300 spectrometer (for metallic ion). IR spectra were
recorded in KBr pellets with a Bruker Tensor 37 spec-
trometer in the range 400–4,000 cm-1
.
Electronic spectra by diffuse reflectance technique, with
Spectralon as standard, were recorded in the range
200–1,500 nm, on a Jasco V 670 spectrophotometer.
The heating curves (TG and DTA) were recorded using
a Labsys 1200 SETARAM instrument, with a sample mass
of 6–12 mg over the temperature range of 30–900 ꢁC,
using a heating rate of 5 ꢁC min-1. The measurements were
Synthesis of complexes
All the complexes were obtained following the general
procedure: a mixture formed from metal carbonate (Co) or
basic carbonate (Ni, Cu), ethylenediamine (in the molar
ratio 1 M:1en) and 25 mL distilled water was stirred at
room temperature for 8 h. The obtained suspension was
filtered off, and the solution was left at room temperature
for several days. The sparingly soluble obtained products
were filtered off, washed several times with ethanol and
air-dried.
carried out in synthetic air (flow rate 16.66 mL3 min-1
using alumina crucibles.
)
The X-ray powder diffraction patterns were collected on
a DRON-3 diffractometer with a nickel filtered Cu Ka
˚
radiation (k = 1.5418 A) in 2h range of 5–70ꢁ, a step
The compounds are soluble in water, alcohols, dimeth-
ylformamide, and dimethylsulfoxide.
width of 0.05ꢁ and an acquisition time of 2 s per step.
X-ray data for crystal [Ni(en)2(H2O)2]CO3 were col-
[Co(en)2CO3]ꢀ0.75H2O (1). Analysis found: Co, 23.28;
C, 23.25; H, 7.04; N, 22.30 %; requires for
lected at room temperature on
a STOE IPDS II
123

Synthesis, physico-chemical characterization and thermal behavior
Table 2 Selected absorption maxima for complexes/cm-1
(1)
(2)
(3)
Assignments
3,421 m
3,332 s
3,296 s
3,245 m
3,171 m
2,945 m
2,883 m
1,586 m
1,546 m
–
3,400 m
3,371 s
3,227 s
3,181 m
3,120 m
2,970 m
2,905 m
1,589 m
–
3,440 m
3,368 s
3,310 s
3,220 m
3,138 m
2,963 w
2,883 w
1,586 m
–
m(H2O)
mas(NH2)
(3)
(1)
ms(NH2)
mas(CH2)
ms(CH2)
d(NH2)
m1(CO3) chelate
m3(CO3) free ion
m5(CO3) chelate
m2(CO3) chelate
m2(CO3) free ion
m4(CO3) free ion
m6(CO3) chelate
qw(H2O)
4000 3500 3000 2500 2000 1500 1000
500
Wavenumber/cm–1
1,463 m
–
1,456 s
–
1,276 m
1,030 s
–
Fig. 1 IR spectra of complexes (1) and (3)
–
–
836 m
690 m
–
851 m
697 m
–
–
The most important bands in the IR spectra are those
assigned to carbonate ion, which are different depending of
its nature (ligand or counter ion). Thus, the free carbonate
ion, of higher symmetry (D3h), presents three IR active
vibrations (m2 7 m4) and one Raman active (m1). These are
preserved even for a lower symmetry (D3) as expect for
complexes with carbonate ion in the ionization sphere.
Since the IR spectra of complexes (2) and (3) contain only
these bands, we assumed the presence of carbonate ion as
counter ion (Fig. 1). When carbonate ion is coordinated
(uni- or bidentate), its symmetry decreases. As a conse-
quence, the m1 vibration becomes IR active and the two
doubly degenerate vibrations (m3 and m4) splits into two
bands. Accordingly, the IR spectra of this kind of com-
plexes contain up to six bands. Furthermore, the splitting of
the degenerate vibrations is larger in the bidentate than in
unidentate coordination. Based on these literature data
[17], we assumed a chelate coordination of carbonate ion
for complex (1).
657 m
–
646 w
524 m
CoC5H17.5N4O3.75: Co, 23.32; C, 23.77; H, 6.98; N,
22.47 %. Reaction yield 90 %
[Ni(en)2(H2O)2]CO3 (2) Analysis found: Ni, 21.27; C,
22.03; H, 7.26; N, 20.41 %; requires for NiC5H20N4O5: Ni,
21. 35; C, 21.84; H, 7.33; N, 20.52 %. Reaction yield 75 %.
[Cu(en)2(H2O)2]CO3 (3) Analysis found: Cu, 22.80; C,
21.39; H, 7.31; N, 19.97 %; requires for CuC5H20N4O5: Cu,
22.71; C, 21.46; H, 7.20; N, 20.02 %. Reaction yield 85 %.
Results and discussion
The reaction of metal carbonates (M: Co, Ni, Cu) with
ethylenediamine in the molar ratio 1 M:1en yields com-
plexes of the general type M(en)2CO3ꢀnH2O. The com-
pounds were fully characterized by elemental analysis, IR,
electronic spectra, thermal analysis and, for nickel com-
plex, single crystal X-ray diffraction. The elemental ana-
lysis allows the formulation of complexes as follows:
CoC5H17.5N4O3.75 or [Co(en)2CO3]ꢀ0.75H2O (1)
A broad band in the 3,400–3,440 cm-1 range that
appears in all spectra can be assigned to m(OH) stretching
vibration of water molecules, presence confirmed by ele-
mental and thermal analyses as well. Additional bands at
646 and 525 cm-1 for complexes (2) and (3), respectively,
assigned to qw(H2O) vibration mode, indicate that the
water molecules are involved in coordination as well [17].
NiC5H20N4O5 or [Ni(en)2(H2O)2]CO3 (2)
CuC5H20N4O5 or [Cu(en)2(H2O)2]CO3 (3)
Infrared spectra
Electronic spectra
Infrared spectra of the metal complexes provide useful
information about the nature of the ligands [17]. The main
absorption bands of the compounds are listed in Table 2.
The IR spectra of all complexes contain, in the
2,880–3,370 cm-1 range, absorption bands due to the
stretching vibrations of the primary amine and methylene
group confirming the presence of ethylenediamine ligand.
The features of electronic spectra of complexes offer
information concerning the oxidation state of the metallic
ion, stereochemistry, as well as the ligand field strength.
Table 3 lists the electronic absorption bands, their assign-
ments as well the crystal field parameters (10Dq, B and b)
¨
calculated with Konig formulas [18].
123

R. Olar et al.
Table 3 Absorption maxima from electronic spectra of complexes (1)-(3), assignments and crystal field parameters
Compound
Absorption maxima/cm-1
Assignments
Crystal field parameters
10Dq/cm-1
B/cm-1
711
b
(1)
38,460
19,600
11,760
6,900
p ? p*
12,700
0.73
4
4T1g ? T1g(P)
4T1g ? A2g
4T1g ? T2g
4
4
(2)
(3)
46,500
28,600
18,020
14,490
11,050
37,040
31,250
14,085
17,090
p ? p*
11,050
898
0.86
3
3A2g ? T1g(P)
3A2g ? T1g
3
3A2g ? Eg
1
3A2g ? T2g
3
p ? p*
LMCT
dz2 ! dx2ꢁy2
dxy,yz, xz ? dx2ꢁy2
LMCT ligand to metal charge transfer
O2
C2
An intense band in the UV region of the complexes
spectra was assigned to p ? p* transition arising from the
C=O moiety of carbonate.
O3
O1
O2'
Three additional bands appear in the electronic spectrum
of the Co(II) complex assigned to spin allowed transitions
for an octahedral geometry. The broad aspect of the bands
arises from lower symmetry generated by different nature
of ligands and donor atoms, respectively [19]. The splitting
parameter value of 12,700 cm-1 is close to an average
value for a [Co(II)N4O2] chromophore, while the nephel-
auxetic parameter of 0.73 is an indicative of a higher
degree of covalency.
C1
N1
N1'''
Nil
N1''
N1''''
O1''
Fig. 2 Perspective view of the complex [Ni(en)2(H2O)2]CO3 with the
atom labeling scheme
The Ni(II) complex (2) exhibits an octahedral geometry
as indicate the three bands that can be assigned to spin
allowed transitions [19]. The low intensity band at
14,490 cm-1 is assigned to the spin forbidden transition
Description of crystal structure
A perspective view of the complex (2) along with the atom
labels is shown in Fig. 2. Selected bond distances and
angles are given in Table 4.
1
3A2g ? Eg. The splitting parameter value of 11,050 cm-1
is in accordance with an [Ni(II)N4O2] chromophore having
a high number of donor atoms that generate a strong field,
such nitrogen ones, while the nephelauxetic parameter of
0.86 is an indicative of a lower degree of covalency
(Table 3).
The crystallographic investigation reveals a mononuclear
2-
unit that contain complex ion [Ni(en)2(H2O)2]2? and CO3
ion as counter ion. The coordination geometry of the nickel
ion is octahedral. Four nitrogen atoms that arise from two
ethylenediamine molecules form the basal plane of coordi-
nation polyhedra. Ethylenediamine acts as bidentate chelate
ligand, coordination manner that is often encountered for this
ligand [1–3]. The lengths of all Ni–N bonds have the same
The electronic spectrum of the Cu(II) complex exhibits a
characteristic broad band with a maximum at 14,085 cm-1
tentatively assigned to dz2 ! dx2ꢁy2 transition and a
shoulder at higher energy, pattern characteristic for a dis-
torted octahedral stereochemistry [19]. The charge transfer
band is observed at 31,250 cm-1 only for complex (3)
having in view that Cu(II) is more easily to reduce in
comparison with both Co(II) and Ni(II).
˚
value [2.091(3) A] and are slightly shorter than Ni–O bonds
˚
that are also equal [2.174(3) A]. Two coordinated water
molecules occupythe apicalpositions. The Ni(II)ion and both
oxygen atoms that belongs to water molecules are collinear,
this suggesting a quite regular octahedral coordination.
123

Synthesis, physico-chemical characterization and thermal behavior
Thermal decomposition of complex
According to packing diagrams (Figs. 3, 4), carbonate
ion is disordered on two crystalographic positions with 0.5
occupancies each.
[Co(en)2CO3]ꢀ0.75H2O
According to TG, DTG, and DTA curves (Fig. 6) the first
decomposition step which occurs in the temperature range
77–110 ꢁC, corresponds to the loss of water molecules. The
anhydrous compound is stable over 70 ꢁC temperature
range. The second thermal event can be associated with the
release of ethylenediamine molecules. Taking into account
of thermal effects (an endothermic one followed by an
exothermic one), we could assume that at the beginning
only Co–N bonds cleavage occurs, the process being an
endothermic one. Once the temperature increases,
For the complexes (1) and (3), on the basis of all
physico-chemical data the proposed coordination is pre-
sented Fig. 5.
Thermal behavior of complexes
The results regarding the thermal decomposition of com-
plexes in synthetic air, using a heating rate of 5 grd min-1
,
are presented in the following section and all data are
summarized in the Table 5.
Table 4 Selected
[Ni(en)2(H2O)2]CO3
distances
and
angles
for
compound
˚
Distances/A
Angles/ꢁ
N1–Ni1
Ni1–N1ii
Ni1–N1iii
Ni1–N1i
Ni1–O1ii
Ni1–O1
2.091(3)
2.091(3)
N1ii–Ni1–N1iii
N1ii–Ni1–N1
N1iii–Ni1–N1
N1ii–Ni1–N1i
N1iii–Ni1–N1i
N1–Ni1–N1i
N1ii–Ni1–O1ii
N1iii–Ni1–O1ii
N1–Ni1–O1ii
N1i–Ni1–O1ii
N1ii–Ni1–O1
N1iii–Ni1–O1
N1–Ni1–O1
83.65(16)
96.35(16)
180.00(11)
180.00(11)
96.35(16)
83.65(16)
91.39(10)
88.61(10)
91.39(10)
88.61(10)
88.61(10)
91.39(10)
88.61(10)
91.39(10)
180.00(0)
2.091(3)
2.091(3)
2.174(3)
2.174(3)
N1i–Ni1–O1
O1ii–Ni1–O1
Symmetry code: (i) -x, y, 1 - z; (ii) x, 1 - y, z; (iii) -x, 1 - y,
1 - z; (iv) -1 - x, y, 1 - z
Fig. 4 Packing diagram of complex [Ni(en)2(H2O)2]CO3 along [112]
direction
Fig. 3 Packing diagram of
complex [Ni(en)2(H2O)2]CO3
along [111] direction
123

R. Olar et al.
10
0
0.3
ethylenediamine molecules suffer oxidative degradation
(the exothermic effect). The IR spectrum recorded for the
intermediate isolated at the maximum in DTG curve
(275 ꢁC) exhibits only CoCO3 vibration bands.
Finally, the third stage of decomposition is associated
with decomposition of CoCO3 to cobalt mixt oxide Co3O4
as powder XRD analyses of the final residues indicate
(ASTM 78-1970).
TG
80
0.2
–10
–20
–30
–40
–50
–60
–70
–80
0.1
60
40
20
0
DTG
0.0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
DTA
–20
Thermal decomposition of complex
[Ni(en)2(H2O)2]CO3
–40
1000
0
200
400
600
800
Temperature/°C
Decomposition of complex (2) starts at 90 ꢁC with one of
water molecules loss (Fig. 7).
Fig. 6 TG, DTG and DTA curves for [Co(en)2CO3]ꢀ0.75H2O (1)
The second thermal event is a complex one, being an
overlap of at least three processes as both DTA and DTG
curves indicates. It comprises the second water molecule
and ethylenediamine molecules elimination. The remaining
nickel carbonate decomposes to nickel oxocarbonate
(NiCO3ꢀ2NiO) and finally to NiO.
20
15
10
5
10
0
0.3
TG
0.2
–10
–20
–30
–40
–50
–60
–70
–80
0.1
DTG
DTA
0.0
OH2
–0.1
–0.2
–0.3
–0.4
–0.5
H2
N
H2
N
NH2
Co
O
O
H2N
0
.
O
0.75 H2O
CO3
Cu
H
N
N
2N
–5
H2
H2
NH2
(1)
OH2
(3)
–10
1000
0
200
400
600
800
Temperature/°C
Fig. 5 The proposed formulation for complexes (1) and (3)
Fig. 7 TG, DTG and DTA curves for [Ni(en)2(H2O)2]CO3 (2)
Table 5 Thermal degradation data (in synthetic air) for the complexes
Complex
Step
Thermal effect
Temperature range/ꢁC
Dmexp/%
Dmcalc/%
[Co(en)2CO3]ꢀ0.75H2O (1)
1
2
3
Endothermic
Miscellaneous
Exothermic
77–110
180–275
275–345
5.2
47.7
15.2
31.9
7.0
5.3
47.6
15.3
31.8
6.6
Residue (Co3O4)
[Ni(en)2(H2O)2]CO3 (2)
1
2
3
4
Endothermic
Exothermic
Exothermic
Exothermic
90–145
160–375
375–465
465–520
49.7
10.9
5.4
50.2
10.7
5.3
Residue (NiO)
27.0
13.1
42.8
5.0
27.2
12.9
43.0
5.2
[Cu(en)2(H2O)2]CO3 (3)
1
2
3
4
Endothermic
Exothermic
Exothermic
Exothermic
75–135
135–210
210–390
390–470
10.6
28.5
10.5
28.4
Residue (CuO)
123

Synthesis, physico-chemical characterization and thermal behavior
40
30
20
10
0
0.2
10
0
synthesized and characterized. Spectral data revealed the
chelate coordination of ethylenediamine, meanwhile car-
bonate acts as bidentate chelate for complex (1) and
counter ion for (2) and (3).
TG
0.1
–10
–20
–30
–40
–50
–60
–70
–80
DTG
0.0
The structural features of complex (2) were fully
revealed by single crystal X-ray analysis.
–0.1
–0.2
–0.3
–0.4
DTA
In the case of all complexes, metallic ions are encoun-
tered in an octahedral environment, quite distorted in the
case of complex (3).
–10
–20
The thermal decomposition have confirmed the com-
plexes formula and provided information concerning the
presence of crystallization or coordination water molecules.
Taking into account their similar composition, com-
plexes (2) and (3) decompose respecting a similar pattern.
The final products in all cases were the most stable metal
oxides.
0
200
400
600
800
1000
Temperature/°C
Fig. 8 TG, DTG, and DTA curves for [Cu(en)2(H2O)2]CO3 (3)
The screening of antibacterial activity revealed that only
complex (3) exhibits good activity against Enterococcus
Thermal decomposition of complex
[Cu(en)2(H2O)2]CO3
faecium E5, with a MIC value of 125 lg mL-1
.
Unlike compound (2), the complex (3) loses both water
molecules in the first stage of decomposition (Fig. 8) as
both DTG and DTA curves show. The remaining product is
not stable, undergoing the ethylenediamine loss. The
obtained copper carbonate slowly (210–390 ꢁC) decom-
poses in copper oxocarbonate (2CuCO3ꢀCuO). After
390 ꢁC, the strong exothermic stage is associated with its
decomposition to CuO.
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using American Type Culture Collection (ATCC) refer-
ence and clinical bacterial strains, i.e., Gram negative
(Escherichia coli ATCC 25922), Gram positive (Staphy-
lococcus aureus ATCC 6538, Bacillus subtilis 6683,
Enterococcus faecium E5), and fungal strains (Candida
albicans 1760).
A literature survey revealed that ethylenediamine com-
plexes reported in literature possess high antibacterial and
antifungal activity [10]. In our case, from all tested com-
plexes only complex (3) exhibited a good activity against
Enterococcus faecium E5, with
a MIC value of
125 lg mL-1; for the other tested strains, the inhibitory
activity was lower or has been missing at the tested con-
centrations range.
˘
˘ ˘
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Three new ethylenediamine complexes of the type
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M:Ni, (3) M:Cu; en: ethylenediamine) have been
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