Thermal study of some new Ni(II) and Cu(II) complexes with ligands derived from N,N-dimethylbiguanide as potential antimicrobials

Article abstract of DOI:10.1007/s10973-009-0487-4

The reaction between [M(DMBG)₂]?nH₂O ((1) M:Ni, n = 0; (4) M:Cu, n = 1), ammonia/hydrazine and formaldehyde in methanol resulted in new complexes of type [ML]?nH₂O ((2) M:Ni, L:L¹, n = 0; (3) M:Ni, L:L²

Full text of DOI:10.1007/s10973-009-0487-4

J Therm Anal Calorim (2010) 99:893–898
DOI 10.1007/s10973-009-0487-4
Thermal study of some new Ni(II) and Cu(II) complexes
with ligands derived from N,N-dimethylbiguanide as potential
antimicrobials
Rodica Olar Æ Mihaela Badea Æ Dana Marinescu
MEDICTA2009 Conference
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract The reaction between [M(DMBG)2]ꢀnH2O ((1)
M:Ni, n = 0; (4) M:Cu, n = 1), ammonia/hydrazine and
formaldehyde in methanol resulted in new complexes of
type [ML]ꢀnH2O ((2) M:Ni, L:L1, n = 0; (3) M:Ni, L:L2,
n = 0, (5) M:Cu, L:L1, n = 0 and (6) M:Cu, L:L2, n = 3;
HDMBG: N,N-dimethylbiguanide, L1 = ligand resulted
from ammonia system and L2 = ligand resulted from
hydrazine system). The features of complexes have been
assigned from microanalytical, IR and UV–Vis data. The
thermal transformations of compounds are complex pro-
cesses according to TG and DTG curves including melting,
phase transition, dehydration, oxidative condensation of
–C=N– units as well as thermolysis processes. The final
products of decomposition are the most stable metal oxides.
to compatibility with a remarkably wide range of metal
ions, specially that have ability to form square planar
complexes as Ni(II) and Cu(II) [8, 9]. A common feature of
these systems is that the anionic forms of the ligands that
occur in the corresponding neutral divalent metal com-
plexes exhibit self-complementary doublet donor–acceptor
(DA) hydrogen bonding motifs [10]. This ability confers to
such complexes the ability to interact with biomolecules
also. It is worth to mention that the Y-shaped CN3 unit is
component of some bioligands as creatine, creatinine and
guanine. This indicates that the biguanide complexes have
the ability to selective recognize the biomolecules that
contain such units.
It was shown also that the N,N-dimethylbiguanide as
well as its complexes, with the neutral or anionic form of
the ligand, display an interesting thermal behaviour [4–7].
Moreover, in last years, many studies concerning the Ni(II)
and Cu(II) complexes that show a good antimicrobial
activity were published [11–19].
Keywords Complex ꢀ N ꢀ N-dimethylbiguanide ꢀ
One pot condensation ꢀ Thermal behaviour
Introduction
In order to improve the biological activity of Ni(II) and
Cu(II) complexes with biguanide moiety, new complexes
with such units incorporated in a macrocycle have been
synthesized and characterized. The thermal behaviour of
these derivatives was investigated by thermal analysis (TG,
DTA) in order to evidence the modifications appeared at
heating and also the thermodynamics effects that accom-
pany them.
N,N-dimethylbiguanide (HDMBG) and its complexes present
a broad spectrum of biological activity. They act as hypogly-
cemic agents but display also the analgesic, antimalarial,
antimetabolite, cytostatic as well as antimicrobial activity
[1–7].
As a species containing the Y-shaped CN3 unit, in
neutral or anionic form, is capable of exhibiting a variety of
coordination modes and a range of donor properties leading
Experimental
R. Olar (&) ꢀ M. Badea ꢀ D. Marinescu
Faculty of Chemistry, Department of Inorganic Chemistry,
University of Bucharest, 90-92 Panduri Str., Sector 5,
050663 Bucharest, Romania
Materials and methods
All reagents were of commercial analytical quality and
have been used without further purification. Chemical
e-mail: rodica_m_olar@yahoo.com
123

894
R. Olar et al.
analysis of carbon, nitrogen and hydrogen has been per-
formed using a Perkin Elmer PE 2400. Copper was deter-
mined using the thiosulphate method while the nickel was
determined gravimetrically as dimethylglyoximate.
[Cu(L2)]ꢀ3H2O (6): Analysis, found: Cu, 12.93; C,
29.58; H, 6.98; N, 40.37, CuC12H34N14O3 requires: Cu,
13.07; C, 29.65; H, 7.05; N, 40.34, IR (KBr pellet), cm-1
:
m(OH), mas(NH2), ms(NH2), 3420vs, large; m(C=N), 1698vs,
1635s; m(chelate ring), 1350w; m(C–M), 1086w; m(Cu–N),
419w.
IR spectra were recorded in KBr pellets with a Bruker
Tensor 37 spectrometer in the range 400–4000 cm-1
.
Electronic spectra by diffuse reflectance technique, with
MgO standard, were recorded in the range 300–1500 nm,
on a Jasco V670 spectrophotometer.
Results and discussions
The heating curves (TG and DTA) were recorded using
a Labsys 1200 SETARAM thermobalance with a sample
mass between 5 and 20 mg over the temperature range of
20–900 °C and a heating rate of 10 °C/min. The mea-
surements were carried out in synthetic air atmosphere
(flow rate 16.66 cm3/min) by using alumina crucible.
The melting was evidenced with Automated Melting
Point System (AMPS) MPA 100 OptiMelt Stanford Research
System.
Synthesis and physico-chemical characterization
of compounds
In this paper, we report the physico-chemical as well as
thermal characterization of N,N-dimethylbiguanidinium
(HDMBG) complexes [M(DMBG)2]ꢀnH2O ((1) M:Ni, n = 0;
(4) M:Cu, n = 1), complexes synthesised according to
literature data [8, 9]. Manipulation of [M(DMBG)2]ꢀnH2O
complexes by one pot condensation with ammonia or
hydrazine and formaldehyde, has resulted in neutral new
complexes [ML]ꢀnH2O ((2) M:Ni, L:L1, n = 0; (3) M:Ni,
L:L2, n = 0, (5) M:Cu, L:L1, n = 0 and (6) M:Cu, L:L2,
n = 3; L1 = ligand resulted from ammonia system and
L2 = ligand resulted from hydrazine system).
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 a 2h range of 5–70°, a step
width of 0.05° and an acquisition time of 2 s on each step.
The IR spectra of complexes reveal the characteristic
bands of biguanide moiety. In the range 1630–1700 cm-1
Synthesis and spectral data of the complexes
,
two intense bands characteristic to m(C=N) vibration mode
appears shifted also to higher wavenumbers in the com-
plexes spectra as result of coordination. The new band at
about 1350 cm-1 can be associated with the chelate ring
formation by the biguanide derivatives [20]. The water
presence in complexes (4) and (6) generates a band or a
shoulder around 3400 cm-1 [21].
The syntheses and structural data for complexes [M(DM
BG)2] were reported elsewhere [8, 9]. The composition of
complexes has been confirmed by chemical analyses.
Syntheses of the compounds [ML]: To a suspension of
[M(DMBG)] (5 mmol) in 100 mL methanol was added
drop wise 2 mL formaldehyde (37%) and 5 mL ammonia/
hydrazine. The reaction mixture was refluxed 24 h until a
sparingly soluble compound was formed. The microcrys-
talline product was filtered off, washed with EtOH and air-
dried.
[Ni(L1)] (2): Analysis, found: Ni, 14.65; C, 36.27; H,
6.51; N, 42.41, NiC12H26N12 requires: Ni, 14.78; C, 36.29;
H, 6.60; N, 42.33; IR (KBr pellet), cm-1: mas(NH2), 3338m,
3364m; ms(NH2), 3209m; mas(CH3), 2968w; ms(CH3), 2890w;
m(C=N), 1685vs, 1650s; d(NH2), 1613m, 1514m; m(chelate
ring), 1341w; m(C–M), 1123w, 1079w; c(NH2), 897w, 814w;
m(Ni–N), 425w.
Electronic spectra of the complexes show a single nar-
row band at about 21000 cm-1, as is usually observed for
Ni(II) and Cu(II) complexes with a square planar stereo-
chemistry [22].
The coordination proposed for new complexes accord-
ing with these data together with that known one for
complexes (1) and (4) [8, 9] are presented in Fig. 1.
Thermal behaviour of compounds
[Ni(L2)] (3): Analysis, found: Ni, 13.68; C, 33.68; H,
6.54; N, 46.03, NiC12H28N14 requires: Ni, 13.74; C, 33.74;
H, 6.61; N, 45.91, IR (KBr pellet), cm-1: mas(NH2), 3388s,
3364s; ms(NH2), 3209s; m(C=N), 1684vs, 1651vs; m(chelate
ring), 1346w; m(C–M), 1080w; m(Ni–N), 419w.
The results concerning the thermal degradation in synthetic
air of the compounds evidenced difference concerned their
thermal behaviour and the general aspect of the TG and
DTA curves.
The complex (1) is anhydrous so no detectable change in
TG curve up to 257 °C is observed. It is worth to mention
that in the 119–217 °C range an endothermic effect can be
noticed on the DTA curve (Fig. 2; Table 1). This behav-
iour could be generated by a phase transition as a result of
hydrogen bonds reorganization by temperature increasing.
[Cu(L1)] (5): Analysis, found: Cu, 15.74; C, 35.77; H,
6.41; N, 41.87, CuC12H26N12 requires: Cu, 15.81; C, 35.86;
H, 6.52; N, 41.82; IR (KBr pellet), cm-1: mas(NH2), 3400m,
3359m; ms(NH2), 3209s; m(C=N), 1678vs, 1646s; m(chelate
ring), 1323w; m(C–M), 1122w, 1078w m(Cu–N), 437w.
123

Thermal study of some new Ni(II) and Cu(II)
895
CH3
IR and powder X-ray diffraction data (ASTM 78-0423).
The endothermic effect noticed over 735 °C is associated
with the NiO crystallisation.
CH3
N
N
N
M
N
NH2
N
N
M
N
NH2
H3C
H3C
N
N
N
N
According to the TG profile the decomposition of
complex (2) occurs in two steps with nickel oxide as final
product (found/calcd. overall mass loss: 80.9/81.2). This
species is very stable and the thermal transformation starts
with this melting at 272 °C (Fig. 3).
The oxidative degradation starts immediately and the
observed mass variation during the first step corresponds to
the loss of a part of ligand with NiO(CN)8 formation
according to the chemical analysis and IR spectrum. The
paracyanide formation generates bands at 1616 (m(C=N)),
1313 (m(C=C)) and 787 cm-1(m(C–C)) in the IR spectrum.
The weak band at 526 cm-1 can be assigned also to the
m(Ni–O) vibration mode, indicating the generation of this
species in the paracyanide network. The final step is an
overlapping of at least three processes according to DTA
curve.
HN
HN
NH
NH
N
R
R
CH3
CH3
N
H2N
1
H2N
N
H3C
CH3
(2) [Ni(L )]
(R=H)
(R=NH2)
(R=H)
(1) [Ni(HDMBG) ]
(4) [Cu(HDMBG) ] H2O
2
2
2
(3) [Ni(L )]
.
1
(5) [Cu(L )]
(6) [Cu(L )] 3H2O (R=NH2)
2
.
Fig. 1 The known coordination for complexes (1) and (4) and the
proposed one for new complexes
20
10
10
0
The anhydrous complex (3) is stable up to 187 °C;
the endothermic effect observed on the DTA curve in the
86–143 °C range (Fig. 4) is generated by a phase transi-
tion. After the thermal decomposition starts, the interme-
diate melts also at 282 °C. The oxidative degradation
occurs in at least two processes (according to both TG and
DTA curves) with NiO(CN)8 formation (bands in the IR
spectrum at 1617 and 1507 (m(C=N)), 1340(m(C=C)),
792(m(C–C)) and 470 cm-1 m(Ni–O)). The next step is an
overlap of five exothermic processes as DTA indicates
generating nickel oxide as final product (found/calcd.
overall mass loss: 81.9/82.6%).
–10
–20
–30
–40
–50
–60
–70
–80
0
–10
–20
0
200
400
600
800
1000
The same observation can be made for the copper
complexes thermal behaviour. The complex (4) decom-
poses in three steps as result of water elimination in the
range 88–167 °C (Fig. 5). The low temperatures that cor-
respond to this transformation are an indicative of unco-
ordinated nature of these water molecules as was observed
for other complexes also [23–26].
Temperature/°C
Fig. 2 TG and DTA curves of [Ni(DMBG)2] (1)
Also, after the thermal decomposition starts, the interme-
diate melts at 286 °C, process evidenced with the Auto-
mated Melting Point System (AMPS) also.
In the IR spectrum of anhydrous complex isolated at
170 °C, the shoulder at 3310 cm-1 assigned to m(OH) dis-
appears. The decomposition of the anhydrous species starts
immediately and comprises three processes, one endo and
two exothermic (according to both TG and DTA profiles),
the endo one being assigned to an intermediate melting at
219 °C. The ligand degradation occurs also in this step
with paracyanide generation as the IR spectrum indicates
((bands at 1533 (m(C=N)), 1318(m(C=C)), 783(m(C–C)) and
472 cm-1, m(Cu–O). The formed intermediate CuO(CN)4, in
the next step leads to CuO as IR (517 cm-1, m(Cu–O)) and
X-ray diffraction indicate (ASTM 5-661) (found/calcd.
overall mass loss: 70.4/71.1%). According to both TG and
DTA curves, this last step is an overlap of at least three
processes.
According to the mass lost, the intermediate formed
after this step is a parcyanide species of type NiO(CN)6.
The IR spectrum of this intermediate display indeed the
characteristic bands of the paracyanide species at 1617 and
1507 (m(C=N)), 1340 (m(C=C)) and 792 cm-1(m(C–C)) [5–7].
The shoulder at 480 cm-1 can be assigned to the m(Ni–O)
vibration mode [22] having in view that in the NiO spec-
trum this appear as a intense and sharp band at 460 cm-1
.
Next step is a very complex one being an overlapping of
at least five processes as DTA indicates. This could com-
prise stepwise depolymerization and oxidative degradation
of paracyanide leading finally to the non-stoichiometric
nickel(II) oxide (found/calcd. overall mass loss: 76.1/
76.3%). The nature of final product was assigned based on
123

896
R. Olar et al.
Table 1 Thermal behaviour of the complexes in synthetic air flow
Compound
Step
Thermal effect
Temperature range/°C
Dmexp/%
Dmcalc/%
[Ni(DMBG)2] (1)
1.
Endothermic
Miscellaneous
Exothermic
119–217
257–328
328–735
0
0
2.
26.9
49.2
23.9
0
26.7
49.6
23.7
0
3.
Residue NiO
[Ni(L1)] (2)
1.
Endothermic
Exothermic
Exothermic
272a
2.
272–380
380–670
28.7
52.2
19.1
0
28.8
52.4
18.8
0
3
Residue NiO
[Ni(L2)] (3)
1.
Endothermic
Miscellaneous
Exothermic
86–143
2.
187–357
357–600
45.3
36.6
18.1
5.3
46.0
36.6
17.5
5.3
3.
Residue NiO
[Cu(DMBG)2]ꢀH2O (4)
1.
Endothermic
Miscellaneous
Exothermic
88–167
2.
167–385
385–605
39.7
30.7
29.6
0
40.3
30.8
28.9
0
3.
Residue CuO
[Cu(L1)] (5)
1.
Endothermic
Exothermic
Exothermic
210a
2.
210–326
326–650
32.0
47.8
20.2
11.0
61.6
10.4
17.0
32.4
47.8
19.8
11.1
61.8
10.7
16.4
3.
Residue CuO
[Cu(L2)]ꢀ3H2O (6)
1.
Endothermic
Exothermic
Exothermic
60–120
2.
120–330
330–650
3.
Residue CuO
a
Melting point
30
20
30
25
20
15
0
–20
0
–20
–40
–60
10
0
–40
10
5
–10
–20
–30
–40
–60
0
–80
–80
–5
–100
–100
–10
1000
0
200
400
600
800
1000
0
200
400
600
800
Temperature/°C
Fig. 3 TG and DTA curves of [Ni(L1)] (2)
Temperature/°C
Fig. 4 TG and DTA curves of [Ni(L2)] (3)
The anhydrous species (5) is very stable up to 210 °C
(Fig. 6). After melting at 210 °C, the decomposition starts
immediately and leads to CuO(CN)8. The IR spectrum of
this intermediate display the characteristic paracyanide
bands together with a band at 472 cm-1 assigned to m(Cu–O).
The next step is an overlap of three processes and the mass
variation corresponds to the paracyanide loss. The mass
variation is in accord with the calculated one (found/calcd.
overall mass loss: 79.8/80.2%).
For complex (6) the water is lost in the first step (Fig. 7)
and the low temperatures corresponding to this step indi-
cates its nature as crystallization one [23–26].
123

Thermal study of some new Ni(II) and Cu(II)
897
60
50
40
30
20
10
0
In the IR spectrum of anhydrous complex isolated at
120 °C the band at 3420 cm-1 assigned to m(OH) disap-
pears. In the 120–300 °C range, the endothermic process
with a mass loss of 61.84% is assigned to a large amount of
ligand oxidation with CuO(CN)2 formation (as the IR
spectrum indicates). The last step is assigned also to
paracyanide elimination in at least two processes with CuO
stabilisation as final residue (found/calcd. overall mass
loss: 83.0/83.6%).
0
–20
–40
–60
–80
–10
–20
–30
1000
Conclusions
0
200
400
600
800
Temperature/°C
Nickel(II) and copper(II) complexes with ligands bearing
biguanide moiety were obtained by one pot condensation
and characterised in order to develop new effective anti-
microbial agents.
Fig. 5 TG and DTA curves of [Cu(DMBG)2]ꢀH2O (4)
The IR spectra indicate the biguanide moieties coordi-
nation while the electronic spectra are consistent with a
square-planar stereochemistry for all complexes.
Some compounds or intermediates melt before or during
the thermal transformation that occur in two or three steps
and comprise water elimination, biguanide moiety trans-
formation as well as paracyanide decomposition. The final
residue was metal(II) oxide in all cases as both IR and
powder X-ray diffraction indicate.
40
30
0
–20
–40
–60
–80
20
10
0
–10
–20
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