Spectroscopic and magnetic studies of some copper(II) and chromium(III) complexes with dithiophosphonates as ligands

Article abstract of DOI:10.1016/S0022-2860(98)00931-4

Cu(II)-bis[4-ethoxyphenyl-O-alkyl]-dithiophosphonate and Cr(III)- tris[4-ethoxyphenyl-O-alkyl]-dithiophosphonate complexes (alkyl = methyl, ethyl, isopropyl) were prepared and studied by magnetic measurements, and electronic, IR and EPR spectroscopic stud

Full text of DOI:10.1016/S0022-2860(98)00931-4

MOLSTR 10786
Journal of Molecular Structure 482–483 (1999) 153–157
Spectroscopic and magnetic studies of some copper(II) and
chromium(III) complexes with dithiophosphonates as ligands
a
b,
b
a
a
b
*
I. Haiduc , L. David , O. Cozar , R. Micu-Semeniuc , G. Mezei , M. Armenean
aDepartment of Chemistry, Babes-Bolyai University, 3400 Cluj-Napoca, Romania
bDepartment of Physics, Babes-Bolyai University, 3400 Cluj-Napoca, Romania
Received 24 August 1998; received in revised form 30 November 1998; accepted 4 December 1998
Abstract
Cu(II)–bis[4-ethoxyphenyl-O-alkyl]-dithiophosphonate
and
Cr(III)–tris[4-ethoxyphenyl-O-alkyl]-dithiophosphonate
complexes (alkyl ˆ methyl, ethyl, isopropyl) were prepared and studied by magnetic measurements, and electronic, IR and
EPR spectroscopic studies. The valence vibrations of the PS2 group show that this group coordinates isobidentate. The
2
2
electronic spectra of copper(II) complexes display two weak bands at 15 200 and 18 500 cmϪ1, (2B1g ! A1g and B1g
!
2Eg) and an intense band at 23 000 cmϪ1 (L ! M charge-transfer). The powder EPR spectra of Cu (II) complexes are typical for
square-planar monomeric species and present hyperfine and superhyperfine structure. These results suggest that the copper(II)
complexes have D4h symmetry. Two bands were observed in the UV-Vis spectra of the chromium complexes at 14 320 and
18 640 cmϪ1 (4A2g(F) ! T2g(F) and 4A2g(F) ! T1g(F)). The EPR bands of the Cr(III) complexes may be attributed to isolated
metallic ions in pseudoocthaedral surroundings and to Cr(III) ions coupled by dipole–dipole interaction. ᭧ 1999 Elsevier
Science B.V. All rights reserved.
4
4
Keywords: Bis[4-ethoxyphenyl-O-alkyl]-dithiophosphonates; Metal complexes; IR spectra; EPR spectra; Magnetic moments
1. Introduction
measurements. The anion structure of the ligands used
is presented in Fig. 1.
Dithiophosphonate complexes have long been
known to possess biologically important properties
[1]. Dithiophosphonate compounds may also inhibit
hydrocarbon oxidation [2]. To clarify the mechanism
of their action the investigation of their structure is
necessary. In this article the structures of new copper–
bis[4-ethoxyphenyl-O-alkyl]-dithiophosphonate and
chromium–tris[4-ethoxyphenyl-O-methyl, ethyl, iso-
propyl]-dithiophosphonate complexes were studied by
means of electronic, IR and EPR spectroscopic
2. Experimental
4-Ethoxyphenyl-thionophosphine sulfide was
prepared by the method of Lecher et al. [3]. This
thionophosphine sulfide reacted with various alcohols
to generate 4-ethoxyphenyl-O-alkyl-dithiophos-
phonic acids (alkyl ˆ methyl, ethyl, isopropyl).
These acids were converted to the ammonium salts
by reaction with dry NH3 in a cooled benzene
solution.
* Corresponding author. Tel.: 0040-64-194315; fax: 0040-64-
191906.
E-mail address: leodavid@hera.ubbcluj.ro (L. David)
The chromium(III) and copper(II) compounds were
prepared by metatheses in aqueous solutions of the
0022-2860/99/$ - see front matter ᭧ 1999 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(98)00931-4

154
I. Haiduc et al. / Journal of Molecular Structure 482–483 (1999) 153–157
4
4
and 18 640 cmϪ1, are assigned to A2g(F) ! T2g(F)
4
4
(n1) and A2g(F) ! T1g(F) (n2) transitions. The third
band (4A2g(F) ! T1g(P)) expected in the UV domain
4
is obscured by the charge-transfer and ligand-specific
bands.
The first broad but not split band (n1), yields the
10 Dq parameter, while the second (n2) shows a
shoulder at 19 120 cmϪ1. This can be explained by a
small distortion from the ideal octahedral symmetry,
because of the Jahn–Teller effect, spin–orbit coupling
and to mixing of neighboring quartet–doublet states
Fig. 1. Anion structure of [4-ethoxyphenyl-O-alkyl]-dithiopho-
sphonate ligands (alkyl ˆ methyl, ethyl, isopropyl).
above ammonium salts and CuSO4·5H2O or
Cr(NO3)3·6H2O in stoichiometric amounts. The
resulting insoluble metal compounds (Cr[S2P(OMe)-
2
2
(4T1g and T2g or A1g).
The position of the third band and the spectral para-
meters were calculated by the method proposed by
Lever [4], using a value of 918 cmϪ1 for the interelec-
tronic repulsion constant [5]. The obtained values are:
Dq/B ˆ 3.5, n3/B ˆ 74.3, B ˆ 409.1, b ˆ 0.445, n3 ˆ
C6H4OEt]3
–
1a; Cr[S2P(OEt)C6H4OEt]3
– 1b;
Cr[S2P(OiPr)C6H4OEt]3
–
1c; Cu[S2P(OMe)-
C6H4OEt]2 – 2a; Cu[S2P(OEt)C6H4OEt]2 – 2b;
Cu[S2P(OiPr)C6H4OEt]2 – 2c) were filtered off and
thoroughly washed with cold distilled water. The
complexes were characterized by elemental analysis
and melting points (Table 1).
Magnetic moment studies were carried on a
Faraday balance. The electronic spectra of the synthe-
sized compounds in CHCl3 solution were recorded
with a SPECORD UV-VIS spectrometer, in the region
13 000–30 000 cmϪ1. IR spectra were recorded with
KBr pellets on a UR20 Carl Zeiss Jena spectrometer.
The EPR spectra were recorded at 9.4 GHz (X band)
using a standard JEOL-JES-3B equipment with a
magnetic field modulation of 100 kHz.
30 400 cmϪ1
.
This latter band (n3), assigned to a forbidden
transition of two electrons, should have low
intensity.
In these complexes, both the interelectronic repul-
sion and the nephelauxetic parameters have very low
values (b ˆ 0.445); although low, this value is usual
for chromium complexes with sulfur as donor atoms
[6], indicating high covalency of the chromium–
sulfur bonds.
Three absorption bands can be observed for the
copper complexes: two weak bands at 15 200 and
2
2
2
18 500 cmϪ1 (2B1g ! A1g and B1g ! Eg) and an
intense band at 23 000 cmϪ1, (L ! M charge-
transfer). Similar bands are observed also for other
Cu(II) dithiophosphates [7, 8]; their positions indicate
a square-planar geometry around the copper atom
involved in the CuS4 chromophore.
3. Results and discussion
3.1. Electronic spectra
Two bands of the chromium complexes, at 14 320
Table 1
Characteristics of the synthesized compounds
Compound
Color
Yield (%)
m.p. (ЊC)
Elemental analysisa (%)
C
H
S
1a
1b
1c
2a
2b
2c
Violet
Violet
Violet
Brown
Brown
Brown
71
68
69
95
96
95
120
93
75
165 (dec.)
185 (dec.)
195 (dec.)
40.77 (40.85)
42.73 (43.10)
44.86 (45.14)
38.27 (38.74)
40.56 (40.98)
42.93 (43.02)
5.01 (4.57)
5.33 (5.06)
5.89 (5.51)
4.53 (4.33)
5.14 (4.82)
5.49 (5.25)
24.08 (24.23)
22.85 (23.01)
21.56 (21.91)
22.86 (22.98)
21.75 (21.88)
20.49 (20.88)
a Calculated values are given in brackets.

I. Haiduc et al. / Journal of Molecular Structure 482–483 (1999) 153–157
155
Fig. 2. Powder EPR spectrum of Cu(II)–bis[4-ethoxyphenyl-O-methyl]-dithiophosphonate at room temperature. Extended parallel (a) and
perpendicular (b) absorptions.
3.2. IR spectra
remain almost constant (ya Ϸ 644 cmϪ1 for the Cr(III)
complexes and ya Ϸ 640 cmϪ1 for the Cu(II)
complexes), while ns slightly decreases with the
increasing of the aliphatic chain attached to the phos-
phorus atom (ys ˆ 567 cmϪ1(1a), 563 cmϪ1(1b),
536 cmϪ1(2c)). This fact can be related to electron-
repulsive effects of the organic radicals. This effect
increases the negative charge density on the phos-
phorus atom and through this, on the sulfur atoms.
Consequently, the sulfur atoms gain stronger donor
Vibrational spectra gave useful information
concerning the coordination made of the PS2 group,
whose vibrations can be considered as group-vibra-
tions (na and ns). The assignments were qualitatively
made by comparison with the spectrum of ammonium
562 cmϪ1(1c),
542 cmϪ1(2a),
537 cmϪ1(2b),
4-ethoxyphenyl-O-methyl-dithiophosphonate (ya
ˆ
632 cmϪ1, ys ˆ 568 cmϪ1) and with some data from
the literature [9, 10].
From the IR data we can infer that the na frequencies

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I. Haiduc et al. / Journal of Molecular Structure 482–483 (1999) 153–157
Table 2
EPR parameters of Cu(II)–bis[4-ethoxyphenyl-O-alkyl]-dithiophosphonate complexes
31P
Compound
g0
A0 (G)
g
k
gЌ
A (G)
k
AЌ (G)
a0 (G)
a2
b2
d 2
2a
2b
2c
2.048
2.047
2.045
69
71
70
2.097
2.095
2.093
2.025
2.023
2.024
145
150
145
34
31
34
7.5
7.6
7.3
0.537
0.547
0.532
0.460
0.504
0.457
0.582
0.525
0.567
capacity, the covalence degree of the chromium–
sulfur bond increases and the ns frequency decreases.
The constant values of na might be related to the fact
that the PS(1) vibration is more involved, while the
small variations of ns values result from both contri-
butions of PS(1) and PS(2) vibrations.
according to Kivelsson and Neiman [11] using the
EPR parameters and the optical spectral data. The
MO parameters (Table 3) indicate that the s bonding
is very covalent and that the p bonds are also appre-
ciably covalent, the in-plane p bonding being
stronger.
All these results show that the copper(II) complexes
have approximately D4h symmetry with a weak D2h
perturbation.
Fig. 3 show the typical EPR spectra of the benzene
Cu(II)–bis[4-ethoxyphenyl-O-methyl, ethyl, iso-
propyl]-dithiophosphonate solutions at room tempera-
ture. The spin Hamiltonian for the investigated
complexes in solution is:
3.3. EPR spectra
The powder EPR spectra of the Cu(II)–bis[4-ethox-
yphenyl-O-methyl, ethyl, isopropyl]-dithiophospho-
nate complexes at room temperature are typical for
square-planar monomeric species (Fig. 2). The sharp
of the spectra show the metallic hyperfine and super-
hyperfine structure.
31P
The spin Hamiltonian used for the axial symmetric
investigated complexes is:
H ˆ g0bBS ϩ A0SI ϩ a0 SIP
where g0 is the isotropic g value, A0 and a031P are the
isotropic values of the hyperfine splitting for 63,65Cu
and 31P, respectively. The isotropic EPR parameters
for investigated complexes are given in the Table 3.
The hyperfine splitting of the EPR spectra in solu-
tion owing to the nuclear spins of the copper isotopes
was resolved at room temperature (for 63Cu and 65Cu
I ˆ 3/2). An additional splitting was observed at the
h
ꢀ
ꢁi
H ˆ b g BzSz ϩ gЌ BxSx ϩ BySy ϩ A SzIz
k
k
2
ꢀ
ꢁ
X
31P
ϩ AЌ SxIx ϩ SyIy ϩ S
a I
Pn
nˆ1
where g and gЌ are the principal values of the g
k
tensor, b is the Bohr magneton, Bx, By and Bz are
the components of the external magnetic field, Sx, Sy
and Sz are the components of the electron magnetic
moments S, Ix, Iy and Iz are the components of the
nuclear spin moment of 63,65Cu and IP the nuclear
spin moment of 31P and a31n the superhyperfine tensor.
The resulted EPR parameters are given in Table 2.
The metal–ligand bond parameters were calculated
Table 3
EPR parameters of Cr(III)–tris[4-ethoxyphenyl-O-alkyl]-dithio-
phosphonate complexes
Compounds g1
g2
D (cmϪ1
)
DB (G) meff (BM)
1a
1b
1c
4.337 1.984 0.100
4.316 1.994 0.094
4.379 1.990 0.096
520
457
369
3.65
3.62
3.60
Fig. 3. EPR spectrum of benzene Cu (II)–bis[4-ethoxyphenyl-O-
isopropyl]-dithiophosphonate solution at room temperature.

I. Haiduc et al. / Journal of Molecular Structure 482–483 (1999) 153–157
157
forbidden transitions the zero-field splitting para-
meters were calculated (Table 3) [14]. These results
suggest a small distortion of the octahedral Cr(III)
environment.
4. Conclusion
The spectroscopic studies of the sulfur-coordinated
copper(II) complexes give insight into the covalent
bonding of metal ion in the molecule. Both s and p
bonds are considerably covalent. The local symmetry
around copper(II) is dominated by the values of the
Cu spin Hamiltonian parameters, although ligand
super hyperfine interactions may suggest considerable
reduction of symmetry.
For the Cr(III) complexes with tris[4-ethoxy-
phenyl-O-alkyl]-dithiophosphonate the interaction of
metallic ions with these ligands occur through the
dithiophosphonate group in a pseudo-octahedral
geometry. The EPR absorption at g Ϸ 2 and the values
of the magnetic moments also suggest the presence of
antiferromagnetic coupling between Cr(III) ions.
Fig. 4. Powder EPR spectrum of Cr (III)–tris[4-ethoxyphenyl-O-
methyl]-dithiophosphonate at room temperature.
line corresponding to mI ˆ Ϫ 3/2, owing to the super-
position of the lines for the two copper isotope, with
slightly different magnetic moments. The intensity
ratio of these two lines corresponds to the natural
abundance of the copper isotopes. The hyperfine lines
of EPR spectra were additionally split into three compo-
nents with intensity ratio 1 : 2 : 1. This superhyperfine
References
31P
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