Copper(II) and Nickel(II) alkylxanthate complexes (R = C2H 5, i-C3H7, i-C4H9, s-C4H9, and C5H11): EPR and solid-state 13C CP/MAS NMR s

Article abstract of DOI:10.1023/B:RUCO.0000034788.80316.d5

Alkylxanthate complexes of the general formula [MS(S)COR₂] (M = Ni, ⁶³Cu, and ⁶⁵Cu; R = C₂H₅, i-C₃H₇, i-C₄H₉, s-C ₄H₉, and C₅

Full text of DOI:10.1023/B:RUCO.0000034788.80316.d5

Russian Journal of Coordination Chemistry, Vol. 30, No. 7, 2004, pp. 480–485. Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 7, 2004, pp. 514–519.
Original Russian Text Copyright © 2004 by Ivanov, Bredyuk, Antzutkin, Forsling.
Copper(II) and Nickel(II) Alkylxanthate Complexes
(R = C2H5, i-C3H7, i-C4H9, s-C4H9, and C5H11):
EPR and Solid-State 13C CP/MAS NMR Studies
A. V. Ivanov*, O. A. Bredyuk**, O. N. Antzutkin***, and W. Forsling***
* Amur Institute of Integrated Research, Amur Scientific Center, Far East Division, Russian Academy of Sciences,
Relochnyi per. 1, Blagoveshchensk, 675000 Russia
** Blagoveshchensk State Pedagogical University, Blagoveshchensk, 675000 Russia
*** Luleå University of Technology, S-971 87, Luleå, Sweden
Received July 4, 2003
Abstract—Alkylxanthate complexes of the general formula [M{S(S)COR}2] (M = Ni, 63Cu, and 65Cu; R =
C2H5, i-C3H7, i-C4H9, s-C4H9, and C5H11) were synthesized and studied by EPR and high-resolution solid-state
13C CP/MAS NMR. In the copper(II) complexes stabilized in the matrix of nickel(II) compounds, square planar
chromophores [CuS4] are characterized by rhombic distortion (EPR data). Experimental EPR spectra were sim-
ulated at the second order of perturbation theory. Nickel(II) complexes were characterized by 13C NMR spectra.
In all cases, the –OC(S)S– groups were found to exhibit intramolecular structural equivalence.
Xanthate derivatives have found a wide practical
application as additives to lubricating oils, antioxidants
for polyolefins, etc. However, alkylxanthates are
mainly used in flotation concentration of nonferrous
metal sulfide ores. Hence, it is of interest to investigate
complexation between transition metals and alkylxan-
thate ligands for better understanding of how the flota-
tion reagent ions interact with the surface of mineral
species.
EXPERIMENTAL
Ni(II) complexes of the formula [Ni{S(S)COR}2]
(R = C2H5 (I), i-C3H7 (II), i-C4H9 (III), s-C4H9 (IV),
and C5H11 (V)) were synthesized by reactions of Ni+2
with the corresponding alkylxanthate ions in aqueous
solutions. Voluminous greenish yellow precipitates
were washed by decantation, filtered off, and dried in
air. Individual copper(II) alkylxanthate complexes can-
not be isolated because they are immediately involved
in the intermolecular redox reaction yielding copper(I)
compounds and the corresponding dixanthogens:
Previously [1], the structures of VO2+ complexes
with alkylxanthates and their chemical properties in
reactions of the adduct formation with cyclic S-donor
bases were studied by EPR. The structures of copper(II)
alkylxanthate complexes were investigated in the matri-
ces of corresponding thallium(I) complexes [2]. Analy-
sis of resolved super-hyperfine structure (HFS) from
thallium atoms in the experimental EPR spectra made
it possible to identify heteropolynuclear Cu(II)-Tl(I)
complexes of the general formula [CuTl6(Xan)8] (Xan =
ROC(S)S–; R = C2H5, C3H7, and C4H9) in the magneti-
cally diluted systems studied. These heptanuclear com-
plexes are generated from paramagnetic copper(II)
compounds and diamagnetic matrices of thallium(I)
complexes and exhibit the Jahn–Teller dynamic effect.
2Cu2+ + 4ROC(S)S– = 2[Cu(S2COR)2]
= [Cu2(S2COR)2] + ROC(S)S–S(S)COR.
Copper(II)
complexes
of
the
formula
[Cu{S(S)COR}2] (R = C2H5 (VI), i-C3H7 (VII), i-C4H9
(VIII), and C5H11 (IX)) were synthesized in a state
magnetically diluted with the corresponding Ni(II)
compounds (Cu : Ni = 1 : 1000). Such a technique
allows one to stabilize [Cu{S(S)COR}2] molecules in
the matrix of nickel(II) complexes (except for plastic
[Ni{S(S)ëO-s-C4H9}2]) and study their structures and
spectroscopic properties. Copper(II) complexes were
obtained as isotope-substituted compounds from isotope-
enriched copper salts containing 63Cu (99.3(1) at. %) and
65Cu (99.2(1) at. %).
In this study, EPR and high-resolution solid-state
13C CP/MAS NMR techniques were used to investigate
the structures and spectroscopic properties of the com-
plexes [M{S(S)COR}2] (M = Ni(II) and Cu(II)) con-
taining alkylxanthate ligands ROC(S)S– (R = C2H5,
i-C3H7, i-C4H9, s-C4H9, and C5H11).
Sodium and potassium alkylxanthates (Cheminova
Agro A/S and Hoechst) were additionally characterized
by 13C MAS NMR data:
Na{S2ëOC2H5} (δ, ppm): 231.1, 230.0, 229.5
(−S2CO–), 73.4, 72.6 (–OCH2–), 15.9, 14.5, 14.1 (–CH3).
1070-3284/04/3007-0480 © 2004 åÄIä “Nauka /Interperiodica”

COPPER(II) AND NICKEL(II) ALKYLXANTHATE COMPLEXES
DPPH DPPH
481
a
b
H
85 Oe
H
85 Oe
a'
b'
Fig. 1. Experimental EPR spectra of magnetically Ni(II)-diluted isotope-substituted complexes of the formula
63/65
63
65
[
Cu{S(S)COC H } ] as the (‡, ‡') first and (b, b') third derivatives for (a, b) Cu and (a', b') Cu isotopes.
2 5 2
Na{S2ëO-i-C3H7} (δ, ppm): 231.8 (–S2CO–), 79.2 resonance frequency [3]. Samples (~350 mg) of the
(–OCH=), 23.5, 20.6 (1 : 1, –CH3).
complexes were placed in a zirconium dioxide rotor
7.5 mm in diameter. The spinning rates in 13C MAS
NMR experiments were 2700 to 5500 Hz; the number
of scans was 256 to 2820; the duration of proton π/2
Na{S2ëO-i-C4H9} (δ, ppm): 233.4, 232.8, 232.4,
229.9 (–S2CO–), 81.2 (–OCH2–), 28.5 (–CH=), 21.7,
21.1, 20.2 (–CH3).
Na{S2ëO-s-C4H9} (δ, ppm): 231.9 (–S2CO–), 84.0,
83.7 (–OCH=), 30.0, 29.2 (–CH2–), 19.4, 17.2 (1 : 1,
−CH3), 12.0 (–CH3).
K{S2ëOC5H11} (δ, ppm): 234.0, 233.5 (–S2CO–),
80.9, 75.5 (1 : 3, –OCH2–), 35.0, 28.5, 27.5, 23.2, 20.8,
17.9 (−CH2–), 17.0, 14.5, 12.5 (–CH3).
EPR spectra were recorded on a 70-02 XD/1
radiospectrometer (~9.5 GHz, MP SZ, Minsk) at
~295 K. The working frequency was measured with a
ChZ-46 microwave frequency meter. g Factors were
calculated with reference to DPPH. The errors in g
value and HFS constant (Oe) determination were
0.002 and 2%, respectively. The EPR parameters
were refined by simulating the experimental spectra
within the second order of perturbation theory with the
use of the WIN-EPR SimFonia program (Bruker Co.
software, version 1.2).
1
pulses was 4.5 µs; the H–13C contact time was 2.0 to
5.0 ms; excitation pulses were spaced at 2.0 s.
Isotropic 13C chemical shifts δ (ppm) are referenced
to a line of crystalline adamantane used as the external
standard (δ 38.56 ppm relative to tetramethylsilane
[4]). The width of a reference line for crystalline ada-
mantane (2.1 Hz) was used to check the homogeneity
of the magnetic field. The isotropic chemical shifts
were corrected for drift of the magnetic field strength
during the NMR experiments (its frequency equivalent
13
for C nuclei was 0.051 Hz/h). Chemical shifts and
integrated intensity ratios for overlapping signals in the
13C NMR spectra were additionally refined by frag-
ment-by-fragment simulation considering line posi-
tions and widths and contributions from the Lorentz
and Gauss components to the line shapes.
The simulation was performed in two steps. First,
theoretical EPR spectra were simulated for first deriva-
tives and finally approximated for second and third
derivatives characterized by substantially narrower res-
onance signals. In the approximation, g values, HFS
constants, resonance line widths, and contributions (in
percent) from the Lorentz and Gauss components to the
line shape were varied.
RESULTS AND DISCUSSION
Experimental EPR spectra of magnetically diluted
copper(II) alkylxanthate complexes (Figs. 1, 2) are
nearly axially symmetric, which suggests the square
planar structure of chromophores [CuS4] with predom-
inant localization of the unpaired electron at the Cu
3dx2 – y2 AO. Therefore, the complexes obtained contain
Room-temperature 13C NMR spectra were recorded
on a CMX-360 pulse spectrometer (90.52 MHz; Che-
magnetics Infinity Co., USA) with a superconducting
magnet (B0 = 8.46 T) and a Fourier transform. The 13C–
1H cross polarization technique was used. The 13C–1H
dipolar couplings were suppressed via proton decou-
the sp2d-hybridized copper atom (s- + px- + py- + dx2 – y2
AO) and, since the 4d AO is involved, can be classified
as outer-orbital ones (in contrast to the corresponding
inner-orbital nickel(II) compounds).
In all cases, the computer simulation of the experi-
pling in a magnetic field with the corresponding proton mental spectra revealed noticeable anisotropy of g and
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 7 2004

482
IVANOV et al.
DPPH
DPPH
a
b
H
89 Oe
H
89 Oe
a'
b'
Fig. 2. (a, b) Experimental and (a', b') simulated EPR spectra of magnetically Ni(II)-diluted isotope-substituted bis(O-isobutylxan-
65
thato)copper(II), [ Cu{S(S)CO-i-C H } ], as the (‡, ‡') first and (b, b') third derivatives.
4
9 2
A tensors in the xy plane (Figs. 1, 2; Table 1), which can adducts with N-donor bases [19]. One can state that the
EPR spectra of copper(II) complexes accurately reflect
the structural features of nickel(II) alkylxanthates.
The experimental EPR parameters were refined by
computer simulation. The best fit results are given in
be attributed to rhombic distortion of the chelate unit
[CuS4] due to diagonal nonequivalence of the Cu–S
bonds. These conclusions are fully consistent with X-
ray diffraction data for the molecular structures of some
nickel(II) alkylxanthate complexes [5–18] and their Table 1. The totality of the parameters unambiguously
Table 1. EPR parameters of magnetically diluted copper(II) alkylxanthate complexes
Complex
g1
A1(Cu)*
g2
A2(Cu)*
g3
A3(Cu)*
[Cu(S2COC2H5)2]
[Cu(S2CO-i-C3H7)2]
[Cu(S2CO-i-C4H9)2]
[Cu(S2COC5H11)2]
2.094
2.085
2.084
156/167
154/165
155/166
152/163
2.029
2.026
2.026
2.028
35/38
39/42
39/42
42/45
2.022
2.021
2.019
2.023
32/34
35/37
35/37
34/36
2.086
63
65
* The HFS constants are given for Cu/ Cu nuclei.
Table 2. Chemical shifts (δ, ppm; Me4Si) of the signals in the 13C NMR spectra of crystalline nickel(II) complexes of the
formula [Ni{S(S)COR}2]
Complex
–OC(S)S–
–OCH2–
71.5
–OCH=
–CH=
–CH2–
–CH3
[Ni(S2COC2H5)2]
[Ni(S2CO-i-C3H7)2]
[Ni(S2CO-i-C4H9)2]
[Ni(S2CO-s-C4H9)2]
Melt
230.9
229.9
231.8
230.6
230.4
14.2
81.4
23.9, 23.0 (1 : 1)
21.6, 19.8 (1 : 1)
21.1
81.8
29.0
85.6, 84.7
30.6
83.3 d (148.5)*
30.0 t (126.7)*
13.2, 11.9
20.7 q (127.6)*
10.9 q (126.1)*
[Ni(S2COC5H11)2]
231.2 80.1, 75.8 (1 : 3)
35.6, 28.5 (1 : 3) 16.9, 14.5, 12.0 (1 : 2 : 1)
27.7, 26.5 (3 : 1)
22.8
1
13
1
* The spin–spin coupling constants J( C– H), Hz (d, t, and q denote doublet, triplet, and quadruplet, respectively).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 7 2004

COPPER(II) AND NICKEL(II) ALKYLXANTHATE COMPLEXES
483
(a)
*
*
*
*
(b)
(c)
(d)
*
*
*
*
*
*
*
*
*
*
*
*
250
200
150
100
50
0
δ, ppm
13
Fig. 3. C NMR spectra of polycrystalline complexes [Ni{S(S)COR} ] at 295 K (R = (a) C H , (b) i-C H , (c) i-C H , and (d)
2
2
5
3
7
4 9
C H ); number of scans/spinning rate are 1000/4600, 256/4300, 2820/5500, and 600/2700 Hz, respectively. Components obtained
5
11
13
as a result of incomplete averaging of the anisotropy of the C chemical shift in the MAS experiment are asterisked.
indicates the S-homogeneous environment of the cop- Table 2). The spectra contain resonance signals due to
per atom in all the complexes obtained. The EPR spec- –OC(S)S– fragments and the alkyl groups at the O
tra contain characteristic quartets of the resolved HFS atom. The –OC(S)S– fragments are manifested by a
from the 63/65Cu nucleus (I = 3/2) in all the three orien- single signal in the 13C NMR spectra (Fig. 3, Table 2),
tations and an additional intense high-field peak of which suggests the structural equivalence of the xan-
“extra feature” [20, 21]. Comparative analysis revealed thate ligands in complexes I–V. This correlates with the
a high qualitative similarity of the simulated and exper- mononuclear centrosymmetric structure of nickel(II)
imental EPR spectra. The former fit very exactly to the alkylxanthates [5–18].
latter as regards the positions and relative intensities of
Interestingly, in many nickel(II) dialkyldithiocarbam-
not only the HFS components of all the three orienta-
ate complexes, which are structurally close to alkyl-xan-
tions but also the additional peak, which is not at all
thate ones, the –C(S)S– fragments exhibit both intra-
represented parametrically in the simulation.
and intermolecular nonequivalence [22]. According to
13
According to the C NMR data, all the nickel(II) the 13C NMR data, the δ values of the –OC(S)S– frag-
complexes obtained are individual compounds (Fig. 3, ments are systematically much higher (230 to 232 ppm)
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 7 2004

484
IVANOV et al.
(a)
(b)
250
200
150
100
50
0
δ, ppm
13
Fig. 4. C NMR spectra of melted [Ni{S(S)CO-s-C H } ] at 295 K (a) without and (b) with proton decoupling (numbers of scans
4
9 2
are 152 and 300, respectively). The signal of the –OC(S)S– fragment is marked with an arrow.
than those of the =NC(S)S– groups in nickel(II) dialky-
ldithiocarbamate complexes (203–209 ppm), which is
due to the stronger displacement of the electron density
from the C atom of the –C(S)S– fragments in alkylxan-
thate complexes.
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