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Spectral and electrochemical studies on oxoisothiocyanatobis(pyrrolidinyldithiocarbamato)molybdenum(V)
Polyhedron Vol. 3. No. 8, pp. 907-909, Rinte4inlhcU.S.h.
1984
SPECTRAL AND ELECTROCHEMICAL STUDIES ON OXOISOTHIOCYANATOBIS(PYItROLIDINYLDITHIOCARBAMATO)MOLYBDENUM(V) K. S. NAGARAJA and M. R. UDUPA* Department of Chemistry, Indian Institute of Technology, Madras 600 036, India (Received 4 March 1983; accepted 17 January 1984) Abstract-The complex, oxoisothiocyanatobis(pyrrolidinyldithiocarbamato)molybdenum(V), MoO(NCS) (pyrroldtc), was prepared. The IR spectra of the complex suggest that the thiocyanate group is attached through nitrogen and the presence of Mo03+ moiety. The voltammograms of the complex in acetonitrile exhibited a pronounced cathodic wave at -0.23 V vs S.C.E. which was attributed to Mo(V)/Mo(IV) couple. The magnetic, epr and electrochemical studies indicate that the compound is mononuclear and molybdenum is in + 5 oxidation state.
In spite of the extensive development in the chemistry of bioucleat ma1_ykkaurn~ compkxes in r-t v, tk mwpe*s & m&j+f&-e~% are pener2Qy ink~~~%eb on tie batis D? a mononuclear molybdenum(V) centre.’ Few examples of Mo03+ complexes with halide and dithiocarbamate ligands such as MoOCl(Et,dtc), and MoOBr(EbdtQ2 have been reported.2 The interesting ambidentate nature3 of the pseudohalide tbiocyanate @and led to the study’ of mononuclear oxoisothiocyanatomolybdenum(V) compk.%&. <% ~rrc&&&, arce tisc-nss&.
Molybdenum trioxide (1.0 g) was dissolved in Cont. HCl (1 cm’) containing water (10 cm3). To the resultant solution, hydrazine (2 cm3) was added and warmed over water bath. The solution obtain& was coaled aad to wti& ammonium tiecyan&e j%%,& ‘m w&er j%c&:z was a&&&ianb filtered. To the filtered solution sodium pyrrolidinyldithiocarbamate (1.2 g) in water (200 cm3) was added. The complex thrown out was filtered, washed with water and finally with methanol and
dried. Found C, 28.6; H, 3.4; N, 9.1; S, 34.5; MO, 2&k C&c. ‘iorMoQ2GzQ Q?yr&&&: c, z&s; H, 3.*, K, S.W, S, 34.7; ?&, %.$.?A me \R a& 3, \R sper?ua were rec&eb DI Perkin-Elmer 257 and Polytech IR 12 respectively. The electronic spectra were recorded on Carl Zeiss DMR-21 recording spectrophotometer. The EPR spectra were obtained on a Varian E-4 X-band spectrometer. Magnetic measurements were made at room temperature using Gouy balance. The voltammograms of the complex were %W&& k ,zzW&&* W&Y&+G%B34 ‘1[4 +&& WqJporting electrolyte. The voltammetric measurements were carried out by a three electrode %Wke-%&ersenp &KG1 con&rufk& kOm
DJWitiDD~
i3Dl~&?YS~ The
WDJb&’
&kfTiJDik
was a Pt foil and Pt wire served as auxillary electrode along with a saturated calomel electrode a%%%W=W ?ki%0&. The nOn-apueo;u SCih$lDn under investigation and the reference electrode were separated by non-aqueous salt bridge. Sweep rates varied between 0.01 and 5 V/set. De-aeration of the solution was performed before commencing &e expetiimenz by a s&e&m of pm-%&k n.&Ggen >a~. %e sas was pas& &~e ‘Sne &titi throughout the experiment... RESULT!?+ The measured magnetic moment of the complex was found to be 1.71 B.M. The powder EPR W at mm ~perature has a singIe line tit! 8 %&Z.. 2.5% Zk EPR spw7trum of &e 907
908
K. S. NAGARAJA
and M. R. UDUPA
Fig. 1. I&ear sweep voltanunograms of A. Sodium perchlorate (supporting electrolyte) (0.1 M) and B. MoO(NCS)@rroldtc), (1 x 10e3 M) + NaCIO, in acetonitrile. Voltammograms C, D and E are recorded after baking the potentials at -0.40, +0.75, + 1.05 and + 1.02 V respectively. Sweep rate: 0.1 V/see.
complex in dichloromethane at room temperature exhibits a six line pattern with a strong zero field centre line, which is expected’ since the nuclear spins of gsMo and WMo are 512. The g,, and A,, values, 1.961 and 40 G, are in good agreement with the reported’ values for similar type of complexes. The electronic spectrum recorded in methanol exhibits shoulders at 730(100), 465(5200) and 270(13760) nm. The first two absorptions are assigned6 to d+d and n;(S)+d(Mo) chargetransfer transitions. The third absorption is assigned to R +R* internal ligand transition. The infrared spectral bands at 2020 m, 830 m, 480 m and 340m are assigned’** to vNcs, vcs, &a and vhleN respectively, which suggest that thiocyanate group is attached to molybdenum through nitrogen and not through sulphur. The strong band at 930 cm-’ is characteristic? of Mo=O stretching mode. The bands at 1525 and 1005cm-’ suggestg,lo that the dithiocarbamate act as univalent bidentate ligand. The Mo-S(dtc) stretching is observed around 365 cm-‘. The voltammograms of the complex MoO(NCS)
(Pyrroldtc), are given in Fig. 1 and the electrochemical data are given in Table 1. As seen from the Fig. 1, an irreversible wave is observed at - 0.23 V when the sweep rate was 0.1 V/see. The wave position did not change when sweep rates from 40 to 200 mV/sec were employed. During the anodic sweep rates, three waves were observed. The potentials were biased at both cathodic and anodic potentials and the voltammograms were recorded. When the potential at -0.3OV was biased, the voltammogram gave no further infor: mation. However, biasing at the first anodic potential (+0.60 V) showed a pronounced wave at -0.55 V along with the wave at -0.23 V. The voltammogram recorded after biasing at + 1.05 V and a well defined wave at -0.55 V. But biasing the potential at + 1.20 V, the wave at -0.55 V completely disappeared and only one cathodic wave was observed at -0.23V. DISCUSSION moment value of 1.71 B.M. indi-
The magnetic cates that the complex
is mononuclear
and molyb-
909
Spectral and electrochemical studies
Table 1. Electrochemical data of MoO(NCS)(F’yrroldtc), E1/2 Volts
Mo”0 (NCS) (@yrroldtc)2
+
Ho’“O(NCS) (pyrroldtc)
2
Mo”O(NCS) (pyrroldtc)2
+
MoVIO(NCS) (pyrroldtc)
2 + le-
WoO(NCS)(pyrroldtc)2
2 7
McQ$(NCS)2(pyrro~dtc)q
Yo~O~(NCS)~( pyrroldtc)4
+
Mov~oV~(NCS)2(pyrroldtc)4
Oxidation
+ le’
of dithiocarbamate
-0.23 a!55
+ le’
ligand
denum has the d’ configuration. The EPR studies further reveal that the complex is mononuclear. The electronic spectrum also suggests a d’ configuration for the MO atom in the complex. The infrared spectral studies unequivocally point out that the thiocyanate group is attached to molybdenum through nitrogen and the presence of Mo03+ moiety. The complex may assume a distorted octahedral geometry with the bidentate chelation of the ligand. The complex showed a cathodic wave at -0.23 V. The complex, MoO(OH) (Oep) (Oep = octaethylporphyrin) is found” to undergo reduction from MO(V) to Mo(IV) at -0.21 V vs S.C.E. in DMSO medium. Thus the reduction in the present complex is assigned12 to Mo(V)/Mo(IV) couple which strongly indicates that the complex is monomeric and molybdenum is in +5 oxidation state. The fist anodic wave at +0.55 V is attributed to the oxidation” of MO(V) to Mo(V1). The wave observed at +0.92 V is assigned to the oxidation of dimeric MO(V) species in solution to Mo(V1). Such types of electrochemical processes are not uncommon in the chemistry of molybdenum. 12*13The third wave at + 1.15 V is due to the oxidation of the ligand, which is also observed4 in the voltammogram of voltammograms Mo(NO),(Pyrroldtc),. The recorded after biasing the potentials indicate that the first two anodic waves are dut to oxidation of Mo(V1). Biasing at the potentials + 0.60 V and + 1.05 V, Mo(V1) species are stored in solution and in the reverse cycle undergo reduction to MO(V) at -0.55 V vs S.C.E. The third oxidation step raptures the coordinated molybdenum(V1)
vs S.C.E.
+O. 92 +1.15
species by the oxidation of the ligand and thus on the reverse cycle no reduction wave is observed. The electrochemical studies support the conclusion that the complex is mononuclear and molybdenum is in the +5 oxidation state, which is also confirmed by the magnetic and EPR studies. Acknowledgement-We are grateful to the Council of Scientific and Industrial Research (India) for the financial support. REFERENCES 1. K. B. Swedo and J. H. Enemark, J. Chem. Educ. 1979, 56, 70. 2. G. J. J. Chen, J. W. McDonald and W. E. Newton, Znorg. Chim. Actu, 1980, 41, 49. 3. A. H. Norbury, Adv. Znorg. Radiochem. 1975, 17, 231. 4. K. S. Nagaraja, Ph.D. Thesis. Indian Institute of
Technology, Madras (1982). 5. H. Carrington, Eiectron Paramagnetic Resonance. Academic Press, New York (1974). 6. H. Sabat, M. F. Rudolf and B. J. JezowskaTrzebiatowska, Inorg. Chim. Acta, 1973, 7, 365. 7. P. C. H. Mitchell and R. J. P. Williams, J. Chem. Sot. 1960,1912. 8. J. Lewis, R. S. Nyhohn and P. W. Smith, J. Chem. Sot. 1961, 4590. 9. D. Coucouvanis, Prog. Inorg. Chem. 1969, 11, 233. 10. K. Nakamoto, J. Fuji& R. A. Condrate and Y. Mormoto, J. Chem. Phys. 1963, 39, 423. 11. J. H. Fuhrhop, K. M. Kadish and D. G. Davis, J. Am. Gem. Sot. 1973, 95, 5140. 12. L. J. Dehayes, H. C. Faulkner, W. H. Doub and D. T. Sawyer, Inorg. Chem. 1975, 14, 210. 13. J. K. Howie and D. T. Sawyer, Znorg. Chem. 1976, 15, 1892.
1984
SPECTRAL AND ELECTROCHEMICAL STUDIES ON OXOISOTHIOCYANATOBIS(PYItROLIDINYLDITHIOCARBAMATO)MOLYBDENUM(V) K. S. NAGARAJA and M. R. UDUPA* Department of Chemistry, Indian Institute of Technology, Madras 600 036, India (Received 4 March 1983; accepted 17 January 1984) Abstract-The complex, oxoisothiocyanatobis(pyrrolidinyldithiocarbamato)molybdenum(V), MoO(NCS) (pyrroldtc), was prepared. The IR spectra of the complex suggest that the thiocyanate group is attached through nitrogen and the presence of Mo03+ moiety. The voltammograms of the complex in acetonitrile exhibited a pronounced cathodic wave at -0.23 V vs S.C.E. which was attributed to Mo(V)/Mo(IV) couple. The magnetic, epr and electrochemical studies indicate that the compound is mononuclear and molybdenum is in + 5 oxidation state.
In spite of the extensive development in the chemistry of bioucleat ma1_ykkaurn~ compkxes in r-t v, tk mwpe*s & m&j+f&-e~% are pener2Qy ink~~~%eb on tie batis D? a mononuclear molybdenum(V) centre.’ Few examples of Mo03+ complexes with halide and dithiocarbamate ligands such as MoOCl(Et,dtc), and MoOBr(EbdtQ2 have been reported.2 The interesting ambidentate nature3 of the pseudohalide tbiocyanate @and led to the study’ of mononuclear oxoisothiocyanatomolybdenum(V) compk.%&. <%
Molybdenum trioxide (1.0 g) was dissolved in Cont. HCl (1 cm’) containing water (10 cm3). To the resultant solution, hydrazine (2 cm3) was added and warmed over water bath. The solution obtain& was coaled aad to wti& ammonium tiecyan&e j%%,& ‘m w&er j%c&:z was a&&&ianb filtered. To the filtered solution sodium pyrrolidinyldithiocarbamate (1.2 g) in water (200 cm3) was added. The complex thrown out was filtered, washed with water and finally with methanol and
dried. Found C, 28.6; H, 3.4; N, 9.1; S, 34.5; MO, 2&k C&c. ‘iorMoQ2GzQ Q?yr&&&: c, z&s; H, 3.*, K, S.W, S, 34.7; ?&, %.$.?A me \R a& 3, \R sper?ua were rec&eb DI Perkin-Elmer 257 and Polytech IR 12 respectively. The electronic spectra were recorded on Carl Zeiss DMR-21 recording spectrophotometer. The EPR spectra were obtained on a Varian E-4 X-band spectrometer. Magnetic measurements were made at room temperature using Gouy balance. The voltammograms of the complex were %W&& k ,zzW&&* W&Y&+G%B34 ‘1[4 +&& WqJporting electrolyte. The voltammetric measurements were carried out by a three electrode %Wke-%&ersenp &KG1 con&rufk& kOm
DJWitiDD~
i3Dl~&?YS~ The
WDJb&’
&kfTiJDik
was a Pt foil and Pt wire served as auxillary electrode along with a saturated calomel electrode a%%%W=W ?ki%0&. The nOn-apueo;u SCih$lDn under investigation and the reference electrode were separated by non-aqueous salt bridge. Sweep rates varied between 0.01 and 5 V/set. De-aeration of the solution was performed before commencing &e expetiimenz by a s&e&m of pm-%&k n.&Ggen >a~. %e sas was pas& &~e ‘Sne &titi throughout the experiment... RESULT!?+ The measured magnetic moment of the complex was found to be 1.71 B.M. The powder EPR W at mm ~perature has a singIe line tit! 8 %&Z.. 2.5% Zk EPR spw7trum of &e 907
908
K. S. NAGARAJA
and M. R. UDUPA
Fig. 1. I&ear sweep voltanunograms of A. Sodium perchlorate (supporting electrolyte) (0.1 M) and B. MoO(NCS)@rroldtc), (1 x 10e3 M) + NaCIO, in acetonitrile. Voltammograms C, D and E are recorded after baking the potentials at -0.40, +0.75, + 1.05 and + 1.02 V respectively. Sweep rate: 0.1 V/see.
complex in dichloromethane at room temperature exhibits a six line pattern with a strong zero field centre line, which is expected’ since the nuclear spins of gsMo and WMo are 512. The g,, and A,, values, 1.961 and 40 G, are in good agreement with the reported’ values for similar type of complexes. The electronic spectrum recorded in methanol exhibits shoulders at 730(100), 465(5200) and 270(13760) nm. The first two absorptions are assigned6 to d+d and n;(S)+d(Mo) chargetransfer transitions. The third absorption is assigned to R +R* internal ligand transition. The infrared spectral bands at 2020 m, 830 m, 480 m and 340m are assigned’** to vNcs, vcs, &a and vhleN respectively, which suggest that thiocyanate group is attached to molybdenum through nitrogen and not through sulphur. The strong band at 930 cm-’ is characteristic? of Mo=O stretching mode. The bands at 1525 and 1005cm-’ suggestg,lo that the dithiocarbamate act as univalent bidentate ligand. The Mo-S(dtc) stretching is observed around 365 cm-‘. The voltammograms of the complex MoO(NCS)
(Pyrroldtc), are given in Fig. 1 and the electrochemical data are given in Table 1. As seen from the Fig. 1, an irreversible wave is observed at - 0.23 V when the sweep rate was 0.1 V/see. The wave position did not change when sweep rates from 40 to 200 mV/sec were employed. During the anodic sweep rates, three waves were observed. The potentials were biased at both cathodic and anodic potentials and the voltammograms were recorded. When the potential at -0.3OV was biased, the voltammogram gave no further infor: mation. However, biasing at the first anodic potential (+0.60 V) showed a pronounced wave at -0.55 V along with the wave at -0.23 V. The voltammogram recorded after biasing at + 1.05 V and a well defined wave at -0.55 V. But biasing the potential at + 1.20 V, the wave at -0.55 V completely disappeared and only one cathodic wave was observed at -0.23V. DISCUSSION moment value of 1.71 B.M. indi-
The magnetic cates that the complex
is mononuclear
and molyb-
909
Spectral and electrochemical studies
Table 1. Electrochemical data of MoO(NCS)(F’yrroldtc), E1/2 Volts
Mo”0 (NCS) (@yrroldtc)2
+
Ho’“O(NCS) (pyrroldtc)
2
Mo”O(NCS) (pyrroldtc)2
+
MoVIO(NCS) (pyrroldtc)
2 + le-
WoO(NCS)(pyrroldtc)2
2 7
McQ$(NCS)2(pyrro~dtc)q
Yo~O~(NCS)~( pyrroldtc)4
+
Mov~oV~(NCS)2(pyrroldtc)4
Oxidation
+ le’
of dithiocarbamate
-0.23 a!55
+ le’
ligand
denum has the d’ configuration. The EPR studies further reveal that the complex is mononuclear. The electronic spectrum also suggests a d’ configuration for the MO atom in the complex. The infrared spectral studies unequivocally point out that the thiocyanate group is attached to molybdenum through nitrogen and the presence of Mo03+ moiety. The complex may assume a distorted octahedral geometry with the bidentate chelation of the ligand. The complex showed a cathodic wave at -0.23 V. The complex, MoO(OH) (Oep) (Oep = octaethylporphyrin) is found” to undergo reduction from MO(V) to Mo(IV) at -0.21 V vs S.C.E. in DMSO medium. Thus the reduction in the present complex is assigned12 to Mo(V)/Mo(IV) couple which strongly indicates that the complex is monomeric and molybdenum is in +5 oxidation state. The fist anodic wave at +0.55 V is attributed to the oxidation” of MO(V) to Mo(V1). The wave observed at +0.92 V is assigned to the oxidation of dimeric MO(V) species in solution to Mo(V1). Such types of electrochemical processes are not uncommon in the chemistry of molybdenum. 12*13The third wave at + 1.15 V is due to the oxidation of the ligand, which is also observed4 in the voltammogram of voltammograms Mo(NO),(Pyrroldtc),. The recorded after biasing the potentials indicate that the first two anodic waves are dut to oxidation of Mo(V1). Biasing at the potentials + 0.60 V and + 1.05 V, Mo(V1) species are stored in solution and in the reverse cycle undergo reduction to MO(V) at -0.55 V vs S.C.E. The third oxidation step raptures the coordinated molybdenum(V1)
vs S.C.E.
+O. 92 +1.15
species by the oxidation of the ligand and thus on the reverse cycle no reduction wave is observed. The electrochemical studies support the conclusion that the complex is mononuclear and molybdenum is in the +5 oxidation state, which is also confirmed by the magnetic and EPR studies. Acknowledgement-We are grateful to the Council of Scientific and Industrial Research (India) for the financial support. REFERENCES 1. K. B. Swedo and J. H. Enemark, J. Chem. Educ. 1979, 56, 70. 2. G. J. J. Chen, J. W. McDonald and W. E. Newton, Znorg. Chim. Actu, 1980, 41, 49. 3. A. H. Norbury, Adv. Znorg. Radiochem. 1975, 17, 231. 4. K. S. Nagaraja, Ph.D. Thesis. Indian Institute of
Technology, Madras (1982). 5. H. Carrington, Eiectron Paramagnetic Resonance. Academic Press, New York (1974). 6. H. Sabat, M. F. Rudolf and B. J. JezowskaTrzebiatowska, Inorg. Chim. Acta, 1973, 7, 365. 7. P. C. H. Mitchell and R. J. P. Williams, J. Chem. Sot. 1960,1912. 8. J. Lewis, R. S. Nyhohn and P. W. Smith, J. Chem. Sot. 1961, 4590. 9. D. Coucouvanis, Prog. Inorg. Chem. 1969, 11, 233. 10. K. Nakamoto, J. Fuji& R. A. Condrate and Y. Mormoto, J. Chem. Phys. 1963, 39, 423. 11. J. H. Fuhrhop, K. M. Kadish and D. G. Davis, J. Am. Gem. Sot. 1973, 95, 5140. 12. L. J. Dehayes, H. C. Faulkner, W. H. Doub and D. T. Sawyer, Inorg. Chem. 1975, 14, 210. 13. J. K. Howie and D. T. Sawyer, Znorg. Chem. 1976, 15, 1892.