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The far-infrared spectra of pyridine complexes of transition metal(II) isothiocyanates
Journal of Molecular Structure, 42 (1977) 0 Elsevier Scientific Publishing Company,
51-58
Amsterdam -
Printed in The Netherlands
THE FAR-INFRARED SPECTRA OF PYRIDINE COMPLEXES OF TRANSITION METAL(H) ISOTHIOCYANATES
CAROLA
ENGELTER
and DAVID
Department of Inorganic (South Africa) (Received
1 January 1977;
Chemistry,
A. THORNTON University
in revised form
of Cape Town,
Rondebosch
7700
14 June 1977)
ABSTRACT
The infrared spectra (500-140 cm-‘) of the complexes [M(pyridine),(NCS),] (n = 2, M = Mn, Co, Ni, Cu, or Zn; n = 4, M = Mn, Fe, Co, or NI) are discussed. The uM-pyridine and uM-NCS bands are assigned by observing the band shifts induced by isotopic labelling of the coordinated pyridine and isothiocyanate, by comparing the spectra with those of the [M(pyridine),Cl,] complexes and from symmetry considerations based on their known structures. The two types of metal-ligand stretchmg bands occur within a rather narrow frequency range and there is evidence of some vibrational coupling between these two modes. Some earlier assignments of vM-pyridine bands require revision. The spectra of the yellow [Fe(py),(NCS),] complex and its violet oxidation product suggest that the oxidation reaction involves the transformation of trans-[Fe(py)a(NCS),l into cis-[Fe(py),(NCS),]
INTRODUCTION
The infrared spectra of pyridine (py) complexes of metal(I1) isothiocyanates have received considerably less attention than those of metal(I1) halides. A review [1 J and the more recent literature reveal that no attempts have been made to use the isotopic labelling technique for the assignment of metal-ligand bands in these complexes. We have now applied the technique [2] of independent labelling of the two species of nitrogen donors to the spectra of the complexes [M(py),(NCS),] (n = 2, or 4). EXPERIMENTAL
The complexes, trans-[M(py),(NCS),] (M = Mn, Fe, Co, or Ni) and CM(PY)~(NCS)~I(M = Cu, or Zn) were synthesized by the reported methods [3]. The labelled complexes were similarly prepared from pyridine-“N of 99% isotopic purity (Merck) and sodium thiocyanate-“N of 96% isotopic purity (Merck, Sharp and Dohme, Canada). The unlabelled and labelled complexes [M(py)2(NCS)2] (M = Mn, Co, or Ni) were obtained by thermal decomposition of the analogous [M(py),(NCS)J compounds. Composition and purity of the complexes were established by microanalysis.
52
Infrared spectra were observed from Nujol mulls between caesium iodide plates on a Beckman IR-12 spectrophotometer (2200-250 cm-‘) and from Nujol mulls between polyethylene film on a Perkin-Eimer 180 spectrophotometer (250-140 cm-‘). RESULTS
AND
DISCUSSION
The spectra are depicted in Fig. 1 and the kequency data are recorded in Table 1. Bands shifted by lSNCS-labelling are termed “NCS-sensitive bands while those shifted by pyridine deuteration are termed d-sensitive bands. In a previous paper [2], a clear distinction between the two species of metal-ligand stretching bands (vM-NH2 and YM-NCS) in the complexes ]M(a&(NCS)*I (an = aniline) was achieved by observing the band shifts induced by ‘SN-labelling of each nitrogen donor. The success of the technique was aided by the wide frequency separation between the YM-NH2 (WI. 400 cm-‘) and vM-NCS (ca. 200 cm-‘) bands. Under these circumstances, very little vibrational coupling is expected to occur. Thus, none of the ‘*NCS-sensitive bands exhibited any ‘*NH,-sensitivity and none of the ‘*NH2-sensitive bands was shifted by 15NCS-labelling. Furthermore, the magnitude of the shifts induced by donor-atom labelling lay well outside the limits of experimental error which are determined by the reproducibility of the’absorption maxima in replicate spectral determinations.
Fig. 1. Infrared spectra of [M(py),(NCS),] (n = 2, or 4). The spectra of pyridine and [Mn(py),Cl,] are included for comparison. Abbreviations: p-o. = polymeric octahedral, p-t. = polymeric tetragonal, t = tetrahedral, m-0. = monomeric octahedral.
53
In a subsequent infrared study [ 41 of the complexes [ M( py)2C11], the vM-py
bands were assigned by observing the band shifts induced by labellmg
of the pyridine ring. Since the vM-py frequencies (ca. 200 cm-‘) are similar
to those characteristic of vM-NCS, some vibrational coupling between these two modes in the complexes [M(py),(NCS),] is expected to occur. Such coupling has two ramifications with respect to the isotopic assignment technique. Firstly, the coupled bands are expected to shift on both ‘“NCSand pyridine-labelling. Secondly, the magnitude of the shift of a coupled band will be smaller than that of a vibrationally pure band. Both effects are observed in the spectra of the pyridine-isothiocyanate complexes. The existence of bands sensitive to labelling of both species of nitrogen donors provides evidence for some coupling between uM-py and vM-NCS. The problem of the small shifts induced by ‘5NCS-labelling (frequently on the border-hne of significance) was overcome by comparing the spectra of the complexes [M(py),(NCS),] with the structurally analogous [M(py),Cl,] in the expectation that substitution of chloride by isothiocyanate would cause significant shifts in vM-X (X = Cl or NCS) but relatively small shifts in vM-py. The bis(pyridine)
complexes
[M(py),(NCS),
J (M
= Mn,
Co, or Ni)
The Con complex has a polymeric octahedral structure with bridging -NCSunits [ 71. Since the spectra of the MxP and NP complexes exhibit a band-for-band correspondence with that of Con, including the feature diagnostic [l] of NCS bridging (doubling of the 470 cm-’ 6NCS band) they are also considered to be octahedral polymers. The spectrum of each of these complexes has seven bands within the range 500-140 cm-’ (the band of lowest frequency for the Mnn complex lies beyond the low-frequency limit of measurement). Following the numbering system depicted in Fig. 1, I+ is firmly assigned to the GNCS vibration by virtue of its position [ 11, its lSNCS-sensitivity and its doublet nature which is characteristic [l] of bridging -NCSunits. v2 is the 406 cm-’ out-of-plane ring vibration of pyridme, raised some 20 to 30 cm-’ by coordination. The origin of this band is clear from its high d-sensitivity: it undergoes a 40-cm-’ shift towards lower frequency on deuteration of pyridine [ 41. Since neither pyridine nor-the isothiocyanate ion absorbs below 400 cm-‘, all lower frequency bands originate in metaliigand modes. Although the lSNCS-sensitivity of v3 is not significant (
Band
417 417
268(1 ,O) 264 2!6
6 6
This work 6 6
b.r. 168
163&b.) b.r. 166
b.r. b.r. b.r.
This work 6 6
ThL work 6 6
164(1.4)
This work
6 6
196(0,2) b.r. 201
This work 6 6
n.a,
GNMN
n.a.
uM-PY
vM-UY
uM-NCSC
uM-NCS uM-NCS uM-NCS
UQY
WY
UPY
418(0,40)
Thb work
6
6 GNCS
6NCS 6NCS GNCS GNCS 6NCS
476(&l) 470(4,0) 476 468 476 468
Thls work
146(0,3) b-r. b.r.
162(1.3) b,r. 166
bar. n,r.
186(1.3)
GNMN
ma.
GNMN
vM-py
vM-NC@ PM-PY vM-PY
vM-NCS vM-NCS vM-NCS
270(0.0) 268 270 208(2.2) 213 211
VPY
VPY
upy
GNCS GNCS GNCS GNCS GNCS
422 426
426(0,40)
476&O) 470(t.b.) 472 468 473
uN-CS
2096
6
2099
2102b( 27,O) vN+S
2o94”(28.1) uN_CS
Thia work
UN423
[C~(PYMNW,I
[Mn(py)ANCW
Ref,
166(1,4) b.r. 168
179(0,3) b.r. n.r.
b.r. n.r.
206( 1.9)
226(2,4) 229 230
286(2,0) 280 283
429 432
433(0,40)
477(0,1) 469(4,0) 474 466 477 469
2100
2114b(29,0)
n.a.
GNMN
GNMN
vM--py
vM-NC@ FM-PY PM-PY
vM-NCS vM-NCS vM-NCS
VPY
WY
VPY
GNCS GNCS LNCS GNCS GNCS GNCS
UN-CS
UN-CS
Frequencies, isotopic shifts (cm-‘) and band assignments for complexes [M(py),(NCS),la
TABLE 1
193(0,8) b.r. 197
212(1,6) 214 218
n.r. 218
226(0,6)
267(&O) 266 266
324( 1,3) 319 324
431 436
434(0,40)
478(4,0) 469(3,0) 477 468 478 468
2086
2098b(30,1)
b.r. b.r. b.r.
bNh4N ma.
n.a.
vM-PY
162(4,6) b.r. 166
232(0,4) 207(0,6) 216 231
270(0,2) 208 268
316(&l) 312 313
426(0,39) 414(0,39) n.r, 427 414
486(3,0) 481(3,0) 484 478 486
2100(29,0) 2081(29,0) 2100 2076
6NMN
ma.
vM-py
vM-NCS vM-PY vM-PY
vM-NCS uM-NCS uM-NCS
VPY WY
vpy
GNCS GNCS GNCS GNCS 6NCS GNCS
UN-B
vN-CS
n.a.
GNMN
vM--py uM--py vhf-UY n.a.
uM-NCS UM-PY ~M-PY
uM-NCS vM-NC9 VM-tics
VPY VPY
WY
WY
GNCS GNCS GNCS GNCS GNCS
uN-CS vN-CS vN-CS UN+.%
[WpyMNW,l
266(0,0) 264 269
lae(o.0)
This work 6 6
Thin work
174(1,3) b.r. 172
b-r. b.r. b.r.
b.r. hr. b.r.
This work 6 6
Thls work
This work 6 6
6 6
b.r. 196
5 6
rid.
vM-py
uM-PY
vM-pyf
VM-NCS vM-NCS vtd-NCS
VPY VQY
422 416e
6
?li
b.r.
163(0,2) b.r. -h
“?i
193(0,4)
2oag -h
201(0,3)
-h
2661
271(&O)
-h
WY
420(0,3a)
GNMN
VM-py
uM-PY
vM-py t vM-NCS
vM-NCS vM-NCS
VPY WY
VQY
428(o,aa)
YPY VPY VQY
422(0,40) 414(0,40) 420 414
Thla work
4241 420g
6NCS
6
6~~s
483 6a,o) 482 g -h
GNCS GNCS 6NCS
481 63,0) 482 482
Thle work 6 6
b.r. bmr. bar.
n.8.
6NMN
uM-QY n.a.
lbS(t,b.) b,r. 170
VM-PY
202(2,4)
uM-QY vM-PY
vM-py t vM-NCS
vM-NCS vM-NCS vM-NCS
WY LTY WY VPY VPY VPY
6NCS GNCS GNCS
206 204
216 212
212( 2,O)
272(0,0) 268 272
431(0,40) 423(0,39) 426 420 433 423e
482 63,O) 481 483
2074b(27,1) 2072
vN-CS vN+X
2066( 29,O) 20701
vN_CS VN-CS
2062b(27,1) 2066
Thla work 6
vN-CS vN-CS
P~PY~OJWI
[WpyMNCQl
[WpyMNW,l
Ref.
160(1,7) b.r. 164
172(1,3) b.r. 174
220(0,4) n.r. n.r.
233 232
230(0,2)
287(0,0) 280 287
437(0,3a) 430(0,3a) 434 429 438 432e
ma.
GNMN
ma.
GNMN
“M--py
“M-PY “M-PY
tvM-NCS
“M--py
vM-NCS vM-NCS vM-NCS
VPY VPY VPY "PY “PY “PY
GNCS GNCS GNCS
27,0) UN-CS vN-CS
483 63.0) 483 482
;;W;b(
IN~PYM~W,I
aAbbreviations: b,r. = beyond range of measurement, n.a, = not assigned, n.r. = not reported, t.b. = too broad for determination of shift. Figures in parentheses following the frequencies are the shifts (nearest integral values in cm-‘) towards lower frequency induced by “NCS-labellmg (first figure) and pyridine deuteration (second figure). Shifts < 1 cm-’ are not regarded as significant and are reported as zero shifts. bSharp shoulders on UN-CS bands ignored (see Fig. 1). CSome d-sensitivity in these bands indicates coupling with vM-py. dShoulders reported to precede these bands by ca. 2 cm-’ were not observed In this work. eAdditional bands reported near 400 cm-’ (not observed in present work nor cited in ref. 5). fCoupled with vM-NCS. Qompound incorrectly formulated as cis.lsomer. hCompound not studied
“1
“h
“4
“I
“1
“I
Band
57 deep violet in transmitted light). OriginaUy, the yellow and violet compounds were thought Cl11 to be cis- and fans-IFe(py).(NCS),I, respectively. More recent examination of their MGssbauer, ESR, electronic and infrared spectra, X-ray powder patterns, magnetic moments and chemical properties /lOI has established beyond reasonable doubt that the violet form is the normal yellow trams-[ Fe( py)4( NCS)zJ isomer contaminated with a violet Feni oxidation product, most probably [Fe( py)s( Nca)J. The infrared measurements were not extended below 200 cm-’ and it could not be established with certainty which isomer of the FenI compound resuWed from the oxidation. The yellow Fen complex is undoubtedly tiaras-[Fe(py)~(NCS)~I since its spectrum (Fig. 1) i=sidentical titb the other [M(py)4(NCS)2j complexes for two of which a trans-configuration has been crystaUographicaUy estabxshed [Q]’ Furthermore, the spectrum yields one vM-py and one YM-NCS band as required for the trans (I&,) isomer whereas the-c& (C,,) isomer would require four vM-py and two vM-NCS bands. A sample of the violet oxidation product, obtained by recrysfallization of yeUow frans-IFe(py)a(NCS)2] from chloroform, yields an infrared spectiurn (Fig. 2) comprising bands which correspond in position with those of the yenow FeLr complex and additional bands at higher frequencies. These highfrequency shifts of metal-ligand bands are expected [lZj to accosnpany the increase in oxidation state Fen -+ Fctn while the coordination number remains constant. Thus, the vM-NCS band (zJ~)at 271 cm-’ in the E’errspectrum becomes a doublet in the spectrum of the oxidation product with peaks at 313 and 296 cm-‘rSimilarly, the coupled (PM---py f uM-NCS) band at 201. cm-l, with its vibrationally pure u@--py shoulder at 193 cm-‘, is resolved into two widely separated bands at 253 and 219 cm-’ in the spectrum of the oxidation product, suggesting that the latter contains cis-[Fe( py ) &NCS) 3I_ The Cs,, symmetry of this complex requires two VW--NCS and two v&l-py infrared-active modes whereas the bans-IFe(py),(NCS),J isomer (C,, symmetry) would require three of each. The oxidation of the yellow Fen
2. hErared spectra of tiaras-[Fe(py),(NCS), 1, its oxidation product and cisiI?a(py),{NCS), 1. Shaded bands :vFe-NCS.Solid bandsruFe-py.
Fig.
58
complex is therefore considered to involve the transformation: trans-3 cis-[Fe(py),(NCS),]. IWwMNCW In order to confirm the identity of the oxidation product, a sample of cis-[Fe(py)3(NCS)3] was prepared from iron(III) thiocyanate and pyridine [ 91. The spectrum of this compound contains bands which correspond precisely, in position, with the additional bands in the spectrum of the oxidation product. Comparison of present assignments with those previously reported Table 1 lists, for comparison with the present work, the assignments which result from the two principal earlier studies [5,6] on pyridine-isothiocyanate complexes. There is essentially little difference between the earlier and present assignments for vN-CS, ul, v2 and ZQ.v4 is now preferentially assigned to vM-NCS rather than uM-py although the observed d-sensitivity of this baud clearly indicates that some coupling with vM-py occurs in several of the complexes. v5is now regarded as the principal vM-py band since it has a higher d-sensitivity than v4. The uM-py values are now consistent with the range of vM-py in the complexes [M(py)2C12] for which erroneously high values of YM-py had also previously been reported 141. In the earlier reports [5,6] on the spectra of the pyridine-isothiocyanate complexes, v5 was either beyond the range of measurement or, if observed, was not assigned. A single exception is the complex [Co(py)4(NCS)2] in which vs was assigned to vCo-py; we agree with this assignment. In earlier studies, v6 and v7 were generally unobserved or unassigned. ACKNOWLEDGEMENTS
We thank the University of Cape Town Research Grants Committee and the Council for Scientific and Industrial Research for financial assistance.
REFERENCES 1 R. A. Bailey, S. L. Kozak, T. W. Michelson and W. N. Mills, Coord. Chem. Rev., 6 2 3 4 5 6 7 8 9 10 11 12
(1971) 407. C. Engelter and D. A Thornton, J. Mol. Struct., 33 (1976) 119. G. B: Kauffman, R. A. Alberts and F. L. Harlan, Inorg. Synth., 12 (1970) 251. J. E. Rdede and D. A Thornton, J. Mol. Struct., 34 (1976) 75. R. J. H. Clark and C. S. Williams, Spectrochim. Acta, 22 (1966) 1081. C. W. Frank and L. B. Rogers, Inorg. Chem., 5 (1966) 615. M. A. Porai-Koshits and G. N. Tischenko, Sov. Phys. Crystallogr., 4 (1959) 216. R. J. H. Clark and C. S. Williams, Inorg. Chem., 4 (1965) 350. M. A. Porai-Koshits and A. S. Antsyshkina, Sov. Phys. Crystailogr., 3 (1958) 694. C. D. Burbidge, M. J. Cleare and D. M. L. Goodgame, J. Chem. Sot. A, (1966) 1698. G. Spacu, Z. Anorg. Aug. C&em., 216 (1933) 165. L. G. Hulett and D. A. Thornton, J. Inorg. Nucl. Chem., 35 (1973) 2661.
51-58
Amsterdam -
Printed in The Netherlands
THE FAR-INFRARED SPECTRA OF PYRIDINE COMPLEXES OF TRANSITION METAL(H) ISOTHIOCYANATES
CAROLA
ENGELTER
and DAVID
Department of Inorganic (South Africa) (Received
1 January 1977;
Chemistry,
A. THORNTON University
in revised form
of Cape Town,
Rondebosch
7700
14 June 1977)
ABSTRACT
The infrared spectra (500-140 cm-‘) of the complexes [M(pyridine),(NCS),] (n = 2, M = Mn, Co, Ni, Cu, or Zn; n = 4, M = Mn, Fe, Co, or NI) are discussed. The uM-pyridine and uM-NCS bands are assigned by observing the band shifts induced by isotopic labelling of the coordinated pyridine and isothiocyanate, by comparing the spectra with those of the [M(pyridine),Cl,] complexes and from symmetry considerations based on their known structures. The two types of metal-ligand stretchmg bands occur within a rather narrow frequency range and there is evidence of some vibrational coupling between these two modes. Some earlier assignments of vM-pyridine bands require revision. The spectra of the yellow [Fe(py),(NCS),] complex and its violet oxidation product suggest that the oxidation reaction involves the transformation of trans-[Fe(py)a(NCS),l into cis-[Fe(py),(NCS),]
INTRODUCTION
The infrared spectra of pyridine (py) complexes of metal(I1) isothiocyanates have received considerably less attention than those of metal(I1) halides. A review [1 J and the more recent literature reveal that no attempts have been made to use the isotopic labelling technique for the assignment of metal-ligand bands in these complexes. We have now applied the technique [2] of independent labelling of the two species of nitrogen donors to the spectra of the complexes [M(py),(NCS),] (n = 2, or 4). EXPERIMENTAL
The complexes, trans-[M(py),(NCS),] (M = Mn, Fe, Co, or Ni) and CM(PY)~(NCS)~I(M = Cu, or Zn) were synthesized by the reported methods [3]. The labelled complexes were similarly prepared from pyridine-“N of 99% isotopic purity (Merck) and sodium thiocyanate-“N of 96% isotopic purity (Merck, Sharp and Dohme, Canada). The unlabelled and labelled complexes [M(py)2(NCS)2] (M = Mn, Co, or Ni) were obtained by thermal decomposition of the analogous [M(py),(NCS)J compounds. Composition and purity of the complexes were established by microanalysis.
52
Infrared spectra were observed from Nujol mulls between caesium iodide plates on a Beckman IR-12 spectrophotometer (2200-250 cm-‘) and from Nujol mulls between polyethylene film on a Perkin-Eimer 180 spectrophotometer (250-140 cm-‘). RESULTS
AND
DISCUSSION
The spectra are depicted in Fig. 1 and the kequency data are recorded in Table 1. Bands shifted by lSNCS-labelling are termed “NCS-sensitive bands while those shifted by pyridine deuteration are termed d-sensitive bands. In a previous paper [2], a clear distinction between the two species of metal-ligand stretching bands (vM-NH2 and YM-NCS) in the complexes ]M(a&(NCS)*I (an = aniline) was achieved by observing the band shifts induced by ‘SN-labelling of each nitrogen donor. The success of the technique was aided by the wide frequency separation between the YM-NH2 (WI. 400 cm-‘) and vM-NCS (ca. 200 cm-‘) bands. Under these circumstances, very little vibrational coupling is expected to occur. Thus, none of the ‘*NCS-sensitive bands exhibited any ‘*NH,-sensitivity and none of the ‘*NH2-sensitive bands was shifted by 15NCS-labelling. Furthermore, the magnitude of the shifts induced by donor-atom labelling lay well outside the limits of experimental error which are determined by the reproducibility of the’absorption maxima in replicate spectral determinations.
Fig. 1. Infrared spectra of [M(py),(NCS),] (n = 2, or 4). The spectra of pyridine and [Mn(py),Cl,] are included for comparison. Abbreviations: p-o. = polymeric octahedral, p-t. = polymeric tetragonal, t = tetrahedral, m-0. = monomeric octahedral.
53
In a subsequent infrared study [ 41 of the complexes [ M( py)2C11], the vM-py
bands were assigned by observing the band shifts induced by labellmg
of the pyridine ring. Since the vM-py frequencies (ca. 200 cm-‘) are similar
to those characteristic of vM-NCS, some vibrational coupling between these two modes in the complexes [M(py),(NCS),] is expected to occur. Such coupling has two ramifications with respect to the isotopic assignment technique. Firstly, the coupled bands are expected to shift on both ‘“NCSand pyridine-labelling. Secondly, the magnitude of the shift of a coupled band will be smaller than that of a vibrationally pure band. Both effects are observed in the spectra of the pyridine-isothiocyanate complexes. The existence of bands sensitive to labelling of both species of nitrogen donors provides evidence for some coupling between uM-py and vM-NCS. The problem of the small shifts induced by ‘5NCS-labelling (frequently on the border-hne of significance) was overcome by comparing the spectra of the complexes [M(py),(NCS),] with the structurally analogous [M(py),Cl,] in the expectation that substitution of chloride by isothiocyanate would cause significant shifts in vM-X (X = Cl or NCS) but relatively small shifts in vM-py. The bis(pyridine)
complexes
[M(py),(NCS),
J (M
= Mn,
Co, or Ni)
The Con complex has a polymeric octahedral structure with bridging -NCSunits [ 71. Since the spectra of the MxP and NP complexes exhibit a band-for-band correspondence with that of Con, including the feature diagnostic [l] of NCS bridging (doubling of the 470 cm-’ 6NCS band) they are also considered to be octahedral polymers. The spectrum of each of these complexes has seven bands within the range 500-140 cm-’ (the band of lowest frequency for the Mnn complex lies beyond the low-frequency limit of measurement). Following the numbering system depicted in Fig. 1, I+ is firmly assigned to the GNCS vibration by virtue of its position [ 11, its lSNCS-sensitivity and its doublet nature which is characteristic [l] of bridging -NCSunits. v2 is the 406 cm-’ out-of-plane ring vibration of pyridme, raised some 20 to 30 cm-’ by coordination. The origin of this band is clear from its high d-sensitivity: it undergoes a 40-cm-’ shift towards lower frequency on deuteration of pyridine [ 41. Since neither pyridine nor-the isothiocyanate ion absorbs below 400 cm-‘, all lower frequency bands originate in metaliigand modes. Although the lSNCS-sensitivity of v3 is not significant (
Band
417 417
268(1 ,O) 264 2!6
6 6
This work 6 6
b.r. 168
163&b.) b.r. 166
b.r. b.r. b.r.
This work 6 6
ThL work 6 6
164(1.4)
This work
6 6
196(0,2) b.r. 201
This work 6 6
n.a,
GNMN
n.a.
uM-PY
vM-UY
uM-NCSC
uM-NCS uM-NCS uM-NCS
UQY
WY
UPY
418(0,40)
Thb work
6
6 GNCS
6NCS 6NCS GNCS GNCS 6NCS
476(&l) 470(4,0) 476 468 476 468
Thls work
146(0,3) b-r. b.r.
162(1.3) b,r. 166
bar. n,r.
186(1.3)
GNMN
ma.
GNMN
vM-py
vM-NC@ PM-PY vM-PY
vM-NCS vM-NCS vM-NCS
270(0.0) 268 270 208(2.2) 213 211
VPY
VPY
upy
GNCS GNCS GNCS GNCS GNCS
422 426
426(0,40)
476&O) 470(t.b.) 472 468 473
uN-CS
2096
6
2099
2102b( 27,O) vN+S
2o94”(28.1) uN_CS
Thia work
UN423
[C~(PYMNW,I
[Mn(py)ANCW
Ref,
166(1,4) b.r. 168
179(0,3) b.r. n.r.
b.r. n.r.
206( 1.9)
226(2,4) 229 230
286(2,0) 280 283
429 432
433(0,40)
477(0,1) 469(4,0) 474 466 477 469
2100
2114b(29,0)
n.a.
GNMN
GNMN
vM--py
vM-NC@ FM-PY PM-PY
vM-NCS vM-NCS vM-NCS
VPY
WY
VPY
GNCS GNCS LNCS GNCS GNCS GNCS
UN-CS
UN-CS
Frequencies, isotopic shifts (cm-‘) and band assignments for complexes [M(py),(NCS),la
TABLE 1
193(0,8) b.r. 197
212(1,6) 214 218
n.r. 218
226(0,6)
267(&O) 266 266
324( 1,3) 319 324
431 436
434(0,40)
478(4,0) 469(3,0) 477 468 478 468
2086
2098b(30,1)
b.r. b.r. b.r.
bNh4N ma.
n.a.
vM-PY
162(4,6) b.r. 166
232(0,4) 207(0,6) 216 231
270(0,2) 208 268
316(&l) 312 313
426(0,39) 414(0,39) n.r, 427 414
486(3,0) 481(3,0) 484 478 486
2100(29,0) 2081(29,0) 2100 2076
6NMN
ma.
vM-py
vM-NCS vM-PY vM-PY
vM-NCS uM-NCS uM-NCS
VPY WY
vpy
GNCS GNCS GNCS GNCS 6NCS GNCS
UN-B
vN-CS
n.a.
GNMN
vM--py uM--py vhf-UY n.a.
uM-NCS UM-PY ~M-PY
uM-NCS vM-NC9 VM-tics
VPY VPY
WY
WY
GNCS GNCS GNCS GNCS GNCS
uN-CS vN-CS vN-CS UN+.%
[WpyMNW,l
266(0,0) 264 269
lae(o.0)
This work 6 6
Thin work
174(1,3) b.r. 172
b-r. b.r. b.r.
b.r. hr. b.r.
This work 6 6
Thls work
This work 6 6
6 6
b.r. 196
5 6
rid.
vM-py
uM-PY
vM-pyf
VM-NCS vM-NCS vtd-NCS
VPY VQY
422 416e
6
?li
b.r.
163(0,2) b.r. -h
“?i
193(0,4)
2oag -h
201(0,3)
-h
2661
271(&O)
-h
WY
420(0,3a)
GNMN
VM-py
uM-PY
vM-py t vM-NCS
vM-NCS vM-NCS
VPY WY
VQY
428(o,aa)
YPY VPY VQY
422(0,40) 414(0,40) 420 414
Thla work
4241 420g
6NCS
6
6~~s
483 6a,o) 482 g -h
GNCS GNCS 6NCS
481 63,0) 482 482
Thle work 6 6
b.r. bmr. bar.
n.8.
6NMN
uM-QY n.a.
lbS(t,b.) b,r. 170
VM-PY
202(2,4)
uM-QY vM-PY
vM-py t vM-NCS
vM-NCS vM-NCS vM-NCS
WY LTY WY VPY VPY VPY
6NCS GNCS GNCS
206 204
216 212
212( 2,O)
272(0,0) 268 272
431(0,40) 423(0,39) 426 420 433 423e
482 63,O) 481 483
2074b(27,1) 2072
vN-CS vN+X
2066( 29,O) 20701
vN_CS VN-CS
2062b(27,1) 2066
Thla work 6
vN-CS vN-CS
P~PY~OJWI
[WpyMNCQl
[WpyMNW,l
Ref.
160(1,7) b.r. 164
172(1,3) b.r. 174
220(0,4) n.r. n.r.
233 232
230(0,2)
287(0,0) 280 287
437(0,3a) 430(0,3a) 434 429 438 432e
ma.
GNMN
ma.
GNMN
“M--py
“M-PY “M-PY
tvM-NCS
“M--py
vM-NCS vM-NCS vM-NCS
VPY VPY VPY "PY “PY “PY
GNCS GNCS GNCS
27,0) UN-CS vN-CS
483 63.0) 483 482
;;W;b(
IN~PYM~W,I
aAbbreviations: b,r. = beyond range of measurement, n.a, = not assigned, n.r. = not reported, t.b. = too broad for determination of shift. Figures in parentheses following the frequencies are the shifts (nearest integral values in cm-‘) towards lower frequency induced by “NCS-labellmg (first figure) and pyridine deuteration (second figure). Shifts < 1 cm-’ are not regarded as significant and are reported as zero shifts. bSharp shoulders on UN-CS bands ignored (see Fig. 1). CSome d-sensitivity in these bands indicates coupling with vM-py. dShoulders reported to precede these bands by ca. 2 cm-’ were not observed In this work. eAdditional bands reported near 400 cm-’ (not observed in present work nor cited in ref. 5). fCoupled with vM-NCS. Qompound incorrectly formulated as cis.lsomer. hCompound not studied
“1
“h
“4
“I
“1
“I
Band
57 deep violet in transmitted light). OriginaUy, the yellow and violet compounds were thought Cl11 to be cis- and fans-IFe(py).(NCS),I, respectively. More recent examination of their MGssbauer, ESR, electronic and infrared spectra, X-ray powder patterns, magnetic moments and chemical properties /lOI has established beyond reasonable doubt that the violet form is the normal yellow trams-[ Fe( py)4( NCS)zJ isomer contaminated with a violet Feni oxidation product, most probably [Fe( py)s( Nca)J. The infrared measurements were not extended below 200 cm-’ and it could not be established with certainty which isomer of the FenI compound resuWed from the oxidation. The yellow Fen complex is undoubtedly tiaras-[Fe(py)~(NCS)~I since its spectrum (Fig. 1) i=sidentical titb the other [M(py)4(NCS)2j complexes for two of which a trans-configuration has been crystaUographicaUy estabxshed [Q]’ Furthermore, the spectrum yields one vM-py and one YM-NCS band as required for the trans (I&,) isomer whereas the-c& (C,,) isomer would require four vM-py and two vM-NCS bands. A sample of the violet oxidation product, obtained by recrysfallization of yeUow frans-IFe(py)a(NCS)2] from chloroform, yields an infrared spectiurn (Fig. 2) comprising bands which correspond in position with those of the yenow FeLr complex and additional bands at higher frequencies. These highfrequency shifts of metal-ligand bands are expected [lZj to accosnpany the increase in oxidation state Fen -+ Fctn while the coordination number remains constant. Thus, the vM-NCS band (zJ~)at 271 cm-’ in the E’errspectrum becomes a doublet in the spectrum of the oxidation product with peaks at 313 and 296 cm-‘rSimilarly, the coupled (PM---py f uM-NCS) band at 201. cm-l, with its vibrationally pure u@--py shoulder at 193 cm-‘, is resolved into two widely separated bands at 253 and 219 cm-’ in the spectrum of the oxidation product, suggesting that the latter contains cis-[Fe( py ) &NCS) 3I_ The Cs,, symmetry of this complex requires two VW--NCS and two v&l-py infrared-active modes whereas the bans-IFe(py),(NCS),J isomer (C,, symmetry) would require three of each. The oxidation of the yellow Fen
2. hErared spectra of tiaras-[Fe(py),(NCS), 1, its oxidation product and cisiI?a(py),{NCS), 1. Shaded bands :vFe-NCS.Solid bandsruFe-py.
Fig.
58
complex is therefore considered to involve the transformation: trans-3 cis-[Fe(py),(NCS),]. IWwMNCW In order to confirm the identity of the oxidation product, a sample of cis-[Fe(py)3(NCS)3] was prepared from iron(III) thiocyanate and pyridine [ 91. The spectrum of this compound contains bands which correspond precisely, in position, with the additional bands in the spectrum of the oxidation product. Comparison of present assignments with those previously reported Table 1 lists, for comparison with the present work, the assignments which result from the two principal earlier studies [5,6] on pyridine-isothiocyanate complexes. There is essentially little difference between the earlier and present assignments for vN-CS, ul, v2 and ZQ.v4 is now preferentially assigned to vM-NCS rather than uM-py although the observed d-sensitivity of this baud clearly indicates that some coupling with vM-py occurs in several of the complexes. v5is now regarded as the principal vM-py band since it has a higher d-sensitivity than v4. The uM-py values are now consistent with the range of vM-py in the complexes [M(py)2C12] for which erroneously high values of YM-py had also previously been reported 141. In the earlier reports [5,6] on the spectra of the pyridine-isothiocyanate complexes, v5 was either beyond the range of measurement or, if observed, was not assigned. A single exception is the complex [Co(py)4(NCS)2] in which vs was assigned to vCo-py; we agree with this assignment. In earlier studies, v6 and v7 were generally unobserved or unassigned. ACKNOWLEDGEMENTS
We thank the University of Cape Town Research Grants Committee and the Council for Scientific and Industrial Research for financial assistance.
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(1971) 407. C. Engelter and D. A Thornton, J. Mol. Struct., 33 (1976) 119. G. B: Kauffman, R. A. Alberts and F. L. Harlan, Inorg. Synth., 12 (1970) 251. J. E. Rdede and D. A Thornton, J. Mol. Struct., 34 (1976) 75. R. J. H. Clark and C. S. Williams, Spectrochim. Acta, 22 (1966) 1081. C. W. Frank and L. B. Rogers, Inorg. Chem., 5 (1966) 615. M. A. Porai-Koshits and G. N. Tischenko, Sov. Phys. Crystallogr., 4 (1959) 216. R. J. H. Clark and C. S. Williams, Inorg. Chem., 4 (1965) 350. M. A. Porai-Koshits and A. S. Antsyshkina, Sov. Phys. Crystailogr., 3 (1958) 694. C. D. Burbidge, M. J. Cleare and D. M. L. Goodgame, J. Chem. Sot. A, (1966) 1698. G. Spacu, Z. Anorg. Aug. C&em., 216 (1933) 165. L. G. Hulett and D. A. Thornton, J. Inorg. Nucl. Chem., 35 (1973) 2661.