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Evidence for ligated hexafluorophosphate(V)
INORG. NUCL.
CHEM. LETTERS
Vol. 7, pp. 405-407,
1971.
Pergamon
Press.
Ftrinted in
Great Britain.
E V I D ~ C E FOR L1GATI~ HEXAFLUOROPHOSPHATE(V)
By Sheila A. Bell, J.C. Lancaster and W.R. McWhinnie Department of C~Sem!stry, The University of Aston in Birmingham Birmingham 4. ( R e c e i v e d I December 1970)
The hexafluorophosphate(V)
anion is commonly used to precipitate cationic
species when a non-co-ordinating anion is required.
This note presents data
for the tetrakis pyridine complex of copper(II) hexafluorophosphate, [Cu(py)4(PF6)2] , which constitutes the first example of hexafluoropho sphat e co-ordination. The vibrational spectra of simple hexafluorophosphate salts have been examined in detail by two groups (1,2) and the i.r. and Raman data are satisfactorily interpreted in terms of Oh symmetry.
Perturbation of the
PF6 ion, for example by co-ordination of one fluorine atom to a metal, lowers the local symmetry to C4v which, in turn, leads to resolution of some degeneracies and to alteration of the selection rules. the vibrational modes in % irreducible
alter as shown in table lald now span the
representat~ns 4A 1
+ 2B 1 + B2 + 4E of C4v , of which the A 1 and
E modes are active in the infra-red.
u~(558 cm-I)
(2)
More specifically
Thus modes u3(830 cm-I) (2) and
of the PF6 ion should split and, in addition, new bands
corresponding to infra-red active components of the previously Raman active Ul, u2 and u 5 should appear in the region of respectively.
750
cm-I, 580 cm-I and 480 cm-I
The latter band, an i.r. active E mode derived from us(F2g )
may be obscured by the X-sensitive u16 b of pyridine which has undergone a large shift to higher wave number (440 m, 430 m-w cm-l).
Also the
inactive F2u (u6) mode of PF6 will be split (B1 + E) in C4v symmetry and the E mode is now i.r. active.
This band is however expected below 400 cm-I 405
EVIDENCE FOR LIGATED HEXAFLUOROPHOSPHATE(V)
406
Vol. 7, No.
5
(2).
TABLE 1 Analysis of the I.R. Bands of the Hexafluorophosphate(V) Group in [Cu(py)4(PF6)2]
Oh
o1(751+) 02(580)
Ii C4v
E
A1
A1
742m-s
572w
v3(830)
v4(558)
Flu
Ftu
B1 A1 -
E
885s
A1
E
06(?)
F2g
F2u
B2
(830s 560sh (555s -
1850s ~-
05(477)
E
B1
*
-
E
(40o
~550sh
°
Frequenczes in wave numbers from (2).
*Band obscured.
The predictions of the above paragraph are in good accord with the observed spectrum of [Cu(py)4(PF6)2] (TABLE 1) except that some Further splitting of the E modes derived from v 3 and v4 has occured.
This may be
due to a low site synsnetry within the crystalj which could of course, in principle~ explain the other observations.
However the intensity of the
A 1 mode at 742 cm-1 and the appearance of the other important A 1 mode at 572 cm-1, which is expected to be o£ weak intensity in the i.r., together with the clean splitting o£ u3 would argue for a relatively strong perturbation o£ the PF 6 group such as would occur ££ it were "semi co-ordinated,, (3) to copper(II). We have examined the corresponding perchlorate complex and here too~ not surprizingly, the infra-red data (TABLE 2) support the presence o£ semi coordinated percb_lorato-groups
(3).
The visible spectra o£ [Cu(py)4(PF6)2] and
[Cu(py)4(Cl04)2] are sim£1ar~ but not identical.
A tetragonal environment is
indicated for copper(II) in both complexes with the stronger interaction in the perc~1orate case.
The two g factor e.s.r, spectra also suggest approximately
Vol. 7, No. 5
EVIDENCE FOR LIGATED HEXAFLUOROPHOSPHATE(V)
407
t e t r a g o n a l environments f o r c o p p e r ( I I ) and, s i g n i f i c a n t l y , the values of g l l TABLE 2
Further Spectroscopic Data for LCu(py)4(PF6)2] and for [Cu(py)4(Cl04)2] .
(a)
,
,,
[Cu(pY)4(PF6)23 Visible ~
(by d i f f u s e r e f l e c t a n c e )
-
(18:300 cm-I 16,700 sh.
e.s.r, data--
(b)
~
=
2.027
gll =
2.248
[Cu(py)4(C]04) 2] Visible maxima (by diffuse reflectance) e.s.r, datai.r.
gl =
2.027
gll =
17~650 cm-1 (asynn).
2.261
data (C10~ group) 1113 cm-l(s): 1055 cm-1)(s), 933 cm-l(m): 630 cm-l(sh) lO45 cm-l~
623 cm-1
d i f f e r f o r the two complexes. The i n f r a - r e d data do not c o n s t i t u t e conclusive proof of hexafluorophosphate co-ordination.
Since i t i s c l e a r t h a t the environment of c o p p e r ( I I ) d i f f e r s in
the p e r c h l o r a t e and hexafluorophosphate complexes: the only reasonable a l t e r n a t i v e i n t e r p r e t a t i o n i s t h a t square planar Cu(py)~+ ions e x i s t in Cu(pY)4(PF6) 2.
This appears unlikely becausej apart from one exceptional case (4), this stereochemistry for copper(ll) is generally achieved only with n bonding ligands (5) and the necessary geometry of a planar Cu(py) 2+ ion
c
~
o
t
favour
bond formation,
I!
1.
VON K. BUHL]~ and W. BUES: Z. Anorg. a l l g . Chem. 308, 62 (1961)
2.
G.M. B]~DUNand A.C. RlYrENBER3, Inorg. Chem. 6, 2212 (1967)
3.
D.S. BROWN, J.D. LEE, B.G.A. I~LSON, B.J. HATHAWAY, I.M. PROCTER and A.A.G. TOMLINSON, Chem. Conmmn., 369 (1967)
4.
B.J. HATHAWAYand F.S. STEPHENS, J. Chem.Soc. (A) 884 (1970)
5.
B.J. HATHAWAYand D.E. BILLE~O, Coordin. Chem. Rev. 5 : 1 4 3 (1970)
CHEM. LETTERS
Vol. 7, pp. 405-407,
1971.
Pergamon
Press.
Ftrinted in
Great Britain.
E V I D ~ C E FOR L1GATI~ HEXAFLUOROPHOSPHATE(V)
By Sheila A. Bell, J.C. Lancaster and W.R. McWhinnie Department of C~Sem!stry, The University of Aston in Birmingham Birmingham 4. ( R e c e i v e d I December 1970)
The hexafluorophosphate(V)
anion is commonly used to precipitate cationic
species when a non-co-ordinating anion is required.
This note presents data
for the tetrakis pyridine complex of copper(II) hexafluorophosphate, [Cu(py)4(PF6)2] , which constitutes the first example of hexafluoropho sphat e co-ordination. The vibrational spectra of simple hexafluorophosphate salts have been examined in detail by two groups (1,2) and the i.r. and Raman data are satisfactorily interpreted in terms of Oh symmetry.
Perturbation of the
PF6 ion, for example by co-ordination of one fluorine atom to a metal, lowers the local symmetry to C4v which, in turn, leads to resolution of some degeneracies and to alteration of the selection rules. the vibrational modes in % irreducible
alter as shown in table lald now span the
representat~ns 4A 1
+ 2B 1 + B2 + 4E of C4v , of which the A 1 and
E modes are active in the infra-red.
u~(558 cm-I)
(2)
More specifically
Thus modes u3(830 cm-I) (2) and
of the PF6 ion should split and, in addition, new bands
corresponding to infra-red active components of the previously Raman active Ul, u2 and u 5 should appear in the region of respectively.
750
cm-I, 580 cm-I and 480 cm-I
The latter band, an i.r. active E mode derived from us(F2g )
may be obscured by the X-sensitive u16 b of pyridine which has undergone a large shift to higher wave number (440 m, 430 m-w cm-l).
Also the
inactive F2u (u6) mode of PF6 will be split (B1 + E) in C4v symmetry and the E mode is now i.r. active.
This band is however expected below 400 cm-I 405
EVIDENCE FOR LIGATED HEXAFLUOROPHOSPHATE(V)
406
Vol. 7, No.
5
(2).
TABLE 1 Analysis of the I.R. Bands of the Hexafluorophosphate(V) Group in [Cu(py)4(PF6)2]
Oh
o1(751+) 02(580)
Ii C4v
E
A1
A1
742m-s
572w
v3(830)
v4(558)
Flu
Ftu
B1 A1 -
E
885s
A1
E
06(?)
F2g
F2u
B2
(830s 560sh (555s -
1850s ~-
05(477)
E
B1
*
-
E
(40o
~550sh
°
Frequenczes in wave numbers from (2).
*Band obscured.
The predictions of the above paragraph are in good accord with the observed spectrum of [Cu(py)4(PF6)2] (TABLE 1) except that some Further splitting of the E modes derived from v 3 and v4 has occured.
This may be
due to a low site synsnetry within the crystalj which could of course, in principle~ explain the other observations.
However the intensity of the
A 1 mode at 742 cm-1 and the appearance of the other important A 1 mode at 572 cm-1, which is expected to be o£ weak intensity in the i.r., together with the clean splitting o£ u3 would argue for a relatively strong perturbation o£ the PF 6 group such as would occur ££ it were "semi co-ordinated,, (3) to copper(II). We have examined the corresponding perchlorate complex and here too~ not surprizingly, the infra-red data (TABLE 2) support the presence o£ semi coordinated percb_lorato-groups
(3).
The visible spectra o£ [Cu(py)4(PF6)2] and
[Cu(py)4(Cl04)2] are sim£1ar~ but not identical.
A tetragonal environment is
indicated for copper(II) in both complexes with the stronger interaction in the perc~1orate case.
The two g factor e.s.r, spectra also suggest approximately
Vol. 7, No. 5
EVIDENCE FOR LIGATED HEXAFLUOROPHOSPHATE(V)
407
t e t r a g o n a l environments f o r c o p p e r ( I I ) and, s i g n i f i c a n t l y , the values of g l l TABLE 2
Further Spectroscopic Data for LCu(py)4(PF6)2] and for [Cu(py)4(Cl04)2] .
(a)
,
,,
[Cu(pY)4(PF6)23 Visible ~
(by d i f f u s e r e f l e c t a n c e )
-
(18:300 cm-I 16,700 sh.
e.s.r, data--
(b)
~
=
2.027
gll =
2.248
[Cu(py)4(C]04) 2] Visible maxima (by diffuse reflectance) e.s.r, datai.r.
gl =
2.027
gll =
17~650 cm-1 (asynn).
2.261
data (C10~ group) 1113 cm-l(s): 1055 cm-1)(s), 933 cm-l(m): 630 cm-l(sh) lO45 cm-l~
623 cm-1
d i f f e r f o r the two complexes. The i n f r a - r e d data do not c o n s t i t u t e conclusive proof of hexafluorophosphate co-ordination.
Since i t i s c l e a r t h a t the environment of c o p p e r ( I I ) d i f f e r s in
the p e r c h l o r a t e and hexafluorophosphate complexes: the only reasonable a l t e r n a t i v e i n t e r p r e t a t i o n i s t h a t square planar Cu(py)~+ ions e x i s t in Cu(pY)4(PF6) 2.
This appears unlikely becausej apart from one exceptional case (4), this stereochemistry for copper(ll) is generally achieved only with n bonding ligands (5) and the necessary geometry of a planar Cu(py) 2+ ion
c
~
o
t
favour
bond formation,
I!
1.
VON K. BUHL]~ and W. BUES: Z. Anorg. a l l g . Chem. 308, 62 (1961)
2.
G.M. B]~DUNand A.C. RlYrENBER3, Inorg. Chem. 6, 2212 (1967)
3.
D.S. BROWN, J.D. LEE, B.G.A. I~LSON, B.J. HATHAWAY, I.M. PROCTER and A.A.G. TOMLINSON, Chem. Conmmn., 369 (1967)
4.
B.J. HATHAWAYand F.S. STEPHENS, J. Chem.Soc. (A) 884 (1970)
5.
B.J. HATHAWAYand D.E. BILLE~O, Coordin. Chem. Rev. 5 : 1 4 3 (1970)