- Email: [email protected]
The structure of phosphino and phosphoranyl radicals
Volume 29, number 1
CHEMICAL.PHYSICS
,THE STRUCTURE
OF PHOSPHINO
LFITERS
I November 1974
AND PHOSPHfJXt.ANYL RADICALS
A.HUDSON and J-T. WIFFEN ScJ1001 0fMolccubr
Sciences,. Universily of Sussex.
Brighton.BNl9QJ,UK Received 10 July 1974
Equilibrium geometries and &tropic nuclea hypzrfme coupling constants have been czkulzted fx the radiuk PX2 znd P& (x = H, F, Cl) using the INDQ approximations; PHg and PFz have ako been investigatti by ab inirio methods.
Phosphino, PX,, and phosphoranyl, PX,, radicals have been the subject of several spectroscopic investi@ions [l] but few theoretical studies have been reported. In none of the published calculations. 1241 have molecular geometries been fully optimised; all bond lengths in PX4 radicals have invariably been taken as equal. An assumed geometry was used in a recent ab initio calculation [S] on PF2.
bond angle in PF2 is close to that found in PF2H (99’) supporting t.he idea [9] that the structures of many phosphorus radicals and their protic parents are close;y similar. Our predicted structures for the phosphorany radicals, which can be regarded as distorted trigonal bipyramids (C2Vj with the unpti?ed electron in an equatorial position, are in line with generally held views about such species [l] . The INDO results sug-
We have obtained minimum energy geometries for six of these radicals using the INDO approximations; ab initio results are presented for PH2 and PF2. The WO results were obtained using procedures originally described by Benson and Hudson [6] but with Cl. for P equal to 3.45 eV; Us and lJpp hence become, -59.7495 and -54.0226 ev. Both minimal and ex-
gest that the PX, structure is derived fr!m FX, by the addition of two approximateiy &al X atoms with ionger PX bonds; only minor changes occur in the shape-of the PX, moiety. The predicted differen&s of about 10 pm between equatorial and axiai
bond lengths are.sizClar to those found in pentacoordinate phosphorus compounds such as FF5, Our
tended basis sets were used in ab initio ATMOL c-alcdations, The minimal basis was at the ST@3G level
bond angles for PH4 and PF41are quite close to those
but with a 2p atomic orbital on fluorine [7] i Extended basis ca&uiations were performed ai the equilibrium
Table 1
geometry obtained using the minimal basis with
Calculated equilibrium geometries for PX2 and Pk4
double zeta functions for valence orbit& and &lie zeta functions for inner shells; exponents were taken from Clementi_ [8] . Dir&t comparison of our calculated geometries,
suriunarised in table-l, tiith.experiment
: &clipm) INDO
PH;! PF2. PH4
151 183. 222 151
,-
ya:
iz
*TMoL
F:i
is o,nly.pos-
Paz
sible fo; PH2 which has [l] a PH bond length of
143 pm and a bond angle of 91.7”. This is in good, agreement ‘with the ab initib result. As is generally ‘_
ilie cat?! the INIjO m&hod overestimates bond’lengthi but is more satisfactory for bond a&l&The predicted
:
-. 160 192 235
1
;
-
LXiFX, .97 ,9.5 99, 98. 96
.,98 52 98.6
._
L%PL& L48 156 142 -
-
; ,,
‘.,.
14’ 2 ,165
RP~
113
_ ..
‘v’olume.29, nymbeerl ‘,.:
CHEMICAL PHYSIC!; LE-I-ERS
.’ ..
: ,. A comparison
of experimenti
and ukulated
I November
Table i hypdrfinc coupI& cor~.tants (G).VaIues
obtained after spin annihilation
1974
are in
brackets
O(p)’ ‘.
RadicaI
‘.
cdc. rim0
_:
.-
PH2
‘.
PF2
Pa; PF4
',
PC4
:
.-
‘, PH2
ATMOL-STO3G
PF2 ATMOL-extended
:
basis
PHz
PFz
‘,
‘.
.-
am
‘.
exgtl.
c&o.
80
-33.1
113.6 (74.8) 73.7 (48.4) 29.9 (19.7) 1449 (1462)
71 1330
1038
1206
exptl. (-23.2)
‘.
18
[131 iI41 WI
(2.2j (206) (6.4) (9.4) 4.4 (-1,7)
5 2&i 59 62 7
18
[I31
32
1141
118
(131 I141
3.7 159 0.4 5.3
78.9 (29.6) .75.6 (30.1)
-GO f:5
-22.6 (-7.4) 42.6 (14.7)
117.9 (45.0) 205.6 (78.6)
.!O E5
-19.7 (-6.5). 89.2 (30.2)
”
.”
32
43.5 (30.6)
?5
(ioI9j
Ref..
.[I61 [151
32
.. obtained using the UNDO method and equal assumed bond lengths [3,4] but differ.frorn those determined by Higuchi [2] (18‘6’ and.1 IO”) as a best fit to the hyperfine splittings. *Publishedinformation on the hyperfme inter&tions of PX, and PX4. radicals, as tabulated by Bentru+ [I J , indicates results tie present
that i? some cases conflicting
The relatively small number of GTF’s used in the ab initio calculations are not expected to give a good description of the wavefunctions near the nucleus and, as in other related studies of small free radicals [12], the calculated coupling constmts are in only moderate :rgreement with experiment. With the exception
:
of the extended
basis calcukttion
on PF2, best results
are obtained with the UHF wavefunctions
in the literature. Subsequent to his
before spin
review, spectra originally assigned to a rapidly i&rannjhilation. The results xe sufficiently good, however., to confii Nelson et al’s experimental values converting form of PF4 have been reassigned [lo] to PFS; doubts have been expressed [I I] about spectra for PF2 and to rule out alternative values, cited by assigned to PIiI;_We have therefore omitted PH, from Bentrude [l] , which give + 2 +. our correlation of hyperfme splittings with calculated We thank the S.R.C. for Fmancial support and for spin densities. Results for the remaining radicals are given in table.2.together with the generally accepted making available computing time at the ATLAS labexperimental results. In the INDO calculations 31P oratory. : splittings were obtained, from a least mean squares fit.to the experimental results; the scaling factor for 3s sp’m densities was 5482 G. Scaling factors for H, F References and Cl were those derived by Biddles and Hudson [6] . [l] \V.G. BentrJdc, in: F&z mdic&, ed. J.K. Kochi (Wiley-, .,The results for PI-I, ,and PF2 are-in quite good agreeInterscience, New York, 1973) p. 595. ment ,with experiment but for PCl, and P Cl4 aze less [2], J. Higuchi,J. Chem. Phys. 50 (lS69) 1001. ~ktisfactoj; The 31P and larger rgF splitting in PF4 [3] C.A. M,cDowell, K.A.R. Wtchell and P. kghunathan, are well accounted for but the remaining lgF splitting I. &em; Whys.57 (1972) 1699. is considerably underestimafed. A similar diffculty ” [ij.D. KiIr=lst ank C. Thomson, J. Chem. Sot. Faraday II was reported by I&cast and Tho$on [4] who could (:!972) 435. L.51. J:C. Cobb and A. Hmchbffe, eem. Phys. Letters 24 fiid no geometj which rcpi0duce.d the experimental: ,!1.974)75. : .ratio of fluorine’sphttings; aFz was also underestimated [6]~H.G~‘Bknson and A. Hudson, Theoset Chim.-Acta 23 in Hig+‘s extended H&&e1 calcula&s [2] and ‘. :. c1970125g. furtter work on this system is required: ., I. Biddles a:d A. Hudson, MoL Phys. 25 (1973).707. ,’ :
‘?114 ,,
: :.
:’ (,Jf’ :.:.;-
,:_ :,:
._ ‘.
.‘.
... .-.
.:. _; -’ .’ :
-. .
” _.
”
,., ..
,..
.
‘. ‘,.
,-
CHEMICAL PHYSICS LETTERS .-
\[oIume 29, number 1
[7]~.H.kier and V.R. Saunders, Trans. Faraday Sac, 66 C197Oj2401.
-‘.
,:[S]8.Ctemznti and D.L. R&ion&i, J. Chem. Phys. 38 :. (1963) 2686; 3%Clementi, IBM J. Res. L&Mop. 9 (1965) 2, s&pl. [9]A.G. ?z.-fIes,‘R;VI. Dennis, D. Grillor, K.U:Irgold and B.P. Roberts, Mol. Phys. 25 (1973) 989. [10] SP. Mishra and hi.C.R. Symons,J.Chem. Sac. C&em: Commun. (197Sf 279. Ill] D..GrilIer and ES. Roberts; J.Chem. Sot. P&&II .. (1973) 1339. .’ (121 Lf. Aarons, I.H. HiUier and hiF. Guest, 1. Chem. Sac. Faraday If (1974) 167. .
.,
..
? Navember 1974
[13] 8.L. hforehotlsc, J.J. Ciistianser. and W. Gordy, f. Chem. Phys. 45. (1966) 1747. 1141 W. Nelson, G. Jackel and W. Gordy, f. Cf~em. Phys. 52 (1970)4572, {!!5] C.F. Rokoszka and F. E&inck.m.znn, J. A&. Chcm. Sac 92 (f970) 1199; A. Begum and M.C.R: Syrnocs, I. them. Sot A (1971)2065; MS. WeI, J.H. Ctxrent and J. Gend&, f. Chem. Phys. : 57 (1972) 243~ [16] R&‘. Fcssenden and R-H. S&tier, J. &m. Phys.45 .,(1966) 1845.
:
:
CHEMICAL.PHYSICS
,THE STRUCTURE
OF PHOSPHINO
LFITERS
I November 1974
AND PHOSPHfJXt.ANYL RADICALS
A.HUDSON and J-T. WIFFEN ScJ1001 0fMolccubr
Sciences,. Universily of Sussex.
Brighton.BNl9QJ,UK Received 10 July 1974
Equilibrium geometries and &tropic nuclea hypzrfme coupling constants have been czkulzted fx the radiuk PX2 znd P& (x = H, F, Cl) using the INDQ approximations; PHg and PFz have ako been investigatti by ab inirio methods.
Phosphino, PX,, and phosphoranyl, PX,, radicals have been the subject of several spectroscopic investi@ions [l] but few theoretical studies have been reported. In none of the published calculations. 1241 have molecular geometries been fully optimised; all bond lengths in PX4 radicals have invariably been taken as equal. An assumed geometry was used in a recent ab initio calculation [S] on PF2.
bond angle in PF2 is close to that found in PF2H (99’) supporting t.he idea [9] that the structures of many phosphorus radicals and their protic parents are close;y similar. Our predicted structures for the phosphorany radicals, which can be regarded as distorted trigonal bipyramids (C2Vj with the unpti?ed electron in an equatorial position, are in line with generally held views about such species [l] . The INDO results sug-
We have obtained minimum energy geometries for six of these radicals using the INDO approximations; ab initio results are presented for PH2 and PF2. The WO results were obtained using procedures originally described by Benson and Hudson [6] but with Cl. for P equal to 3.45 eV; Us and lJpp hence become, -59.7495 and -54.0226 ev. Both minimal and ex-
gest that the PX, structure is derived fr!m FX, by the addition of two approximateiy &al X atoms with ionger PX bonds; only minor changes occur in the shape-of the PX, moiety. The predicted differen&s of about 10 pm between equatorial and axiai
bond lengths are.sizClar to those found in pentacoordinate phosphorus compounds such as FF5, Our
tended basis sets were used in ab initio ATMOL c-alcdations, The minimal basis was at the ST@3G level
bond angles for PH4 and PF41are quite close to those
but with a 2p atomic orbital on fluorine [7] i Extended basis ca&uiations were performed ai the equilibrium
Table 1
geometry obtained using the minimal basis with
Calculated equilibrium geometries for PX2 and Pk4
double zeta functions for valence orbit& and &lie zeta functions for inner shells; exponents were taken from Clementi_ [8] . Dir&t comparison of our calculated geometries,
suriunarised in table-l, tiith.experiment
: &clipm) INDO
PH;! PF2. PH4
151 183. 222 151
,-
ya:
iz
*TMoL
F:i
is o,nly.pos-
Paz
sible fo; PH2 which has [l] a PH bond length of
143 pm and a bond angle of 91.7”. This is in good, agreement ‘with the ab initib result. As is generally ‘_
ilie cat?! the INIjO m&hod overestimates bond’lengthi but is more satisfactory for bond a&l&The predicted
:
-. 160 192 235
1
;
-
LXiFX, .97 ,9.5 99, 98. 96
.,98 52 98.6
._
L%PL& L48 156 142 -
-
; ,,
‘.,.
14’ 2 ,165
RP~
113
_ ..
‘v’olume.29, nymbeerl ‘,.:
CHEMICAL PHYSIC!; LE-I-ERS
.’ ..
: ,. A comparison
of experimenti
and ukulated
I November
Table i hypdrfinc coupI& cor~.tants (G).VaIues
obtained after spin annihilation
1974
are in
brackets
O(p)’ ‘.
RadicaI
‘.
cdc. rim0
_:
.-
PH2
‘.
PF2
Pa; PF4
',
PC4
:
.-
‘, PH2
ATMOL-STO3G
PF2 ATMOL-extended
:
basis
PHz
PFz
‘,
‘.
.-
am
‘.
exgtl.
c&o.
80
-33.1
113.6 (74.8) 73.7 (48.4) 29.9 (19.7) 1449 (1462)
71 1330
1038
1206
exptl. (-23.2)
‘.
18
[131 iI41 WI
(2.2j (206) (6.4) (9.4) 4.4 (-1,7)
5 2&i 59 62 7
18
[I31
32
1141
118
(131 I141
3.7 159 0.4 5.3
78.9 (29.6) .75.6 (30.1)
-GO f:5
-22.6 (-7.4) 42.6 (14.7)
117.9 (45.0) 205.6 (78.6)
.!O E5
-19.7 (-6.5). 89.2 (30.2)
”
.”
32
43.5 (30.6)
?5
(ioI9j
Ref..
.[I61 [151
32
.. obtained using the UNDO method and equal assumed bond lengths [3,4] but differ.frorn those determined by Higuchi [2] (18‘6’ and.1 IO”) as a best fit to the hyperfine splittings. *Publishedinformation on the hyperfme inter&tions of PX, and PX4. radicals, as tabulated by Bentru+ [I J , indicates results tie present
that i? some cases conflicting
The relatively small number of GTF’s used in the ab initio calculations are not expected to give a good description of the wavefunctions near the nucleus and, as in other related studies of small free radicals [12], the calculated coupling constmts are in only moderate :rgreement with experiment. With the exception
:
of the extended
basis calcukttion
on PF2, best results
are obtained with the UHF wavefunctions
in the literature. Subsequent to his
before spin
review, spectra originally assigned to a rapidly i&rannjhilation. The results xe sufficiently good, however., to confii Nelson et al’s experimental values converting form of PF4 have been reassigned [lo] to PFS; doubts have been expressed [I I] about spectra for PF2 and to rule out alternative values, cited by assigned to PIiI;_We have therefore omitted PH, from Bentrude [l] , which give + 2 +. our correlation of hyperfme splittings with calculated We thank the S.R.C. for Fmancial support and for spin densities. Results for the remaining radicals are given in table.2.together with the generally accepted making available computing time at the ATLAS labexperimental results. In the INDO calculations 31P oratory. : splittings were obtained, from a least mean squares fit.to the experimental results; the scaling factor for 3s sp’m densities was 5482 G. Scaling factors for H, F References and Cl were those derived by Biddles and Hudson [6] . [l] \V.G. BentrJdc, in: F&z mdic&, ed. J.K. Kochi (Wiley-, .,The results for PI-I, ,and PF2 are-in quite good agreeInterscience, New York, 1973) p. 595. ment ,with experiment but for PCl, and P Cl4 aze less [2], J. Higuchi,J. Chem. Phys. 50 (lS69) 1001. ~ktisfactoj; The 31P and larger rgF splitting in PF4 [3] C.A. M,cDowell, K.A.R. Wtchell and P. kghunathan, are well accounted for but the remaining lgF splitting I. &em; Whys.57 (1972) 1699. is considerably underestimafed. A similar diffculty ” [ij.D. KiIr=lst ank C. Thomson, J. Chem. Sot. Faraday II was reported by I&cast and Tho$on [4] who could (:!972) 435. L.51. J:C. Cobb and A. Hmchbffe, eem. Phys. Letters 24 fiid no geometj which rcpi0duce.d the experimental: ,!1.974)75. : .ratio of fluorine’sphttings; aFz was also underestimated [6]~H.G~‘Bknson and A. Hudson, Theoset Chim.-Acta 23 in Hig+‘s extended H&&e1 calcula&s [2] and ‘. :. c1970125g. furtter work on this system is required: ., I. Biddles a:d A. Hudson, MoL Phys. 25 (1973).707. ,’ :
‘?114 ,,
: :.
:’ (,Jf’ :.:.;-
,:_ :,:
._ ‘.
.‘.
... .-.
.:. _; -’ .’ :
-. .
” _.
”
,., ..
,..
.
‘. ‘,.
,-
CHEMICAL PHYSICS LETTERS .-
\[oIume 29, number 1
[7]~.H.kier and V.R. Saunders, Trans. Faraday Sac, 66 C197Oj2401.
-‘.
,:[S]8.Ctemznti and D.L. R&ion&i, J. Chem. Phys. 38 :. (1963) 2686; 3%Clementi, IBM J. Res. L&Mop. 9 (1965) 2, s&pl. [9]A.G. ?z.-fIes,‘R;VI. Dennis, D. Grillor, K.U:Irgold and B.P. Roberts, Mol. Phys. 25 (1973) 989. [10] SP. Mishra and hi.C.R. Symons,J.Chem. Sac. C&em: Commun. (197Sf 279. Ill] D..GrilIer and ES. Roberts; J.Chem. Sot. P&&II .. (1973) 1339. .’ (121 Lf. Aarons, I.H. HiUier and hiF. Guest, 1. Chem. Sac. Faraday If (1974) 167. .
.,
..
? Navember 1974
[13] 8.L. hforehotlsc, J.J. Ciistianser. and W. Gordy, f. Chem. Phys. 45. (1966) 1747. 1141 W. Nelson, G. Jackel and W. Gordy, f. Cf~em. Phys. 52 (1970)4572, {!!5] C.F. Rokoszka and F. E&inck.m.znn, J. A&. Chcm. Sac 92 (f970) 1199; A. Begum and M.C.R: Syrnocs, I. them. Sot A (1971)2065; MS. WeI, J.H. Ctxrent and J. Gend&, f. Chem. Phys. : 57 (1972) 243~ [16] R&‘. Fcssenden and R-H. S&tier, J. &m. Phys.45 .,(1966) 1845.
:
: