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The structure and hyperfine splittings of simple phosphoranyl radicals
-Volume 39,h&r~2
_
,.-
__
_’
CHEhkU.
li.April
PHYSICS LETTERS
1976
..
: :, :
I -THE
STRtiCTtiRE AND HWEiFlNE
SPLITTINGS OF SIMPLE PHOSPHORAWL
RAtiICALs
A. ‘HtiDSON and R,F. TREWEEK Sckxd of Molecular Sciences,- iiniversiry of Sussex. Brighton BlVl 9QJ, UK Received
18 December
1975
The ab initio UHF method has been employed to calculate ccnstantsfor the radicals PHI, PFa, PH4 and PF4.
fn an eariier note [i] we have discussed the application of INDO caiculations to the series of free radicals PX2 and PXb (X = H, F, Cl). Subsequently reliable ESR data has been published for PH, [2] ; doubts about the assignment of the PF, spectrum have been resolved [3] confirming conclusions drawn from our INDO and AThlOL calculations_ It has become clea:, however, that the iND0 method is less successful when applied to phosphoranyl radicals since it predicts that the 31P hyperfiie coupling constant of PH4 should be greater than that of PF, whereas the re-verse is found experimentally. Similar conclusions have been reached by Colussi et al. [4,53 who have performed INDO caJculations on these radicals using a different set of parameters. Their equilibrium geometries are close to those obtained in our own wo:k [I]. We now report the results of ab initio ATMOL caku-
equilibrium geometries
and isotopic hype&&e
lations on PHI, PF2, PH4 and PF, and compare them with the semi-empirical investigations. Equilibrium geometries were estimated for each of the four radicais using a minimal basis of Slater orbit& pIus 3d orbitals on phosphorus. Extended basis calculations were then perfomed at these geometries using double zeta functions. The exponents far both the single and double zeta functions were taken from Ciementi [6] and each atomic function was fitted as a sum of three gaussians. For PH, we also performed a calculation in which the hydrogen Is functions were expanded as a sum of six gaussians. Our predicted geometries are summarised in table 1 and the hyperfine coupling constants in table 2. For PH, and PF, the geometries are close to “ihose found earlier using an STO-3G basis [ll and are not very different from the INDO values although the
Table 1 Calculated
equilibrium geometries
(distances
in pm, angles in de)
---
RPX,
RPXz
LX*PX*
Ref.
-
ATMOL PH2
141.9
92.1
PFz PH4 .PF4
164.8 141.3 -162.0
98.5 100.8 104.7
PI-l4
151 145 182
160 153 192
98 98 96
148 150 156
180
189
96
158
INDO
PF4
.2$8_----/-. _ -__
LXlPXl
___--_
--
_..
‘_
149.2 166.9
,:-.----.
coupling
172.6 166.4
:__
_.:
*ais work
t:f [II 141
CHEMICAEPHYSICS LETTERS
Volume 391 number 2 Table 2 A compakn
of experimental and theoretical hypcrfme coupling constants(G).
I5 April 1976
Valuesobtained after spin annihilation are in
brackets Basis
Cil!C.
__~_-_--_--_--__ SZ+d PH2 PF2
DZ+d
PH4 PF4
691.6(731-g)
PH2 PH4
77.8(29.7) 136.3c52.1) 305.7t326.2)
PF4
910.9(880.5)
PH2 -
exptl.
-talc.
exptl.
--134.3(46.9) 134.2c51.6) 330.7 (366.3)
PF2
6Gs
a (Xl
au-9
g3.0(32.4) _-__--.-_---
bond lengths are significantly shorter. For PH, and PF4 the discrepancy between INDO and ATMOL is more pronounced, particularly for the angle sub-
tended by the apical hydrogen atoms in PH4. The ATMOE calculations predict smaller changes from a’ regular trigonal bipyramidal structure than the INDO results. The theoretical hyperfine coupling constants reproduce the experimental trends and, unlike the INDO method, predict correctly the ratio of the 31P splittings for PF4 and PH4. The opposite signs obtained for the two proton splittings in the latter radical are consistent with lineshape studies of fluxional r-EuOPH, [ 7 1. However, the overall agreement with experiment is only moderate with, on the whole, better results before spin annihilation. Enlarging the basis set does not produce any marked improvement in the sPin densities. This would appear to be a general feature of the UHF method associated with the difficulty that the wave functioqis not an eigenfunction of S2. In a recent note [S] it has been shown that using a RHF wavefunction and performing CI including ali single excitations gives much better results for PF2 thari a UHF calculation with the same basis set and an in-
80 84.6 519.3 1344 80 84.6 519.3 1344 80
-.-
-21.5(-7.0) 32.0(11.0) 185.5(145.0) -l&1(-4.5) 87.6(X6.7) 9.2(11.1)
18 32.5 198.7 6.0 291 58
-19.4(-6.4) 43.4(14.9) 152.0(115.7) -12.8(-2.9) 119.4(107.2) 13.3C14.4)
18 32.5 198.7 6.0 291 58
-25.7<-8.4) ---..--.
H3
creased use of this procedure is to be expected in the future. We thank the S.R.C. for financial support and for making available computing time at the ATLAS laboratory.
References [I] A. Hudson and J.T. Wiffen, Chem. Phys. Letters 29 (1974) 113. [2] A.J. CoIussi,J.R. Morton and K.F. Preston, J. Chem. Phys. 62 (1975) 2004. 13) A.J. Colussi, J.R. Morton, K.F. Preston and R.W. Fessenden, J. Chem. Fhyr 61(1974) 1247. [4] A.J. Colussi, J.R. Morton and K.F. Preston, J. Phys. Chem. 79 (1975) 651. [S] A-J. Colussi. JR. Morton and K.F. Preston, J. Phys.Chem. 79 (1975) 1855. [6] R. Clementi and D-f_. Rnimondi. J. Chem. Phys. 38 (1963) E. Clemerrti, IBhl J. Res. Develop. 9 (1965) 2, suppl. P.J. Krusic and P. hfea!!i, Chem. Phys. Letters 18 (1973)
347. J. Kendrick, LH. Hillier and hf_F. Guest, Chem. Phys.
Letters 33 (1975) 173.
249
_
,.-
__
_’
CHEhkU.
li.April
PHYSICS LETTERS
1976
..
: :, :
I -THE
STRtiCTtiRE AND HWEiFlNE
SPLITTINGS OF SIMPLE PHOSPHORAWL
RAtiICALs
A. ‘HtiDSON and R,F. TREWEEK Sckxd of Molecular Sciences,- iiniversiry of Sussex. Brighton BlVl 9QJ, UK Received
18 December
1975
The ab initio UHF method has been employed to calculate ccnstantsfor the radicals PHI, PFa, PH4 and PF4.
fn an eariier note [i] we have discussed the application of INDO caiculations to the series of free radicals PX2 and PXb (X = H, F, Cl). Subsequently reliable ESR data has been published for PH, [2] ; doubts about the assignment of the PF, spectrum have been resolved [3] confirming conclusions drawn from our INDO and AThlOL calculations_ It has become clea:, however, that the iND0 method is less successful when applied to phosphoranyl radicals since it predicts that the 31P hyperfiie coupling constant of PH4 should be greater than that of PF, whereas the re-verse is found experimentally. Similar conclusions have been reached by Colussi et al. [4,53 who have performed INDO caJculations on these radicals using a different set of parameters. Their equilibrium geometries are close to those obtained in our own wo:k [I]. We now report the results of ab initio ATMOL caku-
equilibrium geometries
and isotopic hype&&e
lations on PHI, PF2, PH4 and PF, and compare them with the semi-empirical investigations. Equilibrium geometries were estimated for each of the four radicais using a minimal basis of Slater orbit& pIus 3d orbitals on phosphorus. Extended basis calculations were then perfomed at these geometries using double zeta functions. The exponents far both the single and double zeta functions were taken from Ciementi [6] and each atomic function was fitted as a sum of three gaussians. For PH, we also performed a calculation in which the hydrogen Is functions were expanded as a sum of six gaussians. Our predicted geometries are summarised in table 1 and the hyperfine coupling constants in table 2. For PH, and PF, the geometries are close to “ihose found earlier using an STO-3G basis [ll and are not very different from the INDO values although the
Table 1 Calculated
equilibrium geometries
(distances
in pm, angles in de)
---
RPX,
RPXz
LX*PX*
Ref.
-
ATMOL PH2
141.9
92.1
PFz PH4 .PF4
164.8 141.3 -162.0
98.5 100.8 104.7
PI-l4
151 145 182
160 153 192
98 98 96
148 150 156
180
189
96
158
INDO
PF4
.2$8_----/-. _ -__
LXlPXl
___--_
--
_..
‘_
149.2 166.9
,:-.----.
coupling
172.6 166.4
:__
_.:
*ais work
t:f [II 141
CHEMICAEPHYSICS LETTERS
Volume 391 number 2 Table 2 A compakn
of experimental and theoretical hypcrfme coupling constants(G).
I5 April 1976
Valuesobtained after spin annihilation are in
brackets Basis
Cil!C.
__~_-_--_--_--__ SZ+d PH2 PF2
DZ+d
PH4 PF4
691.6(731-g)
PH2 PH4
77.8(29.7) 136.3c52.1) 305.7t326.2)
PF4
910.9(880.5)
PH2 -
exptl.
-talc.
exptl.
--134.3(46.9) 134.2c51.6) 330.7 (366.3)
PF2
6Gs
a (Xl
au-9
g3.0(32.4) _-__--.-_---
bond lengths are significantly shorter. For PH, and PF4 the discrepancy between INDO and ATMOL is more pronounced, particularly for the angle sub-
tended by the apical hydrogen atoms in PH4. The ATMOE calculations predict smaller changes from a’ regular trigonal bipyramidal structure than the INDO results. The theoretical hyperfine coupling constants reproduce the experimental trends and, unlike the INDO method, predict correctly the ratio of the 31P splittings for PF4 and PH4. The opposite signs obtained for the two proton splittings in the latter radical are consistent with lineshape studies of fluxional r-EuOPH, [ 7 1. However, the overall agreement with experiment is only moderate with, on the whole, better results before spin annihilation. Enlarging the basis set does not produce any marked improvement in the sPin densities. This would appear to be a general feature of the UHF method associated with the difficulty that the wave functioqis not an eigenfunction of S2. In a recent note [S] it has been shown that using a RHF wavefunction and performing CI including ali single excitations gives much better results for PF2 thari a UHF calculation with the same basis set and an in-
80 84.6 519.3 1344 80 84.6 519.3 1344 80
-.-
-21.5(-7.0) 32.0(11.0) 185.5(145.0) -l&1(-4.5) 87.6(X6.7) 9.2(11.1)
18 32.5 198.7 6.0 291 58
-19.4(-6.4) 43.4(14.9) 152.0(115.7) -12.8(-2.9) 119.4(107.2) 13.3C14.4)
18 32.5 198.7 6.0 291 58
-25.7<-8.4) ---..--.
H3
creased use of this procedure is to be expected in the future. We thank the S.R.C. for financial support and for making available computing time at the ATLAS laboratory.
References [I] A. Hudson and J.T. Wiffen, Chem. Phys. Letters 29 (1974) 113. [2] A.J. CoIussi,J.R. Morton and K.F. Preston, J. Chem. Phys. 62 (1975) 2004. 13) A.J. Colussi, J.R. Morton, K.F. Preston and R.W. Fessenden, J. Chem. Fhyr 61(1974) 1247. [4] A.J. Colussi, J.R. Morton and K.F. Preston, J. Phys. Chem. 79 (1975) 651. [S] A-J. Colussi. JR. Morton and K.F. Preston, J. Phys.Chem. 79 (1975) 1855. [6] R. Clementi and D-f_. Rnimondi. J. Chem. Phys. 38 (1963) E. Clemerrti, IBhl J. Res. Develop. 9 (1965) 2, suppl. P.J. Krusic and P. hfea!!i, Chem. Phys. Letters 18 (1973)
347. J. Kendrick, LH. Hillier and hf_F. Guest, Chem. Phys.
Letters 33 (1975) 173.
249