Spectrochimica Acta. Vol. 24A. pp. 1669 to 1676. Pergamon Press 1968. Printed in Northern Ireland
The molecular complexes of N,N-dimethylmethanesulphinamide
and N,N-dimethylmethanesulphonamidewith iodine,
iodine cyanide and phenol*
H. MØLLENDAL,J. GRUNDNESand P. KLABOE
Department
of Chemistry,
(Reeeived
University
of Oslo, Oslo 3, Norway
15 February
1968)
Abstract-The
charge-transfer
complex between N,N-dimethyhnethanesulphinamide
and iodine
in solution was studied in the visible, ultra-violet
and infrared regions and the thermodynamic
functions and spectral parameters
for the complex are reported.
The corresponding
interactions
with iodine cyanide and phenol were investigated.
The basicities of N,N-dimethyhnethanesulphinamide
and dimethyl sulphoxide were found to be very similar.
N,N-Dimethylmethanesulphonamide
was such aweak base that the iodine and iodinecyanide
interactions
could not be studied quantitatively.
The complex with phenol was investigated,
revealing a close similarity to tetramethylene
sulphone.
INTRODUCTION
DURINGthe last five years the complex formation between various sulphoxides and
iodine [1-7], iodine cyanide [2] and phenol [l, 8] have been investigated. The data
reveal that the sulphoxides are moderately strong donors to these acceptors. On
the other hand, the related sulphones [l] seem to form very weak complexes.
In the present paper we wanted to extend such studies to the corresponding
amides in order to relate them with the sulphoxides and the sulphones. It is well
known [9] that the ketoamides are much stronger bases to iodine than the ketones,
explai~ed as a result of delocalization of the nitrogen lone pair electrons, giving a
higher electron density on the carbonyl oxygen. Moreover, the cyanamides [10] give
considerably stronger complexes with iodine and the interhalogens than do the
nitriles. The main purpose of this research was to establish if a corresponding effect
on the basicity of these sulphur compounds could be observed. Therefore the
thermodynamic
functions -!:lGo, -!:lHo and -!:lSo and various spectroscopic
parameters for complexes of sulphin- and sulphonamides were determined. The two
* This work was supported
Humanities.
[l]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
l
in part by the Norwegian
Research
Council
for Science and the
R. S. DRAGo, B. WAYLANDand R. L. CARLSON,J. Am. Chem. Soc. 85, 3125 (1964).
E. AUGDAHLand P. KLABOE,Aeta Chem. Seand. 18, 18 (1964).
P. KLABOE,Aeta Chem. Scand. 18, 27 (1964).
P. KLABOE,Aeta Chem. Scand. 18, 999 (1964).
J. GRUNDNESand P. KLABOE, Trans. Faraday Soe. 60, 1991 (1964).
B. MUSULIN,W. J. JONES and M. J. BLEEM,J. Inorg. Nuel. Chem. 26, 239 (1964).
M. C. GIORDANO,J. C. BAZANand A. J. ARVlA, J. Inorg. Nuel. Chem. 28, 1209 (1966).
T. GRAMSTAD,
Spectroehim. Aeta 19, 829 (1963).
R. S. DRAGo, D. A. WENZ and R. L. CARLSON,J. Am. Chem. Soe. 84, 1106 (1962).
E. AUGDAHLand P. KLABOE,Aeta Chem. 8cand. 19, 807 (1965).
1669
1670
H. MØLLENDAL, J. GRUNDNES and P. KLABOE
simp1est mo1ecu1es were se1ected: N,N-dimethy1methanesu1phinamide
(CHgk
NS(O)CHg (SIA) and N,N-dimethy1methanesu1phonamide
(CHg)2NS02CHg (SOA)
which are derived from dimethy1 su1phoxide and dimethy1 sulphone, respective1y.
We have studied not on1y the SIA and SOA comp1exes with iodine, but with iodine
cyanide and pheno1 as well. The interactions were investigated in the visib1e and the
u1travio1et spectroscopic regions and perturbations in the donor and the acceptor
infrared spectra detected.
EXPERIMENTAL
Ohemicals
SIA and SOA were synthesized as described [lI]. The PMR spectrum of SIA was
identica1 with the one reported [11-12], but weak signals at 117, 171 and 180 c/s
indicated small amounts of impurities, which cou1d not be removed by repeated
distillations under reduced pressure.
Since SIA is extreme1y hygroscopic, the
impurities might part1y be water. SOA was re-crystallized from hexane (m.p.
48.4°C). Iodine and iodine cyanide we repurified as before [2, 3]. The solvents
were of spectrograde qua1ity, Uvasole, from Merck. Carbon disu1phide was used
without further purification, carbon tetrach10ride was dried over P 205 in a desiccator,
and the other solvents were dried and distilled.
Instrumental
The ultraviolet and visib1e spectra were recorded with a Beckman DK-l recording
speetrometer and a Zeiss PMQ Il manual speetrometer equipped with thermostatted
cell ho1ders. Matched pairs of ground glass stoppered silica cells of thickness 1.00 cm
were employed. A Perkin-E1mer model 21 speetrometer with NaC1 and CsBr optics
and a Beckman IR-9 grating speetrometer were used for the infrared recordings.
The temperature was controlled by p1acing the infrared cells inside a thermostatic
box. Infrared cells of thickness 1-2 mm were employed for the quantitative studies
in order to keep the solute concentrations low.
RESULTS
SIA-iodine complex
When SIA was added to a solution of iodine in CC14the visib1e absorption band
at 517 mfl was blue shifted to 440 mfl and for varying SIA concentrations an isosbestie point was observed at 485 mfl. No spectral changes were observed for several
hours if the SIA-iodine solutions were kept in darkness neither with CCl4nor CH2C12
as solvents, but in CS2 rapid reactions occurred. The formation constant for the
SIA-iodine comp1ex at 20°C was determined from the absorption data at 550 mfl
for a series of mixed solutions, using a modified LANG equation [13]
°nOAl
E - EA
l
l
E-E
A
= (O n+ OA+Be - BA) Be - BA K(Be - BA)
[Il] R. M. MORlARTY,Tetrahedron Lett. 10, 509 (1964).
[12] R. M. MORIARTY,J. Org. Chem. 30, 600 (1965).
[13] R. P. LANG,J. Am. Chem. Soc. 84, 1185 (1962).
(l)
The molecular
complexes
of N,N-dimethylmethanesulphinamide
1671
with iodine
OD and 0..1are the initial donor and acceptor concentrations, respectively, E - EA is
the difference in absorbance between a mixed solution of concentrations OD and 0..1
and a solution with acceptor concentration 0..1' Ba - BAis the difference in the molar
extinction coefficients between the complex and the acceptor (the donor has no
absorption in this region) and l is the celliength.
In a cyclic iteration procedure a
reasonable value for Ba - BAwas used as a first approximation and K and Ba - BA
calculated. The procedure was worked out with a least-squares program for the
IBM 1620 Il computer. A series of 9 mixed solutions were measured at 20°0, the
iodine concentration kept at 1.466 X 10-3 M and the SIA concentration varying
between 1.567 X 10-2 and 11.759 X 10-2 M. From the data at 550 mfl we obtained
K = 11.7 l/mole. The absorbance of one particular mixed solution was measured
at six temperatures at 550 mfl, assuming [14] a constant difference Ba BA =
-596 l/mole cm. The formation constants at six temperatures between 17 and 41°0
were calculated from equation (1). The thermodynamic functions -tlHo and -tlSo
-
were determined
in the usual way by a least
0.3 kcal/mole and -tlSo
= 7 ::f: 1 e.u.
squares
procedure:
tlHo
=
3,4 ::f:
Since 0014 is not transparent below 270 mfl, OH2012was used as a solvent for the
ultraviolet studies. However, it was observed that photochemical reactions occurred
in the SIA-iodine solutions in OH2012which produced 13- ions, as apparent from the
absorption bands at 290 and 360 mfl. An absorption peak was detected at 261 mfl,
undoubtedly caused by the SIA-iodine charge transfer band, but no quantitative
studies were possible.
The infrared spectrum of SIA was recorded as a capillary (4000-650 cm-l) and
in solution (4000-300 cm-l) and the observed frequencies are listed in Table 1.
Table 1. Infrared spectral data for N,N-dimethylmethanesulphinamide
pure liquid and in solution
Solution
Liquid
Ca 2900
1644
1458
1412
s
s
m
m
1354 sh
1300 VW
1264 vw
1228 vw
ll78 m
ll35vw
1070 vs
923m
703m
666 vw
Ca 2900
1666
1466
1452
1415
1395
1290
1247
s
s
m
m
sh
vw
vw
vw
Solvent
CI.CCC!.
C!.CCC!.
C!. CCC!.
CI.CCCI.
C!.CCC!.
CS.
CS.
es.
ll73 w
ll33 vw
1080 vs
918m
693m
CS.
OS.
635w
483m
420m
323 vw
e6Hl2
C6H6
C6H6
°6H6
ess
es.
es.
Tentative
assignment
VCR
VSO
+ vcs
J'""'
VaCNC
rCRs
vso
VSN
VsCNO
VOS
def. modes
}skeietal
s = strong, m = medium, w = weak, sh = shoulder, v = very.
[14] R. L. CARLSONand R. S. DRAGO,J. Am. Okern. SOC.84, 2320 (1962).
as
1672
H. MØLLENDAL, J. GRUNDNES and P. KLABOE
When iodine, iodine cyanide or phenol were added to an SIA solution, various changes
occurred in the infrared spectrum. The perturbations are listed in Table 2, and it
Table 2. Perturbed infrared bands in N,N-dimethylmethanesulphinamide
complex formation
Donor
v
Donor- 12
1666*
1080t
918t
693t
635t
Solvents:
v
bov
1616
1022
946
715
50
58
-28
-22
* tetrachloromethylene;
Donor-ION
V
1626
1040
925
703
646
t
carbon
disulphide
on
Donor-phenol
bov
V
bov
40
40
-7
-10
-11
1637
1048
925
703
645
29
32
-7
-10
-10
and
t cyclohexane.
appears that the same infrared band of SIA were shifted for each added acceptor.
The largest shifts were observed in the iodine complexes, but irreversible reactions
occurred for these high iodine concentrations.
BIA complexes with iodine cyanide and phenol
The SIA-iodine cyanide complex could best be studied in the infrared region,
and spectral perturbations were observed both for the donor and the acceptor spectra.
Quite concentrated, mixed SIA-iodine cyanide complexes were perfectly stable with
time, and we found the displaced S=O stretching band at 1080 cm-l best suited for
a quantitative calculation. It appeared that for a constant SIA concentration in
CS2 an isosbestie point was observed. Series of mixed solutions were recorded at
various temperatures between 20 and 35°C. The formation constants were calculated
by the described method, using the absorbance values at 1080 cm-l. The following
values were calculated: K = 83,1, 69.0, 67,5 and 59'81/mole at 20,25,30 and 35°C,
respectively, giving b.Ho = -3.7 ::!::0.5 kcal/mole and b.Bo = -4,1 ::!::1.6 e.u.
Iodine cyanide displays the C-I stretching band at 476 cm-l when dissolved in
C6H6' This band was shift ed to 454 cm-l when SIA was added and an isosbestie
point observed at 466 cm-l for constant iodine cyanide concentrations.
It appears from Table 2 that addition of phenol to SIA perturbed the infrared
spectrum somewhat less than adding iodine and iodine cyanide. The free O-H
stretching band of phenol situated at 3611 cm-l in CCl4 was shifted 360 cm-l in the
complex. The revised relationship suggested by EPLEY and DRAGO[15] gives the
enthalpy of formation equal to: b.Ho = -6.8 kcal/mole. The formation constant
for the SIA-phenol complex was determined at 20°C in CCl4 from the variations in
the phenol absorption at 284 mfl, Kc = 155 l/mole.
BOA complexes
A very small increase in the absorption at the short wave length side of the
visible iodine band was observed for SOA-concentrations approaching the saturation
value in CCl4 at about 0.5 M. An attempt to analyze the data in the usual way
[15] T. D. EPLEY and R. S. DRAGO,J. Am. Ohem. Soc. 89, 5770 (1967).
The molecular
complexes
of N,N-dimethylmethanesulphinamide
with iodine
1673
revealed that the PERSON criterion [16] was not satisfied. A formation constant
could therefore not be determined and it must be smaller than 0'41/mole. No added
ultraviolet absorption was detected in the region 360-240 mfl for SOA-iodine
solutions in OH2012.
The infrared spectrum of SOA was recorded (Table 3), but no perturbations
were observed for saturated solutions of iodine or iodine cyanide in OS2' Thus SOA
forms no (or an extremely weak) charge transfer complex with these acceptors.
Table 3. Infrared spectral data for N,N-dimethylmethanesulphonamide
obtained as KBr pellet and in so1ution
Peilet
Ca 2900
1486 w
1468 w
1415 w
1328 s
1256 w
1186 w
1150 s
1046 vw
960 s
942w
780m
669w
* The spectral
Solution
Ca 2900
1474
1460
1408
1346
1267
1196
1156
1050
958
Solvent
w
w
vw
s
vw
vw
s
vw
s
CIsCCCIs
CIsCCCIs
CIsCCCIs
CIsCCCIs
CSs
CSs
CS.
CSs
CS.
CS.
769m
653w
*
512m
486 m
353 vw
region between
Tentative
assignment
VOR
} bORa
VaOSO
rORa
VsOSO
VaONO
VSN
VsONO
VOS
CS.
es.
CaHa
def. modes
} skeIetal
650 cm-l and 560 cm-l was not studied.
However, the OH-stretching vibration in phenol was shifted 155 cm-1 upon
complexing with SOA. The formation constant for this complex was determined at
20°0 using the variations in the phenol absorption at 284 mfl, giving Xc = 15.2 l/
mole. The enthalpy of formation was determined from absorbance data at 10
temperatures between 19 and 40° in 0014, !lHo = -5,2 kcal/mole, in fairly good
agreement with the frequency shift correlation [15], giving !lHo = -4.5 kcal/mole.
Eventual perturbations in the SOA infrared spectrum with added phenol could not
be detected in the symmetric and asymmetric S-O stretching vibrations because of
the strong phenol absorption in these regions.
DlseUSSION
Our spectral data reveal that SIA forms moderately strong complexes with
iodine, iodine cyanide or phenol. The isosbestic points observed for several bands of
these systems and the small standard deviations obtained for the formation constants
strongly suggest that these complexes are of 1:1 stoichiometry.
The N, O and S
atoms in SIA have lone pair electrons which might serve as the donor site. However,
the "red shift" of the 1080 cm-l band (Table 2) on complex formation must be
interpreted in terms of complex formation from the oxygen in agreement with the
[16] W. B. PERSON,J. Am. Ohem.Soo.87, 167 (1965).
1674
H. MØLLENDAL, J. GRUNDJ'."'ESand P. KLABOE
corresponding data for the sulphoxides [2]. Thus, SIA conforms with other oxo
compounds which form complexes to the halogens from the oxygen, [2, 17-23].
The most significant conclusion to be reached from the present result is the
striking similarity between SIA and dimethyl sulphoxide regarding their complexes.
It appears from Table 4 that Xc and !:J..Ho
as well as the various spectral parameters
Table 4. Comparison between the thermodynamic and the spectral parameters
for dimethylmethanesulphinamide
(SIA), dimethyl sulphoxide (DMSO) and
their complexes with iodine, iodine cyanide and phenol
SIA
DThISO
Donor
vso
Bdt
VI/Ot
Bd§
cm-l
I/mole cm
cm-l
cm/m mole
!1HO
K(20°C)
!1So
BSmax
CTm.x
!1vso
kcal/mole
I/mole
e.n.
mfl
mfl
cm-l
1080
407
14
5,7
1072
444*
1I*
4.9*
-3.4:1:
0.3
1I'7:1: 0.5
-7,0
440
261
58
- 3.7 :I: 0.3**
1I'5**
-7.6**
446**
272**
51 H
Donor/iodine
!1Ho
K(20°C)
!1So
!1VCI
!1VSO
Bet
Vl/2t
B,§
BclBd
K(20°C)
!1VSO
!1voH
Donor-iodine
kcal/mole
I/mole
e.u.
cm-l
cm-l
l/mole cm
cm-l
cm/m mol e
I/mole
cm-l
cm-l
cyanide
-3.7 :I: 0,5
83
-4
22
40
410
32
13.6
2.3
Donor-phenol
155 :I: 5
32
360
-3'2:1:
0,5*
105*
-3*
22U
36tt
310*
40*
12,5*
2,6*
182§§
27***
350* * *
* This work.
t Extinction coefficient.
t Half intensity width.
=
B . jll/o'
* * Ref. [3].
ti" Ref. [2].
U Ref. [34].
§§ Ref. [l].
* * * Ref. [8].
§B
for the SIA and dimethyl sulphoxide complexes are nearly identical. Accordingly,
the substitution of a methyl group in dimethyl sulphoxide with an amino group has
a very small effect on the basicity.
[17]
[18]
[19]
[20]
[21]
[22]
r. LINDQVIST,Inorganic Addttct Molcculcs oJ Oxocompmlnds. Springer (1963).
E. AUGDAHLand P. KLABOE,Acta Ohem. Scand. 16, 1637 (1962).
H. YAMADAand K. KOZIMA,J. Am. Ohem. Soc. 82, 1543 (1960).
C. D. SOHMULBAOH
and R. S. DRAGo,J. Am. Ohem. Soc. 82, 4484 (1960).
S. L SNAPRUDand T. GRAMSTAD,
Acta Ohem. Scand. 16, 999 (1962).
J. GRUNDNESand P. KLABOE,Acta Ohem. Scand. 18, 2022 (1964).
[23] E. AUGDAHL, J. GRUNDNES and P. KLABOE, Inorg.
Ohem. 4, 1475 (1965).
The mo1ecular
complexes
of N,N-dimethylmethanesulphinamide
with iodine
1675
The position of the charge transfer band for SIA-iodine also indicates that
the ionization potential for SIA is slightly higher than for dimethyl sulphoxide. The
question then arises if delocalization of the lone pair electrons on the nitrogen into
the d-orbitals on the sulphur takes place in SIA, since this effect is not reflected in the
donor ability of the oxygen. In the carbonyl compounds (the amides) the delocalization increases the electron density on the oxygen considerably in spite of negative
inductive effect of the dimethyl-amino group. The PMR spectra revealed rapid
rotation around the S-N bond down to -60°C [11-12], supposedly because the
p7T-d7T overlap has no strict conformational requirements due to the five-fold
degeneracy and diffuse character of the sulphur d-orbitals. However, a barrier to
internal rotation was recently reported in N,N-dimethyltrichloromethanesulphinamide [24]. Thus, it might be proposed that the p7T-d7Toverlap in SIA is small, but
is enhanced when the chlorine atoms are introduced into the S-methyl group.
On the other hand the sulphur-nitrogen bond in SIA as in e.g. S4N4 is probably
shorter than the S-N single bond [11]. Furthermore the medium intense infrared
band at 918 cm-l appears to be mainly connected with the S-N stretching mode,
compared to 698 cm-1 for a S-N single bond [25]. It has also been reported that a
possible p7T-d7Tdelocalization in the sulphinyl and phosphoryl compounds is not
transferred to the S-O and P-O bonds, as concluded from the nearly constant
stretching frequencies [26-27]. In the N,N-dialkylaminophosphoryl
compounds there
are chemical evidence for delocalization [26]. Nevertheless, GRAMSTADhas found a
lower donor strength in C2H5P(0)N(C2H5h compared to C2H5P(0)(C2H5)2 and
concluded that the electron density on the oxygen was largely controlled by inductive
effects [26].
For SOA it has been shown [28] that the sulphonyl group draws electrons from
the nitrogen by resonance. Since the basicity of SOA towards phenol, iodine cyanide
and iodine is lower than for a sulphone [l], the effect of delocalization for this
molecule is again unlike the ketoamides. The d-orbitals on the sulphur and phosphorus evidently act as a "sink" for the P7Telectrons donated from the nitrogen.
Because of the large number of atoms in SIA and SOA (around 40 fundamental
vibrations) only certain skeIet al modes in the spectra will be discussed. The number
of infrared bands observed is not large enough to account for all the methyl stretching,
deformation and rocking modes, indicating partly degeneracy of several methyl
modes. The spectra of SIA and SOA can be compared with those of dimethyl
sulphoxide [29] and dimethyl sulphone [30] for which detailed vibrational analyses
have been carried out.
The very strong band at 1080 cm-l in SIA (Table 2) is red-shifted on complex
formation and is undoubtedly connected with the S-O stretching mode. In dimethyl sulphoxide this vibration is located at nearly the same frequency [29], it is
[24] H. J. JAKOBSEN
and A. SENNING,
Chem. Commun. 617 (1967).
[25] A. J. BANISTER,
L. F. MooREand J. S. PADLEY,Spectrochim.Acta 23A, 2705 (1967).
[26] T. GRAMSTAD,
Spectrochim.Acta 20, 729 (1964),and references cited there.
[27] L.J.BELLAMYOrganicSuljurCompounds (EditedbyN.KHARAscH),Vol.l,p. 51.Pergamon
Press (1961).
[28] R. G. LAUGHLIN,
J. Am. Chem. Soc. 89, 4268 (1967).
[29] W. D. HORROCKS
and F. A. COTTON,
Spectrochim.Acta 17, 134 (1961).
[30] W. R. FEAIRHELLERand J. E. KATON,Spectrochim. Acta 20, 1099 (1964).
1676
H. MØLLENDAL, J. GRUND1-."ESand P. KLABOE
highly solvent sensitive [31], red shifted on complex formation and of nearly the
same extinction coefficient.
The bands at 1178 and 703 cm-1 are tentatively assigned to the asymmetric and
symmetri c CNC stretching modes, respectively. The 923 and 635 cm-l bands are
assigned, respectively, to the SN and the CS stretching modes. It seems quite
significant thatthe 918,695 and 635 cm-l bands are all shifted to higher frequencies
on complex formation (Table 4), suggesting increased bond order for the CN, SN and
CS bonds. The intense band at 1666 cm-l which is solvent sensitive and red-shifted
on complex formation, represents a puzzling problem. It was reported earlier [11, 12]
and can hardly be an impurity peak. No fundamental is expected in this region and
since there are no neighbour bands, a combination band cannot be enhanced by
Fermi resonanee.
We have tentatively
assigned
the band as 1080 + 635
=
1715 cm-l
which is not quite satisfactory neither concerning the position nor the shift.
In SOA no corresponding band around 1700 cm-l was observed. The OSO
asymmetric and symmetric stretching vibrations are assigned to the strong bands at
1346 and 1156 cm-l in good agreement with dimethyl sulphone [30]. The strong
band at 958 cm-l in solution is split into a doublet at 960 and 992 cm-l in the KBrpeIlet. These bands are assigned to the S-N stretching mode.
For aromatie sulphonamides [32, 33, 25] the S-N stretching mode is generally
found in the region 800-920 cm-1 suggesting a somewhat larger p7T-d7Toverlap in
SOA. The 1050 and 769 cm-l bands are tentatively assigned to the asymmetric and
symmetric CNC stretching modes, respectively. The 653 cm-l band is assigned to
the CS stretching mode.
Very few studies have been made of donor-iodine cyanide complexes. Thermodynamic functions for these interactions are more difficult to obtain than for the
iodine complexes, since we are restricted to the ultraviolet region around 225 mfl
or the infrared region [2]. From infrared data it was shown that for complexes to
the sulphoxides [2,34] and to phosphinoxides [35] iodine cyanide give higher
formation constants, but smaller infrared shifts ~'}J(S-O) or ~'}J(P-O) than iodine
in agreement with the present results. For a few donors the enthalpies of formation
(~HO) have been determined for interaction with iodine and iodine cyanide in the
same solvent [21, 35, 36] indicating very similar values. The same conclusion can be
drawn from the present SIA complexes with iodine and iodine cyanide and the data
for dimethyl sulphoxide. Since iodine cyanide has a high dipole moment (3.74 D
in C6H6) [37], the donor-iodine cyanide interactions with polar donors are undoubtedly caused partly by dipole-dipole effects. Since the enthalpy of formation ~Ho
appears nearly identical for iodine and iodine cyanide complexes [35, 36] the dipole
term in the latter is probably compensated by the higher contribution of dative
forces in the former.
[31]
[32]
[33]
[34]
[35]
[36]
[37]
T. CAlRNS,G. EGLINGTONand D. T. GIBSON,Spectrochim. Acta 20, 31 (1964).
A. MASCHKAand H. AusT, Monatsh. Ohem. 85, 891 (1955).
G. TOSOLINE,Ohem. Ber. 94, 2731 (1961).
R. DAHL, T. GRAMSTAD
and P. KLABOE,Acta Ohem. Scand. 19, 2248 (1965).
R. DAHL, Thesis, University of Oslo (1966).
H. D. BIST and W. B. PERSON,J. Phys. Ohem. 71, 3288 (1967).
F. FAIRBROTHER,J. Ohem. Soc. 180 (1950).