The enthalpies of formation of bis(dimethylamino)cyanophosphine, (dimethylamino)dicyanophosphine, and tricyanophosphine

Article abstract of DOI:10.1006/jcht.1995.0059

The standard molar enthalpies of formation at the temperature 298.15 K of <(CH3)2N>2PCN(l), (CH3)2NP(CN)2(l), and P(CN)3(cr) have been determined by reaction calorimetry as -(0.4 +/- 3.2) kJ * mol^-1, (189.3 +/- 5.0) kJ * mol^-1, and (373.1 +/- 6.8) kJ * mol^-1, respectively.Enthalpies of vaporization have been obtained from vapour-pressure measurements for the first two compounds and the corresponding values of Δ_fH⁰_m(g)/(kJ * mol^-1) derived as (54.2 +/- 3.5), (228.7 +/- 5.5), and 448.4 +/- 7.4), respectively.The values of the bond enthalpies D(P-CN) in the cyanophosphines are discussed.

Full text of DOI:10.1006/jcht.1995.0059

M-3086(P)
J. Chem. Thermodynamics 1995, 27, 575–584
The enthalpies of formation of
bis(dimethylamino)cyanophosphine,
(dimethylamino)dicyanophosphine, and
tricyanophosphine
H. M. A. Al-Maydama,a Arthur Finch, P. J. Gardner,
and A. J. Head
Department of Chemistry, Royal Holloway and Bedford New College
(University of London), Egham Hill, Surrey TW20 0EX, U.K.
(Received 22 August 1994)
The standard molar enthalpies of formation at the temperature 298.15 K of {(CH3)2N}2PCN(l),
(CH3)2NP(CN)2(l), and P(CN)3(cr) have been determined by reaction calorimetry as
−(0.4 2 3.2) kJ·mol−1
, , , respectively.
(189.3 2 5.0) kJ·mol−1 and (373.1 2 6.8) kJ·mol−1
Enthalpies of vaporization have been obtained from vapour-pressure measurements for the first
two compounds and the corresponding values of DfHm°(g)/(kJ·mol−1) derived as (54.2 2 3.5),
(228.7 2 5.5), and (448.4 2 7.4), respectively. The values of the bond enthalpies D(P–CN) in
the cyanophosphines are discussed.
1. Introduction
This paper reports thermochemical measurements by solution-reaction calorimetry
leading to the molar enthalpies of formation of {(CH3)2N}n P(CN)3 − n , (where
n = 0, 1, 2) in the condensed state. Values for the compounds where n = 1, 2 have
not been reported previously and the new value for P(CN)3 disagrees with the current
literature value; the discrepancy is discussed and resolved. Enthalpies of vaporization
at the temperature T = 298.15 K for two compounds (n = 1, 2) have been derived
from vapour-pressure measurements. This study provides further information on
the enthalpies of (P–CN) bonds and extends the work previously reported on the
thermochemistry of (dimethylamino)chlorophosphines.(1)
2. Experimental
Bis(dimethylamino)cyanophosphine was prepared by refluxing
a
stirred
stoichiometric mixture of {(CH3)2N}2PCl(l), prepared as described in reference 1, and
AgCN in trichloromethane for 12 h. The product was filtered from AgCl, the
a Present address: Faculty of Science, Sana’a University, Sana’a, Republic of Yemen.
0021–9614/95/060575 + 10 $08.00/0
7 1995 Academic Press Limited

576
H. M. A. Al-Maydama et al.
solvent removed by pumping, and the residue distilled under reduced pressure.
The liquid boiling at temperatures between 325 K and 326 K (pressure p = 0.20 kPa)
was collected and allowed to solidify (melting temperature: 294 K to 296 K) in
the condenser. The purity was estimated, after hydrolysis with excess HCl and
subsequent oxidation with H2O2 of the H3PO3 produced, by titrimetric determination
(standard NaOH) of the H3PO4. The difference between the two end-points yields
a value for the mole fraction of P: found, 0.2130; calculated for C5H12N3P, 0.2134.
(Dimethylamino)dicyanophosphine was prepared by refluxing a stoichiometric
mixture of (CH3)2NPCl2(l), prepared as described in reference 1, and AgCN in
acetonitrile for 20 h with stirring. The mixture was filtered under nitrogen, the solvent
removed by pumping, and the product distilled under reduced pressure followed
by two further distillations (boiling temperature: 339 K to 341 K at p = 0.13 kPa).
The purity was assessed by determination of the mole fraction of P by the method
described above: found, 0.2420; calculated for C4H6N3P, 0.2437.
Tricyanophosphine was prepared according to the method described by Jones
and Coskran.(2) A mixture of dry AgCN and freshly-distilled PCl3 was stirred in
acetonitrile (dried over CaH2) for 3 h under nitrogen at room temperature. The
mixture was filtered to remove AgCl, the solvent removed, and the crude product
twice sublimed in vacuo. The mass-fraction purity was assessed as 0.995 by the
method described for the other cyanophosphines.
Enthalpies of hydrolysis of the three compounds were determined using an
isoperibol twin-vessel solution-reaction calorimeter.(3) The calorimeter was operated
at T = 298.15 K and the precision and accuracy of the results were frequently
successfully checked by measurements of the molar enthalpy of neutralization of
tris(hydroxymethyl)aminomethane (THAM) with excess 0.1 mol·dm−3 HCl(aq).
Bis(dimethylamino)cyanophosphine and (dimethylamino)dicyanophosphine both
undergo rapid hydrolysis in water and HCl(aq). To avoid the formation of an
unidentified yellow precipitate which formed when the latter compound reacted
with water alone, 2 mol·dm−3 HCl(aq) was used in the calorimetric experiments on
both compounds.
The hydrolysis of P(CN)3 in 2 mol·dm−3 HCl(aq) has been reported to yield H3PO3
as the only phosphorus-containing product, whereas the reaction with 5 mol·dm−3
NaOH(aq) resulted in approximately 20 per cent of the phosphorus as species other
than HPO23−.(4) The formation of by-products, however, appears to be related to the
violence of the reaction since the aqueous alkaline hydrolysis of a solution of P(CN)3
in diethyl ether produced only HPO23−. In the present study the hydrolysis of P(CN)3
was investigated using (i), de-ionised de-oxygenated water; (ii), water containing
dissolved HCN; and (iii), 0.5 mol·dm−3 NaOH(aq) where, after hydrolysis, Na2HPO3
was assumed to be the only phosphorus-containing product. Titration of the alkaline
hydrolysate with standard HCl(aq) produced the calculated difference between the
first (Na2HPO3) and second (NaH2PO3) end-points, and between the second and
third (NaCN) end-points for the reaction:
P(CN)3 + 5NaOH = Na2HPO3 + 3NaCN + 2H2O.

DfHm°[{(CH3)2N}n P(CN)3 − n , l or cr and g, 298.15 K] for n = 2, 1, 0
577
TABLE 1. Hydrolysis of a mass m of {(CH3)2N}2PCN(l) in a volume 100 cm3 of 2 mol·dm−3 HCl(aq)
X (HCl in 27.76H2O) at T=298.15 K {equation (1)}
a
m/g
−DrHm/(kJ·mol−1
)
DHm/(kJ·mol−1
)
−DrHm/(kJ·mol−1
)
(observed)
(concentration)
(corrected)
0.01707
0.01878
0.02725
0.03132
0.03259
0.04066
0.05427
240.34
241.30
241.38
241.29
241.44
240.55
241.53
3.60
3.47
3.52
3.49
3.47
3.49
3.50
236.74
237.83
237.86
237.80
237.97
237.06
238.03
237.61
(20.46)
Mean:
a Weighings in air corrected using r/(g·cm−3) = 0.974,(15) where r denotes density.
With all three hydrolytic agents the reaction was shown to be complete within the
main reaction period (about 10 min) of a calorimetric experiment.
Vapour pressures were determined using the apparatus previously described.(1)
3. Results
The results obtained for the hydrolysis of {(CH3)2N}2PCN and (CH3)2NP(CN)2 are
reported in tables 1 and 2, respectively, and refer to the reactions:
{(CH3)2N}2PCN(l) + {(m + 2)HCl + (p + 3)H2O}(sln)=
{2(CH3)2NH2Cl + H3PO3 + mHCl + pH2O + HCN}(sln),
(CH3)2NP(CN)2 + {(m + 1)HCl + (p + 3)H2O}(sln)=
{(CH3)2NH2Cl + H3PO3 + mHCl + pH2O + 2HCN}(sln).
(1)
(2)
Because the reactions involve consumption of HCl, the results include a correction
term for concentration of the final solution to the initial composition of (HCl +
27.76H2O). The molar enthalpies of solution of H3PO3(cr) and (CH3)2NH2Cl(cr)
TABLE 2. Hydrolysis of a mass m of (CH3)2NP(CN)2(l) in a volume 100 cm3 of 2 mol·dm−3 HCl(aq)
X (HCl in 27.76H2O) at T=298.15 K {equation (2)}
m/g a
−DrHm/(kJ·mol−1
)
DHm/(kJ·mol−1
)
−DrHm/(kJ·mol−1
)
(observed)
(concentration)
(corrected)
0.01281
0.02286
0.02292
0.02814
0.03076
0.04127
0.04512
210.79
210.72
210.00
211.86
210.99
210.76
210.00
1.58
1.62
1.61
1.61
1.64
1.67
1.64
209.21
209.10
208.39
210.25
209.35
209.09
208.36
209.11
(20.59)
Mean:
a Weighings in air corrected using r/(g·cm−3) = 1.077.(15)

578
H. M. A. Al-Maydama et al.
TABLE 3. Hydrolysis of a mass m of P(CN)3(cr) at T = 298.15 K in a volume 100 cm3 of (a),
de-oxygenated de-ionised water; and (b), de-oxygenated de-ionised water containing HCN (concentration
about 0.01 mol·dm−3
)
a
m
g
−DrHm
−DsolHm(H3PO3)
DfHm°{P(CN)3, cr}
kJ·mol−1
kJ·mol−1
kJ·mol−1
(a)
0.01583
0.02770
0.03411
0.03992
0.04102
0.04116
0.04270
0.05845
186.65
185.41
188.21
184.76
184.44
184.33
185.80
186.02
5.59
5.34
5.23
5.14
5.12
5.12
5.10
4.89
371.55
370.56
373.47
370.11
369.81
369.70
371.19
371.62
371.00
(21.04)
Mean:
(b)
0.09585
0.09597
0.10302
184.01
184.68
185.27
4.47
4.47
4.41
370.03
370.70
371.35
370.69
Mean:
(16)
a Weighings in air corrected using r = 1.35 g·cm−3
.
in (HCl + 27.76H2O) have been reported as (7.94 2 0.17) kJ·mol−1 and
(3.24 2 0.01) kJ·mol−1, respectively, and showed no concentration dependence
over the ranges studied.(1) Thus, using the following ancillary values of
DfHm°/(kJ·mol−1):
(HCl
in
27.76H2O),
−(164.44 2 0.10);(1)
− (289.21 2 0.03);(1)
H3PO3(cr),
H2O(l),
− (957.1 2 2.3);(1)
(CH3)2NH2Cl(cr),
−(285.83 2 0.04);(5) and HCN(aq), (96.7 2 2.2):
DfHm°[{(CH3)2N}2PCN] = −(0.4 2 3.2) kJ·mol−1,
neglecting any enthalpy of mixing between (CH3)2NH2Cl and H3PO3 in
HCl solution.† The value for DfHm°(HCN, aq) was derived from
DfHm°(CN−, aq)/(kJ·mol−1) = (140.3 2 2.2),(6) and the molar enthalpy of ionization of
HCN(aq):(7) (43.6 2 0.1) kJ·mol−1. Similarly, using the same ancillary quantities:
DfHm°{(CH3)2NP(CN)2} = (189.3 2 5.0) kJ·mol−1.
The results obtained for the hydrolysis of P(CN)3(cr) using (a), de-oxygenated
deionised water; and (b), water containing dissolved HCN(g), are reported in table 3.
Davies et al.(8) carried out a similar determination at T = 298.15 K using distilled
water ‘‘pre-saturated at ambient temperature’’ with HCN(g), assuming that the
HCN (boiling temperature: 299 K) produced would be wholly gaseous under these
conditions. HCN is, however, infinitely soluble in water and the reaction product
must, therefore, be HCN(aq). The results listed in table 3 confirm that there is
no significant difference between the values obtained using water and HCN(aq) as
hydrolytic reagents. The physical state of the HCN produced in this reaction was
further confirmed by measuring the molar enthalpy of reaction between NaCN(cr)
† Throughout this paper uncertainty intervals of reported experimental results denote 95 per cent
confidence limits, calculated using Student’s t at the appropriate number of degrees of freedom.

DfHm°[{(CH3)2N}n P(CN)3 − n , l or cr and g, 298.15 K] for n = 2, 1, 0
579
TABLE 4. Hydrolysis of a mass m of P(CN)3(cr) in a volume 100 cm3 of 0.5 mol·dm−3 NaOH(aq) at
T = 298.15 K {equation (3)}
m/g
n(H2O)/n{P(CN3)}
−DrHm/(kJ·mol−1
)
0.04114
0.04982
0.05267
0.05534
0.06217
0.06891
0.07159
0.07789
0.08653
0.12938
14710
12140
11490
10930
9732
8780
8452
7768
6992
4677
343.97
343.97
343.26
343.59
344.72
345.01
344.05
343.97
344.09
344.72
Mean:
344.14 2 0.38
and 0.1 mol·dm−3 HCl(aq) at (293.65, 298.15, and 303.15) K. The results were
independent of temperature, indicating that HCN(g) was not a reaction product,
even at 4 K above the boiling temperature of HCN(l). The presence of H3PO3
(pKa = 2.0) in the solution {about (1.5 to 5.4) mmol·dm−3} was sufficient to suppress
completely the ionisation of the very weak hydrocyanic acid (pKa = 9.3).
The value of DfHm°(H3PO3, aq) has been derived from that for H3PO3(cr) (see
above) and recent measurements of DsolHm(H3PO3, cr), which show a marked
concentration dependence.(9) The appropriate molar enthalpy of solution, calculated
from equation (2) in reference 9, is included in table 3. Thus from the reaction:
P(CN)3(cr) + 3H2O(l) = H3PO3(aq) + 3HCN(aq, undissociated),
using the auxiliary thermodynamic quantities given above,
DfHm°{P(CN3), cr} = (371.0 2 7.1) kJ·mol−1.
The results for the alkaline hydrolysis of P(CN)3 are reported in table 4 and refer
to the reaction:
P(CN)3(cr) + {(m + 5)NaOH + (p − 2)H2O}(sln) =
{Na2HPO3 + 3NaCN + mNaOH + pH2O}(sln),
(3)
where {(p − 2)/(m + 5)} = 111.
The molar enthalpy of neutralization of H3PO3(cr) with 0.5 mol·dm−3 NaOH(aq)
was also measured and the results are reported in table 5 and refer to the reaction:
H3PO3(cr) + {(m + 5)NaOH + (p − 2)H2O}(sln)=
{Na2HPO3 + (m + 3)NaOH + pH2O}(sln).
(4)
These measurements were also carried out in the presence of NaCN {mole ratio
n(NaCN)/n(H3PO3) = 3.0} which had no significant effect on the results previously
obtained (table 5).

580
H. M. A. Al-Maydama et al.
TABLE 5. Neutralization of a mass m of H3PO3(cr) at T = 298.15 K with a volume 100 cm3 of (a),
0.5 mol·dm−3 NaOH(aq) {equation (4)}; and (b), 0.5 mol·dm−3 NaOH(a) containing NaCN
{n(NaCN)/n(H3PO3) = 3.0}
a
m/g
n(H2O)/n(H3PO3)
−DrHm/(kJ·mol−1
)
(a)
0.04624
0.05906
0.07587
0.07637
0.08914
0.11205
9844
7707
5999
5960
5706
4062
122.67
121.50
121.46
122.51
122.38
122.88
Mean:
Mean:
122.23 2 0.64
(b)
0.06035
0.08616
0.09113
0.12584
7542
5283
4995
3617
121.96
123.18
121.50
123.22
122.47 2 1.38
a Weighings in air corrected using r/(g·cm−3) = 1.651.(17)
The molar enthalpy of the reaction:
P(CN)3(cr) + 3NaOH(cr) = 3NaCN(aq) + H3PO3(cr),
(5)
=
may be obtained from DHm(5)
=
DHm(3)
−
DHm(4)
−
DHm(6)
−(354.18 2 0.77) kJ·mol−1, where DHm(6) is calculated from literature values(10) of
DfHm° for the components of the reaction:
{Na2HPO3 + (m + 3)NaOH + pH2O}(sln)=
3NaOH(cr) + (Na2HPO3 + mNaOH + pH2O)(sln).
(6)
This calculation was made by re-arranging the relation derived from equation (6) in
the form:
DHm(6) = 3·DfHm°(NaOH, cr) + DfHm°(mNaOH in pH2O, sln)−
DfHm°{(m + 3)NaOH in pH2O, sln}
= 3·DfHm°(NaOH, cr)−
3·DfHm°[NaOH in {p/(m + 3)}H2O, sln]+
m·DfHm°{NaOH in (p/m)H2O, sln}−
m·DfHm°[NaOH in {p/(m + 3)}H2O, sln].
Substituting values obtained from reference 10, with m = 45 and p = 5553,
DHm(5) = (132.3 2 0.2) kJ·mol−1, (estimated uncertainty).
The value: DfHm°/(kJ·mol−1) = −425.86 for NaOH(cr) was derived from the value in
reference 10, corrected for the difference between the values for NaOH(aq,a)
in reference 10 and the more recent reference 5. The value: DfHm°/(kJ·mol−1) =
−(100.2 2 2.2) for NaCN(aq,a) was obtained from the values for Na+(aq,a),(5)

DfHm°[{(CH3)2N}n P(CN)3 − n , l or cr and g, 298.15 K] for n = 2, 1, 0
581
TABLE 6. DfHm°(l or cr), DvapHm°(l or cr), and DfHm°(g) for {(CH3)2N}n P(CN)3 − n (n = 0, 1, 2) at
T = 298.15 K
DfHm°(l or cr)
D
vapHm°(l or cr)
DfHm°(g)
kJ·mol−1
kJ·mol−1
kJ·mol−1
0
1
2
373.1 2 6.8
189.3 2 5.0
−0.4 2 3.2
75.3 2 2.9
39.4 2 2.3
54.6 2 1.4
448.4 2 7.4
228.7 2 5.5
54.2 2 3.5
and CN−(aq,a);(6) no correction was applied for concentration to the final state
of reaction (3): NaCN in 1850H2O. Using these values for DfHm° of NaOH(cr) and
NaCN(aq), and those previously listed for DfHm°(H3PO3,cr) and DHm(5):
DfHm°{P(CN)3,cr} = (374.7 2 7.0) kJ·mol−1.
The difference between the two values obtained for DfHm°{P(CN)3,cr} is
(3.7 2 3.5) kJ·mol−1, ignoring the uncertainty associated with DfHm°(CN,a), which
is common to both determinations. A simple statistical test (t test) reveals that this
difference is not significant and we recommend the weighted mean value:
DfHm°{P(CN)3,cr} = (373.1 2 6.8) kJ·mol−1.
Molar enthalpies of vaporization for {(CH3)2N}n P(CN)3 − n (n = 1, 2) were derived
from vapour-pressure measurements over temperature ranges which included
298.15 K and are reported in table 6, together with the corresponding values
of DfHm°(g). The value DsubHm°{P(CN)3,cr} = (75.3 2 2.9) kJ·mol−1, obtained by
effusion manometry, was taken from reference 8.
4. Discussion
No values of DfHm°(l) or DfHm°(g) for (CH3)2NP(CN)2 or {(CH3)2}2PCN have
been previously reported. The two values obtained for DfHm°{P(CN3),cr} obtained by
neutral and alkaline hydrolysis are in good agreement: most of the
uncertainty of 27 kJ·mol−1 arises because of the uncertainty in DfHm°(CN−,aq),
which is common to both determinations. The experimental results for neutral
hydrolysis reported herein and by Davies et al.(8) are in excellent agreement. However,
misinterpretation of their measurements by the latter authors and the use of an
early value for DfHm°(HCN,g) led to an erroneous value for DfHm°{P(CN)3,cr}:
{(493 2 25) kJ·mol−1}.
An estimate of DfHm°{P(CN)3,g} has been made by ab initio molecular-orbital
calculation(11) of the molar electronic-energy change at T 4 0 for the isogyric
(spin-conserved) reaction:
PH3(g) + 3HCN(g) = P(CN)3(g) + 3H2(g).
(7)
After correcting this molar energy change for changes in zero-temperature
molar energy and for the change in molar enthalpy increment: DD2098.15 KHm°(7),
DrHm(7, 298.15 K)
=
(82.4 2 13) kJ·mol−1, from which DfHm°{P(CN)3,g} =

582
H. M. A. Al-Maydama et al.
(459 2 15) kJ·mol−1, using DfHm°(298.15 K)/(kJ·mol−1) = (5.4 2 1.7), and
(123.7 2 2.2), for PH3(g),(12) and HCN(g),(6) respectively. An earlier report(11) using the
same method gave DfHm°{P(CN)3,g} = (493 2 15) kJ·mol−1, but this was calculated
using DfHm°(HCN,g) = 135.1 kJ·mol−1,(10) a value to which some doubt has been
ascribed.(6) The new calculated value: DfHm°{P(CN)3,g} = (459 2 15) kJ·mol−1
overlaps with the experimental result reported here: (448 2 7) kJ·mol−1.
The enthalpy changes for the redistribution reactions:
(1/3)P(CN)3(g) + (2/3){(CH3)2N}3P(g) = {(CH3)2N}2P(CN)(g),
(8)
FIGURE 1. Effect on DfHm°(g) of progressive substitution of (CH3)2N– in {(CH3)2N}3P by w, Cl;
q, CN.

DfHm°[{(CH3)2N}n P(CN)3 − n , l or cr and g, 298.15 K] for n = 2, 1, 0
583
(9)
(2/3)P(CN)3(g) + (1/3){(CH3)2N}3P(g) = (CH3)2NP(CN)2(g),
DrHm°(8)=−(47.8 2 4.6) kJ·mol−1; DrHm°(9)=−(46.4 2 7.4) kJ·mol−1.
provide a useful check on the internal consistency of the results. Comparison with
the limited values available for P(III) compounds(13) suggests that these values are
reasonable. It is interesting to note that these molar redistribution enthalpies are
about 50 per cent larger than the corresponding values(1) for the (dimethylamino)-
chlorophosphines; this is a consequence of the fact that ꢀDꢁ(P–CN) (see below) is
73 kJ·mol−1 larger than ꢀDꢁ(P–Cl).
The mean bond-dissociation enthalpy: ꢀDꢁ(P–CN) = (394.7 2 3.2) kJ·mol−1 is
readily obtained from our experimental result, using DfHm°((P,g)
=
(316.5 2 1.0) kJ·mol−1,(5) and DfHm°(CN,g) = (438.7 2 2.0) kJ·mol−1. The latter value
is derived from a recent study(14) of the photodissociation of (CN)2 from which
DfHm°(CN,g,T 4 0) = (435.4 2 2.0) kJ·mol−1, corrected to T = 298.15 K using the
value of DD2098.15 KHm° from reference 10. Cyanide is a pseudohalogen and this
result places ꢀDꢁ(P–CN) between ꢀDꢁ(P–F) (506 kJ·mol−1) and ꢀDꢁ(P–Cl)
(322 kJ·mol−1).
Assuming the transferability of ꢀDꢁ{P–N(CH3)2} in {(CH3)2N}3P,(1)
(274 2 8) kJ·mol−1, into the (dimethylamino)cyanophosphines, the following bond
enthalpies have been calculated, using the auxiliary quantities listed above:
E(P–CN) in (CH3)2NP(CN)2 = (418 2 7) kJ·mol−1,
E(P–CN) in {(CH3)2N}2PCN = (443 2 20) kJ·mol−1.
The effect of progressive substitution by CN on the molar enthalpy of formation of
{(CH3)2N}3P(g) is shown in figure 1. The non-linearity of the curve demonstrates that
the bond-dissociation enthalpies ꢀDꢁ(P–N) and ꢀDꢁ(P–CN) are not constant in the
series, which is further shown by the fact that the enthalpies of the redistribution
reactions are not zero (see above). The corresponding values for the
chloro-substituted dimethylaminophosphines(1) are included in the figure which
shows smooth curves for both series.
Despite the satisfactory agreement between these two solution-reaction
calorimetric results for DfHm°{P(CN)3,cr}, they both depend on ancillary values
of DfHm° for H3PO3 and CN−(aq). Two additional procedures are appropriate
for independent further measurements, namely rotating-bomb calorimetry and
fluorine-bomb calorimetry; this is discussed elsewhere.(18)
Financial support (to H.M.A.A-M) from the British Council is gratefully
acknowledged.
REFERENCES
1. Al-Maydama, H. M. A.; Finch, A.; Gardner, P. J.; Head, A. J. J. Chem. Thermodynamics 1995, 27,
273–279.
2. Jones, C. E.; Coskran, K. J. Inorg. Chem. 1971, 10, 1536.
3. Peake, S. J. Ph.D. Thesis, University of London. 1976.
4. Pollard, F. H.; Nicklaus, G.; Rothwell, M. T. J. Chromatog. 1963, 11, 383.

584
H. M. A. Al-Maydama et al.
5. CODATA Key Values for Thermodynamics. Cox, J. D.; Wagman, D. D.; Medvedev, V. A.: editors.
Hemisphere: New York. 1989.
6. Finch, A.; Gardner, P. J.; Head, A. J.; Wu Xiaoping; Yefimov, M. E.; Furkaluk, M. E. J. Chem.
Thermodynamics 1993, 25, 1385.
7. Christensen, J. J.; Johnson, H. D.; Izatt, R. M. J. Chem. Soc. A 1970, 454.
8. Davies, R. H.; Finch, A.; Gardner, P. J.; Hameed, A.; Stephens, M. J. Chem. Soc. Dalton 1976, 556.
9. Al-Maydama, H. M. A.; Gardner, P. J. Thermochim. Acta 1990, 6, 51.
10. NBS Tables of Chemical Thermodynamic Properties. Wagman, D. D.; Evans, W. H.; Parker, V. B.;
Schumm, R. H.; Halow, I.; Bailey, S. M.; Churney, K. L.; Nuttall, R. L.: editors. J. Phys. Chem.
Ref. Data 1982, 11, Supplement No. 2.
11. Gardner, P. J. Thermochim. Acta 1992, 205, 65.
12. Gunn, S. R.; Green, L. G. J. Phys. Chem. 1961, 65, 779.
13. Pilcher, G. Thermochemistry of phosphorus(III) compounds. Chap.
5 in The Chemistry of
Organophosphorus Compounds. Hartley, F. R.: editor. Wiley: London. 1990.
14. Huang, Y.; Barts, S. A.; Halpern, J. B. J. Phys. Chem. 1992, 96, 425.
15. Noth, H.; Vetter, H. J. Chem. Ber. 1963, 96, 1109.
16. Emerson, K.; Britton, D. Acta Cryst. 1964, 17, 1134.
17. Thomsen, J. Thermochemistry. Longmans Green: London. 1908, p. 47.
18. Al-Maydama, H. M. A. Ph.D. Thesis, University of London. 1992.