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Thermochemistry of organosilicon compounds
99
Journal of Organometallic
Chemistty,
406 (1991) 99-104
Elsevier Sequoia S.A., Lausanne
JOM 21365
Thermochemistry of organosilicon compounds VI *. Thermochemical properties of organosilicon compounds with a Si-N bond M.G. Voronkov * Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR, 664033 Irkutsk (USSR)
V.A. Klyuchnikov, L.I. Marenkova, T.F. Danilova, G.N. Shvets, S.I. Tsvetnitskaya Kemerovo
State Medical Institute,
650027 Kemerovo (USSR)
and Yu.1. Khudobin Institute of Chemistry of Silicates, Academy of Sciences of the USSR, Leningrad B-164 (USSR)
(Received August 26th, 1990)
We have evaluated the enthalpies of combustion and formation in the condensed and gaseous states, of fifteen organosilicon compounds containing an Si-N bond, of the general formula R,_,Si(NR’R”), where R = H, alkyl; R’ = H, akyl, Si(CH,),; R” = alkyl. Si(CH,),. The enthalpies of atomization in the gaseous phase and parameters for evaluating the enthalpies of formation and atomization of the above compounds by use of the Frankhn-Fknson and Tatevskii schemes have bean calculated. The Si-N bond energy ranges from 316.5 to 329 kJ mol-t. In compounds containing an Si-N-Si group, the Si-N bond energy is lowest.
Introduction
Monomeric and polymeric organosilicon compounds having one or more Si-N bonds are of great theoretical and practical interest. However, their thermochemical constants are scarce in the literature and most of them are contradictory and need re-examination [l-6]. The Si-N bond energies calculated from experimental thermochemical data, have been evaluated within the range of 305.9 to 376.6 kJ mol-’ [l--5].
* For Part V see J. Organomet. Chem., 406 (1991) 91. 0022-328X/91/$03.50
0 1991 - Ekevier Sequoia S.A.
100
Results and discussion The enthalpies of combustion and evaporation have been measured for 15 monomeric organosilicon compounds with the Si-N bond, of the general formula R ,_,Si(NR’R”) with R = H, alkyl; R’ = H, alkyl, Si(CH,),; R” = alkyl, Si(CH,), (Table 1). The energies of fragments in the Franklin-Benson (Table 2) and the Tatevskii schemes (table 3) have been determined. From this the enthalpies of formation in the condensed state and the enthalpies of atomization in the gas phase have been calculated (Table 4). In evaluating the enthalpies of formation and atomization use was made of the following key values (AHto, kJ mol-’ at 298.15 K): - 285.830 f 0.042 (H,O, liquid); - 393.514 f 0.13 (CO,, gas) [B]; - 939.39 + 0.52
Table 1 Enthalpies of combustion, formation and evaporation of the investigated organosilicon containing an Si-N bond at 298.15 K, kJ mol-’ - A If o (cycl. (liq.)
Compound
9684.2 f 4.5 4096.1 f 5.1 4771.1 f 5.0 6082.7 f 5.2 8064.4 f 4.5 7107.7 f 5.7 7385.8 i 5.5 8054.1 f 6.5 10684.5 f 6.3 10667.4 f 7.5 8694.6 f 7.2 10668.6 f 7.8 6462.2rt8.1 7140.5 f 8.3 9498.2 f 9.6
HW’W~WJ~ (CH,),SiNHCH, (CHs)sSiN(CHs)s (CHs)sSiN(CsHs)s (C,H,)sSrN(C,Hs), (C,H,),SiNHCH,CH,CH, (C,H,),SiNHCH(CH,), (C,HMiNHC(CHs)s (C,H,),SiN(CHsCH,CH,CH,),
(C,H,),SiN[CH(CH,)CH,CH,I, (C,H,),SiNHCH(CHs)CH,CH,CHsCHs (CsHs)sSiNH(CHs)rCHs
IP-%)~SWJH IW-UWPCH~ IWW$iW Note: [(CH,),Si],N in ref. 7.
-AH:
(hq.)
407.7* 5.0 275.2+ 6.0 279.6* 6.0 326.7* 6.0 383.0* 5.0 374.5i 6.0 382.3* 6.0 393.3f 7.0 480.3f 7.0 497.4* 8.0 432.1k 8.0 496.2k 8.0 493.0* 9.0 494.1* 9.0 720.3 f 10.0
compounds
AH0 58.4f 1.0 37.4iO.8 33.6kO.8 37.9 f 0.8 42.2 f 1.0 41.5 kO.8 38.6 f 0.8 40.3*0.9 56.3rtl.O 51.4*0.9 46.9 f 1.0 59.1 f 1.0 42.2 f 0.9 38.1 kO.8 54.3*1.0
is a solid, its enthalpies of formation and sublimation were determined as described
Table 2 Numeric contributions of fragments in the Franklin-Benson Fragment
C-+X-O, C-(C),(H), C-(C)(Si)(H)s C-(NW(H), C-(C)s(N) C-(C),(N)(H) C-(Si)(H),
C-U’JXW,
scheme, kJ mol-’
Fragment
Value Ei
- Hi
1414.93 1173.46 1166.26 1174.42 690.56 943.63 1410.93 1414.93
44.27 20.80 13.60 21.76 - 26.11 8.96 40.27 44.27
Si-(C)s(N) SW%(H) N-(Si)(C), N-(Si)(C)(H) N-(B),(C) N-(Si), N-(CXH), N-(S&(H)
Value Ei
- Hi
589.20 931.00 369.40 624.20 365.20 359.40 889.35 621.42
139.20 263.00 - 103.28 - 66.48 - 107.48 - 113.28 - 19.32 - 68.26
101 Table 3 Numeric contributions of fragments in the Tatevskii scheme, kJ mol-’ Fragment
Cl--G
c*-c, c,-Cl G-C.3
c*-c,
C,-Si C, -Si C,-N C,-N
Fragment
Value Eli
- Hi,
2002.27 1173.46 1728.77 1592.70 898.68 1540.60 707.43 1540.50 712.46
55.58 20.80 46.55 42.87 10.79 57.44 18.60 12.28 -21.43
C,-N C,-NH C,NH C,-NH C,,-NH Si-N Si-H Si-NH
Value Eij
- Hij
443.02 1919.30 1093.60 822.80 664.20 320.00 325.10 511.40
- 26.10 15.52 - 15.85 - 21.87 - 48.09 49.94 - 5.40 53.56
(SiO, amorph. hydr.) [9,10]; 716.67 f 0.44 (C, gas); 217.997 f 0.006 (H, gas); 450.00 f 8 (Si, gas); 472.68 f 0.12 (N, gas) [S]. Calculation of the enthalpies of formation and atomization by additive schemes was performed by use of: (i) the Franklin-Benson formula [11,12]
AH,0 (gas) = i
KiEi
i=l
A&“
(gas)
= 2
KiHi
i=l
Here Hi = - Ei + Z CIAHP (atom) where Hi is the enthalpy of formation of a given fragment; Ei is the energy of the fragment, which takes into account the mutual effect of the atoms separated by not more than one atom in the molecular chain; Ki is the number of fragments; El the number of moles of C, H, Si and N atoms. For the compounds studied the fragments are as follows: C-C,-(H),,
C-(C)-(Si)(H,),
C-(N)(H),,
etc.
(ii) The Tatevskii formula [13]: AH:
(gas) = 2
nij Hii, i~j
i,j=l
AH,0
(gas) = 5
nij Eij, i
i,j=1
Here Hi j = - Eij + X CIAHP (atom) where Eij is the energy of the fragment, which takes into account the mutual effect of the atoms separated by not more than one other atom in the molecular chain; nij is the number of fragments. The substances studied contain the following fragments: Ci-Si, Si-N, C-N,
etc.
LIBy the Fmnklin-Benson
W-W,SWH WW3SWCH3 WH,MW
(C,HMiNH(CH,),CH,
(gas)
compounds
349.6* 6.0 237.8* 7.0 246.0* 7.7 288.8* 7.0 340.8k 6.0 333.0* 7.0 353.0* 8.0 424.0* 8.0 446.0* 9.0 385.2* 9.0 437.1* 9.0 450.8 f 10.0 456.0 f 10.0 656.0 f 11.0
-A&’ (exp.)
of organosilicon
scheme. b By the Tatevskii scheme.
(C,H,),SiNHCH(CH,)CH2CH,CH&Hs
(C,H,),SiN[CH(CH,)CH,CH,I,
(CsHs)sSiNHWHs)s (C,H,)sSiN(CH&H,CHsCcH,),
(CH,),StN(CH,), (CHs)sSiN(CsHs)s (C,H,),SiNHCH,CH,CH, (C,Hs)sSiNHCH(CH,),
(CH,),SiNHCH,
HWW,H,M,
Compound
Enthalpies of formation and atomization at 298.15 K, kJ mol-’
Table 4
349.3 237.8 245.3 288.8 341.6 332.2 353.0 424.8 446.1 ,385.4 437.2 451.7 456.8 666.8
AH: (gas) (talc.) o
containing
B-N
349.3 237.8 246.8 290.6 340.8 332.2 353.0 423.9 446.1 384.3 437.0 451.8 456.8 666.8
-AHi’ (gas) (talc.) b 17575.3 f 7.8 6861.1 f 8.1 8022.0* 8.5 10379.1 f 8.8 13880.1 f 8.0 12719.6 f 8.6 13892.3 f 9.0 18574.0 f 7.5 18596.0 f 10.0 15077.2 f 10.2 18587.1 f 9.9 10265.4f11.5 11423.3kll.O 14814.6 f 12.5
(exp.)
AH,0
17575.3 6861.1 8021.3 10370.1 13880.9 12719.8 13892.3 18574.7 18596.7 15077.4 18587.1 10265.4 11424.1 14825.4
A& (talc.) a
group, measured and calculated by the Franldir-Benson
17575.3 6861.1 8022.8 10371.9 13880.1 12719.6 13892.3 18573.9 18596.1 15076.3 18586.9 10266.4 11424.1 14825.4
AH, (talc.) b
and Tatevslcii schemes
of the experimental
((CHMilsN
WW3%NCH3
KCW3W2NH
(C,Hs)sSiNH(CH&CH,
(C~HMiN~CH(CH~)CH&H,I, (C,H,),SiNHCH(CH&H,CH,CH,
(GHs)sSiNHC(CH& (C,H,),SiN(CH,CH,CH,CH,),
(C,Hs)sSiN(C,Hs), (C,H,),SiNHCH,CH,CH, (C,H,),SiNHCH(CH&
(CHMiN(CH,), (CHMiN(GHs)~
(CH,),SiNHCH,
I-WW,Hd,I,
Compound
Comparison
Table 5
and published
456.0 f 10.0 656.0 f 11.0
340.8* 6.0 333.0* 7.0 343.7f 1.0 353.0f 8.0 424.0* 8.0 446.0* 9.0 385.2* 9.0 437.1 f 9.0 450.8 f 10.0 432.2 416.6 411.0 448.5 670.7
330.5
f 7.1 f 6.1 f 7.5 f 1.5 f 12.1
k6.3
2 4 4 4 4
5
319.5 316.5
321 327 328 319 326 326 326 327 319
329 320 324 325
221.2 f 241.1 f 251.04&
349.6& 231.8f 246.0* 288.8f 4 4 2
Our data
6.0 7.0 7.7 7.0
Esi_N, kJ mol-’
state and the Si-N
Lit Refs.
in the gaseous
-AH~,l~Jmole-’
4.2 3.8 6.3
of formation
Our data
(Lit.) data on the enthalpies
322.6* 319.7 317.1 314.2 310.0
-
3.8
322.2 f 20.9 305.9 331.0 309.2f 4.2 348.5 376.6 f 20.9
Lit.
bond energies
2 3 4 4 4
5
5 4 4 2
Refs.
104
The numerical contributions of fragments in the Franklin-Benson (Hi, E,) and Tatevskii schemes (Hii, Eij) were calculated by the least squares method, using the enthalpies of formation and atomization of tri- and tetrasilanes as well as those of alkylalkoxysilanes determined experimentally [7]. In Table 4 the experimental AHf“ and AH,” values are summarized and compared with well-established values calculated by the Benson and Tatevskii schemes. From the experimental AHf“ values, the bond energies depending on the bond surrounding have been calculated (Table 5). The data of Table 5 provides strong evidence for the Si-N bond energy not being constant and not depending much on the nature of substituents attached to the Si and N atoms. In the compounds studied the Si-N bond energies vary from 316.5 to 329 kJ mol-‘, i.e. within a fairly narrow range. The lowest Si-N bond energy value is observed in compounds containing a Si-N-Si group: in hexamethyland heptamethyldisilazane (319.0 and 319.5 kJ mol-‘, respectively) and N-(trimethylsilyl)hexamethyldisilazane (316.5 kJ mol-‘). This seems to be due to a lower Si-N bond order in compounds containing this group. Our experimental values of the enthalpies of formation of organosilicon compounds containing a Si-N bond, and the Si-N bond energies coincide, within the limits of experimental error, with analogous values obtained from the heats of hydrolysis [4], and can therefore be regarded as reliable. Experimental The purity of the substances studied, which was assessed by GLC and the melting point curves, exceeds 99.3%. The heats of combustion were measured in a precision calorimeter [7] (calorific value 151.16 + 0.02 J a-‘). The heats of formation and sublimation were determined by means of calorimetry (DAK-1IA calorimeter) and the Knudsen effusion method on a vacuum installation. Liquid compounds (0.130-0.165 g sample) were burnt in Terylene ampoules with benzoic acid pellets (0.30-0.35 g). The procedure of burning of organosilicon compounds was described previously [7]. The degree of combustion was 98.5-99.8%. References 1 2 3 4 5 6 7 8 9 10 11 12 13
A.P. Claydon and C.T. Mortimer, J. Chem. Sot., 8 (1962) 3212. C.T. Mortimer, Reaction Heats and Bond Strengths, Pergamon Press, Oxford, 1962. A.E. Beezer and C.T. Mortimer, J. Chem. Sot., 5 (1966) 514. J.C. Baldwin, M.F. Lappert, J.B. Pedley and J.A. Toverton, J. Chem. Sot. A, 12 (1967) 1980. T.I. Kolyakova, I.B. Rabinovich and N.S. Vyazankin, Dokl. Akad. Nauk SSSR, 200 (1971) 111. V.I. Telnoi and I.B. Rabinovich, Usp. Khim., 49 (1980) 1137. M.G. Voronkov, V.A. Klyuchnikov, T.F. Danilova, V.I. Pepekin, A.N. Korchagina, Yu.1. Khudobin and V.P. Baryshok, J. Organomet. Chem., 345 (1988) 27. CODATA Recommended Key Values for Thermodynamics, 1977, J. Chem. Thermodyn., 10 (1978) 903. V.A. Klyuchnikov, M.G. Voronkov, L.I. Landa, V.I. Pepekin, T.M. Tikhenko, G.N. Shvets and V.T. Popov, Dokl. Akad. Nauk SSSR, 292 (1987) 395. V.A. Klyuchnikov, V.I. Pepekin, T.V. Popov, LA. Balykova and Ye.S. Kuxmina, Dokl. Akad. Nauk SSSR, 298 (1988) 398. S.W. Benson and J.H. Buss, J. Chem. Phys., 29 (1958) 546. J.L. Franklin, Chem. Phys., 21 (1953) 2039. V.M. Tatevskii, The Structure of Molecules, Khimiya Publishers, Moscow, 1977, 511 pp.
Journal of Organometallic
Chemistty,
406 (1991) 99-104
Elsevier Sequoia S.A., Lausanne
JOM 21365
Thermochemistry of organosilicon compounds VI *. Thermochemical properties of organosilicon compounds with a Si-N bond M.G. Voronkov * Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR, 664033 Irkutsk (USSR)
V.A. Klyuchnikov, L.I. Marenkova, T.F. Danilova, G.N. Shvets, S.I. Tsvetnitskaya Kemerovo
State Medical Institute,
650027 Kemerovo (USSR)
and Yu.1. Khudobin Institute of Chemistry of Silicates, Academy of Sciences of the USSR, Leningrad B-164 (USSR)
(Received August 26th, 1990)
We have evaluated the enthalpies of combustion and formation in the condensed and gaseous states, of fifteen organosilicon compounds containing an Si-N bond, of the general formula R,_,Si(NR’R”), where R = H, alkyl; R’ = H, akyl, Si(CH,),; R” = alkyl. Si(CH,),. The enthalpies of atomization in the gaseous phase and parameters for evaluating the enthalpies of formation and atomization of the above compounds by use of the Frankhn-Fknson and Tatevskii schemes have bean calculated. The Si-N bond energy ranges from 316.5 to 329 kJ mol-t. In compounds containing an Si-N-Si group, the Si-N bond energy is lowest.
Introduction
Monomeric and polymeric organosilicon compounds having one or more Si-N bonds are of great theoretical and practical interest. However, their thermochemical constants are scarce in the literature and most of them are contradictory and need re-examination [l-6]. The Si-N bond energies calculated from experimental thermochemical data, have been evaluated within the range of 305.9 to 376.6 kJ mol-’ [l--5].
* For Part V see J. Organomet. Chem., 406 (1991) 91. 0022-328X/91/$03.50
0 1991 - Ekevier Sequoia S.A.
100
Results and discussion The enthalpies of combustion and evaporation have been measured for 15 monomeric organosilicon compounds with the Si-N bond, of the general formula R ,_,Si(NR’R”) with R = H, alkyl; R’ = H, alkyl, Si(CH,),; R” = alkyl, Si(CH,), (Table 1). The energies of fragments in the Franklin-Benson (Table 2) and the Tatevskii schemes (table 3) have been determined. From this the enthalpies of formation in the condensed state and the enthalpies of atomization in the gas phase have been calculated (Table 4). In evaluating the enthalpies of formation and atomization use was made of the following key values (AHto, kJ mol-’ at 298.15 K): - 285.830 f 0.042 (H,O, liquid); - 393.514 f 0.13 (CO,, gas) [B]; - 939.39 + 0.52
Table 1 Enthalpies of combustion, formation and evaporation of the investigated organosilicon containing an Si-N bond at 298.15 K, kJ mol-’ - A If o (cycl. (liq.)
Compound
9684.2 f 4.5 4096.1 f 5.1 4771.1 f 5.0 6082.7 f 5.2 8064.4 f 4.5 7107.7 f 5.7 7385.8 i 5.5 8054.1 f 6.5 10684.5 f 6.3 10667.4 f 7.5 8694.6 f 7.2 10668.6 f 7.8 6462.2rt8.1 7140.5 f 8.3 9498.2 f 9.6
HW’W~WJ~ (CH,),SiNHCH, (CHs)sSiN(CHs)s (CHs)sSiN(CsHs)s (C,H,)sSrN(C,Hs), (C,H,),SiNHCH,CH,CH, (C,H,),SiNHCH(CH,), (C,HMiNHC(CHs)s (C,H,),SiN(CHsCH,CH,CH,),
(C,H,),SiN[CH(CH,)CH,CH,I, (C,H,),SiNHCH(CHs)CH,CH,CHsCHs (CsHs)sSiNH(CHs)rCHs
IP-%)~SWJH IW-UWPCH~ IWW$iW Note: [(CH,),Si],N in ref. 7.
-AH:
(hq.)
407.7* 5.0 275.2+ 6.0 279.6* 6.0 326.7* 6.0 383.0* 5.0 374.5i 6.0 382.3* 6.0 393.3f 7.0 480.3f 7.0 497.4* 8.0 432.1k 8.0 496.2k 8.0 493.0* 9.0 494.1* 9.0 720.3 f 10.0
compounds
AH0 58.4f 1.0 37.4iO.8 33.6kO.8 37.9 f 0.8 42.2 f 1.0 41.5 kO.8 38.6 f 0.8 40.3*0.9 56.3rtl.O 51.4*0.9 46.9 f 1.0 59.1 f 1.0 42.2 f 0.9 38.1 kO.8 54.3*1.0
is a solid, its enthalpies of formation and sublimation were determined as described
Table 2 Numeric contributions of fragments in the Franklin-Benson Fragment
C-+X-O, C-(C),(H), C-(C)(Si)(H)s C-(NW(H), C-(C)s(N) C-(C),(N)(H) C-(Si)(H),
C-U’JXW,
scheme, kJ mol-’
Fragment
Value Ei
- Hi
1414.93 1173.46 1166.26 1174.42 690.56 943.63 1410.93 1414.93
44.27 20.80 13.60 21.76 - 26.11 8.96 40.27 44.27
Si-(C)s(N) SW%(H) N-(Si)(C), N-(Si)(C)(H) N-(B),(C) N-(Si), N-(CXH), N-(S&(H)
Value Ei
- Hi
589.20 931.00 369.40 624.20 365.20 359.40 889.35 621.42
139.20 263.00 - 103.28 - 66.48 - 107.48 - 113.28 - 19.32 - 68.26
101 Table 3 Numeric contributions of fragments in the Tatevskii scheme, kJ mol-’ Fragment
Cl--G
c*-c, c,-Cl G-C.3
c*-c,
C,-Si C, -Si C,-N C,-N
Fragment
Value Eli
- Hi,
2002.27 1173.46 1728.77 1592.70 898.68 1540.60 707.43 1540.50 712.46
55.58 20.80 46.55 42.87 10.79 57.44 18.60 12.28 -21.43
C,-N C,-NH C,NH C,-NH C,,-NH Si-N Si-H Si-NH
Value Eij
- Hij
443.02 1919.30 1093.60 822.80 664.20 320.00 325.10 511.40
- 26.10 15.52 - 15.85 - 21.87 - 48.09 49.94 - 5.40 53.56
(SiO, amorph. hydr.) [9,10]; 716.67 f 0.44 (C, gas); 217.997 f 0.006 (H, gas); 450.00 f 8 (Si, gas); 472.68 f 0.12 (N, gas) [S]. Calculation of the enthalpies of formation and atomization by additive schemes was performed by use of: (i) the Franklin-Benson formula [11,12]
AH,0 (gas) = i
KiEi
i=l
A&“
(gas)
= 2
KiHi
i=l
Here Hi = - Ei + Z CIAHP (atom) where Hi is the enthalpy of formation of a given fragment; Ei is the energy of the fragment, which takes into account the mutual effect of the atoms separated by not more than one atom in the molecular chain; Ki is the number of fragments; El the number of moles of C, H, Si and N atoms. For the compounds studied the fragments are as follows: C-C,-(H),,
C-(C)-(Si)(H,),
C-(N)(H),,
etc.
(ii) The Tatevskii formula [13]: AH:
(gas) = 2
nij Hii, i~j
i,j=l
AH,0
(gas) = 5
nij Eij, i
i,j=1
Here Hi j = - Eij + X CIAHP (atom) where Eij is the energy of the fragment, which takes into account the mutual effect of the atoms separated by not more than one other atom in the molecular chain; nij is the number of fragments. The substances studied contain the following fragments: Ci-Si, Si-N, C-N,
etc.
LIBy the Fmnklin-Benson
W-W,SWH WW3SWCH3 WH,MW
(C,HMiNH(CH,),CH,
(gas)
compounds
349.6* 6.0 237.8* 7.0 246.0* 7.7 288.8* 7.0 340.8k 6.0 333.0* 7.0 353.0* 8.0 424.0* 8.0 446.0* 9.0 385.2* 9.0 437.1* 9.0 450.8 f 10.0 456.0 f 10.0 656.0 f 11.0
-A&’ (exp.)
of organosilicon
scheme. b By the Tatevskii scheme.
(C,H,),SiNHCH(CH,)CH2CH,CH&Hs
(C,H,),SiN[CH(CH,)CH,CH,I,
(CsHs)sSiNHWHs)s (C,H,)sSiN(CH&H,CHsCcH,),
(CH,),StN(CH,), (CHs)sSiN(CsHs)s (C,H,),SiNHCH,CH,CH, (C,Hs)sSiNHCH(CH,),
(CH,),SiNHCH,
HWW,H,M,
Compound
Enthalpies of formation and atomization at 298.15 K, kJ mol-’
Table 4
349.3 237.8 245.3 288.8 341.6 332.2 353.0 424.8 446.1 ,385.4 437.2 451.7 456.8 666.8
AH: (gas) (talc.) o
containing
B-N
349.3 237.8 246.8 290.6 340.8 332.2 353.0 423.9 446.1 384.3 437.0 451.8 456.8 666.8
-AHi’ (gas) (talc.) b 17575.3 f 7.8 6861.1 f 8.1 8022.0* 8.5 10379.1 f 8.8 13880.1 f 8.0 12719.6 f 8.6 13892.3 f 9.0 18574.0 f 7.5 18596.0 f 10.0 15077.2 f 10.2 18587.1 f 9.9 10265.4f11.5 11423.3kll.O 14814.6 f 12.5
(exp.)
AH,0
17575.3 6861.1 8021.3 10370.1 13880.9 12719.8 13892.3 18574.7 18596.7 15077.4 18587.1 10265.4 11424.1 14825.4
A& (talc.) a
group, measured and calculated by the Franldir-Benson
17575.3 6861.1 8022.8 10371.9 13880.1 12719.6 13892.3 18573.9 18596.1 15076.3 18586.9 10266.4 11424.1 14825.4
AH, (talc.) b
and Tatevslcii schemes
of the experimental
((CHMilsN
WW3%NCH3
KCW3W2NH
(C,Hs)sSiNH(CH&CH,
(C~HMiN~CH(CH~)CH&H,I, (C,H,),SiNHCH(CH&H,CH,CH,
(GHs)sSiNHC(CH& (C,H,),SiN(CH,CH,CH,CH,),
(C,Hs)sSiN(C,Hs), (C,H,),SiNHCH,CH,CH, (C,H,),SiNHCH(CH&
(CHMiN(CH,), (CHMiN(GHs)~
(CH,),SiNHCH,
I-WW,Hd,I,
Compound
Comparison
Table 5
and published
456.0 f 10.0 656.0 f 11.0
340.8* 6.0 333.0* 7.0 343.7f 1.0 353.0f 8.0 424.0* 8.0 446.0* 9.0 385.2* 9.0 437.1 f 9.0 450.8 f 10.0 432.2 416.6 411.0 448.5 670.7
330.5
f 7.1 f 6.1 f 7.5 f 1.5 f 12.1
k6.3
2 4 4 4 4
5
319.5 316.5
321 327 328 319 326 326 326 327 319
329 320 324 325
221.2 f 241.1 f 251.04&
349.6& 231.8f 246.0* 288.8f 4 4 2
Our data
6.0 7.0 7.7 7.0
Esi_N, kJ mol-’
state and the Si-N
Lit Refs.
in the gaseous
-AH~,l~Jmole-’
4.2 3.8 6.3
of formation
Our data
(Lit.) data on the enthalpies
322.6* 319.7 317.1 314.2 310.0
-
3.8
322.2 f 20.9 305.9 331.0 309.2f 4.2 348.5 376.6 f 20.9
Lit.
bond energies
2 3 4 4 4
5
5 4 4 2
Refs.
104
The numerical contributions of fragments in the Franklin-Benson (Hi, E,) and Tatevskii schemes (Hii, Eij) were calculated by the least squares method, using the enthalpies of formation and atomization of tri- and tetrasilanes as well as those of alkylalkoxysilanes determined experimentally [7]. In Table 4 the experimental AHf“ and AH,” values are summarized and compared with well-established values calculated by the Benson and Tatevskii schemes. From the experimental AHf“ values, the bond energies depending on the bond surrounding have been calculated (Table 5). The data of Table 5 provides strong evidence for the Si-N bond energy not being constant and not depending much on the nature of substituents attached to the Si and N atoms. In the compounds studied the Si-N bond energies vary from 316.5 to 329 kJ mol-‘, i.e. within a fairly narrow range. The lowest Si-N bond energy value is observed in compounds containing a Si-N-Si group: in hexamethyland heptamethyldisilazane (319.0 and 319.5 kJ mol-‘, respectively) and N-(trimethylsilyl)hexamethyldisilazane (316.5 kJ mol-‘). This seems to be due to a lower Si-N bond order in compounds containing this group. Our experimental values of the enthalpies of formation of organosilicon compounds containing a Si-N bond, and the Si-N bond energies coincide, within the limits of experimental error, with analogous values obtained from the heats of hydrolysis [4], and can therefore be regarded as reliable. Experimental The purity of the substances studied, which was assessed by GLC and the melting point curves, exceeds 99.3%. The heats of combustion were measured in a precision calorimeter [7] (calorific value 151.16 + 0.02 J a-‘). The heats of formation and sublimation were determined by means of calorimetry (DAK-1IA calorimeter) and the Knudsen effusion method on a vacuum installation. Liquid compounds (0.130-0.165 g sample) were burnt in Terylene ampoules with benzoic acid pellets (0.30-0.35 g). The procedure of burning of organosilicon compounds was described previously [7]. The degree of combustion was 98.5-99.8%. References 1 2 3 4 5 6 7 8 9 10 11 12 13
A.P. Claydon and C.T. Mortimer, J. Chem. Sot., 8 (1962) 3212. C.T. Mortimer, Reaction Heats and Bond Strengths, Pergamon Press, Oxford, 1962. A.E. Beezer and C.T. Mortimer, J. Chem. Sot., 5 (1966) 514. J.C. Baldwin, M.F. Lappert, J.B. Pedley and J.A. Toverton, J. Chem. Sot. A, 12 (1967) 1980. T.I. Kolyakova, I.B. Rabinovich and N.S. Vyazankin, Dokl. Akad. Nauk SSSR, 200 (1971) 111. V.I. Telnoi and I.B. Rabinovich, Usp. Khim., 49 (1980) 1137. M.G. Voronkov, V.A. Klyuchnikov, T.F. Danilova, V.I. Pepekin, A.N. Korchagina, Yu.1. Khudobin and V.P. Baryshok, J. Organomet. Chem., 345 (1988) 27. CODATA Recommended Key Values for Thermodynamics, 1977, J. Chem. Thermodyn., 10 (1978) 903. V.A. Klyuchnikov, M.G. Voronkov, L.I. Landa, V.I. Pepekin, T.M. Tikhenko, G.N. Shvets and V.T. Popov, Dokl. Akad. Nauk SSSR, 292 (1987) 395. V.A. Klyuchnikov, V.I. Pepekin, T.V. Popov, LA. Balykova and Ye.S. Kuxmina, Dokl. Akad. Nauk SSSR, 298 (1988) 398. S.W. Benson and J.H. Buss, J. Chem. Phys., 29 (1958) 546. J.L. Franklin, Chem. Phys., 21 (1953) 2039. V.M. Tatevskii, The Structure of Molecules, Khimiya Publishers, Moscow, 1977, 511 pp.