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A comment on the heats of deaquation and anation of [Co(NH3)5H2O]X3 complexes
Notes
2955
Molecular weights Attempts to estimate mol. wt by cryoscopy failed as the solvents (dioxane and DMSO) seemed to undergo chemical reactions with these complexes. In two cases the assumed mol. wt was confirmed by X-ray diffraction method.
X-ray diffraction Sharp diffraction patterns were obtained in the powder photographs of all the complexes but the patterns were complex and no attempt was made to index them. Unit cell dimensions were obtained for two complexes by single crystal Weissenberg photographs. a Tris(diethylammonium)hexabromoantimonate(III). The unit cell was found to be rhombic but it was indexed on a hexagonal unit cell a = 15" 19 A and c = 20-16 A. Space group was R3C or R3C. V = 4028.3 A :~and Z = 6. Deal,. = 2'036 and Dexp = 2'043. b Tris(dipropylammonium)hexabromoantimonate(II I). Unit cell was monoclinic in the space group P21/C but the angle/3 was not determined. However the volume oftbe unit cell, V was calculated to be 3328.6 A a, Z = 4. Dca,e = 1"805 and Dexp = 1'782.
Structure I.R. spectra have been recorded in the region 4000-400 cm -1 but they are of no help as far as the symmetry around the Sb atom is concerned because the Sb-Br vibrations occur below 200 cm -J, far i.r. and Raman work are needed for structure elucidation. Crystal structure analysis of the tris (diethylammonium hexabromoantimonate(III) is in progress. From the preliminary work it is indicated that hexabromoantimonate, SbBr6a- ions are present in the lattice.
A c k n o w l e d g e m e n t - T h e authors are thankful to Dr. D. R. Russell, Department of Chemistry, University of Leicester, U.K. for his help with X-ray work. Department o f Chemistry Indian Institute o f Technology N e w Delhi-29 India
N . K . JHA S . S . A . RIZVI
••
J. inorg, nucl. Chem., 1972, Vol. 34, pp. 2955-2957.
Pergamon Press.
Printed in Great Britain
A comment on the heats of deaquation and anation of [Co(NH3)sH20]X 3 complexes (Received 18 October 1971) A RECENT Note in this Journai[1] reported heats of deaquation and anation of [Co(NH3)sH20]Xa complexes: (A) [Co(NHa)sH20]X3(c) ~ [Co(NHa)r,X]Xz(c) + HzO(g) AHA (B) [Co(NHa)sH20]Xa(C) ~ [Co(NHz)sX]X2(c) + H20(I) AHB The data were determined from quantitative differential thermal analyses at approximately 120°C by use of (A) open and (B) sealed-capillary tubes (to yield H20(g) or H20(/) respectively). We wish to amplify and to comment on certain assumptions and results presented in this paper. The authors indicated that the essential difference between reactions in open and sealed tubes is in the physical state of the product H20. However, if the two reactions differ only in this respect, then 1. W.W. Wendlandt, G. D'ascenzo and R. H. Gore, J. inorg, nucl. Chem. 32, 3404 (1970).
2956
Notes
for given anions X, the two AH values should differ by a constant quantity, the heat of vaporisation of water AHv at 120°C, i.e. AHA -- AHa = AHv ~ 9.9 kcal mole-' [2, 3]. The data show that this relationship holds approximately for the chloro, bromo and iodo complexes but not for the nitrato complex (Table I'., AHA(calc) = AHB +9"9 kcal mole-'). The enthalpy change for the anation reaction can be calculated for 25°C by use of the enthalpy cycle below, using published standard heats of formation of reactants and products [4, 5]. [Co(NH3)~HzO]3+(aq) + 3X-(aq) AH,, [Co(NH3)r,X]2+(aq) + 2X-(aq) + H20(I) [Co(NH3)sH20]X3(c)
an% [Co(NH3)sX]Xz(c) + H20(I).
The resultant values of AHB are shown in Table 1. Now at 25°C, AHA = AHB+ AHv, and AHA at 120°C can be calculated by considering the heat capacities at constant pressure for the reactants and products. The necessary data are known only for the reaction of the aquopentaamminechloride complex[4], and for this ACp = - - 0 ' 6 cal deg-' mole-' and AHA(120°C)--AHA(25°C)=-0.06 kcal mole-' ~ 0. It is assumed that this relationship holds for the other complexes. Data for AHA(120°C) are shown in the Table and these agree well with those published[1 ]. In particular we confirm that the observed[I] value of AHA for the nitrato complex is less positive than expected on the basis of AHB. This observation suggests that reaction (A) for the nitrato complex is coupled with a secondary exothermic reaction (possibly to give [Co(NH3)sNO3](NO2)2); the compound nature of AHB (nitrato) (Table 1) supports this postulate. The authors suggest that there is little or no difference between the lattice energies for the compounds [Co(NH3)sX]Xz and [Co(NH3)sH20]X3. (It is not clear whether this statement applied to X constant or varying.) However, reference to the Kapustinskii equation [6] for lattice energies of coordination compounds indicates that the aquo complexes (3 : 1 salts) and the acido complexes (2 : 1 salts) will not have similar lattice energies. (These energies will possibly differ by a factor of two.) Table 1. AH* values for the deaquation/anation reaction of complexes [Co(NHn)sH20]Xa, X = CI-, Br-, I - and NOaAHA Compound [Co(NH:05H~O]CI:, [Co(NH3)~H~O]Brz [Co(NH3)sH20]l~ [Co(NH:,)zH~O](NO3)z
AHB AHA(calc)tAHa(25°C)$ AHa(25°C)§ AHA(calc)It Wendlandtet al. [ 1] This work
6"3+0"6 -4.6±0.5 5"3+-0'5 2"4±1"3 -3'6+-2"5 6.3+-0.6 -3.7±0,4 6.2±0.5 0.5±1.3 --2.0±2.5 6.4±0.6 -1.7+-0.2 8.2+-0.2 -0.9+- 1.3 -3.6±2.5 5.6+-0.5 0.9 +0.1 (102°C) 10.8+0.1 -0.7+-1.3 0.8+-2.5 -1.2_+0,1 (120°C)
6'8±2"5 8.4+_2.5 6.8+-2.5 11.3±2.5
*All data refer to ca. 120°C unless otherwise stated. tAHA(Calc) = AHB + AHv (9.9 kcal. mole-'). ~Enthalpy change for the anation reaction in aqueous solution, 25°C. § AH~ = AHsoln+ A H R - AHII~, where AH~olnand AH~,n are computed [4, 5] for X = CI-, Br-, I% NO3- as AHso~n= 7"0, 10"3, 13'5 and 16.2 kcal. mole-' and AH]ol~= 13.0, 12.8, 16.2 and 14.7 kcal. mole-', respectively. IbData calculated for 120°C; AHA ~ AHB + AHv(25°C).
2. JANAF Thermochemical Tables. Dow Chemical Co., Midland, Michigan (1965). 3. International Critical Tables of Numerical Data, Vol. VII, p. 232. Physics, Chemistry and Technology, National Research Council, U.S.A. (1930). 4. Selected Values of Chemical Termodynamic Properties, National Bureau of Standards Technical Notes 270-3 and 270-4 (1969). 5. D . A . House and H. K. J. Powell, lnorg. Chem. 10, 1583 (1971). 6. K. B. Yatsimirskii in Advances in the Chemistry of Coordination Compounds (Edited by S. Kirschner) p. 96. MacMillan, New York (1961).
Notes
2957
Also variation in anion radius and complex cation (thermochemical) radius [7] will cause the lattice energies for the aquo and acido complexes to be strongly dependent on the anion X. We consider that, because of lattice energy contributions to this solid state reaction, AH (observed) may not reflect the energies associated with bond breaking and bond making processes. It is interesting to note in contrast that AHR for the anation reaction in aqueous solution (Table 1) is least favourable for the chloride complex. The enthalpy change for a reaction is a state function and independent of the reaction path. Therefore it is incorrect for the authors to state[l] that the data "appears to favour an SN1 type mechanism". It has been shown previously that thermodynamic data of this kind can be used in the interpretation of mechanisms only when it is added algebraically to the activation enthalpy to give a transition enthalpy[5]; the transition enthalpy relates to the difference between the heat content of the transition state species and the heat content of a common reactant (or product).
Chemistry Department University o f Canterbury Christchurch, N e w Zealand
H . K . J . POWELL
7. L. L. Pankova and K. B. Yatsimirskii, Chem.Abs. 43, 2855 (1949). J. inorg, nucl. Chem., 1972, Vol. 34, pp. 2957-2959.
Pergamon Press.
Printed in Great Britain
ESR investigations of complexes of niobium(IV) chloride with oxygen donors (First received 14 October 1971 ; in revised form 16 December 197 I) NIOBIUM(IV) chloride is known to react with many donor molecules to form hexacoordinate complexes which are observable by electron spin resonance techniques [ 1-3]. During the course of these investigations several oxygen donors were examined in conjunction with oxochloro species[l] to determine the extent of axial and equitorial ~--bonding to the chlorides since the oxygen would be observed in different states of bonding to the metal. This note reports the result of that study. Table 1*. Experimental values of niobium(IV) ESR values, NbC14L2 L+? DMF DIO DME HMPA (1) (2) THF (solution) DMA DEF
gll
g±
(g)$
Ajl
Al
(a)$
N~
1'9014 1'9065 1'9069 1.8991 1-8869 1.9131
1"8953 1"8759 1"8779 1"8869 (1"8869)§ 1-8943
282-9 277"0 277"8 289"5 301-5 270'8
140-0 138-9 135'6 149'2 (149.2)§ 122'3
1.8969 1.8990
187'7 184"9 183"0 195"9 (199-9)§ 171"8 177" 1 189.5 186.9
0"81 0'79 0'81 0'80 0'87 0"85
1.8988 1.8954
1-8971 1-8861 1"8876 1"8910 (1-8869)§ 1.9006 1.8920 1-8975 1-8978
285.5 282-5
141-5 139-1
0.82 0"82
* All splittings are given in G; estimated errors are: gtl + 0.0005, g± ++.0-0008, ,4~r+ 0.3, 3_ + 0.5 G. t D M F = N,N-dimethylformamide, DIO = dioxane, DME = dimethoxyethane, HMPA = hexamethylphosphoramide, T H F = tetrahydrofuran, DMA = N,N-dimethylacetamide, DEF = N,N-diethylformamide. $Calculated values except for T H F solution. §Estimated assuming A t and g± were the same for each species since the Z lines overlapped almost perfectly. 1. Dennis P. Johnson and Robert D. Bereman, J. inorg, nucl. Chem. 34, 679 (1972). 2. Dennis P. Johnson and Robert D. Bereman. To be published. 3. Dennis P. Johnson and Robert D. Bereman. In preparation.
JINC VoL 34no. 9 - J
2955
Molecular weights Attempts to estimate mol. wt by cryoscopy failed as the solvents (dioxane and DMSO) seemed to undergo chemical reactions with these complexes. In two cases the assumed mol. wt was confirmed by X-ray diffraction method.
X-ray diffraction Sharp diffraction patterns were obtained in the powder photographs of all the complexes but the patterns were complex and no attempt was made to index them. Unit cell dimensions were obtained for two complexes by single crystal Weissenberg photographs. a Tris(diethylammonium)hexabromoantimonate(III). The unit cell was found to be rhombic but it was indexed on a hexagonal unit cell a = 15" 19 A and c = 20-16 A. Space group was R3C or R3C. V = 4028.3 A :~and Z = 6. Deal,. = 2'036 and Dexp = 2'043. b Tris(dipropylammonium)hexabromoantimonate(II I). Unit cell was monoclinic in the space group P21/C but the angle/3 was not determined. However the volume oftbe unit cell, V was calculated to be 3328.6 A a, Z = 4. Dca,e = 1"805 and Dexp = 1'782.
Structure I.R. spectra have been recorded in the region 4000-400 cm -1 but they are of no help as far as the symmetry around the Sb atom is concerned because the Sb-Br vibrations occur below 200 cm -J, far i.r. and Raman work are needed for structure elucidation. Crystal structure analysis of the tris (diethylammonium hexabromoantimonate(III) is in progress. From the preliminary work it is indicated that hexabromoantimonate, SbBr6a- ions are present in the lattice.
A c k n o w l e d g e m e n t - T h e authors are thankful to Dr. D. R. Russell, Department of Chemistry, University of Leicester, U.K. for his help with X-ray work. Department o f Chemistry Indian Institute o f Technology N e w Delhi-29 India
N . K . JHA S . S . A . RIZVI
••
J. inorg, nucl. Chem., 1972, Vol. 34, pp. 2955-2957.
Pergamon Press.
Printed in Great Britain
A comment on the heats of deaquation and anation of [Co(NH3)sH20]X 3 complexes (Received 18 October 1971) A RECENT Note in this Journai[1] reported heats of deaquation and anation of [Co(NH3)sH20]Xa complexes: (A) [Co(NHa)sH20]X3(c) ~ [Co(NHa)r,X]Xz(c) + HzO(g) AHA (B) [Co(NHa)sH20]Xa(C) ~ [Co(NHz)sX]X2(c) + H20(I) AHB The data were determined from quantitative differential thermal analyses at approximately 120°C by use of (A) open and (B) sealed-capillary tubes (to yield H20(g) or H20(/) respectively). We wish to amplify and to comment on certain assumptions and results presented in this paper. The authors indicated that the essential difference between reactions in open and sealed tubes is in the physical state of the product H20. However, if the two reactions differ only in this respect, then 1. W.W. Wendlandt, G. D'ascenzo and R. H. Gore, J. inorg, nucl. Chem. 32, 3404 (1970).
2956
Notes
for given anions X, the two AH values should differ by a constant quantity, the heat of vaporisation of water AHv at 120°C, i.e. AHA -- AHa = AHv ~ 9.9 kcal mole-' [2, 3]. The data show that this relationship holds approximately for the chloro, bromo and iodo complexes but not for the nitrato complex (Table I'., AHA(calc) = AHB +9"9 kcal mole-'). The enthalpy change for the anation reaction can be calculated for 25°C by use of the enthalpy cycle below, using published standard heats of formation of reactants and products [4, 5]. [Co(NH3)~HzO]3+(aq) + 3X-(aq) AH,, [Co(NH3)r,X]2+(aq) + 2X-(aq) + H20(I) [Co(NH3)sH20]X3(c)
an% [Co(NH3)sX]Xz(c) + H20(I).
The resultant values of AHB are shown in Table 1. Now at 25°C, AHA = AHB+ AHv, and AHA at 120°C can be calculated by considering the heat capacities at constant pressure for the reactants and products. The necessary data are known only for the reaction of the aquopentaamminechloride complex[4], and for this ACp = - - 0 ' 6 cal deg-' mole-' and AHA(120°C)--AHA(25°C)=-0.06 kcal mole-' ~ 0. It is assumed that this relationship holds for the other complexes. Data for AHA(120°C) are shown in the Table and these agree well with those published[1 ]. In particular we confirm that the observed[I] value of AHA for the nitrato complex is less positive than expected on the basis of AHB. This observation suggests that reaction (A) for the nitrato complex is coupled with a secondary exothermic reaction (possibly to give [Co(NH3)sNO3](NO2)2); the compound nature of AHB (nitrato) (Table 1) supports this postulate. The authors suggest that there is little or no difference between the lattice energies for the compounds [Co(NH3)sX]Xz and [Co(NH3)sH20]X3. (It is not clear whether this statement applied to X constant or varying.) However, reference to the Kapustinskii equation [6] for lattice energies of coordination compounds indicates that the aquo complexes (3 : 1 salts) and the acido complexes (2 : 1 salts) will not have similar lattice energies. (These energies will possibly differ by a factor of two.) Table 1. AH* values for the deaquation/anation reaction of complexes [Co(NHn)sH20]Xa, X = CI-, Br-, I - and NOaAHA Compound [Co(NH:05H~O]CI:, [Co(NH3)~H~O]Brz [Co(NH3)sH20]l~ [Co(NH:,)zH~O](NO3)z
AHB AHA(calc)tAHa(25°C)$ AHa(25°C)§ AHA(calc)It Wendlandtet al. [ 1] This work
6"3+0"6 -4.6±0.5 5"3+-0'5 2"4±1"3 -3'6+-2"5 6.3+-0.6 -3.7±0,4 6.2±0.5 0.5±1.3 --2.0±2.5 6.4±0.6 -1.7+-0.2 8.2+-0.2 -0.9+- 1.3 -3.6±2.5 5.6+-0.5 0.9 +0.1 (102°C) 10.8+0.1 -0.7+-1.3 0.8+-2.5 -1.2_+0,1 (120°C)
6'8±2"5 8.4+_2.5 6.8+-2.5 11.3±2.5
*All data refer to ca. 120°C unless otherwise stated. tAHA(Calc) = AHB + AHv (9.9 kcal. mole-'). ~Enthalpy change for the anation reaction in aqueous solution, 25°C. § AH~ = AHsoln+ A H R - AHII~, where AH~olnand AH~,n are computed [4, 5] for X = CI-, Br-, I% NO3- as AHso~n= 7"0, 10"3, 13'5 and 16.2 kcal. mole-' and AH]ol~= 13.0, 12.8, 16.2 and 14.7 kcal. mole-', respectively. IbData calculated for 120°C; AHA ~ AHB + AHv(25°C).
2. JANAF Thermochemical Tables. Dow Chemical Co., Midland, Michigan (1965). 3. International Critical Tables of Numerical Data, Vol. VII, p. 232. Physics, Chemistry and Technology, National Research Council, U.S.A. (1930). 4. Selected Values of Chemical Termodynamic Properties, National Bureau of Standards Technical Notes 270-3 and 270-4 (1969). 5. D . A . House and H. K. J. Powell, lnorg. Chem. 10, 1583 (1971). 6. K. B. Yatsimirskii in Advances in the Chemistry of Coordination Compounds (Edited by S. Kirschner) p. 96. MacMillan, New York (1961).
Notes
2957
Also variation in anion radius and complex cation (thermochemical) radius [7] will cause the lattice energies for the aquo and acido complexes to be strongly dependent on the anion X. We consider that, because of lattice energy contributions to this solid state reaction, AH (observed) may not reflect the energies associated with bond breaking and bond making processes. It is interesting to note in contrast that AHR for the anation reaction in aqueous solution (Table 1) is least favourable for the chloride complex. The enthalpy change for a reaction is a state function and independent of the reaction path. Therefore it is incorrect for the authors to state[l] that the data "appears to favour an SN1 type mechanism". It has been shown previously that thermodynamic data of this kind can be used in the interpretation of mechanisms only when it is added algebraically to the activation enthalpy to give a transition enthalpy[5]; the transition enthalpy relates to the difference between the heat content of the transition state species and the heat content of a common reactant (or product).
Chemistry Department University o f Canterbury Christchurch, N e w Zealand
H . K . J . POWELL
7. L. L. Pankova and K. B. Yatsimirskii, Chem.Abs. 43, 2855 (1949). J. inorg, nucl. Chem., 1972, Vol. 34, pp. 2957-2959.
Pergamon Press.
Printed in Great Britain
ESR investigations of complexes of niobium(IV) chloride with oxygen donors (First received 14 October 1971 ; in revised form 16 December 197 I) NIOBIUM(IV) chloride is known to react with many donor molecules to form hexacoordinate complexes which are observable by electron spin resonance techniques [ 1-3]. During the course of these investigations several oxygen donors were examined in conjunction with oxochloro species[l] to determine the extent of axial and equitorial ~--bonding to the chlorides since the oxygen would be observed in different states of bonding to the metal. This note reports the result of that study. Table 1*. Experimental values of niobium(IV) ESR values, NbC14L2 L+? DMF DIO DME HMPA (1) (2) THF (solution) DMA DEF
gll
g±
(g)$
Ajl
Al
(a)$
N~
1'9014 1'9065 1'9069 1.8991 1-8869 1.9131
1"8953 1"8759 1"8779 1"8869 (1"8869)§ 1-8943
282-9 277"0 277"8 289"5 301-5 270'8
140-0 138-9 135'6 149'2 (149.2)§ 122'3
1.8969 1.8990
187'7 184"9 183"0 195"9 (199-9)§ 171"8 177" 1 189.5 186.9
0"81 0'79 0'81 0'80 0'87 0"85
1.8988 1.8954
1-8971 1-8861 1"8876 1"8910 (1-8869)§ 1.9006 1.8920 1-8975 1-8978
285.5 282-5
141-5 139-1
0.82 0"82
* All splittings are given in G; estimated errors are: gtl + 0.0005, g± ++.0-0008, ,4~r+ 0.3, 3_ + 0.5 G. t D M F = N,N-dimethylformamide, DIO = dioxane, DME = dimethoxyethane, HMPA = hexamethylphosphoramide, T H F = tetrahydrofuran, DMA = N,N-dimethylacetamide, DEF = N,N-diethylformamide. $Calculated values except for T H F solution. §Estimated assuming A t and g± were the same for each species since the Z lines overlapped almost perfectly. 1. Dennis P. Johnson and Robert D. Bereman, J. inorg, nucl. Chem. 34, 679 (1972). 2. Dennis P. Johnson and Robert D. Bereman. To be published. 3. Dennis P. Johnson and Robert D. Bereman. In preparation.
JINC VoL 34no. 9 - J