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ESR investigations of complexes of niobium(IV) chloride with oxygen donors
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
2958
Notes
EXPERIMENTAL Samples were prepared from anhydrous solvents and spectra were obtained and corrected for second order effects as previously reported [t, 2]. The results are given in Table 1 and a representative spectrum is given in Fig. 1.
Fig. 1. ESR spectrum of NbCI4 in T H F at 77°K. ~ indicates ]llines; t indicates _l_lines. DISCUSSION Two of the complexes investigated here have been isolated before[4], NbCI4.2 tetrahydrofuran and N b C 4 . 2 dioxane, and were described as cis compounds. All the complexes investigated here exhibit spectra characteristic of a trans geometry. [5]. Spectra of the glasses could be resolved into parallel and perpendicular components, which requires at least most of the compound be an isomer with axial symmetry: the trans isomer with D4h symmetry. This apparent contradiction may be due to the fact that the complexes investigated were not isolated but we observed in solution as glasses where the trans geometry must predominate. The ESR spectra of niobium tetrachloride in various nitriles[3] where the cis-NbCI4(RCN)2 complexes are thought to predominate are much more complicated, further substantiating the assignment of a trans geometry for the oxygen donor ligands. It was thought that perhaps in the case of NbC14.2DMF that some water may have been present to yield the brilliant blue color which also was characteristic of the NbOCL4 -~ species.J1] This however was shown not to be the case. Deliberate preparations of NbOCI4. D M F -2 proved unsuccessful. In nearly all the cases the hyperfine parameters are significantly different from the oxo species [1 ] and lead one to conclude that only coordinate bonding to oxygen is present. In the case of HMPA, two species were detected, which are likely mono and bis complexes, since the bulkiness of the ligand would probably hinder rapid coordination. It is also interesting to note that gH and g± are almost equal for the DMA, D M F and D E F complexes. This is in contrast to the other compounds and the oxo species [1] where g~ > g.t. The complexes of NbC14 with various substituted pyridines were noted to behave in an opposite way [2]. A simple calculation of the molecular orbital normalization constant for the ground state 1B2 >* molecular orbital shows that in general these complexes form more covalent ~r-bonds with the equitorial halides than the oxo species (See Table 2). This would indicate that ~--bonding to the various oxygen donor ligands in the axial site is certainly less important than in the oxo species as one would have postulated. This simple calculation assumes that AF~ and A± are positive so that (a) = 1/3/ (A~t+2A.L). Note in Table 1 that the solution spectrum values for NbCI4.2THF show this to be a valid assumption. Further work on several other oxohalide systems is underway, hopefully to allow a detailed understanding of the importance of the g values relative to one another. 4. G . W . A . Fowles, D. J. Tidmarsh and R. A. Walton, lnorg. Chem. $, 631 (1969). 5. D. A. McClung, L. R. Dalton, and C. H. Brubaker, Jr., Inorg. C h e m . 5, 1985 (1966).
Notes
2959
Table 2 [1]*. Experimental values of niobium(IV) oxo species Complex
gll
g±
(g)~c
Arl
A±
(a)
NbOCI4(H20) -2 NbOCI4(C2HsOH) -z NbOCI5 -3
1.9165 1.9194 1'9215
1.8833 1.8946
1.8943 1.9029
277-0 269.3 294.4
130.6 131.8
179.4 177.6
N~, 0.83 0-95§
*~§See footnotes, Table 1.
Department of Chemistry State University of New York at Buffalo Buffalo, New York 14214
D E N N I S P. J O H N S O N ROBERT D. B E R E M A N *
*To whom inquiries should be addressed.
J. inorg,nucl.Chem., 1972,Vol. 34, p. 2959. PergamonPress. Printedin Great Britain
Tensimetric study of the system uranium tetrafluoride-anhydrous hydrazine (Received 29 November 1971) WE REPORTED earlier[l] that uranium tetrafluoride yields with anhydrous hydrazine addition compounds of the composition UF4"N2H4 and UF4" 1,5N2H4. During that work we obtained an indication that adducts with higher hydrazine content might be existing though on the basis of the results at hand we could not have reached a definite conclusion about that. A tensimetric study of the system uranium tetrafluoride-anhydrous hydrazine was initiated therefore in hope to clarify the situation. A measured quantity of anhydrous hydrazine was distilled into the reaction vessel filled with UF4 (the reaction vessel and the preparation of U F4 are described elsewhere[1 ]). After some days, a small amount of the decomposition products was pumped off at -80°C. The vessel was subsequently warmed up to 22°(2 and the vapour pressure was measured with a mercury manometer. Readings were taken with a cathetometer. The equilibrium pressure at various uranium tetrafluoride to hydrazine mole ratios were examined. Although the vapour pressure of hydrazine and the dissociation pressures of the compounds were low, the curve definitely reveals the existence of three phases with the following composition and dissociation pressures: POV,.N2n, = 0
mm Hg
PUF,.~,SN~H,= 1,3 mm Hg POF,.2N2m = 3,4 mm Hg while the vapour pressure of hydrazine is known to be 11,8 mm Hg at 22°C [2]. These data together with the chemical analysis of the products confirm the existence of the compound UF4'2NzH4 which was doubtful. No higher or lower hydrazine adducts were found at room temperature. UFa'2N2H4 is extremely reactive to traces of moisture. It reacts with all usual i.r. window-materials and also with silver chloride, which was successfully used with the lower adducts. The surface of the plates is immediately reduced to silver and the decomposition of UF4"2N2H4 takes place, leaving UF4.1,5N2H4 as a reaction product.
Institute "Jo~ef Stefan" Ljubljana 61000 Jamova 39 Yugoslavia
PETER GLAVIC A N Z E BOLI~
1. P. Glavi~ andJ. Slivnik,J. inorg, nucl. Chem. 32, 2939 (1970). 2. L. F. Audrieth and B. Ackerson-Ogg, The Chemistry ofHydrazine, p. 59. John Wiley, New York (1951).
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
2958
Notes
EXPERIMENTAL Samples were prepared from anhydrous solvents and spectra were obtained and corrected for second order effects as previously reported [t, 2]. The results are given in Table 1 and a representative spectrum is given in Fig. 1.
Fig. 1. ESR spectrum of NbCI4 in T H F at 77°K. ~ indicates ]llines; t indicates _l_lines. DISCUSSION Two of the complexes investigated here have been isolated before[4], NbCI4.2 tetrahydrofuran and N b C 4 . 2 dioxane, and were described as cis compounds. All the complexes investigated here exhibit spectra characteristic of a trans geometry. [5]. Spectra of the glasses could be resolved into parallel and perpendicular components, which requires at least most of the compound be an isomer with axial symmetry: the trans isomer with D4h symmetry. This apparent contradiction may be due to the fact that the complexes investigated were not isolated but we observed in solution as glasses where the trans geometry must predominate. The ESR spectra of niobium tetrachloride in various nitriles[3] where the cis-NbCI4(RCN)2 complexes are thought to predominate are much more complicated, further substantiating the assignment of a trans geometry for the oxygen donor ligands. It was thought that perhaps in the case of NbC14.2DMF that some water may have been present to yield the brilliant blue color which also was characteristic of the NbOCL4 -~ species.J1] This however was shown not to be the case. Deliberate preparations of NbOCI4. D M F -2 proved unsuccessful. In nearly all the cases the hyperfine parameters are significantly different from the oxo species [1 ] and lead one to conclude that only coordinate bonding to oxygen is present. In the case of HMPA, two species were detected, which are likely mono and bis complexes, since the bulkiness of the ligand would probably hinder rapid coordination. It is also interesting to note that gH and g± are almost equal for the DMA, D M F and D E F complexes. This is in contrast to the other compounds and the oxo species [1] where g~ > g.t. The complexes of NbC14 with various substituted pyridines were noted to behave in an opposite way [2]. A simple calculation of the molecular orbital normalization constant for the ground state 1B2 >* molecular orbital shows that in general these complexes form more covalent ~r-bonds with the equitorial halides than the oxo species (See Table 2). This would indicate that ~--bonding to the various oxygen donor ligands in the axial site is certainly less important than in the oxo species as one would have postulated. This simple calculation assumes that AF~ and A± are positive so that (a) = 1/3/ (A~t+2A.L). Note in Table 1 that the solution spectrum values for NbCI4.2THF show this to be a valid assumption. Further work on several other oxohalide systems is underway, hopefully to allow a detailed understanding of the importance of the g values relative to one another. 4. G . W . A . Fowles, D. J. Tidmarsh and R. A. Walton, lnorg. Chem. $, 631 (1969). 5. D. A. McClung, L. R. Dalton, and C. H. Brubaker, Jr., Inorg. C h e m . 5, 1985 (1966).
Notes
2959
Table 2 [1]*. Experimental values of niobium(IV) oxo species Complex
gll
g±
(g)~c
Arl
A±
(a)
NbOCI4(H20) -2 NbOCI4(C2HsOH) -z NbOCI5 -3
1.9165 1.9194 1'9215
1.8833 1.8946
1.8943 1.9029
277-0 269.3 294.4
130.6 131.8
179.4 177.6
N~, 0.83 0-95§
*~§See footnotes, Table 1.
Department of Chemistry State University of New York at Buffalo Buffalo, New York 14214
D E N N I S P. J O H N S O N ROBERT D. B E R E M A N *
*To whom inquiries should be addressed.
J. inorg,nucl.Chem., 1972,Vol. 34, p. 2959. PergamonPress. Printedin Great Britain
Tensimetric study of the system uranium tetrafluoride-anhydrous hydrazine (Received 29 November 1971) WE REPORTED earlier[l] that uranium tetrafluoride yields with anhydrous hydrazine addition compounds of the composition UF4"N2H4 and UF4" 1,5N2H4. During that work we obtained an indication that adducts with higher hydrazine content might be existing though on the basis of the results at hand we could not have reached a definite conclusion about that. A tensimetric study of the system uranium tetrafluoride-anhydrous hydrazine was initiated therefore in hope to clarify the situation. A measured quantity of anhydrous hydrazine was distilled into the reaction vessel filled with UF4 (the reaction vessel and the preparation of U F4 are described elsewhere[1 ]). After some days, a small amount of the decomposition products was pumped off at -80°C. The vessel was subsequently warmed up to 22°(2 and the vapour pressure was measured with a mercury manometer. Readings were taken with a cathetometer. The equilibrium pressure at various uranium tetrafluoride to hydrazine mole ratios were examined. Although the vapour pressure of hydrazine and the dissociation pressures of the compounds were low, the curve definitely reveals the existence of three phases with the following composition and dissociation pressures: POV,.N2n, = 0
mm Hg
PUF,.~,SN~H,= 1,3 mm Hg POF,.2N2m = 3,4 mm Hg while the vapour pressure of hydrazine is known to be 11,8 mm Hg at 22°C [2]. These data together with the chemical analysis of the products confirm the existence of the compound UF4'2NzH4 which was doubtful. No higher or lower hydrazine adducts were found at room temperature. UFa'2N2H4 is extremely reactive to traces of moisture. It reacts with all usual i.r. window-materials and also with silver chloride, which was successfully used with the lower adducts. The surface of the plates is immediately reduced to silver and the decomposition of UF4"2N2H4 takes place, leaving UF4.1,5N2H4 as a reaction product.
Institute "Jo~ef Stefan" Ljubljana 61000 Jamova 39 Yugoslavia
PETER GLAVIC A N Z E BOLI~
1. P. Glavi~ andJ. Slivnik,J. inorg, nucl. Chem. 32, 2939 (1970). 2. L. F. Audrieth and B. Ackerson-Ogg, The Chemistry ofHydrazine, p. 59. John Wiley, New York (1951).