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Computer simulation of the structure and proton transport in orthoiodates
Solid State Ionics 145 Ž2001. 459–462 www.elsevier.comrlocaterssi
Computer simulation of the structure and proton transport in orthoiodates T.S. Zyubina, G.V. Shilov, Yu.A. Dobrovolsky, L.O. Atovmyan, A.V. Chernyak, L.S. Leonova, A.E. Ukshe ) Institute of Problems of Chemical Physics RAS, 142432, ChernogoloÕka, Moscow region, Russia Received 25 September 2000; received in revised form 9 January 2001; accepted 8 February 2001
Abstract The crystal structure and properties of CsH 4 IO6 P H 5 IO6 have been studied by electrochemistry, X-ray methods, and calculated by density functional theory ŽDFT. methods. High protonic conductivity in crystals of CsH 4 IO6 P H 5 IO6 has been discovered and is discussed. q 2001 Published by Elsevier Science B.V. Keywords: Protonic conductivity; DFT; Crystal structure; Chemical compound, CsH 4 IO6 P H 5 IO6
1. Introduction We have discovered high protonic conductivity in crystals of CsH 4 IO6 P H 5 IO6 . X-ray diffraction study has shown that the compound crystallizes as a monoclinic cell, space group Cc w1x. The crystal structure is represented by two wCsI 2 O 12 H 9 x layers of hydrogen bonded to each other, and parallel to the unit cell Žbc. plane. The layers are formed by IOŽOH.4 entities and Cs atoms. One unit cell contains two independent ŽIO6 . octahedra and one Cs atom. The crystal structure fragment of CsH 4 IO6 P H 5 IO6 ŽX-ray data. is shown in Fig. 1. The aim of this work is to determine the structure and proton transport properties by quantum-chemical
calculations and to compare the numerical results with X-ray data for CsH 4 IO6 P H 5 IO6 .
2. Methods The calculations were made within the framework of density functional theory ŽDFT. using a threeparameter potential B3LYP with LanL2DZ plus polarization Žthe exponents a d s 0.266. and effective core potential LanL2 for I atom and basis 6-31G ) ) for O and H atoms. The computation employed the GAUSSIAN-94 package w2x.
3. Results and discussion )
Corresponding author. Tel.: q7-95-742-0142x3774; fax: q796-576-4009. E-mail addresses: [email protected] ŽT.S. Zyubina., [email protected] ŽA.E. Ukshe..
The calculations show that the transition from orthoiodic acid to its singly charged ion, then to its
0167-2738r01r$ - see front matter q 2001 Published by Elsevier Science B.V. PII: S 0 1 6 7 - 2 7 3 8 Ž 0 1 . 0 0 9 4 4 - 4
T.S. Zyubina et al.r Solid State Ionics 145 (2001) 459–462
460
Fig. 1. Crystal structure fragment of CsH 4 IO6 PH 5 IO6 Žfrom X-ray data..
two-charged ion H 5 IO6 –H 4 IO6y–H 3 IO62y leads to a ˚ successive increase of all the I`O distances by 0.9 A ˚ for each anion charge, see Table 1 and Ž0.4–0.5 A Fig. 2.. The O`H distance in all the calculated ˚ and the H`O`I angle is 998. compounds is 0.97 A The oxygen atoms that are not bound to the hydro˚ than gen have an I`O bond shorter by 0.18–0.19 A the oxygen atoms ŽO H . bound to the hydrogen atoms. The single-charged H 4 IO6y anion has O`I`O bond angles for the opposite oxygens close to 1808, while for the acid, two of the three angles are 10–118 less ŽTable 1..
Table 1 ˚ and 8. of the orthoiodic acid The main geometric parameters ŽA and its anions H 5 IO6 , H 4 IO6y and H 3 IO62y Žtheir structures are given in Fig. 2. Parameter
H 5 IO6 H 5 IO6 Ža. H 4 IO6y H 4 IO6y Ža. H 3 IO62y
I ` O2 1.95 1.97 I ` O3 1.94 2.74 I ` O4 1.96 1.99 I ` O5 1.94 2.02 I ` O6 1.96 1.99 I ` O7 1.77 2.07 O 2 ` I ` O 7 176.5 166.5 O 3 ` I ` O6 168.3 O4 ` I ` O5 167.0 160.7
1.81 1.99 1.99 1.99 1.99 1.81 179.7 178.3 178.2
2.05 2.81 2.11 2.04 1.81 2.12 174.2 112.0 171.9
1.86 2.10 2.06 2.06 1.81 1.84 164.8 178.9 168.2
Fig. 2. Calculated structures of orthoiodic acid and its anions H 5 IO6 , H 4 IO6y and H 3 IO62y.
It was found from the calculations that along with the H 4 IO6y ion, there is one more minimum on the potential surface of H 4 IO6yŽ a. whose structure is shown in Fig. 2 and geometric parameters are given in Table 1. This isomer is characterized by the ˚ presence of an O 3`O 7 peroxide bond of 1.46 A ` ` ŽO 3 O 7 I angle of 109.58.. On the energy scale, this isomer lies 7 kcalrmol higher than the main one. For the acid, an analogous isomer with a peroxide fragment lies 6.1 kcalrmol higher in energy than the main isomer. The calculated structure of monosubstituted cesium salt CsH 4 IO6 is given in Fig. 3, and its geometric parameters are listed in Table 2. It is seen that the minimum corresponds to the isomers of the three-coordinates through the oxygen position of the Cs atom. The main isomer is that in which Cs is bound to iodine through two bridging O atoms and one O H atom. The salt isomer II with two bridging
T.S. Zyubina et al.r Solid State Ionics 145 (2001) 459–462
Fig. 3. Calculated structures of different isomers and transition states of monosubstituted cesium salt CsH 4 IO6 .
O H atoms and one O atom lies higher in energy. Depending on the position of two O atoms, diametric ŽIIa. or not ŽIIb., the salt isomer II position on the energy scale is higher than that of salt isomer I by 0.75 kcalrmol ŽIIa. or by 1.44 kcalrmol ŽIIb.. Salt isomer III with three bridging O H atoms lies 4.96 kcalrmol higher than the main isomer. The octahedral unit of H 4 IO6y may turn relative to the Csq cation with an activation energy of 2.7 kcalrmol in the case of salt isomer I and with an activation energy of 4.5 kcalrmol in the case of salt isomer IIa. In all the considered configurations of the ˚ . and I`O H cesium salts, the I`O Ž1.79–1.81 A ˚ . distances to an accuracy of 0.01–0.02 Ž1.99–2.02 A ˚ are close to the analogous distances in the singly A charged H 4 IO6y anion. A comparison of the experimental and theoretical values for geometrical parameters shows that two
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types of octahedra IŽ1.O6 and IŽ2.O6 identified by the X-ray study may be assigned to equal quantities of molecules of orthoiodic acid and H 4 IO6y anions present in the crystal. The geometric parameters of structure IŽ1. are in reasonably good agreement with the calculated parameters of salt isomer II Žaccording to Fig. 3., while the I parameters, with the acid parameters. The X-ray data for the I`O valence bond lengths are ˚ less and the Cs`I non-valence bond 0.01–0.11 A ˚ in comparison to lengths are larger by 0.55–1.30 A the values obtained in the calculations for a single molecule. Nevertheless, the comparison of the calculated and experimental values of difference between I`O and I`O H has allowed us to identify the hydrogen atom positions in the crystal ŽTable 3.. In the crystal, six IO6 octahedra lie about the Cs atom so that the nearest oxygen atoms from the neighbouring octahedra are at a distance of 2.5–2.7 ˚ from each other. This fact allows us to expect the A relay-race mechanism of proton transport. The calculated activation energy of the relay mechanism is about 0.3–0.5 eV; the experimental estimate of activation energy of conductivity is 0.5 eV. The phase transition observed in experiments on increasing the temperature to 508C may be a result of
Table 2 ˚ and 8. and The most significant geometric parameters Žin A relative energies of isomers Ž D E with zero-point correction. in kcalrmol for cesium salt of orthoiodic acid a Parameters I
IIa
IIb
III
TSŽI.
TSŽII.
Cs ` I 3.64 3.78 3.78 3.94 3.76 3.97 Cs ` O 2 3.07 2.98 3.09 3.02 2.96 2.94 Cs ` O 3 3.04 3.09 2.98 2.99 2.97 2.93 Cs ` O4 3.18 3.06 3.05 3.06 I ` O2 1.81 1.81 2.02 2.02 1.80 1.82 I ` O3 1.81 2.01 1.81 2.02 1.80 2.03 I ` O4 2.01 2.03 2.02 2.03 1.98 1.98 I ` O5 1.97 1.96 1.79 1.97 1.98 1.98 I ` O6 1.99 1.98 1.99 1.79 2.00 1.97 I ` O7 1.99 1.80 1.97 1.79 1.99 1.79 O 2 ` I ` O 7 170.1 177.2 168.9 164.9 169.1 176.9 O 3 ` I ` O6 166.5 171.4 164.9 164.0 168.6 179.2 O4 ` I ` O5 170.1 177.2 165.3 166.3 171.2 176.7 DE 0 0.75 1.44 4.96 2.70 5.27 a
Isomer numbering in the table corresponds to the numbering in Fig. 3.
T.S. Zyubina et al.r Solid State Ionics 145 (2001) 459–462
462
Table 3 Bond lengths of CsH 4 IO6 PH 5 IO6 calculated from X-ray data
Acknowledgements
Parameters
IŽ1.
Cs ` I
4.267 4.381 4.407 3.147 3.232 3.299 1.789 1.834 1.877 1.893 1.902 1.906
This work was supported by the Russian Foundation for Basic Research ŽProject no. 01-03-33178a.. The calculations were made on RM600 supercomputers in a computing center of the Institute of Problems of Chemical Physics RAS and Power Challenger L in the Institute of Organic Chemistry RAS ŽRFBR, Project no. 98-07-90290..
Cs ` O I`O
IŽ2. 4.370 4.400 3.199 3.203 1.824 1.857 1.858 1.878 1.894 1.932
rotation of the octahedral skeleton IO6 around iodine atoms through a rib of the octahedron, O 2`O 3 ŽFig. 3., for example. The activation barrier of such a rotation, estimated at the B3LYPrLanL2DZ level from calculation of CsIO6 H 4 , is 0.1–0.2 eV. The additional possibility for ion transport inside a monomer, supplied by such rotation, can sharply increase the proton conductivity.
References w1x A.V. Chernyak, G.V. Shilov, Yu.A. Dobrovolsky et al., Proc. Vth Int. Symposium ‘Fundamental Aspects of Solid States Ionics’, Chernogolovka. 2000, p. 59 Žin Russian.. w2x M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.M.W. Gill, B.G. Johnson, M.A. Robb, J.R. Cheeseman, T. Keith, G.A. Petersson, J.A. Montgomery, K. Raghavachari, M.A. Al-Laham, V.G. Zakrzewski, J.V. Ortiz, J.B. Foresman, J. Cioslowski, B.B. Stefanov, A. Nanayakkara, M. Challacombe, C.Y. Peng, P.Y. Ayala, W. Chen, M.W. Wong, J.L. Andres, E.S. Replogle, R. Gomperts, R.L. Martin, D.J. Fox, J.S. Binkley, D.J. Defrees, J. Baker, J.P. Stewart, M. Head-Gordon, C. Gonzalez, J.A. Pople, Gaussian 94. Revision D.1. Gaussian, Pittsburgh, PA, 1995.
Computer simulation of the structure and proton transport in orthoiodates T.S. Zyubina, G.V. Shilov, Yu.A. Dobrovolsky, L.O. Atovmyan, A.V. Chernyak, L.S. Leonova, A.E. Ukshe ) Institute of Problems of Chemical Physics RAS, 142432, ChernogoloÕka, Moscow region, Russia Received 25 September 2000; received in revised form 9 January 2001; accepted 8 February 2001
Abstract The crystal structure and properties of CsH 4 IO6 P H 5 IO6 have been studied by electrochemistry, X-ray methods, and calculated by density functional theory ŽDFT. methods. High protonic conductivity in crystals of CsH 4 IO6 P H 5 IO6 has been discovered and is discussed. q 2001 Published by Elsevier Science B.V. Keywords: Protonic conductivity; DFT; Crystal structure; Chemical compound, CsH 4 IO6 P H 5 IO6
1. Introduction We have discovered high protonic conductivity in crystals of CsH 4 IO6 P H 5 IO6 . X-ray diffraction study has shown that the compound crystallizes as a monoclinic cell, space group Cc w1x. The crystal structure is represented by two wCsI 2 O 12 H 9 x layers of hydrogen bonded to each other, and parallel to the unit cell Žbc. plane. The layers are formed by IOŽOH.4 entities and Cs atoms. One unit cell contains two independent ŽIO6 . octahedra and one Cs atom. The crystal structure fragment of CsH 4 IO6 P H 5 IO6 ŽX-ray data. is shown in Fig. 1. The aim of this work is to determine the structure and proton transport properties by quantum-chemical
calculations and to compare the numerical results with X-ray data for CsH 4 IO6 P H 5 IO6 .
2. Methods The calculations were made within the framework of density functional theory ŽDFT. using a threeparameter potential B3LYP with LanL2DZ plus polarization Žthe exponents a d s 0.266. and effective core potential LanL2 for I atom and basis 6-31G ) ) for O and H atoms. The computation employed the GAUSSIAN-94 package w2x.
3. Results and discussion )
Corresponding author. Tel.: q7-95-742-0142x3774; fax: q796-576-4009. E-mail addresses: [email protected] ŽT.S. Zyubina., [email protected] ŽA.E. Ukshe..
The calculations show that the transition from orthoiodic acid to its singly charged ion, then to its
0167-2738r01r$ - see front matter q 2001 Published by Elsevier Science B.V. PII: S 0 1 6 7 - 2 7 3 8 Ž 0 1 . 0 0 9 4 4 - 4
T.S. Zyubina et al.r Solid State Ionics 145 (2001) 459–462
460
Fig. 1. Crystal structure fragment of CsH 4 IO6 PH 5 IO6 Žfrom X-ray data..
two-charged ion H 5 IO6 –H 4 IO6y–H 3 IO62y leads to a ˚ successive increase of all the I`O distances by 0.9 A ˚ for each anion charge, see Table 1 and Ž0.4–0.5 A Fig. 2.. The O`H distance in all the calculated ˚ and the H`O`I angle is 998. compounds is 0.97 A The oxygen atoms that are not bound to the hydro˚ than gen have an I`O bond shorter by 0.18–0.19 A the oxygen atoms ŽO H . bound to the hydrogen atoms. The single-charged H 4 IO6y anion has O`I`O bond angles for the opposite oxygens close to 1808, while for the acid, two of the three angles are 10–118 less ŽTable 1..
Table 1 ˚ and 8. of the orthoiodic acid The main geometric parameters ŽA and its anions H 5 IO6 , H 4 IO6y and H 3 IO62y Žtheir structures are given in Fig. 2. Parameter
H 5 IO6 H 5 IO6 Ža. H 4 IO6y H 4 IO6y Ža. H 3 IO62y
I ` O2 1.95 1.97 I ` O3 1.94 2.74 I ` O4 1.96 1.99 I ` O5 1.94 2.02 I ` O6 1.96 1.99 I ` O7 1.77 2.07 O 2 ` I ` O 7 176.5 166.5 O 3 ` I ` O6 168.3 O4 ` I ` O5 167.0 160.7
1.81 1.99 1.99 1.99 1.99 1.81 179.7 178.3 178.2
2.05 2.81 2.11 2.04 1.81 2.12 174.2 112.0 171.9
1.86 2.10 2.06 2.06 1.81 1.84 164.8 178.9 168.2
Fig. 2. Calculated structures of orthoiodic acid and its anions H 5 IO6 , H 4 IO6y and H 3 IO62y.
It was found from the calculations that along with the H 4 IO6y ion, there is one more minimum on the potential surface of H 4 IO6yŽ a. whose structure is shown in Fig. 2 and geometric parameters are given in Table 1. This isomer is characterized by the ˚ presence of an O 3`O 7 peroxide bond of 1.46 A ` ` ŽO 3 O 7 I angle of 109.58.. On the energy scale, this isomer lies 7 kcalrmol higher than the main one. For the acid, an analogous isomer with a peroxide fragment lies 6.1 kcalrmol higher in energy than the main isomer. The calculated structure of monosubstituted cesium salt CsH 4 IO6 is given in Fig. 3, and its geometric parameters are listed in Table 2. It is seen that the minimum corresponds to the isomers of the three-coordinates through the oxygen position of the Cs atom. The main isomer is that in which Cs is bound to iodine through two bridging O atoms and one O H atom. The salt isomer II with two bridging
T.S. Zyubina et al.r Solid State Ionics 145 (2001) 459–462
Fig. 3. Calculated structures of different isomers and transition states of monosubstituted cesium salt CsH 4 IO6 .
O H atoms and one O atom lies higher in energy. Depending on the position of two O atoms, diametric ŽIIa. or not ŽIIb., the salt isomer II position on the energy scale is higher than that of salt isomer I by 0.75 kcalrmol ŽIIa. or by 1.44 kcalrmol ŽIIb.. Salt isomer III with three bridging O H atoms lies 4.96 kcalrmol higher than the main isomer. The octahedral unit of H 4 IO6y may turn relative to the Csq cation with an activation energy of 2.7 kcalrmol in the case of salt isomer I and with an activation energy of 4.5 kcalrmol in the case of salt isomer IIa. In all the considered configurations of the ˚ . and I`O H cesium salts, the I`O Ž1.79–1.81 A ˚ . distances to an accuracy of 0.01–0.02 Ž1.99–2.02 A ˚ are close to the analogous distances in the singly A charged H 4 IO6y anion. A comparison of the experimental and theoretical values for geometrical parameters shows that two
461
types of octahedra IŽ1.O6 and IŽ2.O6 identified by the X-ray study may be assigned to equal quantities of molecules of orthoiodic acid and H 4 IO6y anions present in the crystal. The geometric parameters of structure IŽ1. are in reasonably good agreement with the calculated parameters of salt isomer II Žaccording to Fig. 3., while the I parameters, with the acid parameters. The X-ray data for the I`O valence bond lengths are ˚ less and the Cs`I non-valence bond 0.01–0.11 A ˚ in comparison to lengths are larger by 0.55–1.30 A the values obtained in the calculations for a single molecule. Nevertheless, the comparison of the calculated and experimental values of difference between I`O and I`O H has allowed us to identify the hydrogen atom positions in the crystal ŽTable 3.. In the crystal, six IO6 octahedra lie about the Cs atom so that the nearest oxygen atoms from the neighbouring octahedra are at a distance of 2.5–2.7 ˚ from each other. This fact allows us to expect the A relay-race mechanism of proton transport. The calculated activation energy of the relay mechanism is about 0.3–0.5 eV; the experimental estimate of activation energy of conductivity is 0.5 eV. The phase transition observed in experiments on increasing the temperature to 508C may be a result of
Table 2 ˚ and 8. and The most significant geometric parameters Žin A relative energies of isomers Ž D E with zero-point correction. in kcalrmol for cesium salt of orthoiodic acid a Parameters I
IIa
IIb
III
TSŽI.
TSŽII.
Cs ` I 3.64 3.78 3.78 3.94 3.76 3.97 Cs ` O 2 3.07 2.98 3.09 3.02 2.96 2.94 Cs ` O 3 3.04 3.09 2.98 2.99 2.97 2.93 Cs ` O4 3.18 3.06 3.05 3.06 I ` O2 1.81 1.81 2.02 2.02 1.80 1.82 I ` O3 1.81 2.01 1.81 2.02 1.80 2.03 I ` O4 2.01 2.03 2.02 2.03 1.98 1.98 I ` O5 1.97 1.96 1.79 1.97 1.98 1.98 I ` O6 1.99 1.98 1.99 1.79 2.00 1.97 I ` O7 1.99 1.80 1.97 1.79 1.99 1.79 O 2 ` I ` O 7 170.1 177.2 168.9 164.9 169.1 176.9 O 3 ` I ` O6 166.5 171.4 164.9 164.0 168.6 179.2 O4 ` I ` O5 170.1 177.2 165.3 166.3 171.2 176.7 DE 0 0.75 1.44 4.96 2.70 5.27 a
Isomer numbering in the table corresponds to the numbering in Fig. 3.
T.S. Zyubina et al.r Solid State Ionics 145 (2001) 459–462
462
Table 3 Bond lengths of CsH 4 IO6 PH 5 IO6 calculated from X-ray data
Acknowledgements
Parameters
IŽ1.
Cs ` I
4.267 4.381 4.407 3.147 3.232 3.299 1.789 1.834 1.877 1.893 1.902 1.906
This work was supported by the Russian Foundation for Basic Research ŽProject no. 01-03-33178a.. The calculations were made on RM600 supercomputers in a computing center of the Institute of Problems of Chemical Physics RAS and Power Challenger L in the Institute of Organic Chemistry RAS ŽRFBR, Project no. 98-07-90290..
Cs ` O I`O
IŽ2. 4.370 4.400 3.199 3.203 1.824 1.857 1.858 1.878 1.894 1.932
rotation of the octahedral skeleton IO6 around iodine atoms through a rib of the octahedron, O 2`O 3 ŽFig. 3., for example. The activation barrier of such a rotation, estimated at the B3LYPrLanL2DZ level from calculation of CsIO6 H 4 , is 0.1–0.2 eV. The additional possibility for ion transport inside a monomer, supplied by such rotation, can sharply increase the proton conductivity.
References w1x A.V. Chernyak, G.V. Shilov, Yu.A. Dobrovolsky et al., Proc. Vth Int. Symposium ‘Fundamental Aspects of Solid States Ionics’, Chernogolovka. 2000, p. 59 Žin Russian.. w2x M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.M.W. Gill, B.G. Johnson, M.A. Robb, J.R. Cheeseman, T. Keith, G.A. Petersson, J.A. Montgomery, K. Raghavachari, M.A. Al-Laham, V.G. Zakrzewski, J.V. Ortiz, J.B. Foresman, J. Cioslowski, B.B. Stefanov, A. Nanayakkara, M. Challacombe, C.Y. Peng, P.Y. Ayala, W. Chen, M.W. Wong, J.L. Andres, E.S. Replogle, R. Gomperts, R.L. Martin, D.J. Fox, J.S. Binkley, D.J. Defrees, J. Baker, J.P. Stewart, M. Head-Gordon, C. Gonzalez, J.A. Pople, Gaussian 94. Revision D.1. Gaussian, Pittsburgh, PA, 1995.