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Ba3Ir2H12, a new ternary hydride containing octahedral [IrH6]3 - complex anions
Journal of Alloys and Compounds, 209 (1994) 213-215 JALCOM 1080
213
Ba3IrzH12 , a new ternary hydride containing octahedral [IrH6] 3c o m p l e x anions K. K a d i r a n d D. N o r 6 u s * Department of Structural Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm (Sweden)
(Received November 17, 1993)
Abstract A new ternary hydride, Baalr2H12, has been synthesized by reacting a mixture of BaH2 and iridium powders in a hydrogen atmosphere. The crystal structure was determined by combining Guinier-H~iggX-ray powder diffraction and neutron diffraction data from a deuterated compound. The structure was refined (space group, P-3ml; a=5.4865(3) /~ and c=8.8459(10) /~; Z=I). The unit cell contains two slightly distorted [IrH6]3- octahedra which form a La203-type structure with the three Ba2÷ counterions. Two different Ir-H bond lengths were refined with neutron diffraction data from Ba3IrED12: 1.60(1) /~ and 1.77(2) ~.
1. Introduction By reacting powdered transition metals and binary hydrides of electropositive alkali and alkaline earth metals it has been possible to synthesize a large number of new hydrides based on formally low valence transition metal-hydrogen complexes balanced by alkali and alkaline earth counterions. There are now numerous examples, as described in a recent review by Bronger
[11 During the reaction carried out at elevated temperatures in a hydrogen atmosphere, hydrogen atoms form bonds with the transition metal atoms. The transition metal-hydrogen bond distance indicates a covalent bond type, and the stable complexes most commonly have 18-electron, but also 16- or even 14-electron configurations. It can be noted, however, that the distances between the hydrogen atoms and the alkali or alkaline earth counterions in the new hydrides are only very slightly longer than in the corresponding binary alkali or alkaline earth hydrides, indicating a remaining strong ionic influence by the electropositive metal on the bond. The hydride complexes in the new hydrides prepared in this way have so far been found to have the transition metal in a formally zerovalent, monovalent or divalent oxidation state. That is, this sintering method has been most successful when the formal oxidation state of the transition metal has changed very little from that of the free metal. *Author to whom correspondence should be addressed.
Hydrides with a formally high valence transition metal such as K2Re(VII)H9 [2] have so far not been synthesized by this method. Hydrides containing formally trivalent rhodium and iridium complexes were, however, recently made by Bronger et al. [3] using binary alkali hydrides for the reaction with the transition metal. In the present paper we wish to report a new Ba3Ir2(III)H12 hydride with a novel structure type as a result of our search for hydrides with higher formal oxidation states.
2. Experimental details The new ternary hydrides were made by sintering a pressed tablet (0.2 g) of finely powdered BaH2 and iridium at 873 K in an 8 MPa hydrogen atmosphere for 6 days. During the reaction, the grey tablet changed into a very fine, almost white powder. Several syntheses were made using different reaction conditions before an acceptable sample was obtained. The Ba3Ir2H12 was very reactive upon contact with air; so the sample had to be handled in an inert atmosphere of continuously purified argon. For the neutron diffraction, a corresponding BaaIrED12 sample was synthesized in a similar way. The sample (6 g) was enclosed in a cylindrical vanadium container of diameter 8 mm during the recording of the diffraction pattern. The starting materials, BaH2 and BAD2, were synthesized by direct combination of the elements at 670 K in a 6 MPa hydrogen atmosphere. The starting metal was delivered by Aldrich from their standard assortment. The iridium powder had a nominal purity of 99.9%.
0925-8388/94/$07.00 © 1994 Elsevier Science S.A. All rights reserved SSDI 0925-8388(93)01080-N
K. Kadir, D. Nor~us / Ba3Ir2Hlz containing [IrHd 3-
214
TABLE 1. Observed and calculated 20 values for Ba3Ir2D~2 with a hexagonal unit cell with a =5.4761(4) /~ and c=8.8318(8) /~, using Cu Kat radiation (A= 1.540 598 1 /~) (unit-cell volume, 229.4 /~3; Mzo= 103) h k l
20oh s
20¢a1¢
dobs
lobs
1 0 1 1 0 1 1 2 1 2 2 1 1 2 2 2 1 2 1 3 2 3 1 2 3 2 2 2 1 3 4 2
18.684 20.114 21.253 27.578 30.337 32.674 35.876 37.911 38.664 39.298 43.271 45.197
18.696 20.092 21.248 27.578 30.337 32.679 35.874 37.913 38.662 39.310 43.274 45.188 45.267 49.306 50.902 52.017 53.253 55.264 55.467 58.324 60.415 62.338 62.526 65.884 67.158 67.218 68.480 75.505 78.361 79.797 84.554 87.510
4.7453 4.4111 4.1773 3.2319 2.9439 2.7385 2.5011 2.3714 2.3269 2.2908 2.0892 2.0046
26.17 11.63 51.92 98.10 5.29 100.00 45.62 2.23 13.99 10.71 25.29 40.62
1.8468 1.7932 1.7567 1.7183 1.6608 1.6558 1.5813 1.5310 1.4875 1.4845 1.4163 1.3925
14.94 2.76 6.80 5.25 25.52 16.12 21.94 19.57 4.70 2.96 8.87 4.56
1.3688 1.2586 1.2194 1.2010 1.1451 1.1136
9.43 22.92 7.49 8.37 4.70 2.10
0 0 0 0 0 1 0 0 1 0 0 1 0 0 1 1 1 1 0 0 1 0 1 0 0 1 2 1 0 1 0 0
0 2 1 2 3 0 3 0 2 1 2 3 4 3 0 1 4 2 5 0 3 2 5 5 3 4 0 5 7 3 2 7
49.303 50.879 52.016 53.269 55.267 55.450 58.304 60.416 62.376 62.517 65.896 67.170 68.496 75.472 78.352 79.792 84.555 87.534
TABLE 2. The atomic parameters for Ba3Ir2Dn in the space group P3rnl, Z = 1, refined from neutron data recorded at the R2 reactor, Studsvik, Sweden ( a = 1.460 /~) Atom
Site
x
y
z
Bi~
Ba(1) Ba(2) Ir D(1) D(2)
la 2d 2d 6i 6i
0.0 ~ ~ 0.383(2) 0.478(3)
0.0 ~ ~ 0.192(2) 0.957(3)
0.0 0.643(3) 0.250(2) 0.652(1) 0.125(1)
0.3(8) 1.2(5) 1.9(3) 1.7(3) 2.2(3)
Interatomic distance (~) Ir-Ba(1) Ir-Ba(2) Ir-Ba(2) Ir-D(1) Ir-D(2) D(1)-D(1) D(2)-D(2)
3.86(1) 3.30(1) 3.47(3) 1.60(1) 1.77(2) 2.33(2) 2.25(2)
(A2)
Interatomic distance (*) Ba(2)-Ba(1) Ba(2)-Ba(2) Ba(1)-D(2) Ba(2)-D(1) Ba(2)-D(2)
4.461(9) 4.05(2) 2.96(1) 2.75(1) 2.72(2)
The Rietveld refinement program DBW32.s was used. Rv=0.075; Rw = 0.0916 [7].
The X-ray photographs were obtained in a subtraction-geometry Guinier-H/igg focusing camera of diameter 80 mm, using strictly monochromated Cu K~I radiation. The 0 scale was calibrated by means of the internal standard technique, using a parabolic correction curve. Silicon was chosen as the internal standard. The neutron diffraction pattern was recorded at the Studsvik reactor in Sweden, using a neutron wavelength of 1.460
3. Results and discussion The X-ray pattern of Ba3Ir2H12 could be indexed with a hexagonal unit cell with dimensions a = 5.4865(3) /~ and c = 8.8459(10)/~, using the "rREOR program [4]. No reflections were systematically absent, and, as the 2:3 ratio applied for the metal atoms gave a singlephase sample, we suspected the metal atom structure
Fig. 1. Structure of Ba3Ir2H~2. The large circles represent barium, the small circles represent hydrogen and the full circles represent iridium.
of new hydride to be isotypic with the La203 structure, described in the space group P3ml (No 164) [5]. We could confirm this by using the intensities of the 30 non-overlapping reflections given in Table 1 as input to the SHELX [6] refinement program.
K. Kadir, D. Nor~us / Baflr2Hlz containing [lrHJ 3-
The metal atom structure of the hydride was refined down to an R value of 7.7%. The final structure refinement was made with neutron diffraction data from the corresponding Ba3Ir2D12 phase. The R value was 7.5%, and the result is given in Table 2. Each iridium atom is linked to six hydrogen atoms at the corners of a nearly regular octahedron (Fig. 1). The hydrogen atom positions are described by two non-equivalent sites in this space group; the two Ir-H distances are 1.60(1) and 1.77(2) ~. It is interesting to note that each I r D 6 complex is surrounded by seven Ba 2+ counterions forming an "anti-La203 structure". This structure is distantly related to the "antifluorite structure", which is adopted by many of these new ternary hydrides [81. The Ba-H distances in the coordination sphere around the Ba atom, 2.96, 2.75 and 2.72 /~ are all slightly longer than the shortest distances in BAH2, 2.56 and 2.61/~ [9], but are almost the same as in Ba2PtH6 [10] and Ba2OsH6 [11], indicating a similarity between these hydrides.
Acknowledgments This work has received support from the Swedish National Board for Industrial and Technical Devel-
215
opment and the Swedish Research Council for Engineering Sciences. We are also indebted to Hfikan Rundlff for collecting the neutron diffraction pattern at the R2 reactor in Studsvik.
References 1 W. Bronger, Angew. Chem., Int. Edn. Engl., 30 (1991) 759. 2 S.C. Abrahams, A.P. Ginsberg and K. Knox, Inorg. Chem., 3 (1964) 558. 3 W. Bronger, M. Gehlen and G. Auffermann, J. Alloys Comp., 176 (1991) 299. 4 P.-E. Werner, L. Eriksson and M. Westdahl, J. AppL Crystallogr., 18 (1985) 367. 5 L. Pauling, Z. Krystallogr., 69 (1928) 415. 6 G.M. Sheldrick, SHELX,A Program for Crystal Structure Determination, University of Cambridge, Cambridge, 1978. 7 D.B. Wiles, A. Sakthivel and R.A. Young, Program DBW3.2S, School of Physics, Georgia Institute of Technology, Atlanta, 1988. D.B. Wiles and R.A. Young, J. AppL Crystallogr., 14 (1981) 149. 8 A.F. Wells, Structural Inorganic Chemistry, Clarendon, Oxford, 1984, Chapter 12. 9 W. Bronger, Scha Chi-Chien and P. Mtiller, Z. Anorg. Allg. Chem., 545 (1987) 69. 10 K. Kadir and D. NorEus, Z. Phys. Chem., 179 (1993) 237. 11 M. Kritikos and D. Nor6us, J. Solid State Chem., 93 (1991) 256.
213
Ba3IrzH12 , a new ternary hydride containing octahedral [IrH6] 3c o m p l e x anions K. K a d i r a n d D. N o r 6 u s * Department of Structural Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm (Sweden)
(Received November 17, 1993)
Abstract A new ternary hydride, Baalr2H12, has been synthesized by reacting a mixture of BaH2 and iridium powders in a hydrogen atmosphere. The crystal structure was determined by combining Guinier-H~iggX-ray powder diffraction and neutron diffraction data from a deuterated compound. The structure was refined (space group, P-3ml; a=5.4865(3) /~ and c=8.8459(10) /~; Z=I). The unit cell contains two slightly distorted [IrH6]3- octahedra which form a La203-type structure with the three Ba2÷ counterions. Two different Ir-H bond lengths were refined with neutron diffraction data from Ba3IrED12: 1.60(1) /~ and 1.77(2) ~.
1. Introduction By reacting powdered transition metals and binary hydrides of electropositive alkali and alkaline earth metals it has been possible to synthesize a large number of new hydrides based on formally low valence transition metal-hydrogen complexes balanced by alkali and alkaline earth counterions. There are now numerous examples, as described in a recent review by Bronger
[11 During the reaction carried out at elevated temperatures in a hydrogen atmosphere, hydrogen atoms form bonds with the transition metal atoms. The transition metal-hydrogen bond distance indicates a covalent bond type, and the stable complexes most commonly have 18-electron, but also 16- or even 14-electron configurations. It can be noted, however, that the distances between the hydrogen atoms and the alkali or alkaline earth counterions in the new hydrides are only very slightly longer than in the corresponding binary alkali or alkaline earth hydrides, indicating a remaining strong ionic influence by the electropositive metal on the bond. The hydride complexes in the new hydrides prepared in this way have so far been found to have the transition metal in a formally zerovalent, monovalent or divalent oxidation state. That is, this sintering method has been most successful when the formal oxidation state of the transition metal has changed very little from that of the free metal. *Author to whom correspondence should be addressed.
Hydrides with a formally high valence transition metal such as K2Re(VII)H9 [2] have so far not been synthesized by this method. Hydrides containing formally trivalent rhodium and iridium complexes were, however, recently made by Bronger et al. [3] using binary alkali hydrides for the reaction with the transition metal. In the present paper we wish to report a new Ba3Ir2(III)H12 hydride with a novel structure type as a result of our search for hydrides with higher formal oxidation states.
2. Experimental details The new ternary hydrides were made by sintering a pressed tablet (0.2 g) of finely powdered BaH2 and iridium at 873 K in an 8 MPa hydrogen atmosphere for 6 days. During the reaction, the grey tablet changed into a very fine, almost white powder. Several syntheses were made using different reaction conditions before an acceptable sample was obtained. The Ba3Ir2H12 was very reactive upon contact with air; so the sample had to be handled in an inert atmosphere of continuously purified argon. For the neutron diffraction, a corresponding BaaIrED12 sample was synthesized in a similar way. The sample (6 g) was enclosed in a cylindrical vanadium container of diameter 8 mm during the recording of the diffraction pattern. The starting materials, BaH2 and BAD2, were synthesized by direct combination of the elements at 670 K in a 6 MPa hydrogen atmosphere. The starting metal was delivered by Aldrich from their standard assortment. The iridium powder had a nominal purity of 99.9%.
0925-8388/94/$07.00 © 1994 Elsevier Science S.A. All rights reserved SSDI 0925-8388(93)01080-N
K. Kadir, D. Nor~us / Ba3Ir2Hlz containing [IrHd 3-
214
TABLE 1. Observed and calculated 20 values for Ba3Ir2D~2 with a hexagonal unit cell with a =5.4761(4) /~ and c=8.8318(8) /~, using Cu Kat radiation (A= 1.540 598 1 /~) (unit-cell volume, 229.4 /~3; Mzo= 103) h k l
20oh s
20¢a1¢
dobs
lobs
1 0 1 1 0 1 1 2 1 2 2 1 1 2 2 2 1 2 1 3 2 3 1 2 3 2 2 2 1 3 4 2
18.684 20.114 21.253 27.578 30.337 32.674 35.876 37.911 38.664 39.298 43.271 45.197
18.696 20.092 21.248 27.578 30.337 32.679 35.874 37.913 38.662 39.310 43.274 45.188 45.267 49.306 50.902 52.017 53.253 55.264 55.467 58.324 60.415 62.338 62.526 65.884 67.158 67.218 68.480 75.505 78.361 79.797 84.554 87.510
4.7453 4.4111 4.1773 3.2319 2.9439 2.7385 2.5011 2.3714 2.3269 2.2908 2.0892 2.0046
26.17 11.63 51.92 98.10 5.29 100.00 45.62 2.23 13.99 10.71 25.29 40.62
1.8468 1.7932 1.7567 1.7183 1.6608 1.6558 1.5813 1.5310 1.4875 1.4845 1.4163 1.3925
14.94 2.76 6.80 5.25 25.52 16.12 21.94 19.57 4.70 2.96 8.87 4.56
1.3688 1.2586 1.2194 1.2010 1.1451 1.1136
9.43 22.92 7.49 8.37 4.70 2.10
0 0 0 0 0 1 0 0 1 0 0 1 0 0 1 1 1 1 0 0 1 0 1 0 0 1 2 1 0 1 0 0
0 2 1 2 3 0 3 0 2 1 2 3 4 3 0 1 4 2 5 0 3 2 5 5 3 4 0 5 7 3 2 7
49.303 50.879 52.016 53.269 55.267 55.450 58.304 60.416 62.376 62.517 65.896 67.170 68.496 75.472 78.352 79.792 84.555 87.534
TABLE 2. The atomic parameters for Ba3Ir2Dn in the space group P3rnl, Z = 1, refined from neutron data recorded at the R2 reactor, Studsvik, Sweden ( a = 1.460 /~) Atom
Site
x
y
z
Bi~
Ba(1) Ba(2) Ir D(1) D(2)
la 2d 2d 6i 6i
0.0 ~ ~ 0.383(2) 0.478(3)
0.0 ~ ~ 0.192(2) 0.957(3)
0.0 0.643(3) 0.250(2) 0.652(1) 0.125(1)
0.3(8) 1.2(5) 1.9(3) 1.7(3) 2.2(3)
Interatomic distance (~) Ir-Ba(1) Ir-Ba(2) Ir-Ba(2) Ir-D(1) Ir-D(2) D(1)-D(1) D(2)-D(2)
3.86(1) 3.30(1) 3.47(3) 1.60(1) 1.77(2) 2.33(2) 2.25(2)
(A2)
Interatomic distance (*) Ba(2)-Ba(1) Ba(2)-Ba(2) Ba(1)-D(2) Ba(2)-D(1) Ba(2)-D(2)
4.461(9) 4.05(2) 2.96(1) 2.75(1) 2.72(2)
The Rietveld refinement program DBW32.s was used. Rv=0.075; Rw = 0.0916 [7].
The X-ray photographs were obtained in a subtraction-geometry Guinier-H/igg focusing camera of diameter 80 mm, using strictly monochromated Cu K~I radiation. The 0 scale was calibrated by means of the internal standard technique, using a parabolic correction curve. Silicon was chosen as the internal standard. The neutron diffraction pattern was recorded at the Studsvik reactor in Sweden, using a neutron wavelength of 1.460
3. Results and discussion The X-ray pattern of Ba3Ir2H12 could be indexed with a hexagonal unit cell with dimensions a = 5.4865(3) /~ and c = 8.8459(10)/~, using the "rREOR program [4]. No reflections were systematically absent, and, as the 2:3 ratio applied for the metal atoms gave a singlephase sample, we suspected the metal atom structure
Fig. 1. Structure of Ba3Ir2H~2. The large circles represent barium, the small circles represent hydrogen and the full circles represent iridium.
of new hydride to be isotypic with the La203 structure, described in the space group P3ml (No 164) [5]. We could confirm this by using the intensities of the 30 non-overlapping reflections given in Table 1 as input to the SHELX [6] refinement program.
K. Kadir, D. Nor~us / Baflr2Hlz containing [lrHJ 3-
The metal atom structure of the hydride was refined down to an R value of 7.7%. The final structure refinement was made with neutron diffraction data from the corresponding Ba3Ir2D12 phase. The R value was 7.5%, and the result is given in Table 2. Each iridium atom is linked to six hydrogen atoms at the corners of a nearly regular octahedron (Fig. 1). The hydrogen atom positions are described by two non-equivalent sites in this space group; the two Ir-H distances are 1.60(1) and 1.77(2) ~. It is interesting to note that each I r D 6 complex is surrounded by seven Ba 2+ counterions forming an "anti-La203 structure". This structure is distantly related to the "antifluorite structure", which is adopted by many of these new ternary hydrides [81. The Ba-H distances in the coordination sphere around the Ba atom, 2.96, 2.75 and 2.72 /~ are all slightly longer than the shortest distances in BAH2, 2.56 and 2.61/~ [9], but are almost the same as in Ba2PtH6 [10] and Ba2OsH6 [11], indicating a similarity between these hydrides.
Acknowledgments This work has received support from the Swedish National Board for Industrial and Technical Devel-
215
opment and the Swedish Research Council for Engineering Sciences. We are also indebted to Hfikan Rundlff for collecting the neutron diffraction pattern at the R2 reactor in Studsvik.
References 1 W. Bronger, Angew. Chem., Int. Edn. Engl., 30 (1991) 759. 2 S.C. Abrahams, A.P. Ginsberg and K. Knox, Inorg. Chem., 3 (1964) 558. 3 W. Bronger, M. Gehlen and G. Auffermann, J. Alloys Comp., 176 (1991) 299. 4 P.-E. Werner, L. Eriksson and M. Westdahl, J. AppL Crystallogr., 18 (1985) 367. 5 L. Pauling, Z. Krystallogr., 69 (1928) 415. 6 G.M. Sheldrick, SHELX,A Program for Crystal Structure Determination, University of Cambridge, Cambridge, 1978. 7 D.B. Wiles, A. Sakthivel and R.A. Young, Program DBW3.2S, School of Physics, Georgia Institute of Technology, Atlanta, 1988. D.B. Wiles and R.A. Young, J. AppL Crystallogr., 14 (1981) 149. 8 A.F. Wells, Structural Inorganic Chemistry, Clarendon, Oxford, 1984, Chapter 12. 9 W. Bronger, Scha Chi-Chien and P. Mtiller, Z. Anorg. Allg. Chem., 545 (1987) 69. 10 K. Kadir and D. NorEus, Z. Phys. Chem., 179 (1993) 237. 11 M. Kritikos and D. Nor6us, J. Solid State Chem., 93 (1991) 256.