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Orientational disorder of the ammine group in Ni(ND3)6Br2
Physica B 156 & 157 (1989) 85-87 North-Holland, Amsterdam
ORIENTATIONAL DISORDER OF THE AMMINE GROUP IN Ni(ND,),Br, A. HOSER’, W. PRANDL’,
P. SCHIEBEL’
and G. HEGER’
‘Institut fiir Kristallographie, Universitiit Tiibingen, D-7400 Tiibingen, Fed. Rep. Germany 2Laboratoire Lion Brillouin, CEN Saclay, France
Single crystal Bragg intensities of cubic Ni(ND,),Br, (space group FmSm) were analysed with several models for the orientationally disordered ND, group. The maxima of the observed density distribution of the hydrogen atoms are located at the comers of a square. The best approximation of this density is given by a model of ammonia molecules tumbling in an anharmonic translational-rotational potential on the Ni surface.
1. Introduction Structural instabilities in the metal hexammine complexes have been extensively investigated by different methods since a long time [l-3]. It is commonly believed that the freezing of an axial reorientation of the six ammine groups plays a decisive role at the phase transition. The reorientation of the NH, molecules at room temperature studied by Raman [4] and quasielastic neutron scattering experiments QNS [5] was interpreted by a 120” rotational jump model. In our previous single crystal study of the nitrate analogue [6] we have observed, however, an unexpected quadratic density distribution of the hydrogen atoms. In Ni(NH,)JNO,), both the NH, and NO, groups are disordered. We therefore choose the deuterated bromide analogue to concentrate our attention on the ammine group. In this paper we present some experimental details and an interpretation of the results which show again a very well developed density distribution at the corners of a square. 2. Experimental The title complex was synthesized in a standard way [6]. The single crystal, grown from a concentrated deuterated ammonia solution had a volume of 32 mm3. The experiment was performed on the 4-circle diffractometer PllO at the ORPHEE reactor in Saclay. We measured 858 Bragg intensities with A = 0.832 A up to 20 =
100” (sine/A = 0.917 A-‘). They were averaged with PROMETHEUS [7] giving 232 unique reflections (consistency factor R, = 0.016). We applied the isotropic extinction corrections after Becker and Coppens [B] for a standard model assuming a Gaussian distribution of the mosaic spread. 3. Data analysis and results The data were analysed by three methods: by the standard crystallographic model, with symmetry adapted functions, and with the Fourier technique. In the standard model, refined with the program PROMETHEUS [7], we distinguish the so-called ‘split atom’ model from the ‘Frenkel model’ [9]. In a ‘split atom model’ the only aim is to reproduce the density given by the data no matter whether the split positions comply with the molecular geometry or not. In the ‘Frenkel model’ molecular disorder is described by superimposing several fractional images of our rigid molecule in different orientations. The second method [lo-121 treats the density of the disordered molecules as a continuous function which is written in terms of symmetry adapted functions. The ND,-ligand occupies a site having symmetry 4 mm which is higher than molecular symmetry, i.e. 3 m, and therefore, similar to the nitrate analogue, must be disordered. We began the analysis refining the simple ‘split atom’ model down to the R, value of 0.033. It corre-
0921-4526/89/$03.50 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
-u103 au~mulexaq jay~!u aq~ 30 anSolsue ap!t.uolq aql u! se pm se aw~p aq~ u! lClymp Dpe.rpenb srq1 30 uopeluasqo aq] Imyuo:, a.Io3a.Iaq1 um aM ~(1 *%y) &suap ua2olpdq aql 30 uognql_rwp hrsuap aa.r3-lapour !senb e a@ IapouI Iayua.rg JO uum wds ,,wq,, aql JO saseqd aql pue s&j patiasqo aql mo.13 pamaw% sdmu .Ia!rnod
~1.1033 pagap las ~a~atuemd DrlsqeaI e dq (A ‘x)~ Icgualod ~m~%o~ouaurouaqd u! s~alaumed aql 8upeldaJ liq Iapotu aq3 aAordwr 01 wasaId ]e h$ aM ‘2 ‘sy U! UMOIJS S! IfD!gM UO!lOU.l s!yl 01 thpuodsa~ro~ uoynqpwp Al!suap uolold aql paiepmIm amq aM .1CeMpimwu e ur pamp -OWI! SF%uqdno~ ~~uo~)elo~-~euo~~e~o~e ~EM syl LIP :O~/I “x %uph?a ql!~ Iepualod aq$ ,,saqold,, almalow aqi $sql s! suaddeq @mm $eqM OS .hrls@a~ OJU! iq%o.rq aq ~ouue:, a@3e!.x~-E~ aqi pm (X ‘x)/i 30 eurrupu mo3 aqA ‘E ‘2 ‘1 = / 103 (E/LLZ) . (1 - /) + O/f,= !* a@2 pzuogeluauo pm ‘8 io$DaAssetu 30 ialua:, aqi liq paqimap aq dno.SEa aql30 uogwuauo pm uogsod puoDas lenm aql la? .uogeuI!xoJdde 1s.1~ e se 0 = v la8 aM aqes s,rCtpqdur!s ION ‘,SE~T ‘,g~+ = $J Ou h?s 1e 0 < Q ‘0 < g 103 seq (A ‘x)/1
pue
:sz’o = 2 aueld aq$ II! SW qD!qrn (X ‘x)~ Iegualod paldepe li~~au.u.ulisB auyap pue z = p 01 E = p
legualod
pz r~!uom~equr? aql ~11013pavqn31e3
byma
‘z ‘%!d
71'1
1x10.13 tualqord aq1 ampar lila+mua~ ‘alo3alaq) aM ~Apueu!wopald pelalu! 6aqi q”.‘qM l@IM SUOI .IQ lsaleau mo3 aq$ JO sz.0 = 2 q]fM pa_wduIo:, SE pz-0 = 2 awnploo:, 2 aqj amq dno&i EaN auo 30 suomnap aql leqi akxasqo 11e 30 Isly aM -UO!~O.I %UOJISe 30 Alq!q!ssod aql slsaS%ns uogtmasqo s!qL -sla)atueled pauyal 30 laqumu lea18 B alrdsap suoyDaga.! laplo q2hq aql .103 KlleI3adsa ‘hropqs!]es IOU os~e SBM E~OU.IUI~ 30 SSIXII30 lalua:, aq] u! w!od uogqo~ aql ql!M [zr] II! paqu3sap se patulopad q3eoJdde pi ay,L wep aIqrq!eAe aql 30 ~!urq aql dq paupldxa aq hu [cl] anilopzur! aprpor aql u! pahlasqo umai “.Iaqi Quo ql!M pau!elqo jy I(roptz3sym aqJ ‘1 ‘fly u! umoqs uoynq!w!p &suap aql 30 suoy -enlmg aql ampoldal IOU saop I! asnmaq ‘load AlaA s! uoyeur!xoldde s!qJ *([EJ] .33) or raplo olaz 30 uogmn3 lassaH e Aq lcp.10 passaldxa s! qmqM lapour palaplosrp dpnonuguo3 e 01 speaj s!qJ *lap10 qiz[ aql 30 ma1 aq) va@au ‘laha -hioq ‘um ah4 a%tm-0 pahIasq0 aql u!qsM *hr -iamul(s p103-zl isea le ‘8ul-r e uo suaifo.Ipliq aqj JO uognqgsrp E saumsse qXqM q3eoldde liiisuap snonuguo3 aql u! sa+nbar rC~~ar.uuIlCs .nzpwaIour pue aits 30 uog!so&adng .ICqauIoaS e~uomue aqi 01 uoyelal ou ‘.IaAaMoq ‘seq [apour s!qJ .suog!sod uolalnap 8 laqla8olIe ql!M [9] alell!u aulumexaq layD!u aq, II! 1 lapour aql 01 spuods
A. Hoser et al. I Orientational disorder of ND, group in Ni(ND,),Br,
plex. This cannot be realized by assuming only a simple reorientation of the NH, molecule in a plane perpendicular to the Ni-N bond. The tumbling reorientation in an anharmonic translational-rotational potential proposed above gives a good explanation of this observation. The latest QNS results [14] which found the reorientation radius of the ammonia ligand to be larger than the hydrogen radius observed in the free molecule apparently confirm our model. A more detailed discussion of our results will appear in Molecular Physics. References [l] S.H. Yii, Nature 141 (1938) 1.58. [2] A.R. Bates, S.R. Hughes and D.J. Somerford, J. Phys. C 16 (1983) 2847.
87
A. Hoser, Thesis, University of Poznari, Poland (1981). T.E. Jenkins, L.T.H. Ferris, A.R. Bates and R.D. Gillard, J. Phys. C 11 (1978) L77. J.M. Janik, J.A. Janik, R.M. Pick and M. Le Postollec, J. Raman Spect. 18 (1987) 493. J.A. Janik, J.M. Janik and K. Otnes, Physica B 90 (1977) 275. t61 A. Hoser, W. Joswig, W. Prandl and K. Vogt, Mol. Phys. 56 (1985) 853. ]71 U.H. Zucker, E. Perenthaler, W.F. Kuhs, R. Bachmann and H. Schulz, J. Appl. Cryst. 16 (1983) 358. k31P. Becker and P. Coppens, Acta Cryst. A 31 (1975) 417. 191 J. Frenkel, Acta Phys. Chem. U.S.S.R. 3 (1935) 23. [lOIW. Press and A. Huller, Acta Cryst. A 35 (1979) 876. 1111W. Prandl, Acta Cryst. A 37 (1981) 811. K. Vogt and W. Prandl, J. Phys. C 16 (1983) 4753. 1121 [I31J. Eckert and W. Press, J. Chem. Phys. 73 (1980) 451. 1141G.J. Kearley and H. Blank, submitted to Can. J. Chem. (1988).
ORIENTATIONAL DISORDER OF THE AMMINE GROUP IN Ni(ND,),Br, A. HOSER’, W. PRANDL’,
P. SCHIEBEL’
and G. HEGER’
‘Institut fiir Kristallographie, Universitiit Tiibingen, D-7400 Tiibingen, Fed. Rep. Germany 2Laboratoire Lion Brillouin, CEN Saclay, France
Single crystal Bragg intensities of cubic Ni(ND,),Br, (space group FmSm) were analysed with several models for the orientationally disordered ND, group. The maxima of the observed density distribution of the hydrogen atoms are located at the comers of a square. The best approximation of this density is given by a model of ammonia molecules tumbling in an anharmonic translational-rotational potential on the Ni surface.
1. Introduction Structural instabilities in the metal hexammine complexes have been extensively investigated by different methods since a long time [l-3]. It is commonly believed that the freezing of an axial reorientation of the six ammine groups plays a decisive role at the phase transition. The reorientation of the NH, molecules at room temperature studied by Raman [4] and quasielastic neutron scattering experiments QNS [5] was interpreted by a 120” rotational jump model. In our previous single crystal study of the nitrate analogue [6] we have observed, however, an unexpected quadratic density distribution of the hydrogen atoms. In Ni(NH,)JNO,), both the NH, and NO, groups are disordered. We therefore choose the deuterated bromide analogue to concentrate our attention on the ammine group. In this paper we present some experimental details and an interpretation of the results which show again a very well developed density distribution at the corners of a square. 2. Experimental The title complex was synthesized in a standard way [6]. The single crystal, grown from a concentrated deuterated ammonia solution had a volume of 32 mm3. The experiment was performed on the 4-circle diffractometer PllO at the ORPHEE reactor in Saclay. We measured 858 Bragg intensities with A = 0.832 A up to 20 =
100” (sine/A = 0.917 A-‘). They were averaged with PROMETHEUS [7] giving 232 unique reflections (consistency factor R, = 0.016). We applied the isotropic extinction corrections after Becker and Coppens [B] for a standard model assuming a Gaussian distribution of the mosaic spread. 3. Data analysis and results The data were analysed by three methods: by the standard crystallographic model, with symmetry adapted functions, and with the Fourier technique. In the standard model, refined with the program PROMETHEUS [7], we distinguish the so-called ‘split atom’ model from the ‘Frenkel model’ [9]. In a ‘split atom model’ the only aim is to reproduce the density given by the data no matter whether the split positions comply with the molecular geometry or not. In the ‘Frenkel model’ molecular disorder is described by superimposing several fractional images of our rigid molecule in different orientations. The second method [lo-121 treats the density of the disordered molecules as a continuous function which is written in terms of symmetry adapted functions. The ND,-ligand occupies a site having symmetry 4 mm which is higher than molecular symmetry, i.e. 3 m, and therefore, similar to the nitrate analogue, must be disordered. We began the analysis refining the simple ‘split atom’ model down to the R, value of 0.033. It corre-
0921-4526/89/$03.50 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
-u103 au~mulexaq jay~!u aq~ 30 anSolsue ap!t.uolq aql u! se pm se aw~p aq~ u! lClymp Dpe.rpenb srq1 30 uopeluasqo aq] Imyuo:, a.Io3a.Iaq1 um aM ~(1 *%y) &suap ua2olpdq aql 30 uognql_rwp hrsuap aa.r3-lapour !senb e a@ IapouI Iayua.rg JO uum wds ,,wq,, aql JO saseqd aql pue s&j patiasqo aql mo.13 pamaw% sdmu .Ia!rnod
~1.1033 pagap las ~a~atuemd DrlsqeaI e dq (A ‘x)~ Icgualod ~m~%o~ouaurouaqd u! s~alaumed aql 8upeldaJ liq Iapotu aq3 aAordwr 01 wasaId ]e h$ aM ‘2 ‘sy U! UMOIJS S! IfD!gM UO!lOU.l s!yl 01 thpuodsa~ro~ uoynqpwp Al!suap uolold aql paiepmIm amq aM .1CeMpimwu e ur pamp -OWI! SF%uqdno~ ~~uo~)elo~-~euo~~e~o~e ~EM syl LIP :O~/I “x %uph?a ql!~ Iepualod aq$ ,,saqold,, almalow aqi $sql s! suaddeq @mm $eqM OS .hrls@a~ OJU! iq%o.rq aq ~ouue:, a@3e!.x~-E~ aqi pm (X ‘x)/i 30 eurrupu mo3 aqA ‘E ‘2 ‘1 = / 103 (E/LLZ) . (1 - /) + O/f,= !* a@2 pzuogeluauo pm ‘8 io$DaAssetu 30 ialua:, aqi liq paqimap aq dno.SEa aql30 uogwuauo pm uogsod puoDas lenm aql la? .uogeuI!xoJdde 1s.1~ e se 0 = v la8 aM aqes s,rCtpqdur!s ION ‘,SE~T ‘,g~+ = $J Ou h?s 1e 0 < Q ‘0 < g 103 seq (A ‘x)/1
pue
:sz’o = 2 aueld aq$ II! SW qD!qrn (X ‘x)~ Iegualod paldepe li~~au.u.ulisB auyap pue z = p 01 E = p
legualod
pz r~!uom~equr? aql ~11013pavqn31e3
byma
‘z ‘%!d
71'1
1x10.13 tualqord aq1 ampar lila+mua~ ‘alo3alaq) aM ~Apueu!wopald pelalu! 6aqi q”.‘qM l@IM SUOI .IQ lsaleau mo3 aq$ JO sz.0 = 2 q]fM pa_wduIo:, SE pz-0 = 2 awnploo:, 2 aqj amq dno&i EaN auo 30 suomnap aql leqi akxasqo 11e 30 Isly aM -UO!~O.I %UOJISe 30 Alq!q!ssod aql slsaS%ns uogtmasqo s!qL -sla)atueled pauyal 30 laqumu lea18 B alrdsap suoyDaga.! laplo q2hq aql .103 KlleI3adsa ‘hropqs!]es IOU os~e SBM E~OU.IUI~ 30 SSIXII30 lalua:, aq] u! w!od uogqo~ aql ql!M [zr] II! paqu3sap se patulopad q3eoJdde pi ay,L wep aIqrq!eAe aql 30 ~!urq aql dq paupldxa aq hu [cl] anilopzur! aprpor aql u! pahlasqo umai “.Iaqi Quo ql!M pau!elqo jy I(roptz3sym aqJ ‘1 ‘fly u! umoqs uoynq!w!p &suap aql 30 suoy -enlmg aql ampoldal IOU saop I! asnmaq ‘load AlaA s! uoyeur!xoldde s!qJ *([EJ] .33) or raplo olaz 30 uogmn3 lassaH e Aq lcp.10 passaldxa s! qmqM lapour palaplosrp dpnonuguo3 e 01 speaj s!qJ *lap10 qiz[ aql 30 ma1 aq) va@au ‘laha -hioq ‘um ah4 a%tm-0 pahIasq0 aql u!qsM *hr -iamul(s p103-zl isea le ‘8ul-r e uo suaifo.Ipliq aqj JO uognqgsrp E saumsse qXqM q3eoldde liiisuap snonuguo3 aql u! sa+nbar rC~~ar.uuIlCs .nzpwaIour pue aits 30 uog!so&adng .ICqauIoaS e~uomue aqi 01 uoyelal ou ‘.IaAaMoq ‘seq [apour s!qJ .suog!sod uolalnap 8 laqla8olIe ql!M [9] alell!u aulumexaq layD!u aq, II! 1 lapour aql 01 spuods
A. Hoser et al. I Orientational disorder of ND, group in Ni(ND,),Br,
plex. This cannot be realized by assuming only a simple reorientation of the NH, molecule in a plane perpendicular to the Ni-N bond. The tumbling reorientation in an anharmonic translational-rotational potential proposed above gives a good explanation of this observation. The latest QNS results [14] which found the reorientation radius of the ammonia ligand to be larger than the hydrogen radius observed in the free molecule apparently confirm our model. A more detailed discussion of our results will appear in Molecular Physics. References [l] S.H. Yii, Nature 141 (1938) 1.58. [2] A.R. Bates, S.R. Hughes and D.J. Somerford, J. Phys. C 16 (1983) 2847.
87
A. Hoser, Thesis, University of Poznari, Poland (1981). T.E. Jenkins, L.T.H. Ferris, A.R. Bates and R.D. Gillard, J. Phys. C 11 (1978) L77. J.M. Janik, J.A. Janik, R.M. Pick and M. Le Postollec, J. Raman Spect. 18 (1987) 493. J.A. Janik, J.M. Janik and K. Otnes, Physica B 90 (1977) 275. t61 A. Hoser, W. Joswig, W. Prandl and K. Vogt, Mol. Phys. 56 (1985) 853. ]71 U.H. Zucker, E. Perenthaler, W.F. Kuhs, R. Bachmann and H. Schulz, J. Appl. Cryst. 16 (1983) 358. k31P. Becker and P. Coppens, Acta Cryst. A 31 (1975) 417. 191 J. Frenkel, Acta Phys. Chem. U.S.S.R. 3 (1935) 23. [lOIW. Press and A. Huller, Acta Cryst. A 35 (1979) 876. 1111W. Prandl, Acta Cryst. A 37 (1981) 811. K. Vogt and W. Prandl, J. Phys. C 16 (1983) 4753. 1121 [I31J. Eckert and W. Press, J. Chem. Phys. 73 (1980) 451. 1141G.J. Kearley and H. Blank, submitted to Can. J. Chem. (1988).