摘要:
1974 2473Crystal Structure of Cadmium Hexacyanopalladate( iv)By Hans-Jorg Buser, Gideon Ron, and Andreas Ludi,' lnstitut fur Anorganische Chemie, Universitat Bern,CH 3000 Bern 9, SwitzerlandPeter Engel, Abteilung fur Kristallographie, Universitat Bern, CH 301 2 Bern, SwitzerlandThe crystal structure of the title compound has been determined from diffractometer data. Crystals are cubic,a = 10.91 1 (4) A, Z = 4, space group Fm3m. The structure has been refined by least-squares techniques toR 0.057 for 172 observed independent reflections. Interatomic distances are : Pd-C 2-07(2), Cd-N 2.27(3),and C-N 1 . l l(4) A.THE crystal structures of a variety of cubic polynucleartransition-metal cyanides have been described in termsof a general structural mode1.l Corresponding crystallo-graphic studies have been carried out so far with com-pounds of the composition M11s[M111(CN)6]2,xHa0.Aparticular property of these structures is given by astoic heionietrically determined fraction of vacant latticesites which are assumed to occur completely at random.2I n the case of Cd[Pd(CN),] the general model predicts athree-dimensional framework without vacancies. Thepresent X-ray study was undertaken to test the validityof our general structural description. The determinationof this structure was further initiated by the lack ofstructural data for cyano-complexes of palladium(1v).half the edge of the complete face-centred cell. Because ofthe existence of the pseudo-mirror-plane intersecting thesequence M-C-N-M', the even-index reflections did not allowa distinction to be made between Cd and Pd, or between C andN.The small number and the low intensity of the odd-index reflections provided insufficient information for usconclusively to distinguish between the possible orderedarrangements Pd-C-N-Cd and Pd-N-C-Cd, or the dis-ordered structure (Cd,Pd)-( c , N) -( C,N)-( Cd , Pd) . Furtherexperimental data, in addition to X-ray intensities, hadtherefore to be used. Chemical intuition predicted the link-age Pd-C-N-Cd, by consideration of the structures of othercadmium-cyanometallates. This arrangement, i .e. [Pdc,]and [CdN,] octahedra, is in complete agreement with X rayphotoelectron spectra. The ionization potentials of the3d312, 3d5l2, aiid 4d orbitals of Cd in Cd[Fd(CK),] are 4 9.8,EXPEKIMEXTALCrystals of Cd[Pd(CS),j wcre prepared as described in ref.2.The crystal used was a cube, cu. 0.10 x 0-10 x 0.09 mni.Crystal hta.-Cd[Pd(CN),], &%f = 374.9 cubic, a =10.911(4) A, U = 1209 A3, D , = 1.92(1) (by flotation),2 = 4, D, == 1-92, F(000) = 688. Filtered Mo-A', radi-ation, A = 0.7107 A, ~(Mo-h',) = 29.5 cm-l. Systematicabsences: Iikl if Ii -i- k , iz 4- I, I + A = 2% + 1, face-centred;space group Oi, FirtSnt (by convention).'The unit-cell parameter, a, was determined froin silicon-calibrated higli-angle Weissenberg photographs by use ofCu-K radiation [a(Si) 5.4308 A]. Intensities for tlic layerslr0-141 were collectccl by use of a semi-automatic Supper-l'ace diffractonietcr equipped with a scintillation detector.Scan rates were 0.5-lo min-1, scan widths 2-3".Oneoctant of thc ortliorhombic,zlly indexed reciprocal lattice wasincluded in tlw data collection. 541 (172 independent)rcflcctions having I > 2 . 3 3 4 I ) were considered ob~erved.~Only 14 (13 itidepeiiclcnt) reflections with odd indices werc( ) bsem ed .Data reduction, inclucling corrections for Lorentz andpolarization effects but not for absorption, was carried outby use of an IBM 1620 computer. Thc ' X-Ray ' system *itnplcmented on a C I X 6400/6500 computer was used forrefinement.Solution and Refi,te~~teitt.--'The X-ray intensities wereoverwhelmingly domiriatctl by reflections with only evenindices. Only a very few extremely weak reflections withodd indices were observed, which is not surprising since thescattering factors of Cd tind I'd and of C and N are verysimilar.The dotniiiating reflections with even indicesdefined a cubic primitive pseudo-cell with a = 5-46 -4, i.e.A. Ludi and H. U. Giidcl, Sfrzscttcre and Bonding, 1973, 14, 1. " A. Ludi and G. Ron, Chiinin (Switzerland), 1971, 25, 333.Y. Engel and W. Nowacki, Z. Kvist., 1964.129, 178.' X-Ray ' system of programs, eds. J. M. Stewart. I?. A.Kundell. and J. C. Ualdwin, I yniversity of Maryland, TcchnicnlReport TR 192, 1973.Unit cell of Cd[Pcl(CN),] with most of the C aiid N atomsomitted for clarity413.0, and 19.4 eV.5 The corresponding values forCd,[Cr(CN),],,xH,O with nitrogen-co-ordinated Cd are 41 9.6,412.8, and 19.3 eV.5 Conclusive evidence for the linkagePd-C-N-Cd is also furnished by i.r.spectroscopy. The CNstretching vibration (cm-1) occurs at 2145 for K,[Cd(CN),],@2185 for K2[Pd(CN),],7 and 2223 for Cd[Pd(CK),],2 thus show-ing its typical shift from a mono- to a poly-nuclear cyanide.*The solution of the crystal structure of Cd[Pd(Cx),] thereforerelied on conclusions obtained from spectroscopic experi-ments, which clearly showed the linkage to be Pd-C-N-Cd.Throughout the structural calculations thc distinctionbetween Cd and Pd and between C and N was made, eventhough it was not apparent from consideration of the X-rayintensities.Since the unit cell contains four formula units Cd[Yd(CN),],the metal atoms Ccl and Pd have to occupy the two four-foldpositions 4n and 4b of space group Fm3m (see Figure), soC.li. Jorgensen and H. Berthou, Mat. Fys. Mcdd. Dan. Vid.Selsk., 1972, 88, 16.6 D. M. Adams, ' Metal-Ligand and Related Vibrations,'Arnold, London, 1967, p. 168.H. Siebert and A. Siebert, Z. miorg. Chem., 1970, 378, 160.8 D. F. Shriver, S. A. Shriver, and S. E. .4nderson, Inorg.Chena., 1965, 4, 725J.C.S. Daltonthat carbon and nitrogen are on two non-equivalent sets ofthe twenty-four-fold position 24e. Only two positionalparameters, x(C) and x(N) had therefore to be determined.Atomic scattering factors from ref. 9 were used for allatoms with corrections for the effects of anomalous disper-sion for the two metal atoms. Starting parameters for theleast-squares refinement were chosen by consideration of theC-N and Cd-N distances in Cd,[Cr(CN),],,xH20.10The starting thermal parameters affected the phase angleof the odd-index reflections, because for these reflections thecontribution of the two metal atoms to the structure factorwas almost equal, but opposite in sign.All even-indexreflections, however, have zero phase-angle (disregarding theeffects of anomalous dispersion), because all metal atomsscatter in-phase with the Cd atom at the origin. Twoleast-squares calculations were carried out, starting withB(Cd) > B(Pd), and B(Cd) < B(Pd), respectively, in orderTABLE 1Results from least-squares calculations for phaseassignment+ ve * -ve *0.057 0.0620-034 0.0330.231 0.3260.107 0.188AU reflections {g,Oddonly {g,BIKZ Cd 0.73 3.6Pd 3-7 0.64C 4.1 2.0N 4.6 10C-N/A 1.11 1.03* Sign of most odd-index structure factors.TABLE 2Atomic co-ordinates (fractional) and thermal parameters,with estimated standard deviations in parenthesesX Y z B (mean) 8 } 2-2(2) ; } 4*4(7)Cd 0 0Pd 0.5 0C 0*3102(30) 0N 0*2081(18) 0to distinguish between the two possible sign assignments forthe odd reflections.The function minimized was Cw(F, -F,)2 and the weight was chosen as l/02(Fo). After fourcycles of isotropic refinement for both cases, all parameter* See Notice to Authors No. 7 in J.C.S. Dalton, 1973, Indexissue (items less than 10 pp. are supplied as full size copies).9 ‘ International Tables for X-Ray Crystallography,’ vol. 111,Kynoch Press, Birmingham, 1962, pp.202, 211.shifts were <a. The Rfactors and the C-N distances clearly favour the assignmentof a positive sign to the structure factors with odd indices.Final parameters, corresponding to R 0.057, are in Table 2 .Final observed and calculated structure factors are inSupplementary Publication No. SUP 21079 (3 pp., 1 micro-fiche), * A diff erence-Fourier map, calculated with thefinal parameters, showed a diffuse maximum around (&,$,a), corresponding to ca. 25% of the electron density ofthe carbon atom, and may be assigned to some residualzeolitic water molecules. Such zeolitic water moleculeslocated within the cell octants have been found in the struc-tures of other polynuclear cyanides.l Analytical data forCd[Pd(CN),] indeed show a small amount of water corre-sponding to about two water molecules per unit cell.Results are presented in Table 1.RESULTS AS’D DISCUSSIONThe poor distinction between Cd and Pd by the X-rayintensities is reflected by a least-squares correlationcoefficient of -0.81 between the two thermal parameters.The corresponding value for C and N is -0434.Themean values B(Cd,Pd) and B(C,N) are therefore moremeaningful than the individual temperature factors.The crystal structure of Cd[Pd(CN),] fits completelywithin the general scheme of the structural chemistry ofpolynuclear transition-metal cyanides. It consists of anuninterrupted cubic Pd-C-N-Cd framework. Bothmetal ions sit in a perfectly octahedral co-ordinationgeometry with the following interatomic distances :Pd-C 2-07(2), Cd-N 2.27(3), and C-N l.ll(4) A. Sinceno other data for the bond-length PdIV-C are available,this distance may be compared with the isoelectronicRuII-C bond distance (2.03 A) in Mn2[Ru(CN)&3H2O.l1The values of the Cd-N and C-N distances are in agree-ment with those found in other cyano-compounds.l9l2We thank Professor D. Schwarzenbach for assistance withthe calculations, and the Schweizerischer Nationalfonds andthe Entwicklungsfonds Stiftung Seltene Metalle for financialsupport.[3/774 Received, 11th April, 1973110 H. U. Gudel, Acta Chem. Scand., 1972, 26, 2169.11 M. Riiegg, A. Ludi, and K. Rieder, Inorg. Chem., 1971, 10,12 D. Britton, Perspectives in Structural Chem., 1967, 1, 109.1773
ISSN:1477-9226
DOI:10.1039/DT9740002473
出版商:RSC
年代:1974
数据来源: RSC