199803a0Nature1994895196308248038040028-0836196310.1038/199803a0ukNatureNatureNATUREnatureNature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public./nature/journal/v199/n4895issueJournal homeArchiveCurrent issueAdvance online publicationPrivacy policySubscribeNature Publishing GroupCurrent issue199803a0Binding of the Thiocyanate Ion in Complexes with Palladium (II)-containing Tertiary Phosphines
AU  - FRASSON, E.
AU  - PANATTONI, C.
AU  - TURCO, A.Centro Strutturistica Chimica CNR, Istituto Chimica Generale, University of Padova, Italy.THE infra-red spectra of several thiocyanate complexes of platinum and palladium suggest that these metals must be bound to nitrogen in compounds with the general formula [M(PR3)2(CNS)2] (R = aliphatic tertiary phosphine)1. Adams and Booth more recently reported that platinum must be co-ordinated to nitrogen in the complexes trans-[Pt(CNS)CH3(PEt3)2] and trans-[Pt(CNS) (COCH3)(PEt3)2] (ref. 2). On the other hand, palladium and platinum invariably appear to be bound through sulphur in a variety of complexes with the thiocyanate ion and other different ligands3. It thus appears that the binding of these metal ions with the thiocyanate group is peculiarly affected by the presence of phosphine ligands in the molecule of the complex. The occurrence of this unexpected nitrogen-metal binding may be of more general interest, being clearly related to important changes in the binding properties of the metal ions brought about by the presence of the phosphine ligands. However, all the previous evidence on which these conclusions were based came exclusively from infra-red spectra. A more direct demonstration of the nature of the metal-thiocyanate bond seemed desirable to us. Therefore, a determination by X-ray analysis of the structure of the compound [Pd(PPr3n)2(CNS)2] was undertaken to resolve the question of the bonding of the thiocyanate group.The compound crystallizes in the triclinic system. The space group may be either the P1 or P1. The centro-symmetric space group has been chosen on the basis of intensity statistics. The unit cell has the following constants a =19.53 [angst]; b = 8.72 [angst]; c = 9.36 [angst]; a = 87 58'; b=119 04'; g = 94 12' and contains two molecules of complex. The hk0 and h0l reflexions were recorded on Weissenberg equatorial photographs. The intensities were determined by means of photometric integration. From the vector analysis of the Patterson projections on (001) and (010) it can be concluded that the molecule is square tfrans-planar and that the complex is actually an isothiocyanate with nitrogen atoms co-ordinated to palladium. The projection on (001) is shown in Fig. 1. There are four Patterson maxima arising from the relatively heavy phosphorus and sulphur atoms. Two of them are at 4.6 [angst] and therefore cannot represent the palladium-phosphorus distance. Since the PdNCS grouping must be approximately linear this must be the palladium-non-bonded sulphur distance expected for PdNCS units. It can be compared with the distance 4.8 [angst] between platinum and non-bonded sulphur in [Pt2(SCN)2Cl2(PPr3)2]4. The other two maxima are at 2.2 [angst] in agreement with the expected palladium-phosphorus distance (2.16 [angst] in the platinum compound4).
Fig. 1. Patterson projection on (001) for [Pd(PPrsn),(NCS)al. Contours at arbitrary but equal intervals
These results show that the conclusions derived from the infra-red spectra were correct. The reasons for the change from the usual PdSCN co-ordination to the PdNCS coordination are not apparent at present. With metals of the first transition series, tertiary phosphines apparently affect the metal-thiocyanate bonding in a more complicated way. Cobalt (II), which is usually co-ordinated through nitrogen, is reported to be bound to sulphur in [Co(PPh3)2(SCN)2]5 and to be bound to nitrogen in [Co(PCy3)2(lSrCS)2] (Cy = cycZohexyl)3. It is interesting to note that in the complex [Pd(PPh3)2(NCS)2] the palladium atom must be bound to nitrogen as it is in the compounds with aliphatic phosphines. This is clearly shown by the value of the CS stretching frequency (850 cm1)6.Turco, , A., and Pecile, , C., Nature, 191, 66 (1961).ArticleISIChemPortAdans, % %, and Booth, % %, J. Chem. Soc., 1112 (1962).Giacometti, , Pecile, , C., and Turco, , A., Abst. Seventh Conf. Coordination Chemistry, 9 (Stockholm, 1962).Owston, %, and Rowe, % %, Acta Cryst., 13, 253 (1960).ArticleISIChemPortCotton, % %, Goodgame, % %, and Sacco, % %, J. Amer. Chem. Soc., 83, 4157 (1961).ArticleISIChemPortPecile, , C., and Turco, , A. (unpublished results).