Table VII4

Gold CfuslerpStruclurally, Characterized b X-t'ay Methods

SpecialCluster'' References Crystallographie Comments

5ymmelry

P rnöhödantäWOhosphineligandbid''bntät6phogphitaeHgarid

*'= mörc öualerft anionic ligandWltereeppliceb1p;ccntredJoosehedronerfragrnentthereof

l isd[t erlpseOdosymmetryr

`Mrd Craw'Tour yslaltograjptjallyirydepenc!entclusers

t Few crystaIlographf4d6failsgiven

'tIÄ^I.^1g )90Q121,3ä,

.IAu,1(PP)J1

:^/e1"9Ar .►Sl^Ff 111}311

LA[!8F'r,15lf

f^^rCPJ^ 4

JAu Sn&f

(A (PPa(u I)z1.

la`^af^^l

184

10

22.23

24

184a185;18621,186a6®187y8S:

129$x,18979019118,19219389a1Z,18(3194195

3 or 32

Rf

222

3'22

4 2rrt

i.^

X-Ray Structural Investigations of Gold CompoundsA COMPILATION OF REFERENCE DATA. SUPPLEMENT I

Peter G. Jones

Inorganic Chemistry Institute, University of Göttingen, Federal Republic of Germany

Parts I and II of this article reviewed X-ray struct uralanalysis ofgold co mpo ands up to early1980. Thisfirst supplement coverstheperiod1980-1982; somepublicationsfromearly1983are also included.

The period 1980-1982 hasseen a continued increase in the use ofX-ray crystallography to investigate chemical structure; this increaseis reflected in the numberofcontributions to thestructural chemistryof gold. An update of the previous two articles in this series (GoldBull., 1981, 14, 102-118 and 159-166) thus seems worthwhile.

As before, the author would like to thank the curators of variouscrystallographic data centres and their co-workers for their invaluablehelp in compiling this supplement: Drs. O. Kennard and S. Bellard,Cambridge; Dr. I.D. Brown, `BIDICS', Ontario; and Prof. G.Bergerhoff, Bonn. Dr. J.W.A. van der Velden (Univ. of Nijmegen)kindly made unpublished results available,

References, Figures and Tables are numbered to follow on fromParts I and II.

Omissions in Parts I and IIRegrettably but perhaps inevitably, some addenda are necessary.

The author would be grateful to be notified of any further errors oromissions; these will be dealt with in a future supplement.

To the early studies of naturally occurring gold tellurides (7,8)should be added related investigations of the mixed gold/silvertellurides, selenides and sulphides, sylvanite AuAgTe, 3 (168),petzite Ag 3Au Tee (169, 170), Ag3 AuSe 2 (170) and Ag 3AuS2 (171).Since all these structures are of low accuracy, they will not be discussedfurther here. Reference (168) discusses the close structuralrelationship between some Au/Ag/Te minerals.

Recent X-ray powder investigations of double oxides ABO(A = alkali metal, B =coinage metal) (172), including CsAuO, largelyrepeat the earlier work of Hoppe and co-workers (64).

The following structures were previously reported as preliminaryor private communications, but have now been published in full:HAuCI4 .4H20 (111, 173); Os 3(CO),0(Ph3PAu)X (X= H, SCN; 31a,174); Au,1 Cl 8 (49, 175); `CS H3NAuX' (X=Cl, I; 37a, 37b, 176);Na3 Au,O6 (123, 177); C,H 5 NH , AuCl,1, CS HSNAuCl 3 and(C5 H 5N) 2 AuC' 2 .Cl - .H 2 O (37b, 178); Me 3 AuCH2SOMe 2 (134,179); and the cluster compound (Au 5 (dppm) 3(dppm , )] (NO 3 ) 2

(17, 180).The remainder of this supplement is subdivided into the same

sections as Parts I and II.

I. Simple Binary and Ternary CompoundsThe reaction of gold with selenic acid affords yellow crystals,

previously formulated as Au 2 (SeO4 ) 3 , which are used to colour

114 Goldau//., 1983, 16, (4)

FIE. 31 The layet smallOirhrdeddtclesilarge a,,smali i.lSTotetiu cesenccgf luP.,Cl,A 0,Claand^lüC34units. After (183)

glass. It has now been shown that at least two products are involved,both of which contain selenium in oxidation state +IV rather than+VI. Au 2 Se40 11 contains selenite and diselenite ions and can berewritten as Au 2(SeO 3 )2(Se2O s ) (181); the structure consists of threecross-linked chains of the form [...Au—(selenite or diselenite)-Au... ]. Au 2 Se2 O7 is a layer structure containing selenite and oxideions and can be regarded as Au 2(Se03)2 0 (182); the structure is oflimited accuracy because of pseudosymmety. Although strictly nota ternary compound, the related material Au(SeO 3 )Cl also has alayer structure, and can best be mentioned here (183; Figure 31).

II. Gold Cluster CompoundsInterest in these compounds, which have an aesthetic as well as

a scientific appeal, continues unabated. Despite appreciablepractical difficulties bothwithsynthesis/purification and with crystalstructure determination (gold cluster compounds often displaydisorder and/or pseudosymmetry (183a) ), several new structureshave appeared in the last two years. Some of those mentioned herewere briefly alluded to in footnotes to Parts I and II. A summary ofcrystallographically characterized clusters is given in Table VIII. Adiscussion of the physical characteristics of gold clusters by D.M.P.

GoldBull., 1983, 16,(4) 115

'WF.. lbodustert u'v{P^6^W Ph&,y1 roups ^nAbondatatheceht^al-

AUomftdanC^j^Itfp^etäeciib ne sype'l^nairam ve^tr9ra ilthQrerticçhefà!axlAe&7,

I+i i The Au alceletpn of JAuafPPha zla* fltwd tu Rn 4 os^he^cä^Icam rit ' ^ dotted aEotü ebmliPytes ^h^ [A^y t'^'Ir ^}al^ srstt :;1Cep^oäuocl,^iom (1$9^ • . .

Mingos will appear in the next issue of GoldBulletin.Au13 clusters, The compound [Au 13 (PMe 2Ph) 10C12 1 (PF6)3

contains a centred icosahedron of gold atoms (184); this unit isrecognised as the parent polyhedron of many smaller clusters. Asimilar unit could be identified in the [Au 13(dppm)6 ] ion (180), butdisorder of the ligands and the additional presence of anunidentified disordered cluster rendered the structure of lowaccuracy; the ionic charge could not be determined.

Au„ clusters. The Au,, core geometry in [Au,, (dppp),] (SCN) 3

(185, 186) is the same as that in previously reported Au,, clusters(22,23,24). Disorderofsomeligand light atoms limited the accuracyof the structure. A further Au le halide cluster [Au 11(Ph3P)7 13 ] (184a)also differs little from the earlier structures.

Aug clusters. The first neutral Au g cluster is [Au 9(Pcy3 )S(SCN)3 ](166; see conclusion to Part II). It can be formally regarded as derivedfrom a centred icosahedron by removal offourvertices, although oneperipheral Au-Au bond must also be broken.

The [Au 9(PPh 3 )e] 3 + cluster (21, 186a) can be electrochemicallyreduced to give [Au9(PPh3 )e ] + ; the centred Au, chair is effectivelyunchanged, but the remaining two atoms now lie on the three-foldaxis (Figure 32). Again the structure determination was somewhatinaccurate, only gold and phosphorus atoms being located (187).

A complete departure from icosahedral frameworks is providedby [Au9 (P (i5 — C6H4OMe)3] e ]3+ ; the Au g skeletonis acentred crown(188). The authors suggest that Au — Au P bonds (for nomenclaturesee Part I) may not be energetically significant in centred goldclusters, since there are four fewer such bonds in the centred crownthan in the other Au g}* clusters.

Au8 clusters. Chemical removal of one ligand from the knowncluster [Au 8(PPh3)8 ] 2 + (19, 20) gives [Au 8(PPh3)7 ]2 * ; as would beexpected from the long Au c — P bond of the former cluster, it is theAuc atom which loses its ligand (189). The gold framework remainsbased on the central icosahedron, the Au, atom being ratherexposed (Figure 33).

Au7 clusters. [Au 7(Ph3P)7 ]+ is prepared by the evaporation ofmetallic gold into a toluene solution of the ligand. The crystalstructure (190) is one of unusual complexity, with fourindependentbut very similar clusters. The Au7 skeleton is a pentagonalbipyramidwith averyshortaxial-axial Au-Au bond of 258.4pm. Thisgeometry can be formally regarded as derived from a centredicosahedron by removal of a pentagonal pyramid, but this may beextending the formal analogy too far!

Although alloys have been specifically excluded from thesearticles, an exception should be made in the case of Rb 4Au 7 Sn,(191). This contains Au7 clusters (Au-Au bond length = 275.7,278.0pm)intheformof two tetrahedra linked at acommonvertex;Sn2 units link these clusters (Figure 34) (Au-Sn = 260.1, Sn-Sn= 286.8 pm).

Au6 clusters. [Au,(dppp),](NO 3)2 contains a tetrahedron ofgold atoms, each bonded to one phosphorus of a bidentate dpppligand, and two further gold atoms bridging opposite edges of the

116 GoldBull., 1983,16, (4)

Figzm

Fig,34 TheAuy6DwbfRb,,,Auäti ztishowingiheSizunitswhi'cftbrid'get^1uttherofustetLAfie (191p

tetrahedron and each bonded to two phosphorus atoms (Figure 35;192). This contrasts with the distorted octahedral geometry of thepreviously known Au, cluster (18). A heteronuclear Au6 cluster withCo(CO)4 ligands has also been reported (193); the Au6 moiety in[ Au6(PPh3 )4 [Co(CO)4] Z ] consists of two tetrahedra with a commonedge, the cobalt atoms being bonded to the apical golds.

Au4 clusters. The cluster [Au4(PPh3 )4I2 ] contains a tetrahedralAu4unit bridged on two opposite edges by iodide ligands (194). Theassembly of six heavy atoms is thus strikingly similar to the[Au6(dppp)4 ] 2 cluster mentioned above. A further iodine-

ig. 36 The [Ag4(djipm),Udustet; Phepylgroopsotnittedfö elariry. 1^, Ibondlengths: totetminat[; S'3.3 pmj to'l ridgingT 313 .2, 334.3, 3^6 pm.Afier:(195)

Gold Bull. , 1983, 16, (4) 117

Fig.ä7 Compounds containing a iccl goiä Jnetat bonds.(i)the h lae-ba t(GO)^Cr(i AuPPb, i

M rl,2Q0';2U res vely,partsöfsömepheng dngsomittedfocciaiity.In (b) the 14 of HR $ra's not found

containing cluster [Au4 (dppm) 31 2 1195 also contains a tetrahedronof gold atoms; one is coordinated to iodine, while the remainingtriangle is bound to the three diphosphine ligands and cappedasymmetrically by a distant iodine atom (Figure 36).

Aue `cluster: As was mentioned in a footnote to Part II, thezerovalent [Au 2(PPh3 )2 ], prepared by methods analogous to thoseused for many larger clusters, has been structurally characterized(196). Regrettably, few details of this interesting structure areavailable (although slightly more than were given in Part II): thePLAu-Au-P sequence adopts a trans-bent geometry, with Au-Au= 276 pm, Au-Au-P = 129°.

III. Compounds with Gold Transition Metal BondsAn Au -V bond of 269.0 pm occurs in [PPh3AuV(CO)4 ] (197),

which possesses crystallographic3 symmetry along the P ­Au-Vaxis.A more complex gold-vanadium species, which may be regarded asa mixed cluster, is [(Ph 3PAu)3V(CO),] (189), which was found tocontain an Au 3V tetrahedron (Au-V = 270.9-275.6 pm, andAu-Au = 276.8-285.5 pm). The allyl-iron derivative[Ph 3PAuFe(CO)3 (t1 3 — C3H5)] (199) shows an Au-Fe bond of length251.9 pm, appreciably shorter than in the loosely relatedcyclopentadienyl species (31); the carbonyl ligands bend backtowards the gold atom, as in [Au {Co(CO)4} 2 ] - (29).

An important new classofcompoundsis that of the mixed metalhydrides containing Au/H\M bridges. The first compoundknown to involve an Au-H bond is [(CO ),Cr (µ — H)AuPPh 3 1(200 ).The hydrogen atom cannot be located precisely in such structures,but the Au-H bond is approximately 172 pm (e.s.d. = 11 pm);Au-Cr = 277.0 and Cr-H = 164 pm (Figure 37a). In a similarcomplex [(PPh3)3IrH2(µ — H) AuPPh 3 ]+, the bridging hydrogenatom could not be found (201), but its presence could be inferredfrom the bent P-Au ... Jr geometry, and on chemical grounds.

The compound [(cp) (CO)2W (µ —CHR)AuPPh 3 1 (whereR = p —C4H4Me) (202) displays a W/C\Au triangle, withAu -W = 272.9(.1) and Au-C = 226.8(1.4) pm (Figure 37b).

It is a surprising but theoretically justifiable fact that the Ph 3PAugroup is electronically analogous to hydride. This fact has beenexploited in the syntheses of many mixed metal clusters withperipheral Ph 3PAu groups, and/or in the rationalization of theirstructures. More than one gold atom may be incorporated into acluster, sometimes with the formation of an Au-Au bond. Asummary of mixed clusters is given in Tables IX and X; see also (174).One mixed cluster is unusual enough to be omitted from theseTables, because it contains no phosphine group; the Au-PR 3 bondof [Os 3 (CO) 10H(AuPR 3 )} (174) breaks on reaction with[N(PPh3)2 ]Cl, to give [Os4Au(CO)20H2 ] (213). This cluster containsa planar four-coordinated gold atom on a crystallographic sym-metry centre, bonded to edges of two Os 3 triangles (Au-Os =280.6-281.4 pm); the overall geometry is thus two Os 3 Aubutterflies with a shared Au wingtip (Figure 38).

A completely differentkind of mixed-metal aggregate is seen inthe chain polymer [(C4F5 )AuAg (SC4H8 )] (214); Aue units (Au-Au= 288.9 pm) are bridged by pairs of Ag atoms (Au-Ag = 271.7,272.6 pm) (Figure 39). This is thefirst known example of an Au-Agbond.

118 Go/dBu11., 1983, 16, (4)

Table iXMixed Ciustei nvoivJn Peliphersi AuP Units'

Au-übÖdQomp. und Gqetiy Au position iencth(sk

,OM06 exiijiiAU pni

teIrahecrO TrilridgesoJa6 1444ifluCo3(Q 2CAu 203a iupoIetrah?drot ditto 79-274 $L0oRu3(C0 13(AuP)r 208b coRu3tetrahedron Triply bridges CoRuface " !yep,F 4Q (j4 -H) (CQ I2(AUP)1 204 Fe4 uttertly BrIdgoswlpgtis 285,4i 2880

tFQ(C 4(AuF)- I Fb6suare pyramid Auo)- bridgembosal edoet 269. WalAu(2}caps squarebasa 282&-QaQ

LRuÖ)9(OaBu')(Aur1 206 Ru triangle Completes butterfly sspgti:

[Ö)'(QOMe)AuP)J * 207 ditto ditto 2760 2?62208 ditto ditto 2149 ^763

(RuO - -COMeXAuF)1 209 ditto ditto 272 ?763(CO)1+ - 'HXAuP)r 210 Qs4tetrahedtop Edgebridging 274v 79

Ö54(à}12 » -U}3 AuP)1 210 dittO ditto .782 280S

P plorT9dentate phosphine4igand Directanalogueotahydrideapectesbitftiè ãtcénfrOfokstèr -*- TWO indepen dent rnö1ulos;onl' one set ái bond iengthsgiver

TabtokMixed CIUstø whhAuAu Bonds

éfer- dbometiy ßoiidLengths, pm

once Au-Au Au-M

vqgyui 8 1btraedrn 27.82e5.5 270.9-275.6(F(CQ 12C(AuP)21 204 Fff1butteJ'fiy plus

AuAu unit gives'islortedIDptahedrer1*t $01 1 2770-2999

10s400) 1 H2{AuF%J 211 0s4 tetrhedrÖn oneedge bridged byAuAUunit 27.3 283.9-3004

L0s3(O0)11 H2(AuP)21 212 PianarOs3hu 'butterfly'Au-Os edg bridged by

seoondAustom 245 27-3o3O[Ru3Qo(cO) 12(AtP 3] 203b AuC6Rv3MgonaIbipyramid

AuRu and AuCoR*daCOnädescappedbytwolurUier 2836,2784 271.2 272 6'(Co)Auatorfle 278 3-3054(Iiu

[Ru3(CQ)0 '-COMO)(AuP)31 2Q9 AuRU3 tetrahedron, twofaces tnpiy bñdged bytwofurtherAuatoms 930O10 2798-29&7

1Ru4(CO) 2( .-H)(AuP)3J 209 Ru(OO)ropiaces -COMa 281.9 2842 825-3o1

08(90)4(iu 21 209aof prevIQu StructureNÖnforoiatiÖn (co, nfu-rencoAbtraöt)

ImonodentatophosphnehgandCarbidd 0 st Centre of cluster

GoIdBuII., 1983, 16, (4) 119

$rg.38' 'I'licmixed'duster[Osµ'ü(GO)^ oHzl' '>ii the prepaEauon of whit a gold-PR3 bond isöboken, The'Hatomswerenotlosated. After(2J3)

IV. Gold (I) Complexes with Short Au ... Au ContactsPride of place in this section must go to the dimeric

2-pyridylphosphine complex [2— C 5H4N.PMe 3 .Au] 2 2 + (215), withAu ... Au aslowas 277.6pm(Figure40). Theligandwasdeliberatelychosen to force a short contact. A further 8-membered dimeric ringis found in [Au(Ph 2P)2 CH]2 (216), with Au ... Au = 288.8 pm; thestructure exhibits disorder, the molecules adopting either of twoorthogonal orientations. The complicated mixed nickel/goldcomplex of penicillamine (Pen = HSCMe2 .CH(NH2 ).COOH),formulaNa2 [Au2Ni2Pen22- ], alsocontains thiscommon structuralfeature; the rings are of the form (— S — Au — S — Ni — )2 and the Au ...Au contacts are 294, 299 pm in two independent molecules (217).

The tridentate ligand CH3C(CH2PPH2)3 (= PPP) farms a simplegold (I) complex [PPP(AuCl)3], in which two of the P-Au -Cl 'arms'form an intramolecular Au ... Au contact of 309.1 pm (218).

The mixed complex [(Ph3P) 2Au2 (bbzim)Rh (cod)] + (where cod= cycloocta-1,5-diene, bbzim = bibenzimidazolate)(219)containstwo N-Au-PPh3 moieties; since the nitrogen atoms are closetogether on the bbzim ligand, ashortAu ... Au distance of 313.4 pmresults.

The series of complexes [(Ph 3PAu)3X] + ,where Xis an elementofperiodic table main group VI, is now structurally characterized forX = 0, S and Se (220, 48, 221). All three form dimeric units withshort Au ... Au distances of about 300-330 pm, thus giving rise toAu6 'chairs' (see Part I). The structure of the related neutral complex[(Ph3PAu)2 S] was also determined (221) but was of limited accuracybecause ofpseudosymmetry. The Au-S bond lengths are appreciably(about 16 pm) shorter than in [(Ph 3PAu)3 S]+ ; a slightly acuteAu-S-Au angle gives an Au ... Au contact of 301.8 pm. The ease offormation ofsuch Au 3X+ units is also reflected in the breaking of anAu-P bond in the formation of the [Au (S(AuPPh 3)2] 2 ]' cation

(222), whichhasAu ... Au in the range 303-321 pm andallAu-S-Auangles acute.

The [(Ph3PAu)30] + cation has been used as an aurating reagentin organometallic chemistry; for example reaction with malonitrile,H2 C(CN) 2 , gives [(Ph 3PAu)2 C(CN2)], with Au-C = 209.5,210.7 (.9) pm, Au ... Au = 291.2 pm (223). A more complicatedseries of reactions with tetraphenylcyclopentadiene, Ph 4C5H2 , leadsto [Ph4 Cs(AuPPh3) 3]+ (224, 225); an Au 2 C triangle (Au ... Au= 282.0 pm)ismoreweaklylinked to the third Au atom (Au ... Au= 302.1 pm), which is itself bonded to the cyclopentadienyl ring byone short(221 pm)Au-C bond and two appreciably longer contactsof 260 and 271 pm (Figure 41).

V. Other Au (I) ComplexesThe reaction of the aurating agent [(Ph3PAu)30] + (see previous

section) with tetraphenylcyclopentadiene gives Ph 4C5H(AuPPh 3 )(224, 226); this compound, like the triply aurated derivativementioned above, is unusual in that the bonding mode of gold tothe ring is intermediate between i1' and r1 3 (Au-C = 215, 267, 276pm).

The two dicyanoaurate (I) salts Co[Au(CN) z ] Z (227) andKCo [Au(CN)2] 3 (228) show no unusual features; the same can besaid for the 2-pyridylphosphine complex (C,H 4N.PPh 2 )AuCI(229), although one ring is disordered.

The anti-rheumatoid arthritis drug AURANOFIN (thetriethylphosphinegold (I) complexofapenta-acetyl thioglucosateanion) is only the second gold (I) thiolate for which a structuredetermination has beenperformed (230). The bond lengths at goldare comparable with the previous study (51).

Compounds [(Ph3P)2XPt-AuPPh 3], synthesized from (Ph 3P)3Ptand Ph3PAuX, are assumed to contain an Au-Pt bond (as is implied

120 GoIdBu%',, 1983, 16, (4)

ig,4d jUiddlclMheni aboudnotäbond?Thetwogöidatomshereairefofmaliy non-bonded, but only 277:4 pm apaii. t1Mt€r (213)

Fig, 39 (Tgp) Part of thelineacehairtpotymet [(C P, AUA#Q t,4 8)j.... ftet ( 2'1ä)

Fig 41 (Bottom) The P4Cf(AuPPhj)3j+ Cation; ligand phenyl ringsomitted ochbaringsrcprese ttedbythefirstatonionly.Weakerinteractions:indicatedby open bonds. After (22'5)

GoldBull. , 1983, 16, (4) 121

Fig. 4?` 11ecentc4$ii otthc'[(ßhy 1 tGL{C CFY At^i'P1i, malecul ;.PhosphinaphenylAnisomittc 1fordarüyv 'ter l(2;2p

Fig.; 43 The four-thordinatc goid(I) `complex I(lth3Pl3AuC1]. After (236)

by this formula). ForX = C 6CIs , however, a C-CI bond is brokenand the product is [(Ph 3P)2C1Pt(,u-3,4,5,6-C6Cl4 )AuPPh 3 ], asshown by its crystal structure (Figure 42; 231, 232).

The important synthetic intermediate carbonyl gold(I) chloride,(OC)AuCI, consists ofexactly linear molecules. The bond lengthswere systematically in error because of thermal motion and must beregarded as unreliable. Despite the expected ease of packing of linearmolecules, the shortest Au ... Au contacts are 338 pm (233).

VI. Gold(I) Complexes withHigher Coordination NumberThe three-coordinate [(Ph 3P)2Au(SCN)] shows regular planar

geometry,withAu-P = 234.6, 234.9pm, Au-S = 246.8pm(234).The Au-P bond lengths are in good agreement with those in[(Ph 3P)2AuCI] (See Part I). The tricyclohexylphosphine analogue[(cy 3 P)2 Au]+SCN - contains linearly coordinated geld, thethiocyanate not being bonded to the metal (81); the difference isthought to be due to steric effects of the bulky cyclohexyl. groups.

A new modification of the three-coordinate [(Ph 3P)2AuCI]formed only twinned crystals, as had been previously reported.Nevertheless, a structure of moderate accuracy was obtained (234a).The Au-Cl bond length was 252.6(1.0), with Au-P = 231.3(.8),223.0(.9)pm, and bond angles Cl-Au-P = 115.1, 108.1(.3), P-Au-P= 136.4 (.3)°. The geometry is thus somewhat different from thatof the hemibenzenate (89).

A three-coordinate mixed gold-silver complex of formula[(Ph 3P)3M]+(NO 3 ) - where M = 2/3 Au, 1/3 Ag has beencharacterized (234b). The cation geometryissimilarto that in other[(Ph3P)3Au]+ salts.

Following the author's provocative statement that '... theassumptionof tetrahedral coordination in gold(I) complexes is notjustified...' (based on structures of three modifications of[(Ph3P)44Au+ ] BPh4 (97)), several tetrahedral complexes have beencharacterized. In [(Ph2MeP)4Au+] PF6 - (235) the cation displayscrystallographic 4 symmetry (Au-P = 244.9 pm) and in[(Ph3Sb)4Au]+ [Au(C6F,)2 ] - (236) there are three independentcationsofsymmetry3(Au-Sb = 259-267pm).Itislikelythatstericeffects are important in deciding whether regular tetrahedralcoordination can be achieved.

Four-coordinate species of the form L 3AuX (L = phosphine,X = anionic ligand) have also been studied. [(Ph3P)3AuCl] (Figure43; 236) completes the series [(Ph 3P)„AuCI] (see also 89, 78); Au-Pand Au -Cl bond lengths increase with coordination number alongthis series (Au-P = 223.5, 233.1 (ay.), 241.0 (ay.), Au-CI = 227.9,2 50.0, 271.0 pm for n = 1, 2, 3). The related thiocyanate derivative[(Ph3P)3Au(SCN)] shows ay. Au-P = 239.9, 239.2 and unusuallylong Au-S = 279.1, 293 pm in two crystallographic modifications(237, 238). In all of these compounds the long Au X bond representsa distortion towards trigonal geometry.

VII/VIII. Gold(III) ComplexesThe two simple salts KAuCI4 .2H20 (239) and

(CS H5NO)2 H+AuCI4 - (240) show no unusual features (Au -Cl =228.5, 229.1; 227.0, 227.1 pm respectively). The related bromo-derivative Bu4N+ AuBr4 - (241) presented problems of disorder andspace group ambiguity (Au-Br = 240.4 pm). The rather morecomplicated AuX4 - compound Cs3(AuBr4 )2 (Br3 ) (242) with ay.Au-Br = 242.2 pm decomposes slowly at room temperature to givemixed valency, non-stoichiometric compounds in which thesimilarly shaped AuBrz - and Br3 - ions can occupy the same site(243).

122 GoldBu11. , 1983, 16,(4)

Planar macrocyclic complexes of gold(III) containing a centralAuN4 unit have been investigated in order ro study the pattern ofbond lengths in the ligands (244,245). The accuracy of light atombond lengths is, of course, somewhat limited in the presence of gold.One of the structures contains four complex cations of charge 1+ andeight chloride ions per cell (244); in fact the chloride ions aredisordered over the eight sites with occupancy 1/2 (I thank theauthors for clarifying this in a private communication).

The bis-1, 2-dithiolate complex (Bu 4N) ` [Au(C,HGSZ)Z] - couldbe isolated and structurally characterized (246), in spite of thegeneral readiness of such ligands to reduce Au(III). Au-S bondlengths of from 229.0 to 2 31.9 pm are comparable with those i n other1,2-dithiolate complexes.

A rather unusual methylene-bridged compound[(Me2 P(CH2 )2AuCI) 2 CH2 ] was obtained by the oxidative additionof dichloromethane to a gold(I) ylid complex (Figure 44; 247).Crystallographic evidence was also adduced for the formation of adihydroxymethane ligand by hydration of a ketone; the structure ofdichloro(dihydroxy-di-2-pyridylmethane) gold(III) chloride (248)shows a short intramolecular Au ... 0 contact (277 pm), thuscompleting irregular five-coordination at the metal atom.Deliberate attempts to prepare gold(III) derivatives with higher co-ordination number were unsuccessful. The normally bidentatearsenic ligand diars (o-C6 H4 (AsMe 2 ) 2 ) is monodentate in[(diars)Au(C6 Fs ) 3 ] (249). Several complexes of normallypolydentate nitrogen ligands were also examined; in compoundsofthe form [AuMe2L] (NO3), the shortest Au ... N contact outside theusual square planar coordination geometry was 314 pm (250)(L = tri-2-pyridylmethanol, tri-1-pyrazolylmethane or aa-di-2-pyridyltoluene).

Three trimethylgold(III) complexes [Me 3AuL] (L = PPh 3 ,CH 2 PPh 3 and CH 2 S(0)Me2 ) were investigated to obtaininformation on gold(III) ylid structures (134, 179). Again theaccuracy of molecular dimensions involving carbon atoms waslimited. The Au-C bonds were slightly longer in the ylid complexesthan in the reference compound [Me 3AuPPh3 ] (213.7 compared to206.5 pm). The Au-C bond trans to L was shorter in all threecompounds than those cis to L.

Concluding RemarksAttention has.been drawn in Part I of this review to one of the main

problems involved in the X-ray structure determination of goldcompounds, namely the inaccuracy of light atom positions (broughtabout by the dominance of the X-ray scattering power of the heavyatom). A further problem not yet discussed is that of X-rayabsorption. Heavy atoms absorb X-rays to an appreciable extent;since the path lengths of X-rays through a crystal are, in general,different for different reflections, systematic errors in the measuredintensities arise. This is asomewhatoversimplified explanation, sinceabsorption effects lead to systematic errors even with sphericalcrystals. An extreme case is Au203(2), for which the Mo Ka X-rays

Frgt 44 The:'riie[^aylene=^tidg $°lc^(IIJ( 1Gl^p()CHzlcomplex The bpdgtcarbon atom (top) lies tn cryscallogräphic tiwdföld 1

ds.,After 42'äp;

used in the structure determination are attenuated by a factor ofabout 50 000 after travelling 0.1 mm through the crystal. Fortunatelymost gold compounds show less severe absorption effects, althoughthe systematic errors often remain highly significant.

It is thus clear that a correction for absorption effects is highlydesirable (if not essential) for gold compounds. The mathematicsinvolved is far from trivial, but recent advances in theory and practicehave made the application of absorption corrections usually verystraightforward. Itis thusratherdepressing to findpublished goldstructures based on data lacking absorption corrections. In manycases the effort involved in inventing an excuse for this omission ismuch greater than would have been needed to perform an adequatecorrection (for example `the expense to information ratio wasdeemed too high'). This supplement thus concludes with aplea toall crystallographers to be dissatisfied with data containingsystematic errors, and therefore to perform absorption correctionsas a matter of routine.

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