Template self-assembly of polyiodide networks Alexander J. Blake,a Francesco A. Devillanova,b Robert O. Gould,c Wan-Sheung Li,a Vito Lippolis,a Simon Parsons,c Christian Radekc and Martin Schr�oder*a 09124 Cagliari Italy c Department of Chemistry The University of Edinburgh Edinburgh UK EH9 3JJ A range of metal thioether macrocyclic complexes has been used as templating agents in the preparation of extended multi-dimensional polyiodide arrays. A selection of unusual Alexander J. Blake received both his BSc and PhD degrees in Chemistry from Aberdeen University where he was first introduced to crystal structure determination. Following a period of postdoctoral work at Exeter University he moved to the Chemistry Department at the University of Edinburgh in 1982 initially to develop new methods for the study of lowmelting compounds by single crystal X-ray diffraction.From 1985 he took over responsibility for the running of the Department’s Crystal Structure Service as a Staff Crystallographer. He has been a Co-Editor of Acta Crystallographica since 1995 and in August of that year moved to the Chemistry Department of the University of Nottingham where he is currently a Research Officer and the Manager of the Crystal Structure Service. Research interests include supramolecular structure and the exploitation of low-temperature techniques for crystallographic data collection. Francesco A. Devillanova graduated in Chemistry at the University of Bari in 1964. In the same year he moved to the University of Modena as temporary Professor of General and Inorganic Chemistry.In 1972 he moved to the University of Cagliari where in 1980 he was appointed to the Chair of Inorganic Chemistry. His scientific interests focus on sulfur and selenium chemistry and on the donor–acceptor interaction between chalcogen donors and transition metal ions halogens and interhalogens. Robert O. Gould was an undergraduate at Williams College Williamstown Mass and gained his PhD from Queen’s College Dundee (University of St. Andrews) under the supervision of Dr R. F. Jameson in 1963. He was appointed to the staff in the Chemistry Department University of Edinburgh in 1962 and was subsequently promoted to lecturer (1964) Senior Lecturer (1985) and Reader (1997). His research interests are primarily in the study of complexes by X-ray diffraction and to improving methods of crystal structure determination.Wan-Sheung Li gained both her BSc and PhD degrees at the University of North London. The latter under the supervision of Professor Mary McPartlin was devoted to the study of homoand hetero-nuclear metal–metal bonded complexes. In early 1996 she took up a postdoctoral position in the Department of Chemistry of the University of Nottingham where she was a Department of Chemistry The University of Nottingham Nottingham UK NG7 2RD b Dipartmento di Chimica e Tecnologie Inorganiche e Metallorganiche University of Cagliari Via Ospedale 72 and intriguing polyiodides is described and the role played by the size shape and charge of the metal macrocyclic complex discussed.involved in the running of the Departmental Crystal Structure Service. In January 1998 she took up a position in the Computational Chemistry Group within the Institute of Chemistry Academia Sinica Taipei Taiwan. Vito Lippolis graduated in Chemistry in 1991 at the University of Pisa and in the same year gained a Diploma in Chemistry at the ‘Scuola Normale Superiore’ of Pisa. In 1992 he was appointed permanent researcher in Inorganic Chemistry at the University of Cagliari. He is currently a 2nd year PhD student at the University of Nottingham under the supervision of Professor Martin Schr�oder. Simon Parsons gained a BSc Degree in 1987 from the University of Durham and PhD in Chemistry in 1991 from the University of New Brunswick Canada under the supervision of J.Passmore. After postdoctoral research at the University of Oxford (with A. J. Downs) he was appointed to a postdoctoral position in crystallography at the University of Edinburgh in 1993. In 1995 he was appointed Staff Crystallographer in the same Department. Christian Radek gained his first degree (1990) from the Ruhr- University Bochum and carried out his Diplom-arbeit with Professor Karl Wieghardt. He was awarded his PhD from the University of Edinburgh under the supervision of Professor Martin Schr�oder in 1995 and is currently studying for a degree in Economics at the Hogeschool van Utrecht. Martin Schr�oder gained a BSc Degree in Chemistry from the University of Sheffield in 1975 and a PhD in Inorganic Chemistry from Imperial College London under the supervision of W.P. Griffith in 1978. After postdoctoral research at the ETH Z�urich (with A. Eschenmoser) and Cambridge (with J. Lewis) he was appointed in 1982 to a Demonstratorship in Inorganic Chemistry at the University of Edinburgh. He was subsequently promoted in Edinburgh to lecturer reader and in 1994 to a personal chair in Inorganic Chemistry. In 1995 he was appointed to the Chair and Head of Inorganic Chemistry at the University of Nottingham. He has been awarded the Corday Morgan Medal and Prize of the Royal Society of Chemistry and a Royal Society of Edinburgh Support Research Fellowship. 195 Chemical Society Reviews 1998 volume 27 1 Introduction It is well known that the heavier halogens can form oligomeric catenated cations and anions.1 Since I2 exhibits the highest tendency to form stable catenated anionic species,1 the synthesis and structural characterisation of polyiodides continue to be an active area of investigation.Recent interest in this aspect of the chemistry of I2 comes from its use as an acceptor in the synthesis of mixed-valence donor–acceptor materials which exhibit unusual electrical behavior.2 The resulting polyiodide species fit favourably in the crystal lattice of these materials by occupying one-dimensional channels within stacks of partially oxidized donor molecules. 32 I4 22 Numerous examples of small polyiodides such as I and I52 have been reported but relatively few extended and very extended discrete oligomeric anionic polyiodides such as I72,3–7 I8 22,8–11 I92,12 I10 42,13 I12 22,14,15 I16 22,15 I16 42,16 I22 42,17 and I29 3218 have been characterised structurally.Although these higher polyiodides can all be described on the basis of crystallographic structural data and spectroscopic studies19 as a combination of perturbed (slightly elongated) I2 molecules [I–I = 2.75–2.80 Å] with long-range interactions to I32 and I2 ions [I···I = 3.4–3.6 Å] their geometrical features can be very different. ‘Z’ and ‘S’-shaped chains have been found for I8 228 and I16 4216 units respectively; a ‘T’-bonding motif has been observed for I9212 whereas for I72 different arrangements from a twisted ladder in N-methyl-g-picolinium heptaiodide20 to a trigonal pyramidal shape in the iodonium salt [(N-methylbenzothiazole-2(3H)-thione)2I]I7,5 have been reported.Thus variation of the counter-cation leads to variation in counter-anion structures. Some of these polyiodides are present in the crystal lattice as discrete aggregates but they frequently tend to form polymeric one-dimensional chain structures or infinite three-or two-dimensional networks15,21–24 in which the identification of the basic polyiodide unit becomes arbitrary. In these cases the polyiodide arrays form ‘unusual supramolecular inorganic matrices’ (ref. 25 in ref. 15) and are better described as aggregates of I2 I2 and I32 entities held together by I···I bonding interactions of varying strengths from rather strong [ca.3.4 Å] to fairly weak [ca. 4.1 Å]. Some authors have recognised the nature (shape size and charge) of the cation as playing a crucial role on the structural and geometrical features of the associated polyiodide species. For example small cations in the crystal lattice tend to be associated wtric I32 ions whereas larger cations seem to induce a symmetrical shape.25 It is commonly accepted that large anions are stabilised best by large cations and Mertes et al.9,26 recognised the use of bulky metal macrocyclic complexes for the stabilization of unusual extended polyiodide species. They expected that the steric properties of the chosen aza-macrocyclic ligand would be more important than the nature of the metal ion in determining the nature of polyiodide ion.Indeed macrocyclic thioether complexes seem to be ideal reaction partners in the preparation of oligomeric anionic polyiodides since they are relatively chemically inert and their size shape and charge can be fine-tuned by changing either the metal ion or the thioether ligand. Furthermore thioether macrocycles are known as free ligands to form a range of charge-transfer (CT) adducts with I2.27 We describe in this review the synthesis and structures of a selection of unique polyiodide arrays using thioether macrocycle complexes28 as templating agents. For some of these structures it has been found necessary to consider I···I nonbonding contacts of lengths similar to the sum of the van der Waals radii for I2 [4.3 Å] in order to allow adequate description of the polyiodide lattice.The discussion has been organised into two sections. The first dealing with structural results has been divided into several subsections according to the chemical formula of the starting template metal macrocyclic complex used for the formation of the polyiodide array. In the second section an overview will be given of the information obtainable Chemical Society Reviews 1998 volume 27 196 from the use of the FT-Raman spectroscopy in the characterisation of polyiodide species; finally this background will be used to interpret the FT-Raman spectra of the polyiodides described. 2 Structural characterisation 2.1 [Ag([15]aneS5)]BF4 ([15]aneS5 = 1,4,7,10,13-pentathiacyclopentadecane) The co-ordination chemistry of AgI with [15]aneS5 has already attracted some attention because of the predicted stereochemical mismatch between the co-ordination preferences of the AgI ion (octahedral or tetrahedral) and the macrocycle (five coordinate).The structure of the [Ag([15]aneS5)]+ cation has been found to be dependent upon the nature of the counter-anion29 and we thought that this structural flexibility might be a useful attribute in a templating agent for polyiodide anions. S S S S S S S S S S S S S S [18]aneS6 [9]aneS3 [15]aneS5 H S S N S S S S S N S H [16]aneS4 [18]aneN2S4 O O O O O [15]aneO5 2.1.1 [Ag2([15]aneS5)2]I12 Reaction of [Ag([15]aneS5)](BF4) (prepared in situ from [15]aneS5 and AgBF4) with three molar equivalents of I2 in MeCN and slow evaporation of the solvent affords dark red plates.An X-ray crystal structure determination shows30 the asymmetric unit to consist of two independent [Ag([15]aneS5)]+ cations and a discrete I12 22 polyiodide anion interacting with each other through Ag–I bonds the two cations being located on the same side of the polyiodide anion (Fig. 1). The AgI ions are four co-ordinate with a very distorted tetrahedral geometry. Only three of the five potential S-donor atoms of the macrocyclic ligand are co-ordinated to each AgI ion [Ag–S = 2.593(6)–2.783(6) Å] and the fourth co-ordination site is occupied by an I2 ion [Ag–I = 2.781(3) 2.830(3) Å]. Fig. 1 View of [Ag([15]aneS5)]2I12.The asymmetric unit consists of two independent [Ag([15]aneS5)]+ cations and a discrete I12 22 polyiodide anion. The I12 22 polyiodide anion can be viewed as an almost linear I4 22 unit interacting at each of its termini with two di-iodine molecules to give an overall twisted ‘H’ configuration (Fig. 1) (the twisting angle between the two peripheral I2···I2···I2 fragments is ca. 40.3°). The I4 22 unit is built up from one diiodine molecule and two I2 and consequently the overall I12 22 polyiodide is best described as [2I2·5I2]. The I–I bond distances in the perturbed I2 molecules [2.755(2)–2.770(2) Å] are longer than that in I2 in the vapour [2.667(2) Å] or in the solid state [2.715(6) Å].19 This elongation is attributable to donation of electron density from I2 to the s*-antibonding LUMO of the I2 molecules with I2···I–I contacts ranging from 3.242(2) to 3.563(2) Å.2I12,14 I12 22 polyiodides are quite rare in the literature with only four examples being reported [K(Crypt-2.2.2)] (Me2Ph2N)2I12,15 [Cu(dafone)3]I12 (dafone = 4,5-diazafluoren-9-one),31 and (MePh3P)4I22.17 In these compounds the I12 22 polyiodides are crystallographically centrosymmetric and consist of two pentaiodide groups bridged through their central I2 by di-iodine molecules [I52···I2 = 3.360(2)–3.481(2) Å]; in the last compound two further end-on interacting pentaiodides [I52···I2 = 3.667(2) Å] give rise to an overall discrete I22 42 ion. In [Ag2([15]aneS5)2]I12 an extended three-dimensional superstructure is built up via a network of additional I···S interactions with the terminal iodine atoms [I(1) I(2) I(3) and I(4) in Fig.2] Fig. 2 View of [Ag2([15]aneS5)2]I12. I···S interactions link adjacent asymmetric units. I(1)···S(1) = 2.987(6) I(2)···S(2) = 3.131(6) I(3)···S(3) = 3.056(6) I(4)···S(4) = 3.498(6) Å. of each I2 unit interacting with one S-donor atom of four adjacent [Ag([15]aneS5)]+ cations. These interactions involve sulfur atoms unco-ordinated to AgI [I···S = 2.987(6)–3.131(6) Å] and sulfur atoms already bound to the metal ion [I···S = 3.498(6) Å] and generate spirals of I12 22 and [Ag([15]aneS5)]+ ions which alternate through the crystal lattice along the (001) direction with a distorted square projection in the (110) plane (Fig.3). 2.2 [Ag([18]aneS6)]BF4 [Ag([9]aneS3)2]BF4 ([18]aneS6 = 1,4,7,10,13,16-hexathiacyclooctadecane [9]aneS3 = 1,4,7-trithiacyclononane) Our postulate that the shape and the charge of the cation might play the main role in the assembly of the polyiodide anions led us to investigate [Ag([18]aneS6)]+ and [Ag([9]aneS3)2]+ as potential templates. The charge on these cations is the same as for [Ag([15]aneS5)]+ but the shape is very different with [Ag([18]aneS6)]+ and [Ag([9]aneS3)2]+ regarded as essentially spherical. Furthermore these AgI cations are octahedral and therefore co-ordinatively saturated with no further co-ordination sites available for I2 ions. The structures of the [Ag([18]aneS6)]+ and [Ag([9]aneS3)2]+ cations have been Fig.3 View of [Ag([15]aneS5)]2I12. Alternating I12 22 anions and [Ag([15]aneS5)]+ cations spiral along the (001) direction reported previously28 and show the AgI ion to have trigonally distorted octahedral co-ordination geometries. Reaction of [Ag([18]aneS6)]BF4 with three molar equivalents of I2 in CHCl3–MeNO2 (8 5 v/v) affords after the evaporation of the solvent in vacuo a dark-blue powder presumed to be [Ag([18]aneS6)]I5. Re-crystallisation of this product from MeCN and EtOH gives deep red crystals of [Ag([18]aneS6)]I7 and brown crystals of [Ag([18]aneS6)]I3 respectively. [Ag([18]aneS6)]I3 can also be prepared by metathesis of [Ag([18]aneS6)]BF4 with Bu4NI3 while addition of two molar equivalents of I2 to [Ag([18]aneS6)]I3 affords [Ag([18]aneS6)]I7 in high yield.Likewise the reaction of [Ag([9]aneS3)2]BF4 with I2 in MeCN affords [Ag([9]- aneS3)2]I5 crystals of which have been isolated by slow evaporation of the solvent. 2.2.1 [Ag([18]aneS6)]I7 The single crystal structure of [Ag([18]aneS [Ag([18]aneS polymeric polyiodide matrix of I 6)]I7 32 shows the 6)]+ cations embedded in a three-dimensional 72 anions (Fig. 4). The overall Fig. 4 View of {[Ag([18]aneS6)]I7}H structure of the [I72]H network can best be described as a distorted cube in which I2 ions occupy the lattice points of a primitive rhombohedral lattice with one slightly elongated I2 molecule [I–I = 2.7519(14) Å] placed along each edge bridging two I2 ions [I2···I2 = 3.3564(15) Å]. Each cube edge in this unique three-dimensional network (Fig.5) consists therefore of an I2···I–I···I2 arrangement and each I2 interacts with six molecules of I2 with a local D3d symmetry. None of the previously reported I72 polyiodide species exhibit a comparable cube-like structure. Before 1991 only two structurally characterised heptaiodide ions namely [NEt4]I7 23 and [(py)2I]I7 24 were known. Both of these show threedimensional networks of symmetrical I32 anions and I2 197 Chemical Society Reviews 1998 volume 27 Fig. 5 View of one cube-like array in {[Ag([18]aneS6)]I7}H 52·I2] molecules and are best described as adducts of the type [I32·(I2)2]. In 1992 Poli et al. reported4 the crystal structure of [PPh4]I7 as the first example of a discrete I72 ion but the presence of a significantly asymmetric I32 unit [I–I = 2.814(1) 3.07(1) Å] means that the [I32·(I2)2] description cannot be ruled out.The same might be said of the trigonal pyramidal heptaiodides in EtPh3PI7 and Bipy·HI7 reported by Tebbe et al.,21,22 the latter being better described perhaps as [I rather than [I32·(I2)2] or [I2·(I2)3] because of the pattern in the bonding-interactions between the central I2 and the three perturbed di-iodine molecules [I2···I2 = 3.089(3) 3.094(4) 3.440(4) Å]. In 1993 Devillanova et al. reported5 the first example of an I72 ion—in [(N-methylbenzothiazole -2(3H)-thione)2I]I7—which is a genuine [I2·(I2)3] adduct. This has approximate C3v symmetry and I–I distances within the 2 three perturbed I2 molecules ranging from 2.746(1) to 2.771(1) Å; the three I2···I interactions lie in the range 3.237(1)–3.260(1) Å.Only three other I72 ions with the same trigonal pyramidal geometry are known. In (Hpy)2I7I3,3 [Cu(OETTP)]I7 6 and [(H3O+·18-crown-6)]I7 7 one of the three I2···I2 interactions is either much longer or much shorter than the other two with a distance in the range 3.154(9) to 3.354(3) Å. These I72 anions can still be described as [I2·(I2)3] adducts but with approximate Cs symmetry. The I72 anions in (Hpy)2I7I3,3 and [(H3O+·18-crown-6)]I7,7 like the one in [(N-methylbenzothiazole-2(3H)-thione)2I]I7 5 are characterised by head-to-tail long-range interactions [3.426(3)–3.545(13) Å] of the I2 of one I72 unit with an I2 molecule of the next to give infinite one-dimensional chains.6)]+ cation in the The template effect of the [Ag([18]aneS formation of the unique cubic [I72]H structure may be rationalised by comparing the diagonals of the cube of iodines with the spacing of the S3 triangles making up the faces of the distorted co-ordination octahedron around AgI. The diagonal along the threefold axis of the cation is 11.850 Å while the other diagonals are 17.635 Å. The thickness of the cation may be estimated as the separation of the S3 triangles [2.48 Å] plus twice the van der Waals radius of the sulfur [1.85 Å] giving 6.18 Å. Its mean diameter may be considered as twice the mean distance of the carbon atoms from the threefold axis [3.55 Å] plus twice the van der Waals radius of carbon [1.50 Å] giving 72]H 10.10 Å.Therefore the [Ag([18]aneS6)]+ cations fit very well into the cubic second-sphere polyiodide framework. Conceptually therefore the formation of the cube-like [I matrix may be regarded as a second-sphere template reaction around a central metal-complex cation. 2.2.2 [Ag([18]aneS6)]I3 The structure of this complex shows [Ag([18]aneS6)]+ cations and symmetrical I32 ions [I–I 2.9137(3) Å] in the crystal Chemical Society Reviews 1998 volume 27 198 lattice.32 Fig. 6 shows parallel stacks of macrocycle complexes and I32 ions. This I32 salt may be considered a structural precursor to [Ag([18]aneS6)]I7 via the addition of two equivalents of I2 to [Ag([18]aneS6)]I3. Thus addition of I2 to [Ag([18]aneS6)]I3 converts a one-dimensional (1D) lattice of I32 to 2D and 3D lattices of I52 and I72 respectively.Unfortunately we have thus far been unable to crystallise the I52 salt of [Ag([18]aneS6)]+ due to its relative instability. Fig. 6 The single crystal structure of [Ag([18]aneS6)]I3; packing diagram in the (110) plane It is important to note the different structural modifications of the [Ag([18]aneS6)]+ cation observed in [Ag([18]aneS6)]PF6 [Ag([18]aneS6)]I7 and [Ag([18]aneS6)]I3. In all three cases the macrocyclic cation adopts a trigonally compressed octahedral geometry with S–Ag–S chelate angles of about 80° and nonchelate angles of about 100°. However in the I72 salt all the Ag–S distances are equivalent [2.754(2) Å] while the PF shows a tetragonal compression [Ag–S 2.753(4) Å]28 and the I 62 salt ax = 2.697(5) Ag–Seq = 32 salt a tetragonal elongation [Ag–Sax = 2.8007(10) Ag–Seq = 2.7255(7) Å].32 The cation is therefore able to modify its shape slightly thereby perhaps offering different templating effects to the polyiodide anion.3)2]I5 2.2.3 [Ag([9]aneS Although the [Ag([9]aneS3)2]+ cation has potentially the same shape dimensions and charge as [Ag([18]aneS6)]+ it does not show the same template effect under the same reaction conditions as above it forms an I52 salt rather than a cube-like [I72]H polyiodide array.30 The crystal structure shows [Ag([9]aneS3)2]+ cations and discrete V-shaped pentaiodide units. The cation shows very similar structural features to those already reported in other salts28 with two molecules of [9]aneS3 bound facially to the AgI metal centre conferring a distorted octahedral arrangement of six sulfur atoms.Each I52 unit is best described as an [I2·(I2)2] adduct [I–I = 2.7898(9) I2···I = 3.1118(9) Å I2···I2···I2 84.61(4)°] which is located on a plane perpendicular to the approximate threefold axis of the cation. The terminal atoms of each I52 unit interact weakly with one sulfur atom in each of two adjacent cations [I···S = 3.618(2) Å] so that a sinusoidal polymeric succession of cations and I52 ions develop along the (110) direction (Fig. 7). Each chain alternates with its inversion mate such that the chains pack efficiently. The chains themselves may be regarded as being disposed in phase even though their constituent anions and cations have been interchanged.2.3 [M([16]aneS4)](PF6)2 (M = Pd Pt) ([16]aneS4 = 1,5,9,13-tetrathiacyclohexadecane) In our attempts to synthesise unusual polyiodide arrays by using metal macrocycle complexes as template agents we have always obtained the metathesis product whenever Bun 4NI3 was used as starting material. In this way [M([9]aneS3)2](I3)2 (M = Ni Co Pd) [Pd([12]aneS4](I3)2 [Pd([15]aneN4)](I3)2 and [Ni([15]aneN4)(MeCN)2](I3)2 have all been synthesised and structurally characterised.33 All of these complexes show but with the cations and anions interchanged. Fig. 7 View of [Ag([9]aneS3)2]I5. Adjacent chains are related through inversions centres and may be regarded as being in phase with each other isolated I32 anions in the crystal lattice.However in the case of [M([16]aneS4)](PF6)2 (M = Pd Pt) the reaction with Bun 4NI3 in MeCN afforded unexpected products on slow evaporation of the solvent. These are isostructural and contain the binuclear cations [([16]aneS4)M–I–M([16]aneS4)]3+ (M = Pd Pt) involving a highly unusual linear M–I–M moiety in which an I2 bridges two MII centres symmetrically (Fig. 8).34 The M–I Pd([16]aneS4)]3+ cation template Fig. 8 View of 14-membered polyiodide belt at the [([16]aneS4)Pd–I– distances are relatively long [3.135(3) for Pd and 3.194(2) Å for Pt] so the I2 anion may be regarded as being trapped inside a pseudo cavity formed by two [M([16]aneS4)]2+ cations with the linear M–I–M bridge being imposed by the steric bulk of the tetrathioether crown.The [16]aneS4 ligand is bound via all four S-donors to the MII centres which are formally five co-ordinate in each cation. The M–S distances in [([16]aneS4)M– I–M([16]aneS4)]3+ lie in the range 2.300(10)–2.315(9) Å (Pd) and 2.332(3)–2.339(3) Å (Pt) and are slightly elongated compared to those of the parent [Pd([16]aneS4)]2+ and [Pt([16]aneS4)]2+ cations.28,35 The PdII and PtII centres lie 0.352 and 0.306 Å respectively out of the least-squares mean plane of their S4 donor sets in the direction of the bridging I2 ion. Interestingly this displacement is into the methylene manifold of the macrocycle the opposite to that observed for [Pd([16]aneS4)]2+ and [Pt([16]aneS4)]2+.28,35 The same counter-polyanion structure is present in both PdII and PtII complex crystal structures.The basic units of the polyiodide array are a I2 a distorted L-shaped I52 fragment which can be described either as [I2·(I2)2] or as [I32·I2] and a highly asymmetric I32 moiety. In fact choosing the first description the I–I bond distances in the two perturbed I2 molecules [I(1)–I(2) I(4)–I(5)] are 2.798(2) and 2.836(2) Å whereas the associated I2···I2 bond lengths are 3.409(2) [I(2)–I(3)] and 3.044(2) Å [I(3)–I(4)] respectively. The I2–I(3)– I2 angle is approximately 90° as normally found in discrete L-shaped I52 units. The I52 units are connected to each other through contacts of 3.806(2) Å between two perturbed I2 molecules to form planar zig-zag polymeric chains (Fig. 9); two of these chains flank a row of cations and are linked by pairs of bond-interactions [I(5)···I(6) = 3.285(2) Å] between an iodide [I(6)] and two terminal iodine atoms from two I52 units.Considering the reasonably short I2···I52 bond lengths an Fig. 9 View of [([16]aneS4)Pd–I–Pd([16]aneS4)]3+·I11 32 showing the 14-membered polyiodide rings fused to give an infinite polycyclic ribbon. Starred atoms identify the basic I11 32 unit. I(1)–I(2) = 2.798(2) I(2)– I(3) = 3.409(2) I(3)–I(4) = 3.044(2) I(4)–I(5) = 2.836(2) I(5)– I(6) = 3.285(2) Å. overall and unique I11 32 can be identified as a basic unit of the resulting polyiodide array (Fig. 9). An infinite polycyclic ribbon is therefore built up of 14-membered polyhalide rings sharing three iodine atoms.Each ring measures 9.657 by 12.640 Å (diagonal length 16.383 Å) and surrounds a binuclear metal cation with the M–I–M bridging I2 placed exactly at its centre (Figs. 8 and 9). Therefore the central complex cation may be regarded as acting as a template for the synthesis of this unique cyclic polyhalide array in which the binuclear complex cation sits. 2.4 [Pd2Cl2([18]aneN2S4)](PF6)2 ([18]aneN2S4 = 1,4,10,13-tetrathia-7,16-diazacyclooctadecane) On the basis of the results obtained with [M([16]aneS4)](PF6)2 (M = Pd Pt) the binuclear complex [Pd2Cl2([18]- aneN2S4)](PF6)2 having the same overall charge but different shape was treated with Bun 4NI3 in MeCN solution. After several days two different crystal morphologies black facetted prisms and brown elongated plates were obtained and X-ray diffraction studies undertaken to determine their structure.2.4.1 [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2 For the black prisms the asymmetric unit consists of one I52 and two I32 ions and 1.5 [Pd2Cl2([18]aneN2S4)]2+ dications.36 The structure of the cations is similar to that in the corresponding PF62 salt.37 The PdII ions are each co-ordinated to one Nand two S-donor atoms with a Cl2 ligand completing the square planar co-ordination. The two co-ordination planes lie parallel to each other but the overall binuclear dication adopts a stepped conformation in order to minimise steric interactions. Interestingly the dications are linked by an extensive network of hydrogen bonds between the (N)H and Cl atoms to form infinite chains in the crystal lattice [N···Cl = 3.254(14)–3.356(12) (N)H···Cl = 2.57 Å].The intra-cation Pd···Pd distances are 4.055(2) and 4.155(2) Å while the Pd–Pd distances between adjacent cations are significantly shorter [3.449(2) 3.463(2) Å] (Fig. 10). Fig. 10 View of cation in [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2 The infinite chains of binuclear dications are embedded into a unique polyiodide matrix whose fundamental units are one L-shaped I52 ion consisting of an asymmetric I32 [I(1)–I(2) = 2.845(2) I(2)–I(3) = 3.045(2) Å < I(1)–I(2)–I(3) = 179.69(9)°] and a di-iodine molecule [I(10)–I(11) = 2.775(3) Å] linked by I(3)–I(10) = 3.349(2) Å and forming an I(2)–I(3)– 199 Chemical Society Reviews 1998 volume 27 I(10) angle of 90.00(6)° and two slightly asymmetric I32 ions [I(4)–I(5) = 2.904(2) I(5)–I(6) = 2.959(2) Å I(4)–I(5)–I(6) = 176.47(6)°; I(7)–I(8) = 2.948(2) I(8)–I(9) = 2.929(2) Å I(7)–I(8)–I(9) = 171.58(5)°].The I32 ions including those belonging to the I52 units lie on parallel planes and form unprecedented continuous planar two-dimensional layers. Each layer [Fig. 11(a)] consists of alternating fused ribbons of 14-membered and 24-membered rings with contacts among the Fig. 11 (a) View of polyanion in [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2 showing two-dimensional layers comprising linked I32 anions form alternating fused ribbons of 14-membered and 24-membered rings. I(1)–I(2) = 2.845(2) I(2)–I(3) = 3.045(2) I(4)–I(5) = 2.904(2) I(5)–I(6) = 2.959(2) I(7)–I(8) = 2.948(2) I(8)–I(9) = 2.929(2) I(10)–I(11) = 2.775(3) I(3)–I(10) = 3.349(2) I(3)···I(6) = 4.217(2) I(3)···I(7) = 4.184(2) I(6)···I(7) = 4.006(2) I(1)···I(9i) = 3.812(2) I(4)···I(4ii) = 4.017(2) I(9)···I(9iii) = 3.758(2) I(6)···I(11iv) = 3.579(2) Å.Symmetry operations i = x 2 1 y 2 1 1 + z; ii = 1 2 x 1 2 y 1 2 z; iii = 2 2 x 1 2 y 2z; iv = 2 2 x 2y 1 2 z. (b) Alternate view of polyanion in [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2. The poly-I32 layers are linked by di-iodine bridges which link two 14-membered rings through a 24-membered ring. Open circles identify the basic I8 22 unit. Chemical Society Reviews 1998 volume 27 200 I32 ranging from 3.758(2) to 4.217(2) Å. Pairs of parallel I2 molecules [I2···I2 = 4.257(2) Å] from two symmetry-related I52 fragments lie orthogonal to the two-dimensional layers and connect two of these by passing through the centres of the 24-membered rings of a third layer located in between them [Fig.11(a) and (b)]. The connection of two alternating layers takes place through an I52···I32 interaction of 3.573(2) Å so that an overall I8 22 [shown as open circles in Fig. 11(b)] can be envisaged as the yarn interlocking the infinite two-dimensional poly-I32 sheets. The 24-membered rings of each layer measure ca. 25.31 3 13.31 Å the dimensions of each half [ca. 12.65 3 13.31 Å] are similar to those of the 14-membered rings [ca. 12.18 314.73 Å] resulting in channels along the body diagonal of the unit cell. These channels are occupied by the chains of hydrogen-bonded binuclear complexes described above (Fig.10) to give a pseudo-rotaxane structure (Fig. 12) and it appears that it is these chains rather than the individual dication which act as the template for the polyiodide architecture.36 Fig. 12 View of overall structure of [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2. Chains of [Pd2Cl2([18]aneN2S4)]2+ dications occupy channels in the threedimensional polyiodide network in [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2. 2.4.2 [Pd2Cl2([18]aneN2S4)](I3)2 The elongated plates obtained from the same reaction above give a much simpler structure even although the complex cation is the same.33 The asymmetric unit consists of half of a 2Cl2([18]- 2S4)]1.5I5(I3)2 but it does not generate infinite poly-cation [Pd2Cl2([18]aneN2S4)]2+ cation and one slightly asymmetric I32 anion [I(1)–I(2) = 2.8649(6) I(2)–I(3) = 2.9889(5) Å < I(1)–I(2)–I(3) = 174.55(2)°].The geometry of the dinuclear PdII complex is similar to that observed in [Pd aneN chains through hydrogen-bonding. Instead the I32 ions form polymeric sinusoidal chains in the crystal lattice via head-to-tail I32···I32 interactions of 4.0236(6) Å. These chains propagate along the (100) direction and are linked together by dinuclear Pd complex units via Pd···I contacts of 3.5429(6) Å [Fig. 13(a) (b)]. As shown in Fig. 13(a) the dications are arranged in an alternating side-to-side arrangement along the poly-I32 chains giving rise to infinite two-dimensional undulating layers [Fig. 13(b)]. 5)5]I12 {[M([16]aneS2)]2I}(I5)2I (M = Pd Pt) and 2.5 [RhCl2([16]aneS4)]PF6 The RhIII complex [RhCl2[16]aneS4]+ allowed variation of both the overall charge of the metal cation and its shape compared to the above PdII and PtII complexes.In fact the presence of the two co-ordinated chloride ligands gives an overall ellipsoidal shape to the [RhCl2([16]aneS4)]+ cation and furthermore does not allow interactions between the metal centre and I2 or I2. Such interactions are observed in the structures of [Ag2([15]- aneS [Pd2Cl2([18]aneN2S4)](I3)2 described above and may play an important role in the overall organization of these polyiodide arrays. The reaction of [RhCl2([16]aneS4)]PF6 with three molar 2 in MeCN solution afforded dark crystalline equivalents of I blocks after slow evaporation of the solvent.A structure determination showed the compound to have the formulation [RhCl2([16]aneS4)]I5I2.33 As for its parent PF62 complex,28 the RhIII ion has a distorted octahedral geometry being bound to all 52 four S-donors of the thioether macrocycle in an equatorial plane and to two chloride ligands in trans-axial positions [Rh–S = 2.352(4)–2.361(4) Rh–Cl = 2.330(3) Å]. The [RhCl2([16]aneS4)]+ cations are encapsulated within a threedimensional polymeric polyiodide matrix made up of I52 anions and slightly elongated I2 molecules [I(6)–I(7) = 2.732(2) Å]. The I52 ions consist of an asymmetric I32 [I(3)–I(4) = 2.962(2) I(4)–I(5) = 2.884(2) Å < I(3)–I(4)–I(5) 175.18(5)°] and a di-iodine molecule [I(1)–I(2) 2.752(2) Å] linked by I(2)–I(3) [3.172(2) Å] and forming an angle I(2)–I(3)–I(4) of 103.01(5)° (Figs.14 and 15). Puckered anionic layers can be identified within the polyiodide network in the crystal lattice. They are composed of I32 from the I52 fragments and the I(6)–I(7) di-iodine molecules to form 4- 10- and 12-membered polyiodide rings through I···I interactions of 3.336(2)–4.133(2) Å (Fig. 14). These two-dimensional infinite sheets stack along the (001) direction such that the 10-membered rings in one layer lie approximately above and below the 12-membered rings of the adjacent layers. The I(1)–I(2) molecules from the I fragments link consecutive anionic layers through I···I bridging interactions of 4.106(2) Å to form very irregular cages (Fig. 15). The four vertical edges of each cage are made up of four bridging I2 units whereas the upper and lower faces each consists of one four- and one ten-membered ring.The cages have dimensions ca. 11.14 3 9.09 3 8.03 Å and the guest [RhCl2([16]aneS4)]+ cation is located centrally within this cavity. 2.6 [K([15]aneO5)2]I ([15]aneO5 = 1,4,7,10,13-pentaoxacyclopentadecane) In order to determine whether other types of metal macrocyclic complexes could have the same templating effect on the selfassembly of polyiodide arrays we treated the potassium complex [K([15]aneO5)2]I with an excess of I2 in MeCN. After a few days dark crystals were obtained by slow evaporation of the solvent. The crystal structure determination established the formulation [K([15]aneO5)2]I9.36 Within the cation two molecules of the crown ether sandwich one K+ ion within a ten coordinate environment with K–O bond distances in the range 2.62(2)–3.21(2) Å.These cations are embedded into a threedimensional polyiodide matrix made up of nona-iodide units (Fig. 16). Each I92 ion can be described as an [I32·(I2)3] chargetransfer complex with the three perturbed I2 molecules showing intermolecular distances ranging from 2.716(3) to 2.740(4) Å and interacting with the slightly asymmetric I32 [I(7)–I(8) = 2.874(3) I(8)–I(9) = 2.978(3) Å < I(7)–I(8)–I(9) = 178.2(1)°] through bonding contacts of 3.396(4)–3.503(4) Å. Two of the three I2 molecules [I(5)–I(6) and I(3)–I(4)] and the I32 ion [I(7)–I(8)–I(9)] lie approximately in the same plane whereas the third I2 molecule [I(1)–I(2)] is perpendicular to it [ < I(1)–I(9)–I(8) = 92.4 < I(1)–I(9)–I(3) = 97.6°].This configuration for the I92 polyiodide ions allows them to form a three-dimensional network of puckered cube-like cages through I···I interactions of 3.732(4)–4.074(4) Å (Fig. 17). Each cage measures 9.658 3 9.521 3 9.959 Å the diagonals across are 17.371 and 17.393 Å and the [K([15]crownO5)2]+ cations lie almost at the centre of the cages. This polyiodide array is surprisingly similar to the ideal cubic polyiodide network in [Ag([18]aneS6)]I7 the main difference being the extra I2 molecule of the I92 ion located in the middle of the lower face of each cage reflecting the different topologies of the AgI and KI complexes (Fig. 5 and 17).There is therefore a clear link between the templating of I72 vs. I92 anions. The puckered cube-like cages are arranged in a centred lattice and in projection along the crystallographic (100) axis each cage can be seen to lie above the midpoint of four cages in the layer below. Furthermore it is clear that the concept of self-assembly of polyiodide arrays is not restricted to transition metal thioether and aza macrocyclic complexes but can in principle be extended to any complex cationic system. 201 Chemical Society Reviews 1998 volume 27 Fig. 13 (a) View of [Pd2Cl2([18]aneN2S4)](I3)2 showing polymeric sinusoidal chains of I32 ions cross-linked by [Pd2Cl2([18]aneN2S4)]2+ dications I(1)–I(2) = 2.8649(6) I(2)–I(3) = 2.9889(5) Å. (b) View of [Pd2Cl2([18]aneN2S4)](I3)2 projection onto the (011) plane.Fig. 14 View of polyanion in [RhCl2([16]aneS4)]I5I2 showing the puckered anionic layer within the polyiodide network sharing 4- 10- and 12-membered rings I(5)···I(7i) = 3.336(2) I(5)···I(7ii) = 4.133(2) I(3)···I(3iii) = 3.871(2) Å. i = 2x 1 2 y 2z; ii = x 2 1 + y z; iii = 1 2 x 1 2 y 2z. Chemical Society Reviews 1998 volume 27 202 3 FT-Raman spectroscopy When dissolved in solvents such as CHCl3 CH2Cl2 CCl4 and heptane I2 normally interacts with molecules (D) containing Group V and Group VI donor elements (N P O S Se) to give charge-transfer (CT) complexes via an acid–base equilibrium reaction.38 In the solid state a variety of products is observed (D·I2 C–T complexes D·nI2 C–T complexes hypervalent compounds characterised by the I–D–I group iodonium salts polyiodides and mixed-valence compounds) depending upon the nature of the donor atom the solvent and the reaction molar ratio.5,38 This great variability of products calls for other techniques for their identification; this is particularly necessary when X-ray crystal structure determination is not available.Raman spectroscopy has been used widely for this purpose and it provides a simple way to obtain qualitative information on the nature of iodine in the crystal lattice. Fig. 15 View of [RhCl2([16]aneS4)]I5I2 showing the puckered polyiodide cages enclosing the metal cations I(1)–I(2) = 2.752(2) I(2)–I(3) = 3.172(2) I(1)···I(7iv) = 4.106(2) I(3)–I(4) = 2.962(2) I(4)–I(5) = 2.884(2) I(3)···I(6) = 3.776(2) I(6)–I(7) = 2.732(2) Å iv = 1/2 + x 1/2 2 y 1/2 + z Fig.16 View of [K([15]aneO5)2]I9 along the crystallographic c axis In the past resonance Raman (RR) spectroscopy has been widely employed and the assignment of typical spectra to polyiodides have been generally made on model compounds which had been previously structurally characterized by X-ray diffraction.19 However RR uses visible laser excitation sources which may induce fluorescence sample pyrolysis or photoreactions so that spurious peaks can appear in the spectrum.19 This is a real possibility for polyiodides which absorb strongly in the visible region (where RR laser sources emit) and those with and the formation of I high iodine content are potentially prone to decomposition to give I2 I2 and I32 as final products.19 This decomposition causes changes in the Raman spectrum due to elimination of I2 32 which may be incorrectly assigned to the starting polyiodide material.Recently introduced Fourier transform Raman spectrometers use a near-infrared laser excitation source and thereby reduce or eliminate the above problems so that the resulting spectra can be more confidently attributed to the starting compound.19 Fig. 17 View of one polyiodide cage in [K([15]crownO5)2]I9 I(1)–I(2) = 2.740(4) I(3)–I(4) = 2.716(3) I(5)–I(6) = 2.728(4) I(7)–I(8) = 2.874(3) I(8)–I(9) = 2.978(3) I(1)···I(9) = 3.503(4) I(3)···I(9) = 3.396(4) I(7)···I(6) = 3.346(4) Å 3.1 Neutral charge-transfer complexes The n(I–I) Raman band at 180 cm21 for I2 in the solid state [d(I–I) = 2.715 Å] is expected to move to lower frequencies when I2 interacts with donor molecules to form CT-adducts.Donation of electron density occurs from a non-bonding orbital on the donor atom into the LUMO of the I2 molecule as this LUMO is an antibonding s* orbital lying along the interatomic axis the net bond order decreases and a longer bond distance is observed within the perturbed I2 molecule. The lowering of the FT-Raman frequencies n(I–I) upon formation of CT complex occurs for all the adducts in which the I2 unit can be considered a perturbed diatomic molecule (weak or medium-weak complexes) irrespective of the nature of the donor atom. In this case a linear relationship has been found to exist between the FTRaman frequencies n(I–I) and the d(I–I) bond distances.39 In order to differentiate weak or medium-weak adducts from strong complexes a useful criterion is based on the value of the I–I bond order (n) calculated as a function of the I–I bond lengthening according to the equation d = do 2 clogn (d and do are the I–I bond distances in co-ordinated and free I2 respectively and c = 0.85 Å is an empirical constant).39 For values of n higher than 0.6 the I2 moiety in the CT complexes may be considered a perturbed diatomic molecule and a band in the range 180–150 cm21 is expected in the FT-Raman spectrum.This hypothesis is supported by the observation that polyiodides which may be described as weak or medium-weak adducts of the type I2·(I2)n give very similar FT-Raman spectra and the recorded frequencies fit the linear correlation n(I–I) versus d(I–I).19 When the interaction between a donor molecule and I2 is strong (0.4 < n < 0.6) as in the case of adducts with selenium-containing molecules or in symmetric triiodide only by describing the D–I–I vibrating group as a three-body system is it possible to predict and/or assign the FT-Raman spectrum.19 3.2 Triiodides and other higher polyiodide species In the linear and symmetric I32 anion the Raman-active symmetric stretch (n1) occurs near 110 cm21 while the antisymmetric stretch (n3) and the bending deformation (n2) are only infrared-active. The latter two may also become Ramanactive if a distortion of the I32 occurs in which case they are normally found near 130 (n3) and 70 cm21 (n2) having medium and medium-weak intensities respectively.19,39 For highly asymmetric I32 ions [I2·I2] as found in neutral CT adducts the FT-Raman spectrum shows only one strong band in the range 180–150 cm21 indicative of a perturbed I2 molecule.39 203 Chemical Society Reviews 1998 volume 27 On the basis of structural determinations all the higher 52 to I16 42) may be regarded as weak polyiodide species (from I or medium-weak adducts of the type [I2·(I2)n] or [I32·(I2)n].Consequently the corresponding FT-Raman spectra will show peaks due to perturbed di-iodine molecules for [I2·(I systems and characteristic peaks due to both perturbed diiodine molecules and symmetric or slightly asymmetric I32 ions for polyiodides describable as [I32·(I2)n].39 It is therefore evident that except for symmetric I32 cases the Raman technique is unable to distinguish between the different types of polyiodides or to discriminate unambiguously between the polyiodides and the neutral adducts.However it can give valuable information on the extent of the lengthening of the I–I bond whether or not it has been produced by interaction with a neutral donor or an ion. FT Raman spectroscopy cannot give any structural information on the nature of an extended polyiodide matrix as the technique cannot elucidate the Table 1 Structural and Raman parameters for some representative polyiodides and for the polyiodides arrays synthesised by using metal macrocycle complexes as templating agents Polyiodide anion I32 (very asymm.) I52 (bent) I52 (bent) I72 I16 42 I12 22 I52 I72 I52 I52 + I32 I32 I52 + I2 I92 131 w 109 w a For polyiodides not described herein see refs 19 and 39.b Note br = broad s = strong m = medium w = weak br = broad. c The I–I bond order (n) e has been calculated using the equation d = do-clogn (do = 2.67 Å c = 0.85) ref. 19. d (EtNH2)dtl = 3,5-bis(ethylamino)-1,2-dithiolylium. moH = morpholinium. f modtc = morpholinecarbodithioato. g bntSeMe = N-methylbenzothiazole-2(3H)-selone. h mo2ttl = 3,5-bis(N-morpholinio)- 1,2,3-trithiolate. Chemical Society Reviews 1998 volume 27 204 Compounda [(EtNH2)dtl]I3 d [moH]I5 e [Mn(modtc)3]I5 f [bntSeMe)2I]I7 g [mo2ttl]2I16 h [Ag2([15]aneS5)2]I12 [Ag([9]aneS3)2]I5 [Ag([18]aneS6)]I7 [(M([16]aneS4))2I](I5)I (M = Pd Pt) [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2 [Pd2Cl2([18]aneN2S4)](I3)2 [RhCl2[16]aneS4)]I5I2 [K([15]aneO5)2]I9 2)n] structure beyond the basic polyiodide unit in terms of combinations of I2 I2 and I32 fragments.In Table 1 the I–I distances the bond orders and the proposed combinations of I2 I2 and slightly asymmetric I32 are collected for some polyiodides reported in the literature19,39 as well as for the polyiodides described herein. For every compound the recorded FT-Raman spectrum is in accordance with the structural features of the basic polyiodide unit as given in the last column on the right. Further information may be extracted from the FT Raman spectrum of [Ag([18]aneS6)]I7 in which each I2 interacts with six I2 molecules arranged in D3d symmetry.Because all six I2 molecules have the same I–I bond distance only one band should be present in the FT Raman spectrum below 180 cm21. However the stretching vibrations of the six individual I2 units can combine and in D3d symmetry give rise to two Raman-active normal modes of A1g + Eg types. The 179 and 165 cm21 bands can therefore be assigned to A1g Raman data (cm21)b 167 s 164 s 135 m 106 mw 165 s 143 s 175.2 m 157.4 s 174 s 139 m 112 mw 161 ms 172 br s 162 s 151 s 179 m 165 s 157 s 149 m 168 w 147 w 138 w 108 s 130 s 108 w 172 s 126 w 107 w 180 br s Bond orderc X-Ray d(I–I)/Å 0.82 0.28 0.74 0.58 0.44 0.80–0.81 0.68–0.65 0.30–0.38 0.25–0.23 0.81 0.77 0.76 0.83 0.60 0.44 0.65 0.39 0.79 0.79 0.78 0.77 0.76 0.72 0.30 0.80 0.16 0.71 0.64 0.14 0.36 0.75 0.62 0.36 0.16 0.53(0.50) 0.46(0.47) 0.59 0.42 0.85 0.80 0.45 0.56 0.88 0.85 0.83 0.58 0.43 2.714 3.141 2.783 2.872 2.973 2.750–2.759 2.810–2.827 3.117–3.031 3.186–3.216 2.746 2.766 2.771 2.741 2.858 2.976 2.827 3.018 2.755 2.756 2.760 2.768 2.770 2.790 3.112 2.752 3.357 2.798 2.836 3.409 3.044 2.775 2.847 3.045 3.349 2.904(2.929) 2.959(2.948) 2.865 2.989 2.732 2.752 2.962 2.884 2.716 2.728 2.740 2.874 2.978 Comments I2·I2 I2 I32 (asymm.) I2·2I2 I2·3I2 (C3v symm.) I2 I32 (asymm.) I2·I2 2I2·5I2 I2·2I2 (C2v symm.) I2·3I2 (D3d symm.) I2·2I2 I2·2I2 I32 (sl.asymm.) I32 (asymm.) I2 + I32·I2 I32 (asymm.) I2 I32 (asymm.) g modes respectively. It is important to note that the 2 and E Raman spectrum of [Ag([18]aneS6)]I7 is very similar to that recorded for [(butSeMe)2I]I7 in which the I72 unit has an approximate C3v symmetry describable as [I2·(I2)3]. In the C3v point group the stretching vibrations of the three individual I molecules combine to give normal modes of A1 + E type.A slight distortion of the symmetry from C3v to Cs may redistribute the contribution of the individual I2 groups the shorter I2 unit giving a greater contribution to the higher frequency band and the longer I2 units to the lower frequency band.5 Similarly the case of the I52 ion with a C2v symmetry in [Ag([9]aneS3)2]I5 can be tackled; the vibrations of the two individual I2 units combine to give normal modes of the A1 + B2 types. A lowering of the symmetry due to different bond distances for the two perturbed I2 units will increase the energy of the higher and lower the energy of the lower energy stretch. 32 The extended interactions in the crystal lattice can play an important role in determining the intensities of the FT-Raman bands.Indeed quite surprisingly in the Raman spectrum of [Pd2Cl2([18]aneN2S4)]1.5I5(I3)2 a lower intensity is found for the peaks due to the perturbed I2 molecules compared to the intensity of the peak assigned to the symmetric stretch of the I units at 108 cm21. The FT Raman spectra have also been recorded after mixing solutions of the metal complex and diiodine for several hours. The presence of only the broad peak at around 208 cm21 due to I2 in solution clearly indicates that the template effect of the metal macrocyclic complexes takes place during the crystallization process. 4 Conclusions Although extended oligomeric anionic polyiodides are a well established aspect of the chemistry of I2 no attempts have been made previously to control their geometrical features by tuning the size shape and charge of the cation partner.On the grounds that large anions tend to be stabilised by large cations we thought that thioether macrocyclic complexes could be useful templating agents for extented polyiodide arrays they are relatively inert species and their size shape and charge can be varied readily through changes of the metal ion the macrocyclic crown and co-ligands. The results presented in this review clearly show our aim partially fulfilled. Undoubtedly the shape of the cation plays the major role on the overall templating effect. For example essentially spherical cations such as [Ag([18]aneS6)]+ and [K([15]aneO5)2]+ appear to be good template agents for cage-like polyiodide arrays.However longrange S···I and metal···I contacts can tip the balance and lead to different geometrical motifs in the resulting polyiodide arrays. The synthetic approach also has its own importance; the use of an excess of I2 instead of preformed I32 or I52 salts is recommended in the first instance with the preferred polyiodide nuclearity being formed by self-assembly. Once the preferred nuclearity is known high yielding routes can be developed by the use of preformed I32 or I52 salts and titration with I2. The use of thioether macrocyclic and related protected complexes appears to be a promising way to template-synthesize extended polyiodide matrices and to control their geometrical features. Moreover these results suggest that shape-selectivity can be achieved via template synthesis of for example helicate polyanions at helicate metal-complexes and related hosts.5 Acknowledgements We thank the EPSRC and the University of Nottingham for support. Figures 4 5 12 and 16 have been reproduced with permission. 6 References 1 K.-F. Tebbe in Polyhalogen cations and Polyhalide Anions. Homoatomic Rings Chains and Macromolecules of Main-Group Elements ed. A. L. Rheingold Elsevier Amsterdam 1977 p. 551. 2 J. R. Ferraro and J. M. Williams in Introduction to Synthetic Electrical Conductors Academic Press New York 1987. 3 T. L. Hendixson M. A. ter Horst and R. A. Jacobson Acta Crystallogr. Sect. C 1991 47 2141. 4 R. Poli J. C. Gordon R. K. Khanna and P. E. Fanwick Inorg. Chem. 1992 31 3165.5 F. Demartin P. Deplano F. A. Devillanova F. Isaia V. Lippolis and G. Verani Inorg. Chem. 1993 32 3694. 6 M. W. Renner K. M. Barkigia Y. Zhang C. J. Medforth K. M. Smith and J. Fajer J. Am. Chem. 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