Isostructural Salts Research Articles

Bilayer Mott System Based on Ni(dmit)2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate) Anion Radicals: Two Isostructural Salts Exhibit Contrasting Magnetic Behavior

A new class of Ni(dmit)(2) anion radical salt (Et-2,5-DBrP)[Ni(dmit)(2)](2) (1) (Et-2,5-DBrP = ethyl-2,5-dibromopyridinium) was developed. Single-crystal X-ray diffraction analysis indicates that this salt contains two crystallographically independent anion layers in the crystal with effective Br···S halogen bonds between the cation and the anion. The crystal and electronic structures, and electrical and magnetic measurements reveal that 1 is a novel bilayer Mott system, in which two different Mott-insulating anion layers coexist in one crystal. Selective halogen substitution of Br with I at the 2-position in the cation affords the isostructural bilayer salt (Et-2I-5BrP)[Ni(dmit)(2)](2) (2) (Et-2I-5BrP = ethyl-2-iodo-5-bromopyridinium), while substitution at the 5-position results in a structural change, yielding the monolayer salt (Et-2Br-5IP)[Ni(dmit)(2)](2) (3) (Et-2Br-5IP = ethyl-2-bromo-5-iodopyridinium). These results indicate that the halogen bond plays an important role to realize the bilayer system, and that the crystal structure is controlled by tuning the strength of the halogen bond. The low temperature magnetic properties of the two isostructural salts 1 and 2 are significantly different, because they are affected by fluctuated spins that do not participate in the formation of short-range antiferromagnetic domains. The bilayer salt generates the fluctuated spins more easily than conventional monolayer salts, and such fluctuated spins are expected to result in unique physical properties.

Exploring supramolecular interactions between inorganic tetrachlorometallate and organic pyridinium dication: Synthesis, characterization and structural investigations

Abstract The crystal structures of three isostructural salts 2, 3 and 4 consisting of dication (α,α′-p-xylylene-N,N′-bis(3-hydroxymethylpyridinium) (L2+)), and tetrachlorometallates, [MCl4]2− (M = Co(II), Zn(II) and Cu(II) in 2, 3 and 4 respectively) have been reported. Synthesized salts are well characterized by various physico-chemical techniques such as CHN analysis, IR, TGA, DSC, NMR, PXRD and single crystal X-ray diffraction. The crystal lattice of complex 2 is constructed from two types of interactions viz., C–H⋯Cl and O–H⋯Cl H-bonding between the pyridinium dication and the complex anions [CoCl4]2−, whereas only C–H⋯Cl interaction was found to play major role in stabilizing the structures of organic inorganic hybrid complexes 3 and 4. The hierarchy of intermolecular interactions present in solid state, factors controlling the adopted structures of these compounds and their thermal stability are discussed in detail by using various analytical techniques including single crystal X-ray.

Infrared and Raman studies of the anion ordering transitions in paramagnetic organometallic radical cation salts [Cp2Mo(dmit)]X (X = PF6, SbF6)

Temperature dependence of infrared and Raman spectra of the two isostructural salts [Cp2Mo(dmit)]PF6 and [Cp2Mo(dmit)]SbF6 is studied. At room temperature the physical properties of both compounds are very similar but at lower temperatures they undergo phase transitions associated with anion ordering, which are surprisingly different. The phase transitions in [Cp2Mo(dmit)]PF6 salt at T1=120K and T2=89K have no important influence on infrared and Raman spectra, while the phase transition in [Cp2Mo(dmit)]SbF6 salt at T1=175K causes a splitting of Raman bands assigned to the CC stretching at about 1334cm−1 and the in-plane Mo(dmit) ring deformation at about 353cm−1, and also an infrared band at about 939cm−1 related to the C–S stretching. The splitting of vibrational bands demonstrates a clear distortion of [Cp2Mo(dmit)]+ cations in the [Cp2Mo(dmit)]SbF6 salt. This molecular distortion is related to a lattice distortion providing thus a good argument for applicability of the compressible model of the anion ordering transition.

X‐ray Structures, Spectroscopic and Magnetic Studies of a Coordination Polymer Series Based on a TTF Derivative and Paramagnetic Transition Metals

AbstractThe oxidation of 2,3,6,7‐tetrakis(2‐cyanoethylthio)tetrathiafulvalene (TCE‐TTF) with hexafluoroacetylacetonate (hfac) salts of paramagnetic (CoII, MnII) and diamagnetic (ZnII, CdII) ions in the presence of tetrahedral anions (BF4– and ClO4–) resulted in the isolation of four isostructural salts. The structure of these salts revealed an infinite two‐dimensional network due to the coordination of the nitrilo arms of TCE‐TTF to the metal. Short interplanar S···S interactions between two planes involving TCE‐TTF give a third dimension to this polymer. TTF ligands are fully oxidized, and hence these materials show semiconducting behaviour. Spectroscopic and magnetic studies of the paramagnetic‐transition‐metal‐containing polymers are also presented.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Room-Temperature First-Order Phase Transition in a Charge-Disproportionated Molecular Conductor (MeEDO-TTF)2PF6

Electrochemical oxidation of 4,5-ethylenedioxy-4′-methyl-tetrathiafulvalene (MeEDO-TTF) afforded three types of (MeEDO-TTF)2PF6 radical cation salts under different conditions: black powder, dark green plates, and black plates. The optical absorption spectra of these modifications were very similar to each other. The black powder and dark-green plate modifications were semiconducting and metallic, respectively, and the latter showed a semiconducting behavior below 200 K. The black plate modification exhibited a semiconductor-to-semiconductor first-order phase transition at around room temperature (303 K). The donor molecules in both the high- and low-temperature phases of this modification showed similar packing patterns, based on which the tight-binding approximation afforded similar two-dimensional Fermi surfaces. The phase transition of this modification is accompanied by a subtle change in the relative orientation of the neighboring donor molecules. The vibrational spectra proved that a nearly localized charge disproportionation takes place in the high-temperature phase and the distinct charge disproportionation is developed in the low-temperature phase. These results indicate that the slight lattice distortion assists the stabilization of charge disproportionation. The comparison of the isostructural salts of metallic (MeEDO-TTF)2X (X = BF4, ClO4) and the semiconducting high-temperature phase of the (MeEDO-TTF)2PF6 demonstrated that the side-by-side intermolecular interaction is most effectively modulated according to the anion size. The unit cell parameter corresponding to this intermolecular interaction was varied only ca. 2% among these isostructural salts. This observation demonstrates the very sensitive nature of the transport property to the lattice modulation.

Coexistence of Quasi-One- and -Two-Dimensional Electronic Structures in (EDO-TTF)2X (X = GaCl4, ReO4)

Crystal structures and physical properties of (EDO-TTF)2X where EDO-TTF=ethylenedioxytetrathiafulvalene, X=GaCl4 and ReO4 were investigated. These isostructural salts belonged to triclinic system with space group P1, and. two kinds of the donor layers coexisted in a crystal. EDO-TTF formed head-to-tail and head-to-head type columnar structures in each donor layer, for which quasi-one- and -two- dimensional Fermi surfaces were calculated, respectively.

An aqueous route to [Ta6O19]8– and solid-state studies of isostructural niobium and tantalum oxide complexes

A new soft chemical route to [Ta6O19]8- has been developed by the dissolution of [Ta(O2)4]3- in conditions alkaline enough to arrest formation of Ta2O5, followed by [VO4]3--catalyzed decomposition of the peroxide ligands and crystallization of the salt. An average of bond lengths and angles from isostructural salts of [Ta6O19]8- and [Nb6O19]8- indicate there is an increase in terminal M(eta=O) bond lengths and M-micro2-O-M angles and a decrease in bridging micro2-O-M bond lengths in [Ta6O19]8-, although the central micro6-O-M bond lengths are identical within experimental error. Two new structures of Na7[HNb6O19].15H2O () and Na8[Ta6O19].15H2O () are exemplary of the fact that protonated micro2-OH are observed exclusively in the niobates. In these structures, the metal-oxide framework, seven sodium atoms, and all fifteen water molecules are located in identical unit cell positions, but in an eighth charge-balancing sodium is located in close proximity to the protonated micro2-OH in . Differences in the basicity of Nb(v)- and Ta(v)-bound oxygen atoms are also manifested at the surfaces of 17O-enriched powders of Nb2O5 and Ta2O5. Oxygen exchange at the surface of these materials readily takes place at both terminal and bridging sites in Nb2O5 but only at terminal sites in Ta2O5.

Pressure dependence of the Shubnikov-de Haas oscillation spectrum of $\beta''$ -(BEDT-TTF)4(NH4)[ Cr(C2 O4)3] .DMF

The Shubnikov-de Haas (SdH) oscillation spectra of the beta''-(BEDT-TTF)4(NH4)[Cr(C2O4)\_3].DMF organic metal have been studied in pulsed magnetic fields of up to either 36 T at ambient pressure or 50 T under hydrostatic pressures of up to 1 GPa. The ambient pressure SdH oscillation spectra can be accounted for by up to six fundamental frequencies which points to a rather complex Fermi surface (FS). A noticeable pressure-induced modification of the FS topology is evidenced since the number of frequencies observed in the spectra progressively decreases as the pressure increases. Above 0.8 GPa, only three compensated orbits are observed, as it is the case for several other isostructural salts of the same family at ambient pressure. Contrary to other organic metals, of which the FS can be regarded as a network of orbits, no frequency combinations are observed for the studied salt, likely due to high magnetic breakdown gap values or (and) high disorder level evidenced by Dingle temperatures as large as about 7 K.

Perylene salts of unsymmetrical nickel and gold dithiolene complexes with 3 ? 2 stoichiometry: conformational polymorphism and strong antiferromagnetic interactions

The square-planar AuIII complex of the unsymmetrical tfadt dithiolate ligand (tfadt: 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate) is found to exhibit conformational polymorphism in its n-Bu4N+ salt, as both cis and trans isomers were found to crystallize separately in the same crystallization batch. Electrocrystallization of perylene in the presence of the diamagnetic [n-Bu4N][Au(tfadt)2] or the paramagnetic (S = 1/2) [n-Bu4N][Ni(tfadt)2] nickel analog affords isostructural salts with an unusual 3 ∶ 2 stoichiometry, that is [Per]3[M(tfadt)2]2 (M = Au, Ni), with an alternation of dicationic [Per]32+ perylene triads and dianionic [M(tfadt)2]22− dithiolene complex dyads within one-dimensional chains. These salts are characterized by strong antiferromagnetic interactions within perylene triads and [Ni(tfadt)2]22− dyads and an essentially diamagnetic behaviour.

Strong π-d interaction based on brominated TTF-type donor EDT-TTFBr2

New π-d interacting system based on brominated TTF-type donor EDT-TTFBr2 (= 4,5-dibromo-4,5-ethylenedithiotetrathiafulvalene) was investigated. Magnetic (EDT-TTFBr 2 ) 2 FeBr 4 and non-magnetic (EDT-TTFBr 2 ) 2 GaBr 4 are isostructural salts, which have strong anion-donor interaction through Br-Br atomic contacts with weak direct anion-anion interaction. The iron salt takes an antiferromagnetic transition at T N = 11 K owing to strong π-d interaction, which originates from the strong anion-donor interaction. The strong π-d interaction also plays an important role in the electron transport phenomenon in the variation of temperature and applied magnetic field.

Nucleation of solid solutions crystallizing from aqueous solutions.

The study of nucleation and growth mechanisms of salts from aqueous solutions, as a function of supersaturation, is described using both macroscopic and microscopic experiments. In situ observations in a fluid cell in an atomic force microscope (AFM) reveal phenomena not accounted for in standard crystal-growth theories, specifically on the role of the crystal structure of the substrate in controlling spiral growth and two-dimensional nucleation. As a model example, the crystallization of two isostructural salts, BaSO(4) and SrSO(4), is described. The growth of solid-solution crystals is considerably more complex. The supersaturation of a given aqueous solution relative to a solid solution is different with respect to each solid composition, and it leads to the possibility that different compositions can simultaneously grow by different mechanisms on the same crystal face. Oscillatory compositional zoning is another consequence of the interplay between the thermodynamics and the kinetics of nucleation. The factors which control nucleation and growth of the solid solution (Ba,Sr)SO(4) from an aqueous solution are described. The predictions made from the theory are compared with direct observations of crystal growth in an AFM.

Reply to Comment by H. Kitano and A. Maeda

In our recent Letter, we reported that, in the metallic state of -(BEDT-TSF)2FeCl4 at TMI 1⁄4 8:3K T TFM 1⁄4 70K, the microwave conductivity 1 along the c axis is much more resistive than the dc conductivity dc, and a ferroelectric-like response is revealed in the dielectric constant 1, which is enhanced to the order of 10 . The unusual metallic state is identified by other experiments such as specific heat, NMR and ESR. From the absence of these anomalous features in the non-magnetic, isostructural GaCl4 salt, we pointed out the possible importance of the -d interaction for the ferroelectric-like anomaly as well as for the exchange-induced MI transition. In the preceding Comment, Kitano and Maeda (hereafter abbreviated as KM) insist that the probable metallic shift =n may be 4:25 10 5 obtained by eq. (1) (see below) applied to the depolarization peak, and hence 1 may result in a negative value. We point out here that the method to determine a metallic shift cannot be applicable to the depolarization peak in the present system, and the premise of KM, that the system might be in a usual highly-metallic state above TMI, is contrary to the experimental facts. First of all, we start to discuss on the anomalous behavior in =2f0 at TMI T TFM. We had carried out microwave measurements at 16.3GHz on about 20 single crystals before we submitted our paper. Every data has exhibited a saturation as shown in Fig. 1 of ref. 1 or a shallow minimum of =2f0 around 40–50K as depicted here in Fig. 1. Recently such minimum is also reproduced clearly in cavityperturbation measurements at 45GHz, which will be published elsewhere. According to the dc resistivity dc, which indicates a metallic reduction down to TMI, =2f0 could be expected to approach to zero with decreasing temperature, if the present system be a usual metal. In fact, in case of the GaCl4 salt, =2f0 decreases, in the same temperature range, in accordance with the dc resistivity as demonstrated in Fig. 2 of ref. 1. Thus, the enhancement of microwave loss is confirmed to be so intrinsic in the FeCl4 salt that the anomalous metallic state is realized above TMI. The anomalous microwave loss must be taken into account in a consistent way for the evaluation of the microwave skin depth mw using 1. As mentioned later, 1 becomes two-orders of magnitude lower than dc, so that mw is about 10 times larger than dc. Hence the system never enters a skin depth regime and still remains in a depolarization regime. From these results, it is concluded that the system responses quite anomalously to microwave in the highly metallic state as far as the dc conductivity concerned. This surprisingly important fact is little recognized in KM, which described shortly ‘‘due to some extrinsic origin’’. Secondly, we shall now look more carefully into the determination of the metallic shift from the observed depolarization peak. Whenever a depolarization peak in =2f0 is detected, one first tries to use a following relation to determine a metallic shift =n as KM also mentioned:

High Pressure X-ray Crystal Structure Analysis of Pd(dmit) 2 Salts

We have performed X-ray diffraction study under pressure for isostructural anion radical salts g '-Et 2 Me 2 Z[Pd(dmit) 2 ] 2 (Z = P, As, Sb) at room temperature. The unit cells remained monoclinic and no satellite reflection was detected up to 18 kbar. For the high-pressure superconductor Et 2 Me 2 P salt, high-pressure crystal structure analyses were carried out. Obtained band parameters indicate an increase of bandwidth and a decrease of the dimensionality of a HOMO-based band. This is related to a pressure-induced metallic state and a non-metallic state in the higher pressure region. molecular conductor metal dithiolene complex crystal structure pressure effect

Infrared and Raman studies of the κ-phase charge-transfer salts formed by BEDT-TTF and magnetic anions M(CN)63− (where M = CoIII, FeIII, CrIII)

The isostructural charge-transfer salts κ-[Et4N](BEDT-TTF)4M(CN)6·3H2O (M = CoIII, FeIII, CrIII) are organic semiconductors undergoing two intriguing phase transitions at T = 240 and 150 K. Polarized IR reflectance spectra (from 650 to 6500 cm−1) of these compounds were studied at room temperature. An electronic dispersion in IR spectra was analyzed in terms of a Drude–Lorentz model and optical transport parameters were determined. IR reflectance spectra of FeIII crystals were measured in the temperature range from 190 to 300 K and the influence of the phase transition at 240 K was studied. We report also FT-NIR Raman studies of FeIII salt as a function of temperature from 110 to 300 K. The Raman line related to the ν3(Ag) CC mode of BEDT-TTF splits below 240 K into three components providing evidence of charge redistribution in the BEDT-TTF layers.

Mixtures of Trihalide Anions in Isostructural BEDT-TTF Salts as Seen by Raman Spectroscopy

Low frequency Raman spectra have been recorded at room temperature for β-type structure of the (BEDT-TTF)2X single crystals (where BEDT-TTF is bis(ethylenedithio) tetrathiafulvalene and X stands for mono or mixed trihalide anions). This technique has permitted us to detect a presence of the (Br-I-Cl)−, (I-I-Cl)− and (Cl-I-Cl)− anions in addition to a mixture of the (I-I-I)−, (I-I-Br)− and (Br-I-Br)− anions in some recently grown single crystals. The observed low-frequency Raman bands were compared with the ab initio calculated vibrational frequencies of trihalide anions and a very good agreement between experimental and calculated data was found.

Hal⋯Hal interactions in a series of three isostructural salts of halogenated tetrathiafulvalenes. Contribution of the halogen atoms to the HOMO–HOMO overlap interactions

The halogenated tetrathiafulvalenes, Br2-EDT-TTF and I2-EDT-TTF were prepared by the coupling route from the corresponding 4,5-dibromo- or 4,5-diiodo-1,3-dithiole-2-thione. In the isostructural series, (Br2-EDT-TTF)2IBr2, (Br2-EDT-TTF)2I3 and (I2-EDT-TTF)2I3, noted Br2/IBr2, Br2/I3 and I2/I3 respectively, short (3.42–3.60 A) and directional Hal⋯Hal interactions are identified between donor molecules and with the anions, stabilising rare β′ phases. These interactions play not only a structural role but also contribute to the electronic dispersion thanks to sizeable coefficients on the halogen atoms in the HOMOs of Br2-EDT-TTF and I2-EDT-TTF. The three salts behave as Mott insulators as reflected by a high room temperature conductivity (0.5 S cm−1) with an activation energy which increases in the order Br2/IBr2 (730 K), Br2/I3 (1260 K), I2/I3 (1330 K) and a weak magnetic susceptibility, which decreases abruptly below 150 K with no sign of an antiferromagnetic ground state.

Superelectrophilic tetrakis(carbonyl)palladium(II)- and -platinum(II) undecafluorodiantimonate(V), [Pd(CO)4][Sb(2)F(11)]2 and [Pt(CO)4][Sb(2)F(11)]2: syntheses, physical and spectroscopic properties, their crystal, molecular, and extended structures, and density functional calculations: an experimental, computational, and comparative study .

The salts [M(CO)(4)][Sb(2)F(11)](2), M = Pd, Pt, are prepared by reductive carbonylation of Pd[Pd(SO(3)F)(6)], Pt(SO(3)F)(4) or PtF(6) in liquid SbF(5), or HF-SbF(5). The resulting moisture-sensitive, colorless solids are thermally stable up to 140 degrees C (M = Pd) or 200 degrees C (M = Pt). Their thermal decompositions are studied by differential scanning calorimetry (DSC). Single crystals of both salts are suitable for an X-ray diffraction study at 180 K. Both isostructural salts crystallize in the monoclinic space group P2(1)/c (No. 14). The unit cell volume of [Pt(CO)(4)][Sb(2)F(11)](2) is smaller than that of [Pd(CO)(4)][Sb(2)F(11)](2) by about 0.4%. The cations [M(CO)(4)](2+), M = Pd, Pt, are square planar with only very slight angular and out-of-plane deviations from D(4)(h)() symmetry. The interatomic distances and bond angles for both cations are essentially identical. The [Sb(2)F(11)](-) anions in [M(CO)(4)][Sb(2)F(11)](2,) M = Pd, Pt, are not symmetry-related, and both pairs differ in their Sb-F-Sb bridge angles and their dihedral angles. There are in each salt four to five secondary interionic C- -F contacts per CO group. Of these, two contacts per CO group are significantly shorter than the sum of the van der Waals radii by 0.58 - 0.37 A. In addition, structural, and spectroscopic details of recently synthesized [Rh(CO)(4)][Al(2)Cl(7)] are reported. The cations [Rh(CO)(4)](+) and [M(CO)(4)](2+), M = Pd, Pt, are characterized by IR and Raman spectroscopy. Of the 16 vibrational modes (13 observable, 3 inactive) 10 (Pd, Pt) or 9 (Rh), respectively, are found experimentally. The vibrational assignments are supported by DFT calculations, which provide in addition to band positions also intensities of IR bands and Raman signals as well as internal force constants for the cations. (13)C NMR measurements complete the characterization of the square planar metal carbonyl cations. The extensive characterization of [M(CO)(4)][Sb(2)F(11)](2), M = Pd, Pt, reported here, allows a comparison to linear and octahedral [M(CO)(n)()][Sb(2)F(11)](2) salts [M = Hg (n = 2); Fe, Ru, Os (n = 6)] and their derivatives, which permit a deeper understanding of M-CO bonding in the solid state for superelectrophilic cations with [Sb(2)F(11)](-) or [SbF(6)](-) as anions.

Syntheses, molecular structures, and vibrational spectra of chloropentacarbonylrhodium(III) and -iridium(III) undecafluorodiantimonate(V), [Rh(CO)5Cl][Sb2F11]2 and [Ir(CO)5Cl][Sb2F11]2: an experimental and density functional study.

The reactions of either bis(mu-chloro)tetracarbonyldirhodium(I), [Rh(CO)2(mu-Cl)]2, or chlorotricarbonyliridium(I), [Ir(CO)3Cl]n, in the conjugate Brønsted-Lewis superacid HF-SbF5 and in a CO atmosphere, produce [Rh(CO)5Cl][Sb2F11]2 or [Ir(CO)5Cl][Sb2F11]2, respectively. In these oxidative carbonylation reactions, antimony(V) fluoride functions as an oxidizing agent. The reduced product is identified as 6SbF3.5SbF5. [Rh(CO)5Cl][Sb2F11]2 is obtained in the form of single crystals. Crystal data: monoclinic, space group P2(1) (No. 4); a = 9.721(1), b = 12.602(1), c = 10.538(1) A; beta = 106.51(1) degrees; V = 1237.7(2) A3; Z = 2; T = 300 K; R1 [I > 3 sigma (I)] = 0.0367, wR2 = 0.0739. Single crystals of [Ir(CO)5Cl][Sb2F11]2 are produced in small amounts from a solution of mer-Ir(CO)3(SO3F)3 in magic acid, HSO3F-SbF5. The possible source of chlorine will be discussed. Crystal data for [Ir-(CO)5Cl][Sb2F11]2: monoclinic, space group P2(1) (No. 4); a = 9.686(2), b = 12.585(2), c = 10.499(2) A; beta = 106.59(2) degrees; V = 1226.5(4) A3; Z = 2; T = 294 K; R1[I > 3 sigma (I)] = 0.032, Rw = 0.031. The bond lengths and bond angles are nearly identical in the two isostructural salts; however, the cell volume of [Ir(CO)5Cl][Sb2F11]2 is slightly smaller than that of [Rh(CO)5Cl][Sb2F11]2. The cations (point group C4v) feature unusually long M-C bonds (M = Rh, Ir) and correspondingly short CO bonds, as well as high CO stretching wavenumbers and high CO stretching force constants. The [Sb2F11]- anions are not symmetry related, and their dihedral and bridge angles differ slightly in both salts. There are significant interionic contacts in [Ir(CO)5Cl][Sb2F11]2 exclusively of the C-F type (about 2 for each C atom of the five carbonyl groups) resulting in extended structures. The vibrational spectra for both [M(CO)5Cl]2+ cations (M = Rh, Ir) are assigned with the help of density functional calculations, which also provide intensities for IR and Raman bands. While [Rh(CO)5Cl]2+ is the first cationic carbonyl derivative of Rh(III), the vibrational and structural parameters for [Ir(CO)5Cl]2+ are compared to data for [Ir(CO)6]3+ and mer-Ir(CO)3(SO3F)3.

Lattice-parameter dependence of translation/rotation coupling potentials

Translation/rotation coupling leads to a square distribution of nuclear-density for three-fold rotors. Experimentally, the orientation of this square is found to vary between the isostructural salts Co(NH 3) 6(PF 6) 2 and Ni(NH 3) 6(PF 6) 2 . Ab initio calculations show the same orientation for any isolated hexammine ion, but the use of pair-potentials for extended models reveals a lattice-parameter dependence of the orientation which is in broad agreement with experiment.

Structure dependence on redox state and charge in [Fe4(μ3-S4)(η-C5H5)4]m[M(mnt)2]n (M = Ni or Pt, m, n = 1 or 2)

The complex salts [Fe4(μ3-S)4(η-C5H5)4]m[M(mnt)2]n {M = Ni, n = 2, m = 1 1; n = 1, m = 1 2 or 2 3: M = Pt, n = 2, m = 1 4; n = 1, m = 1 5 or 2 6; mnt = S2C2(CN)2} have been synthesized by stoichiometric reactions between [NEt4]n[M(mnt)2] (n = 1 or 2, M = Ni or Pt) and [Fe4(μ3-S)4(η-C5H5)4][PF6]n (n = 1 or 2); the salts 2–6 have been structurally characterised. The molecular structures of the [Fe4(μ3-S)4(η-C5H5)4]z+ (z = 1 or 2) cations and the [M(mnt)2]z− (M = Ni or Pt, z = 1 or 2) anions show mean Fe⋯Fe and M–S distances characteristic of z. The isostructural salts [Fe4(μ3-S)4(η-C5H5)4]2[M(mnt)2] (M = Ni 3 or Pt 6) comprise two monocations and one dianion; the planar anions, which form a ruffled ribbon arrangement, are interleaved by the near-spherical cations. The structure of [Fe4(μ3-S)4(η-C5H5)4][Pt(mnt)2]2, 4, with two monoanions and one dication, has face-to-face metal–metal pairs of [Pt(mnt)2]− ions separated by individual [Pt(mnt)2]− units, leading to anion layers interleaved by layers of cations. Salts 2 and 5 have very different structures. The nickel complex [Fe4(μ3-S)4(η-C5H5)4][Ni(mnt)2] 2 comprises dications and dianions whereas the platinum complex [Fe4(μ3-S)4(η-C5H5)4][Pt(mnt)2] 5 has monocations and monoanions. In salt 2 the dianions are well separated while in 5 the monoanions are weakly dimerised.