Arene complexes of zirconium containing triangular cluster cations [(η6-C6H6Me3)3Zr3(μ-Cl)6]n+,n = 2,3

Ionic -mesitylene zirconium complexes (1–4) have been obtained by a reaction between ZrCl₄ and a metal reducer (Al, Zn or Mg) in the presence of AlCl₃ in mesitylene. An X-ray study has shown that in the triangular cluster cations [(-C₆H₃Me₃Zr₃(-Cl₆)]ⁿ⁺ an increase in the charge from 2+ (1,2) to 3+ (3,4) is accompanied by shortening of the Zr-Zr distances from 3.32–3.33 A to 3.27–3.28 Å. AlCl₄ ^– (1), Al₂Cl₇ ^– (1–3), and Mg[(-Cl)₂AlCl₂]₃ ^– (4), the latter found here for the first time, are present in the complexes studied as counterions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 134–142, January, 1994.     

Metal-betaine interactions. Part 17: A study of intradimer Cu · · · Cu distance variation in copper(II) betaine complexes containing [Cu2 (carboxylato-O,O′)4L2]n+ species

Four copper(II) complexes of betaines, [Cu₂(BET)₄Cl₂][Cu(BET)₂Cl₂]Cl₂ (2), [Cu₂(pyBET)₄Cl₂]₃[CuCl₄]₂Cl₂ (3), [Cu, (pyBET)₄ (H₂O)₂] (NO₃)₄ · 2H₂O (4), and [Cu₂(ppBET)₄(H₂O)₂](ClO₄)₄ · 4H₂O (5), (BET = Me₃N⁺CH₂COO^–; pyBET = C₅H₅N⁺CH₂COO^–; ppBET=C₅H₅N⁺CH₂CH₂COO^–), have been prepared and characterized by X-ray crystallography. These complexes all contain dimeric [Cu₂ (carboxylato-O,O)₄L₂] structures [basal Cu-O=1.955(4) 1.991(2), Cu Cu=2.602(1) 2.759(1) Å] with the apical ligand L=Cl^– in (2) and (3) [Cu-Cl=2.415(1) 2.436(3) Å] and L = H₂O in (4) and (5) [Cu-OH₂=2.158(4) 2.192(3) Å]; also present are a discrete [Cu(BET)₂Cl₂] molecule with a compressed tetrahedral CuO₂Cl₂ chromophore involving two unidentate carboxylate ligands [Cu-O=1.916(2), Cu-Cl=2.254(1) Å] in (2), and a discrete C_3v [CuCl₄]^2– anion in (3). Generally the intradimer Cu Cu distance may be correlated to the electronic repulsion of the metal-ligand bonds in the CuO₄L chromophore, as well as the steric interaction between the carboxylate moieties and the apical ligand.     

Synthesis and crystal structures of supramolecular adducts of molybdenum and tungsten selenide aqua complexes with macrocyclic cavitand cucurbituril

The supramolecular compounds {[W₃Se₄Cl₃(H₂O)₆]₂[PyHC₃₆H₃₆N₂₄O₁₂]}Cl₃·18H₂O (1) and {[Cl₃SnMo₃Se₄Cl₃(H₂O)₆][Cl₃SnMo₃Se₄Cl₂(H₂O)₇](C₃₆H₃₆N₂₄O₁₂)}Cl·26H₂O (2) were isolated from solutions of the selenium-containing tungsten and molybdenum clusters [W₃Se₄(H₂O)₉]⁴⁺ and [Cl₃SnMo₃Se₄(H₂O)₉]³⁺, respectively, and organic cavitand cucurbituril. X-ray diffraction analysis demonstrated that the macrocylcic cucurbituril molecule is coordinated on both sides by the cluster cations through the formation of complementary hydrogen bonds. Compound 1 has a chain structure stabilized by Se...Se interactions between the adjacent cluster cores. In compound 2, the bridging ₂-selenium atoms of the cluster fragment Mo₃Se₄ are coordinated to the tin atom of the SnCl₃ ^– ligand, thus losing the ability to be involved in Se...Se interactions.     

[Et3PH][W4O3Cl7(PEt3)3]. A 12-electron tetrahedral tungsten cluster with an interesting arrangement of ligands

From the reaction between W₂Cl₆(PEt₃)₂ and H₂O in tetrahydrofuran the dark green crystalline compound [Et₃PH][W₄O₃Cl₇(PEt₃)₃] was obtained and characterized by X-ray crystallography. At –155° the cell dimensions werea=b=c=20.392(3) Å,Z=8,d _calcd=2.36 g cm^–3 in the space group I23. The compound is a triethylphosphonium salt of the [W₄O₃Cl₇(PEt₃)₃]^– anion. The latter contains a tetrahedron of tungsten atoms with W–W=2.61 Å (ave) and may be viewed as a W₃(-Cl)₃Cl₃(PEt₃)₃ cluster capped by ad ⁰-[WO₃Cl]^– unit and this has proved useful in examining the bonding within the cluster by use of the M.O. calculational method of Fenske and Hall. The cluster anion has crystallographically imposed C_3v symmetry. Theoxo-groups bridge the tungsten atoms in a notably asymmetric manner W–O=1.87(2) Å and 2.04(2) Å with the shorter distances being involved with the capping [WO₃Cl]^– unit. The W–P bonds lie in the W₃(₃-Cl)₃ plane and the three terminal W–Cl bonds are trans to theoxo-bridges.     

Synthesis,characterisation and solid state thermal behaviour of nickel(II) diamine complexes

Summary [NiL₂X₂] (L =N,N-dimethyl-1,2-ethanediamine; X = Cl^–, CF₃CO ₂ ^– , CC1₃CO ₂ ^– and CBr₃CO ₂ ^– ), [NiL₂C₂O₄] · H₂O and [NiL₂X₂] · 2 H₂O (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^– ) have been synthesised and their thermal studies carried out. Thermally induced phase transition phenomena are noticed in [NiL₂X₂] (X = CF₃CO ₂ ^– and CCl₃CO ₂ ^– ) and their probable mechanisms are described. [NiL₂X₂] (X = Br^–, 0.5 SO ₄ ^2– and 0.5 SeO ₄ ^2– ) and [NiLX₂] (X = Cl^–, 0.5 C₂O ₄ ^2– and 0.5 SO ₄ ^2– ) have been prepared by solid state pyrolysis from the respective parent diamine complexes. [NiL₂X₂] have been made in solid state by temperature arrest technique from [NiL₂(CX₃CO₂)₂] (X = Cl^– and Br^–).     

Structural Dynamics of Isomorphic Substitution in N,N′-Diallylbenzimidazolium Copper Halide π-Complexes [C7H5N2(C3H5)2]+[Cu2Cl3?xBrx]? (x=0, 1.60, 2.33, 3)

Two new -complexes of copper(I) halides with the 1,3-diallylbenzimidazolium cation, [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl_1.40Br_1.60]^– and [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Br₃]^–, have been synthesized and structurally defined (space group P2 ₁/c for both; a = 22.094(6), b = 9.272(8), c = 9.22(1) , = 118.26(4)° and a = 22.267(5), b = 9.311(3), c = 9.263(2) , = 117.51(2)°). The mutual effects of chlorine–bromine substitution and the efficiency of -interactions are discussed based on XRD data for these two compounds and for the compounds [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl₃]^– and [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl_0.67Br_2.33]^– studied previously.     

Three Heterometallic Mo–M′ Cubane-Like Tetranuclear Cluster Compounds (M′=Cu, Pb, Sb): Synthesis, Structure and Third-Order NLO Property

Three new heterometallic tetranuclear cluster compounds with a [Mo₃YS₃M] cubane-like cluster core (M=Cu, Pb, Sb; Y=O, S), [Mo₃OS₃(CuI)(-OAc)₂(dtp)₂(DMF)] (1), (dtp=S₂P(OC₂H₅)^– ₂), [Mo₃OS₃(PbI₃)(dtc)₃(py)₃] (2) (dtc=S₂CN(C₂H₅)^– ₂), [Mo₃S₄(SbI₃)(dtcpyr)₄(py)]·2H₂O (3) (dtcpyr=S₂CNC₄H^– ₈) have been synthesized and structurally characterized by IR, Raman, UV–Vis, ¹H NMR, ¹³C NMR spectroscopies and single-crystal X-ray diffraction studies. Their structure and bonding features are discussed. Compounds 1 and 2 show a good third-order optical nonlinearity, as measured by degenerate four-wave mixing technique.     

Reaction of Adenine and Guanine with [Ru(RaaiR′)2(EtOH)2](ClO4)2 · Spectral and Electrochemical Characterization of the Products [RaaiR′ = 1-Alkyl-2-(arylazo)-Imidazole]

[Ru(RaaiR)₂(EtOH)₂](ClO₄)₂[RaaiR= 1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-N = N-C₃H₂N-N(1)-R, R = H (a), Me (b), Cl (c), R= Me (1, 3), Et (2, 4)] reacts with nucleobases [NB – adenine (A), guanine (G)] in aqueous EtOH to give red–violet mixed ligand complexes of the type [Ru(RaaiR)₂(NB)(H₂O)](ClO₄)₂. The solution electronic spectra exhibit a strong MLCT band at 540–560 nm in MeCN. The cyclic voltammogram shows a Ru^III/Ru^II couple at 1.3–1.4 V versus Ag/AgCl along with three successive ligand reductions.     

Studies on transition-metal nitrido and oxo complexes. Part VII(1). Substituted nitrido complexes of osmium and ruthenium

Summary Addition reactions of [MNCl₄]^– (M = Os or Ru) with ligands L or L to give [MNCl₄ · L]^– or [(MNCl₄)₂L]^2– (L = pyridine, pyridine-N-oxide,iso-quinoline or DMSO; L = hexamethylenetetramine, pyrazine or dioxan) are described. With NCO^–, [OsNCl₅]^– gives [OsN(NCO)₅]^2– but NCS^– gives a thionitrosyl complex, [Os(NS)(NCS)₅]^2–. Reactions of OsNCl₃(AsPh₃)₂ with pyridine, 1,10-phenanthroline and tertiary phosphites and phosphinites have been studied, as have reactions of triphenylphosphine with OsOCl₄ andtrans- [MO₂Cl₄]^2– (M = Os or Ru). The nitrido-iodo complexes [OsNI₄]^– and OsNI₃, (SbPh₃)₂ are also reported.     

Cobalt(II) complexes of 1,2-(diimino-4′-antipyrinyl)ethane and 4-N-(4′-antipyrylmethylidene)aminoantipyrine

Cobalt(II) complexes of the Schiff bases 1,2-(diimino-4-antipyrinyl)ethane (GA) and 4-N-(4-antipyrylmethylidene)aminoantipyrine (AA) have been prepared and characterised by elemental analysis, electrical conductance in non-aqueous solvents, i.r. and electronic spectra, as well as by magnetic susceptibility measurements. The complexes have the general formulae [Co(GA)X]X (X = ClO^– ₄ or NO₃ ^–), [Co(GA)X₂] (X = Cl^–, Br^– or I^–), [Co(AA)₂]X₂ (X = ClO₄ ^–, NO₃ ^–, Br^– or I^–) and [Co(AA)Cl₂]. GA acts as a neutral tetradentate ligand, coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate and nitrate complexes of GA one anion is coordinated in a bidentate fashion, whereas in the halide complexes both anions are coordinated to the metal, generating an octahedral geometry around the Co ion. AA acts as a neutral bidentate ligand, coordinating through the carbonyl oxygen derived from the aldehydic moiety and the azomethine nitrogen. Both anions remain ionic in the perchlorate, nitrate, bromide and iodide complexes of AA, whereas both anions are coordinated to the metal ion in the chloride complex, resulting tetrahedral geometry around the Co ion.     

Synthesis and Molecular Structure of the Mercury-Bridged Heteronuclear Complex [Pt3(dppm)3 {(μ4-Hg)-RuCp(CO)2}2][PF6]2

Addition of a THF solution prepared by stirring [CpRu(CO)₂]₂ over Na/Hg amalgam to a solution of the triplatinum cluster [Pt₃(dppm)₃(CO)][PF₆]₂ (1) in THF gives the heteronuclear cluster [Pt₃(dppm)₃{(₄-Hg)–RuCp(CO)₂}₂] [PF₆]₂ (2) in 40% yield following chromatography. A single crystal X-ray study of 2 reveals structural parameters for the Pt₃Hg₂ molecular core that are consistent with those of other structurally characterized complexes of this type. ¹H, ¹³C, and ³¹P NMR spectra of this complex indicate that the structure observed in the solid state is retained in solution.     

Interaction Between Pd(RaaiR′)Cl<Subscript>2</Subscript> and Adenine: Reaction Dynamics and Mechanism [RaaiR′ = 1-alkyl-2-(arylazo)imidazole]

Nucleophilic substitution of Pd(RaaiR′)Cl₂ [RaaiR′=1-alkyl-2-(arylazo)imidazole, p-R—C₆H₄— N=N—C₃H₂NN-1-R′; where R= H(a)/Me(b)/Cl(c) and R′ = Et(1)/Bz(2)] with adenine (A) in MeCN–water (1:1) at 298 K, to form [Pd(A)₂]Cl₂, has been studied spectrophotometrically under pseudo-first-order conditions and the analyses support a nucleophilic association path. The reaction follows the rate law, rate = {a+k [A] ₀²[Pd(RaaiR′)Cl₂]: first-order in Pd(RaaiR′)Cl₂ and second-order in A. The rate increases as follows: Pd(RaaiEt)Cl₂(1) < Pd(RaaiBz)Cl₂(2) and Pd(MeaaiR′)Cl₂(b) < Pd(HaaiR′)Cl₂(a) < Pd(ClaaiR′)Cl₂(c). External addition of Cl⁻ (LiCl) suppresses the rate (rate 1/[Cl⁻]). The activation parameters, H⁰ and S⁰ of the reactions were calculated from the Eyring plot and support the proposed mechanism.     

Synthesis and Characterization of Cobalttelluride Clusters with the Cubic Body-Centered Co9Te6(CO)8 Core

Reduction of Cp₂NbTe₂H (Cp=tBuC₅H₄) with CH₃Li results in a red-violet solution which reacts with Co₂(CO)₈ to give the neutral cluster {Cp₂Nb(CO)}₂[Co₉Te₆(CO)₈] (2) and a mixture of salts, from which [Na(THF)₆][Co₉Te₆(CO)₈] (4) was obtained by crystallization from THF in very poor yield, probably due to Na impurities in CH₃Li. Clusters 2 (123 valence electrons) and 4 (122 valence electrons) possess hexacapped cubic Co@Co₈ cores. The structure of 2 was identified by comparison of spectroscopic data with those of parent clusters: Two Cp₂Nb(CO) fragments are fixed at two opposite ₄-Te bridges of the Co₉Te₆(CO)₈ skeleton. A crystal structure determination of 4 shows this compound to contain discrete ions. Nearly equal diameters of ca. 10.5Å for the [Co₉Te₆(CO)₈]^– anion and the octahedral [Na(THF)₆]⁺ cation as well as electrostatic interactions between them and attractive C–HO contacts may be responsible for the formation of layers throughout the crystal.     

Complexes of dioxouranium(VI) with zwitter-ionic forms of Bi- and tetra-dentateSchiff bases

Potentially bi- and tetra-dentateSchiff bases derived from salicylaldehyde react with hydrated uranyl salts to give complexes: UO₂H₂ LX ₂, UO₂H₂ LX ₂ and UO₂(HL)₂ X ₂ [H₂ L=N,N-propane-1,3-diylbis(salicylideneimine), H₂ L=N,N-ethylenebis(salicylideneimine) and HL=N-phenylsalicylideneimine;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^–, and NCS^–]. Because of marked spectral similrities with the structurally known Ca(H₂ L) (NO₃)₂, theSchiff bases are coordinated through the negatively charged phenolic oxygen atoms and not the nitrogen atoms of the azomethine groups which carry the protons transferred from phenolic groups on coordination. Halide, nitrate, perchlorate and thiocyanate groups are covalently bonded to the uranyl ion, resulting a 6-coordinated uranium ion in the halo and thiocyanato complexes and 8-coordinated in nitrato and perchlorato complexes.

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Komplexe von Dioxouranyl(VI) mit zwitterionischen Formen von zwei- und vierzähnigen Schiff-Basen

Zusammenfassung Von Salizylaldehyd abgeleitete zwei- und vierzähnigeSchiff-Basen reagieren mit hydratisierten Uranylsalzen zu Komplexen folgenden Typs: UO₂H₂ LX ₂, UO₂H₂ LX ₂ und UO₂(HL)₂ X ₂ [H₂ L=N,N-Propan-1,3-diylbis(salicylidenimin), H₂ L=N,N-Ethylen-bis(salicylidenimin) und HL=N-Phenylsalicylidenimin;X ^–=Cl^–, Br^–, I^–, NO₃ ^–, ClO₄ ^– und NCS^–]. Auf Grund eindeutiger spektraler Ähnlichkeiten mit dem bekannten Ca(H₂ L) (NO₃)₂ wird auf Koordination über die negativ geladenen phenolischen Sauerstoffatome (und nicht über die Azomethin-Stickstoffe) geschlossen. Die AnionenX ^– sind kovalent an das Uranyl-Ion gebunden; damit ergibt sich ein hexakoordiniertes Uranyl-Ion für die Halogen- und Thiocyanat-Komplexe und Oktakoordination für die Nitrat- und Perchlorat-Komplexe.

     

Thermally induced solid-state isomerisation and decomposition of 2,2-dimethyl-1,3-propanediamine nikel(II) complexes

Summary Complexes [NiL₃]Br₂·H₂O (L=2,2-dimethyl-1,3-propanediamine), [NiL₂X₂] (X=Cl, Br, NCS, CF₃CO₂, HCCl₂CO₂ or CCl₃CO₂ and X₂=SO₄ or SeO₄) and [NiL(HCCl₂CO₂)₂]·H₂O have been synthesised and their thermal studies have been investigated in the solid state. The complexes, [NiL₂X₂] (X=Cl or Br) and NiLX₂ (X=Cl or HCCl₂CO₂) have been isolated thermally in the solid state. All the complexes possess octahedral geometry. [NiL₂Br₂] and [NiL₂(CF₃CO₂)₂] exist in two interconvertible isomeric forms. H for the conversions were determined. [NiL₂(HCCl₂CO₂)₂] (5) undergoes an irreversible phase transition (178–188°C; H=4.4kJ mol^–1]. NiL(HCCl₂CO₂)₂·H₂O shows an exothermic irreversible phase transition (104–128°C; H=–5.8 kJ mol^–1) after losing water. The phase transitions are assumed to be due to the conformational changes in the chelate ring of diamine.     

Synthesis, crystal structure, spectroscopic and thermal properties of [Et4N][Ta6Br12(H2O)6]Br4·4H2O (Et=ethyl)—A new compound with the paramagnetic [Ta6Br12] cluster core

A new hexanuclear cluster compound, [Et₄N][Ta₆Br₁₂(H₂O)₆]Br₄·4H₂O (Et=ethyl) (1), with the paramagnetic [Ta₆Br₁₂]³⁺ cluster entity, was synthesized and characterized by elemental and TG/DTA analyses, IR and UV/Vis spectroscopy and by a single-crystal X-ray diffraction study. The presence of the paramagnetic [Ta₆Br₁₂]³⁺ unit was confirmed also by the room-temperature magnetic and EPR measurements. The compound crystallizes in the tetragonal I4₁/a space group, with a=14.299(5), c=21.241(5) Å, Z=4, R₁(F)/wR₂(F²)=0.0296/0.0811. The structure contains discrete [Ta₆Br₁₂(H₂O)₆]³⁺ cations with an octahedron of metal atoms edge-bridged by bromine atoms and with water molecules occupying all six terminal positions. The cluster units are positioned in the vertices of the three-dimensional (pseudo)diamond lattice. The structure shows similarities with literature reported structures of cluster compounds crystallizing in the diamond space group.     

Deprotonated Amines Formed Through Coordination to Sulfur/Oxygen-Bridged Incomplete Cubane-Type Molybdenum Clusters

Oxygen/sulfur-bridged incomplete cubane-type molybdenum aqua clusters [Mo₃( ₃-S)(-X)(-S)₂(H₂O)₉]⁴⁺ (X=O, S) in hydrochloric acid react with dien (diethylenetriamine) to give [Mo₃( ₃-S)(-X)(-S)₂(dien^–)(dien)₂]Cl₃·nH₂O [1, X=O, n=3; 2, X=S, n=4; dien^–=NH₂(CH₂)₂NH(CH₂)₂NH^–], respectively, where each cluster has a deprotonated dien. The X-ray structural analysis of 1 revealed proton dissociation from an amino group of one of the three dien ligands: one Mo–N distance [1.987(4) Å] is clearly shorter than the other eight Mo–N distances [2.229(3)–2.276(3) Å]. The ¹H NMR spectra of the Mo–dien clusters 1 and 2 in D₂O show two well-resolved methylene proton signals in the 2.8- to 3.0-ppm region, which indicates that both deprotonated amines in 1 and 2 receive D⁺ ions from solvent D₂O. The factors for the proton dissociation are discussed.     

Substitution of ligands in dichloro-2-(arylazo)heterocyclepalladium(II) by 8-quinolinol: kinetics and mechanistic studies

Nucleophilic substitutions of Pd(N,N)Cl₂[(N,N = 1-methyl-2-(arylazo)imidazole (RaaiMe), p-RC₆H₄N=NC₃H₂NN-1-Me; 2-(arylazo)pyridine (Raap), p-RC₆H₄N=NC₅H₄N; 2-(arylazo)pyrimidine (Raapm), p-RC₆H₄N=NC₄H₃N₂ where R = H (a), Me (b), Cl (c)] with 8-quinolinol (HQ) have been examined by spectrophotometry at 298 K in MeCN solution. The product, Pd(Q)₂, has also been confirmed by independent synthesis from Na₂[PdCl₄] and HQ in EtOH. The kinetics of the reaction have been studied under pseudo-first-order conditions and the analyses support a nucleophilic association path. A single phase reaction has been observed and follows the rate law, rate = a + k [Pd(N,N)Cl₂] [HQ]². Thus, the reaction is first order in [Pd(N,N)Cl₂] and second order in [HQ]. External addition of Cl^–(LiCl) suppresses the rate. The rate increases as follows: Pd(RaaiMe)Cl₂ < Pd(Raap)Cl₂ < Pd(Raapm)Cl₂.     

2,4′-Bipyridyl complexes with cobalt(II) and nickel(II)

Summary Complexes of empirical formulae [ML₂Cl₂(OH₂)₂], [CoL₂Br₂(OH₂)₂]L·4H₂O, [NiL₂Br₂(OH₂)₂]L₂·2H₂O, [ML₂(OH₂)₄]L₂(NO₃)₂ and [ML₄(OH₂)₂](ClO₄)₂·2H₂O (M = Co^II, Ni^II, L = 2,4-bipyridyl) were synthesized and characterized by elemental and spectral analyses. The thermal decomposition of the complexes was also investigated.Author to whom all correspondence should be directed.     

Multicentered bonding and quasi-aromaticity in metal-chalcogenide cluster chemistry

On the basis of the localized molecular orbital (LMO) theory, the bonding schemes for the following types of cluster compounds are briefly reviewed in this paper; the linear [Et₄N][Cl₂FeS₂MoS₂Cu(PPh₃)₂] cluster, triangular trinuclear [M ₃(₃–X)(–Y ₃]⁴⁺ (M = Mo, W;X = O, S;Y = O, S, Se) clusters, triangulated polyhedral clusters: closo-boranes B _n H _n ^2–, octahedral [Co₆(CO)₁₄]^4–, [Ni₂Co₄(CO)₁₄]^2– and [Co₆(₃ –X ₈ ·L ₆ ⁿ⁺ (X = S, Se;L = PPh₃, PEt₃, CO;n = 0,1) as well as quasi-aromatic cluster ligands in cubane-type [Mo₃S₄ ·ML _n ^{(4 +q) +} (M = Mo, W, Fe, Ni, Cu, Sn, Sb;L = Ligand and sandwich-type [Mo₃S₄ ·M · S₄Mo₃]⁸⁺ (M = Mo, Sn, Hg). We put emphasis upon the characteristics of multicentered bonding in these cluster molecules, and, especially, point out existence of a novel species of quasi-aromatic cluster compounds.