Chemie und Strukturchemie von Phosphiden und Polyphosphiden. 53. Darstellung,Eigenschaften und Schwingungsspektren der Käfiganionen P113− und As113−

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 53. Preparation, Properties, and Vibrational Spectra of the Cage Anions P₁₁^3? and As₁₁^3? The Zintl-phases M₃X₁₁ (M = Na, K, Rb, Cs; X = P, As) are prepared from the elements or from M₃X₇ and X. The compounds undergo a first-order phase transition from the crystalline to the plastically crystalline state. Unit cell and space group of both modifications and the transition temperature T_c are determined. The vibrational spectra of the crystalline compounds and the Raman spectrum of the P₁₁^3? anion in en-solution as well are measured. The assignment of the frequencies is given, based on the 32-D₃ symmetry of the X₁₁^3? cage anion. Normal coordinate analysis is carried out in terms of Cartesian coordinates to avoid the problem of redundancies in using internal coordinates. The force constants [mdyn Å^?1] obtained for the characteristic bonds r, s, and t are: f = 1.34, f = 1.20, f = 1.08; f = 1.1, f = 0.91. Normal vibrations and the potential energy distribution (PED) are discussed.     

Röntgenographische Untersuchungen und Strukturchemie von Chalkogenomolybdaten und -wolframaten

X-Ray Investigations and Structure Chemistry of Chalkogenomolybdates and - tungstates. I. Crystallographic data of compounds of the type A₂MeX₄, A₂MeOX₃, and A₂MeO₂X₂ (A = K, NH, Rb, Cs; (Me = Mo, W; X = S, Se) are discussed and general trends are illustrated. The molybdates and tungstates A₂MeX₄ and A₂MeOX₃ (A = K, NH, Rb, Cs; X = S, Se) crystallize in the rhombic space group D? Pnma. The compounds (NH₄)₂MeO₂X₂ (Me = Mo, W; X = S, Se) crystallize in the monoclinic space group C? C2/c.     

Darstellung und Struktur der Tetrafluoroaurate(III) MI[AuF4] mit MI = Li,Rb

Synthesis and Structure of Tetrafluoroaurates(III) M^I[AuF₄] with M^I = Li, Rb Single crystal investigations on Rb[AuF₄], light yellow, confirm the tetragonal unit cell (K[BrF₄]-type) with a = 618.2(1) and c = 1191(1) pm, Z = 4, space group I 4/mcm-D (No. 140). Li[AuF₄], light yellow too, crystallizes monoclinic with a = 485.32(7), b = 634.29(8), c = 1004.43(13) pm, β = 92.759(12), Z = 4; space group P 2/c-C (No. 13). The structure of Li[AuF₄] is related to the Rb[AuF₄]-type of structure.     

Silaheterocyklen. III. Erzeugung und Reaktivität von Di-tbutyl-Neopentylsilaethen,BuSiCHCH2But

Silaheterocycles. III. Synthesis and Reactivity of Di-^tbutylneopentylsilaethene, Bu Si?CHCH₂Bu^t The three di-^tbutylvinylsilanes BuSi(X)CH?CH₂ (X = H 5 , X = F 9 , X = Cl 22 ) are prepared by the reaction of their SiCl precursors with vinyl lithium. In the treatment with LiBu^t the first step is the generation of the α-lithio compound BuSi(X)CH(Li)CH₂Bu^t, the following reactions are governed by the nature of the substituent X and the reaction conditions (solvent, concentration, temperature). For X = H 2,3-LiH elimination leads to BuSi(H)CH?CHBu^t ( 7 ), with X = F or Cl Si?C formation by 1,2-LiX elimination competes with intermolecular Si-C-coupling producing BuSi(H)CH(SiBuCH?CHBu^t)CH₂Bu^t ( 13 ) as the main product. BuSi?CHCH₂Bu^t ( 1 ) probably coordinates to LiBu^t and reacts to yield BuSiCH?CHBu^t ( 3 ) and 7 , forms tetrabutyl-dineopentyl-1,3-disilacyclobutane 2 by cyclodimerization and 13 by addition of BuSi(X)CH(Li)CH₂Bu^t.     

Synthese und Struktur von MII[AuF4]2 (MII  Cd,Hg)

Synthesis and Structure of M^II[AuF₄]₂ (M^II ? Cd, Hg) Cd[AuF₄]₂ and the isotypic compound Hg[AuF₄]₂, both are yellow, crystallize tetragonal in the space-group P4/mcc-D (No. 124) with a = 575.0/575.6 pm, c = 1034.8/1042.3 pm and Z = 2. The single-crystals were obtained by solid-state reactions in goldtubes.     

Evaluation of strontium isotope abundance ratios in combination with multi-elemental analysis as a possible tool to study the geographical origin of ciders

In order to evaluate alternative analytical methodologies to study the geographical origin of ciders, both multi-elemental analysis and Sr isotope abundance ratios in combination with multivariate statistical analysis were estimated in 67 samples from England, Switzerland, France and two Spanish regions (Asturias and the Basque Country). A methodology for the precise and accurate determination of the ⁸⁷Sr/⁸⁶Sr isotope abundance ratio in ciders by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) was developed. Major elements (Na, K, Ca and Mg) were measured by ICP-AES and minor and trace elements (Li, Be, B, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Y, Mo, Cd, Sn, Sb, Cs, Ba, La, Ce, W, Tl, Pb, Bi, Th and U) were measured by ICP-MS using a collision cell instrument operated in multitune mode. An analysis of variance (ANOVA test) indicated that group means for B, Cr, Fe, Ni, Cu, Se, Cd, Cs, Ce, W, Pb, Bi and U did not show any significant differences at the 95% confidence level, so these elements were rejected for further statistical analysis. Another group of elements (Li, Be, Sc, Co, Ga, Y, Sn, Sb, La, Tl, Th) was removed from the data set because concentrations were close to the limits of detection for many samples. Therefore, the remaining elements (Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba) together with ⁸⁷Sr/⁸⁶Sr isotope abundance ratio were considered for principal component analysis (PCA) and linear discriminant analysis (LDA). Finally, LDA was able to classify correctly 100% of cider samples coming from different Spanish regions, France, England and Switzerland when considering Na, Mg, Al, K, Ca, Ti, V, Mn, Zn, As, Rb, Sr, Mo, Ba and ⁸⁷Sr/⁸⁶Sr isotope abundance ratio as original variables.     

Zur Kenntnis von BiBr und BiBr1,167

On BiBr and BiBr_1,167 Preparation and crystal structures of BiBr_1,167 and BiBr are describe as well as their phase relationships. BiBr_1,167 is isotypic with the familiar BiCl_1,167, the structures comprising the cluster Bi with the same Bi? Bi distances and deviations from trigonal symmetry. A simple electrostatic attraction-repulsion calculation with respect to the stability of the particular cluster configuration is given. The structure of BiBr consists of infinite onedimensional chains [Bi₄Br₄] as the structure of BiI. These compounds are structurally classified as special stacking variants of a common motif.     

Übergangsmetallchalkogenverbindungen. Darstellung,IR- und Raman-Spektren sowie röntgenographische Untersuchungen von Verbindungen des Typs A3(MeOS3)Cl und A2MeOS3 (A = K,Rb; Me = Mo W)

Transition Metal Chalkogen Compounds. Preparation, I.R. spectra, Raman Spectra, and X-Ray Investigations on Compounds of the Type A₃(MeOS₃)CI and A₂ MeOS₃(A = K, Rb; Me = Mo, W) The preparation, vibrational spectra, and x-ray data of compounds of the type A₃(MeOS₃)Cl and A₂MeOS₃ (A = K, Rb; Me = Mo, W) are reported. K₃(MoOS₃)Cl, K₃(WOS₃)Cl, and Rb₃(WOS₃)Cl are novel salts which can be prepared by passing H₂S through strong alcaline aqueous MoO and WO solutions containing KCl or RbCl. The salts crystallize in space group Pca2₁? C (No. 29) (Z = 4) with discrete MeOS tetrahedrons. The compounds A₂MeOS₃ (A = K, Rb; Ne = Mo, W) which are in part precipitable only by addition of organic solvents crystallize in space group Pnma? D (No. 62) with four formula units per unit cell.     

L'action de l'ammoniac sur l'hydroxyde de cadmium et la stabilité des complexes en milieu aqueux

The solubility of precipitated Cd(OH)₂ was determined at 25°C in 1 M NaClO₄, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH⁺, Cd(OH)₂, Cd(OH), CdNH, Cd(NH₃), Cd(NH₃), Cd(NH₃) and Cd(OH)₂NH₃. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration.     

K2NaGaP2, Cs2NaGaP2, K2NaGaAs2, K2NaInP2 und K2NaInAs2, Verbindungen mit den SiS2-isosteren Polyanionen [MX4/2]3− (MGa,In; XP,As)

K₂NaGaP₂, Cs₂NaGaP₂, K₂NaGaAs₂, K₂NaInP₂ and K₂NaInAs₂, Compounds with the Polyanions [MX_4/2]^3? (M?Ga, In; X?P, As) isosteric with SiS₂ The title compounds are synthesized from stoichiometric mixtures of the elements or from Na, KP(KAs), Cs₄P₆ and MX (M?Ga, In; X?P, As) at 950K. They are isotypic and crystallize in the space group Ibam (No. 72) with Z=4. The anionic partial structure is characterized by infinite chains [MX_4/2]^3? which are isosteric to SiS₂. Vibrational spectra are measured and interpreted based on the symmetry D_4h-P(2/m 2/c)4₂/m of the isolated polymer chain [MX₂]^3?. A good agreement between observed and calculated frequencies is obtained by using a force field of the tetrameric fragment [M₄X₁₀]^18? (three four-membered M₂X₂ rings).     

Photoelektronen-Spektren und Moleküleigenschaften. 133 [1, 2]. Trifluormethyldisulfan und Derivate F3CSSX (X  CF3, F,Cl, Br)

Photoelectron Spectra and Molecular Properties. 133. Trifluoromethyldisulfane and Derivates F₃CSSX (X?CF₃, F, Cl, Br) The He(I) photoelectron spectra of trifluoromethyldisulfane F₃CSSH and its derivatives F₃CSSX (X?CF₃, F, Cl, Br) are assigned by Koopmans correlations, IE = ?ε, with MNDO eigenvalues and by radical cation state comparison. Of special interest are the n/n splittings, which amount to 1.15 eV F₃C? SS? F or 0.87 eV in F₃? SS? Cl, and the dependance of which on the dihedral angle ω(XS? SX), on the SS bond length and on the acceptor effect of the F₃C substituents is discussed.     

Bis[N-(trimethylsilyl)iminobenzoyl]phosphanide des Lithiums und Zinks – Synthese sowie NMR-spektroskopische,strukturelle und quantenchemische Untersuchungen

Acyl- and Alkylidenephosphanes. XXXV. Bis[ N -(trimethylsilyl)iminobenzoyl]phosphanides of Lithium and Zinc – Syntheses as well as NMR Spectroscopic, Structural, and Quantumchemical Studies From the reaction of bis(tetrahydrofuran)lithium bis(trimethylsilyl)phosphanide with two equivalents of benzonitrile in 1,2-dimethoxyethane, the yellow dme complex ( 2 a ) of lithium bis[N-(trimethylsilyl)iminobenzoyl]phosphanide ( 2 ) was obtained in 69% yield. However, the intermediate {1-[N-lithium-N-(trimethylsilyl)amido]benzylidene}trimethylsilylphosphane ( 1 ), formed by an analogous 1 : 1 addition in diethyl ether, turned out to be unstable and as a consequence could be characterized by nmr spectroscopic methods only; attempts to isolate the compound failed, but small amounts of the neutral complex 2 b , with the ligands benzonitrile and tetrahydrofuran coordinated to lithium, precipitated. The reaction of compound 2 with zinc(II) chloride in diethyl ether gives the orange-red spiro-complex zinc bis{bis[N-(trimethylsilyl)iminobenzoyl]phosphanide} ( 3 ); this complex is also formed from bis[N-(trimethylsilyl)iminobenzoyl]phosphane ( 4 ), easily amenable by a lithium hydrogen exchange of 2 a with trifluoroacetic acid [18], and zinc bis[bis(trimethylsilyl)amide]. As derived from nmr spectroscopic studies and x-ray structure determinations, compounds 2 a {δ³¹P +63.3 ppm; P2₁/n; Z = 4; R₁ = 0.067}, 2 b {δ³¹P +63.3 ppm; P2₁/c; Z = 4; R₁ = 0.063}, 3 {δ³¹P +58.2 ppm; C2/c; Z = 4; R₁ = 0.037} and 4 {δ³¹P +58.1 ppm [18]} exist as cyclic 3-imino-2λ³σ²-phosphapropenylamides and -propenylamine, respectively, in solution as well as in the solid state. Unlike hydrogen derivative 4 the bis[N-(trimethylsilyl)iminobenzoyl]phosphanide fragments N,N′-coordinating either a lithium or a zinc cation are characterized by almost completely equalized bond lengths; typical mean distances and angles are: PC 180.3 and 178.7; CN 130.5 and 131.8; N–Si 175.3 and 179.3; N–Li 202.3; N–Zn 203.5 pm; CPC 108.8° and 110.5°; PCN 130.9° and 132.9°; CN–Li 113.0°, CN–Zn 117.4°; N–Li–N 104.6°; N–Zn–N 108.8°. Alterations in the shape of the six membered chelate rings, caused by an exchange of the 3-imino-2λ³σ²-phosphapropenylamide or related 2λ³σ²-phospha-1,3-dionate units for the corresponding phosphorus free ligands, are discussed in detail. The results of quantumchemical DFT-B3LYP calculations coincide very well with the experimentally obtained findings.     

Darstellung,Kristallstrukturen und Schwingungsspektren von [OsCl(acac)(EPh3)], E = P,As, Sb

Synthesis, Crystal Structures, and Vibrational Spectra of [OsCl(acac)(EPh₃)], E = P, As, Sb By reaction of tetrachloroacetylacetonatoosmate(IV) with PPh₃, AsPh₃ or SbPh₃ in ethanol the complexes [OsCl(acac)(EPh₃)], E = P, As, Sb are formed, which are purified by chromatography on silica gel. X-ray crystal structure determinations of the isotypic single crystals of [OsCl(acac)(EPh₃)] (monoclinic, space group P 2₁/c, Z = 4; E = P ( 1 ): a = 12.972(2), b = 18.255(2), c = 16.517(2) Å, β = 112.61(2)°; E = As ( 2 ): a = 13.173(5), b = 18.299(5), c = 16.429(5) Å, β = 112.346(5)°; E = Sb ( 3 ): a = 13.573(3), b = 18.520(3), c = 16.440(9) Å, β = 111.78(2)°) result in mean bond distances Os–P = 2.412, Os–As = 2.485, Os–Sb = 2.619, Os–Cl = 2.354 and Os–O = 2.032 Å. The IR spectra (10 K) exhibit the inner ligand vibrations of the acac and EPh₃ groups with nearly constant frequencies and the stretching vibrations of OsP at 500–524, of OsAs at 330–339, of OsSb at 271–278, of OsCl at 317–322 and of Os–O in the range 460–694 cm^–1.     

Die Deprotonierung von Metall-Aquoionen I.: Be · aq2+ Solvatations-Isomerie

The reaction of Be · aq²⁺ with OH^? leeds not only to loss of protons by the metalaquo ion but also to structural changes in the solvation sphere. These can be studied by following the pH variations during the first decisecond after mixing the solutions of metal salt and alkali hydroxide. The equilibrium Be²⁺ ? BeOH⁺ is reached within 5 milliseconds if acid free Beryllium solutions are used. If the metal solution is strongly acidic, however, the establishment of the equilibrium needs more time because of the slowness of the process H⁺ + BeOH⁺ → Be²⁺ (k ～ 10⁵ M^?1, s^?1). The extraction of two protons produces in the first instance an unstable Be(OH) species which transforms into the stable isomer Be(OH)₂ (solvatation isomerism) in a first-order reaction of half-life of 7 ms. This isomerisation causes almost complete disappearance of BeOH⁺ from the equilibrium Be²⁺ ? BeOH⁺ ? Be(OH)₂. (KAKIHANA & SILLEN state that the relaxed solutions contain only Be²⁺, Be(OH)₂, Be₃(OH) and some Be₂OH³⁺.) The formation of the polynuclear species Be₃(OH) needs about 30 seconds to go to completion.     

Comparative instrumental multi-element analysis I: Comparison of ICP source mass spectrometry with ICP atomic emission spectrometry, ICP atomic fluorescence spectrometry and atomic absorption spectrometry for the analysis of natural waters from a granite region

Summary Multi-element analysis by ICP source mass spectrometry for practically matrix-free natural waters, coming from a granitic area and, therefore, rich in trace elements, has been compared with ICP-atomic emission, ICP atomic fluorescence and atomic absorption spectrometry. The following elements have been investigated and their concentrations are in the decreasing order: Ca, Si, Na, Mg, K, Al; Sr, Mn, Ba, Fe, Rb, Zn, B, U, Y, Li, La, Be, Cs, Co, Cr, V, Sb, Bi, Th, Cu, Cd, Ni, Se, Pb, As, Hg, Mo, Tl, Sn. The concentration ranges were between 10 ppm and <0.01 ppb.As a measure of agreement between the different methods under investigation, two criteria have been used (a) the relative variation coefficient VK (%) of the mean element concentration of an element, determined by different methods in all the 98 water samples and (b) the linear, logarithmic and Spearman rank correlation coefficients between ICP-MS and each of the other methods. Detection limits are given from literature for about 32 elements using different methods.The elements Ca, Na, Mg, K, Mn, Sr, Zn, Fe, Li, Cu have been determined with ICP-MS, ICP-AES and AAS; Al, Ba with ICP-MS and ICP-AES; Si only with ICP-AES, whereas B, Be, Bi, Co, Cr, Cs, Hg, La, Mo, Ni, Pb, Rb, Sb, Sn, Th, Tl, U, V, Y only with ICP-MS. In all 34 of the investigated 36 elements could be analysed by ICP-MS, 14 (from about 20 possible) by AAS, 13 by ICP-AES and 12 by ICP-AFS.The agreement between ICP-MS and ICP-AES as well as between ICP-MS and AAS in most cases is remarkably good according to (a). VK (%) for each element in 98 water samples is in the range from ±2.6 to 10% for Na, Mg, Ca, K, Fe, Sr, Ba, Cu, Li (increasing order). Cd and Zn have unexpectedly higher values (±17.3 and ±20.5%); Cd concentrations are, however, near the detection limit.Comparing the different methods on the basis of correlation coefficients according to (b), gives for the Spearman rank correlation coefficient over the whole range of concentrations, respectively for ICP-MS/ICP-AES, AAS, ICP-AFS in case of Ca: 0.998; 0.984; 0.899; Na: 0.993; 0.991; 0.978; Mg: 0.997; 0.993; 0.959; K: 0.986; 0.942; 0.677; Al: 0.987; -; -; Fe: 0.864; 0.974; 0.701; Mn: 0.989; 0.990; 0.198; Sr: 0.988; 0.992; -; Zn: 0.894; 0.819; 0.300; Cu: -; 0.977; 0.202; Li: -; 0.907; 0.586.It is evident from these trace element concentrations as well as the electrical conductivities, that only about three fourths of the investigated samples are typical granitic waters and the remaining ones are associated with different geological background. The samples have been mainly radon waters with more than 18 nCi/l of Rn-222.

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Vergleichende Instrumentelle Multielementanalyse I: Vergleich von ICP-Massenspektrometrie mit ICP-Atomemissionsspektrometrie, ICP-Atomfluorescenzspektrometrie und Atomabsorptionsspektrometrie zur Analyse natürlicher Wässer aus einem Granitgebiet

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6th Contribution to the principles of trace analysis of elements and radionuclides

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Dedicated to Professor Dr. H. Kelker, Frankfurt, on the occasion of his 65th birthday     

Darstellung und Elektronenspektren neuer Trithiocarbonato-Komplexe; Struktur,Eigenschaften und Photoelektronenspektren von Ni(NH3)3CS3 und Zn(NH3)2CS3

Preparation and Electronic Spectra of new Trithiocarbonato Complexes; Structure, Properties, and Photoelectronic Spectra of Ni(NH₃)₃CS₃ and Zn(NH₃)₂CS₃ The complex anions [Zn(CS₃)₂]^2?, [Cd(CS₃)₂]^2?, [Co(CS₃)₃]^3?, [Cr(CS₃)₃]^3?, [As(CS₃)₃]^3?, [Sb(CS₃)₃]^3?, [Bi(CS₃)₃]^3?, [Sn(CS₃)₂]^2?, and [Cu(CS₃)] could be isolated as tetraphenylphosphonium and tetraphenylarsonium salts. From the electronic spectra of the transition metal complexes it follows that the CS ion exhibits, in comparison with other sulfur containing ligands, relatively large Δ-values and only a small nephelauxetic effect (e.g. in [Cr(CS₃)₃]^3?: Δ = 16.0 kK; β₃₅ = 0.57). The trithiocarbonate ion in all the above complexes acts as a bidentate ligand and forms fourmembered ring systems CS₂M. Further it was proved by means of infrared, electronic and photoelectronic spectra that the structure of “Ni(NH₃)₃CS₃” is [Ni(NH₃)₆][Ni(CS₃)₂] whereas Zn(NH₃)₂CS₃ has not such an ionic structure.     

Über Perowskite ABBWVIO6

On Perovskites A B B W^VIO₆ Compounds of type ABBW^VIO₆ can be obtained with A^II ? Ba; B^I ? Li, Na and B^III ? La, Nd, Sm, Gd, Y, In, Sc just as with A^II ? Sr, B^I ? Li and B^III ? La, Nd, Sm, Gd, Y, In (all cubic ordered perovskites). For the cubic perovskites Sr₂Na_0,5La_0,5WO₆ and Sr₂Na_0,5Nd_0,5WO₆ additional superlattice reflections are observed (a ∽ 16.4 Å). The compounds Sr₂Na_0,5BWO₆ crystallize with B^III ? Sm, Gd in a monoclinic and with B^III ? Y, In in a rhombic distorted perovskite lattice. For the perovskites with A = Sr — dependent on ionic radii of the B ions — two different lattice types are present.     

Determination of trace elements of some Egyptian crops by instrumental neutron activation,inductively coupled plasma-atomic emission spectrometric and flameless atomic absorption spectrophotometric analysis

Instrumental neutron activation analysis was used for the determination of Al, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, K, La, Mg, Mn, Na, Rb, Sb, Sc, Se, Ti, Th, V and Zn, ICP-AES for the determination Al, Ag, Ba, Be, Ca, Co, Cr, Cu, Fe, Ga, K, Li, Mg, Mn, Na, Ni, P, Sc, Sr, Ti, V and Zn and flameless AAS for the determination of Cd, Hg and Pb in egg plant, potatoes, green pepper (Leguminosae), vegetable marrow (Cucurbitaceae), pears, apple (Rosaceae), castor oil plant (Euphorbiaceae), lettuce (compositae), dill, parsley, coriander (Umbelliferae), and in some soil samples collected from Aswan province.     

Über das Auftreten von Monoselenan- und Monotelluran-disulfandiphosphonat bei der Umsetzung von SPO mit Seleno- und Telluropolythionaten

On the Formation of Monoselenane and Monotellurane Disulphane-diphosphonate by the Reaction of SPO with Seleno and Telluropolythionates In the reaction of seleno- and telluropolythionates with SPO, SeS₂P₂O and TeS₂P₂O are formed and are described for the first time. Polysulfphane-diphosphonates, -disulphonates and -phosphonsulphonates occur as side and consecutive products. By evaluation of radiochemical double labelling with the nuclide pairs ³⁵S? ³²P and ³⁵S? ⁷⁵Se, it is possible to identify the products formed and obtain information about the reaction mechanism.     

Theoretical study of aromaticity in small hydrogen and metal cation clusters X (X=H,Li, Na,K, and Cu)

Five cation clusters X (X=H, Li, Na, K, and Cu) with two possible isomers, i.e., regular trigonal structure (D_3h) and linear structure (D_∞h), have been investigated using four methods: B3LYP, B3PW91, MP2, CCSD(T) and basis set 6‐311+G(3df). The calculations show that only the regular trigonal structure (D_3h) is stable. The related neutral clusters X₃Cl (X=H, Li, Na, K, and Cu) are also investigated using two methods: B3LYP, MP2, and basis set 6‐311+G(3df). For H₃Cl species, there is no a stable structure to be found. For other four X₃Cl (X=Li, Na, K, and Cu) species, there are two stable isomers, for which the bidentate structures (C_2v‐1) [see Fig. 1 (d)] are global minima. According to the general criteria for aromaticity including resonance energy (RE) and nucleus‐independent chemical shift (NICS), the five trigonal isomers exhibit a higher degree of aromaticity. Molecular orbital analysis reveals that the five trigonal X(X=H, Li, Na, K, and Cu) isomers possess only σ‐aromaticity originating from s orbitals. For the Cu ring the d orbitals do not play a significant role in the electron delocalization effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007