An Ab Initio Study and NBO Analysis of the Stability and Conformational Properties of Hexakis(trimethylelementhyl)benzene (Element = C,Si, Ge,and Sn)

Ab initio molecular orbital and density functional theory were used to investigate energetic and structural properties of the various conformations of hexa-tertbutylbenzene (1), hexakis(trimethylsilyl)benzene (2), hexakis (trimethylgermyl)benzene (3), and hexakis(trimethylstannyl)benzene (4). HF/3-21G//HF/3-21G and B3LYP/3-21G//HF/3-21G results revealed that the Twist-Boat (TB) conformer of compound 1 is more stable than the 1-Chair (C), 1-Boat (B), and 1-Planar (P) conformers. B3LYP/3-21G//HF/3-21G results show that the 1- TB conformer is more stable than 1- C, 1- B, and 1- P conformers of about 1.13, 4.34, and 99.94 kcal mol^?1 , respectively. Contrary to the stability order of compound 1 conformers, the C conformer of compounds 2–4 is more stable than TB, B, and P conformations, as calculated by B3LYP/3-21G//HF/3-21G and HF/3-21G//HF/3-21G levels of theory. The energy gap between the C and P conformers in compounds 1–4 is decreased in the following order: ΔE(4: C, P) < ΔE (3: C, P) < ΔE(2: C, P) < ΔE (1: C, P). This fact can be explained in terms of the increase of C _aromatic -M (M═C, Si, Ge, and Sn) bond lengths and the decrease of steric (van der Waals) repulsions in the previously discussed compounds. For compounds 1–3, the calculations were also performed at the B3LYP/ 6-31G*//HF/3-21G level of theory. However, the comparison showed that the results at B3LYP/3-21G//HF/3-21G methods correlated well with those obtained at the B3LYP/6-31G*// HF/6-31G method. Further, NBO analysis revealed that in compounds 1–4, the resonance energy associated with the σ_M-C1 to σ*_C2-C3 delocalization is 5.20, 9.68, 11.15, and 12.27 kcal mol^?1, respectively. These resonance energy values could explain the easiness of the ring flipping processes of C, B, and TB conformers of compounds 4 to 1. Also, the NBO results showed that by an increase of the σ_M-C1 → σ *_C2-C3 resonance energies in compounds 1–4, the σ_M-C1 bonding orbital occupancies decrease. This fact could fairly explain the increase of the C_aryl-M bond length from compound 1 to 4. The NBO results are also in good agreement with the calculated energy barriers for the ring flipping of the chair conformations in compounds 1–4, as calculated by B3LYP and HF methods.     

Ab initio and density functional study of the conformational space of 1C4 α-L-fucose

The conformational space of ¹C₄ α-L-fucose was searched by the MM2^*-SUMM molecular mechanics conformational search technique. The molecular geometries of the first 17 structures of lowest energy were analyzed at the HF/3-21G, 6-31G(d), and generalized gradient approximation (GGA) DFT levels of theory. © 1997 by John Wiley & Sons, Inc.     

Bowl-shaped hydrocarbons related to C60

Ab initio studies at the HF/6-31G* and B3LYP/6-31G* levels are reported for two bowl-shaped hydrocarbons related to C₆₀: C₃₀H₁₂ and C₃₆H₁₂, of C₃ and C_3v symmetry, respectively. The former has an approximate heat of formation of 211 kcal/mol. Bowl-to-bowl interconversion may occur through a planar (C_3h) form of ca. 64 kcal/mol greater energy having one imaginary vibrational frequency. The larger C₃₆H₁₂ bowl has a calculated ΔH°_f of 265 kcal/mol. Its HF/6-31G*, B3LYP/6-31G*, and MM3 bond lengths are in good agreement with a recent X-ray structure. Chemical shifts for both compounds calculated by the GIAO method are in good agreement with the measured NMR spectra. The observed ¹³C chemical shifts increase with the extent of pyramidalization. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 189–194, 1998     

Molecular Structure of Tetrahydroxycalix[4]arene [-(C<Subscript>6</Subscript>H<Subscript>3</Subscript>OH)-CH<Subscript>2</Subscript>-]<Subscript>4</Subscript> in the Gas Phase

Gas-phase electron diffraction and HF/6-31G*, HF/6-31G**, and B3LYP/6-31G* ab initio calculations were used to find that in the gas phase at 242°C the calix[4]arene [-(C₆H₃OH)-CH₂-]₄ molecule possesses a C₄ conformation. Geometric parameters of the molecule were determined, and the energies of C-H?O hydrogen bonds (7.3 kcal mol^?1) were estimated by the AM1 method.     

Conformational analysis of 2-methyl-5-nitro-1,3,2-dioxaborinane

Quantum-chemical methods HF/6-31G(d), HF/6-31+G(d), MP2/6-31G(d)//HF/6-31G(d), and MP2/6-31+G(d)//HF/6-31+G(d) were used to investigate the conformational isomerization of 2-methyl-5-nitro-1,3,2-dioxaborinane. It has been shown that a potential energy surface of this compound includes two minima: an axial form of semi-chair and equatorial sofa together with a transition state belonging to the conformation of 2,5-twist-form. A comparison between experimental NMR ¹H and theoretical vicinal coupling constants was used to determine the quantitative conformational composition of cyclic boric acid ester and a value of ΔG ⁰ for nitro group at the ring carbon atom C⁵ in CCl₄ and C₆D₅NO₂ solutions.     

Assigning the major isomers of fullerene C88 by theoretical 13C NMR spectra

The IPR isomers of fullerene C₈₈ have been studied using density functional theory. Structures of all C₈₈ isomers with non-zero HOMO–LUMO gaps were optimized at the B3LYP/STO-3G level. Those isomers having energies lower than 25 kcal/mol were subjected to geometry optimization using the 6-31G basis set. Isomer 17 has the lowest energy, followed by 7 and 33. All three isomers have large HOMO–LUMO gaps. ¹³C NMR chemical shifts were obtained employing the GIAO method. The comparison between predicted and measured NMR spectra strongly supports the observed C₈₈-1(C_s) as isomer 17, and isomers C₈₈-2(C₂) and C₈₈-3(C₂) as 7 and 33, respectively.     

Steric and Electronic Structure of C6H5XCF3 Molecules (X = O or S): A Quantum-Chemical Study

The potential functions of internal rotation around the Csp ²-X bond in C₆H₅XCF₃ molecules (X = O or S) were obtained by quantum-chemical calculations in the HF/6-31G(d), MP2(f)/6-31G(d), and B3LYP/6-31G(d) approximations. The calculations were performed in the range of torsion angles (angle between the planes of the benzene ring and Csp ²-X-Csp ³ bonds) from 0° to 90° with a 15° step. The barriers to rotation around the Csp ²-X bonds (kJ mol^{- 1}) were evaluated: for C₆H₅XCF₃, 7.60 (HF), 3.04 (MP2), and 1.04 (B3LYP); for C₆H₅XCF₃, 16.57 (HF), 14.67 (MP2), and 8.73 (B3LYP). The geometries (bond angles and bond lengths), Koopmans ionization potentials, and dipole moments of the molecules were calculated. The hybridization, energy, and population of the lone electron pairs of the heteroatoms, and also the energy of their resonance interaction with antibonding orbitals and the natural atomic charges were evaluated using the NBO approach.     

AB INITIO MOLECULAR ORBITAL STUDY OF 1,2-DITHIANE AND 1,2,4,5-TETRATHIANE

Ab initio calculations at HF/6-31+G? level of theory for geometry optimization, and MP2/6-31+G?//HF/6-31+G? and B3LYP/6-31+G?//HF/6-31+G? levels for a single-point total energy calculation, are reported for the chair and twist conformations of 1,2-dithiane (1), 3,3,6,6-tetramethyl-1,2-dithiane (2), 1,2,4,5-tetrathiane (3), and 3,3,6,6-tetramethyl-1,2,4,5-tetrathiane (4). The C₂ symmetric chair conformations of 1 and 2 are calculated to be 21.9 and 8.6 kJ mol^?1 more stable than the corresponding twist forms. The calculated energy barriers for chair-to-twist processes in 1 and 2 are 56.3 and 72.8 kJ mol^?1, respectively. The C_2h symmetric chair conformation of 3 is 10.7 kJ mol^?1 more stable than the twist form. Interconversion of these forms takes place via a C₂ symmetric transition state, which is 67.5 kJ mol^?1 less stable than 3-Chair. The D₂ symmetric twist-boat conformation of 4 is calculated to be 4.0 kJ mol^?1 more stable than the C_2h symmetric chair form. The calculated strain energy for twist to chair process is 61.1 kJ mol^?1.     

Unusual pentagon and hexagon geometry of three isomers (no 1, 20, and 23) of fullerene C84

Three isomers 23 (D_2d), 1 (D₂), and 20 (T_d) of fullerene C₈₄ have been investigated by PM3, HF/6‐31G*, and DFT methods with B3LYP functional at the 6‐31G and 6‐31G* levels. In this article we reveal for the first time that some distortion of hexagon (pentagon), measured as its maximal dihedral angles, caused by local molecular strains may serve as a new criterion of stability of fullerenes with closed shell. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Iminopropadienones R–NCCCO and carbon suboxide, C3O2. Theoretical and experimental C NMR spectra

The ¹³C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C₃O₂, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10 ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.     

An Ab Initio Molecular Orbital Theory and Density Functional Theory (DFT) Study of Conformers and Rotamers of 4-Substituted (Methyl, Hydroxymethyl, Methanoyl, Ethanoyl, Cyano, Fluoro, Chloro, Bromo, Acetoxy) Tetrahydro-2H-thiopyran-1,1-dioxides

The structures and energies of axial and equatorial conformers and rotamers of 4-substituted tetrahydro-2H-thiopyran-1,1-dioxides (tetrahydrothiopyran-1,1-dioxides, thiacyclohexane-1,1-dioxides, thiane-1,1-dioxides, and 1,1-dioxothianes; CH₃, CH₂OH, CHO, COCH₃, CN, F, Cl, Br, and OCOCH₃) were calculated using the hybrid density functionals B3LYP, B3P86, and B3PW91, as well as MP2 and the 6-31G(d), 6-31G(2d), 6-31G(3d), 6-31G(d,p), and 6-31+G(d) basis sets. MP2/6-31+G(d)/ /HF/6-31+G(d) [–G° = 1.73 kcal/mol], B3P86/6-31G(d) [–G° = 1.75 kcal/mol], and B3PW91/6-31G(d) [–G° = 1.85 kcal/mol] gave conformational free energy (G°) values at 180 K for 4-methyltetrahydro-2H-thiopyran-1,1-dioxide which were similar to the reported experimental values for methylcyclohexane (–G° = 1.80 kcal/mol), 4-methyltetrahydro-2H-thiopyran (–G° = 1.80 kcal/mol), and other 4-methyl-substituted heterocycles. All levels of theory showed that the conformational preferences of the 4-methanoyl (4-formyl), 4-ethanoyl (4-acetyl), and 4-cyano substituents were small. The HF calculations gave conformational free energy (G°) values for 4-chlorotetrahydro-2H-thiopyran-1,1dioxide which were closer to the experimental value than the MP2 and density functional methods. The best agreement with available experimental data for 4-bromotetrahydro-2H-thiopyran-1,1-dioxide was obtained from the HF/6-31G(2d), HF/6-31G(3d), and B3LYP/6-31G(2d) calculations, and, for 4-acetoxytetrahydro-2H-thiopyran-1,1-dioxide, from the HF/6–31G(3d) calculations. The conformational free energies (G°) and relative energies (E) of the conformers and rotamers have been compared with the correspondingly substituted cyclohexanes and tetrahydro-2H-thiopyrans and are discussed in terms of dipole–dipole (electrostatic) interactions and repulsive nonbonded interactions (steric) in the most stable axial and equatorial conformers. The axial S=O bond lengths are shorter than the equatorial S=O bond lengths and the C2–C3 bond lengths in the substituents with carbon-bonded to the ring are shorter than the C3–C4 and C4–C-5 bond lengths. In contrast, the C2–C3 bond lengths in the 4-halogen and 4-acetoxy substituents are longer than the C3–C4 and C4–C-5 bond lengths.     

FT-IR, FT-Raman vibrational spectra and molecular structure investigation of 2-chloro-4-methylaniline: A combined experimental and theoretical study

In this work, the experimental and theoretical vibrational spectra of 2-chloro-4-methylaniline (2Cl4MA, C₇H₈NCl) were studied. FT-IR and FT-Raman spectra of 2Cl4MA in the liquid phase have been recorded in the region 4000–400 cm⁻¹ and 3500–50 cm⁻¹, respectively. The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock (HF) and density functional method (B3LYP) with the 6-31G(d), 6-31G(d,p), 6-31+G(d,p), 6-31++G(d,p) and 6-311G(d), 6-311G(d,p), 6-311+G(d,p), 6-311++G(d,p) basis sets. The vibrational frequencies have been calculated and scaled values have been compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. The DFT-B3LYP/6-311++G(d,p) calculations have been found more reliable than the ab initio HF/6-311++G(d,p) calculations for the vibrational study of 2Cl4MA. The optimized geometric parameters (bond lengths and bond angles) were compared with experimental values of aniline and p-methylaniline molecules.     

Substituent effects on 13C chemical shifts of ketenimines: a GIAO/HF and DFT study

GIAO/HF and DFT methods were utilized to predict the ¹³C chemical shifts of substituted ketenimines. GIAO HF/6–311+G(2d,p) and B3LYP/6–311+G(2d,p) methods were applied on the optimized B3LYP/6–31G(d) geometries and ¹³C chemical shifts of C_α and C_β of substituted ketenimines were correlated with group electronegativities. HF and DFT calculations indicated that increasing substituent group electronegativity leads to increasing chemical shift of C_β of substituted ketenimines, whereas the C_α values decrease. Copyright © 2003 John Wiley & Sons, Ltd.     

Ab initio HF-SCF study of naphthazarin: Geometries,isomerism, hydrogen bonding,and vibrational spectrum

The structural properties and intramolecular hydrogen bonding of a series of structures of naphthazarin molecule were investigated by ab initio HF-SCF methods. The geometries of theC _2v ,C _2h ,D _2h , andC _s symmetry structures were optimized using split-valence basis sets. MP2/6-31G^*// HF/6-31G single-point energy calculations indicate that theC _2v isomer (5,8-dihydroxy-1,4-naphthoquinone) is the lowest energy structure of the molecule and that theC _2h symmetry one (4,8-dihydroxy-1,5-naphthoquinone), lying 37 kJ/mol above theC _2v form, is the other stable isomer of naphthazarin. At the HF/6-31G level, the intramolecular proton exchange between two equivalentC _2v structures is a two-step process where each proton can be independently transferred through an unsymmetrical potential having a 1,5-quinone intermediate, theC _2h symmetry structure, and two equivalent transition states ofC _s symmetry, with a barrier height equal to 38 kJ/ mol (MP2/6-31G^*//HF/6-31G). The study of naphthazarin molecule is flanked by a theoretical investigation on theC _2v andC _2h isomers of the parent naphthoquinone and dihydroxynaphthalene molecules. The SCF vibrational spectrum of the ground state of naphthazarin, harmonic frequencies, and infrared and Raman band intensities were computed at the HF/6-31G level. The results of the calculations are compared with the matrix isolation FT-IR spectroscopy measurements and with the infrared and Raman spectra of the crystal molecule.     

A theoretical study on C2HXSi silylenes (X = H,CN, NH2, and OMe)

Relative stabilities and structural characters of 30 silylenic C₂HXSi species (X = H, NH₂, CN, and OMe), with singlet (s) and/or triplet (t) states, are calculated at six levels of theory: HF/6‐311++G**, MP3/6‐31G*, B1LYP/6‐311++G**, B3LYP/6‐311++G**, MP2/6‐311++G**, and MP4(SDTQ)/6‐311++G**. The four possible isomers considered for C₂SiHX are (i) 3‐X‐1‐silacyclopropenylidene ( 1 _s‐X and 1 _t‐X ), (ii) X‐vinilydensilylene ( 2 _s‐X and 2 _t‐X ), (iii) ethynyl‐X‐silylene ( 3 _s‐X and 3 _t‐X ), and (iv) (X‐ethynyl)silylene ( 4 _s‐X and 4 _t‐X ). The GIAO–NICS calculations show that singlet cyclic structures, 1 _s‐X , are considerably more aromatic than benzene. Conversely, triplet cyclic C₂HCNSi breaks down through optimization, and transforms into a novel high‐spin acyclic carbenosilylene minimum ( 1 _t‐CN ). Singlet 3 and triplet 3 cross at a divalent angle (|XSiC) of 152°. This angle narrows to 137° for crossing of singlet 3 _s‐CN and triplet, 3 _t‐CN . The smallest |XSiC occurs at 132° for crossing of 3 _s‐H and 3 _t‐H . © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:283–293, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20297     

Theoretical studies of structure,stability, and chemical bonding in oxohydride OM4H6 complexes

The results of ab initio RHF/3-21G, RHF/6-31G*, and MP2/6-31G** / / HF/6-31G* calculations for 10 possible configurations of OM₄H₆ molecules (MO · 3MH₂, M = Be, Mg) are reported. Five isomers of OBe₄H₆ and three isomers of OMg₄H₆ have been found within an energy range of ã 15 kcal mol⁻¹. The “lanternlike” C_3v structure is the most favorable one for both complexes. Both molecules OM₄H₆ are stable to decomposition through all of the studied pathways. Chemical bonding in the OM_k polyhedra containing two-, three-and four-coordinated oxygen atoms is discussed. © 1996 John Wiley & Sons, Inc.     

An ab initio study of the structure,dissociation energy,and heat of formation of Na2S

The equilibrium geometries and fundamental frequencies of Na₂S are calculated at HF, MP2(FC, FU), and MP3 with the 6–31G(d) basis set and at HF and MP2(FC, FU) with the 6–31G(d) basis set, respectively. The total energy at MP2(FU)/6–31G(d)-optimized geometry is computed at MP4 with 6–311G(d, p), 6–311 + G(d, p), and 6–311G(2df, p), at QCISD(T)/6–311G(d, p), and at MP2/6–311G(3df, 2p) levels, respectively. The dissociation energy, the atomization energy, and the heat of formation for Na₂S are evaluated using the G1 and G2 models. The calculated results indicated that Na₂S in its ground state was a bent structure (C_2v). Electron correlation corrections on the bending angle are very significant. The equilibrium geometrical parameters are R_e(Na-S) = 2.45 Å and ∠Na-S-Na = 111.13° at the MP2(FU)/6–31G(d) level. The theoretically estimated dissociation energy, total atomization energy, and heat of formation are 67.07, 117.55, and 0.35 kcal mol⁻¹, respectively, at 298.15 K. © 1997 John Wiley & Sons, Inc.     

Quantum-Chemical Study of Electronic and Steric Structure of Vinyltetrazoles: I. 2-Substituted 5-Vinyltetrazoles

The total Mulliken charges on the carbon atoms of the vinyl group, populations of S-trans-(N¹)conformers, and internal rotation energies were calculated ab initio (HF/6-31G**, MP2/6-31G**, and MP2/6-31G**//AM1) for a series of 2R-5-vinyltetrazoles (R = CH₃, C₂H₅, i-C₃H₇, t-C₄H₉, C₆H₅). The calculation results were compared to the available experimental data.     

Triazene: An ab initio Molecular-Orbital Study of Structure,Properties, and Hydrogen-Transfer Reaction Pathways

Ab initio calculations of structure, properties, and tautomerization reactions of triazene ( 1 ) at the HF/3-21G//3-21G, HF/6-31G*//6-31G*, HF/6-31G**//6-31G*, and MP2/6-31G*//6-31G* levels led to the following conclusions and predictions: (a) Calculations of the ground-state structure of (E)- and (Z)-triazene ( 1a and 1b , respectively) at various levels of theory show for both isomers C₁ geometry with a rather flat pyramidal configuration at N(3), and small energy differences (0.2–7.2 kJ/mol) between C₁ and C_s geometry, i.e. inversion at N(3) is a quasi-free process. With all levels of calculations, 1a is found to be of lower energy than 1b by 23-30 kJ/mol. (b) Comparison of vibrational frequencies of (E)-diazene ( 3 ) calculated at the HF/3-21G level with experimental values reveals that HF/3-21G calculations are reliable for the prediction of vibrational frequencies of polyaza compounds, if corrected by a factor of 0.91. On this basis, the harmonic vibrational frequencies of 1a and 1b were predicted. (c) For the rotation around the N(2)—N(3) bond of 1a two conceivable transition states, 5a (syn) and 5b (anti) were located (HF/3-21G). The energy differences between 5a or 5b , and 1a are in the order of magnitude of 50-56kJ/mol and show a slight preference for the anti-mode, i.e. energy barriers for the N(2)—N(3) rotation are obtained comparable to those observed experimentally with substituted (E)-triazenes ( 4 ). (d) Protonation of 1a at N(1), N(2), or N(3) leads to 6a , 6b , and 6c , respectively –the last one resembling an intermediate of formation of 1 from hydrogendiazonium ion ( 7 ) and ammonia ( 8 ). Energetically, the conjugate acids of 1a follow the sequence 6a < 6c < 6b . (e) The preference of N(1) protonation of 1a is also reflected in the relatively high gain of energy in the formation of H-bonded dimers of 1a with H-bonds from N(3)—H to N(1). Calculations of three different H-bonded dimers 9a–c of 1a with the 3-21G basis show that an eight-membered cyclic dimer 9c with two H-bonds from N(3)? H to N(1) is energetically most favoured (67.5 kJ/mol below two separate molecules of 1a ). This dimer might well be the starting situation of double intermolecular H-transfer leading to an automeric dimer 9c via an energetically low-lying transition state 12 , thus offering a low-energy pathway for the known easy tautomerization of mono- or disubstituted (E)-triazenes. For 9c?9c , the activation energy including correction for polarization and correlation effects as well as for vibration zero-point energy is estimated to be ca. 54kJ/mol. (f) A six-membered cyclic dimer 9b of 1a with two H-bonds from N(3)? H to N(2) might be involved for double H-transfer via a transition state 11 to a dimer 10 of (E, Z)-azimine ( 2 ). This process, however, turns out to be energetically highly disfavoured (estimated energy barrier for 9b → 10 : 232 kJ/mol) in contrast to the reverse reaction ( 10 → 9b via 11 : 4 kJ/mol). This leads to the prediction that azimines bearing an H-atom at N(2) might be kinetically too instable for isolation, being, instead, easily tautomerized to triazenes by bimolecular H-transfer.     

Conformational study of the structure of free 12-thiacrown-4 and some of its cation metal complexes

Conformational search of 12-thiacrown-4, 12t4, was performed using the CONFLEX method and the MMFF94S force field whereby 156 conformations were predicted. Optimized geometries of the 156 predicted conformations were calculated at the HF, B3LYP, CAM-B3LYP, M06, M06L, M062x and M06HF levels using the 6-311G** basis set. The correlation energy was recovered at the MP2 level using the same 6-311G** basis set. Optimized geometries at the MP2/6-311G** level and G3MP2 energies were calculated for some of the low energy conformations. The D ₄ conformation was predicted to be the ground state conformation at all levels of theory considered in this work. Comparison between the dihedral angles of the predicted conformations indicated that for the stability of 12t4, a SCCS dihedral angle of 180° requirement is more important than a gauche CSCC dihedral angle requirement. Conformational search was performed also for the 12t4?CAg⁺, Bi³⁺, Cd²⁺, Cu⁺ and Sb³⁺ cation metal complexes using the CONFLEX method and the CAChe-augmented MM3 and MMFF94S force fields. Conformations with relative energies less than 10?kcal/mol at the MP2/6-31+G*//HF/6-31+G* level, with double zeta quality basis set on the metal cations, were considered for computations at the same levels as those used for free 12t4, using also the 6-311G** basis set. The cc-pVTZ-pp basis set was used for the metal cations. The predicted ground state conformations of the 12t4?CAg⁺, Bi³⁺, Cd²⁺, Cu⁺ and Sb³⁺ cation metal complexes are the C ₄, C ₄, C ₄, C _2v and C ₄ conformations, respectively. This is in agreement with the experimental X-ray data for the 12t4?CAg⁺ and Cd²⁺ cation metal complexes, but experimentally by X-ray, the 12t4?CBi³⁺ and Cu⁺ cation metal complexes have C _s and C ₄ structures, respectively.