The x-ray structure determinations and semiempirical PM3 calculations of two chloro(piperidyl)cyclotri(phosphazenes)

Single crystals of 2,4,6,6-tetrachloro-2,4-bis(piperid-yl)cyclotri(phosphazene) ( 1a ) and of 2,4,6-trichloro-2,4,6-tris(piperidyl)cyclotri(phosphazene) ( 2a ) were grown from petroleum ether solution. The structures of both compounds were determined by single-crystal X-ray diffraction analyses. Compound 1a crystallizes in the monoclinic space group P 2₁/n with Z = 4 and unit cell dimensions a = 9.3994(4), b = 19.204(3), c = 11.5664(4) Å, and β = 108.718(4)°. Compound 2a crystallizes in the triclinic space group P 1 with Z = 4 and unit cell dimensions a = 12.8289(2), b = 13.8856(2), c = 14.63810(10) Å, and α = 100.7621(5), β = 91.0094(2), γ = 113.9757(6)°. The experimentally obtained structural parameters for the covalent molecules 1a and 2a compare well with those calculated at the semiempirical PM3 level of theory. These results give credence to the PM3 calculated structures of 2,4,6,6-tetraazido-2,4-bis(piperidyl)cy-clotri(phosphazene) ( 1b ) and 2,4,6-triazido-2,4,6-tris(piperidyl)cyclotri(phosphazene) ( 2b ) for which presently there are no experimental data available.

1 Non-SI units employed: 1 kcal≈︁4.184 kJ, 1 Å = 10⁻¹⁰ m (since these units are still used in computational chemistry, we employed them throughout this article).

© 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 267–271, 1997.     

PM3 semiempirical study and its comparison with X-ray crystal structure of 2-methyl-4-(4-methoxyphenylazo)phenol

The crystal and molecular structure of 2-methyl-4-(4-methoxyphenylazo)phenol have been determined by X-ray single crystal diffraction technique. The compound crystallizes in the monoclinic space group P2₁/c with a=9.7763(8) Å, b=11.3966(8) Å, c=11.9531(8) Å and β=108.752(6)°. In addition to the molecular geometry from X-ray experiment, its optimized molecular structure has been obtained with the aid of PM3 semiempirical quantum mechanical method, and then the corresponding geometric parameters were compared with those of X-ray crystallography. To determine conformational flexibility and crystal packing effects on the molecules, molecular energy profile of the title compound was obtained with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 10°. Crystal structure of the title compound is a fibroid structure constructed by C–H···O and O–H···N type intermolecular hydrogen bonds. The most favorable conformer of the title compound has been determined by the crystal packing effects and there is no steric hindrance during rotation around the selected torsion angles.     

PM3 semiempirical calculations of lithium-cation and proton affinities for XYZPO and XYSO2 compounds

Proton affinities (PAs) of a series of phosphorous compounds bearing the phosphoryl function have been calculated using AM1 and PM3, as well as lithium-cation affinities (LCAs) using the recent PM3 lithium parametrization. Sulfonyl derivatives PAs and LCAs have been also calculated using PM3. The Li⁺ cation can be bonded in a “chelate” form with the two oxygens of the sulfonyl group. Nevertheless, the “linear” adduct, with the lithium-oxygen bond collinear with one of the SO bonds, is more stable. This is confirmed by ab initio calculations on Me₂SO₂ Li⁺ adducts. © 1996 John Wiley & Sons, Inc.     

The first x-ray structure determination of a -phosphaethylene: -2-phenyl-1-(2,4,6-tri-t-butylphenyl)phosphaethylene

The sterically protected -phosphaethylene, -2-phenyl-1-(2,4,6-tri-t-butylphenyl)phosphaethylene (1-Z), was analyzed by X-ray crystallography.     

Development of optimized MST/SCRF methods for semiempirical calculations: The MNDO and PM3 Hamiltonians

The self-consistent reaction field (SCRF) method proposed by Miertus, Scrocco, and Tomasi (MST) has been optimized for MNDO and PM3 semiempirical Hamiltonians. Different algorithms used to compute the molecular electrostatic potential (MEP) and different solute cavities have been investigated. The ability of the optimized models to reproduce experimental free energies of solvation and to mimic the solvent effect in several chemical processes has been compared with the ab initio and AM1 versions of the MST method as well as with experimental data. © 1995 by John Wiley & Sons, Inc.     

Conformation and reactivity of α-oxo-ketenes: Ab initio and semiempirical (AM1, PM3) calculations

Ab initio MP2/6-31G*//MP2/6-31G* and semiempirical AM1 and PM3 calculations on a series of differently substituted α-oxo-ketenes are used to investigate E/Z-isomerism and rotational barriers in these molecules. Sterically crowded derivatives are found to exist solely as s-E conformers. The unusual stability of these derivatives thus can be attributed to their inability to adopt the s-Z conformation required for the normal α-oxo-ketene reactions. With respect to structures and energies, the PM3 method (especially in the case of highly crowded molecules) is found to be less reliable than AM1. Ab initio HF/3-21G and PM3 vibrational frequencies appear to be of sufficient accuracy for a distinction between s-Z and s-E conformers. In this respect, the AM1 method appears less reliable. © 1994 by John Wiley & Sons, Inc.     

Crystal structures,semiempirical PM3 calculations and NMR studies of trimesityllead bromide and dimesityllead dibromide

Trimesityllead bromide has been synthesized by the reaction of mesityllithium with lead(II) chloride in tetrahydrofuran (THF). As a side product, dimesityllead dibromide was formed. The structures of both compounds were determined by single-crystal X-ray diffraction analysis. Both Mes₃PbBr and Mes₂PbBr₂ were characterized by NMR (¹H, ¹³C and ²⁰⁷Pb) and other spectroscopic methods. ²⁰⁷Pb–¹H and ²⁰⁷Pb–¹³C coupling constants were determined. The experimentally obtained X-ray data were compared with those calculated at the semiempirical PM3 level.     

Electronic and structural properties of the metalloporphyrin structural isomers: semiempirical AM1 and PM3 calculations

Semiempirical calculations using AM1 and PM3 have been performed on the zinc(II) and magnesium(II) complexes of nine structural isomers of tetrapyrrole macrocycles such as porphyrin, porphycene, corrphycene and hemiporphycene, N-confused porphyrin and other isomers that have not been synthesized. The optimized geometry and the bond parameters obtained compare favorably with results obtained from X-ray and spectral studies. Heats of formation, ionization potentials, HOMO-LUMO energy differences, dipole moments, and the splitting of HOMOs and LUMOs of the metal complexes of each of these isomers are also reported and compared with experimental results. The “four-orbital model” of Gouterman remains valid for the investigated structural isomers. The present study represents an unusually appropriate opportunity to study, via molecular orbital methods, the interaction between various metal ions, and the electronic and geometrical environment of the central cavity of the closely related isomeric macrocycles. The major outcome of this study is the verification of the expected differential behavior of metal ions employed in the present study as a sophisticated probe of cavity properties which also suggests that this procedure can be extended to other metal complexes. This study also serves as an interesting prototype for more elaborate ab initio calculations. However, such calculations on the presently investigated macrocyclic systems may have to be performed at a higher level than MP2 or DFT to account for the unusual delocalization, as suggested by a recent study by Schaefer and co-workers on delocalized [10]annulene (H.M. Sulzbach, H.F. Schaefer, W. Klopper and H.P. Luthi, J. Am. Chem. Soc., 118 (1996) 3519).     

Aminolysis of P-trichloro-N-dichlorophosphorylmonophosphazene and the crystal structure of 1-(dichlorophosphinyl)-2-chloro-2,2-bis(diisopropylamino)phosphazene

The reactions of Cl₃PN P(O)Cl₂ ( 1 ) with primary and secondary amines have been studied. The following monophosphazenes, (RRN)₃PN P(O)(NRR)₂, and bis(phosphinoyl)amines, [(RRN)₂P(O)]₂NH were isolated: NRR = NHCH₂Ph, Net₂, NH(CH₂)₂CH₃ groups for monophosphazenes, and Net₂, NH(CH₂)₂CH₃ for phosphinoyl amines. The unexpected geminal phosphazene, Cl(RRN)₂PN P(O)Cl₂, {RRN = N[CH(CH₃)₂]₂}, was also obtained in moderate yield. The spectral data (IR, ¹H, ¹³C, and ³¹P NMR, and MS) are presented. The structure of 1-(dichlorophosphinyl)-2-chloro-2,2-bis(diisopropylamino)phosphazene ( 5 ) was determined by X-ray crystallography. The basicities of these and related compounds in nonaqueous nitrobenzene solution were obtained by potentiometric titration.     

The reaction of H2Os3(CO)10 with trifluoroacetonitrile and the x-ray crystal structure of HOs3(CO)9(μ3-η2-HNCCF3)

The reaction of H₂Os₃(CO)₁₀ with CF₃CN in hexane at 80°C leads to two isomeric products. The isomer constituting the major product contains a 1,1,1-tri-fluoroethylidenimido ligand which bridges one edge of the Os₃ triangle via the nitrogen, atom and may be formulated as (μ-H)Os₃(CO)₁₀(μ-NC(H)CF₃) (I). The minor product, formulated as (μ-H)Os₃(CO)₁₀(μ-η²-HNCCF₃) (II), contains a 1,1,1-trifluoroacetimidoyl ligand which is also edge-bridging, being N-bonded to one Os atom and C-bonded to the other. Thermolysis of I and II in solution results in loss of a CO group in each case to give (μ-H)Os₃(CO)_9^? (μ₃-η²-NC(H)CF₃) (III) and (μ-H)Os₃(CO)₉(μ₃-η²-HNCCF₃) (IV), respectively, which, it is proposed, are structurally related to I and II, but with the CN group coordinated also to the third Os atom in place of a CO group. In the case of IV this proposal has been confirmed by an X-ray crystallographic analysis. The compound crystallises in space group C2/c with a = 14.258(7), b = 13.486(10), c = 18.193(8) Å, β = 92.68(4)°, and Z = 8. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by full-matrix least squares to R = 0.054 for 2489 unique observed diffractometer data. Reaction of I with Et₃P gives a 1 : 2 adduct which is formulated as (μ-H)Os₃(CO)₁₀[μ-N?C(H)(CF₃)PEt₃] (V) on the basis of NMR evidence.     

Molecular and crystal structure of 2,4,4,6,6,8,8-heptamethyl-2-[3-{[2,4,4,6,6-pentakis(dimethylamino)-2,2,4,4,6,6-hexa-hydro-1,3,5,2,4,6-triazatriphosphorine-2-yl]amino}propyl]-cyclotetrasiloxane

Molecular and crystal structure of the title compound has been determined. The (PN)₃ and (SiO)₄ rings form the dihedral angle of 100.1° and with the HNCH₂CH₂CH₂ plane the angles of 110.2° and 75.7° respectively. The molecular packing is built of alternating layers of (PN)₃ and (SiO)₄ beterocycles.     

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one by Hartree-Fock and density functional theory calculations

The molecular structure and vibrational spectra of 3-acetyl-4-[N-(2'-aminopyridinyl)-3-amino]-3-buten-2-one (C(11)H(13)N(3)O(2)) in the ground state have been investigated by Hartree-Fock and density functional method (B3LYP and BLYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of title compound and calculated results by HF and DFT methods indicate that B3LYP is superior to the scaled HF approach for molecular problems.