Synthesis, characterization and crystal structure of bis(acetylacetonato)dichlorotin(IV)

The compound bis(acetylacetonato)dichlorotin(IV) [Sn(acac)₂Cl₂] forms a distorted octahedral structure involving both oxygen atoms of the acetylacetone group. The two chlorides occupy the cis position, with Sn-Cl distances of Sn1-Cl1 = 2.380(2) Å, Sn1-O1 = 2.043(2) Å and Sn1-O2 = 2.093(2) Å. We report here a new and simple method for the synthesis of Sn(acac)₂Cl₂, its spectroscopic characterization and, for the first time, we report its crystal structure.     

Organometallic bis(p-hydroxyphenyl) derivatives of group IV elements and related compounds

Dimethyl- and diphenylbis(p-hydroxyphenyl) Group IV metal compounds have been synthesized. Scope and limitations of the following methods were investigated: (a) reaction of the halogen-metal exchange product of p-bromophenol and n-butyllithium with organometallic dihalides; (b) protection of the phenolic group with trimethyl or benzyl groups and subsequent hydrolysis or hydrogenolysis.     

Novel seven coordination geometry of Sn(IV): crystal structures of phthalocyaninato bis(undecylcarboxylato)Sn(IV), its Si(IV) analogue, and phthalocyaninato bis(chloro)silicon(IV). The electrochemistry of the Si(IV) analogue and related compounds

Three newly elucidated crystal structures of group IV phthalocyaninato complexes are reported, along with data for two further SiPc carboxylate complexes. In one of these crystal structures, bis(undecylcarboxylate)Sn(IV) phthalocyanine, the tin ion is seven coordinate, which is a unique finding for this atom in phthalocyanine ring coordination. Comparison of these structures with other group IV phthalocyaninato and related structures reveals differences, illustrating features significant in the chemistries of Si(IV) and Sn(IV) ions. These differences are thought to originate from their differing sizes and polarizabilities. The structures show that the Sn(IV) ion can only occupy an in-plane location in the phthalocyaninato ring where it elongates toward the two axial ligands. When the axial ligands do not facilitate this elongation cis coordination is preferred and the Sn(IV) ion sits above the phthalocyaninato ring plane. In contrast, the Si(IV) structures, with smaller, harder (i.e., less polarizable) Si(IV) ions, are six coordinate with the Si(IV) ion in the phthalocyaninato ring plane in a distorted octahedral symmetry. The electronic spectra and cyclic voltammetry of some of the Si compounds indicate that on the electrode the oxidized/reduced species behave as though they are in a solid film, rather than a soluble freely diffusing species.     

Barrier of rotation around C-N bond in 1-(N,N-dimethylcarbamoyl)-π-cyclopentadienyl-π-(3)-1, 2-dicarbollylcobalt

Conclusions The barriers of rotation around the C-N bond in the amides C₅H₅CoB₉H₉C₂HCON(CH₃)₂, 1-(CH₃)₂NCO-1, 2-B₁₀C₂H₁₁ and 1-(CH₃)₂NCO-1,7-B₁₀C₂H₁₁ are substantially lower than in ordinary amides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2119–2120, September, 1977.     

Crystallographic report: Dibenzyltin(IV) bis(N,N‐dibenzyldithiocarbamate)

A distorted octahedron C₂S₄ geometry is found for the tin atom in the title compound; C? Sn? C is 136.61(19)°. Copyright © 2004 John Wiley & Sons, Ltd.     

Hindered rotation around the N(sp2)-C(sp3) single bond in 2,4,6-trimethyl-N-alkylpyridinium cations:H DNMR analysist

Pairwise chemical shift nonequivalence of the 2,6-methyl and 3,5-protons in ¹H NMR spectra, as well as of the 2,6-methyl, 2,6-ring and 3,5-ring carbons in ¹³C NMR spectra, was observed for N-alkyl-2,4,6-trimethylpyridinium salts 2. Dynamic NMR spectroscopy demonstrates appreciably higher activation free energies ΔG^# for rotation around the N(sp²)-C(sp³ bond than ΔG# for the analogously substituted mesityl derivatives, in agreement with the shorter N-C bond distance than for the C-C bond.     

Adducts of bis(acetylacetonato)- and bis(trifluoroacetylacetonato) oxovanadium(IV) with 1,10-phenanthroline and related nitrogen bases

Bis(acetylacetonato)oxovanadium(IV), VO(acac)₂, reacts with 1,10-phenanthroline in methanol to afford an adduct VO(acac)₂(phen) · 2CH₃OH (1). The IR and electronic spectra of 1 show a close resemblance to those of the corresponding α- and β-naphthoquinoline adducts, and 1 is assumed to have a trans octahedral structure containing the phenanthroline molecule as a unidentate ligand. Although 1 attains a reversible dissociation equilibrium in dichloromethane, the trifluoroacetylacetonato complex VO(tfac)₂(phen) (2) is quite stable even in solution. The cis octahedral structure is assigned to 2 and also to the corresponding pyridine, α- and β-naphthoquinoline adducts VO(tfac)₂L on the basis of IR data.     

Internal rotation in squaramide and related compounds. A theoretical ab initio study

The structural and energetic changes associated with C–N bond rotation in a squaric acid derivative as well as in formamide, 3-aminoacrolein and vinylamine have been studied theoretically using ab initio molecular orbital methods. Geometry optimizations at the MP2(full)/6-31+G* level confirmed an increase in the C–N bond length and a smaller decrease in the C=O length on going from the equilibrium geometry to the twisted transition state. Other geometrical changes are also discussed. Energies calculated at the QCISD(T)/6-311+G** level, including zero-point-energy correction, show barrier heights decreasing in the order formamide, squaric acid derivative, 3-aminoacrolein and vinylamine. The origin of the barriers were examined using the atoms-in-molecules approach of Bader and the natural bond orbital population analysis. The calculations agree with Pauling's resonance model, and the main contributing factor of the barrier is assigned to the loss of conjugation on rotating the C–N bond. Finally, molecular interaction potential calculations were used to study the changes in the nucleophilicity of N and O (carbonyl) atoms upon C–N rotation, and to obtain a picture of the abilities of the molecules to act in nonbonded interactions, in particular hydrogen bonds. The molecular interaction potential results confirm the suitability of squaramide units for acting as binding units in host–guest chemistry. Received: 13 March 2002 / Accepted: 23 June 2002 / Published online: 21 August 2002     

Crystal structure of bis(4-methylimidazole)tetraphenylporphyrinatoiron(III) chloride and related compounds. Correlation of ground state with Fe-N bond lengths

The crystal structure of the title compound is presented and shown to be one of a class of low-spin iron porphyrin complexes having a ground-state electronic configuration of (dxy)2(dxz)2(dyz)1. If their Fe-N bond lengths (average N-porphyrin plotted against average N-axial) are considered, this class of low-spin iron(III) porphyrins of general formula [Fe(III)Por(L)2]+X- and of 2B ground state is shown to be distinctly different crystallographically from a similar class of compounds with the same general formula but with a 2E or a (dxy)2(dxz,dyz)3 ground state. A third group of compounds with the same general formula have a (dxz,dyz)4(d)1 ground state and again are in a different region of the plot. Compounds showing intermediate properties can be forecast from the simple relationship presented in this work. The electron paramagenetic resonance data are shown to be dependent on the ground state, and those of configuration (dxy)2(dxz,dyz)3 and the 2B ground state obey a correlation previously suggested in the literature.