Jindřich Hašek

Trigonal bipyramidal penta-aquazinc(II): crystal structure of penta-aquazinc(II) bis(3,3′,3″-phosphinetriyltripropionato)dizincate(II,II) heptahydrate

Crystals of the title compound are hexagonal, space group P61 or P65. The crystal structure was determined by the heavy-atom method from 2 675 unique reflections and refined to R= 0.059. The structure can be best formulated as an ionic polymer with the composition ([Zn(H2O)5][Zn2{P(CH2CH2CO2)3}2]·7H2O)n. It consists of a three-dimensional network of [Zn{P(CH2CH2CO2)3}]– anions, where the zinc atoms are each tetrahedrally co-ordinated by three carboxyl oxygen atoms belonging to three different 3,3′,3″-phosphinetriyltripropionato ligands [Zn–O, 1.950(12)–1.991 (13)A] and by one phosphorus atom from a fourth ligand [Zn–P, 2.405(4) and 2.429(4)A; the first crystallographically documented zinc–phosphine bond]. Zinc cations are located in holes of the network as the hitherto unknown [Zn(H2O)5]2+ moieties with trigonal bipyramidal arrangement. The structure is stabilized by hydrogen bonding in which carboxylate oxygen atoms and both coordinated and lattice water molecules are involved.

A study of photochromic sydnones: structure of the sydnone ring

Abstract The chemical structure of the sydnone ring O(1)-N(2)-N(3)-C(4)-C(5) is discussed using X-ray structural data and results of theoretical calculations obtained by the INDO method. The ring is semiaromatic, the N(2)-N(3)-C(4)-C(5) part being conjugated. The exocyclic C(5)-0(6) bond is close to a double bond and participates in the conjugation.

Molecular structure of (E)- and (Z)-methylcyanovinyl sulphone in the gas phase and in crystal☆

Abstract The structure of (E)- and (Z)-methylcyanovinyl sulphone has been determined by gas electron diffraction and by X-ray crystallography. Considerably widened bond angles in the Z-isomer indicate steric repulsions across the CC bond. The conformer occurring in the crystal and prevailing in the gas phase has nearly eclipsed CC and SO bonds and is stabilized by an intramolecular hydrogen bond in the E-isomer, and by an attractive interaction, O···C(N) 2.78–2.81 A, in the Z-isomer. Parameters (rg with estimated total errors) SO, SCmean, CC, CN and OSCvinyl, OSCmethyl, CSC, SCC, CCC, OSO in the free E-isomer: 1.437(3), 1.781(4), 1.344(5). 1.165(3) A and 105.2(5), 110.2(2), 102.3(9), 114.9(6), 121.5(7), 121.4(7)°; in the free Z-isomer: 1.437(3), 1.780(4), 1.344(5), 1.168(3) A and 109.6(3), 104.3(3), 108.4(5), 124.7(4), 127.3(7), 119.8(0)°. Crystal data: E-isomer: P1, a=5.798(1), b=6.185(1), c=8.959(2) A, α=102.83(2), β=108.74(2), γ=92.18(2)°, Z=2,ϱm=1.476(7),ϱc=1.480 g cm−3; Z-isomer; P21/c, a=10.613(4), b=16.066(4), c=8.630(2) A, α=90, β=122.14(2), γ=90°, Z=8, ϱm=1.395(4), ϱc=1.398 g cm−3. There is an O⋯H contact of 2.26 A between the two independent molecules in the asymmetric unit of the Z-isomer.

Studies in quinoxaline series. Part 18. Structure of products of a new reaction of tetrazolo[1,5-a]quinoxaline 5-oxide with carbanions. X-Ray molecular structure of 4-acetyl-4-methyl-3b,4-dihydroazirino[1,2-a]tetrazolo-[5,1-c]quinoxaline

Tetrazolo[1,5-a]quinoxaline-5-oxide 4 reacts with the carbanions of β-diketones and β-keto esters to give enaminoketones and enamino esters, respectively. The N-oxide 4 reacts with 3-methyl- and 3-ethyl-pentane-2,4-dione under similar conditions to give a racemic mixture of the derivatives of aziridinotetrazoloquinoxaline 10 and 11. Their structure and the trans configuration of hydrogen atom and methyl group on the aziridine ring of compound 10 were estimated by means of 1H and 13C NMR spectroscopy, and were in accord with the results of X-ray diffraction measurements, which also provided bond lengths, and valence, torsion, and dihedral angles.

New Trends in Determination of Crystal Structure

Direct methods1 have become dominant in the determination of well-ordered crystal structures. They are based on an estimate of seminvariant values from distributions of seminvariants.* From any seminvariant one can thus form an equation

The crystal and molecular structure of tetramethylammonium 1-dimethylamino-1-carba-undecahydro-closo-dodecaborate

{{f}_{i}}({{\varphi }_{1}}, \ldots ,{{\varphi }_{n}}) = {{\Phi }_{i}}\pm {{d}_{i}},

The structure of 1,2,4,4,6-pentaphenyl-1,4-dihydropyridine

(1) where Фi is the expected value of seminvariant and di. is an unknown error related statistically to the distribution width. (When fi is a periodic function, the right side has to be taken modulo.)