Harrison M. M. Shearer

Azomethine derivatives. Part 20. Crystal and molecular structures of the lithioketimine [{Li(NCBut2)}6] and lithioguanidine [{Li[NC(NMe2)2]}6]; electron-deficient bridging of Li3 triangles by methyleneamino-nitrogen atoms

The lithioketimine Li(NCBut2)(1) and lithioguanidine Li[NC(NMe2)2](2) have remarkably similar hexameric structures [{Li(NCR2)}6](R = But or NMe2) in the crystal phase, based on slightly folded chair-shaped Li6 rings held together by triply-bridging methyleneamino-groups, NCR2, thus providing examples of electron-deficient bridging by the nitrogen atoms of organonitrogen ligands. The mean distance between adjacent metal atoms in the Li6 rings is 2.35(2)A in (1), and 2.445(2)A in (2), and the mean dihedral angles between Li6 chair seats and backs are 85 and 78° respectively. The nitrogen atoms of the bridging methyleneamino-groups are approximately equidistant from the three bridged metal atoms, the mean Li–N distance being 2.06(1)A in (1) and 2.00(1)A in (2). The NC distances of 1.30(1) and 1.244(3)A respectively lie within the range expected for carbon–nitrogen double bonds. Features of these structures are compared with those of related compounds, and some bonding implications are discussed.

The Crystal and Molecular Structure of Cyclopentadienylzinc methyl, Zn(C5H5)Me

Abstract In the crystal, cyclopentadienylzinc methyl, Zn(C 5 H 5 )Me, adopts a puckered -Zn(C 5 H 5 Zn(C 5 H 5 - chain structure in which the bridging cyclopentadienyl groups co-ordinate di- or tri-hapto to the bridged zinc atoms, apparently functioning as five-electron ligands.

The crystal and molecular structure of dimethylindium-pyridine-2-carbaldehyde oximate [InMe2(ON=CHC5H4N)]2

Abstract Dimethylindium-pyridine-2-carbaldehyde oximate crystallises from benzene in the orthorhombic space group Pbcn, with cell dimensions a 33.15, b 9.54, c = 14.30 A. The unit cell contains eight dimeric oximate molecules [InMe2(ON=CHC5H4N)]2 and four molecules of benzene. Each oximate group coordinates through both its nitrogen atoms to one indium atom, and through its oxygen atom to the other indium atom of the dimer. The dimer thus consists of a row of five fused rings, two terminal pyridine rings, a central 6-membered InONInON ring, and two intervening 5-membered InNCCN rings (I). The indium atoms are 5-coordinate, and adopt a distorted trigonal bipyramidal geometry, in which the NInN “bite” of the oximate ligand is only 69°, and the axial InN bonds to the pyridine nitrogen atoms (2.51 A) are significantly longer than the equatorial InN bonds to the oximate nitrogen atoms (2.28 A). The CInC angle between the bonds to the equatorial methyl groups averages 138°.

Electron precise versus electron deficient bonding in (Be2C2)n ring systems: Crystal structure of (Me3N)(MeCC)Be(μ-CCMe)2Be(CCMe)(NMe3)

Abstract The solid state structure of the 1/1 trimethylamine complex of dipropynylberyllium has been determined from X-ray data by direct methods. All non-hydrogen atoms were refined by least-squares methods with anisotropic temperature factors to an R value of 0.074 for the 1493 reflections classified as observed. The crystals of [(MeCC)2Be·NMe3]2 contain two independent centrosymmetric dimers in which the μ-alkynyl groups exhibit quite different types of interactions with the beryllium atoms. In one dimer the bridging alkynyl groups function as 1 electron donors leading to a predominantly electron-deficient Be2C2 ring system in which significant cross-ring metal-metal bonding is present, giving rise to a short Be…Be distance (2.319(6) A). In the second dimer the ring is effectively electron-precise with the μ-alkynyl groups acting as 3e (σ,π) donors, with the associated Be…Be distance being considerably increased (2.549(6) A).

Terminal zinc–hydrogen bonding. X-Ray and neutron diffraction studies of 2-dimethylaminoethyl(methyl)aminozinc hydride dimer

The crystal structure of the title compound reveals that hydrogen bound to zinc occupies a terminal position and that each zinc atom is four co-ordinate by virtue of the formation of four- and five-membered rings with the diamine.

Preparation and X-ray structure of sulphur–nitrogen oxides

The compounds [S5N5]+[S3N3O4]– and S4N4O2 have been prepared from the same reaction; the crystal structures show that the shape of the [S5N5]+ cation differs from that previously reported and that [S3N3O4]– and S4N4O2 contains S–N rings with exocyclic oxygen atoms.

Bonding in electron-deficient and electron-precise Be2C2 ring systems: X-ray crystal structure of the dimeric dipropynylberyllium—trimethylamine

An X-ray crystal structure determination shows that [(MeCC)2BeNMe3]2 contains two independent centrosymmetric dimers in which the µ-alkynyl groups exhibit quite different types of interactions with the beryllium atoms.

Terminal beryllium–hydrogen bonding. X-Ray crystal structure of the (2-dimethylamino-N-methylethylamido)hydridoberyllium dimer

An X-ray crystal structure determination shows that in [HBeN(Me)C2H4NMe2]2 the hydrogen atom bound to beryllium occupies a terminal position with amido nitrogen atoms as the bridging atoms in a four-membered Be2N2ring; the metal and nitrogen atoms achieve four-co-ordination via formation of four- and five-membered rings with the diamine.

X-Ray crystal and molecular structure of hexameric di-t-butylmethyleneaminolithium, (LiNCBut2)6: electron-deficient bridging of Li3 triangles by methyleneamino nitrogen atoms

An X-ray crystallographic study of the title compound, (LiNCBut2)6, has revealed a ‘folded chair’ arrangement of its metal atoms held together by triply bridging methyleneamino groups in what is believed to be the first example of electron-deficient bridging through the nitrogen atom of an organonitrogen ligand.

Beryllium-nitrogen π-bonding: the X-ray structure of bis(di-t-butylmethyleneamino)beryllium dimer, [Be(N:CBut2)2]2

X-Ray crystal structure analysis of bis(di-t-butylmethyleneamino)beryllium dimer, [Be(N:CBut2)2]2, prepared from the ketimine But2C:NH and di-isopropyl-beryllium, shows that it adopts a structure containing both bridging and terminal methyleamino-groups, the latter attached to the 3-co-ordinate metal atoms by Be–N bonds only 150 pm long, the shortest yet reported for a solid beryllium–nitrogen compound.