Zur Kenntnis der Struktur von Sr3(BN2)2

Syntheses, Geometric and Electronic Structures of Inorganic Cumulenes

Molecular chains of two-coordinate carbon atoms (cumulenes) have long been targeted, due to interest in the electronic structure and applications of extended π-systems, and their relationship to the carbon allotrope, carbyne. While formal (isoelectronic) B═N for C═C substitution has been employed in two-dimensional (2-D) materials, unsaturated one-dimensional all-inorganic "molecular wires" are unknown. Here, we report high-yielding synthetic approaches to heterocumulenes containing a five-atom BNBNB chain, the geometric structure of which can be modified by choice of end group. The diamido-capped system is bent at the 2-/4-positions, and natural resonance theory calculations reveal significant contributions from B═N(:)-B≡N-B resonance forms featuring a lone pair at N (consistent with observed N-centered nucleophilicity). Molecular modification to generate a linear system best described by a B═N═B═N═B resonance structure involves chemical transformation of the capping groups (using B(C5F5)3) to enhance their π-acidity and conjugate the N-lone pairs.

Synthesis, Structure, and Electronic Properties of Sn9O5Cl4(CN2)2

The formation of the new compound Sn₉O₅Cl₄(CN₂)₂ is reported and placed in the context of several other recently discovered tin carbodiimide compounds (Sn(CN₂), Sn₂O(CN₂), and Sn₄Cl₂(CN₂)₃), all of which contain divalent tin. The crystal structure of Sn₉O₅Cl₄(CN₂)₂, as determined by X-ray powder diffraction, includes an unusual [Sn₈O₃] cluster, in which tin atoms form the motif of a hexagonal bipyramid. An additional tin atom and two oxygen atoms connect these clusters into chains. Mössbauer spectroscopy shows tin to predominantly adopt the +2 oxidation state, and electronic structure calculations predict Sn₉O₅Cl₄(CN₂)₂ to be a semiconductor.

The [BN2]3− anion – a carbon dioxide isosteric building unit for a large family of complex nitridoborate structures

The crystal chemistry of nitridoborates with the CO2 analogous [BN2]3− ion is reviewed. Such nitridoborates form with the alkali and alkaline earth metals as well as with divalent europium. Also quaternary compounds with mixed cations along with nitridoborate nitrides, oxides, halides and hydrides are discussed. The spectroscopic (IR, Raman, solid state NMR and Mössbauer spectroscopy) and magnetic behavior as well as optical properties are discussed in the light of structure-property relationships.

The Triply Deprotonated Acetonitrile Anion CCN3- Stabilized in a Solid

The unprecedented, fully deprotonated form of acetonitrile, the acetonitriletriide anion CCN^3- , is experimentally realized for the first time in the stabilizing bulk host framework of the Ba₅ [TaN₄ ][C₂ N] nitridometalate via a one-pot synthesis from the elements under moderate conditions (920 K). The molecular structure of this long-sought acetonitrile derivative is confirmed by X-ray diffraction, as well as NMR, IR, and Raman spectroscopy. The anion is isoelectronic to the CO₂ molecule, and, in contrast to acetonitrile (H₃ C-C≡N), the electron pairs are shifted towards two double bonds, that is, [C=C=N]^3- .

Superstructure formation in SrBa8[BN2]6 and EuBa8[BN2]6

X-ray pure samples of SrBa8[BN2]6 and EuBa8[BN2]6 were synthesized from appropriate amounts of binary nitrides (Sr3N2, Ba3N2 and BN in sealed niobium ampoules and EuN, Ba3N2 and BN in BN crucibles, respectively) at temperatures up to 1370 K. The structure of SrBa8[BN2]6 was refined from single crystal X-ray diffractometer data: Fd3[combining macron]m, a = 1595.1(1) pm, wR(F(2)) = 0.0515, 387 F(2) values and 21 variables. EuBa8[BN2]6 has a lattice parameter of 1595.00(9) pm. Both nitridoborates adopt a new 2 × 2 × 2 superstructure variant of the LiCa4[BN2]3 type, realized through ordering of vacancies and Sr(2+) and Eu(2+) cations, respectively. The structures of SrBa8[BN2]6 and LiCa4[BN2]3 are related by a group-subgroup scheme. The Sr(2+)/vacancy ordering leads to an asymmetric coordination (1 × Sr(2+) and 8 × Ba(2+) in a distorted, mono-capped square prism) for the [BN2](3-) units with B-N distances of 132 and 136 pm. Vibrational spectra of SrBa8[BN2]6 and EuBa8[BN2]6 confirm the discrete linear [BN2](3-) units and (11)B solid state MAS NMR spectra are compatible with single crystallographic sites for the boron atoms. In EuBa8[BN2]6 the spectra are profoundly influenced by interactions of the (11)B nuclei with the unpaired electrons of the paramagnetic Eu(2+) ions.