Sr4N3: ein bisher fehlendes Glied in der Stickstoff-Druck-Reaktionsreihe Sr2N→Sr4N3→SrN→SrN2

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.

Synthesis of alkaline earth diazenides M(AE)N2 (M(AE) = Ca, Sr, Ba) by controlled thermal decomposition of azides under high pressure

The alkaline earth diazenides M(AE)N(2) with M(AE) = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at high-pressure/high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wR(p) = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN(2) and BaN(2). Accordingly, CaN(2) is isotypic with SrN(2) (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wR(p) = 0.057) and the corresponding alkaline earth acetylenides (M(AE)C(2)) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN(2) adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wR(p) = 0.049). The N-N bond lengths of 1.202(4) Å in CaN(2) (SrN(2) 1.239(4) Å, BaN(2) 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N(2)](2-). Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides M(AE(2))N (M(AE) = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm(-1) assigned to the N-N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides.

Hydrophobic and hydrophilic yoctowells

Rigid molecular monolayers made of alpha,omega-diamido lipids form yoctoliter-sized gaps ("yoctowells", 1 yL = 10(-24) L or 1 nm3) around porphyrin islands on smooth surfaces. Their hydrophobic walls adsorb cyclic edge amphiphiles, e.g., trans-1,2-cyclohexanediol, cellobiose, and tyrosine, which fill-up the wells slowly and irreversibly by a process called "kinetic trapping". Wells with oligoethylene or oligoamide walls are effective as 3D-crown ethers or oligoamide barrels for reversible "thermodynamic trapping" of amines or amides. Three porphyrins A, B, and C were sorted as stacks within the yoctowells, and a methylammonium ring was established at their rim to fixate a fourth molecule D at a longer distance. Yoctowells are easy to prepare, characterize, and modify and provide simple models of biological modules.