Crystal structure and theoretical investigation of the configurations of 1,3-dichloro-1,3-diazetidine-2,4-dione and 1,3-bis(trimethylsilyl)-1,3-diazetidine-2,4-dione

Crystal structures of 1,3-dichloro-1,3-diazetidine-2,4-dione ( 1 ) and the hitherto unknown compound 1,3-bis(trimethylsilyl)-1,3-diazetidine-2,4-dione ( 2 ) have been determined by X--ray crystallography: 1 : (CINCO)₂, M_r = 154.94, T = 295 K, orthorhombic, Pbca, a = 7.699(1), b = 6.706(1), c = 10.598(2) Å, V = 547.2(2) ų, Z = 4, d_x = 1.881 g/cm³, μ = 10.9 cm⁻¹, R = 3.14%, R_w = 2.82% (660 observations, 38 parameters). 2 : [(CH₃)₃SiNCO]₂, M_r = 230.41, T = 100 K, monoclinic, I2/a, a = 20.257(2), b = 6.416(1), c = 21.260(3) Å, β = 101.29(1)°, V = 2709.7(6) ų, Z = 8, d_x = 1.130 g/cm³, μ = 2.4 cm⁻¹, R = 4.86%, R_w = 4.39% (2375 observations, 151 parameters). In both compounds, the symmetry of the (XNCO)₂ framework (X = Cl, Si) was determined to be nearly C_2h with trans configuration of the exocyclic X atoms. Extreme values were observed for the angles between the ring plane and the exocyclic N–X bonds: 32.5(1)° in 1 and 2.5(2)° and 0.8(2)° in 2 , respectively. Quantum chemical procedures at various levels of theory (ab initio SCF and semi-empirical PM3) applied to 1 revealed the possible appearance of two isomers, a lower energy trans form and a higher energy cis form (approx. 2.4 kcal/mol above trans) differing mainly in the spatial arrangement of the chlorine atoms. The calculations excluded a planar heavy-atom configuration by missing a local energy minimum.     

Membranes of high performance polymers

Membranes, as part of technical processes, are gaining more importance in areas such as chemicals, biotechnology or waste-water treatment. The use of high performance polymers as membrane materials offers unique combinations of properties and allows new applications. Three different approaches towards membrane fabrication from high performance polymers such as polyaryls or polyaramides are discussed, i. e. maintenance of the polymer structure during processing and synthesis of better soluble structures via either polymer-analogous reactions or tailor-made copolymers. Examples of chemistry, property profiles and potential applications are given.