ABSTRACT
The two title compounds, [Re(C(10)H(10)N(6))(CO)(3)]Br and [Re(C(11)H(12)N(6))(CO)(3)]I.0.5C(2)H(6)O, have slightly distorted octahedral geometries about the rhenium centers. The distortions result from the constraints of the eta(3)-coordinated tris(pyrazol-1-yl)methane ligands in each case which reduce the N-Re-N bond angles well below the preferred value of 90 degrees for facially disposed ligands at a six-coordinate metal center.
ABSTRACT
The small synthetic peptide, benzyl 2-(tert-butoxycarbonyl-amino)isobutyrate, C(16)H(23)NO(4), has the alpha-helical conformation [/varphi/ = 55.8 (2) degrees and /psi/ = 37.9 (2) degrees] observed in peptide fragments of peptaibols containing the alpha-aminoisobutyric acid (Aib) residue. The structure shows no intramolecular hydrogen bonding, which would disrupt the limited conformational freedom associated with this amino acid. Two weak intermolecular hydrogen contacts are observed.
