ENANTIOMERIC DISORDER OF AMINO ACID MOIETY IN STRUCTURES OF [Co(III)(EN)2(AA)]I2, AA=DL-ALANINE,DL-VALINE. E. Suresh, Mohan M. Bhadbhade, Central Salt & Marine Chemicals Research Institute, Bhavnagar-364 002, India
Complexes [Co(III)(en)2(aa)2] I2, where aa= DL-Alanine(l), DL-Valine(2) and DL-Isoleucine(3) were synthesized with the aim to resolve them using suitable chiral reagent . Crystal Data: 1: Monoclinic C2/c, a=34 091(7), b=6.839(3), c=16.568(6)Å [[beta]]=91.44(3)deg. V=3887.42Å3, Z=8, R=0.043, Rw =0.065. 2: Monoclinic P21/n, a=6.777(2), b=.742(10), c=7.857(2)Å, [[beta]]=104.9l(2)deg., V=1838(9)Å3, Z=4 ,R=0.096 Rw=0.106(refinement in progress.). 3: Monoclinic P21/n, a=7.732(2), b=20.616(3), c=12.813(4)Å, [[beta]]=104.91(2)deg., V=1838(9)Å3, Z=4, R=0.049, Rw=0.056 The structures were solved by heavy-atom method. Interestingly, C[[alpha]] carbon and the side chain atoms did not appear in the difference fourier map clearly in 1 and 2, whereas the complete molecule could be seen in 3. Careful examination of [[Delta]][[rho]] peaks led us to propose a model of enantiomeric disorder for the amino acid moiety alone, with the chiral carbon and the side chain atoms occupying two sites with almost equal occupancy. In all complexes, Co(III) has a distorted octahedral geometry with two ethylelnediamine moieties in cis fashion and two vacant sites occupied by the nitogen and the oxygen atom of the amino acid The packing patterns will be explained in terms of the size of the side chain which accommodate the disorder in 1 and 2 but not in 3. Local enantomeric disorders observed here are, to the best of our knowledge the first to be reported.