title: Crystal Engineering of Hand-Twisted Helical Crystals.
abstract: A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4'-chlorobenzoate, by introduction of a molecular synthon -O-CO- in lieu of the supramolecular synthon Br···Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4'-nitrobenzoate where the halogen bonding and C-H···O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4'-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, generally orthogonal to each other, allows for the possibility of hand-twisting of the crystals to give grossly helical morphologies. Accordingly, we propose the name hand-twisted helical crystals for these substances.
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore 560 012, India.
authors.forename: Subhankar
authors.initials: S
authors.lastname: Saha
authors.affiliation: Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore 560 012, India.
authors.forename: Gautam R
authors.identifier: 0000-0002-7708-9176
authors.initials: GR
authors.lastname: Desiraju