Chloride carbodiimide K12Pb51(CN2)30Cl54 with an unprecedented 45 Å unit cell axis and a large birefringence†
Abstract
A novel chloride carbodiimide, K12Pb51(CN2)30Cl54 (1), was successfully synthesized by solid state metathesis reaction. It exhibits the longest unit cell value reported among all known carbodiimides, caused by the superhelical configuration of the stereochemically active lone pair (SALP) Pb2+ cations rotating along the c axis. In addition, 1 has a large birefringence of 0.094 at 1064 nm resulting from the synergistic effect of SALP Pb2+ cations and linear (CN2)2− groups based on first principles calculation.