Noncentrosymmetric Cubic Cyanurate K6Cd3(C3N3O3)4 Containing Isolated Planar π-Conjugated (C3N3O3)3- Groups.

Single crystals of K6Cd3(C3N3O3)4 (1) were successfully grown via a solid-state cyclotrimerization reaction method from CdCl2 and KOCN. To our best knowledge, it is the first inorganic compound containing isolated six-membered-ring (6-MR) anionic groups that crystallizes in the cubic system. In the structure, the basic 6-MR anionic unit is a planar π-conjugated (C3N3O3)3- group that is isoelectronic with the (B3O6)3- group, as observed in the benchmark nonlinear-optical (NLO) crystal β-BaB2O4 with strong second-harmonic-generation response. In addition, the electronic structure and linear-optical and NLO properties for 1 were also investigated by the first-principles calculation. The NLO coefficient (d14 = 1.17 pm/V) of 1 is about 3 times that of KH2PO4.