C(NH 2 ) 3 (I 3 O 8 )(HI 3 O 8 )(H 2 I 2 O 6 )(HIO 3 ) 4 ·3H 2 O: An Unprecedented Asymmetric Guanidinium Polyiodate with a Strong Second-Harmonic-Generation Response and a Wide Band Gap.

Herein, we report an unprecedented asymmetric guanidinium polyiodate, namely, C(NH 2 ) 3 (I 3 O 8 )(HI 3 O 8 )(H 2 I 2 O 6 )(HIO 3 ) 4 ·3H 2 O ( 1 ). The title compound was obtained via the hybridization of polyiodate anions and planar π-conjugated C(NH 2 ) 3 + ; meanwhile, its strong second-harmonic-generation (SHG) response (2.1 × KDP, where KDP = KH 2 PO 4 ) and wide band gap (3.89 eV) were mainly dominated by the synergy effect of the aforementioned structural units.