Be 2 (BO 3 )(IO 3 ): The First Anion‐mixed Van der Waals Member in the KBe 2 BO 3 F 2 Family with a Very Strong Second Harmonic Generation Response

To obtain new nonlinear optical (NLO) materials with a large second harmonic generation (SHG) effect has always been a great challenge. We have synthesized the first metal borate‐iodate NLO crystal, Be 2 (BO 3 )(IO 3 ) (BBIO), by multicomponent modification of KBe 2 BO 3 F 2 (KBBF), in which the structural features of KBBF were maintained and (IO 3 ) − groups were connected to honeycomb [Be 2 BO 3 O 2 ] ∞ layers. As the first KBBF family member with mixed anionic groups, BBIO benefited from the synergistic effect of (IO 3 ) − , (BO 3 ) 3− and (BeO 4 ) 6− groups, and exhibited a very strong SHG response of ≈7.2×KH 2 PO 4 (KDP, @1064 nm) and a large birefringence (Δ n ) of 0.172 at 1064 nm. BBIO may, unexpectedly, optimize growth habits via van der Waals forces. This study presents borate‐iodate as a new NLO material and it demonstrates opportunities in KBBF structural engineering.