Two Mixed Alkali-Metal Borates Templated from Cations to Clusters.

Two mixed alkali-metal borates, K 0.5 Li[B 6 O 10 ]·0.5H 3 O ( 1 ) and [(μ 5 -OH)@(Na 4 Li)] 0.5 [B 6 O 10 ]·0.5B(OH) 3 ( 2 ), have been prepared under solvothermal conditions. Both of them are obtained in the same synthetic system and contain a B 6 O 13 8- cluster as the structural-building unit (SBU) but exhibit quite different structural features. 1 is a centric three-dimensional (3D) oxoboron (B-O) framework, where templated mixed K + and Li + cations occupied the cavities of the structure. 2 crystallizes in an acentric space group under the templating effect of a unique acentric alkali-metal cluster [(μ 5 -OH)@(Na 4 Li)] 4+ . The SBU of 2 is also the B 6 O 13 8- cluster, which acts as six-connected nodes linked together to form a 3D B-O framework, showing different characters from 1 because of two types of templates; the acentric [(μ 5 -OH)@(Na 4 Li)] 4+ clusters and the electroneutral B (OH) 3 groups fill in two different cages in the framework and further connect each other via Na-O-B bonds to build a novel two-dimensional (2D) wavy bricklike network, resulting in a 3D B-O framework interpenetrated by a 2D [(μ 5 -OH)@(Na 4 Li)]-B(OH) 3 network. As a crystal material with an acentric space group, 2 shows a good second harmonic generation response of about 2.8 times that of KDP (KH 2 PO 4 ) and has a cutoff edge below 190 nm, which suggests that 2 is a potential deep-UV NLO material.