Two Acentric Aluminoborates Incorporated d10 Cations: Syntheses, Structures, and Nonlinear Optical Properties.

Two acentric aluminoborates (ABOs), [Zn(en)2Al{B5O9(OH)}{BO(OH)2}] (1) and [Cd(en)2AlB5O10]·H2O (2) (en = ethylenediamine), have been solvothermally made. 1 includes a two-dimensional (2D) wavy ABO layer using B5O9(OH) clusters and AlO3{BO(OH)2} groups, in which both units can be regarded as three-connected nodes, and simplifying the ABO layer to a hcb-type network. 2 features an acentric three-dimensional (3D) porous framework with a unique unc-type network constituted by strictly alternating connected B5O10 clusters and AlO4 units. The structural transformation from a 2D layer 1 to a 3D framework 2 was achieved with the elimination of the terminal hydroxyls in layer 1 by adjusting synthetic conditions in the same solvent system. Metal-amine complexes Zn(en)2/Cd(en)2 bond to the inorganic walls and are located in the cavity of frameworks 1 and 2, respectively. Compounds 1 and 2 exhibit large second-harmonic generation (SHG) responses that are 2.2 and 2.7 times those of KH2PO4 (KDP), respectively, which are among the largest powder SHG responses for all deep-ultraviolet (deep-UV) ABOs. The UV-vis diffuse reflectance spectra of 1 and 2 show a wide transparency window below 190 nm. Density functional theory (DFT) calculations indicate that the B-O units and the introduced distorted d10 metal polyhedra played a decisive role in the optical properties of both compounds.