Five new rubidium borates with 0D clusters, 1D chains, 2D layers and 3D frameworks.

Five new rubidium borates, namely Na1/3Rb5/3[B4O5(OH)4] (1), Rb4[B12O18(OH)4] (2), Rb2Ba[B12O18(OH)4] (3), Rb2[B5O8(OH)] (4) and NaRb0.5[B6O10]·0.5H3O (5) have been synthesized under solvothermal conditions. Compound 1 features a 0D structure composed of [B4O5(OH)4]2− clusters. After changing the metal salt, new cyclic [B12O20(OH)4]8− clusters in 2 and 3 are formed, resulting in 1D chains. Such a chain structure is first discovered in dodecaborates. By tuning the reaction temperature and pH of the reaction media, compound 4 with a 4-connected 2D oxoboron layer constructed from partially protonated [B5O10(OH)]6− and compound 5 with a 6-connected 3D framework constructed from [B6O13]8− clusters are successfully isolated. Since compounds 1 and 4 crystallize in the non-centrosymmetric (NCS) space group, second harmonic generation (SHG) measurements and dipole moment calculations have been carried out. The SHG response of 4 is 2.0 times that of KH2PO4 (KDP), which is higher than those of related analogues. [ABSTRACT FROM AUTHOR]