Li2Na2[B12O19(OH)2]: a new open framework borate with a pcu-type net constructed from large cyclic dodeca-oxoboron units

The solvothermal reaction of H3BO3, Li2B4O7, Na2B4O7·10H2O, 1,2-diaminopropane and pyridine led to a new open framework borate, Li2Na2[B12O19(OH)2] (1). Compound 1 crystallizes in the monoclinic space group C2/c. Its structure contains a large cyclic [B12O22(OH)2]10− cluster, which is connected to six neighboring ones via corner-sharing O atoms to give a 6-connected pcu network via B–O–B bonds. Notably, large shuttle-like pores are observed along the [001] direction as well as 8-ring channels along the [101] direction, leading to an intersecting channel system. UV/vis diffuse reflectance analysis indicates that the compound has a wide transparency range with a short-wavelength absorption edge below 200 nm.