Syntheses, structures, photoluminescence, photocatalysis, and photoelectronic effects of 3D mixed high-connected metal-organic frameworks based on octanuclear and dodecanuclear secondary building units

摘要

Four novel metal-organic frameworks (MOFs) based on high-nuclear metal carboxylate clusters, namely, [Zn_4(L)_2(μ_3-OH)_2(H_2O)_(1.5)]·2H_2O (1), [Zn_5Na(L)_2(μ_3-OH)_4(CH_3CH_2O)(H_2O)_2] (2), [Cd_4(L)_2(BIME)_(0.5)(μ_3-OH)_2(H_2O)_(1.5)]·2H_2O (3), and [Zn_4(L)_2(BET)_(0.5)(μ_3-OH)_2(H_2O)] (4), where H_3L = (3,5-dicarboxyl- phenyl)-(4-(2′-carboxyl-phenyl)-benzyl)ether, BET = 1,1′-(2′- oxybis(ethane-2,1-diyl))bis(1,2,4-triazol~(-1)-yl), BIME = 1,2-bis(imidazol~(-1)-yl) ethane, have been synthesized under hydrothermal conditions. In 1, each planar octanuclear zinc cluster [Zn_8(μ_3-OH)_8(CO_2)_(12)(H_2O)_3] is linked by twelve L anions to give an unusual (3,12)-connected framework with (4~3)_2(4~(20)·6~(28)·8~(18)) topology. In_2, dodecanuclear heterometallic clusters [Zn_(10)Na_2(μ_3-OH)_8(CO_2)_(12)(CH_3CH_2O)_2(H_2O)_4] are surrounded by twelve L anions to form a (3,12)-connected net with the same topology as 1. However, 3 exhibits a rare (3,14)-connected (4~3)(3~24)(3~4·4~(20)·5~(14)·6~(34)·7~(11)·8~8) net based on octanuclear cadmium cluster [Cd_8(BIME)_2(μ_3-OH)_4(CO_2)_(12)(H_2O)_4]·2H_2O as a 14-connected node and H_3L as a 3-connected node. In 4, each octanuclear zinc cluster [Zn_8(BET)_2(μ_3-OH)_4(CO_2)_(12)(H_2O)_2] is linked by twelve L anions to furnish a (3,14)-connected net with the same topology as 3. The optical energy gaps and photoluminescence were investigated for the compounds. Moreover, compounds 1-4 exhibit good photocatalytic activities for degradation of methylene blue (MB) under UV irradiation and show good stability towards UV photocatalysis. In addition, 1 and 4 display a photocurrent density under several on-off cycles of illumination.