Inorganic–Organic Hybrid Polyoxoniobates: Polyoxoniobate Metal Complex Cage and Cage Framework

Abstract

The combination of polyoxoniobates (PONbs) with 3d metal ions, azoles, and organoamines is a general synthetic procedure for making unprecedented PONb metal complex cage materials, including discrete molecular cages and extended cage frameworks. By this method, the first two PONb metal complex cages K4@{[Cu29(OH)7(H2O)2(en)8(trz)21][Nb24O67(OH)2(H2O)3]4} and [Cu(en)2]@{[Cu2(en)2(trz)2]6(Nb68O188)} have been made. The former exhibits a huge tetrahedral cage with more than 120 metal centers, which is the largest inorganic–organic hybrid PONb known to date. The later shows a large cubic cage, which can act as building blocks for cage‐based extended assembly to form a 3D cage framework {[Cu(en)2]@{[Cu2(trz)2(en)2]6[H10Nb68O188]}}. These materials exhibit visible‐light‐driven photocatalytic H2 evolution activity and high vapor adsorption capacity. The results hold promise for developing both novel cage materials and largely unexplored inorganic–organic hybrid PONb chemistry.

Directional Bonding in Decaniobate Inorganic Frameworks

“…As discussed in the introduction, most frameworks built of PONbs plus an open‐shell transition metal require organic ligation to solubilize and stabilize the transition metal in neutral‐to‐basic conditions [27, 54, 55] . For example, [Nb 10 ] derivatives compounds have been isolated with 2,2′ bipyridine‐chelated Co, Ni and Zn [32, 33] …”

“…As discussed in the introduction, most frameworks built of PONbs plus an open-shell transition metal require organic ligation to solubilize and stabilize the transition metal in neutral-to-basic conditions. [27,54,55] Fore xample,[ Nb 10 ]d erivatives compounds have been isolated with 2,2' bipyridinechelated Co,Niand Zn. [32,33] In addition to the alkali and alkaline earth frameworks demonstrating increased dimensionality of linking, we show here this is also possible with open-shell transition metals, using Mn 6), similar to that of Li-Nb 10 and Na-Nb 10 .However,the orientation of [Nb 10 ]isrotated relative to the chain direction, in order to accommodate linking of an A-site and aB -site to two Mn 2+ ,o no pposite ends of the cluster.T he regular octahedron of Mn 2+ is completed with four terminal water molecules (Mn-O w = 2.153(5)-2.237(4) ).…”

Two GiantCalixarene‐LikePolyoxoniobate Nanocups {Cu12Nb120} and {Cd16Nb128} Built from Mixed Macrocyclic Cluster Motifs

“…To our knowledge, such a POM‐based nanocup is unprecedented. Furthermore, 1 a with 132 metal centers surpasses the known largest inorganic–organic hybrid PONb with 120 metal centers [6e] . In addition, each 1 a is decorated by four [Cu(en) 2 ] 2+ complexes, and two adjacent 1 a clusters situated in a back‐to‐back style are joined together by an additional [Cu(en) 2 ] 2+ complex to form a dimer with a length of ca.…”

Coordination‐Assembled Molecular Cages with Metal Cluster Nodes

“…In 2019, Zheng group reported the first two examples of superlarge cages based on inorganic−organic hybrid polyoxoniobates (PONbs) [68] . Two molecular cages {K 4 @{[Cu 29 (OH) 7 (H 2 O) 2 (en) 8 (trz) 21 ][H 2 Nb 24 O 69 ‐(H 2 O) 3 ] 4 }} 30− ( MCCC‐116 ) (Figure 31a) and {[Cu 2 (en) 2 ]@{[Cu 2 (en) 2 (trz) 2 ] 6 ‐(Nb 68 O 188 )}} 22− ( MCCC‐117) (Figure 31b) (en=ethanediamine, Htrz=1,2,4‐triazole) were made by a general synthetic procedure by combining PONbs, metal ions, azole and chelating organoamine ligands.…”

“…Polyoxoniobates (PONbs) have unique structural features and stoichiometry with potential applications in photocatalysis and base‐catalyzed reactions. MCCC‐116, 117 and 117 ’s extended cage framework ( 117‐F ) were chosen as the visible‐light‐driven H 2 evolution photocatalysts, which were evaluated in a [Ir(ppy) 2 (dtbbpy)] + /TEOA/CH 3 CN/DMF/H 2 O system [68] . The H 2 production increased with time and the photocatalytic activities of 116, 117 and 117‐F compare favorably with that of the starting PONb precursor K 7 HNb 6 O 19 , Cu(OAc) 2 and CuCl 2 under the same experimental conditions, which indicates that the PONb metal complex cage materials are potential candidates for photocatalysis.…”