Metal oxide-organic frameworks (MOOFs), a new series of coordination hybrids constructed from molybdenum(vi) oxide and bitopic 1,2,4-triazole linkers

Abstract

A series of molybdenum(VI) oxide–organic solids were prepared by hydrothermal reactions employing N-donor tectons, which combine two 1,2,4-triazol-4-yl sites separated by representative aliphatic spacers (ethylene, tr₂eth; 1,3-propylene, tr₂pr; trans-1,4-cyclohexanediyl, tr₂cy; diamondoid 1,3-adamantanediyl, tr₂ad; 1,6- and 4,9-diamantanediyls, 1,6-tr₂dia and 4,9-tr₂dia) and heterofunctional 5-[4-(1,2,4-triazol-4-yl)phenyl]tetrazole (trtz). In all the compounds the 1,2,4-triazol-4-yl group acts as a short-distance N¹,N²-bridge between two Mo ions (Mo–N 2.36–2.50 Å). The 3D framework structure is based upon pseudo-4₁ helices ([Mo₄O₁₂(tr₂eth)₂] 1, [Mo₂O₆(tr₂cy)] 3) or sinusoidal chains ([Mo₂O₆(tr₂pr)] 2, [Mo₂O₆(tr₂ad)]·6H₂O 4, [Mo₂O₆(4,9-tr₂dia)]·0.5H₂O 5) of vertex-sharing MoO₄N₂ octahedra, while the bitopic organic ligands manifest a dual role as connectors for two adjacent octahedra and as links between separate 1D inorganic subtopologies. For linear, lengthy tectons tr₂cy and 4,9-tr₂dia two identical frameworks interpenetrate. In [MoO₃(trtz)] 7, the 4₁ helices aggregate into 3D tetragonal framework (five-fold interpenetrated) by hydrogen bonding between the tetrazole groups. The 2D structure of [Mo₄O₁₂(1,6-tr₂dia)]·2H₂O 6 is influenced by the very bulky aliphatic portion of the ligands, which connect chains of edge-shared octahedra MoO₅N (Mo–N 2.346(2), 2.456(2) Å).