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, tr(2)eth; 1,3-propylene, tr(2)pr; trans-1,4-cyclohexanediyl, tr(2)cy; diamondoid 1,3-adamantanediyl, tr(2)ad; 1,6- and 4,9-diamantanediyls, 1,6-tr(2)dia and 4,9-tr(2)dia) 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 N(1),N(2)-bridge between two Mo ions (Mo-N 2.36-2.50 A). The 3D framework structure is based upon pseudo-4(1) helices ([Mo(4)O(12)(tr(2)eth)(2)] 1, [Mo(2)O(6)(tr(2)cy)] 3) or sinusoidal chains ([Mo(2)O(6)(tr(2)pr)] 2, [Mo(2)O(6)(tr(2)ad)].6H(2)O 4, [Mo(2)O(6)(4,9-tr(2)dia)].0.5H(2)O 5) of vertex-sharing MoO(4)N(2) 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 tr(2)cy and 4,9-tr(2)dia two identical frameworks interpenetrate. In [MoO(3)(trtz)] 7, the 4(1) helices aggregate into 3D tetragonal framework (five-fold interpenetrated) by hydrogen bonding between the tetrazole groups. The 2D structure of [Mo(4)O(12)(1,6-tr(2)dia)].2H(2)O 6 is influenced by the very bulky aliphatic portion of the ligands, which connect chains of edge-shared octahedra MoO(5)N (Mo-N 2.346(2), 2.456(2) A).

Synthesis and Structural Elucidation of Triazolylmolybdenum(VI) Oxide Hybrids and Their Behavior as Oxidation Catalysts

“…Although the acidic−basic properties and the sizes of p-trtzH and trNH 2 are markedly different, the crystal structures of their two complexes, 4a 15 The principle structural changes for triazole−molybdenum oxide hybrids were achieved by introducing the second triazole moiety (p-tr 2 Ph and tr 2 ad). Apparently, the crystal structure of the solids can be rationalized because the formation of [MoO 3 ([N−N]-tr)] n linear motifs seems to be very predictable.…”

“Fluoride molecular scissors”: A rational construction of new Mo(VI) oxofluorido/1,2,4-triazole MOFs

“…Four accessible nitrogen-donor atoms of the ligands predetermine stiff tetradentate coordination for connection of the metal centers at short (~3.6 Å) and long distances (10-12 Å for tr 2 ad and 16-18 Å for tr 2 ad 2 ). Since in a combination with molybdenum(VI) oxide the N 1 ,N 2 -triazole ligands commonly provide bridging of the adjacent Mo ions along infinite (-MoO 2 -O-) n chains [3], the intrinsic role of fluoride may be regarded as a "chemical scissors" cutting off the metal oxide connectivity with formation of the discrete bi-or polynuclear oxo/triazole bridged fragments (Scheme 1). Steric volume of the aliphatic spacer is important for increasing the spacing between functional SBUs and preventing the possible interpenetration of the networks.…”

“…Recently, we utilized an alternative approach toward rational construction of robust and thermally stable coordination hybrids based upon metal oxides. In particular, that the short-distance 1,2-azole bridges are complementary with the common oxo-bridges was employed for preparation of molybdenum(VI) oxide-organic frameworks (MOOFs), in which polymeric molybdenum(VI) oxide subtopologies act in a synergy with a series of neutral bitopic 1,2,4-triazole linkers [3]. The inorganic MoO 3 matrix could be further elegantly modified, while exploiting a concept of "fluoride molecular scissors" [4].…”

Hydrothermal synthesis and structural characterization of an organically-templated open-framework trimolybdates

“…The great interest in the design of molybdenum(VI) oxide−organic frameworks (MOOFs) is not only due to their applications in such areas as catalysis , magnetism, sorption etc ., but also due to its fascinating structural chemistry (Lysenko et al ., 2010;Pope and Müller , 2001;Senchyk et al, 2014). Various synthetic approaches have been used to isolate highly crystalline samples suitable for structural characterization by X-ray diffraction, but the synthesis of organic−inorganic hybrids using hydrothermal conditions has received special attention in the field of coordination solids based on transition-metal oxides, including transition-metal molybdate complexes (Asnani et al, 2012;Hagrman and Zubieta, 1998;Hagrman et al, 1999;Randy et al, 2001;Hagrman and Zubieta, 2000).…”