Hydrothermal assembly and crystal structures of three novel open frameworks based on molybdenum(VI) oxides

Abstract

The hydrothermal syntheses, crystal structures and thermal behaviours of three new 3-D framework molybdenum(VI) oxide hybrid materials, [MoO ₃ (pyz) _0.5 ] 1 (pyz=pyrazine), [{Cu(pip) _0.5 }MoO ₄ ] (pip=piperazine) 2 and [H ₂ Mo ₂ Cu ₃ O ₁₀ ] 3, are presented. 1 and 2 that are hybrids of inorganic oxide layers and bridging organodiamine ligands exhibit a covalent/coordination framework connectivity. 3 represents a novel open framework example of bimetallic oxides based on Mo ^VI and Cu ^II . These new materials are synthesized by a judicious selection of organodiamines accompanied by the concurrent alteration of initial reaction conditions. The choice of organodiamines is found to be critical to the framework composition and construction of solid architectures. The chiral framework of 1 and the 3-D structure of 2 are characterised by one-dimensional channels along the orthorhombic and triclinic b axis respectively circumscribed by six {MoO ₅ N} octahedra and two pyz molecules in 1, and by two {MoO ₄ } tetrahedra, four {CuO ₄ N} square pyramids and two pip molecules in 2. The 3-D open framework of 3 has six-ring channels along the triclinic b axis. The thermal behaviours of the three solids are similar, undergoing a phase transition in the range 260-420 °C upon the removal of organic ligands in 1 and 2 and dehydration in 3.