Alkali Metal Directed Assembly of Heterometallic V^v/M (M = Na, K, Cs) Coordination Polymers: Structures, Topological Analysis, and Oxidation Catalytic Properties

The reactions of [VO­(acac)₂] with bis­(salicylaldehyde)-oxaloyldihydrazone (H₄L) and an alkali metal carbonate M₂CO₃ (M = K, Na, Cs), in EtOH/H₂O medium upon reflux, resulted in the generation of three new heterometallic V^V/M materials, namely the 1D [(VO₂)₂(μ₄-L)­{Na₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>1</b>), 2D [{V­(μ-O)₂}₂(μ₄-L)­{K₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>2</b>), and 3D [{V­(μ-O)­(μ₃-O)}₂(μ₈-L)­{Cs₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>3</b>) coordination polymers. They were isolated as air-stable solids and fully characterized by IR, UV–vis, ¹H, and ⁵¹V NMR spectroscopy, ESI–MS(±), elemental, thermal, and single-crystal X-ray diffraction analyses, the latter showing that <b>1</b>–<b>3</b> are constructed from the resembling [(VO₂)₂(μ_4/8-L)]^2– blocks assembled by the differently bound aqua-metal [M₂(μ-H₂O)₂(H₂O)₂]²⁺ moieties (M = Na, K, Cs). The main distinctive features of <b>1</b>–<b>3</b> arise from the different coordination numbers of Na (5), K (7), and Cs (9) atoms, thus increasing the complexity of the resulting networks from the ladder-like 1D chains in <b>1</b> to double 2D layers in <b>2</b>, and layer-pillared 3D framework in <b>3</b>. The topological analysis of <b>2</b> disclosed a uninodal 4-connected underlying net with a rare <b>kgm</b> [Shubnikov plane net (3.6.3.6)/kagome pattern] topology, while <b>3</b> features a trinodal 4,7,8-connected underlying net with an unprecedented topology. Compounds <b>1</b>–<b>3</b> also show solubility in water (<i>S</i>_25 °C ≈ 4–7 mg mL^–1) and were applied as efficient precatalysts for the homogeneous oxidation of cyclohexane by aqueous H₂O₂, under mild conditions (50 °C) in MeCN/H₂O medium and in the presence of an acid promoter. Total yields (based on substrate) of cyclohexanol and cyclohexanone up to 36% and turnover numbers (TONs) up to 5700 were achieved

Alkali Metal Directed Assembly of Heterometallic V^v/M (M = Na, K, Cs) Coordination Polymers: Structures, Topological Analysis, and Oxidation Catalytic Properties

The reactions of [VO­(acac)₂] with bis­(salicylaldehyde)-oxaloyldihydrazone (H₄L) and an alkali metal carbonate M₂CO₃ (M = K, Na, Cs), in EtOH/H₂O medium upon reflux, resulted in the generation of three new heterometallic V^V/M materials, namely the 1D [(VO₂)₂(μ₄-L)­{Na₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>1</b>), 2D [{V­(μ-O)₂}₂(μ₄-L)­{K₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>2</b>), and 3D [{V­(μ-O)­(μ₃-O)}₂(μ₈-L)­{Cs₂(μ-H₂O)₂(H₂O)₂}]_<i>n</i> (<b>3</b>) coordination polymers. They were isolated as air-stable solids and fully characterized by IR, UV–vis, ¹H, and ⁵¹V NMR spectroscopy, ESI–MS(±), elemental, thermal, and single-crystal X-ray diffraction analyses, the latter showing that <b>1</b>–<b>3</b> are constructed from the resembling [(VO₂)₂(μ_4/8-L)]^2– blocks assembled by the differently bound aqua-metal [M₂(μ-H₂O)₂(H₂O)₂]²⁺ moieties (M = Na, K, Cs). The main distinctive features of <b>1</b>–<b>3</b> arise from the different coordination numbers of Na (5), K (7), and Cs (9) atoms, thus increasing the complexity of the resulting networks from the ladder-like 1D chains in <b>1</b> to double 2D layers in <b>2</b>, and layer-pillared 3D framework in <b>3</b>. The topological analysis of <b>2</b> disclosed a uninodal 4-connected underlying net with a rare <b>kgm</b> [Shubnikov plane net (3.6.3.6)/kagome pattern] topology, while <b>3</b> features a trinodal 4,7,8-connected underlying net with an unprecedented topology. Compounds <b>1</b>–<b>3</b> also show solubility in water (<i>S</i>_25 °C ≈ 4–7 mg mL^–1) and were applied as efficient precatalysts for the homogeneous oxidation of cyclohexane by aqueous H₂O₂, under mild conditions (50 °C) in MeCN/H₂O medium and in the presence of an acid promoter. Total yields (based on substrate) of cyclohexanol and cyclohexanone up to 36% and turnover numbers (TONs) up to 5700 were achieved