Synthesis and Structure of Nickel-Containing Cuboidal Clusters Derived from [W₃Se₄(H₂O)₉]⁴⁺. Site-Differentiated Substitution at the Nickel Site in the Series [W₃NiQ₄(H₂O)₁₀]⁴⁺ (Q = S, Se)

New Ni-containing heterometallic cuboidal cluster aqua complex [W₃(NiCl)Se₄(H₂O)₉]³⁺, the missing link in the family of the M₃NiQ₄ clusters (M = Mo, W; Q = S, Se), has been prepared by the reaction of [W₃Se₄(H₂O)₉]⁴⁺ with Ni in 2 M HCl. Single crystals of edge-linked double-cuboidal cluster [{W₃NiSe₄(H₂O)₉}₂](pts)₈·18H₂O (pts = p-toluenesulfonate) were grown from the solution of the aqua complex in 3 M Hpts, and their structures were determined. The Ni site in the clusters [W₃(NiCl)Q₄(H₂O)₉]³⁺ selectively coordinates typical π-acceptor ligands such as CO, olefins, acetylenes, phosphines, arsines, or SnCl₃^-. This allows stabilization by coordination of such elusive species as HP(OH)₂ and As(OH)₃. The stability constants for coordination of HP(OH)₂, As(OH)₃, and SnCl₃^- were determined. The Se for S substitution increases the stability by 1−2 orders of magnitude. Supramolecular adducts with cucurbit[6]uril (Cuc), [W₃(Ni(HP(OH)₂))Q₄(H₂O)₉]Cl₄·Cuc·11H₂O and [W₃(NiAs(OH)₃)S₄(H₂O)₈Cl]Cl₃·Cuc·13H₂O, were isolated and structurally characterized.