Polynuclear Hydroxido-Bridged Complexes of Platinum(IV) with Terminal Nitrato Ligands

For the first time the polynuclear
hydroxido-bridged platinum­(IV)
nitrato complexes with nuclearity higher than two were isolated from
nitric acid solutions of [Pt­(H2O)2(OH)4] and crystallized as supramolecular compounds of macrocyclic cavitands
cucurbit­[n]­uril (CB­[n], n = 6,8) and 18-crown-6 ether: [Pt4(μ3-OH)2­(μ2-OH)4­(NO3)10]·CB­[6]·25H2O (I), [Pt6(μ3-OH)4­(μ2-OH)6­(NO3)12]­(NO3)2·CB­[8]·50H2O (II), and [H3O⊂18-crown-6]2­[Pt2(μ2-OH)2(NO3)8]­[Pt4(μ3-OH)2­(μ2-OH)4(NO3)10] (III). The isolation of the compounds in the
single crystalline state allows the determination of the structure
of the tetranuclear and hexanuclear complexes [Pt4(μ3-OH)2­(μ2-OH)4(NO3)10] and [Pt6(μ3-OH)4­(μ2-OH)6(NO3)12]2+, which have been previously unknown
in the solid state. Stability of Ptx(OH)y cores of the polynuclear nitrato complexes
toward alkaline hydrolysis was verified by 195Pt NMR spectroscopy.
Analysis of 195Pt NMR spectra of the compound III reveals that addition of every Pt­(μ-OH)2Pt ring
results in ∼260 ppm downfield shift relative to the mononuclear
form, which allows the prediction of signal positions for complexes
of higher nuclearity.