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.

本研究首次从[Pt(H₂O)₂(OH)₄]的硝酸溶液中分离得到核数高于2的多核羟桥连铂(IV)硝酸根配合物，并将其与大环穴状配体葫芦[n]脲（cucurbit[n]uril, CB[n]，n=6、8）及18-冠-6醚（18-crown-6 ether）构筑为超分子化合物，具体包括：[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）以及[H₃O⊂18-crown-6]₂[Pt₂(μ₂-OH)₂(NO₃)₈][Pt₄(μ₃-OH)₂(μ₂-OH)₄(NO₃)₁₀]（III）。通过获得上述化合物的单晶态，得以解析此前在固态中尚未见报道的四核配合物[Pt₄(μ₃-OH)₂(μ₂-OH)₄(NO₃)₁₀]与六核配合物[Pt₆(μ₃-OH)₄(μ₂-OH)₆(NO₃)₁₂]²+的晶体结构。采用195铂核磁共振波谱法（195Pt NMR spectroscopy）验证了这类多核硝酸根配合物的Ptₓ(OH)ᵧ核对碱性水解的稳定性。对化合物III的195Pt NMR光谱分析表明，相较于单核形式，每引入一个Pt-(μ-OH)₂-Pt桥环，信号会发生约260 ppm的低场位移，这一规律可用于预测更高核数配合物的信号峰位置。