Gas-Phase Fragmentation of Host-Guest Complexes of Cyclodextrins and Polyoxometalates

Gas-phase fragmentation pathways of host-guest complexes of cyclodextrins (CDs) and polyoxometalates (POMs) were examined using collision-induced dissociation (CID). The host-guest complexes studied here were composed of two different classes of POMs-Keggin (PW₁₂O₄₀^3-) and Lindqvist (M₆O₁₉^2-, M = Mo, W)-and three types of CDs (α-, β-, and γ-CD) differing in the diameter of the inner cavity. The CD-POM complexes were generated either by mixing methanol solutions of POM and CD or through a one-step acidic condensation of tetraoxometalates MO₄^2- (M = Mo, W) with CDs for complexes with Keggin and Lindqvist anions, respectively, and introduced into the gas phase using electrospray ionization (ESI). We observe distinct differences in fragmentation pathways of the complexes of Keggin and Lindqvist POMs under high- and low-energy CID conditions. Specifically, direct dissociation and proton transfer from CD to POM accompanied by the separation of fragments is observed in CID of Keggin CD-POM complexes. In contrast, dissociation of CD complexes with Lindqvist POMs is dominated by the simultaneous loss of multiple water molecules. This unusual fragmentation channel is attributed to dissociation of the POM cluster inside the CD cavity accompanied by covalent bond formation between the fragments and CD and elimination of multiple water molecules. The observed covalent coupling of metal oxide clusters opens up opportunities for derivatization of macrocyclic host molecules using collisional excitation of gaseous non-covalent complexes.

A molecular crown analogue templated by Keggin polyanions: synthesis, structure, and electrochemical and luminescent properties

A hybrid compound, [CuI 4(bpmb)4][PWVI 11WVO40] (1) (bpmb = 1,4-bis(pyrazol-1-ylmethyl)benzene), has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction analysis, infrared spectroscopy, elemental analyses and powder X-ray diffraction. In compound 1 crown-like [Cu4(bpmb)4]4+ macrocycles templated by Keggin-type [PWVI 11WVO40]4− polyanions (abbreviated PW12) exist. Supramolecular layers are formed by intermolecular hydrogen bonding interactions of discrete crown-like [Cu4(bpmb)4]4+ macrocycles and [PWVI 11WVO40]4− polyanions. The electrochemical and luminescence properties of compound 1 were investigated.

The key role of -CH3 steric hindrance in bis(pyrazolyl) ligand on polyoxometalate-based compounds

Through using two kinds of bis(pyrazolyl) ligands, four polyoxometalate (POM)-based compounds were hydrothermally synthesized and structurally characterized, [Ag3(Hbhpe)2(H2O)(H2PMo12O40)]·H2O (1), [Ag(H2bdpm)2(H2PW12O40)]·4H2O (2), [Ag6(H2bdpm)6(HPW(VI)8W(V)4O40)]·2H2O (2) and [Ag4(H2bdpm)4(H2P2W18O62)]·3H2O (4) (H2bhpe = 1,2-bis(1-H-pyrazolate)ethane, H2bdpm = 1,1'-bis(3,5-dimethyl-1H-pyrazolate)methane). In compound 1, the Ag-Hbhpe subunit is a 2D layer containing large penta-membered cycles and small tri-nuclear Ag(I) clusters. The Keggin anions covalently float on the large cycles. In compound 2, the Keggin anions are fused by [Ag(H2bdpm)2](+) subunits to form a 1D chain. Compound contains hexa-membered metal-organic cycles, which are further linked by Keggin anions to build a 1D chain. Adjacent chains share the Ag(I) ions to construct a 3D framework of 3. Compound 4 exhibits a wavy double-track chain structure, with the Wells-Dawson anions covalently suspended up and down this chain. The steric hindrance of -CH3 groups in H2bdpm leads to the formation of mono-nuclear Ag(I) subunits in 2 - 4. The influence of -CH3 steric hindrance in bis(pyrazolyl) ligands on the structures of 1 - 4 is discussed. The electrochemical and photocatalytic properties of the title compounds have been studied.

Architectural chemistry of polyoxometalate-based coordination frameworks constructed from flexible N-donor ligands

Polyoxometalate-based coordination frameworks (POMCFs) constructed from flexible N-donor ligands can exhibit diverse properties and fascinating architectures, extending the families of material chemistry and structural chemistry.

A series of polyoxometalate-based compounds including infinite Ag belts and circles constructed by two tolyl-1H-tetrazole isomers

Three novel Keggin-based complexes constructed by two new isomeric ligands 5-o-tolyl-1H-tetrazole and 5-m-tolyl-1H-tetrazole have been synthesized under hydrothermal conditions via changing the types of POM anions and organic ligands.