Syntheses And Characterizations Of Novel Mixed Transition Metals Selenites

Selenites and tellurites have attracted a lot of research attentions due to their potential applications in electronic conduction,catalysis,magnetic,fluorescence,nonlinear optics and molecular absorption.Due to the presence of a stereoactive lone-pair on Se⁴⁺ and Te⁴⁺ cations,Se⁴⁺ and Te⁴⁺ cations can form SeO₃,TeO₃ and TeO₄ polar groups,resulting in rich chemical structures.Moreover,transition metal cations can not only feature various coordination geometries with oxygen atoms and organic ligands,but also exhibit good physical properties,such as magnetic and fluorescent properties.Especially,d⁰ transition metals cations also exhibit a variety of coordination polyhedra.Hence the introduction of mixed transition metals in the selenites and tellurites can result in new materials with rich structures and excellent physical properties.The work of this paper can be divided into two parts.In the first part,we prepared three new organic-inorganic mixed transition metal cations selenites in 2,2-bipy-Cu/Ni-V-Se-O system,namely,Ni（2,2-bipy）2V2O₄（SeO₃）₂（1,P2i/n）,Cu（2,2-bipy）V₂O₄（SeO₃）₂ 0.5H₂O（2,P-1）,Cu₂（2,2-bipy）2V₅O₁₂（SeO₃）₂（3,P-1）.Compound 1 features a OD hexanuclear[（Ni（2,2-bipy）₂）₂V₄O₈（SeO₃）₄]clusters composed of two {Ni（2,2-bipy）2}²⁺ moieties bridged by the central {V₄O₈（SeO₃）₄}^4- unit,which is composed of V₄O₁₈ cluster decorated by four SeO₃ units in tridentate or bidentate chelating modes.Compound 2 shows a 1D[Cu（2,2-bipy）V₂O₄（SeO₃）₂]n chain in which the dimeric {Cu₂（2,2-bipy）₂}⁴⁺ moieties composed of two {Cu（2,2-bipy）}²⁺ are bridged by the {V₄O₈（SeO₃）4}^4- clusters similar to those in 1.The lattice waters are located in between the 1D chains.The structure of compound 3 features a new 2D layered composed of mixed valence vanadate layers of {V₅O₁₇}n layers,which consist of VO₄ and VO₅ units interconnected via corner-sharing and edge-sharing,with 12-MRs filled by{Cu（2,2-bipy）}²⁺ moieties and selenites groups.The adjacent layers of compound 3 are stably packed together via the π-π stacking interactions of 2,2-bipy groups.In the second part,we studied the Ag⁺-Ti⁴⁺/Zr⁴⁺/Nb⁵⁺/Ta⁵⁺-Se⁴⁺-O（F）system systematically for the first time and synthesized four new silver-transition metal selenites,namely,Ag₃Ti₃O₃（SeO₃）₄F（4,P63）,Ag₂ZrF₂（SeO₃）₂（5,Cmca）,AgNbO（SeO₃）₂（6,Cmcm）and AgTaO（SeO₃）₂（7,Cmcm）.Compound 4 features an interesting 3D framework composed of a faveolate[Ti)3O₃（SeO₃）)4]^2-3D framework structure,which are composed of[TiO)5])n chains decorated by SeO₃ groups in a unidentate or bidentate chelating fashions,exhibiting hexagonal channels filled by Ag+ cations and isolated F-anions.Compound 5 exhibits[ZrF)2（SeO₃）)2]^2-anionic chains,which are composed of[ZrO₄F₂]n chains decorated by SeO₃ units in bidentate chelating fashions,with Ag+ located at the inter-chain space as charge-balancing cations.Compounds 6 and 7 are isostructural.Their structures feature a new 3D network based on similar 1D chains of[Nb（Ta）O（SeO₃）₂]^-,which are composed of[Nb（Ta）O₅]n chains decorated by SeO₃ units in bidentate chelating modes,respectively,along the c axis,which are interconnected by Ag-O bonds into a 3D network.Compound 4 displays a moderate second harmonic generation（SHG）response of about 2 ×KDP（KH₂PO₄）.