Synthesis, Assembly And Study Of The Sandwich-type Metal-Oxygen Clusters

Six new sandwich-type heteropolytungstates based on lacunary polytungstoantimonates and polytungstophosphates have been obtained by conventional solution synthesis and ionothermal synthesis methods and characterized by IR, elemental analysis, TG, XRD, electrochemical and photochemical catalysis.1. Two new inorganic-organic hybrid Hervé-sandwich-type tungstoantimonates based on trivacant [B-α-SbW₉O₃₃]9- have been obtained by step-by-step synthesis strategy. Na₉[{Na(H₂O)₂}₃{Co(C₄H₆N₂)}3(SbW₉O₃₃)₂]·28H₂O (1) Na₉[{Na(H₂O)₂}₃{Mn(C₄H₆N₂)}3(SbW₉O₃₃)₂]·28H₂O (2) The single-crystal X-ray diffraction analyses reveal that compounds 1 and 2 are isostructural and crystallize in the same space group P-1. The polyoxoanions in 1 and 2 are composed of two lacunary Keggin-type [B-α-SbW₉O₃₃]9- building units, which are linked by three [Na(H₂O)₂]+ cations and three [M(C₄H₆N₂)]2+ (M=Co(1); M=Mn(2)) fragments, resulting in sandwich-type structures. Furthermore, the sandwich-type polyoxoanions are connected into the 3-D frameworks via Na+ cations and extensive hydrogen bonding interactions.2. Three new Krebs-sandwich-type tungstoantimonates based on trivacant [B-β-SbW₉O₃₃]9- have been obtained by the routine synthetic reactions in the aqueous solutions. Na4H₂[{Co(H₂O)3}2Co(H₂O)₂W(H₂O)₂(B-β-SbW₉O₃₃)₂]·33H₂O (3) H₄[Mn₂(H₂O)8Mn3.5(H₂O)7W0.5(H₂O)(B-β-SbW₉O₃₃)₂]·20H₂O (4) Na₂[Mn₂(H₂O)10{Mn(H₂O)3}2Mn(H₂O)₂W(H₂O)₂(B-β-SbW₉O₃₃)₂]·9H₂O·2HTMA (5) Compound 3 is built from the sandwich-type polyoxoanions [{Co(H₂O)3}2Co(H₂O)₂W(H₂O)₂(B-β-SbW₉O₃₃)₂]6-, linked by Na+ cations to construct a pure inorganic 1-D chain-like structure. Compound 2 shows an interesting 2-D structure built up from sandwich-type anions [Mn3.5(H₂O)7W0.5(H₂O)(B-β-SbW₉O₃₃)₂]8- linked by additional Mn2+ ions, which represents the first example of pure inorganic 2-D structure based on the Mn-containing sandwich-type polytungstoantimonate clusters. The framework of compound 5 consists of the sandwich-type polyoxoanion [{Mn(H₂O)3}2W(H₂O)₂Mn(H₂O)₂(B-β-SbW₉O₃₃)₂]6- covalently linked with two Mn2+ cations byμ2-O atoms resulting in one novel transition-metal-containing polyoxoanion [Mn2(H₂O)10{Mn(H₂O)3}2Mn(H₂O)₂W(H₂O)₂(B-β-SbW₉O₃₃)₂]2-. The transition-metal-containing polyoxoanions are connected into the 2-D framework via Na+ cations and extensive hydrogen bonding interactions. 3.One new Weakly-sandwich-type phosphotungstate compound based on trivacant [B-α-PW₉O₃₄]9- has been successfully synthesized by ionothermal method in 1-ethyl-3-methyl imidazolium bromide ([Emim]Br) ionic liquids (ILs). H₃(Emim)7[Ni₄(Mim)₂(PW₉O₃₄)₂]·4H₂O (6)The polyoxoanion of 6 is two ethylimidazole molecules modified sandwich-type hybrid tungstophosphate [Ni₄(Mim)₂(PW₉O₃₄)₂]^10-. In the packing arrangement, the adjacent hybrid polyoxoanions of 6 are connected through C-H···O hydrogen bonds between the dissociative [Emim]⁺ cations and the surface oxygen atoms of the polyoxoanions to form a 3-D open-framework. Parallel experiments show that pH, the sort of transiton metals and reaction temperature play important roles in the formation of 6.