2:2-Type complexes of zirconium(IV)/hafnium(IV) centers with mono-lacunary Keggin polyoxometalates: Syntheses and molecular structures of [(α-SiW11O39M)2(μ-OH)2]10− (M = Zr, Hf) with edge-sharing octahedral units and [(α-SiW11O39M)2(μ-OH)3]11− with face-s

This paper describes the syntheses and crystal structures of a set of novel 2:2-type ZrIV/HfIV-containing Keggin complexes with edge-sharing and face-sharing linkages prepared under different pH conditions, each consisting of di-ZrIV/HfIV cluster cations sandwiched between two mono-lacunary α-Keggin polyoxometalates (POMs) with an Si heteroatom, i.e., (Et2NH2)10[(α-SiW11O39M)2(μ-OH)2]·4H2O (M = Zr, Zr-edge; Hf, Hf-edge) and (Et2NH2)11[(α-SiW11O39M)2(μ-OH)3]·15H2O (M = Zr, Zr-face; Hf, Hf-face). The two central Zr and Hf atoms of the Zr-edge and Hf-edge are linked by two μ-OH groups, i.e., an edge-sharing linkage, whereas those of the Zr-face and Hf-face are linked by three μ-OH groups, i.e., a face-sharing linkage. Previously reported Zr/Hf-containing POM dimers were generally linked by edge-sharing M(OH)2M (M = Zr, Hf) bonds. Therefore, the present Zr-face and Hf-face are the first examples of Zr/Hf-containing POM dimers linked in a face-sharing fashion.

Graphical abstractThis paper describes the syntheses and crystal structures of a set of novel 2:2-type ZrIV/HfIV-containing Keggin complexes with edge-sharing and face-sharing linkages prepared under different pH conditions, each consisting of di-ZrIV/HfIV cluster cations sandwiched between two mono-lacunary α-Keggin POMs with an Si heteroatom, i.e., (Et2NH2)10[(α-SiW11O39M)2(μ-OH)2]·4H2O (M = Zr, Zr-edge; Hf, Hf-edge) and (Et2NH2)11[(α-SiW11O39M)2(μ-OH)3]·15H2O (M = Zr, Zr-face; Hf, Hf-face). Zr-face and Hf-face are the first examples of Zr/Hf-containing POM dimers linked in a face-sharing fashion.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A set of novel 2:2-type ZrIV/HfIV-containing Keggin complexes with edge-sharing and face-sharing linkages were prepared. ► Four complexes were characterized by CHN elemental analysis, FTIR, TG/DTA, and solution and solid-state 29Si NMR. ► Molecular structures were successfully determined by X-ray crystallography. ► Zr-face and Hf-face are the first examples of Zr/Hf-containing POM dimers linked in a face-sharing fashion. ► The 2:2-type Keggin POM with a face-sharing linkage can be prepared only if the heteroatom is Si.