RESUMO
The synthesis and characterization of two dinuclear HfIV and ZrIV complexes sandwiched between 2 mono-lacunary alpha-Keggin polyoxometalates (POMs), i.e., (Et2NH2)8[{alpha-PW11O39Hf(micro-OH)(H2O)}2].7H2O (Et2NH(2)-1) and (Et2NH2)8[{alpha-PW11O39Zr(micro-OH)(H2O)}2].7H2O (Et2NH(2)-2), are described. [Note: the moieties of their polyoxoanions are abbreviated simply as and , respectively.] A pair of HfIV- and ZrIV-containing POMs belonging to the same family were herein isolated as diethylammonium salts and were unambiguously characterized by complete elemental analysis, including sodium and oxygen analyses, TG/DTA, FT-IR, single-crystal X-ray structure analysis and solution (31P and 183W) NMR spectroscopy. Polyoxoanions 1 and 2 were isostructural with each other. The central [M2(micro-OH)2(H2O)2]6+ (M=Hf, Zr) cation unit was composed of 2 edge-sharing polyhedral M units, which were linked through 2 micro-OH groups and contained 1 water molecule coordinated to each metal center. Since the mono-lacunary Keggin POM acts as an oxygen-donor quadridentate ligand, the Hf and Zr centers are 7-coordinate. It should be noted that the present 2 Keggin 2:2-type compounds, Et2NH(2)-1 and Et2NH(2)-2, undergo a reversible conversion to Keggin 1:2-type complexes [M(alpha-PW11O39)2]10-, respectively, in solution under appropriate conditions. The synthesis of Et2NH(2)-1 and Et2NH(2)-2 is based on such an interconversion. The Zr compound Et2NH(2)-2 was rigorously compared with the 3 Zr POMs (OK-1-OK-3), recently reported by Kholdeeva's group: their POMs in a different protonation-state did not contain any coordinating water molecules.
RESUMO
The syntheses and structures of hafnium(iv) and zirconium(iv) complexes with Keggin tri-lacunary polyoxometalates (POM) [A-alpha-PW(9)O(34)](9-), i.e., (Et(2)NH(2))(7)H(2)[Hf(3)(micro-OH)(3)(A-alpha-PW(9)O(34))(2)].11H(2)O (Et(2)NH(2)-) and (Et(2)NH(2))(7)H(2)[Zr(3)(micro-OH)(3)(A-alpha-PW(9)O(34))(2)].12H(2)O (Et(2)NH(2)-) are described. The two POMs, Et(2)NH(2)- and Et(2)NH(2)-, were obtained as analytically pure, colorless crystals in 30.0 and 40.9% yields, respectively, by 1:3-molar ratio reactions of [A-PW(9)O(34)](9-) with Hf(SO(4))(2) and Zr(SO(4))(2), respectively, in aqueous solutions at 80-90 degrees C, followed by refluxing. The two POMs were characterized by elemental analysis, TG/DTA, FTIR, solution ((31)P and (183)W) NMR and X-ray crystallography. X-Ray structure analysis of Et(2)NH(2)- revealed that in polyoxoanion , the three 6-coordinate prismatic Hf(IV) ions linked with the three bridging OH groups, i.e., the [Hf(3)(micro-OH)(3)](9+) cluster cation was sandwiched between two alpha-Keggin tri-lacunary POMs. The molecular structure of was isostructural with that of polyoxoanion in Et(2)NH(2)-. X-Ray crystallography also showed that the crude crystals of Et(2)NH(2)- and Et(2)NH(2)-, which were first formed without refluxing, contained the two isomeric crystalline species in a 7:3 ratio with the alpha,alpha- and alpha,beta-junctions of the two Keggin tri-lacunary POMs. These facts were also confirmed by (31)P NMR in D(2)O. By refluxing the solutions containing the crude crystals, only the alpha,alpha-isomers of Et(2)NH(2)- and Et(2)NH(2)- were finally isolated.
