6533b86ffe1ef96bd12cdb21

RESEARCH PRODUCT

Selective Crystallization of Dimeric vs. Monomeric Dimethyltin‐Containing Tungstoarsenates(III) and ‐antimonates(III) with the Guanidinium Cation

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The use of guanidinium cations [C(NH 2 ) 3 ] + as crystallizing agents allowed us to selectively isolate the dimeric [{(CH 3 ) 2 -Sn(H20)} 4 {(CH 3 ) 2 Sn}(B-β-XW 9 O 33 ) 2 ] 8- (1, X = As III ; 2, X = Sb III ) polyanions from the reaction of (CH 3 ) 2 SnCl 2 with Na 9 [B-a-XW 9 O 33 ) (3:1 ratio) in water at pH 3. This reaction is known to give the monomeric [{(CH 3 ) 2 Sn(H 2 O) 2 } 3 (B-β-XW 9 O 33 )] 3- polyanions as the major species. Polyanions 1 and 2 are composed of one octahedral trans-(CH 3 ) 2 SnO 4 moiety that bridges two trilacunary [B-β-XW 9 O 33 ] 9- Keggin subunits further decorated by two structurally nonequivalent {(CH 3 ) 2 Sn} 2+ functionalities each: one distorted octahedral trans-(CH 3 ) 2 SnO 4 linking moiety and one trigonal-bipyramidal cis-(CH 3 ) 2 SnO 3 pendant group. This results in a dimeric, centrosymmetric assembly where each [B-β-XW 9 O 33 ] 9- subunit is connected to three {(CH 3 ) 2 Sn} 2+ functionalities through two Sn-O(W) bonds. Polyanions 1 and 2 polymerize upon crystallization by forming intermolecular Sn-O-W bridges resulting in the isostructural hybrid materials [C-(NH 2 )3] 8 [{(CH 3 ) 2 Sn(H 2 O)}4{(CH 3 ) 2 Sn}(B-β-XW 9 O 33 ) 2 ]·10H 2 O (1a, X = As III ; 2a, X = Sb III ). Compounds 1a and 2a were characterized in the solid state by elemental analysis, infrared spectroscopy, thermal analysis, and single-crystal X-ray diffraction. The crystal packing shows a 2D arrangement of the polyanions connected by the trans-(CH 3 ) 2 SnO 4 linking moieties, resulting in corrugated hybrid layers parallel to the (101) plane with the cis-(CH 3 ) 2 SnO 3 pendant groups acting as interlamellar spacers.