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

Abstract

AbstractThe use of guanidinium cations [C(NH2)3]+ as crystallizing agents allowed us to selectively isolate the dimeric [{(CH3)2Sn(H2O)}4{(CH3)2Sn}(B‐β‐XW9O33)2]8– (1, X = AsIII; 2, X = SbIII) polyanions from the reaction of (CH3)2SnCl2 with Na9[B‐α‐XW9O33] (3:1 ratio) in water at pH 3. This reaction is known to give the monomeric [{(CH3)2Sn(H2O)2}3(B‐β‐XW9O33)]3– polyanions as the major species. Polyanions 1 and 2 are composed of one octahedral trans‐(CH3)2SnO4 moiety that bridges two trilacunary [B‐β‐XW9O33]9– Keggin subunits further decorated by two structurally nonequivalent {(CH3)2Sn}2+ functionalities each: one distorted octahedral trans‐(CH3)2SnO4 linking moiety and one trigonal‐bipyramidal cis‐(CH3)2SnO3 pendant group. This results in a dimeric, centrosymmetric assembly where each [B‐β‐XW9O33]9– subunit is connected to three {(CH3)2Sn}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(NH2)3]8[{(CH3)2Sn(H2O)}4{(CH3)2Sn}(B‐β‐XW9O33)2]·10H2O (1a, X = AsIII; 2a, X = SbIII). 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‐(CH3)2SnO4 linking moieties, resulting in corrugated hybrid layers parallel to the (101) plane with the cis‐(CH3)2SnO3 pendant groups acting as interlamellar spacers.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)