New synthetic approach and structural characterization of the chloroalkylstannanes (ClCH2)n SnCl4−n (n=2, 4) and the hydrolysis product [(ClCH2)2Sn(Cl)OSn(Cl)(CH2Cl)2]2

The chloroalkylstannanes Cl2Sn(CH2Cl)2 (1) and Sn(CH2Cl)4 (3) have been prepared in high yields by the treatment of tin tetrachloride with diazomethane under the elimination dinitrogen. The established synthetic process was modified in such a way, that the yields were considerably upgraded and the isolation of the products simplified: instead of using CH2N2 in solution, CH2N2 was transported by a nitrogen gas flow in a special apparatus. The compounds 1 and 3 were crystallized and their crystal and molecular structures were obtained (for 1 this was a redetermination) by X-ray diffraction [1: orthorhombic; space group: Pmmn; a=7.760(2), b=10.190(2), c=4.840(1) Å; V=382.7 Å3; Z=2. 3: monoclinic; space group: C2/c; a=9.849(2), b=9.872(2), c=10.611(2) Å, β=96.30(3)°; V=988.3 Å3; Z=4]. Both molecular compounds are connected in the solid state by either intermolecular Sn⋯Cl interactions (1) or weak H⋯Cl bridges (3). In the crystal structure of 1 the molecules adopt almost perfect C2v symmetry (the twofold axis bisecting the ClSnCl angle) and stack together in such a way, that all chlorine atoms are oriented in one direction. The two tin bonded chlorine atoms form an SnCl2 scissor which chelates the neighboring molecule via the two Sn⋯Cl contacts (3.76 Å) upgrading the coordination number at tin from 4 to 6. This feature can best be seen from the increase of the CSnC bond angle to 135.4° (instead of tetrahedral) and from the simultaneous decrease of ClSnCl to 98.9°. In the crystal of 3 the central tin atom is almost tetrahedrally coordinated by four carbon atoms, but there are still weak intermolecular interactions caused by H⋯Cl bridges (3.01 Å). Treatment of compound 1 with moisture converts it to the chlorostannoxane (ClCH2)2ClSnOSnCl(CH2Cl)2 (2) which turns out to crystallize as a distinct centrosymmetric dimer. Compound 2 crystallizes in the monoclinic space group P21/n (a=8.842(2), b=18.704(4), c=8.693(2) Å, β=109.48(3)°, V=1352.3 Å3, Z=2) and the dimeric molecule deviates from the typical ladder like structure of chlorostannoxanes with the three adjacent four-membered cycles (SnClOSn, Sn2O2, SnClOSn) by further Sn⋯Cl interaction (3.450 Å). Through this interaction all tin, tin bonded chlorines and oxygen atoms become assembled within a common plane which is wrapped up by eight CH2Cl-groups above and below this plane (overall point symmetry almost C2h). The ten atoms (4Sn, 4Cl, 2O) can also be described as two oxygen centered interpenetrating Cl2Sn3O distorted hexagons. The tin atoms are either in trigonal bipyramidal or octahedral distorted coordination spheres, while the oxygen atoms are trigonal planarly coordinated by three tin atoms.