SYNTHESIS AND CRYSTAL-STRUCTURES OF [SN(2-[(ME3SI)(2)C]C5H4N)R] [R = C6H2PR3I,4,6 1 OR CH(PPH2)(2) 2], 2 NOVEL HETEROLEPTIC TIN(II) COMPOUNDS DERIVED FROM [SN-(2-[(ME3SI)(2)C]C5H4N)CL], AND FOR [(SN(C6H2PR3I-2,4,6)(2))(3)] 3, A STRUCTURAL REDETERMINATION

Two novel, monomeric heteroleptic tin(II) derivatives, [Sn{2-[(Me3Si)( 2)C]C5H4N}R] [R = C6H2Pr3i,-2,4,6 1 or CH(PPh2)(2) 2], have been prepa red, characterised by multinuclear NMR spectroscopies and their molecu lar structures determined by single crystal X-ray diffraction. Both co mpounds were prepared from the corresponding heteroleptic tin(II) chlo ro-analogue, [Sn{2-[(Me3Si)(2)C]C5H4N}Cl], and thus demonstrate the ut ility of this compound as a precursor to further examples of heterolep tic tin(II) derivatives: such compounds are often unstable with respec t to ligand redistribution. In each case, the central tin(II) is three -co-ordinate, Crystals of trimeric [{Sn(C6H2Pr3i-2,4,6)(2)}(3)] 3 were found to undergo a solid state phase transition, which may be ascribe d to ordering of the ligand isopropyl groups. At 220 K the unit cell i s orthorhombic, space group Pna2(1), compared with monoclinic, space g roup P2(1)/c, for the same crystals at 298 K, in which there is an eff ective tripling of the now b (originally c) axis. This result illustra tes the extreme crowding generated by this bulky aryl ligand.