Crystal and molecular structure of SnMePh[C10H5(OMe-5)(CH2NMe2-8)]Br and proton nuclear magnetic resonance study of the puckering of the chelate ring in five-co-ordinate triorganotin halides SnRR′-[C10H5(OMe-5)(CH2NMe2-8)]X and SnRR′[CH2C6H4(CH2NMe2-2)]X