Synthesis of bis[(ferrocenylmethyl)trimethylammonium] [bis(1,3-dithiole-2-thione-4,5-dithiolato)zincate] and [bis(1,3-dithiole-2-one-4,5-dithiolato)zincate] salts, ([FcCH 2 NMe 3 ] 2 [Zn(dmit) 2 ] and [FcCH 2 NMe 3 ] 2 [Zn(dmio) 2 ]): crystal structures of [FcCH 2 NMe 3 ] 2 [Zn(dmit) 2 ] and [NEt 4 ] 2 [Zn(dmit) 2 ] MeOH