Ditin(IV) Chalcogenide Anions: 77Se, 119Sn and 125Te Solution NMR Study of the Sn2Ch64- and Sn2Ch74- (Ch = Se, Te), X-Ray Crystal Structures and Raman Spectra of K+(N(CH3)4+)3Sn2Se64-, (enH+)2(2,2,2-crypt-K+)2Sn2Se64-, (K+)2(2,2,2-crypt-K+)2-Sn2Te64- a