CONFORMATIONAL POLYMORPHISM OF DI(2-NAPHTHYL) DITELLURIDE

Di(2-naphthyl) ditelluride (1), synthesized by reaction of 2-chloronap hthalene with alkali metal ditelluride reagents in dipolar aprotic sol vents, crystallizes in two polymorphic modifications. Single-crystal X -ray structure determinations show these to be conformational polymorp hs. Polymorph la is monclinic, space group P2(1)/c, a = 8.406(3), b = 6.304(2), c = 32.323(9) angstrom, beta = 99.92(3)-degrees, V = 1687.2 angstrom3, and Z = 4. Polymorph lb is also monoclinic, space group C2/ c, a = 36.654(11), b = 7.840(2), c = 12.084(4) angstrom, beta = 104.56 (3)-degrees, V = 3361.9 angstrom3, and Z = 8. Polymorph la has a C-Te- Te-C torsion angle of 105.2-degrees and relatively long Te...Te contac ts (4.13, 4.41 angstrom), while polymorph lb has a C-Te-Te-C angle of 78.6-degrees and short intermolecular Te...Te contacts of 3.708 and 4. 002 angstrom. Polymorphs la and lb have also been characterized by dif ferential scanning calorimetry and by infrared, Raman, and solid-state electronic spectroscopy. Raman shifted lines at 188 and 182 cm-1 in l a and lb, respectively, are assigned to the ditelluride stretching mod e. Polymorph lb exhibits a shoulder near 510 nm in its solid-state ele ctronic spectrum. This feature is not observed either in solution spec tra or in the spectrum of solid la. It is likely that the shoulder is associated with an extended electronic structure which arises from a c ontinuous set of short Te...Te nonbonded contacts.