Spektroskopische (IR, RA, Elektronenabsorption, PE) Eigenschaften der Cyanothiomolybdate (I)‐(IV), die möglicherweise biologische Bedeutung haben, werden untersucht und auf der Grundlage von EH‐SCCC‐MO‐Berechnungen diskutiert.

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standard distance of 2. 75-2.80 A. In addition, closer contacts (2.23(5)-2.58(2) A) exist between H-atoms in 0(2),0(3) flip-flop bridges and the adjacent glucosidic O(4) atoms than correspcpd to the ideal van der Waals' H . . .O distance of 2.6 A; this points to an attraction, which, however, is weaker than in normal 0-H . . .O hydrogen bridges with significantly shorter H . . .O distances of ca. 1.8 A.The flip-flop bridges should be of general significance in systems in which, similarly as in 0-CD, special steric conditions provide favorable prerequisites. To such systems belong, in particular, polysaccharides such as starch, which has a helical structure-irrespective of whether one considers the A-, Bor V-form-and always contains neighboring 0(2),0(3), hydroxy groups. Flip-flop bridges are entropically favored over normal 0-H . . .O bonds, because of two energetically almost equivalent states. The H/ D exchange, which is markedly smaller for 0-CD than for a-CD and starch, also suggests particularly strong intramolecular interactions for the bonding of the hydrogen atoms to 0(2),0(3).