[Mo2(NO)2(S2)3(S5)OH]3−, a Complex Containing a Bidentate S52− -Bridging Ligand in a {S5Mo2(S2)}- Heterocycle with Cyclooctasulfur Geometry

✍ Scribed by Prof. Dr. Achim Müller; Werner Eltzner; Dr. Hartmut Bögge; Erich Krickemeyer

• Publisher: John Wiley and Sons
• Year: 1983
• Tongue: English
• Weight: 259 KB
• Volume: 22
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.198308841

✦ Synopsis

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).