The structure of reversibly oxidizable [Cu(mmb)
2](BF
4) with 1-methyl-2-(methylthiomethyl)-1
H-benzimidazole(mmb) as bidentate N,S-donor ligand has been determined and compared with that of the copper(II) species[Cu(mmb)
2(
mages/gifchars/eta.gif" BORDER=0 >
1-ClO
4)](ClO
4). In the complex ions of the equilibrium [Cu
I(mmb)
2]
+ + ClO
4- mages/entities/rlhar2.gif"> e
- + [Cu
II(mmb)
2(
mages/gifchars/eta.gif" BORDER=0 >
1-ClO
4)]
+ the almost linear N-Cu-N backbone is invariant whereas the bonds to the thioether sulfur centersand especially the changing S-Cu-S angle (145.18(5)
mages/entities/deg.gif"> for the Cu
II species, 109.33(3)
mages/entities/deg.gif"> for the Cu
I form) reflectthe metal oxidation state. In contrast to the perchlorate coordinating copper(II) species, [Cu
I(mmb)
2](BF
4) containsa cation with a very large vacant site at the metal center, resulting in elliptical channels within the crystal. DFTcalculations on [Cu
I(mb)
2]
+, [Cu
II(mb)
2]
2+, and [Cu
II(mb)
2(OClO
3)]
+ with mb = 2-methylthiomethyl-1
H-benzimidazole confirm the essential role of the metal-sulfur bonds in responding to the reversible Cu
I/II electrontransfer process, even in the absence of electronically stronger interacting thiolate sulfur centers or sophisticatedoligodentate ligands.
