PULLED MOLECULAR STRINGS AND STACKED MOLECULAR DECKS - CHELATE-RING FORMATION VS METAL-METAL BRIDGING IN DICOPPER(I) COMPLEXES OF 2,2'-BIPYRIMIDINE WITH DIPHOSPHINE LIGANDS OF VARIABLE POLYMETHYLENE CHAIN-LENGTH

The ''self-assembly'' reaction between bischelating 2,2'-bipyrimidine, metallic copper, CU2+, and two equivalents of bidentate Ph(2)P(CH2)(n )PPh(2) produces crystallographically characterized dinuclear complexe s with a [Cu-I(mu-bpym)-CUI](2+) core and chelating (n = 5; type I) or bridging diphosphine ligands (n = 6, 8, type II). Structures II may b e designated as ''inverse cryptate'' arrangements. The structural data of the solids and the spectroscopic results for the dissolved species indicate a strained configuration in the case of complex [(mu-bpym)Cu -2{mu-Ph(2)P-(CH2)(n)PPh(2)}(2)](2+) (6) with n = 6. Once the polymeth ylene chain length is reduced one notch further to n = 5 (5), the diph osphines can no longer bridge but help to form eight-membered chelate rings (structure I). In this complex there is a distortion towards a t rigonal-pyramidal coordination geometry at the copper(I) centers, whic h is supported by the formation of an ''organic sandwich'' arrangement between the central bpym acceptor and two phosphino phenyl rings.