PYRAZOLATE-BASED OLIGONUCLEAR COPPER AND SILVER COMPLEXES WITH N S COORDINATION SPHERES/

A series of pyrazole-based potential ligands bearing thioether substit uents in 3- and 5-positions of the heterocycle was synthesized [3,5-bi s(RSCH2)-pyzH; R = Ph (1aH), PhCH2 (1bH), iPr (1cH), tBu (1dH)]. These ligands afford oligonuclear Cu-I and Ag-I coordination compounds [LCu ](x) (2a-c, L = 1a-c) and [LAg](x) (3a-d, L = 1a-d), respectively. The single crystal X-ray analysis of 3c shows the presence of trimeric pl anar arrays of N,N'-bridging pyrazolates and linear coordinated silver ions, with each two of the trinuclear moieties being linked by two un supported short intermolecular Ag ... Ag contacts [3.041(1) Angstrom]. Molecular-weight determinations for 2a (THF) and 3c (toluene) indicat e that hexanuclear entities are preserved in solution. Starting from 1 bH the Cu-II complex [(1b)(2)Cu-2](BF4)(2) (4) was synthesized. Accord ing to an X-ray crystal structure analysis it consists of dinuclear mo lecules with two bridging pyrazolates, distorted square planar N2S2 co ordination spheres for Cu-II and an axially bridging tetrafluoroborate . Magnetic susceptibility data reveal an antiferromagnetic exchange (J = -206 cm(-1)) that is among the highest found for doubly pyrazolate bridged dicopper(II) complexes, which is rationalized on the basis of the rather symmetric dinuclear core of 4. The irreversibility of the e lectrochemical reduction and oxidation processes for the Cu-II and Cu- I compounds, respectively, is explained by the inability of the respec tive coordination framework to adapt to different geometric preference s.