Pyrazolate‐Based Oligonuclear Copper and Silver Complexes with N/S Coordination Spheres

Abstract

AbstractA series of pyrazole‐based potential ligands bearing thioether substituents in 3‐ and 5‐positions of the heterocycle was synthesized [3,5‐bis(RSCH2)‐pyzH R=Ph (1aH), PhCH2 (1bH), iPr (1cH), tBu (1dH)]. These ligands afford oligonuclear Cu1 and Ag1 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 planar arrays of N,N′‐bridging pyrazolates and linear coordinated silver ions, with each two of the trinuclear moieties being linked by two unsupported short intermolecular Ag…Ag contacts [3.041(1) Å]. Molecular‐weight determinations for 2a (THF) and 3c (toluene) indicate that hexanuclear entities are preserved in solution. Starting from 1bH the CuII complex [(1b)2Cu2](BF4)2 (4) was synthesized. According to an X‐ray crystal structure analysis it consists of dinuclear molecules with two bridging pyrazolates, distorted square planar N2S2 coordination spheres for Cu11 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 electrochemical reduction and oxidation processes for the CuII and CuI compounds, respectively, is explained by the inability of the respective coordination framework to adapt to different geometric preferences.