Abstract
Ten new silver and gold trimeric complexes of the type [M~3~(μ‐pz′)~3~] (M=Au, Ag), where pz′ indicate pyrazolato ligands derived from mesogenic 3,5‐disubstituted 1__H__‐pyrazoles $\rm{ Hpz^{R_2}}$ or non‐mesogenic 3‐substituted 1__H__‐pyrazoles Hpz^R^ (R=C~6~H~4~OC~n~H~2__n__+1~), were synthesized and characterized. The gold and silver complexes 7, 8, 10, and 11 containing symmetric pyrazolato ligands as bridging groups ($\rm{ pz^{R_2}}$; R=C~6~H~4~OC~n~H~2__n__+1~, n=4 ($\rm{ pz^{bp_2 }}$) and 8 ($\rm{ pz^{op_2 }}$)) exhibited a trigonal symmetric structure. The same results were obtained for the related silver derivatives 16–18 with 3‐substituted pyrazolato ligands (pz^R^; R=C~6~H~4~OC~n~H~2__n__+1~, n=4 (pz^bp^), 12 (pz^ddp^), and 18 (pz^odp^)). By contrast the 3‐substituted pyrazolato‐gold compounds 13–15 adopted an asymmetric molecular structure related to the position of the substituents on the trinuclear core. The thermal behavior of these complexes was investigated by differential scanning calorimetry and polarized‐light microscopy. The mesomorphism of the parent 3,5‐disubstituted pyrazoles is avoided in their corresponding trinuclear complexes 7, 8, 10, and 11. However, the metal derivatives 14 and 17 containing the asymmetric 3‐[4‐(dodecyloxy)phenyl]pyrazolato ligand were found to have liquid‐crystal properties. These compounds exhibited monotropic behavior with columnar mesophases that could be related to the disc‐like shape of the molecular core and the appropriate length of the alkyloxy chain. For comparative purposes, the X‐ray structure of the related gold complex [Au~3~(μ‐$\rm{ pz^{pp_2 }}$)~3~] (9) having phenoxyphenyl substituents at the 3‐ and 5‐positions of the pyrazolato ligand is also described. The molecular structure is formed by a non‐planar (AuNN)~3~ core, containing three Au‐atoms bridged by three pyrazolato ligands. The molecular packing is described as a columnar organization, the shortest Au ⋅⋅⋅Au distance being 4.639(1) Å between consecutive trimers.