posted on 2021-08-19, 19:44authored byThomas Pickl, Alexander Pöthig
We present the synthesis,
structural characterization, and photophysical
properties of dinuclear PdII and PtII–NHC
complexes Pd2L(PF6)2 and Pt2L(PF6)2 based on a macrocyclic calix[4]imidazolylidene[2]pyrazolate
ligand obtained by in situ deprotonation of the tetraimidazolium
salt H6L(PF6)4. The PtII congener was also prepared by transmetalation from previously published
AgI pillarplex Ag8L2(PF6)4. NMR spectroscopy (1H, 13C, 195Pt) combined with SC-XRD studies elucidated the structure
of the PdII and PtII complexes in the solid
state and in solution. The d8 metal ions of both congeners
are coordinated in a slightly distorted square-planar arrangement.
Similar to the previously reported NiII complex Ni2L(PF6)2, the heavier metal homologues
adopt a bent, saddle-shaped structure. As observed for structurally
similar PtII complexes in solution, bimetallic Pt2L(PF6)2 showed photoluminescence in the blue
region. In the solid state, emission was observed at a similar energy
with unusually short lifetimes compared to other monometallic PtII complexes. DFT and TDDFT studies shed light on the nature
of the most bathochromic transitions, suggesting a significant pyrazolate-
and NHC-centered π–π* character.