Self-assembly of tri-pyrazolate linked cages with di-palladium coordination motifs

Abstract

By employing di-palladium complexes [(N^N)₂Pd₂(NO₃⁻)₂](NO₃⁻)₂ (where N^N = 2,2′-bipyridine, bpy; 4,4′-dimethylbipyridine, dmbpy; 1,10-phenanthroline, phen) as corners and tripyrazole functional ligands (H₃L¹–H₃L⁵) as linkers, a series of highly-positively-charged tripyrazolate-bridged metallo-cages with different conformations and cavities such as [Pd₆L₂]⁶⁺ (1 or 5, where L = L¹ or L⁵), [Pd₁₀L²₄]¹⁰⁺ (2a, 2b and 4b, where L = L² or L⁴) and [Pd₁₂L₄]¹²⁺ (3 or 4a, where L = L³ or L4) have been synthesized through a di-metal coordination directed self-assembly with spontaneous deprotonation of the tripyrazole ligands in aqueous solution. These complexes have been fully characterized by ¹H and ¹³C NMR, cold-spray ionization or electron spray ionization mass spectrometry (CSI-MS, ESI-MS) and elemental analysis. Complexes 1, 2a, 2b, 3 and 4 have also been determined by single-crystal X-ray diffraction structural analysis. In the case of complex 3, six PF₆⁻ anions were encapsulated within the cavity composed of adjacent di-Pd corners.