Structure diversities of ten entangled coordination polymers assembled from reactions of Co(ii) or Ni(ii) salts with 5-(pyridin-4-yl)isophthalic acid in the absence or presence of auxiliary N-donor ligands

Abstract

The self-assembly of transition metal salts with 5-(pyridin-4-yl)isophthalate ligand and N-donor ligands affords a series of entangled coordination frameworks based on different metal cluster cores, namely, [Co(L)(H₂O)₂]·H₂O (1), [Ni(L)(H₂O)]·H₂O (2), [Co₄(L)₂(SO₄)(H₂O)₅(OH)₂]·15.5H₂O (3), [Co₂(L)₂(2,2′-bpy)₂]₂·H₂O (4), [Co₂(L)₂(phen)₂] (5), [Ni(L)(en)(H₂O)₂]₂·2H₂O (6), [Ni(L)(dap)]·3H₂O (7), [Co(L)(bph)(H₂O)₂]·H₂O (8), [Co(L)(bbm)_0.5]·4H₂O (9), [Co(L)(bimb)_0.5]₄·13H₂O (10) [L = 5-(pyridin-4-yl)isophthalic acid; 2,2′-bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline; en = ethane-1,2-diamine; dap = propane-1,2-diamine; bph = (1E,2E)-1,2-bis(pyridin-4-ylmethylene)hydrazine; bbm = 1,4-di(1H-imidazol-1-yl)benzene; bimb = 4,4′-di(1H-imidazol-1-yl)-1,1′-biphenyl]. Their structures were characterized by elemental analysis, IR spectra and TG analyses and further determined by single-crystal X-ray diffraction analysis. The auxiliary ligands play important roles in the formation of various entangled networks. 1–2 show a 2D layer network and its layers are held together by π–π stacking interactions and other unconventional interactions. Complex 3 displays an unusual Co₄ cluster core which is linked by η¹,η¹,η¹,μ₃-SO₄²⁻ and μ₃-OH ions. Upon adding chelating ligands, 4–5 show 2D → 2D entangled polymers with polycatenated and polyrotaxane features based on 4,4-sql layers. 6–7 still exhibit layer strutures, although they have chelating ligands, which may be due to the absence of π–π stacking interactions. 8–10 present pillar-layer structures which are supported by different lengths of pillars. Three-fold interpenetration with polycatenated features are observed in 8–9. 10 exhibits a 4-fold interpenetrating 3D structure with large channel running through its net.