Cubic Metal−Organic Polyhedrons of Nickel(II) Imidazoledicarboxylate Depositing Protons or Alkali Metal Ions

Reactions of nickel(II) nitrate with 4,5-imidazoledicarboxylic acid (H₃L) in neutral or basic environment result in a series of novel nickel coordination polymers with a uniform Ni₈ cubic building block, [(Ni₈(H₂L)₈(HL)₄)]·8(C₂H₅OH)·18(H₂O) 1, K₂₀[Ni₈L₁₂]·74(H₂O) 2a, K₂₀[Ni₈L₁₂]·50(H₂O) 2b, and K₂₀[Ni₈L₁₂]·29(H₂O) 2c. The result shows that complex 1 assembles into a discrete neutral metal−organic polyhedron with 20 protons located in the carboxyl oxygen atoms, which are linked into a three-dimensional supramolecular architecture by intermolecular hydrogen bonds between guest ethanol and host carboxyl oxygen atoms. Complex 2a exhibits a water ocean, in which there are 20 potassium ions and 74 water molecules around each Ni₈ cubic building block. During the course of gradual loss of the guest water molecules, the adjacent cubic building blocks in 2a rearrange to form its dehydrated products 2b and 2c, the crystallinity remaining. The magnetic properties have been investigated.