Crystal structure and spectroscopy of a most unusual Cu(II) coordination compound containing an infinite chain of lattice ligand interwoven with stacked sheets of neutral bis(2-aminopyrimidine-bridged) copper ions: X-ray structure of [Cu(ampym)2(H2O)2(CF3SO3)2](ampym)2(ampym)2

Abstract

Reaction of Cu(II) triflate with an excess of 2-aminopyrimidine (ampym) in ethanol followed by slow crystallization results in a most unusual crystal lattice, which can be considered as consisting of two interpenetrating sublattices. The compound analyzes as [Cu(ampym)₂(H₂O)₂(CF₃SO₃)₂(ampym)₄]. Crystal data: Triclinic, P$\overline 1$, a = 7.6179(5), b = 11.4311(14), c = 11.8373(13) Å, α = 84.098(9), β = 79.998(7), γ = 84.253(8)°, Vol = 1010.151(8) Å, Z = 1, D_calc = 1.592 g/cm³. One part of the lattice consists of the unprecendented linear chain of neutral ampym molecules; the chain is built up by Watson–Crick type bis-hydrogen bonds between imine N atoms and N-H groups of the NH₂. This ampym chain is apparently stabilized by the other part in the crystal lattice, which can best be described by starting from the centrosymmetric trans-Cu^II(ampym)₂(H₂O)₂ ion (Cu-N = 2.01 Å; Cu-O = 1.94 Å). This Cu ion is coordinated by two monodentate ampym ligands, two water molecules and two semi-coordinating triflate oxygen atoms. The Cu chromophore is held in position by hydrogen bonding towards a triflate ion (two times for symmetry reasons), and (again two times) a free ampym ligand. The triflate ion bridges a water hydrogen to a next-neighboring free ampym ligand. The noncoordinating ampym molecule has four bonding sites, of which two are used in H-bonding with the coordinated ligand, one with the triflate and the last one with the water hydrogen atom. The noncoordination ampym molecules in this sublattice finally form aromatic stacks with coordinated ampym and with itself in pairs (ring-ring distance 3.77-3.80 Å).