Anion···π interactions in copper(I) chloride and bromide coordination polymers bearing 1,4-bis(pyridazin-4-yl)benzene ligands.

In poly[[μ4-1,4-bis(pyridazin-4-yl)benzene-1:2:3:4κ(4)N(1):N(2):N(1'):N(2')]di-μ2-chlorido-dicopper(I)], [Cu2Cl2(C14H10N4)]n, (I), and its isomorphous bromide analogue, [Cu2Br2(C14H10N4)]n, (II), the organic ligand is situated across a centre of inversion. The Cu(I) cations adopt a distorted tetrahedral [CuN2X2] [X = Cl in (I) or Br in (II)] environment [Cu-N = 2.0183 (14)-2.0936 (14) Å; Cu-Cl = 2.2686 (6) and 2.4241 (5) Å; Cu-Br = 2.4002 (6) and 2.5284 (5) Å] and the primary coordination motif consists of cuprohalogenide chains accommodating μ-pyridazine groups. The organic ligands are tetradentate and link the inorganic chains into corrugated layers. Their packing is influenced by interlayer anion···π interactions [Cl···π = 3.540 (2) Å and Br···π = 3.593 (2) Å] with the electron-deficient pyridazine rings. This kind of interaction precludes the characteristic slipped π-π stacking and close parallel alignment of the organic tectons; it may be involved as a structure-defining factor for coordination layers based upon lengthy polyaromatic linkers.