Network formation and photoluminescence in copper(i) halide complexes with substituted piperazine ligands

The synthesis, X-ray structures and photophysics of ten complexes of CuX (X = I or Br) with bridging N-substituted and N,N'-disubstituted piperazines (Pip) are presented. Depending on the steric demand of the Pip substituents, the complexes fall into four categories: (CuX)(4)(Pip)(2), which are networks of linked Cu(4)X(4) cubane units, (CuX)(2)(Pip), which are chains of linked Cu(2)X(2) rhombs, and (CuX)(2)(Pip)(2) or (CuX)(4)(Pip)(4), which are simple rhomboid dimers and cubane tetramers. A combination of spectroscopic studies and DFT calculations was used to investigate the luminescence of the products. The results suggest that the relatively high energy emission seen in dimers is due to cluster-centred (XMLT/metal-centred) excitations for the aliphatic amines and MLCT (d →π*) for aromatic amines, and low energy emission seen in the tetramers is the result of cluster-centred transitions. The (CuI)(2)(Pip) complexes act as sensor materials, undergoing irreversible reaction with aliphatic and aromatic amines (Nu) in the vapour state, irreversibly producing cubanes (CuI)(4)Nu(4), with corresponding production of long wavelength emission.     

Piperazinium Chlorocuprates(I)

Abstract  The formation from aqueous solution of networks containing piperazinium hydrochlorides with copper(I) chloride is described. Four new X-ray crystal structures are reported: (H₂Pip)[Cu₂Cl₄] (two isomeric phases: 1A and 1B), (H₂MePip)[Cu₃Cl₅] (2), and (H₂Me₂Pip)[Cu₄Cl₆] (3) (Pip = piperazine, MePip = N-methylpiperazine, Me₂Pip = N,N′-dimethylpiperazine. In 1A (P-1, a = 6.3141(2), b = 6.8248(2), c = 6.9067(2), α = 90.707(2), β = 110.748(2), γ = 110.799(2), V = 256.918(13), Z = 2) corner-sharing Cu₂Cl₂ rhomboid dimers form infinite chains running parallel to the a-axis. In 1B (Pbcn, a = 9.9442(6), b = 8.0622(5), c = 13.1301(7), V = 1052.67(11), Z = 8) the Cu₂Cl₂ dimers are linked by μ-Cl into Cu₆Cl₈ rings which form hexagonally tiled sheets running parallel to the a,b-plane. In 2 (P-1, a = 8.0815(7), b = 9.6584(9), c = 9.7900(8), α = 70.231(4), β = 77.180(4), γ = 70.587(4), V = 673.05(10), Z = 2) alternating Cu₃Cl₃ and Cu₄Cl₄ rings are fused to form ribbons that run parallel to the a-axis. Copper-copper interactions are present. In 3 (C2/c, a = 17.4026(6), b = 10.5295(4), c = 11.7501(8), β = 131.5490(10), V = 1611.35(14), Z = 8) relatively long Cu···Cl interactions connect Cu₄Cl₆ “adamantane” units into chains running parallel to the c-axis. In all cases the piperazinium ions are independent from the chlorocuprate structures, but they do show N–H···Cl interactions. Index Abstract  The synthesis and network structures of four piperazinium hydrochlorides with copper(I) chloride are presented.