Gas-phase and X-ray studies of branched ligands: Cu(II) coordination polymer formed by Nα,Nε,Nε-tris(cyanoethyl)-l-lysine

A small dendrimeric compound, Nα,Nε,Nε-tris(dicyanoethyl)-l-lysine—C15H23N5O2 (1) was synthesized and used for the construction of Cu(II) complex—[Cu(C15H23N5O2)2(ClO4)2·H2O] (3). In the gas-phase, the dimeric and trimeric clusters of 1, surrounding Na+ core were observed. The aggregates with a complex structure were found for the mixtures of 1 and Cu(ClO4)2 at various ratios in ESI-MS experiments. The X-ray studies showed that a new 1D coordination polymer (3), connected by the Cu…NC coordination with the α-N-cyanoethyl group of ligand is formed in a solid-state. The structure contains penta-coordinated Cu(II) with the Cu–Cu separation 7.820(1)–7.927(1) Å. The Cu(II)-coordinated branched ligands form cavities where three perchlorate anions are encapsulated into the void space by the electrostatic and van der Waals interactions. The remaining three perchlorate anions are hydrogen-bonded to the ε-NH+ groups. Thus, the polymeric structure shows properties postulated for dendrimers, where charged groups can be isolated by the non-polar branches from the outside environment. Both gas-phase and X-ray studies show predominance of the 2:1 aggregation pattern between ligand 1 and Cu2+ atoms.