Novel Diazamesocyclic Ligands Functionalized with Pyridyl Donor Group(s) − Synthesis, Crystal Structures, and Properties of Their Copper(II) Complexes

Abstract

Two novel diazamesocyclic ligands based on l,5-diazacyclooctane (DACO) and functionalized with additional pyridyl donor groups, namely 1,5-bis(2-pyridylmethyl)-1,5-diazacyclooctane (L1) and 1-(2-pyridylmethyl)-1,5-diazacyclooctane (L2), have been synthesized and characterized, as have their CuII complexes. Crystal structure analyses revealed that with Cu(ClO4)2 L1 forms a five-coordinate mononuclear complex [CuIIL1Cl]ClO4 (1), whereas L2 forms a µ-Cl−-bridged dinuclear complex [CuII(L2)Cl]2(ClO4)2 (2). Furthermore, it has been found that the apical chloride anion of 1 may be easily exchanged by azide anion, forming the mononuclear complex [CuIIL1(N3)]ClO4 (3). There is a notable difference between 3 and 1 in that 3 forms a quasi-two-dimensional network through intermolecular C−H···O hydrogen bonds and π−π stacking interactions. Each CuII center in the three complexes is pentacoordinated in a distorted square-pyramidal environment and the DACO ring of each ligand adopts a boat-chair configuration in all the complexes. In the mononuclear complexes 1 and 3, the Cl− or N3− anions occupy the apical sites, whereas in the dinuclear complex 2 the two bridging Cl− anions occupy both axial positions as well as one equatorial position, leading to an intramolecular Cu···Cu separation of 3.396 Å. Variable-temperature magnetic susceptibility measurements on 2 in the range 4−300 K indicate a weak intramolecular ferromagnetic coupling between adjacent CuII centers with 2J = 2.28 cm−1; the magneto-structural correlations are discussed in detail. The solution behavior of the complexes has been further studied by UV/vis and ESR techniques.