Synthesis and antimicrobial activities of copper(II) complexes of N(4),N(11)-dimethyl (LBZ & LCZ) and N(4)-monomethyl (LCZ1)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane. Crystal and molecular structure of [CuLCZ1](ClO4)2

•A novel biologically relevant N-pendent cyclic tetraaza ligand was prepared.•Cu(II) complexes of cyclic tetraaza ligands were synthesized and characterized.•X-ray analysis revealed square planar coordination geometry for [CuL](ClO4)2.•Some of the complexes adapt varying geometry in different solvents.•Some of the complexes exhibit antifungal and antibacterial activity.

Naturally occurring azamacrocyclic metal complexes such as haems, chlorophyll, vitamin B12, and the factor F430 carry pendent ring substituemts and axial co-ligands that act as functional components in these important biological systems. Design of related systems with structural features related to their natural counterparts is thus a multifarious challenge. With this in mind, we have recently reported on the characterization and antimicrobial activities of tetraazacyclotetradecanes and their Ni2+ complexes. Here, we present results on modified N-pendent ligands and their Cu2+ complexes: The interaction of two isomers of 3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane, LB and LC (differing in the orientation of the CH3 groups on the chiral C atoms), with CH3I resulted in the substitution of the N(4) and N(11) protons by CH3, forming the dimethyl derivatives LBZ and LCZ, when reacted with CH3I in the ratio 1:2, yielded the N(4) monomethyl derivative LCZ1. On reaction with Cu(ClO4)2·6H2O, the square-planar complexes [CuL](ClO4)2 (L = LBZ, LCZ, or LCZ1).) were obtained. The complex cations [CuLBZ]+ and [CuLCZ]+ undergo axial ligand addition with the anions X = NCS−, NO2−, NO3− Cl−, Br− and I− to form six-coordinate trans-[CuL′X2] (L′ = LBZ or LCZ). The compounds have been characterized on the basis of analytical, spectroscopic, conductometric and magnetochemical data. The structure of [CuLCZ1](ClO4)2 {space group Pn, No. 2, a = 10.3581(12), b = 8.8335(10), c = 14.2584(16) Å; β = 99.917(3) (2)°} has been determined by X-ray crystallography. The copper centre is coordinated to an N4 donor set of LCZ1 in a square planar geometry. The antifungal and antibacterial activities of the compounds have been studied against some phyto-pathogenic fungi and bacteria. Generally, the complexes exhibit a more pronounced antimicrobial activity than the parent ligands.

Graphical abstractCu(ClO4)2 and N-mono/dimethylated tetraazacyclotetradecanes L/L′ react to form the square-planar complexes [CuL/L′](ClO4)2. [CuL](ClO4)2 has been characterized by XDS. With the dimethylated ligands, the complexes undergo axial addition reactions with a variety of mono-anions to form six-coordinate complexes [CuL′X2]. Several of the complexes exhibit pronounced antifungal and antibacterial activity.Figure optionsDownload full-size imageDownload as PowerPoint slide