Coordination chemistry of cis,trans-1,3,5-Triaminocyclohexane : from mononuclear complexes to supramolecular architectures

Abstract

The coordination chemistry of the rigid, aliphatic triamino ligand \(cis,trans\)-1,3,5-triaminocyclohexane (\(trans\)-tach) is investigated. With closed shell transition metals, \(trans\)-tach forms 1-D {Ag(OTf), ZnCl\(_2\)} networks and a 3-D {AgNO\(_3\)} coordination polymer with unprecedented topology. Coordination to the open shell transition metals {NiCl\(_2\), Ni(NO\(_3\))\(_2\), Cu(NO\(_3\))\(_2\), CuBr\(_2\), CuCl\(_2\), CuF\(_2\), CuSO\(_4\)} leads to discrete diligand complexes. Protonation of the copper(II) complexes predominantly forms monoligand species, which can aggregate into higher nuclearity clusters. Protonated Cu(NO\(_3\))\(_2\) and CuBr\(_2\) complexes (HNO\(_3\) and HBr, respectively) remain mononuclear. CuCl\(_2\) and CuBr\(_2\) complexes protonated with HCl, however, form trinuclear species comprising trigonal planar \(\mu_3\)-chloro ligands that aggregate into 1-D trinuclear copper(II) chains via hydrogen-bonded interactions. Protonated CuF\(_2\) forms a tetranuclear cubane type structure that aggregates into a 3-D nanoporous network via hydrogen-bonded interactions. Protonation of the CuSO\(_4\) diligand complex maintains the diligand coordination, forming a 1-D nanoporous network through hydrogen-bonded interactions. Coordination to square planar palladium(II) ions forms all possible coordination motifs (‘Tail’ = monodentate, ‘Head’ = bidentate coordination). ‘Head-to-Head’ coordination results in diligand complexes, ‘Head-to-Tail’ coordination forms cyclic hexanuclear structures and ‘Tail-to-Tail’ coordination leads to a trinuclear species. Extension of \(trans\)-tach via Schiff base formation with pyridine-2-carboxaldehyde results in a hexadonor ligand suitable for metal coordination. Depending on the stoichiometry of the metal, mono- or polynuclear complexes are formed.