Synthesis, Crystal Structure, and Magnetic Properties of an Alkoxo−Hydroxo-Bridged Octanuclear Copper(II) Complex Showing Chemically Significant Hydrogen-Bonding Interactions Involving a Metallamacrocyclic Core

A novel 16-member metallamacrocyclic octanuclear copper(II) complex of formulation [Cu8L4(OH)4] (1) has been
prepared from a reaction of [Cu2L(O2CMe)] and NaOH in methanol, where L is a pentadentate trianionic Schiff
base ligand N,N‘-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine). The complex has been characterized by analytical,
structural, and spectral methods. It crystallizes in the monoclinic space group C2/c with the following unit cell
dimensions:  a = 30.365(3) Å; b = 14.320(2) Å; c = 19.019(2) Å; β = 125.33(2)°; V = 6746.7(13) Å3; Z = 4.
A total of 4589 unique data with I > 2σ(I) were used to refine the structure to R1(Fo) = 0.0525 and wR2 = 0.1156.
The structure consists of four binuclear {Cu2L}+ units linked covalently by four hydroxide ligands to form an
octanuclear core which is stabilized by strong hydrogen-bonding interactions involving the hydroxide ligands. Each
binuclear unit has a pentadentate ligand L showing N2O3 coordination with an endogenous alkoxide bridging atom.
The magnetic susceptibility data of 1, obtained in the temperature range 14−306 K, show the presence of
antiferromagnetic exchange interactions between adjacent spin-1/2 Cu(II) ions. The μeff values are 1.54 and 0.26
μB (per copper) at 295 and 15 K, respectively. The magnetic data have been theoretically fitted using a Heisenberg
spin-1/2 Hamiltonian with nearest-neighbor antiferromagnetic interactions. The spin coupling in the metallamacrocyclic
ring has been modeled using four different coupling constants (J) on the basis of the structural parameters of the
octanuclear core. The coupling constants obtained are J1 = −318.8, J2 = −293.3, J3 = −111.6, and J4 = −63.8
cm-1. The theoretical modeling of the susceptibility data gives a higher magnitude of the antiferromagnetic interaction
within the binuclear {Cu2L}+ unit compared to those involving adjacent dimeric units.