**1. Introduction**

Herein, we present a structural, magnetic susceptibility and EPR study of two supramolecular assemblies of metallacyclic CuII pyrazolates with Cu3(μ3-OH) cores. The focus of this work is the elucidation of weak intermolecular interactions manifested in the magnetic properties and EPR spectra of the supramolecular assemblies.

Supramolecular interactions, such as H-bonding, dipolar, metallophilic and π–π interactions, are important not only for the structural organization of molecules in 3D, but because they often play a crucial role in determining the physical and spectroscopic properties of the assemblies. A corollary of the latter statement is that, in the absence of structural data, the detection of such spectroscopic "signatures" reveals the presence of supramolecular interactions—e.g., in biological systems. Magnetic exchange is among the properties that can be modulated by supramolecular interactions, thereby introducing new functionality into a system [1]. For instance, in the layered Ni(H2O)2[Ni(CN)4]·xH2O solid, H-bonding in the interlayer regions is shown to mediate weak ferromagnetic interactions, but when the coordinated water molecules were replaced by 3-halopyridine ligands, removing H-bonding, anti-ferromagnetic interactions through π-clouds became dominant [2]. Weak intramolecular antiferromagnetic exchange is active within a molecule containing two isolated CuII centers separated by a K<sup>+</sup> ion, whereas relatively strong ferromagnetic interactions were found between adjacent units, along a supramolecular pathway [3]. In ye<sup>t</sup> another dinuclear CuII complex

with chelating 2-hydroxy-1,10-phenanthroline and bridging thiocyanate ligands, it was shown that an intermolecular ferromagnetic exchange was facilitated by π–π interactions between phenanthroline ligands [4–6].

The antiferromagnetic exchange among the CuII centers of the triangular Cu3(μ3-O/OH) units has been studied extensively by us and others [7–12]. We have recently turned our attention to interactions between weakly-coupled Cu3(μ3-O/OH) species and shown that the presence of weak dipolar interactions str evident in the magnetic susceptibility and EPR spectra of H-bonded Cu3(μ3-OH) units [13]. Continuing along the same lines, we report here the structure and magnetochemical studies of a heptanuclear CuII assembly employing 4-phenyl-pyrazole ligands and of a polymeric structure containing Cu3N6 metallacycles with terminal and bridging azido ligands.
