Structural and Magnetic Characterization of a Tetranuclear Copper(II) Cubane Stabilized by Intramolecular Metal Cation−π Interactions

A novel
tetranuclear copper­(II) complex (1) was synthesized
from the self-assembly of copper­(II) perchlorate and the ligand N-benzyl-1-(2-pyridyl)­methaneimine (L1). Single-crystal
X-ray diffraction studies revealed that complex 1 consists
of a Cu4(OH)4 cubane core, where the four copper­(II)
centers are linked by μ3-hydroxo bridges. Each copper­(II)
ion is in a distorted square-pyramidal geometry. X-ray analysis also
evidenced an unusual metal cation−π interaction between
the copper ions and phenyl substituents of the ligand. Calculations
based on the density functional theory method were used to quantify
the strength of this metal−π interaction, which appears
as an important stabilizing parameter of the cubane core, possibly
acting as a driving parameter in the self-aggregation process. In
contrast, using the ligand N-phenethyl-1-(2-pyridyl)­methaneimine
(L2), which only differs from L1 by one methylene
group, the same synthetic procedure led to a binuclear bis­(μ-hydroxo)­copper­(II)
complex (2) displaying intermolecular π–π
interactions or, by a slight variation of the experimental conditions,
to a mononuclear complex (3). These complexes were studied
by X-ray diffraction techniques. The magnetic properties of complexes 1 and 2 are reported and discussed.