New Tetracopper(II) Cubane Cores Driven by a Diamino Alcohol: Self-assembly Synthesis, Structural and Topological Features, and Magnetic and Catalytic Oxidation Properties

Two
new coordination compounds with tetracopper­(II) cores, namely,
a 1D coordination polymer, [Cu4(μ4-H2edte)­(μ5-H2edte)­(sal)2]n·10nH2O (1), and a discrete 0D tetramer, [Cu4(μ4-Hedte)2(Hpmal)2(H2O)]·7.5H2O (2), were easily self-assembled from aqueous
solutions of copper­(II) nitrate, N,N,N′,N′-tetrakis­(2-hydroxyethyl)­ethylenediamine
(H4edte), salicylic acid (H2sal), or phenylmalonic
acid (H2pma). The obtained compounds were characterized
by IR and electron paramagnetic resonance spectroscopy, thermogravimetric
and elemental analysis, and single-crystal X-ray diffraction. In addition
to different dimensionalities, their structures reveal distinct single-open
[Cu4(μ2-O)­(μ3-O)3] (in 1) or double-open [Cu4(μ2-O)2(μ3-O)2] (in 2) cubane cores with 3M4-1 topology. In crystal structures,
numerous crystallization water molecules are arranged into the intricate
infinite 1D {(H2O)18}n water tapes (in 1) or discrete (H2O)9 clusters (in 2) that participate in multiple
hydrogen-bonding interactions with the metal–organic hosts,
thus extending the overall structures into very complex 3D supramolecular
networks. After simplification, their topological analysis revealed
the binodal 6,10- or 6,8-connected underlying 3D nets with unique
or rare 6,8T2 topology in 1 and 2, respectively.
The magnetic properties of 1 and 2 were
investigated in the 1.8–300 K temperature range, indicating
overall antiferromagnetic interactions between the adjacent CuII ions within the [Cu4O4] cores. The
obtained compounds also act as bioinspired precatalysts for mild homogeneous
oxidation, by aqueous hydrogen peroxide at 50 °C in an acidic
MeCN/H2O medium, of various cyclic and linear C5–C8 alkanes to the corresponding alcohols and ketones.
Overall product yields of up to 21% (based on alkane) were achieved,
and the effects of various reaction parameters were studied.