ic6b01199_si_003.cif (598.56 kB)
Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway
dataset
posted on 2016-11-02, 12:23 authored by Roberto Fernández
de Luis, Edurne S. Larrea, Joseba Orive, Luis Lezama, María I. ArriortuaThe
average and commensurate superstructures of the one-dimensional coordination
polymer {Cu(NO3)(H2O)}(HTae)(Bpy)
(H2Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4′-bipyridine)
were determined by single-crystal X-ray diffraction, and the possible
symmetry relations between the space group of the average structure
and the superstructure were checked. The crystal structure consists
in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal–organic
chains stacked along the [100] crystallographic direction. The origin
of the fivefold c axis in the commensurate superstructure
is ascribed to a commensurate modulation of the coordination environment
of the copper atoms. The commensurately ordered nitrate groups and
coordinated water molecules establish a two-dimensional hydrogen-bonding
network. Moreover, the crystal structure shows a commensurate to incommensurate
transition at room temperature. The release of the coordination water
molecules destabilizes the crystal framework, and the compound shows
an irreversible structure transformation above 100 °C. Despite
the loss of crystallinity, the spectroscopic studies indicate that
the main building blocks of the crystal framework are retained after
the transformation. The hydrogen-bonding network not only plays a
crucial role stabilizing the crystal structure but also is an important
pathway for magnetic exchange transmission. In fact, the magnetic
susceptibility curves indicate that after the loss of coordinated
water molecules, and hence the collapse of the hydrogen-bonding network,
the weak anti-ferromagnetic coupling observed in the initial compound
is broken. The electron paramagnetic resonance spectra are the consequence
of the average signals from Cu(II) with different orientations, indicating
that the magnetic coupling is effective between them. In fact, X-
and Q-band data are reflecting different situations; the X-band spectra
show the characteristics of an exchange g-tensor,
while the Q-band signals are coming from both the exchange and the
molecular g-tensors.