Redox-Active Porous Coordination Polymers Prepared by Trinuclear Heterometallic Pivalate Linking with the Redox-Active Nickel(II) Complex: Synthesis, Structure, Magnetic and Redox Properties, and Electrocatalytic Activity in Organic Compound Dehalogenation in Heterogeneous Medium

Linking of the trinuclear
pivalate fragment Fe2CoO­(Piv)6 by the redox-active
bridge Ni­(L)2 (compound 1; LH is Schiff base
from hydrazide of 4-pyridinecarboxylic acid and 2-pyridinecarbaldehyde,
Piv– = pivalate) led to formation of a new porous
coordination polymer (PCP) {Fe2CoO­(Piv)6}­{Ni­(L)2}1.5 (2). X-ray structures of 1 and 2 were determined. A crystal lattice of
compound 2 is built from stacked 2D layers; the Ni­(L)2 units can be considered as bridges, which bind two Fe2CoO­(Piv)6 units. In desolvated form, 2 possesses a porous crystal lattice (SBET = 50 m2 g–1, VDR = 0.017 cm3 g–1 estimated from
N2 sorption at 78 K). At 298 K, 2 absorbed
a significant quantity of methanol (up to 0.3 cm3 g–1) and chloroform. Temperature dependence of molar
magnetic susceptibility of 2 could be fitted as superposition
of χMT of Fe2CoO­(Piv)6 and Ni­(L)2 units, possible interactions between
them were taken into account using molecular field model. In turn,
magnetic properties of the Fe2CoO­(Piv)6 unit
were fitted using two models, one of which directly took into account
a spin–orbit coupling of CoII, and in the second
model the spin–orbit coupling of CoII was approximated
as zero-field splitting. Electrochemical and electrocatalytic properties
of 2 were studied by cyclic voltammetry in suspension
and compared with electrochemical and electrocatalytic properties
of a soluble analogue 1. A catalytic effect was determined
by analysis of the catalytic current dependency on concentrations
of the substrate. Compound 1 possessed electrocatalytic
activity in organic halide dehalogenation, and such activity was preserved
for the Ni­(L)2 units, incorporated into the framework of 2. In addition, a new property occurred in the case of 2: the catalytic activity of PCP depended on its sorption
capacity with respect to the substrate. In contrast to homogeneous
catalysts, usage of solid PCPs may allow selectivity due to porous
structure and simplify separation of product.