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Three Cu(ii)/Fe(ii)-bpy-[Fe(ox)3]3− complexes related by structural conversion were studied by XAS, magnetic methods and theoretical calculations.

In this paper, three new heterometallic compounds were described and compared with the molecular formula [Cu(pn)2Zn(NCS)4] (1), [Cu(N,N-Me2-en)2Zn(NCS)4] (2), [Cu(N-Me-en)2Zn(NCS)4]∙½H2O (3) where pn = 1,2−diaminopropane, N,N-Me2-en = N,N‒dimethylethylenediamine and N-Me-en = N-methylethylenediamine, respectively. The compounds mentioned above were characterized by elemental analysis, infrared (IR), electronic, electron paramagnetic resonance (EPR) spectra, and magnetic studies. Crystal structures for 1 and 2 were determined by X-ray analysis. Copper(II) in these complexes adopts 4 + 2 coordination with two elongated (in 2 very long and considered as semi-coordination) Cu-S bonds. The Cu-N and Cu-S bond lengths depend on substituent position affecting steric hindrance and hence a topology of the chain. Both chains form different zigzag patterns characterized by one or two Cu-Zn distance values. Weak magnetic interaction is observed, ferromagnetic in the case of 1 and antiferromagnetic in the case of 2, due to diversity of the above structural features.

We report a new structure of {[Co(bpy)2(ox)][{Cu2(bpy)2(ox)}Fe(ox)3]}n·8.5nH2O NCU-1 presenting a rare ladder topology among oxalate-based coordination polymers with anionic chains composed of alternately arranged [Cu2(bpy)2(ox)]2+ and [Fe(ox)3]3- moieties. Along the a axis, they are separated by Co(III) units to give porous material with voids of 963.7 Å3 (16.9% of cell volume). The stability of this structure is assured by a network of stacking interactions and charge-assisted C-H…O hydrogen bonds formed between adjacent chains, adjacent cobalt(III) units, and alternately arranged cobalt(III) and chain motifs. The soaking experiment with acetonitrile and bromobenzene showed that water molecules (8.5 water molecules dispersed over 15 positions) are bonded tightly, despite partial occupancy. Water adsorption experiments are described by a D’arcy and Watt model being the sum of Langmuir and Dubinin–Serpinski isotherms. The amount of primary adsorption sites calculated from this model is equal 8.2 mol H2O/mol, being very close to the value obtained from the XRD experiments and indicates that water was adsorbed mainly on the primary sites. The antiferromagnetic properties could be only approximately described with the simple CuII-ox-CuII dimer using H = −J×S1×S2, thus, considering non-trivial topology of the whole Cu-Fe chain, we developed our own general approach, based on the semiclassical model (SC) and molecular field (MF) model, to describe precisely the magnetic superexchange interactions in NCU-1. We established that Cu(II)-Cu(II) coupling dominates over multiple Cu(II)-Fe(III) interactions, with JCuCu = −275(29) and JCuFe = −3.8(1.6) cm−1 and discussed the obtained values against the literature data.

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