Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis, Crystal Structures, and Magnetic Properties

The use of the [FeIII(AA)(CN)4]− complex anion as metalloligand towards the preformed [CuII(valpn)LnIII]3+ or [NiII(valpn)LnIII]3+ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H2valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[CuII(valpn)LnIII(H2O)3(μ‐NC)2FeIII(phen)(CN)2 {(μ‐NC)FeIII(phen)(CN)3}]NO3⋅7 H2O}n (Ln=Gd (1), Tb (2), and Dy (3)) and the trinuclear complex [CuII(valpn)LaIII(OH2)3(O2NO)(μ‐NC)FeIII(phen)(CN)3]⋅NO3⋅H2O⋅CH3CN (4) were obtained with the [CuII(valpn)LnIII]3+ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[NiII(valpn)LnIII(ONO2)2(H2O)(μ‐NC)3FeIII(bipy)(CN)]⋅2 H2O⋅2 CH3CN}n (Ln=Gd (5), Tb (6), and Dy (7)) resulted with the related [NiII(valpn)LnIII]3+ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [CuII(valpn)LaIII(OH2)3(O2NO)(μ‐NC)FeIII(phen)(CN)3]+, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {FeIII(bipy)(CN)4} moiety in 5–7 acts as a tris‐monodentate ligand towards three {NiII(valpn)LnIII} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the CuIILnIII (1–3) and NiIILnIII (5–7) units, as well as through the single cyanide bridge between the FeIII and either NiII (5–7) or CuII (4) account for the overall ferromagnetic behavior observed in 1–7. DFT‐type calculations were performed to substantiate the magnetic interactions in 1, 4, and 5. Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τo) and energy barrier (Ea) through the Arrhenius equation being 2.0×10−12 s and 29.1 cm−1, respectively. In the case of 7, the ferromagnetic interactions through the double phenoxo (NiII–DyIII) and single cyanide (FeIII–NiII) pathways are masked by the depopulation of the Stark levels of the DyIII ion, this feature most likely accounting for the continuous decrease of χMT upon cooling observed for this last compound. Heterotrimetallic complexes of various dimensionality and topology were synthesized from {Fe(AA)(CN)4} metalloligands and 3d–4f heterobimetallic building blocks, with Schiff base compartmental ligands: {Cu