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

The use of the [Fe-III(AA)(CN)(4)](-) complex anion as metalloligand towards the preformed [Cu-II(valpn)Ln(III)](3+) or [Ni-II(valpn)Ln(III)](3+) heterometallic complex cations (AA=2,2'-bipyridine (bipy) and 1,10-phenathroline (phen); H(2)valpn=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(mu-NC)(2)Fe-III(phen)(CN)(2) {(mu-NC)Fe-III(phen)(CN)(3)}]NO3 center dot 7H(2)O}(n) (Ln=Gd (1), Tb (2), and Dy (3)) and the trinuclear complex [CuII(valpn)LaIII(OH2)(3)(O2NO)(mu-NC)FeIII(phen)(CN)(3)]center dot NO3 center dot H2O center dot CH3CN (4) were obtained with the [Cu-II(valpn)Ln(III)](3+) assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[NiII(valpn)LnIII(ONO2)(2)(H2O)(mu-NC)(3)Fe-III(bipy)(CN)]center dot 2H(2)O(2)CH(3)CN}(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, [Cu-II(valpn)LaIII(OH2)(3)(O2NO)(mu-NC)Fe-III(phen)(CN)3]+, nitrate counterions, and non-coordinate water and acetonitrile molecules. The heteroleptic {FeIII(bipy)(CN)4} moiety in 57 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[BOND]LnIII (13) and N-iII[BOND]Ln(III) (57) units, as well as through the single cyanide bridge between the FeIII and either NiII (57) or Cu-II (4) account for the overall ferromagnetic behavior observed in 17. 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 (to) and energy barrier (Ea) through the Arrhenius equation being 2.0x10(-1)2 s and 29.1 cm(-1), respectively. In the case of 7, the ferromagnetic interactions through the double phenoxo (NiIIDyIII) and single cyanide ((FeNiII)-Ni-III) pathways are masked by the depopulation of the Stark levels of the Dy-III ion, this feature most likely accounting for the continuous decrease of MT upon cooling observed for this last compound.