Heterotrimetallic Coordination Polymers: {Cu II Ln III Fe III } Chains and {Ni II Ln III Fe III } 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 {[Cu II (valpn)Ln III (H 2 O) 3 (μ‐NC) 2 Fe III (phen)(CN) 2 {(μ‐NC)Fe III (phen)(CN) 3 }]NO 3 ⋅ 7 H 2 O} n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu II (valpn)La III (OH 2 ) 3 (O 2 NO)(μ‐NC)Fe III (phen)(CN) 3 ] ⋅ NO 3 ⋅ H 2 O ⋅ CH 3 CN ( 4 ) were obtained with the [Cu II (valpn)Ln III ] 3+ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni II (valpn)Ln III (ONO 2 ) 2 (H 2 O)(μ‐NC) 3 Fe III (bipy)(CN)] ⋅ 2 H 2 O ⋅ 2 CH 3 CN} n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni II (valpn)Ln III ] 3+ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu II (valpn)La III (OH 2 ) 3 (O 2 NO)(μ‐NC)Fe III (phen)(CN) 3 ] + , nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe III (bipy)(CN) 4 } moiety in 5 – 7 acts as a tris ‐monodentate ligand towards three {Ni II (valpn)Ln III } binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu II Ln III ( 1 – 3 ) and Ni II Ln III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe III and either Ni II ( 5 – 7 ) or Cu II ( 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 ( τ o ) and energy barrier ( E a ) 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 (Ni II –Dy III ) and single cyanide (Fe III –Ni II ) 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 χ M T upon cooling observed for this last compound.