Magneto-structural variety of new 3d–4f–4(5)d heterotrimetallic complexes

Abstract

Three families of heterotrimetallic chains (type 1–type 3), with different topologies, have been obtained by reacting the 3d–4f complexes, [{Cu(L¹)}_xLn(NO₃)₃] with x = 1 or 2, formed in situ by the reaction of Schiff-base bi-compartmental [Cu^II(L¹)] complexes and lanthanide(III) salts, with (NHBu₃)₃[M(CN)₈] (M = Mo^V, W^V). For type 1 series of compounds, 1-D coordination polymers, with the general formula [{Cu₂(valpn)₂Ln}{M(CN)₈}]·nH₂O·mCH₃CN (where H₂valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol), result from the association of trinuclear {Cu^II₂Ln^III} moieties and [M^V(CN)₈]³⁻ anions acting as tri-connecting spacers [Ln = La (1), Ce (2), Eu (3), Tb (4), Ho (5), M = Mo; Ln = Tb (6), Ho (7), M = W; m = 0, n = 1.5 (7) and 2 (1–4, 6); n = 1, m = 1 (5)]. The type 2 family has the general formula [{Cu(valdp)Ln(H₂O)₄}{M(CN)₈}]·2H₂O·CH₃CN (where H₂valdp = 1,2-propanediylbis(2-iminomethylene-6-methoxy-phenol)) and also consists of heterotrimetallic chains involving binuclear {Cu^IILn^III} units linked to [M(CN)₈]³⁻ anions coordinating through two cyano groups [Ln = Gd (8), Tb (9), Dy (10); M = Mo; Ln = La (11), Gd (12), Tb (13), Dy (14); M = W]. With large Ln^III ions (La^III and Pr^III), the type 3 family of heterotrimetallic compounds are assembled: [{Cu₂(valdp)₂Ln(H₂O)₄}{Mo(CN)₈}]·nCH₃OH·mCH₃CN, n, m = 0, Ln = La (15); n = m = 1, Pr (16), in which the trinuclear {Cu^II₂Ln^III} nodes are connected to [Mo^V(CN)₈]³⁻ anions that act as tetra-connecting spacers. For Tb^III derivatives of the type 1 (compounds 4 and 6), the DC magnetic properties indicate a predominant ferromagnetic Cu^II–Tb^III interaction, while the AC magnetic susceptibility (in the presence of a static magnetic field, H_DC = 3000 Oe) emphasize the slow relaxation of the magnetization (U_eff/k_B = 20.55 K and τ₀ = 5.5 × 10⁻⁷ s for compound 4, U_eff/k_BT = 15.1 K and τ₀ = 1.5 × 10⁻⁷ s for compound 6). A predominant ferromagnetic Cu^II–Ln^III interaction was also observed in the type 2 series (compounds 8–10 and 12–14) as a result of the magnetic coupling between copper(II) and lanthanide(III) ions via the phenoxo-bridge. The magnetic behavior for the La^III derivatives reveals that weak ferromagnetic interactions are also operative between the Cu^II and the 4d/5d centers.