Magnetism in Heterobimetallic and Heterotrimetallic Chains Based on the Use of [WV(bipy)(CN)6]- as a Metalloligand

Two new heterobi- and trimetallic chains of formula (infinity)(1)[{Mn-II(pyim)(2)}{(mu-NC)(2)W-V(bipy)(CN)(4)}][W-V(bipy)(CN)(6)] (1) and (infinity)(1)[{(CuMnL)-Mn-II-L-II}{(mu-NC)(3)W-V(bipy)(CN)(3)}][W-V(bipy)(CN)(6)]center dot 0.75H(2)O center dot 2MeCN (2) were obtained by reacting the cyanido-based AsPh4[W(bipy)(CN)(6)] heteroleptic complex with the pre-formed [Mn-II(pyim)(2)](2+) (1) and [(CuMnL)-Mn-II-L-II](2+) (2) complexes [bipy = 2,2'-bipyridine, pyim = 2-(1H-imidazol-2-yl)pyridine and H2L = macro-cyclic Schiff-base resulting from the stepwise condensation of 2,6-diformyl-p-cresol with ethylenediamine and diethylenetriamine]. The structure of 1 consists of cationic cyanido-bridged {(MnWV)-W-II} chains, assembled from [W-V(bipy)(CN)(6)](-) spacers, each one coordinating in a bis-monodentate fashion, two [Mn-II(pyim)(2)](2+) nodes, and [W-V(bipy)(CN)(6)](-) counteranions. Compound 2 comprises a positively charged 1D coordination polymer, built from [W-V(bipy)(CN)(6)](-) cyanido metalloligands that act as tris-monodentate spacers towards [(CuMnL)-Mn-II-L-II](2+) complexes, the entire assembly being neutralized by [W-V(bipy)(CN)(6)](-) anions. Each manganese(II) ion in 1 is six-coordinate in a somewhat distorted octahedral surrounding. Five-coordinate copper(II) and seven-coordinate manganese(II) ions exhibiting distorted square pyramidal and monocapped trigonal prism environments respectively, occur in each {(CuMnII)-Mn-II} node of 2. The magnetic susceptibility of 1 and 2 investigated down to 1.9 K is characteristic of 1D ferrimagnetic behavior with minima in the chi T-M vs. T plots at 35 (1) and 20 K (2) (chi(M) is the magnetic susceptibility per one Mn-II plus two W-V ions). The magnetic data of 1 in the whole temperature range were analyzed through a model considering S-Mn = 5/2 as a classical spin and S-W = 1/2 as a quantum spin, with two interaction parameters J(1) = J(1 - alpha) and J(2) = J(1 + alpha) {the spin Hamiltonian being defined as H = -J Sigma S-i(W,i)[(1 + alpha)S-Mn,S-j + (1 - alpha)S-Mn,S-j+1] + Sigma(i)(g(W)S(W,i) + g(Mn)S(Mn),(i))beta H}. The values of the intrachain antiferromagnetic interactions for 1 through this model were -3.0(1) (J(1)) and -32.0(1) cm(-1) (J(2)). The complexity of the spin topology in 2, a branched chain with four different intrachain antiferromagnetic interactions (double phenoxido bridge between Mn-II and Cu-II, two single cyanido bridges between Mn-II and Cu-II, and one single cyanido bridge between Cu-II and W-V) precluded any simulation of its magnetic data.