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Two distinct tetranuclear motifs, rectangular vs. extended, are observed for complexes of a bis-tetradentate pyrimidine-based ligand

Gobeze, Worku A., Brooker, Sally
RSC advances 2013 v.3 no.46 pp. 24307-24312
anions, chlorides, crystal structure, encapsulation, ligands, methanol, moieties, nitrogen
The 1 : 2 reactions of 4,6-bis[N,N-bis(2′-pyridylmethyl)aminomethyl]-2-phenylpyrimidine (Lᴹᵉ) and Mnᴵᴵ, Coᴵᴵ, Niᴵᴵ and Cuᴵᴵ chloride salts in MeOH gave the tetranuclear complexes [Mnᴵᴵ₄(Lᴹᵉ)₂Cl₈]·2H₂O (1), Coᴵᴵ₄(Lᴹᵉ)₂Cl₈·10H₂O (2), [Ni₄ᴵᴵ(Lᴹᵉ)₂Cl₄]Cl₄·8H₂O (3) and [Cuᴵᴵ₄(Lᴹᵉ)₂Cl₆]Cl₂·8H₂O (4), respectively. X-ray crystal structure determinations carried out on three of the complexes revealed that in the case of Niᴵᴵ (3′) the Lᴹᵉ ligand is bound in the expected bis-tetradentate fashion, bridging the encapsulated pair of Niᴵᴵ centers via the pyrimidine ring, and that two pairs of chloride anions bridge a pair of such dimetallic units, affording a closed rectangular tetranuclear core overall. In contrast, in the case of Mnᴵᴵ (1′) and Cuᴵᴵ (4′) only one binding pocket of the Lᴹᵉ ligand strand binds in the expected tetradentate manner, whilst the other binds in a terdentate manner as one pyrimidine nitrogen atom does not bind, so in these cases the pyrimidine moiety does not bridge the metal centres, resulting instead in ‘extended’, linear tetranuclear assemblies.