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

Abstract

The 1 : 2 reactions of 4,6-bis[N,N-bis(2′-pyridylmethyl)aminomethyl]-2-phenylpyrimidine (L^Me) and Mn^II, Co^II, Ni^II and Cu^II chloride salts in MeOH gave the tetranuclear complexes [Mn^II₄(L^Me)₂Cl₈]·2H₂O (1), Co^II₄(L^Me)₂Cl₈·10H₂O (2), [Ni₄^II(L^Me)₂Cl₄]Cl₄·8H₂O (3) and [Cu^II₄(L^Me)₂Cl₆]Cl₂·8H₂O (4), respectively. X-ray crystal structure determinations carried out on three of the complexes revealed that in the case of Ni^II (3′) the L^Me ligand is bound in the expected bis-tetradentate fashion, bridging the encapsulated pair of Ni^II 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 Mn^II (1′) and Cu^II (4′) only one binding pocket of the L^Me 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.