Solvent-induced structural transformation from heptanuclear to decanuclear [Co–Ln] coordination clusters: trapping of unique counteranion and understanding of aggregation pathways

Abstract

Five new cobalt(II/III)–lanthanide(III)-based coordination aggregates, [Ln^III₃Co^II₂Co^III₂(L1)₂(O₂CCMe₃)₈(OH)₄(OMe)₂(H₂O)₄]·Ln(η¹-O₂CCMe₃)₂(η²-O₂CCMe₃)₂(MeOH)₂·2MeOH·2H₂O (where Ln = Tb (1), Ho (3), and H₂L1 = N-(2-hydroxyethyl)-salicylaldimine), Tb^III₃Co^II₃Co^III₄(L1)₄(O₂CCMe₃)₉(OH)₁₀(H₂O) (4) and Ln^III₃Co^II₂Co^III₅(L1)₄(O₂CCMe₃)₁₀(OH)₁₀ (Ln = Dy (5), Ho (6)) have been synthesized and characterized, including structural analysis via single-crystal X-ray diffraction. The dysprosium analogue (2) of 1 and 3 was previously reported by us. The heptanuclear monocationic clusters in 1 and 3 were formed by placement of seven metal ions (4 Co and 3 Ln) in a vertex shared dicubane structure from the control of two Schiff base anions and crystallized in the presence of in situ generated and literature unknown counter anions Tb(η¹-O₂CCMe₃)₂(η²-O₂CCMe₃)₂(MeOH)₂⁻ and Ho(η¹-O₂CCMe₃)₂(η²-O₂CCMe₃)₂(MeOH)₂⁻. Interesting solvent-induced cluster structure transformation was observed on dissolving the heptanuclear aggregates in MeCN for the formation of decanuclear clusters 4–6. These high nuclearity clusters consist of a vertex shared heptanuclear dicubane part and a curved trinuclear chain linking the two cubic halves. The dicubane unit differs from that of the heptanuclear precursors in the presence of Co^II/III at the shared vertex as opposed to Ln^III and the absence of OMe⁻ bridges. HRMS (+ve) analysis shed light on the pathway of formation of these heptanuclear molecules, while at the same time revealing a different aggregation process for the decanuclear clusters.