Deacon, Glen B., Forsyth, Craig M., Junk, Peter C., and Urbatsch, Aron (2010) Syntheses at elevated temperature and structures of lanthanoid/alkaline earth heterobimetallic derivatives of 2-methyl-8-hydroxyquinoline. European Journal of Inorganic Chemistry, 2010 (18). pp. 2787-2797.

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Abstract

Rearrangement reactions between Ln(MQ)3 and AE(MQ)2 (MQ = 8-quinaldinolate) at 200–300 °C in a 1,2,4,5-tetramethylbenzene (TMB) flux afforded the homoleptic heterobimetallic complexes [Ln2AE(MQ)8] (Ln = Eu, Gd, Tb, Er with AE = Mg; Ln = La, Eu with AE = Ca) and [Eu3Ba(MQ)11]·2TMB. From an attempt to prepare [La2Mg(MQ)8], [Mg4(MQ)8] was isolated, and it was also obtained with the heterobimetallics from syntheses in which Ln = Eu, Gd, Tb. Surprisingly, [Er3(MQ)7CO3] was isolated from an attempted synthesis of [Er2Ca(MQ)8], and the Eu analogue was prepared from Eu(MQ)3 and CaCO3 in TMB at 210 °C. The [Ln2AE(MQ)8] complexes have a trinuclear structure with a linear or nearly linear Ln–AE–Ln array. Octacoordinate Ln atoms have one terminal chelating (N, O) MQ ligand and three chelating-bridging MQ ligands that link to AE through the phenolic oxygen atoms, leading to hexacoordination of AE. In [Eu3Ba(MQ)11]·2TMB, an Eu atom is positioned above the Ba–Eu vector of a somewhat bent Eu–Ba–Eu unit. All atoms are octacoordinate, and the structure features μ3-η2(N,O):η1(O):η1(O) MQ ligands in addition to terminal chelating and chelating-bridging μ-η2(N,O):η1(O) MQ groups observed in [Ln2AE(MQ)8] complexes. The three modes of ligation are also observed in [Mg4(MQ)8] where Mg is hexacoordinate but with two different arrays. [Ln3(MQ)7CO3] complexes have a perpendicular Ln–Ln–Ln arrangement with two octacoordinate metal atoms flanking a heptacoordinate one. Carbonate binding features the new η1(O)-μ3-η1(O'):η1(O'):η1(O')-η1(O") ligation mode. The carbonate ligand chelates to each of the outer Ln atoms, which are also linked to one chelating and two chelating-bridging MQ ligands. Attached to the central Ln atom is a carbonate oxygen atom, four oxygen atoms from chelating-bridging MQ ligands and a terminal MQ chelate.

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