Organic heterobimetallic complexes of the alkaline earth metals (Ae = Ca, Sr, Ba) with tetrahedral metallate anions of three-valent metals (M = B, Al, Ga, and V)

Abstract

Heterobimetallic compounds with complex cations of the very electropositive alkaline earth metals (Ae) and organic tetrahedral anions of trivalent elements (M) form solvent-separated ions. Depending on the metals, they can be prepared by addition of carbanions or amides to MR₃, via reduction of VMes₄ with the alkaline earth metals and by transmetallation of VMes₃. For comparison reasons selected alkali metal derivatives are also included in this study. Average structural parameters of the boranates [Ca(thf)₆][BPh₄]₂ (1) and [CaI(thf)₅][BPh₄] (2), the alanates [Li(thf)₂(tmeda)][AlPh₃(tmp)] (3), [(thf)₂K(N-carbazolyl)₂AlMes₂] (4), and [Sr(thf)₇][AlPh₄]₂ (5), of the gallate [Ca(dme)₄][GaEt₃(N-carbazolyl)]₂ (6), and of the vanadates [Li(thf)₄][VMes₄] (7), [CaI(thf)₅][VMes₄] (8), [Ca(thf)₆][VMes₄]₂ (9), and [Sr(thf)₆][VMes₄]₂ (10), are discussed. All these complexes contain complex cations of the type [(L)_nM]⁺, and tetrahedral anions of the type [ER₄]⁻. Only 4 crystallizes as a contact ion pair because the soft K⁺ cation shows no preference for hard bases such as ethers or for soft arene π-systems.