Mixed-Ligand Approach to Changing the Metal Ratio in Bismuth–Transition Metal Heterometallic Precursors

A new series of heteroleptic bismuth–transition metal β-diketonates [BiM­(hfac)3(thd)2] (M = Mn (1), Co (2), and Ni (3); hfac = hexafluoroacetylacetonate, thd = tetramethylheptanedionate) with Bi:M = 1:1 ratio have been synthesized by stoichiometric reactions between homometallic reagents [BiIII(hfac)3] and [MII(thd)2]. On the basis of analysis of the metal–ligand interactions in heterometallic structures, the title compounds were formulated as ion-pair {[BiIII(thd)2]+­[MII(hfac)3]−} complexes. The direct reaction between homometallic reagents proceeds with a full ligand exchange between main group and transition metal centers, yielding dinuclear heterometallic molecules. In heteroleptic molecules 1–3, the Lewis acidic, coordinatively unsaturated BiIII centers are chelated by two bulky, electron-donating thd ligands and maintain bridging interactions with three oxygen atoms of small, electron-withdrawing hfac groups that chelate the neighboring divalent transition metals. Application of the mixed-ligand approach allows one to change the connectivity pattern within the heterometallic assembly and to isolate highly volatile precursors with the proper Bi:M = 1:1 ratio. The mixed-ligand approach employed in this work opens broad opportunities for the synthesis of heterometallic (main group–transition metal) molecular precursors with specific M:M′ ratio in the case when homoleptic counterparts either do not exist or afford products with an incorrect metal:metal ratio for the target materials. Heteroleptic complexes obtained in the course of this study represent prospective single-source precursors for the low-temperature preparation of multiferroic perovskite-type oxides.