Structural characterization of methanol substituted lanthanum halides

Abstract

The first study into the alcohol solvation of lanthanum halide [LaX 3] derivatives as a means to lower the processing temperature for the production of the LaBr 3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {[La(μ-Br)(H 2O) 7](Br) 2} 2 ( 1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric [La(H 2O) 7(MeOH) 2](Br) 3 ( 2) compound was isolated where the La metal center retains its original 9-coordination through the binding of two additional MeOH solvents but necessitates the transfer of the innersphere Br to the outersphere. In an attempt to in situ dry the reaction mixture of 1 in MeOH over CaH 2, crystals of [Ca(MeOH) 6](Br) 2 ( 3) were isolated. Compound 1 dissolved in MeOH at reflux temperatures led to the isolation of an unusual arrangement identified as the salt derivative {[LaBr 2.75·5.25(MeOH)] +0.25 [LaBr 3.25·4.75(MeOH)] −0.25} ( 4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr 3 in MeOH forming the 8-coordinated [LaBr 3(MeOH) 5] ( 5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated ( 4 concentrated; 5 dilute) The other LaX 3 derivatives were isolated as [(MeOH) 4(Cl) 2La(μ-Cl)] 2 ( 6) and [La(MeOH) 9](I) 3·MeOH ( 7). Beryllium Dome XRD analysis indicated that the bulk material for 5 appear to have multiple solvated species, 6 is consistent with the single crystal, and 7 was too broad to elucidate structural aspects. Multinuclear NMR ( 139La) indicated that these compounds do not retain their structure in MeOD. TGA/DTA data revealed that the de-solvation temperatures of the MeOH derivatives 4– 6 were slightly higher in comparison to their hydrated counterparts.