Structural characterization of methanol substituted lanthanum halides |
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| Authors: | Timothy J Boyle Leigh Anna M Ottley Todd M Alam Mark A Rodriguez Pin Yang Sarah K Mcintyre |
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| Institution: | 1. Sandia National Laboratories, Advanced Materials Laboratory, 1001 University Boulevard, SE, Albuquerque, NM 87106, USA;2. Sandia National Laboratories, Department of Electronic and Nanostructured Materials, P.O. Box 5800, Mail Stop 0886, Albuquerque NM 87185-0886, USA;3. Sandia National Laboratories, Department of Materials Characterization, P.O. Box 5800 Mail Stop 1411, Albuquerque NM 87185-1411, USA;4. Sandia National Laboratories, Department of Ceramic and Glass, P.O. Box 5800 Mail Stop 0963, Albuquerque NM 87185-0963, USA |
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| Abstract: | The first study into the alcohol solvation of lanthanum halide LaX3] derivatives as a means to lower the processing temperature for the production of the LaBr3 scintillators was undertaken using methanol (MeOH). Initially the de-hydration of {La(μ-Br)(H2O)7](Br)2}2 (1) was investigated through the simple room temperature dissolution of 1 in MeOH. The mixed solvate monomeric La(H2O)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 CaH2, 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 {LaBr2.75·5.25(MeOH)]+0.25 LaBr3.25·4.75(MeOH)]−0.25} (4). The fully substituted species was ultimately isolated through the dissolution of dried LaBr3 in MeOH forming the 8-coordinated LaBr3(MeOH)5] (5) complex. It was determined that the concentration of the crystallization solution directed the structure isolated (4 concentrated; 5 dilute) The other LaX3 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. |
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| Keywords: | Lanthanum Halides Scintillators Methanol Crystal structure |
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