Synthesis And Characterization Of Low Coordinate Transition Metal Complexes And Plastic And Lithium Containing Organic Scintillators With Efficient Neutron Gamma Pulse Shape Discrimination

Download or read book Synthesis and Characterization of Low Coordinate Transition Metal Complexes and Plastic and Lithium-containing Organic Scintillators with Efficient Neutron/gamma Pulse Shape Discrimination written by Michelle Faust and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The characterization of the unstable Ni[superscript II] bis(silylamide) Ni{N(SiMe3)2}2, its THF complex Ni{N(SiMe3)2}2(THF), and the quasi-stable bis(pyridine) derivative trans-Ni{N(SiMe3)2}2(py)2, is described. Both Ni{N(SiMe3)2}2 and Ni{N(SiMe3)2}2(THF) decompose at ca. 25 0C to a tetrameric NiI species, [Ni{N(SiMe3)2}]4, also obtainable from LiN(SiMe3)2 and NiCl2(DME). Experimental and computational data indicate that the instability of Ni{N(SiMe3)2}2 is likely due to ease of reduction of Ni[superscript II] to Ni[superscript I] and the stabilization of [Ni{N(SiMe3)2}]4 through dispersion forces. Additionally, the synthesis and characterization of a short series of first row transition metal(II) dithiolates M(SAr[superscript iPr]4)2 (Ar[superscript iPr]4 = C6H3-2,6-(C6H3-2,6-iPr2)2, M = Cr(1), Fe(3), Co(4), and Zn (5)), Cr(SAr[superscript Me]6)2 (2) (Ar[superscript Me]6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) and of the precursor (NaSAr[superscript iPr]4)2 (6) are described. Compounds 1 and 2 were obtained by the reaction of the lithium terphenyl thiolate salts LiSAr[superscript iPr]4 and LiSAr[superscript Me]6 with CrCl2(THF)2 in a 2:1 ratio respectively. Compounds 3 and 4 were obtained by the reaction of one equivalent of the terphenyl thiolate sodium salt dimer (NaSAr[superscript iPr]4)2 (6) with FeCl2 and CoCl2 respectively. Compound 5 was obtained by the reaction of LiSAr[superscript iPr]4 and ZnCl2. The complexes were characterized by electronic spectroscopy, X-ray crystallography, and magnetization measurements via the Evans’ method and SQUID magnetometry. It was expected that the thiolato ligand –SAr[superscript iPr]4 would induce linear or near-linear metal coordination like those of their bulkier counterparts M(SAr[superscript iPr]6)2 (M = Cr, Fe, Co, and Ni). Herein, we report that this is not the case. All except 5 have varying degrees of bent geometry with significant flanking ring interactions. The reasons for these unexpected structural differences between the relatively similar ligand sets have been explored by DFT methods using the Cr(SAr)2 (7, Ar = C6H3-2,6-(C6H5)2) model structure and optimizing the structures both in linear and bent geometries. The calculations show that bending of the metal coordination geometry requires little energy with energetic differences between bent and linear geometries for 1 and 2 being just 10 and 17 kJ mol−1 respectively. Also, the empirical dispersion corrections had only a minor effect that reduced the energy difference between the bent and linear forms by 6 and 10 kJ mol−1. These results lead to the conclusion that the geometries of the two-coordinate metal dithiolates in the crystalline state are strongly influenced by relatively minor forces, such as ligand flexibility and ligand size. The structures are also in contrast with similarly bulky –OAr[superscript iPr]4 and –N(H)Ar[superscript iPr]4 analogs which have 1800 L-M-L bond angles. The different coordination geometries of this series of thiolates were also investigated computationally by density functional theory using the model system Cr(SAr)2 (Ar = C6H3-2,6-(C6H5)2. Finally, mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M2(Ar’)(O2CR)3 and M2(Ar’)2(O2CR)2, respectively (AR’ = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the bimetal tetracarboxylates, M2(O2CR)4 (M = Mo, R = H, Me, CF3; M = W, R = CF3) with the lithium salts of the appropriate terphenyl groups (Ar’ = Ar[superscript Xyl]2, Ar[superscript Mes]2, Ar[superscript Dipp]2 and Ar[superscript Trip]2). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M-C sigma bond and creates a coordination unsaturation at the other metal atom. Hence in M2(Ar’)2(O2CR)2 complexes the two metal atoms have formally a low coordination number and an also low electron count. However, the unsaturation seems to be compensated by a weak M-C[subscript arene] bonding interaction that implicates one of the aryl substituents of the terphenyl central aryl ring, as revealed by X-ray studies performed with some of these complexes and by theoretical calculations.