Synthesis and Characterization of Low Coordinate Transition Metal Complexes - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis and Characterization of Low Coordinate Transition Metal Complexes write by Aimee M. Bryan. This book was released on 2014. Synthesis and Characterization of Low Coordinate Transition Metal Complexes available in PDF, EPUB and Kindle. This dissertation describes the synthesis, characterization, and reactivity studies of new low-coordinate complexes of readily available and inexpensive transition metals such as iron, cobalt and nickel. The compounds were magnetically characterized in detail and tested for single molecule magnet (SMM) behavior. SMMs are a topic of intense research because of their potential applications in magnetic memory, high-density information storage and quantum computing technologies. Low-coordinate compounds display magnetic moments that indicate high orbital angular momentum and are very promising candidates for SMM behavior because they also tend to have large negative zero-field splitting (D) values. The complexes reported here are stabilized by using a variety of amido, aryloxo and thiolato ligands with bulky terphenyl groups and also using aryl and alkyl substituted silylamides. A superconducting quantum interference device (SQUID) and Evans' methods were used to study the magnetic properties and single crystal X-ray crystallography and NMR (1H and 13C) were used to confirm the structures of these compounds in both the solid and solution states. Further characterization studies included UV-visible, near-IR, and IR spectroscopy, melting point, elemental analysis and DFT calculations, where applicable, in order to determine the electronic configurations and bonding schemes. At present there are ca. 100 stable open shell two-coordinate mononuclear transition metal complexes currently known but ca. 20% have a linear coordination at the metal atom with only a few being strictly 180° at their metal center. Very few of these compounds had been magnetically characterized. In Chapter 2, the synthesis and magnetic characterization of the late transition metal Co2+ (d7) and Ni2+ (d8) primary amido complexes Co{N(H)Ar(iPr6)}2, Co{N(H)Ar(Me6)}2, Ni{N(H)Ar(iPr6)}2 and Ni{N(H)Ar(Me6)}2 (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2, Ar(iPr6) = C6H3-2,6(C6H2-2,4,6-(i)Pr3)2) are described. The investigations showed that they exhibit interesting magnetic behavior. The bent versus linear geometries of the complexes enable direct observation of the effects of orbital angular momentum quenching upon bending the metal coordination geometry. The electronic configuration of the linear cobalt(II) complexes does not predict first order orbital angular momentum and yet, the magnetic moment of Co{N(H)Ar(iPr6))2 is much higher than the spin only value which suggests a large spin-orbit coupling effects due to mixing of the ground and excited states. In Chapter 3, the synthesis and characterization of the mononuclear chromium, iron, cobalt and nickel terphenyl substituted thiolate complexes Cr(SAr(Me6))2, Cr(SAr(iPr4))2, Fe(SAr(iPr4))2, Co(SAr(iPr4))2 and Ni(SAr(iPr4))2 are described. Their structures show bent coordination geometries of varying degree with strong secondary M-[eta]6 and M-C(ipso) flanking aryl ring interactions of ca. 2.153 [Angstrom] for Fe(SAr(iPr4))2, ca. 1.625 [Angstrom] for Co(SAr(iPr4))2 and ca. 1.731 [Angstrom] for Ni(SAr(iPr4))2. This observation is in sharp contrast to the almost linear coordination observed for the derivatives of the related but more crowded terphenyl thiolate ligand, SAr(iPr6), in M(SAr(iPr6))2 complexes where M = Cr, Fe, Co and Ni and the strictly linear geometry observed for the terphenyloxo analogs M(OAr(iPr4))2 where M = Fe and Co. Magnetic moments for these species are, in general, lower than the spin-only values. Expect for chromium, this is an unexpected observation for late transition metal low-coordinate complexes. The suppression of magnetic moments is most like due to the strong M-arene interactions which effectively increases the coordination number at the metal atom. These results demonstrate the important role that substituents play on the flanking rings of the terphenyl ligands and begs further investigations involving the role of dispersion in the isolation of low coordination mononuclear transition metal complexes. The divalent silylamides M{N(SiMe3)2}2 (M = Mn, Fe, and Co) are key synthons for low-coordinate transition-metal derivatives. In Chapter 4, the previously reported, but incorrectly characterized cobalt(II) silylamide, [Co{N(SiMe3)2}2]2 has been spectroscopically and magnetically characterized for the first time. In addition, the new Lewis base complexes [Co{N(SiMe3)2}2(PMe3)], and [Co{N(SiMe3)2}2(THF)], as well as a previously reported complex [Co{N(SiMe3)2}2(py)] were isolated and characterized. Magnetic studies showed that they had considerably larger magnetic moments than the spin-only value of 3.87 [mu](B), which is indicative of a significant zero-field splitting and g-tensor anisotropy. In addition to their interesting magnetic behavior and unexpectedly large D values in the range of -20 to -80 cm−1. The electronic spectrum of [Co{N(SiMe3)2}2]2 in solution showed that earlier characterization spectra of "Co{N(SiMe3)2}2" match that of the bright green THF adduct and not the dark brown cobalt dimer [Co{N(SiMe3)2}2]2. In Chapter 5, it is shown that the reaction of the versatile cobalt(II) amide, [Co{N(SiMe3)2}2]2, with four equivalents of the sterically crowded terphenyl phenols, HOAr(Me6) and HOAr(iPr4) (Ar(iPr4) = C6H3-2,6(C6H3-2,6-(i)Pr2)2) produced the first well-characterized, monomeric two-coordinate cobalt(II) bisaryloxides, Co{OAr(Me6))2 and Co(OAr(iPr4))2. Not only are these very rare examples of two-coordinate transition metal(II) aryloxides, but the magnetic moments of both the linear and the bent species were well in excess of the spin only value for cobalt(II) ion. It was demonstrated that careful manipulation of the synthetic conditions for Co(OAr(iPr4))2 could produce varying occupancies of the cobalt(II) site and that after weighting the magnetic susceptibilities of the compounds accordingly, the moments were shown to be in close agreement with each other. Chapter 6 reports the synthesis of the unstable nickel(II) bis(silylamide) complex Ni{N(SiMe3)2}2 via the reaction of NiI2 and two equivalents of NaN(SiMe3)2 in tetrahydrofuran, as well as two of its Lewis base adducts, Ni{N(SiMe3)2}2(THF) and Ni{N(SiMe3)2}2(py)2. The reaction of two equivalents of LiN(SiMe3)2 with NiCl2(DME) in tetrahydrofuran afforded the reduced homoleptic tetrameric nickel(I) amide complex, [Ni{N(SiMe3)2}]4. This unique polymetallic structure having a Ni4N4 planar array has four S = 1/2 nickel (I) ions and an antiferromagnetic exchange coupling constant of J = -102(2) cm−1. This study provides strong evidence that the formation of nickel(II) and nickel(I) amido complexes is possible without the use of sterically demanding ligand sets.
Synthesis and Characterization of Low Coordinate Transition Metal Complexes and Plastic and Lithium-containing Organic Scintillators with Efficient Neutron/gamma Pulse Shape Discrimination
Synthesis and Characterization of Low Coordinate Transition Metal Complexes and Plastic and Lithium-containing Organic Scintillators with Efficient Neutron/gamma Pulse Shape Discrimination - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis and Characterization of Low Coordinate Transition Metal Complexes and Plastic and Lithium-containing Organic Scintillators with Efficient Neutron/gamma Pulse Shape Discrimination write by Michelle Faust. This book was released on 2016. Synthesis and Characterization of Low Coordinate Transition Metal Complexes and Plastic and Lithium-containing Organic Scintillators with Efficient Neutron/gamma Pulse Shape Discrimination available in PDF, EPUB and Kindle. 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.
Synthesis, Characterization and Reactivity Studies of Low-coordinate Late Transition Metal Complexes and the Preparation and Characterization of a Low-coordinate Samarium Complex
Synthesis, Characterization and Reactivity Studies of Low-coordinate Late Transition Metal Complexes and the Preparation and Characterization of a Low-coordinate Samarium Complex - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis, Characterization and Reactivity Studies of Low-coordinate Late Transition Metal Complexes and the Preparation and Characterization of a Low-coordinate Samarium Complex write by Pei Zhao. This book was released on 2015. Synthesis, Characterization and Reactivity Studies of Low-coordinate Late Transition Metal Complexes and the Preparation and Characterization of a Low-coordinate Samarium Complex available in PDF, EPUB and Kindle. This dissertation focuses on the synthesis, characterization and reactivity study of terphenyl ligand stabilized bis([mu]-oxo) dimeric iron and cobalt complexes. The synthesis and characterization of low-coordinate cobalt alkyl and iron alkyl complexes are also described. In addition, it describes the preparation of the first monomeric homoleptic solvent-free bis(aryloxide) lanthanide complex. The solid state structures of new compounds were determined by single crystal X-ray crystallography. Magnetic properties of paramagnetic compounds were measured by superconducting quantum interference device (SQUID) or Evans' methods for solid state or solution phase, respectively. The new compounds were also characterized by UV-Visible spectroscopy. Furthermore, infrared spectroscopy, Mössbauer spectroscopy, electron paramagnetic resonance spectroscopy, mass spectrometry, cyclic voltammetry and elemental analysis were employed to characterize some of the compounds when applicable. In some cases, DFT calculations were applied to elucidate the bonding and energy levels of molecular orbitals in the complexes. In Chapter 2, The bis([mu]-oxo) dimeric complexes {Ar[superscript iPr8]OM([mu]-O)}2 (Ar [superscript iPr8] = -C6H-2,6-(C6H2-2,4,6-[superscript i]Pr3)2-3,5-[superscript i]Pr2; M = Fe or Co) were prepared by oxidation of the metal (I) half-sandwich complexes {Ar[superscript iPr8]M([eta]6-arene)} (arene = benzene or toluene; M = Fe or Co). The iron species {Ar[superscript iPr8]OFe([mu]-O)}2 was prepared by reacting {Ar[superscript iPr8]Fe([eta]6-benzene)} with N2O or O2 and the cobalt species {Ar[superscript iPr8]OCo([mu]-O)}2 was prepared by reacting {Ar[superscript iPr8]Co([eta]6-toluene)} with O2. Both {Ar[superscript iPr8]OFe([mu]-O)}2 and {Ar[superscript iPr8]OCo([mu]-O)}2 were characterized by X-ray crystallography, UV-vis spectroscopy, magnetic measurements and, in the case of the iron species, by Mössbauer spectroscopy. The solid-state structures of both compounds reveal unique M2([mu]-O)2 (M = Fe or Co) cores with formally three-coordinate metal ions. The Fe···Fe separation in {Ar[superscript iPr8]OFe([mu]-O)}2 bears a resemblance to that in the Fe2([mu]-O)2 diamond core proposed for the methane monooxygenase intermediate Q. The structural differences between {Ar[superscript iPr8]OFe([mu]-O)}2 and {Ar[superscript iPr8]OCo([mu]-O)}2 are reflected in rather differing magnetic behavior. Compound {Ar[superscript iPr8]OCo([mu]-O)}2 is thermally unstable and its decomposition at room temperature resulted in the oxidation of the Ar[superscript iPr8] ligand via oxygen insertion and addition to the central aryl ring of the terphenyl ligand to produce the 5,5'-peroxy-bis[4,6-[superscript i]Pr2-3,7-bis(2,4,6-iPr3-phenyl)oxepin-2(5H)-one]. The structure of the oxidized terphenyl species is closely related to that of a key intermediate proposed for the oxidation of benzene. In Chapter 3, the homoleptic, cobalt(I) alkyl [Co{C(SiMe2Ph)3}]2 was prepared by reacting CoCl2 with [Li{C(SiMe2Ph)3}(THF)] in a 1:2 ratio though the initial intent was to synthesize a dialkyl cobalt (II) complex. Attempts to synthesize the corresponding iron(I) species led to the iron(II) salt [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2]. Both complexes were characterized by X-ray crystallography, UV-vis spectroscopy, and magnetic measurements. The structure of [Co{C(SiMe2Ph)3}]2 consists of dimeric units in which each cobalt(I) ion is [sigma]-bonded to the central carbon of the alkyl group -C(SiMe2Ph)3 and [pi]-bonded to one of the phenyl rings of the -C(SiMe2Ph)3 ligand attached to the other cobalt(I) ion in the dimer. The structure of [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2] features three chlorides bridging two iron(II) ions. Each iron (II) ion is also [sigma]-bonded to the central carbon of a terminal -C(SiMe2Ph)3 anionic ligand. The magnetic properties of [Co{C(SiMe2Ph)3}]2 reveal the presence of two independent cobalt (I) ions with S = 1 and a significant zero-field splitting of D = 38.0(2) cm−1. The magnetic properties of [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2] reveal extensive antiferromagnetic exchange coupling with J = -149(4) cm−1 and a large second-order Zeeman contribution to its molar magnetic susceptibility. Formation of the alkyl [Co{C(SiMe2Ph)3}]2 and the halide complex [Li(THF)4][Fe2([mu]-Cl)3{C(SiMe2Ph)3}2] under similar conditions is probably due to the fact that Co(II) is more readily reduced than Fe(II). Some other synthetic routes were also attempted to synthesize a dialkyl cobalt (II) complex and they are described in this chapter. Neither [Co(NPh2)2]2 nor cobaltocene reacts with [Li{C(SiMe2Ph)3}(THF)] to afford a dialkyl cobalt (II) complex. Metathesis reactions of cobalt halides with lithium salts of alkyl ligand HCPh2R (R = -Ph or -SiMe3) resulted in the reduction of cobalt (II) to cobalt metal and the coupling of ligands, which indicate that homolytic cleavage of the cobalt-carbon bond was probably involved in the metathesis reactions. Furthermore, in chapter 4, reaction of Sm[N(SiMe3)2]2(THF)2 with two equivalents of bulky aryloxide ligand HOAr[superscript iPr6] (Ar[superscript iPr6] = -C6H3-2,6-(C6H2-2,4,6-[superscript i]Pr3)2) afforded the first monomeric homoleptic solvent-free bis(aryloxide) lanthanide complex Sm(OAr[superscript iPr6])2. The complex was characterized by crystallography, UV-Visible spectrum, IR and magnetically by the Evans' method. The O-Sm-O angle is bent at 111.08(9)̊. The samarium ion in Sm(OAr[superscript iPr6])2 also shows weak interactions with the flanking aryl rings of the terphenyloxide ligands. The complex is paramagnetic at room temperature with magnetic moment of 3.51 [mu]B.
Low-coordinate Terphenyl Transition Metal Complexes (M
Low-coordinate Terphenyl Transition Metal Complexes (M - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Low-coordinate Terphenyl Transition Metal Complexes (M write by Chengbao Ni. This book was released on 2009. Low-coordinate Terphenyl Transition Metal Complexes (M available in PDF, EPUB and Kindle.
Synthesis, Structures and Characterization of Coordination Compounds with the Transition Metals, Ni(II), Cu(II), Mn(II), Cr(III), Fe(III), Using Ligands Based on Iminodiacetic Acid and N-heterocycles
Synthesis, Structures and Characterization of Coordination Compounds with the Transition Metals, Ni(II), Cu(II), Mn(II), Cr(III), Fe(III), Using Ligands Based on Iminodiacetic Acid and N-heterocycles - read free eBook in online reader or directly download on the web page. Select files or add your book in reader. Download and read online ebook Synthesis, Structures and Characterization of Coordination Compounds with the Transition Metals, Ni(II), Cu(II), Mn(II), Cr(III), Fe(III), Using Ligands Based on Iminodiacetic Acid and N-heterocycles write by Maria Paula Juanico. This book was released on 2003. Synthesis, Structures and Characterization of Coordination Compounds with the Transition Metals, Ni(II), Cu(II), Mn(II), Cr(III), Fe(III), Using Ligands Based on Iminodiacetic Acid and N-heterocycles available in PDF, EPUB and Kindle.
