Exploring the Correlation Between d-Orbital Splitting and Ligand Identity in Chromium(III) Complexes and Metal Ion Identity in First-Row Transition Metal Complexes By: Vicky Villarosa Reference: This procedure was adapted from the “Analysis of d-orbital splitting in transition metal complexes Part I: UV-Vis spectroscopy Lab Procedure," "Analysis of d-orbital splitting in transition metal complexes Part II: Magnetic susceptibility Lab Procedure,” and the “Data Sheet For SALEN & TP complexes” modules on the Winter 2024 CHM230 Laboratory Canvas page. The synthesis of the iron-tp complex and the iron-salen complex is found in the “Synthesis of Transition Metal Complexes Part I: Salen species Lab Procedure” and the "Synthesis of Transition Metal Complexes Part II & III Lab Procedure” assignments on the Winter 2024 CHM230 Laboratory Canvas page. Abstract: Different approaches were used to explore different transition metal complexes and compare their impact on d-orbital splitting. Part I involved using a spectrophotometer to determine the maximum wavelength for Cr(acac)3, [Cr(en)3]Cl3, Cr(H2O)63, Cr(Tp)2, and CrCl3-6H2O, allowing for the calculation of energy required for electron transitions. This energy, which reflects d-orbital splitting in octahedral complexes, was influenced by the ligand type, leading to the establishment of a spectrochemical ligand series: Cl¯ < H₂O < acac < en<Tp. In Part II, a magnetic susceptibility balance was used to determine the number of unpaired electrons and electron arrangements in various transition metals through effective magnetic moment calculations. Mn(acac)3 had four unpaired electrons, Cr(acac)3 had three, and Fe(C16H14N2O2), CoCl2 6H2O, and Fe(Tp)2 each had one. These findings facilitated the synthesis of a spectrochemical series for metal ligands: Mn²* < Ni²* < Co²* < Fe²* < Fe³* < Cr³*. Overall, these results deepen our understanding of factors influencing electron arrangement in transition metal complexes, particularly d-orbital splitting, highlighting the importance of both ligand and metal cation identity. Introduction: Exploring d-Orbital Splitting in Transition Metal Complexes: Insights from Ligand-Field Theory Understanding ligand strength is key to deciphering d-orbital splitting in transition metal complexes. This involves quantifying the energy gap between d-orbitals using Ao values. Exploring ligand-field theory and the spectrochemical series helps uncover the principles behind the optical and magnetic properties of these complexes. Transition metal complexes are essential in chemical processes, including those related to the origin of magnetism. One fundamental aspect of transition metal complexes is the splitting of d-orbitals in the presence of ligands, known as d-orbital splitting (Figure 1). This phenomenon, led by the ligand's strength and the metal's properties, significantly influences the complex's optical and magnetic properties. Figure 1. D-orbital splitting of a metal ion in an octahedral field. free metal ion eg dz² dx²-y² 125 dxz dyz dxy metal ion in octahedral field Reference: "Analysis of d-orbital splitting in Transition Metal Complexes Part I: UV-vis" Laboratory procedure from the Canvas site for the Winter 2024 Chemistry 230L Course. Through a series of experiments, the relationship between ligand strength, metal-ligand interactions, and the resulting spectroscopic and magnetic behaviors of these complexes is explored. First, a foundational objective could be established by synthesizing and analyzing various chromium(III) complexes. If UV-visible spectroscopy is used, it would help reveal absorption spectra and λmax values, which are crucial for calculating Ao. Hence, magnetic susceptibility measurements offer valuable insights into the magnetic behavior of these complexes, enhancing our comprehension of d-orbital splitting. Furthermore, this data serves as a foundation for establishing a spectrochemical series of varying metal complexes, providing additional insights into their properties. By clarifying the intricate relationships between ligand strength, metal-ligand interactions, and d-orbital splitting, the goal was to provide a comprehensive perspective on transition metal complexes as illustrated in a spectrochemical series: halides < o-ligands <n-ligands < c-ligands. This series incorporated insights into the behavior of metal cations, further enriching our understanding of the factors influencing d-orbital splitting. Experimental Materials: All chemicals were secured from the CHM 230 laboratory stock except iron(II) salen (Fe(C16H14N2O2) made January 21, 2024 using the procedure found in the document titled, "The Synthesis of Transition Metal Complexes Part I: the Salen Ligand and a Salen Complex” and the metal sandwich Fe(Tp)2 and Cr(acac)3 made February 11, 2024 using the procedure found in the document titled "Synthesis of Transition Metal Complexes, Parts II and III.” The Mn(acac)3 was borrowed and the ZnCl2 was included with the lab materials provided. . UV-visible spectra were acquired using the SpectraVis Plus UV vis Spectrophotometer. Magnetic susceptibility was acquired using the Johnson-Matthey Magnetic Susceptibility Balance. Collecting Spectrophotometer Data of Chromium Transition Metal Complexes Part I: UV-vis Solutions of different chromium(III) complexes, including Cr(acac)3 (Chromium(III) acetylacetonate), [Cr(en)3] Cl3 (Tris(ethylenediamine)chromium(III) chloride), Cr(H2O)6C13 (Hexaaquachromium(III) nitrate), and CrCl³·6H₂O (Chromium(III) chloride hexahydrate) were prepared in their designated solvents: toluene for Cr(acac)3 and water for the other complexes. Each solution was placed in a suitable cuvette (quartz/glass for Cr(acac)3 and polystyrene for the others) and ensured to have a concentration suitable for spectroscopic analysis (0.5 < max A < 1.5), with initial concentrations ranging from 5 to 12 mg/mL (Table 1). A glass cuvette was used for toluene since the interaction between toluene and polystyrene is unfavorable, leading to potential damage or dissolution of the polystyrene material. Table 1. Masses of Cr samples and volume of solvent used for UV-Vis. Sample Cr(acac)3 Mass [g] Volume of Solvent [mL] 0.0350 7.40 [Cr(en)3]Cl 0.0250 3.29 [Cr(en)3] Cl 0.0500 3.10 CrCl₂.6H₂O 0.0250 3.10 Complex Observations When dissolving into their designated solvents, CrCl3 • 6H₂O salt created a green solution, [Cr(H2O)6](NO3)3 salt created a black-grey-colored solution, [Cr(en)3]Cl3 salt created a yellow-orange colored solution, and Cr(acac)3 solution was bright purple. Spectrophotometer Analysis and Calulations of Chromium Transition Metal Complexes After the initial scan of CrC13 • 6H2O, it was allowed to settle for two hours before undergoing another UV-vis spectrophotometer analysis. A subsequent plot was generated (see supplemental information), comparing the first scan of CrC13 • 6H2O with Cr(H2O)63, and the second scan of CrC13 • 6H20, to examine the differences between the two scans and another Cr(III) compound with 6H2O as a ligand. Next, UV-visible spectra were recorded for each chromium(III) complex solution using a spectrophotometer displaying the complex's maximum absorbance. The longest wavelength absorption maximum (λmax) for each spectrum was identified and recorded in nanometers (nm). These values were then converted into energy units 1 1.107 nm 0.01196 kJ.cm to calculate Ao using the formula Ao = • To calculate лтах (пт) 1 cm 1 mol concentration, Equation 1 was used. Equation 1. The formula for the concentration of a complex.

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Exploring the Correlation Between d-Orbital Splitting and Ligand Identity in Chromium(III) Complexes and Metal Ion Identity in First-Row Transition Metal Complexes By: Vicky Villarosa Reference: This procedure was adapted from the “Analysis of d-orbital splitting in transition metal complexes Part I: UV-Vis spectroscopy Lab Procedure," "Analysis of d-orbital splitting in transition metal complexes Part II: Magnetic susceptibility Lab Procedure,” and the “Data Sheet For SALEN & TP complexes” modules on the Winter 2024 CHM230 Laboratory Canvas page. The synthesis of the iron-tp complex and the iron-salen complex is found in the “Synthesis of Transition Metal Complexes Part I: Salen species Lab Procedure” and the "Synthesis of Transition Metal Complexes Part II & III Lab Procedure” assignments on the Winter 2024 CHM230 Laboratory Canvas page. Abstract: Different approaches were used to explore different transition metal complexes and compare their impact on d-orbital splitting. Part I involved using a spectrophotometer to determine the maximum wavelength for Cr(acac)3, [Cr(en)3]Cl3, Cr(H2O)63, Cr(Tp)2, and CrCl3-6H2O, allowing for the calculation of energy required for electron transitions. This energy, which reflects d-orbital splitting in octahedral complexes, was influenced by the ligand type, leading to the establishment of a spectrochemical ligand series: Cl¯ < H₂O < acac < en