Synthesis of Hyponitrite Complexes for the Reduction of NO Introduction Climate change has progressively gotten worse since the industrial evolution, to a point where the United Nations has declared we have 10 years to make changes to prevent irreversible 1 damage to Earth. Nitrous oxide (N2O) makes up 6% of the U.S. greenhouse gas emissions, however, it can stay in the atmosphere for around 114 years and has a global warming potential 2 300 times that of 1 pound of carbon dioxide. N2O is naturally reduced though chemical reactions done by N2O reductase, a copper centered enzyme found in a denitrifying bacteria, however, the 3 mechanism is not known and replication is difficult as N2O is a poor ligand for transition metals. The bacteria is unable to keep up with the amount of nitrous oxide produced by humans. Studies regarding the denitrification process began by looking at the heme proteins in humans that are responsible for the regulation of the signal transduction by utilizing NO.4 This has led to the understanding of the intermediate steps for the process, such as the coordination and reduction.5 My research focuses on the speculations that are made about the denitrification process done by nitrous oxide reductase with the goal of creating a complex that can replicate the reduction, leading to a man-made way of reducing the nitrous oxide in the air. Complexes that reduce NO to N2O have signifying factors that are clear indications that the reduction is either complete or there is an unexpected side reaction. Few mechanistic studies provide insight to the transformation between NO to N2O, although the insertion of the coordinated NO is the key to the mechanistic step. Not thermodynamically favorable, the reaction uses a metal catalyst to proceed the reaction, ideally a first-row transition metal, due to the price and abundancy of the metals. Previous studies have also ruled out rate limiting steps as excess NO converts to N2O in a copper catalyst with a single NO attached. The copper gains another NO forming a 6 dinitrosyl, or hyponitrite (N2O2), species that quickly reacts with NO to produce the N2O. The copper catalyst is one of the more stable and effective metals to use and is the center of the study as previous studies using nickel catalyst were unsuccessful due to reactivity. In this study, instrumentation available on campus will be used to identify the product of each step of the synthesis alongside higher methods of analysis for verification of each experimentally determine product. Complexes would be synthesized using common bench workspace and the glovebox in the Stieber Lab to ensure air sensitive are not decomposed. Infrared absorption spectrometry (IR) and X-ray diffraction (XRD) instruments on campus complement each other and will be utilized for the identification of the complexes synthesized for understanding and characterizing hyponitrite intermediates for the reduction process of NO. Nitrogen rich fertilizer used in agriculture is the main contributor for the amount of N2O emission.2 Previous publications indicate that a NO ligand can also bond in either a linear, or a side-on configuration which have an effect of the bonding patterns with a second NO. The linear configuration experiences higher yields (77%), however, it is unable to accept the second NO for reduction. The side on configuration (23% yield) is thought to configure the second NO to promote N-N coupling because of the presence of spin density between the nitrogen attached to the nitrosyl.7 With this configuration, the nitrogen is exposed for binding with a second NO to produce a hyponitrite complex.8 Synthesizing a complex that is able to only side on orientated will be studied. The IR spectroscopy instrument on campus is a Fourier transform infrared spectrometer (FT-IR) which uses a single optical path to collect a spectrum of the complex while also collecting a spectrum of atmospheric molecules for the background to be subtracting by the ratio.9 The data is composed of the sum of sine and cosine terms which produce the constructive and destructive inference of waves.10 An IR beam is shot at the complex which produces energy differences in different molecular species. IR radiation produces small differences between vibrational and rotational states that are amplified in the complex as it exhibits changes in the dipole moment. The dipole moment, determined by the magnitude of the charge difference between the two atom centers, produces a regular fluctuation which can then interact with the electric field from the IR. When the fluctuations produced by the vibrational frequencies and the rotation around asymmetric center matches the frequency of the radiation, the radiation is absorbed and calculated to produce a stretch on the spectrum.11 The data is rapidly acquired, however, there is an increase to the signal to noise ratio.9 IR spectrums can be divided into two regions, the fingerprint region and the functional group region.12 The functional group, or near-IR, region consist of the earlier portion of the spectrum, or 4000 to 15,000 cm-1 displays common functional groups in the complex, such as oxygen, nitrogen, sulfur and some hydrocarbons and can be used for qualitative analysis of the complexes synthesized as able to differentiate between NO and N2O. The fingerprint region is used to identify between different organic and inorganic compounds and consists of the higher region of the IR spectrum.11 IR is a powerful method that can differentiate between many different possibilities for the types of outcomes. To begin, IR can provide information of the metal binding with the NO or even 13 if it is bound to multiple NO molecules. NO reduces to N2O and IR is useful to provide insight qualitative properties of the complexes as it can differentiate between the two. This allows periodic check to ensure the synthesis is indeed successful. Other information provided can be the symmetry of the complex, the coordination, and isomerization of the complexes. IR produces specific stretches for asymmetric N-O (970 cm-1) and can signify the possibility of a trans- hyponitrite complex. A symmetric complex would show a N-O stretch (around 900-1,000 cm-1) due to the nature around the complex.14 A linear configuration would exhibit a longer M-N bond and a peak around 1800 cm-1 while the side on configuration would consist of values similar to other three-coordinate NO species, around 17,000 cm-1.15 IR spectrums also have the capability to distinguish if the NO is reduced as a stretch at 1555 cm-1 would be consistent with a highly reduced linear NO ligand.6,8 IR spectroscopy would be a key source of analysis for the complexes synthesized because of the vast of information provided about the NO chemistry in the complex. IR spectroscopy is unable to characterize all electronic transitions or homonuclear species, making it difficult to understand some of the binding interactions in the complex. This method is useful for ensuring the synthesis is continuing in the right direction. The use of home source XRD would allow characterization of the complete complex that would ideally be built of the hints given from the IR spectrum. X-rays have the same wavelength as 1 Å allowing the determination of bonds to be possible. An X-ray beam is emitted to hit the crystalized complex which diffracts on the lattice planes of the complex. The waves interact constructively and destructively before hitting the detector to produce spots that are reflections of the electrons of the atom. The reflections are then correlated and solved to give a crystalized complex. This method requires crystals, unlike IR spectroscopy which involves a screening process for the crystallization conditions for the complex as well as longer acquisition times, are more complex molecules require longer run periods. The crystallization process is based on trial and error so finding appropriate solvents and time for crystallization further increases the time for this experiment. Some complexes are difficult, and sometimes too reactive to crystallze16 making this an inefficient method for some complexes. Copper is the transition metal of choice because it is less reactive than nickel allowing the XRD to collect a spectrum, but it is anticipated that the X- ray would excite some of the complexes making IR spectroscopy a more efficient method. The XRD would be a beneficial method of analysis for my project, as it could provide clarity on the binding and chemical structure of the complex. Using the XRD would allow the binding of the NO to be analyzed for insight on the linear or side on interaction which could be dependent on the properties of the ligands attached to the complex. Further experimentation of ligand properties, such as electron donating, withdrawing, and steric hinderance, could be further analyzed for future complexes. It would also provide further information on bond lengths and bond angles between NO and the metal of choice. Currently there are limited resources on the relationship between the bond angle, NO length and the IR peak. Creating a table with expected IR stretches for the given NO configuration would provide useful for the future steps of the 17 mechanism. The reduction of NO to N2O is one step of a longer mechanism which still unknown. Understand one portion of the reaction and having a complete table of the expected trends is beneficial for the future steps of the analysis as well. Instruments utilized for this experiment would provide a useful insight on the steps of the process as well ensure the synthesis process is producing the expected outcome. Materials and Methods A mechanism like the one developed by Kogut et.