Ionic Liquids (ILs) are promising CO2 absorbents to attenuate large amounts of CO2 emissions from coal-fired power plants, as they have attractive properties such as negligible vapor pressure, high thermal stability, and tunability. Phenolate based Ionic liquids have been synthesized with phosphonium cations to investigate the potential of the basic oxygen atom of the phenolate anion as a CO2 capture site. Furthermore, the phenolate anions were tuned to adjust the basicity of the oxygen atom by substituting the para position of the phenolate anions with functional groups, such as a nitro group [NO2] and a methoxy group [MeO]. The substitution effects on both the chemical property (CO2 capture capacity) and the physical properties (viscosity, density, and conductivity) were investigated. The results show that the basic oxygen sites of phenolate ILs are able to react with CO2, but there are two reaction channels – a cation intermediated reaction pathway and an anion reaction pathway. The products of the two reaction pathways are characterized by using Infrared Spectroscopy (IR) and phosphonium (31P) Nuclear Magnetic Resonance spectroscopy (NMR). In addition to the work with phenolate ILs, aprotic heterocyclic anions (AHAs) paired with different alkyl chain lengths of phosphonium cations were synthesized to study structural information with and without CO2, as structure studies are necessary to aid in the design of even better CO2 capture ILs. AHAs were previously developed for CO2 capture application in which a reactive amine site is incorporated into five membered ring anions and reacted with CO2 in one to one stoichiometry. In this work, Synchrotron Small Angle X-ray Scattering (SAXS) is utilized to extract the structure factors that include structure-ordering information of AHA ILs. The experimentally generated structure factors give structural information, such as pre-peaks, charge alternation peaks, and adjacency peaks. Furthermore, structure factors determined computationally by our collaborators are validated by comparing them with the experimentally generated structure factors here. The computational structure factors are then deconvoluted into partial structure factors to give more specific structure information. The different anions, 2-cyanopyrrolide [2CNPyr]- and 1,2,4-triazolide [4Triaz]- do not show any significant differences in the structure factors, but in the three-dimensional structure information, they show different solvation systems. Also, changing the alky chain lengths on the cation results in different degrees of cation-cation aggregation.