## 6 Summary  
The structure of GR can be seen as a two-dimensional (2D) network of hexagonal carbon rings (sp\({}^{2}\) hybridized) linked by acetylenic connections (sp hybridized). Baughman et al. [9] proposed graphyne as a structure in which one-third of the C-C bonds in G are substituted with one acetylene unit, and it has been proven to be structurally stable  
Figure 25: (**a,b**) Reaction energy diagrams for \({}^{\star}\)CO\({}_{2}\)\(\rightarrow\)\({}^{\star}\)CO and \({}^{\star}\)COOH \(\rightarrow\)\({}^{\star}\)CHO conversions on various M-GY catalysts. (**c,d**) Projected density of states (PDOS) of CO adsorbed on Cr-GY and Mn-GY, showing interaction between CO states and the metal sites. The Fermi level is set to 0 eV. The figure is adopted with permission from reference [166] @ 2021 Elsevier. and synthetically accessible. Acetylene groups are shown to lower binding energy and modify optical and electrical characteristics in a diverse manner [55; 125]. GR has a similar hexagonal symmetric structure to G. The number of acetylenic bonds can vary, resulting in \(n\) number of GR structures, where \(n\) is the number of -C\(\equiv\)C- bonds in the linkage. The stability of GR structures is lower than that of G owing to the introduction of acetylenic bonds in the structure, resulting in a lowering of cohesive energy. As the number of acetylenic bonds increases in the G structures, the cohesive energy decreases, leading to a decrease in the stability of the compound [9; 167]. G and GR have similar out-of-plane deformation and interfacial adhesion, despite GR having just half of G's density [112]. In theory, GRs have superior and exceptional electronic characteristics than G because of their natural band gap of 0.44-2.23 eV. The existence of a triple carbon-carbon bond in GR enables reversed chirality features and momentum shifts of their Dirac cones, allowing for tunability of their energy gap [168]. In addition, GR is expected to exhibit remarkable spatial flexibility, low thermal conductivities, and electron transfer capabilities equivalent to G due to its covalent bonding. Additionally, its band structure sets it apart from other carbon allotropes that are currently in use, which makes it a potential material for lithium storage, SC components, and electron mobility, and among other uses, also [169]. Zhang et al. [144] examined the thermal conductivity of four different GRs. They found that it is much lower than G. The acetylenic linkages presence in the GRs led to an excess reduction in thermal conductivity because of the weak single bonds and corresponding low atom density in the structures. The most pronounced directional anisotropic thermal conductivity has been observed in 6,6,12-graphyne, and along with tension and rising temperatures, has a negative effect on the thermal conductivity of GRs. While there are some similarities between G and GR, GRs have a few extra benefits. The chemical structure of 6,6,12-graphyne is especially notable since it demonstrates that the creation of Dirac fermions that resemble G does not depend on the presence of hexagonal symmetry. The directional anisotropy in carrier mobility of the 6,6,12-graphyne indicates its uniqueness [170]. It has been noticed that G adopts a maximum in-plane stiffness. Then, when we move from GR to GDR, this parameter diminishes. As a result, the Poisson's ratios rise in the same order. The most straightforward explanation for this behavior is that when compared to the most compact structure, G, long acetylenic (and later diacetylene) linkages for G (and subsequently for GDR) cause a progressive structural weakness (a decrease in the atomic bond energy for more loose structures), with the degree of reduction being proportional to the percentage of linkages [117].