Although the first-generation optimal MOFs demonstrate very promising adsorption performance, upon analyzing their building block composition, we discover that many of them are oxalates structures. These structures correspond to MOFs where the length of the edge building blocks is zero and two [CO2] groups from the nodes are directly connected, forming the oxalate group. We may want to consider them as a separate group of materials and distinguish their properties form MOFs based on non-zero linkers. Other considerations may pertain to the chemical nature of the linkers. For example, based on chemical intuition and general knowledge, it is likely that organic molecules with large nitrogen content are explosive and molecules with large phosphorus content are toxic.