Altermagnets have garnered significant interest owing to their distinct crystallographic and spin symmetries, which exhibit vanishing net magnetization and momentum-dependent spin splitting. However, current research has primarily focused on inorganic altermagnetic materials. In this study, a two-dimensional (2D) Cairo pentagonal metal-organic framework (MOF) family, ${\text{TM}}_2$(TCNQ)${}_2$ [TM = transition metal, TCNQ = 7,7,8,8-tetracyanoquinodimethane], is presented as a versatile platform for $g$-wave altermagnets. The applied tensile strain along the [110] direction results in enhanced spin-splitting and induces a Lifshitz transition between $g$-wave and $d$-wave altermagnet, as evidenced in monolayer ${\mathrm{Ru}}_2$(TCNQ)${}_2$. Additionally, a tight-binding model composed of the $p\text{−}d$ orbital interactions for 2D Cairo pentagonal altermagnets accurately captures the $g$-wave-to-$d$-wave phase transition. Furthermore, the [110]-strained ${\mathrm{Ru}}_2$(TCNQ)${}_2$ exhibits fascinating anisotropic spin plasmon propagation, presenting exciting prospects for spintronic applications. This work opens a novel pathway for the design and investigation of altermagnetic candidates using 2D MOF platforms.

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• Plasmons
• 2-dimensional systems
• Altermagnets
• Metal-organic framework
• Tight-binding model