Layered Nickel-HHTP Networks for Efficient Chemiresistive Sensing of CH₄ and CO₂

The synthesis and single-crystal structural elucidation of Ni-HHTP are reported for the first time, achieved from crystals of sufficient size for electron diffraction analysis. These studies reveal that the crystal structure of Ni-HHTP alternates between radical-rich and closed-shell layers along the c-axis, forming a periodic, sandwich-like architecture. The Ni-HHTP coordination pattern differs between these two types of alternating 2D-networks, reflecting distinct electronic environments. Water molecules are either coordinated to the framework or accommodated within the lattice, giving rise to a swelling effect with increasing water content. The well-defined structure enables direct correlation between framework architecture and function. Ni-HHTP exhibits a distinct chemiresistive response toward CO₂ and CH₄-gases of high relevance to greenhouse gas monitoring. Notably, the sensor delivers a clear and measurable response to both gases at concentrations below their ambient atmospheric levels. Theoretical calculations reveal the nature of intramolecular interactions governing the sensing process, providing molecular-level insight into the chemiresistive behavior of Ni-HHTP-based gas sensors.