Experimental and theoretical studies of alkyl 2-(2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ylidene)hydrazine carboxylates: Synthesis, spectroscopic, crystal structure, Hirshfeld surface, and antimicrobial studies

•Nine different alkyl 2-(2,4,6,8-Tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ylidene)hydrazine carboxylates were synthesized and confirmed using FT-IR, NMR, Mass & SC-XRD.•DFT, MEP, NCI-RDG, LOL, and ELF studies were carried out to evaluate the reactivity and interaction sites of the compounds.•The crystal structure is stabilized by C-H···O & N-H···N hydrogen bonding and van der Waals interactions.•Crystal mechanical stabilities and 3D Energy framework for intermolecular interaction energies were estimated.•Antimicrobial activity studies revealed the medicinal behavior of the synthesized compounds. The nine alkyl 2-(2,4,6,8-Tetraaryl-3,7-diazabicyclo[3.3.1]nonan-9-ylidene)hydrazine carboxylates having bicyclic bispidine core were synthesized and characterized using FT-IR, NMR, and mass spectra. Further confirmation of the structure and positioning of the groups was obtained using single crystal XRD investigation. The analysis revealed that one piperidine ring adopts a chair and another a boat form. The aryl groups in the chair conformation are positioned equatorially, whereas those in the boat conformation are orientated axially. The carbazate group (C=N-NH-COOR) aligned the center of the two piperidine rings, with a small deviation towards the boat conformation piperidine ring. The dihedral angle between the chair and boat conformations of the piperidine ring (2f) is 48.51 Å and 45.12 Å, respectively. Hirshfeld and 2D fingerprint analysis show considerable H···H bonding interactions in the crystal. The intermolecular interaction and mechanical stability of crystals were investigated using interaction energy and crystal void analysis. Reduced density gradient and localized orbital locator analyses were used to investigate intramolecular interactions and electron delocalization. The molecule's higher and lower electron densities were investigated utilizing frontier molecular orbital analysis and Molecular Electrostatic Potential. The antimicrobial activity of the compounds was investigated using four bacterial and two fungus strains. [Display omitted]