The structures, infrared spectra, and electronic properties of the N7,N9-dimethylguaninium chloride have been studied. The interaction of one cation with one to four Cl anions and one Cl anion with two cations were investigated. Fifteen stable conformers are obtained. It is found that there are four acidic regions in the vicinity of the guaninium cations. In these regions, the cation could H-bond with one to three Cl anions but no more than three nearest anions. One Cl anion could H-bond with two cations. Additionally, evidence of a Cl center dot center dot center dot pi interaction between the anion and cation is observed. Among these structures, one cation interaction with two anions and two cations interaction with one anion have the larger interaction energies than the other series. Natural bond orbital analyses and molecular orbitals reveal that the charge transfer from anion(s) to the cation(s) occurs mainly through either the Cl-Ip -> sigma*(C-H), Cl-Ip -> sigma*(N-H), or Cl-Ip -> pi*(C8-N7) interactions. The interaction between Cl and sigma*((C/N-H)) or pi*(C-N) produces a small bond order. This indicates that the Cl center dot center dot center dot H (Cl center dot center dot center dot pi) interaction exhibits a weak covalent character and suggests a strong ionic H-bond (Cl center dot center dot center dot pi bond). What's more, formation of Cl center dot center dot center dot H/Cl center dot center dot center dot pi bond decreases the bond order of the associated C/N-H bond or C-8-N-7 bond. In addition, examination of vibrational spectrum of each conformer explains the origin of H-bonding character.