Synthetic and structural studies of electron donor-acceptor complexes formed by substituted benzenediazonium salts and aromatic donors

Substituted benzenediazonium salts form weak electron donor-acceptor (EDA) complexes with aromatic compounds. The modes of the EDA interaction are established by X-ray diffractometry of a series of diazonium EDA complexes isolated as crystalline materials. Four distinct types of close contacts between diazonium cations and aromatic donors leading to the appearance of charge transfer transition in the UV-Vis spectra were identified: (1) contact between approximately parallel aromatic systems; (2) contact between an electron rich substituent of the donor and an electron deficient substituent of the acceptor; (3) contact between the aromatic system of the donor and an electron deficient substituent of the acceptor; (4) contact between the diazonio group and the aromatic system of the acceptor. The character of the EDA interaction shows a dramatic dependence on the mutual arrangement of the donor and acceptor in the crystal lattice in a series of novel substituted benzenediazonium salts bearing tethered donor moieties. The crystal lattices of the diazonium EDA complexes are stabilized by the inclusion of the donor host in the voids formed between the layers comprising diazonium cations and counter anions due to the penetration of nucleophilic substituents attached to the cations into the coordination spheres of the diazonio groups. Unusual thermal and photochemical stability of the complexes is probably related to the spacer effect of the host molecules. Absence of noticeable structural changes in the components relates the diazonium EDA complexes to the weak complexes formed by other delocalized ;A series of para substituted benzenediazonium tetraphenylborates is isolated and characterized by the X-ray crystallography for the first time. Spectral and chemical properties of the salts depend linearly on the electron withdrawing ability of the substituents.