Inclusion Compounds Formed between Hofmann-(1,9-diaminononane)-type Host and Aromatic Guest

IR spectra of three tetracyanonickelate complexes with 1,9-diaminononane as ligand and three of their clathrates with guest nitrobenzene are presented. It is shown that they have similar structures and exhibit weak hydrogen bonding between the pi-electron cloud of aromatic guest and the ligand of the host lattice which is observed in all clathrates. A second type of hydrogen bonding is present between the NO2 of nitrobenzene and the cyanide group of the lattice. The cyanide vibrational frequencies in the present clathrates are found to be in the order Cd-Ni-NB < Co-Ni-NB < Ni-Ni-NB due to increase in second ionization potential of outer metal ion. Declathration by heating shows that after the elimination of guest, the host lattice is stable since the IR spectra of the heated clathrate sample is the same as it's host. So there is only a very weak hydrogen bonding between the host and guest. These empty sites of host are occupied by moisture and retained as clathrated water. The host lattices are found to be similar to those of Hofmann-α,ω-diamino long chain alkane clathrates. The stability of these compounds are based on H-bonds involving NO2 of nitrobenzene, pi cloud of the guest and the cyanide moieties.