Benzene clathrate. Hofmann-type

Fig. 1 A view of Hofmann-type benzene clathrate [M(NH3)2-MXCN)4]-2C6H6 diamminemetalM(II) (right upper) and tetracyanometallateM (n) (right lower) as building blocks of the host.

Figure 2 Crystal structure for one Hofmann-type clathrate. (a) Single 2D periodic layer outlining the square planar Ni(CN)4 and the octahedral Fe(CN)4(NH3)2. (b) Benzene guest molecules (highlighted in orange) are enclathrated by the 2D layers. Fe (red), Ni (green), C (gray), and N (blue).

Hofmann-type clathrates have the general chemical formula M(NH3)2M (CN)4 2G, usually abbreviated as M-M -G [61]. M (Ni, Fe, Co, Cd) is a six-coordinated and M (Ni, Pt, Pd) is a four-coordinated divalent metal ion. The guest molecule is mostly an aromatic molecule (benzene, aniline, pyrrole). 

Abstract. The infrared spectra of M(4,4 -bipyridyl)Ni(CN)t complexes (M = Ni or Cd) and their dioxane, benzene, toluene, aniline and V,V-dimethylaniline clathrates are reported. Additional information regarding the structure of the host lattice is obtained from the Raman spectra of the M=Cd complex. It is shown that the structure of the host lattice consists of infinite polymeric layers of M-Ni(CN)i analogous to those of Hofmann type clathrates that have tetragonal symmetry. Bidentate 4,4 -bipyridyl molecules form bridges between the metal atoms M in the adjacent M-Ni(CN)4 oo layers. It is found that the 4,4 -bipyridyl molecules are centrosymmetric in this structure. 

Recently three-dimensional metal complex hosts have been developed from the two-dimensional Hofmann type host lattices, M(NH3)2Ni(CN)4, by replacing the ammonia groups by bidentate ligands, with the aim of enlarging the range of guest molecules which can be accommodated in the host lattices [1-5]. In a previous study Mathey et al. reported the preparation of the Ni(4,4 -bipyridyl)Ni(CN)4 host lattice and its benzene, xylene, naphthalene and anthracene clathrates [5]. We have extended this study and prepared M(4,4 -bipyridyl)Ni(CN)4-2G (M = Ni or Cd G = dioxane, toluene, aniline or iV,AT-dimethylaniline) clathrates for the first time. In this study an IR spectroscopic study of the M(4,4 -bipy)Ni(CN)4 -MG compounds (where M = Ni or Cd, G = dioxane, benzene, toluene, aniline or iV,AT-dimethylaniline, n=0-2) (abbreviated henceforth as M-Ni-bipy-G) are reported. Additional information is obtained from the laser-Raman spectrum of the Cd-Ni-bipy complex. We also recorded the powder X-ray diffraction patterns of the M-Ni-bipy complexes. 

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