Gas-chromatographic investigation on clathrate-forming transition metal complexes

Abstract

The use of two clathrate-forming Werner complexes-e.g., Ni(4-methylpyridine)4(NCS)2 and Ni( 1 -phenylethylamine)4-(NCS)2 as stationary phases in gas chromatography has been recently reported in brief (7). The first compound was found to separate molecules depending on their shapes, while for the second electronic interactions appeared to govern retentions in a GC column. The object of the present work was to study the influence of various substituents in the aromatic rings of these complexes on the elution order of molecules of varying shapes and structures; for the substituted pyridine complexes the effect of replacing nickel by cobalt and iron has also been examined. Seven complexes of the type dithiocyanatotetrakis(l-arylalkylamine)nickel(ll) having different substituents in the aromatic ring and the alkyl chain and six complexes of the general composition M7?4(CNS)2 where B is either 4-methylor 4-ethylpyridine and M is Fe, Co, or Ni have been studied. All these Werner complexes are known for their ability to clathrate various organic molecules (2-6). On the basis of the present work an attempt has been made to gain an insight in the mechanism of the clathration process by all these various complexes. EXPERIMENTAL Chemicals. 4-Methylpyridine (4-MePy), B.D.H., L.R., and 4-ethylpyridine (4-EtPy), Fluka, were used as received. The 1-arylalkylamines were synthesized from the corresponding ketones by following suitable procedures ofLeuckart reaction (7-9), the ketones themselves being obtained through general Friedel-Crafts reactions (70). Boiling points of the amines and the melting points of their hydrochlorides agreed well with those in literature (8, 9). Werner complexes were prepared from these amines and pyridines as described in(2) and (5), respectively.Columns. 180-cm stainless steel columns (i.d., 4 mm) were used in each case.

Inclusion Ability of 4-Phenylpyridine-Extended Nickel(II) Dibenzoylmethanate, a New Metal−Complex Host

“…Incorporation of larger ligands is interesting not just from the viewpoint of exploring the possibility for modification; as a rule, complexes with heavy ligands display higher thermal stability that may be useful for some applications. It can be noted, for instance, that excessive thermal dissociation of complexes with such volatile ligands as 4-methylpyridine was the main problem for their utilization in gas chromatography. , …”