Treatment of N, NЈ-di(para-tolyl)formamidine (p-tolylformH) (1) with LiBu n in THF, DME or hexane/TMEDA leads to deprotonation of the amidine affording [Li 2 (p-tolylform) 2 (THF) 3 ]ؒ2THF (2), [Li(DME) 3 ][Li 2 (p-tolylform) 3 ] (3) and [{Li 2 (p-tolylform) 2 (TMEDA)} ∞ ] (4) respectively. Similar treatment of 1 with NaH or [Na{N(SiMe 3 ) 2 }] in THF or DME yields trinuclear [Na 3 (p-tolylform) 3 (THF) 4 ] (5) and dinuclear [{Na(p-tolylform)(DME)} 2 ] ( 6). All complexes were characterised by spectroscopy (NMR and IR) and X-ray crystallography. These show p-tolylform to be a versatile ligand for alkali metals, exhibiting a wide variety of binding modes, viz. µ-η 1 :η 1 in 2 and 3 (i.e. bridging mode), µ-η 2 :η 1 in 4 and 6 (i.e. bridging and chelating) and µ-η 2 :η 2 (i.e. bridging and double chelating) and µ 3 -η 2 :η 1 :η 1 (i.e. chelating and bridging between three metal centres) in 5. DALTON

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Recent structural studies of salts of the 2,2,6,6-tetramethylpiperidinium cation [tmpH] ϩ (chloride, bromide; thiocyanate) present as interesting dimeric or polymeric associations linked by pairs of directional hydrogen-bonds from the cationic ϭ NH ϩ 2 moieties to 'two-coordinate' anions. Present single crystal Xray studies have characterized the iodide, perchlorate, nitrate and trifluoroacetate complexes, all, like those of the preceding studies, of composition [tmpH] ϩ X Ϫ (anhydrous). A variety of forms are found: the nitrate compound is dimeric [[tmpH](O·NO·O) 2 [Htmp]], the trifluoroacetate compound being similar in form while the iodide and perchlorate salts are mixtures of dimers (with the anions essentially single atom bridges) and single-stranded helical polymers, the stoichiometric ratio of these being 1:1 and 2:1 in terms of [tmpH]X formula units, respectively. A study of 4-keto-2,2,6,6tetramethyl-piperidinium thiocyanate shows it to be a dimer ΄ [OtmpH] SCN NSC [HtmpO] ΅ , unlike its previously studied chloride analogue which is a cyclic tetramer. A new P2 1 /n phase of di-isopropylammonium chloride, derivative of the previously described P2 1 2 1 2 1 and P2 1 forms, is reported, together with descriptions of protonated salts of the other hindered unidentate bases 2,6-lutidine (as the chloride salt), quinoline (as the perchlorate, trifluoroacetate, hexachlorostannate and bisulfate salts) and 2-quinaldine (as the chloride (anhydrous and monohydrate) and hexachlorostannate salts), all displaying arrays derivative of ion-pair formation (extended by anion-anion hydrogen-bonds as well in the bisulfate salt) and, in the case of the aromatic bases, dominated by parallel stacking.

The mode of co-ordination of 12-crown-4 with the heavier group(II) ions Ca 2ϩ , Sr 2ϩ and Ba 2ϩ has been studied. Size limitations of the 12-crown-4 ligand enforced co-ordinated metal ions to reside above the macrocyclic plane, with the remaining coordination sphere occupied by water molecules and/or counter anions, or a second crown ether ligand to form a sandwich type