In contrast to what is usually assumed, we have found and proved that thallium(III) forms very strong cyanide complexes in aqueous solution. We have investigated this system using 205T1,13C, and 14N NMR and potentiometry and established the existence of four thallium(III)-cyanide complexes of the composition T1(CN)"3"", = 1-4. We have measured their chemical shifts and spin-spin coupling constants and determined their formation constants at 25 °C in dilute (0.05 M) aqueous solution in the ionic medium ([Na+] = 1 M, [Li+] + [H+] = 3 M, [C104"] = 4 M). The overall formation constants are log ß = 13.2 (1), log ß2 = 26.5 (2), log ß2 = 35.2 (2), and log = 42.6 (2). We have also determined the stability constant for HCN in the same ionic medium, log K" = 10.11 (5). One-bond spin-spin coupling constants between thallium and carbon, 1/(205T1-13C), for the mono-and dicyano complexes of thallium(III) are 14636 and 13749 Hz, respectively, and appear to be the largest known coupling constants between these nuclei. The stability of the T1(CN)"3"" complexes is discussed in terms of their kinetic inertness.

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DA·2BH2CN (1) [DA = N,N,N‘,N‘-tetramethylethanediamine (TMEDA, a), N,N,N‘,N‘-tetramethylpropanediamine (TMPDA, b), and N,N,N‘,N‘-tetramethylbutanediamine (TMBDA, c)], (DA·2BH2CNEt)(BF4)2 (2), and DA·2BH2COOH (3) complexes were prepared from Me2S solution of (BH2CN) n (→ 1 → 2 → 3) in fast procedures, differently from those usually applied, in good yields. Dimethyl esters (4) were prepared from 3 with methanol in very fast reactions catalyzed by HBr. 3 and 4 were transformed into DA·BH2COOH (5a,b) and DA·BH2COOMe (6) with DA in THF. Bromination of 3 in aqueous HBr yielded diamine-bis(monobromocarboxyboranes) (7), in vigorous conditions diamine-bis(dibromocarboxyboranes) (9) were produced. N-Bromosuccinimide in methanol transformed 3a,b directly into diamine-bis(bromomethoxycarbonylboranes) (8a,b). BrH·DA·BH(Br)COOH (10a,b) could be prepared from 5a,b with bromine in strongly acidic medium. N-Deprotonated 10a quickly transformed into a five-membered cyclic cation [TMEDA·BHCOOH]+ (cation in 12a) in both water and methanol. Thus, this ion was formed by dissolution of 10a in water, bromination of 5a or destroying one of the borane moieties in 7a by a base. N-Deprotonated 10b in water decomposed with a pH-dependent rate, but in methanol, in the presence of base, it transformed into a six-membered cyclic cation [TMPDA·BHCOOH]+ (cation in 12b). 8a,b could also be transformed into cyclic cations by destroying one of their borane moieties in methanol, (8b in absence of acids only). All cations were prepared as bromide, hexafluorophosphate and tetraphenylborate salts. pK a values of 12a,b (pK a = 5.5−5.6) are 3 units lower than those of amine-carboxyboranes. Zwitterions (18a,b) formed by their deprotonation were prepared. Cyclic cation [TMEDA·B(Br)COOH]+ (cation in 19a) formed on destroying one dibromocarboxyborane of 9a. This cation, quite a strong acid (pK a ≈ 4.2), was prepared as hexafluorophosphate and tetraphenylborate salt. The latter was transformed with aqueous KOH into the corresponding zwitterion (21a).

The stability constants of the complexes of 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane-l ,I 0-bis(ma1onate) formed with alkaline-earths, lanthanides, zinc, cadmium and lead are larger for larger metal ions, which is manifested in unusually high Sr2+/Ca*+ and Pb2+/Zn2+ selectivities in aqueous solution.