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A New Class of Oligonuclear Platinum‐Thallium Compounds with a Direct Metal−Metal Bond ‐ 3. Unusual Equilibria in Aqueous Solution
Author(s) -
Maliarik Mikhail,
Glaser Julius,
Tóth Imre,
Webba da Silva Mateus,
Zékány László
Publication year - 1998
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199805)1998:5<565::aid-ejic565>3.0.co;2-y
Subject(s) - chemistry , thallium , platinum , aqueous solution , metal , octahedron , cyanide , ionic bonding , crystallography , inorganic chemistry , medicinal chemistry , stereochemistry , crystal structure , ion , catalysis , organic chemistry
A new series of four binuclear platinum‐thallium cyano compounds containing a direct and unsupported by ligands metal−metal bond has been prepared in aqueous solution. These compounds are represented by the formula[(NC) 5 Pt−Tl(CN) n−1 ] (n−1)− ( n = 1−4 for compounds I , II , III IV, respectively) and [(NC) 5 Pt−Tl−Pt(CN) 5 ] 3− (for compound V ). The oligonuclear complexes are synthesised according to the reaction m Pt(CN) 4 2− + Tl 3+ + n CN − █[Pt m Tl(CN) 4m+n ] 3−2−n . Thus, there occurs a change of the coordination number of the Pt center from four (square planar) to six (octahedral). Consequently, the formation of binuclear platinum‐thallium cyano compounds involves at least two steps: (i) formation of metal−metal bond and (ii) formation of (NC) 5 Pt− unit by a cyanide transfer process. − The complexes exist in an equilibrium, which also includes the parent complexes Pt(CN) 4 2− and Tl(CN) n 3−n ( n = 0−4), and can be controlled by varying the cyanide concentration and/or pH of the solution. The stability constants of the compounds β N =[Pt m Tl(CN) 4m+n 3−2m−n {[Pt(CN) 4 2− ] m · [Tl 3+ ] · [CN − ] n } have been determined by means of multinuclear NMR ( 195 Pt, 205 Tl): logβ N = 19.9±0.4, 30.7±0.3, 38.6±0.3, and 44.8±0.2 for I , II , III and IV ( m = 1, n = 1−4), and 32.1±0.3 for V ( m = 2, n = 2), respectively, (in 1 M NaClO 4 as ionic medium, at 25 o C). To our knowledge, the present work constitutes the first detailed equilibrium study of metal−metal bonded compounds; it indicates that also other cluster formation reactions described in the literature may represent real equilibria.