ELECTRON-TRANSFER REACTIVITY OF CUBOIDAL HETEROMETALLIC MO(3)MS(4) CLUSTERS IN AQUEOUS ACIDIC SOLUTIONS

Citation
Pw. Dimmock et al., ELECTRON-TRANSFER REACTIVITY OF CUBOIDAL HETEROMETALLIC MO(3)MS(4) CLUSTERS IN AQUEOUS ACIDIC SOLUTIONS, Inorganica Chimica Acta, 225(1-2), 1994, pp. 157-162
Citations number
30
Categorie Soggetti
Chemistry Inorganic & Nuclear
Journal title
ISSN journal
00201693
Volume
225
Issue
1-2
Year of publication
1994
Pages
157 - 162
Database
ISI
SICI code
0020-1693(1994)225:1-2<157:EROCHM>2.0.ZU;2-3
Abstract
Rate constants (25 degrees C) are reported for the first time for the oxidation of the cuboidal heterometallic Mo3CoS4 cluster, which in 2 M ClO4-/HClO4 solutions exists predominantly as the edge-linked double cube [{Mo3CoS4(H2O)(9)}(2)](8+). Reactions with one-equivalent oxidant s, the outer-sphere reagent [Co(dipic)(2)](-) (E degrees' = 0.75 V) (d ipic = pyridine-2,6-dicarboxalate) and hexaaqua Fe(III) (E degrees' = 0.77 V), have been studied, I = 2.00 M (LiClO4). Comparisons are made with rate constants already reported for the same two oxidants with [M o4S4(H2O)(12)](4+), and heterometallic cuboidal clusters [Mo3CrS4(H2O) (12)](4+), [Mo3FeS4(H2O)(10)](4+), [Mo3NiS4(H2O)(10)](4+), edge-linked [{Mo3PdS4(H2O)(9)}(2)](8+), [Mo3CuS4(H2O)(10)](4+) and [Mo3CuS4(H2O)( 10)](5+), all of which are derivatives of the trinuclear incomplete cu boidal Mo(IV)(3) cluster [Mo3S4(H2O)(9)](4+). Rate constants for the r eactions of [Co(dipic)(2)](-) (k(Co)) are independent of [H+] in the r ange 0.50-2.00 M. In the case of the Fe(III) oxidations (k(Fe)), the d ependence k(Fe) = k(a) + k(b)[H+](-1) is observed for all the clusters except [Mo4S4(H2O)(12)](4+). The term k(a) is assigned as an outer-sp here reaction of [Fe(H2O)(6)](3+), and k(b) as an inner-sphere reactio n of [Fe(H2O)(5)OH](2+). Linear correlations of log k(Co) versus log k (a), and log k(Co) versus log k(b), have slopes close to 1.0. Exceptio ns are the edge-linked [{Mo3PdS4(H2O)(9)}(2)](8+), and to a lesser ext ent the k(b) term for [{Mo3CoS4(H2O)(9)}(2)](8+). The correlation of l og k(Co) versus log k(b) values is unexpected since k(b) is for an inn er-sphere process. It can be concluded that electron transfer followin g OH- bridging of the Fe(III) to the heterometal atom is rate determin ing. Rate constants k(Co) and k(Fe) for [W3CuS4(H2O)(10)](5+), the fir st heterometallic cluster obtained from [W3S5(H2O)(9)](4+), also confo rm to the same two correlations.