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【文章內(nèi)容簡(jiǎn)介】 plexes log K 4 11 Stability Aspects: What governs stability ? 1. charge effects ? Rule of thumb: The higher the charge of the cation, the more stable the plex ? Biophysical reason: Charge rebination is favourable ? But see later: HSAB principle 12 2. Ionic radii ? Ionic radii are dependent on: – position in periodic system – charge (the higher, the smaller) – coordination number (the higher, the larger) ? If covalence (due to differences in electronegativity), steric hindrance etc. would not operate, z/r (charge/radius) would dictate order of stabilities ? In reality: seldom observed, only with very small ligands, . F 13 Hard and Soft Acids and Bases Hard Borderline Soft Acids: H+, Na+, K+, Mg2+, Ca2+, Cr3+, Fe3+, Co3+ Fe2+, Co2+, Ni2+, Cu2+, Zn2+ Cu+, Ag+, Au+, Pt2+, Pb2+, Hg2+, Cd2+ Bases: NH3, RNH2, H2O, OH, O2, ROH, RO, RCO2, PO43 ArNH2, Imidazole RS, RSR ? See Handout 14 Hard and Soft Acids 15 Stability Aspects: The IrvingWilliams Series ? Stability order for highspin divalent metal ion plexes ? Always peaks at Cu(II) ? Mn(II) always the minimum ? Underlying reasons: a) ionic radii b) LFSE Zn(II) 16 Stability Aspects: Interplay between HSAB principle and the IrvingWilliams Series: O,O N,N N,O S,N Cu Fe Figure from Sigel and McCormick, Acc. Chem. Res. 3, 201 (1970). X Y M log K ? Highspin M(II) plexes ? Bidentate ligands ? Trend more pronounced the softer the ligand 17 Competition with protons ? Both metal ions and H+ are positively charged and have an affinity for bases ? The actual concentration of a plex ML therefore
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