Lecture22 - Chem 162, Lect 22, 2011 Coordination Compounds...

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Chem 162, Lect 22, 2011 Coordination Compounds (Complexes) Transition metal ions often form coordination compounds ; such compounds are often colored and paramagnetic . Color ….absorbs light in the visible part of the spectrum Paramagnetic ....species attracted to a magnetic field. ....means species has one or more unpaired (d or f) electrons on the metal ion Diamagnetic ....species repelled by a magnetic field. ....means species has all electrons paired Coordination Complex (complex ion): The result of a Lewis Acid (metal ion)-Lewis Base (ligand) reaction; the complex is held together by coordinate covalent bonds. Coordination compound : a (transition metal) ion with attached ligands, i.e., a complex ion (coordination complex) + counterions (anions or cations) needed to produce a compound with no overall net charge]. Alfred Werner, 'The Father of Coordination Chemistry' (1893, Nobel Prize 1913) EXAMPLES : CoCl 3 . 6NH 3 CoCl 3 . 5NH 3 CoCl 3 . 4NH 3 orange-yellow purple green(trans), purple(cis) Dissolve in H 2 O: 3 moles of Cl - per mole of CoCl 3 . 6NH 3 2 m o l e s o f C l - per mole of CoCl 3 . 5NH
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dissolve in H 2 O [Co(NH 3 ) 6 ]Cl 3 (s) Co(NH 3 ) 6 3+ (aq) + 3Cl - (aq) Hexaaamminecobalt(III) chloride (golden orange) Cation (before) Anion in Name Ligands --- alphabetical order (ignoring prefixes) dissolve in H 2 O [CoCl(NH 3 ) 5 ]Cl 2 (s) CoCl(NH 3 ) 5 2+ (aq) + 2Cl - (aq) Pentaamminechlorocobalt(III) chloride (purple) Cation (before) Anion in Name Ligands ---alphabetical order (ignoring prefixes) dissolve in H 2 O [CoCl 2 (NH 3 ) 4 ]Cl(s) CoCl 2 (NH 3 ) 4 2+ (aq) + Cl - (aq) tetraamminedichlorocobalt(III) chloride (green or purple or mix) Cation (before) Anion in Name Ligands ---alphabetical order (ignoring prefixes) Werner suggested 'octahedral coordination' of the ligands around the Co(III) metal ion in the complexes above. A complex ion consists of a central metal cation surrounded by several ligands. Ligand: Lewis base (negatively charged ion or a neutral species
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Lecture22 - Chem 162, Lect 22, 2011 Coordination Compounds...

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