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COMPLEX IONS

COMPLEX IONS. Compounds in which metal ion is surrounded by a group of anions or neutral molecules. Metal Ions. . . . do not exist in isolation. are accompanied by anions whose negative charge balances the positive charge of metal ion, producing neutral compounds.

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COMPLEX IONS

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  1. COMPLEX IONS Compounds in which metal ion is surrounded by a group of anions or neutral molecules.

  2. Metal Ions. . . • do not exist in isolation. • are accompanied by anions whose negative charge balances the positive charge of metal ion, producing neutral compounds. • have empty valence orbitals therefore act as electron pair acceptors.

  3. Metal Ions. . . • act as Lewis acids. • Anions or molecules with unshared pairs of electrons can act as Lewis bases and bind to metal center. • ability to form complexes increases positive charge increases and size decreases. • Weakest complexes formed by alkali metals. • 2+ and 3+ ions of transition elements show greatest tendency to form complexes. • Cr 3+ forms more stable complexes than does Al 3+

  4. Ligands. . . • Molecules or ions surrounding the metal ion. • Are known as complexing agents. • Normally either anions or polar molecules. • Must have at least one unshared pair of valence electrons. • Therefore act as electron pair donors/Lewis bases.

  5. Coordination Sphere. . . The central metal and the ligands. [Cu(NH3)4]SO4 Placed inside brackets to set it off from other parts of the compound.

  6. Complex Ions. . . • Metal ions in water, the ligand is water. • In aqueous solution, ligands such as SCN- and CN- replace H2O in the coordination sphere. • Different properties than metal or ligands. • Color. • Oxidation state stabilized. Reduction potentials change.

  7. Charge. . . • Is the sum of the charges on the central metal and surrounding ligands. [Cu(NH3)4]SO4 SO4 = 2- (charge of the polyatomic ion) NH3 = 0 (molecule therefore no charge) Cu = 2+ (based on what is needed to balance the charges)

  8. Practice determining charges • 1. What is the oxidation number of the central metal in [Co(NH3)5Cl](NO3)2? • 2. What is the charge of the complex formed by a platinum (V) metal ion surrounded by three ammonia molecules and three bromide ions? • Write the formula for this complex ion. • 3. Given that a complex ion contains a chromium (III) bound to four water molecules and two chloride ions, write its formula.

  9. Nomenclature. . . • [Co(NH3)5Cl]Cl2 • In naming salts, the name of the cation is given before the name of the anion. • [Co(NH3)5Cl]2+ Cl- • Ligands are named before the metal. • [Co(NH3)5Cl]2+ • Ligands named in alphabetical order. • Do not consider charge or prefix. • In writing formula, metal is written first.

  10. Anionic ligands end in the letter o. Others bear the name of the molecule. LigandLigand Name Azide,N3- azido Bromide, Br- bromo Chloride,Cl- chloro Cyanide, CN- cyano Hydroxide, OH- hydroxo Carbonate,CO3 2- carbonato Oxalate, C2O4 2- oxalato

  11. Neutral Molecules. . . LigandLigand Name Ammonia, NH3 ammine Ethylenediamine, en ethylenediamine Water,H2O aqua CH3NH2 methylamine CO carbonyl NO nitrosyl

  12. A Greek prefix is used to indicate the number and kind of each ligand when more than one is present. [Co(NH3)5Cl]Cl2 Pentaammine If the name of the ligand contains a prefix, then the name of the ligand is enlosed in parentheses. Alternate prefixes are used bis-, tris-, tetrakis, petakis-, and hexakis for the name enclosed in the parentheses. [Co(en)3]Cl3 Tris(ethylenediamine)cobalt (III)

  13. Monodentate LigandUnidentate Ligand • Form one bond to the metal ion. • H2O • NH3 • NO2- • SCN- • OH- • X- (halides)

  14. Bidentate Ligand • Form two bonds to the metal ion. . . • Oxalate • Ethylenediamine Use bis-, tris-, tetrakis-, etc.

  15. If the complex is an anion, its name ends in –ate: K4[Fe(CN)6] • The suffix –ate is added to the latin stem. • [Fe(CN)6] 4- hexacyanoferrate (II) ion. • K4[Fe(CN)6] • Iron Ferrate • Copper cuprate • Lead plumbate • Silver argenate • Gold aurate • Tin stannate

  16. The oxidation number of the metal is given in parentheses in Roman numerals following the name of the metal. hexacyanoferrate (II) Tris(ethylenediamine)cobalt (III)

  17. Practice. . . [Ni(C5H5N)6]Br2 Hexapyridinenickel(II)bromide [Co(NH3)4(H2O)CN]Cl2 Tetraammineaquacyanocobalt(III)chloride Na2[MoOCl4] Sodium tetrachlorooxomolybdate(IV) Na[Al(OH)4] Sodium tetrahydroxoaluminate

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