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Complex Ions and Coordination Compounds Nomenclature 1. A complex ion consists of a central metal cation (usually derived from a transition metal) joined by coordinate covalent bonds to molecules or anions called ligands. Complex ions can be cations or anions. The coordination number is the number of places on the metal ion where ligands are bound. The bond between the metal ion and the ligand, where the ligand supplies both electrons, is known as a coordinate covalent bond. Most metal ions exist as water complexes in water solution. For example, Cu+2 is not a bare ion in water: rather, it exists as the Cu(H2O)6+2 ion. Complex Ion Ag(NH3)2+ Cu(H2O)42+ Fe(CN)63- Central Metal Cation Ag+ Cu2+ Fe3+ Ligands 2 NH3 molecules 4 H2O molecules 6 CN- ions Coordination Number (# of bonds) 2 4 6 2. Compounds composed of a complex ion and counter ions are coordinate compounds. Complex ions are often enclosed in brackets. Coordinate compounds are usually colored. Coordinate Complex Ion Compound [Cu(H2O)4]SO4 Cu(H2O)42+ Counter Ion SO42- [Ag(NH3)2]NO3 Ag(NH3)2+ NO3- K3[Fe(CN)6] Fe(CN)63- K+ 3. Ligands: ordinarily contain at least one unshared pair of electrons Note: Ligands are Lewis Bases, Metals are Lewis Acids. If the ligand contains two or more unshared pairs on different, nonadjacent atoms, it can act as a chelating agent, forming more than one bond with the central metal atom. Rhonda Alexander Robert E. Lee High School, Tyler, TX 2 4. Nomenclature of Complex Ions and Coordination Compounds The naming of complex cations and complex anions is similar, except that anions are always made to end in -ate. Coordination compounds, like simpler inorganic compounds, are named with the cation preceding the anion regardless of which one of them is a complex ion. The Rules for Naming Coordinate Compounds: I. Cation name precedes anion name II. Naming complex ion: Ligands are listed first then central metal ion. Negative ligand are often named by replacing the ion ending with an –o. (chloro, bromo, nitrito, etc.). Examples of ligand names are chloro, hydroxo, cyano, aqua (for H2O), ammine (for NH3), and thiosulfato (for S2O32-). Ligands Names Not Ending in –o: H2O - aqua NH3 - ammine CH3NH2 - methylamine CO - carbonyl NO - nitrosyl The number of each kind of ligand is specified by the usual Greek prefix. The ligands are named in alphabetic order. Prefixes are not used to alphabetize. Rhonda Alexander Robert E. Lee High School, Tyler, TX 3 The oxidation state of the central metal ion is designated by a Roman numeral in parentheses. If the complex is the anions the complex name must end in –ate. When a Latin symbol is used for the element, the element takes the Latin name in anions but not in cations. For example: 1. Central metal have a Latin symbol: Cu(NH3)42+ is called the tetraamminecopper(II) ion but Cu(CN)64- is called the hexacyanocuprate(II) ion. 2. Central metal does not have a Latin symbol: Al(NH3)63+ is called the hexaamminealuminum(III) ion but Al(OH)4- is called the tetrahydroxoaluminate(III) ion. Latin Names Used for Metals in Anionic Complex Ions Iron Ferrate Copper Cuprate Pb Plumbate Silver Argentate Gold Aurate Tin Stannate Example. 1. 2. 3. 4. 5. 6. 7. 8. 9. [Co(NH3)4Cl2]Cl: dichlorotetramminecobalt(III) chloride. [Co(NH3)5Cl]Cl2: monochloropentamminecobalt(III) chloride. K3[Co(NO2)6]: potassium hexanitritocobaltate(III). [Pt(NH3)3Cl]2[PtCl4: di(monochlorotriammineplatinum(II)) tetrachloroplatinate(II). [Pt(NH3)4][PtCl4]: tetrammineplatinum(II) tetrachloroplatinate(II). NH4[Cr(NH3)2(SCN)4]: ammonium tetrathiocyanatodiamminechromate(III). [Pt(NH3)6]Cl4: hexammineplatinum(IV) chloride. K[Pt(NH3)Cl3]: potassium trichloroammineplatinate(II). K[Pt(NH3)Cl5]: potassium pentachloroammineplatinate(IV) Rhonda Alexander Robert E. Lee High School, Tyler, TX