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Complex Ion Formation An Introduction to Complex Metal Ions Complex Ions and Ligands A complex ion consists of a central metal ion surrounded by some number of molecules or other ions (called LIGANDS) Ex: simple ligands include water (aquo), ammonia (ammine), chloride (chloro), cyanide (cyano), and hydroxide (hydroxo) ions. Ex: [Co(NH3)6]Cl3 COUNTER IONS can be found around the complex ion in order to create a neutral compound. In above ex, the Cl- are the counter ions. Simple Ligands What do each of these have in common? They each have active lone electron pairs in their outer energy levels. It is these pairs that form the coordinate covalent bonds with the metal ion. They are LEWIS BASES! T-metals as a Lewis Acid All ligands are lone pair donors (Lewis Base). The transition metal is accepting the lone pair in order to fill its d orbital with e-. Accepting lone pair means it acts as a Lewis acid. Note: The resulting lewis structures indicate this donation by replacing the single line (indicating a single bond) with an arrow showing the direction of donation). Co-ordinate Covalent Bonding REVIEW: A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is attracted by both of the nuclei. In the formation of a simple covalent bond, each atom supplies one electron to the bond. But that doesn't have to be the case! A co-ordinate bond is a covalent bond (a shared pair of electrons) in which both electrons come from the same atom (i.e. the lewis base ligand in coordination compounds!) Coordination Chemistry The number of ligands attached to the central metal ion determines the complex ion’s “coordination number” (cannot exceed 6). {Often the coordination number is 2x the oxidation number of the metal.} The are mostly anions (only rarely do complex cations form). The net charge on the coordination complex (the ion) is the sum of the charges of the metal and its attached groups. Practice… Give the formula of the following coordination complex… A Ni2+ ion is bound to 2 water molecules & 2 oxalate ions. 2[Ni(C2O4)2(H2O)2] net charge = 1(2+)2(2-) + 4 (neutral) = 2- Ex: Tetraamminediaquacopper(II) Cu2+ w/ 4 NH3 and 2 H2O Naming Complex Ions 1. To name any complex ion, list first the ligands, then the central atom. 2. The ligand names are made to end in -O if they are negative. Examples of ligand names are chloro, hydroxo, cyano, aqua (for H2O), ammine (for NH3), and thiosulfato (for S2O32-). 3. Anions that end in -ate and, when a Latin symbol is used for the element, the element takes the Latin name in anions but not in cations. For example, Cu(NH3)42+ is called the tetraamminecopper(II) ion but Cu(CN)64- is called the hexacyanocuprate(II) ion. Likewise Al(NH3)63+ is called the hexaamminealuminum(III) ion but Al(OH)4- is called the tetrahydroxoaluminate(III) ion. Naming Complex Ions 4. The number of each kind of ligand is specified by the usual Greek prefix. The ligands are named in alphabetic order. For example, Cu(Cl2Br2I2)4- is the dibromodichlorodiiodocuprate(II) ion while Cu(Cl2Br2INH3)4- is the amminedibromodichloroiodocuprate(I) ion. THIS IS ACTUAL ALPHA ORDER, NOT LIKE ORGO CHEM! 5. The oxidation state of the central metal atom to which the ligands are attached must be indicated. Naming Complex Ions Go for it… I dare you! 1. [Co(NH3)4Cl2]Cl 2. [Co(NH3)5Cl]Cl2 3. K3[Co(NO2)6] 4. [Pt(NH3)3Cl]2[PtCl4] 5. [Pt(NH3)4][PtCl4] 6. Reinecke's Salt, NH4[Cr(NH3)2(SCN)4] 7. Drechsel's Chloride, [Pt(NH3)6]Cl4 8. Cossa's First Salt, K[Pt(NH3)Cl3] 9. Cossa's Second Salt, K[Pt(NH3)Cl5] Naming Complex Ions 1. [Co(NH3)4Cl2]Cl: dichlorotetramminecobalt(III) chloride. 2. [Co(NH3)5Cl]Cl2: monochloropentamminecobalt(III) chloride. 3. K3[Co(NO2)6], known as Fischer's Salt: potassium hexanitritocobaltate(III). 4. [Pt(NH3)3Cl]2[PtCl4], known as Magnus' Pink Salt: di(monochlorotriammineplatinum(II)) tetrachloroplatinate(II). 5. [Pt(NH3)4][PtCl4], known as Magnus' Green Salt: tetrammineplatinum(II) tetrachloroplatinate(II). 6. Reinecke's Salt, NH4[Cr(NH3)2(SCN)4]: ammonium tetrathiocyanatodiamminechromate(III). 7. Drechsel's Chloride, [Pt(NH3)6]Cl4: hexammineplatinum(IV) chloride. 8. Cossa's First Salt, K[Pt(NH3)Cl3]: potassium trichloroammineplatinate(II). 9. Cossa's Second Salt, K[Pt(NH3)Cl5]: potassium pentachloroammineplatinate(IV) When Will a Complex Ion Form? Complex ions are usually formed from a transition metal ion surrounded by ligands (polar molecules or negative ions). As a “rule of thumb” you place twice the number of ligands around an ion as the charge on the ion. Examples: the dark blue copper-ammonia complex, Cu(NH3)42+ (ammonia is a test for Cu2+ ions) and AgCl2(solid AgCl dissolves when excess, concentrated HCl is added). Just so you know…. NOTE: Aluminum forms complex ions as do some of the post transition metals. NOTE: The names are very impressive, but easy… Just follow the naming conventions closely. + NOTE: Acid-base reactions may change NH3 into NH4 (or vice versa) which will alter its ability to act as a ligand. NOTE: Visually, a precipitate may go back into solution as a complex ion is formed. For example, Cu2+ plus a little NH4OH will form the light blue precipitate, Cu(OH)2. With excess ammonia, the complex, Cu(NH3)42+ forms. If a little HCl is + added, the NH3 becomes NH4 and no longer acts as a ligand; theCu(OH)2 will re-form. NOTE: Keywords such as “excess” and “concentrated” may indicate complex ions!!! When Will a Complex Ion Form? Watch for complex ion formation when double replacement does not form new compounds!!! For example, “Excess concentrated sodium hydroxide solution is added to a precipitate of zinc hydroxide”… Zn(OH)2 + 2NaOH Zn(OH)4 + 2 Na 2- + Last thing – Here are particles that generally combine with excess ligand (often water, hydroxide or ammonia) to form complex ions with a charge: Cu2+ + 4 NH3 [Cu(NH3)4]2+ Al3+ + 4 OH- [Al(OH)4]AgCl + 2 NH3 [Ag(NH3)2]+ + ClFe3+ + SCN- [Fe(SCN)]2+