Transition metal chemistry Coordination compounds – ligands and things Coordinate covalent bonds and ligands Nomenclature Isomerism Spectroscopy Electronic structure Coordinate covalent bond Lewis acid/base chemistry Lone pair on water (base) Vacancy on Fe2+ (acid) Positive, neutral, negative The complex can be an ion that forms part of a neutral compound square brackets delineate the complex Or may exist as a standalone neutral compound (no square brackets) NiNH 2 3 6 FeCN 6 3 Pt NH 3 2 Cl2 Things to consider Coordination number – the number of ligands around the central ion Geometry – the shape of the complex Much greater variety and complexity compared with the geometry of covalent molecules of the representative elements Examples of complexes with different coordination numbers Coordination number 2 3 4 5 6 7 8 Complex [Ag(NH3)2]+, [CuCl2][HgI3]- [Zn(NH3)4]2+, [Ni(CN)4]2[Ni(CN)5]-, Fe(CO)5 [Cr(H2O)6]3+, [Fe(CN)6]3[ZrF7]3[Mo(CN)8]4- Geometry - prelude Rules for determining geometry are more involved than the simple VSEPR approach that works well with covalent compounds Note: same composition may adopt different geometries Will be dealt with using ligand-field theory Things to know Overall charge Writing the correct formula M Lm X n ( M ) ( n ) Square bracket Number of neutral ligands Number of anion ligands Determining oxidation state on the central atom Complex charge - Sum of anion charges = o.s. Ligands – entities with teeth Must contain a lone electron pair Classify the ligands according to the number of available pairs Monodentate – one pair Bidentate – two pairs Polydentate – many pairs Common ligands and names in complex ions Anion Name Neutral Name ligand ligand Bromide Bromo Ammonia Ammine Carbonate Carbonato Water Aqua Chloride Chloro Carbon monoxide Carbonyl Cyanide Cyano Ethylene diamine Ethylene diamine Fluoride Fluoro Hydroxide Hydroxo Oxalate Oxalato Thiocyanate Thiocyanato/Iso thiocyanato Chelating – ligands with claws Ligands with greater than one lone pair can form more than one bond to a single metal ion Ethylene diamine (en)– tridentate EDTA - hexadentate Important biological entities (a) The structure of the porphine molecule. Loss of the two NH protons gives a planar, tetradentate 2– ligand that can bond to a metal cation. The porphyrins are derivatives of porphine in which the peripheral H atoms are replaced by various substituent groups. (b) Schematic of the planar heme group, the attached protein chain, and the bound O2 molecule in oxyhemoglobin and oxymyoglobin. The Fe(II) ion has a six-coordinate, octahedral environment, and the O2 acts as a monodentate ligand. What’s in a name Rules, rules, rules 1. If the compound is a salt, naming is as for common salts: cation first and then anion Potassium hexacyanoferrate(III) K 3 FeCN 6 Complex ion or neutral complex 2. Ligands first then metal Endings are the thing Anionic ligands end in –o -ide → -o; -ate → -ato Neutral ligands have normal names except… H2O (aqua), NH3 (ammine), CO (carbonyl) One word: nospacebetweenligandandmetal Diamminedichloroplatinum(II) Pt NH 3 2 Cl2 More than one ligand 3. Indicate number of ligands by prefixes: di-, tri-, etc. Ligands are listed in alphabetical order Tetraaquadichlorochromium(III) chloride CrH 2O4 Cl2 Cl It’s all Greek to me 4. If the ligand name contains a Greek prefix (ethylenediamine), the ligand name is in parantheses and use an alternative prefix: bis(2), tris-(3), tetrakis(4) Tris(ethylenediamine)cobalt(III) chloride Coen3 Cl3 Roman numerals 5. Roman numeral in parantheses to indicate oxidation state of metal in situation where the o.s. is variable -ate crimes 6. -ate is the conventional ending for the metal in an anionic complex Check table for exact wording Metal Anion Name Metal Anion Name Aluminium Aluminate Iron Ferrate Chromium Chromate Manganese Manganate Cobalt Cobaltate Nickel Nickelate Copper Cuprate Platinum Platinate Gold Aurate Zinc Zincate