Daniel L. Reger Scott R. Goode David W. Ball Chapter 19 Transition Metals, Coordination Chemistry, and Metallurgy
Transition Elements Transition elements are characterized by the presence of a partially filled d or f subshell in the metal atom or one of its oxidation states (Groups 3B through 1B). Characteristic properties of transition elements are: They are all high melting metals. Except for Group 3B, they all have two or more stable oxidation states. Most of their compounds are colored.
Oxidation States: Fourth Period The more common oxidation states are shown in black.
Coordination Compounds A coordination compound or complex is one that contains a metal ion bound to ligands by Lewis acid-base interactions. The Lewis bases bound to the metal ion are called ligands. The donor atom in a ligand is the one bound to the metal. The coordination number is the number of donor atoms that are bonded to the metal ion.
Coordination numbers of 2, 4 (two shapes), and 6 are common. Structural Formulas of Complexes
Most ligands are monodentate ligands - they donate only one pair of electrons to the metal atom. Common monodentate ligands are NH 3, H 2 O, CN -, CO, X - (X = F, Cl, Br, I), and NO 2 -. Chelating ligands have more than one atom that can form bonds to the same metal atom. The complexes formed by these ligands are called chelates. Ligands
Polydentate Ligands Ligands with two donor atoms are bidentate. Ethylenediamine (en) - NH 2 CH 2 CH 2 NH 2 oxalate - Diethylenetriamine is a tridentate ligand. NH 2 CH 2 CH 2 NHCH 2 CH 2 NH 2. EDTA 4- (ethylenediaminetetraacetate ion) contains six donor atoms - two nitrogen, and four oxygen. O O C C - O O -
Drawing Chelating Ligands A curved line connecting the donor atoms is often used to indicate chelating ligands, as shown here for [Co(en) 3 ] 3+.
Formulas of Coordination Complexes The metal and its coordinated ligands are enclosed in square brackets. [Co(NH 3 ) 5 Cl]Cl 2 shows that the five ammonia molecules and one chloride ion are ligands. [Fe(CN) 6 ] 4- is the formula of the ion commonly called ferrocyanide.
The ligands are named in alphabetical order, then the name of the metal, and finally the oxidation state of the metal, as a Roman numeral in parentheses. Write the names of the ligands and metal as a single word. Change the name of anionic ligands to end in the letter “o”; the names of neutral ligands are unchanged, except for aquo = H 2 O, ammine = NH 3, carbonyl = CO, and nitrosyl = NO. Naming Complexes
Naming Complexes (cont’d) Numbers of each ligand are given with the prefixes (1) mono (2) di (3) tri (4) tetra (5) penta (6) hexa. The name of the metal is used, except for anionic complexes, in which the ending is changed to “-ate”. The name of the complex [Cr(H 2 O) 4 Cl 2 ] + is tetraaquodichlorochromium(III). The name of the complex [Fe(CN) 5 NO] 2- is pentacyanonitrosylferrate(III).
Test Your Skill Name the complexes. (a) [Co(C 2 O 4 ) 3 ] 3- (b) [Rh(NH 3 ) 5 Cl] 2+ (c) [Ni(CO) 4 ]
Several categories of isomers are possible in coordination complexes Categories of Isomers
Structural Isomers Structural isomers contain the same numbers and kinds of atoms, but differ in the bonding. Coordination isomers differ in the Lewis bases bonded to the metal. [Pt(NH 3 ) 3 Cl]Br and [Pt(NH 3 ) 3 Br]Cl Linkage isomers contain the same ligand coordinated to the metal through a different donor atom. [Pd(NH 3 ) 3 SCN] + and [Pd(NH 3 ) 3 NCS] +
The NO 2 - bonded through the N atom (left) is called nitro; when bonded through the O atom (right) it is called nitrito. Linkage Isomers of NO 2 -
Properties of Coordination Complexes Coordination complexes exhibit a wide variety of colors, that depend on the metal, its oxidation state, and the ligands present. The observed colors result from the absorption of light in the visible region by the complexes. Paramagnetism, a property due to upaired electrons, is common among transition metal complexes.
In the lab Use of the analytical balances. Accuracy and precision Elimination of data T-test Excel Worksheet Used to determine compound