Chapter 25 Transition Metals and Coordination Compounds Part 1 Introduction The transition elements are defined as: those metallic elements that have a partially but incompletely filled d subshell or easily give rise to common ions that have incompletely filled d subshells. Even though Cd, Zn, & Hg are in the d-block, they are not transition elements in the strict sense. Their chemistry will not be represented by our discussions. The f-block elements are sometimes referred to as the We will only be studying the elements Electron Configuration Review s subshell fills first (lower energy); d subshell filled according to Hund's rule. 1. Add one electron to each of the five d orbitals before adding a 2 nd electron. Sc Ti V Cr Mn [Ar]4s23d1 [Ar]4s23d2 [Ar]4s23d3 [Ar]4s23d4 [Ar]4s23d5 Fe Co Ni Cu Zn [Ar]4s23d6 [Ar]4s23d7 [Ar]4s23d8 [Ar]4s23d9 [Ar]4s23d10 25-1
Electron configurations depend on both and. 1. If two valence subshells have similar energies, can't always predict the configurations. 2. Exceptions from the expected orbital filling pattern result in either halffilled or completely filled subshells. 3. Five of the 19 exceptions: a. Group 6: Cr: [Ar] 4s13d5 b. Group 11: Cu: [Ar] 4s13d10 Transition-metal cations. 1. Valence electrons typically occupy the d orbitals. (s shell is emptied before d.) Example: Fe = [Ar]4s23d6 Fe 2+ = Fe 3+ = Oxidation States Determine the oxidation number for the transition metal in each of the following: All charge add to 0 for neutral compounds or to the ion charge for an ion. a) CoSO 4 = b) [PtCl 4 ] 2- = c) K 3 [Cr(CN) 6 ] = d) [Fe(H 2 O) 5 (OH)] 2+ = 25-2
Coordination Compounds Terminology of Transition Metal Complexes: - the molecule or ions that surround the central metal ion in a complex: the! (In Latin, ligare means to bind.) - the atoms attached directly to the metal ion. - the number of ligand donor atoms that surround a central metal ion in a complex. - Most common coordination numbers: and. of metal complex is determined by the metal ion's coordination number. (i.e. tetrahedral, octahedral, etc.) the central metal cation plus the ligands covalently bonded to it. - It is the part inside the [ ] of the formula - Not the part outside the [ ] that is ionically bonded! 25-3
monodentate donates pair of e - bidentate donates pairs of e - tetradentate donates pairs of e - hexadentate donates pairs of e - polydentate donates more than 2 pairs of e - 25-4
For polydentate ligands such as en, we form. The combined complex is known as a. A solution of the ligand is known as a. EDTA is often administered as a chelating agent to treat Geometries and hybridizations (using VSEPR theory) for common coordination number are: Coordination # Hybridization Geometry Example 2 sp linear [Ag(NH 3 ) 2 ] + 4 sp 3 tetrahedral [Zn(CN) 4 ] 2-4 dsp 2 of sp 2 d square planar [Ni(CN) 4 ] 2-5 dsp 3 trigonal bipyrimidal [CuCl 5 ] 3-5 d 2 sp 2 square pyramidal [Ni(CN) 5 ] 3-6 d 2 sp 3 or sp 3 d 2 octahedral [Fe(CN) 6 ] 4-25-5
skip naming coordination compounds section Some Important Ammine Complexes Complex ions are made by NH 3 molecules bonded to metal ions. With a little NH 3 (aq) (aka NH 4 OH) is added, the hydroxide ppt will form. If more NH 3 (aq) is added, a complex ion will form with the metal ion. For example, Cu and Fe both react with aqueous NH 3 to form hydroxides: Cu 2+ (aq) + 2 NH 3(aq) + 2 H 2 O (l) Fe 3+ (aq) + 3 NH 3(aq) + 3 H 2 O (l) Copper will form a complex ion while iron will not. Cu(OH) 2(s) + 4 NH 3(aq) Fe(OH) 3(s) + NH 3(aq) Some metal ions that form soluble ammine complexes in an excess of NH 3 are: Cu +, Ag + (with 2 NH 3 molecules) Cu 2+, Zn 2+, Cd 2+, Hg 2+ (with 4 NH 3 molecules) Co 2+, Co 3+, Ni 2+, (with 6 NH 3 molecules) 25-6
Structure and Isomerization Isomers Structural Isomers atoms are connected to one another in different ways (a.k.a. constitutional isomers) 1. - arise when a ligand can bond to a metal through either of two different donor atoms. [Co(NH 3 ) 5 (ONO)] 2+ [Co(NH 3 ) 5 (NO 2 )] 2+ (NO 2 - ligand bonds through the atom) (NO 2 - ligand bonds through the atom) 2. - isomers that differ in the anion that is bonded to the metal ion. Mistakenly called coordination isomers in TRO!!! [Pt(NH 3 ) 4 Cl 2 ]Br 2 [Pt(NH 3 ) 4 Br 2 ]Cl 2 as counter ion as counter ion Also can have one of each inside the coordination sphere 25-7
3. special case of ionization isomers where water molecules are switch between inside and outside the coordination sphere. [Cr(H 2 O) 6 ]Cl 3 [Cr(H 2 O) 5 Cl]Cl 2 H 2 O [Cr(H 2 O) 4 Cl 2 ]Cl 2H 2 O 6 waters bonded to metal ion 5 waters bonded to metal ion 4 waters bonded to metal ion 4. denote an exchange of ligands between the coordination sphere of the cation and the anion [Pt(NH 3 ) 4 ][PtCl 6 ] [Pt(NH 3 ) 4 Cl 2 ][PtCl 4 ] 2 chlorides moved from the anion to the cation vs 25-8
Stereoisomers atoms have the same connectivities but different spatial arrangement Note: Complexes with only simple ligands can occur as stereoisomes only if they have coordination number >. 1. (a.k.a Diastereoisomers) - have different relative orientations of their metal-ligand bonds. a) Descriptions cis isomer - identical ligands occupy adjacent corners of the square in a square planar complex trans isomer - identical ligands are across from one another in a square planar complex They are different compounds with different properties. Note: no cis-trans isomers exist for four coordinate tetrahedral complexes 25-9
Octahedral cis-trans isomers of the type MA 2 B 4. Two A ligands can be either on adjacent or on opposite corners of the octahedron. b) Octahedral Fac-mer isomers These occur in octahedral complexes with the general formula MA 3 B 3. isomer The three identical ligands all are on the same. isomer The three identical ligands all lie in a single line around the. Two such ions are shown for the ion [Pt(NH 3 ) 3 Cl 3 ] + 25-10
2. Optical Isomers (or enantiomers) Non-superimposable mirror images The molecule is said to be Chiral compounds interact with polarized light. The dextrorotatory isomer rotates plane-polarized light to the. (i.e. the right-handed isomer) The levorotatory isomer rotates plane-polarized light to the. (i.e. the left-handed isomer. Optically active compounds do NOT have a. The molecule to the left (where all 3 pairs are cis) can create a pair of optical isomers. For a tetrahedral molecule to show optical isomerism, it must have a central atom with different atoms attached to it. 25-11
25-12