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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 2nd electron. Sc Ti V Cr Mn [Ar]4s23d1 [Ar]4s23d2 [Ar]4s23d3 [Ar]4s23d4 [Ar]4s23d5 Fe [Ar]4s23d6 Co Ni Cu [Ar]4s23d7 [Ar]4s23d8 25-1 [Ar]4s23d9 Zn [Ar]4s23d10 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 Fe2+ = Fe3+ = 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) CoSO4 = c) K3[Cr(CN)6] = b) [PtCl4]2- = d) [Fe(H2O)5(OH)]2+ = 25-2 Oxidation States of Transition Elements Large variety of oxidation states. First series (Period 4) form __ oxidation state (except Sc). Due to loss of the two ___ electrons. First series - can also lose ___ electrons. 3d and 4s energies are similar Highest oxidation state for the group 3B-7B metals is the ______________ . Common oxidation states are in bold face. 1. Corresponds to loss of all the valence s and d electrons. 2. Later transition metals - loss of all valence electrons is prohibited by the increasing value of ______. Coordination Compounds 25-3 ___________ - 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! Covalent bonding – monodentate – donates bidentate – donates pair of e- pairs of e- tetradentate – donates pairs of e- hexadentate – donates pairs of e- polydentate – donates more than 2 pairs of e25-4 Geometries and hybridizations (using VSEPR theory) for common coordination number are: Coordination # Hybridization Geometry Example 2 sp linear [Ag(NH3)2]+ 4 sp3 tetrahedral [Zn(CN)4]2- 4 dsp2 of sp2d square planar [Ni(CN)4]2- 5 dsp3 trigonal bipyrimidal [CuCl5]3- 5 d2sp2 square pyramidal [Ni(CN)5]3- 6 d2sp3 or sp3d2 octahedral [Fe(CN)6]4- skip naming coordination compounds section Some Important Ammine Complexes Complex ions are made by NH3 molecules bonded to metal ions. With a little NH3(aq) (aka NH4OH) is added, the hydroxide ppt will form. If more NH3(aq) is added, a complex ion will form with the metal ion. For example, Cu and Fe both react with aqueous NH3 to form hydroxides: Cu2+(aq) + 2 NH3(aq) + 2 H2O(l) Fe3+(aq) + 3 NH3(aq) + 3 H2O(l) Copper will form a complex ion while iron will not. Cu(OH)2(s) + 4 NH3(aq) Fe(OH)3(s) + NH3(aq) Some metal ions that form soluble ammine complexes in an excess of NH3 are: Cu+, Ag+ (with 2 NH3 molecules) Cu2+, Zn2+, Cd2+, Hg2+ (with 4 NH3 molecules) Co2+, Co3+, Ni2+, (with 6 NH3 molecules) 25-5 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(NH3)5(ONO)]2+ (NO2- ligand bonds through the ___________ atom) [Co(NH3)5(NO2)] 2+ (NO2- 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(NH3)4Cl2]Br2 __________ as counter ion [Pt(NH3)4Br2]Cl2 __________ as counter ion 25-6 Also can have one of each inside the coordination sphere 3. ______________________ – special case of ionization isomers where water molecules are switch between inside and outside the coordination sphere. [Cr(H2O)6]Cl3 6 waters bonded to metal ion [Cr(H2O)5Cl]Cl2·H2O 5 waters bonded to metal ion [Cr(H2O)4Cl2]Cl·2H2O 5 waters bonded to metal ion 4. ______________________ – denote an exchange of ligands between the coordination sphere of the cation and the anion [Pt(NH3)4][PtCl6] [Pt(NH3)4Cl2][PtCl4] 2 chlorides moved from the anion to the cation vs 25-7 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) relative orientations of their metal-ligand bonds. - have different 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 25-8 Octahedral cis-trans isomers of the type MA2B4. 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 MA3B3. ____ 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(NH3)3Cl3]+ 25-9 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. 25-10 25-11 25-12