Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Bond valence method wikipedia , lookup
Oxidation state wikipedia , lookup
Jahn–Teller effect wikipedia , lookup
Hydroformylation wikipedia , lookup
Cluster chemistry wikipedia , lookup
Metal carbonyl wikipedia , lookup
Spin crossover wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Metalloprotein wikipedia , lookup
Chemistry 1000 Lecture 23: Introduction to transition metal chemistry Marc R. Roussel The transition metals I d and f blocks of periodic table Sc [Ar]3d1 4s2 Y [Kr]4d1 5s2 Lu [Xe]4f14 5d1 6s2 La [Xe]5d1 6s2 Ac [Rn]6d1 7s2 Ti [Ar]3d2 4s2 Zr [Kr]4d2 5s2 Hf [Xe]4f14 5d2 6s2 Ce [Xe]4f2 6s2 Th [Rn]6d2 7s2 V [Ar]3d3 4s2 Nb [Kr]4d4 5s1 Ta [Xe]4f14 5d3 6s2 Pr [Xe]4f3 6s2 Pa [Rn]5f2 6d1 7s2 Nd [Xe]4f4 6s2 U [Rn]5f3 6d1 7s2 Cr [Ar]3d5 4s1 Mo [Kr]4d5 5s1 W [Xe]4f14 5d4 6s2 Pm [Xe]4f5 6s2 Np [Rn]5f4 6d1 7s2 Mn [Ar]3d5 4s2 Tc [Kr]4d5 5s2 Re [Xe]4f14 5d5 6s2 Sm [Xe]4f6 6s2 Pu [Rn]5f6 7s2 Eu [Xe]4f7 6s2 Am [Rn]5f7 7s2 Fe [Ar]3d6 4s2 Ru [Kr]4d7 5s1 Os [Xe]4f14 5d6 6s2 Gd [Xe]4f7 5d1 6s2 Cm [Rn]5f7 6d1 7s2 Co [Ar]3d7 4s2 Rh [Kr]4d8 5s1 Ir [Xe]4f14 5d7 6s2 Tb [Xe]4f9 6s2 Bk [Rn]5f9 7s2 Ni [Ar]3d8 4s2 Pd [Kr]4d10 Pt [Xe]4f14 5d9 6s1 Dy [Xe]4f10 6s2 Cf [Rn]5f10 7s2 Ho [Xe]4f11 6s2 Es [Rn]5f11 7s2 Cu [Ar]3d10 4s1 Ag [Kr]4d10 5s1 Au [Xe]4f14 5d10 6s1 Er [Xe]4f12 6s2 Fm [Rn]5f12 7s2 Zn [Ar]3d10 4s2 Cd [Kr]4d10 5s2 Hg [Xe]4f14 5d10 6s2 Tm [Xe]4f13 6s2 Md [Rn]5f13 7s2 Yb [Xe]4f14 6s2 No [Rn]5f14 7s2 Chemistry of the transition metals I Electronegativities range from 1.1 (La, Ac) to 2.4 (W, Au) I Many transition metal (TM) compounds are essentially covalent I TM atoms/ions typically act as Lewis acids I Rough rule: TMs form ionic compounds in lower oxidation states, covalent compounds in higher oxidation states [Ar]3d104s2 [Ar]3d104s1 [Ar]3d8 4s2 [Ar]3d7 4s2 [Ar]3d6 4s2 [Ar]3d5 4s2 [Ar]3d5 4s1 [Ar]3d3 4s2 [Ar]3d2 4s2 [Ar]3d1 4s2 I Common and less common oxidation states: Sc Ti V Cr Mn Fe Co Ni Cu Zn +1 +2 +3 +4 +5 +6 +7 Complexes and ligands Coordinate bond: bond made between a metal ion and a Lewis base This can almost always be considered to be an ordinary polar covalent bond. The special name only serves to emphasize that coordinate bonds are typically easier to rearrange than other covalent bonds. Coordination complex: complex molecule or ion consisting of a central metal atom or ion acting as a Lewis acid with coordinate bonds to one or (usually) several Lewis bases Ligand: one of the Lewis bases in a coordination complex Complexes and ligands (continued) Coordination number: number of coordinate bonds formed by a metal centre A given metal ion in a given oxidation state typically has a preferred coordination number found in most of its compounds. I Coordination complexes do not obey the VSEPR rules. Rather, the shape is connected to the coordination number. I I Coordination number 6 gives octahedral complexes. Coordination number 4 gives either tetrahedral or square planar complexes. Example: Chloro-anions I Many metal ions form complex anions with chloride ions. I Some examples: Complex [CdCl4 ]2− [HgCl4 ]2− [PtCl4 ]2− [PbCl3 ]− [AgCl2 ]− [CuCl3 ]2− Metal oxidation state 2 2 2 2 1 1 Example: Ammine-cations I Many metal ions form complex cations with ammonia. I Some examples: Complex [Co(NH3 )6 ]3+ [Co(NH3 )6 ]2+ [Ni(NH3 )6 ]2+ [Cd(NH3 )4 ]2+ [Cu(NH3 )4 ]2+ Metal oxidation state 3 2 2 2 2 Square bracket notation I In the preceding examples, you may have noticed that coordination complexes are shown in square brackets. I This is important since it makes the connectivity clear: The metal atom/ion and its ligands are shown in square brackets together. Complex salts A complex ion is a coordination complex with a net charge. A complex salt is a compound in which at least one of the ions is a complex ion. Examples with simple counterions: I Na [CdCl ] 2 4 I [Co(NH ) ]Cl 3 6 3 Note that we list the cation first, then the anion. The following pairs of compounds are different: I [Co(NH ) Br]SO and [Co(NH ) SO ]Br 3 5 4 3 5 4 I [Co(NH ) ][Cr(CN) ] and [Cr(NH ) ][Co(CN) ]. 3 6 6 3 6 6 Monodentate ligands Monodentate: literally, having one ‘tooth’ I These are ligands that coordinate only once to a metal. I Examples of monodentate ligands: F− , Cl− , Br− , I− , OH− , H2 O, NH3 , CO I Note that these are all Lewis bases, but not necessarily Brønsted bases. For example, Cl− is a Lewis base, but it is not a Brønsted base. How do we know that Cl− is not a Brønsted base? Polydentate ligands Bidentate: coordinates twice to a metal, i.e. can donate lone pairs from two different atoms Polydentate: coordinates more than once to a metal Denticity: number of donor atoms in a ligand through which it coordinates Polydentate ligands (continued) Structure .. :O: .. O .. Denticity Abbreviation 2− C 1 or 2 CO2− 3 2 ox2− 2 en 2 phen :O: .. :O: 2− :O: C C :O: .. :O: .. H 2C CH2 H2 N .. N ..H2 N .. ..N C CH2 .. N .. :O .. C C H2 :O: 4− :O: :O: .. :O .. C H2 CH 2 CH 2 C .. O: .. CH 2 C .. O: .. .. N :O: 6 EDTA4− Chelates Chelate: a complex in which a bidentate or polydentate ligand forms a closed ring with a metal atom by forming two or more coordinate bonds Chelating agent: a ligand that can form chelates Examples of chelates: I Chelates tend to be much more stable than similar complexes containing monodentate ligands (chelate effect). Example: 2+ Cu2+ (aq) + 4NH3(aq) [Cu(NH3 )4 ](aq) 2+ Cu2+ (aq) + 2en(aq) [Cu(en)2 ](aq) K = 1.1 × 1013 K = 1.0 × 1020 I Chelation makes ions unavailable in solution. Applications: Added to detergents to reduce water hardness (EDTA) Food additive to prevent catalysis of oxidation by metal ions (EDTA) Chelation therapy for metal poisoning, esp. hypercalcemia, mercury or lead poisoning (dimercaptosuccinate) .. :S :O: .. :O .. C .. :O: CH CH C :S .. :O: H 2− H Isomerism Isomers are compounds with the same chemical formula (same atoms), but arranged differently. Structural isomers differ in what is bonded or coordinated to what. Stereoisomers have identical chemical bonds, but are arranged differently in space. Linkage isomerism: an example of structural isomerism Linkage isomers contain a ligand coordinated to the metal centre through different donor atoms. Example: O O 2+ N N H3N Co H3N O O NH3 NH3 NH3 yellow-orange H3N and Co H3N NH3 NH3 NH3 red-orange 2+ Some types of stereoisomerism Geometrical isomers have identical bonds, but the distances between some nonbonded atoms are different due to a different arrangement of the bonds in space. I In square planar complexes with chemical formula MX2 Y2 or in octahedral complexes with formula MX2 Y4 , the two X ligands can be adjacent (cis) or opposed (trans). Example: NH3 Cl Cl Pt NH3 NH3 cis (cisplatin) and Cl Pt Cl NH3 trans (transplatin) Example: + NH3 H 3N Co Cl Cl H 3N NH3 cis + NH3 Cl NH3 Co and Cl H 3N NH3 trans I In octahedral complexes with formula MX3 Y3 , the three X ligands can be in the same face of the octahedron (fac) or along a meridian (mer): Example: NH3 H 3N NH3 O 2N NH3 Co O 2N NH3 Co NO 2 NO 2 fac and O 2N NO 2 NH3 mer