Chemistry 223 Chapter 26 Coordination Complexes
d-block elements a.k.a. transition metals d-block elements are: • all metals • all have partially filled d subshells • exhibit horizontal & vertical similarities • alloys & compounds are important components of materials in modern world • most first-row transition metals are essential for life
General Trends among Transition Metals Going across row from left toright, e-’s are added to 3d subshell to neutralize increase in (+) charge of nucleus as atomic # increases.
General Trends among Transition Metals • 3dsubshellfill based on • aufbau principle & Hund’s rule • with two important exceptions:
Reactivity: Sizeof neutral atoms of d-block elements gradually decreases left torightacross a row. Why? Due to increase in Zeffwith increasing atomic # Atomic radius increases going down a column. Why?
Transition metals become less reactive (more “Noble”) going from left to right across a row
Trends in Transition Metal Oxidation States: Transition metals form cations by initial loss of ns e-’s, even though ns orbital is lower in energy than (n–1)d subshell in the neutral atom. d-electron configuration for di-cations of 1st row of transition metals
Trends in Transition Metal Oxidation States: Small E difference btwn ns and (n-1)d plus screening effect means less Elosing ns e-’s before (n-1)d e-’s All transition-metal cations possess dnvalence e- configurations for 2+ ions of 1st row.
Trends in Transition Metal Oxidation States: Electronegativities of first-row transition metals increase (somewhat) smoothly from Sc to Cu Sc Ti V Cr Mn Fe Co Ni Cu Zn 1.36 1.54 1.63 1.66 1.55 1.83 1.88 1.91 1.901.65
Trends in Transition Metal Oxidation States: maxoxid states for 2nd & 3rd row transition metals in Groups 3 thru 8 increase from +3 for Y and La to +8 for Ru and Os
Trends in Transition Metal Oxidation States: Going farther to right, maximum oxidation state decreases, reaching +2 for elements of Group 12,
Compounds of Mn in +2 to +7 oxidation states Different # of d electrons = different colors Why is that?
Coordination Compounds Metallic elements act as Lewis acids form complexes with various Lewis bases. Metal complex:
Coordination Compounds Central metal atom (or ion) bonded to one or more ligands. Ligands: Ligands
Coordination Compounds metal & ligand complexes asions:
Coordination Compounds Coordination compounds & complexes are distinct chemical species properties & behavior diff from metal atom / ion or the ligands
History of Coordination Compounds Coordination compounds used since ancient times, but chemical nature unclear. Werner: modern theory of coordination chemistry - based on studies of several series of metal halide complexes with ammonia
History of Coordination Compounds Werner postulated that metal ions have 2 different kinds of valence: primary valence(oxidation state) = secondary valence(coordination #)
Same chemical composition, same # of groups of same types attached to same metal. What made the two different colors?
Structures of Metal Complexes Coordination #’s of metal ions in metal complexes can range from 2to9. Differences in Ebtwn different arrangements of ligands greatest for complexes w/ low coordination #’s & decrease as coordination # increases.
Structures of Metal Complexes Only one or two structures possible for complexes w/ low coordination #’s. Several different energetically = structures are possible for complexes with high coordination #’s (n > 6)
Structures of Metal Complexes Coordination # 2 = linear Rare for most metals; common for d10 metal ions, especially: Cu+, Ag+, Au+, and Hg2+
Coordination # 4 Two common structures: tetrahedral& square planar Tetrahedral: all 4-coordinate complexes of • non-transition metals & • d10ions and first-row transition metals,
Coordination # 4 Two common structures: tetrahedral & square planar Square planar: 4-coordinate complexes of 2nd & 3rd row transition metals with d8e- configurations, e.g. Rh+ , Pt2+ and Pd2+, also encountered in some Ni2+ &Cu2+ complexes.
Structures of Metal Complexes Coordination # 6 Most common: six ligands at vertices of an octahedron or a distorted octahedron.
Other Structures of Metal Complexes Possible: Coordination # 3 Encountered with d10 metal ions e.g.Cu+ & Hg2+ trigonal planar structure Coordination # 5 geometries
… and 2nd & 3rd row transition metals 7, 8 & 9 coordination #’s, give other geometries:
Metal-ligand interaction is an example of Lewis acid-base interaction. Lewis acid Lewis base Lewis bases Must have
Transition metal ions tend to form coordination complexes which we encountered back in Chapter 22. e.g. AgClis more soluble in 0.10 M NH3 than it is in pure water because Ag+ forms a complex with NH3 with a very large formation constant: Ag+ + 2NH3 Ag(NH3)2+
The complex ion Ag(NH3)2+ that forms is called diamminesilver(I) (review rules on pp. 1055-1056). Why does it form? It forms because each NH3is a Lewis base and forms a coordinate covalent bond with the silver ion, Ag+, in solution The complex has a linear geometry.
to purify the Ag(NH3)2+complex ion & store it in a bottle it would need an anion to neutralize the charge e.g. diamminesilver(I) chloride, [Ag(NH3)2+]Cl or diamminesilver(I) nitrate: [Ag(NH3)2+]NO3.
[Ag(NH3)2+]Clor [Ag(NH3)2+]NO3. In these compounds, silver is ____________ NH3is ______________ and Cl or NO3 is ____________________. Ligandsare attached by ___________ bonds Counterionsare attached by _______ bonds!
Another complex formation reaction is: Co3+ + 6 NH3 Co(NH3)63+ Kf= [Co(NH3)63+] = 2.3 x 1033 [Co3+][NH3]6 This complex ion is called: This complex has an octahedral geometry.
Another example is: Cu2+ + 4 CN Cu(CN)42 Kf= [Cu(CN)42] = 1.0 x 1025 [Cu2+][CN]4 This complex ion is called This complex has a tetrahedral geometry.
A polydentate ligand is a chelating agent, complexes containing polydentate ligands: Ethylenediaminetetraacetate ion: hexadentate ligand
chelate effect: metal complexes of polydentateligands are more stable than complexes of chemically similar monodentate ligands.
Nomenclature (IUPAC) rules for • Naming coordination compounds: • Cation named before anion (as usual); but, transition metal atom in the complex • is named last • with oxidation state in • roman numerals in parentheses
Nomenclature (IUPAC) rules for • Naming coordination compounds: • Cation named before anion (as usual), no D; • anion ending for transition metal will be “ate” • e.g. Cobalt anion = • [Ni(NH3)6] (NO3)2 cation complex • K3[Co(Cl)6] anion complex
Anionic complex metal ending: Scandium = Scandate Titanium = Titanate Vanadium = Vanadate Chromium = Chromate Manganese = Manganate Iron = Ferrate Cobalt = Cobaltate Nickel = Nickelate Copper = Cuprate Zinc = Zincate
Special names for some transition metals in an anioncomplex