Transition Metals (Ligands)

Labs

Dry Lab 5 Preface to Qualitative Analysis

#34/35/36/37 Common Anions/Qualitiataive I/II/III

#38 Transition Metal Chemistry

Chemical Equations

Chapter 5, 13

Characteristics of Transition Metals

• Representative elements show similarities in groups, but changes occur within period as # valence electrons changes

• Chemical/physical properties of transition metal elements vary only slightly across period/ within given group

• Difference due to inner electrons being last electrons added

– Inner d/f electrons cannot participate as easily in bonding as valence s and p electrons

– Chemistry of transition elements not affected as greatly by gradual change in # electrons as representatives

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• Hard, tough and strong (compared to IA)

– Due to strong metallic atom-atom bonding

• Typical metallic characterisctics– 1st row-in general, electrical conductivity increases

• Ag best conductor of heat/electric current• Cu close 2nd

• High MP/BP– Bonding between atoms very strong– Only weakened at high Ts– Mercury liquid at room T (very low MP)

• High density – Due to strong bonding between atoms– 1st row-shows steady increase with exception of zinc

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• Oxidation states– Variability due to similar energy in 4s/3d subshells

• Atom form ions of roughly same stability by losing different numbers of electrons

• +3 oxidation states more stable at beginning of series, but +2 oxidation states more stable toward end

– Nickel, copper, zinc• Only have s electrons available• Requires too much energy to strip d electrons away• Fewer oxidation states available

– Vanadium, chromium, manganese• Many common oxidation states from availability of s/d electrons

– Some elements exhibit +4 state, and Mn even shows +5, +6, and +7

• Transition metals usually exhibit their highest oxidation states in compounds with oxygen, fluorine, or chlorine

– KMnO4 and K2Cr2O7 examples

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• Atomic Radius– Representative elements decrease across period– Transition metals decrease only slightly across period

• Consistent w/increase in effective nuclear charge as atomic number increases– Greater the charge, smaller the atom

• All 1st row transition elements have 4s orbitals as outermost occupied orbitals– Radius decreases, then increase after iron

• Ionization Energy– 1st IE of 1st transition metal series remarkably similar,

increasing very gradually from left to right– Slight increase over 1st 5 elements then IE barely

changes from Fe to Cu

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• Effective nuclear charge experienced by outermost electrons depends on shielding provided by inner electrons– Nuclear charge increases from scandium to

copper (electrons added to inner 3d subshell)

– 3d electrons shield 4s electrons from increasing nuclear charge for most part

– Consequently 4s electrons of 1st row transition elements feel only slightly increasing effective nuclear charge as atomic number increases, and atomic radii makes only gradual decrease

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• Other properties, including chemical reactivity, show great differences

– Less reactive than IA/IIA• Do not react as quickly w/water or oxygen so

they do not corrode as quickly• Iron forms oxides that scale off, constantly

exposing new metal to corrosion• Others do not readily form oxides (noble metals-

Au, Ag, Pt, Pd)

– Greater strength than IA/IIA-used as alloys• Some form oxides that adhere tightly to metallic

surface (Cr, Ni, Co), protecting metal from further oxidation

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• In forming ionic compounds w/nonmetals– More than one oxidation state is often found– Cations are often complex ions (transition

metal ion is surrounded by certain # of ligands-molecules or ions that behave as Lewis bases)

– Most compounds are colored, because transition metal ion in complex can absorb visible light of specific wavelengths

– Many compounds paramagnetic (contain unpaired electrons)

1. Sc/Zn- scandium (ScCl3)/Zinc (ZnSO4) salts are colorless/ not typical of transition metals

2. Ti - titanium(III) chloride, TiCl3, is purple

3. Cr - chromium(III) sulfate, Cr2(SO4)3, is dark green (chromate(VI) salts are yellow, dichromate(VI) salts are orange)

4. Mn – manganese -  potassium(VII) permanganate, KMnO4, is purple (manganese(II) salts-MnCl2-pale pink)

5. Iron(II) compounds usually light green/Iron(III) compounds orange/brown

6. Co - cobalt sulfate, CoSO4, is pinkish

7. Ni - nickel chloride, NiCl2, is green

8. Cu – most common copper compounds [copper(II) sulfate, CuSO4] are blue in crystals/solution and sometimes green

9. V - vanadium(III) chloride, VCl3, is green 9

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Electron Configuration Exceptions

• Electrons are removed from 4s orbital before they are taken out of 3d

– Energies of 3d/4s orbitals are not as close together in ions of transition metals as in neutral atoms

– In ions of transition elements, 3d orbitals are lower in energy than 4s orbitals

– Therefore, electrons most easily lost are those in outermost principal energy level, the ns

– Additional electrons may then be lost from (n – 1)d orbital

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Complex Ions

Ligands

Definitions:• Coordination compound

– Complex ion and counter ions– Are neutral

• Complex ion– Central transition metal with attached ligands– Has net charge (+/-)– Complex is set off in brackets that isolate it from the

rest of compound– Ions outside brackets-free (uncomplexed) ions– Metal cation-central atom

• Counter ions– Anions/cations needed to balance charge so it has no

net charge

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• Ligand (complexing agent)– Neutral molecule or anion w/lone pair that can

be used to form bond to central metal ion

• (Mono)Unidentate ligand– Can form one bond to metal ion – One donor atom present and can occupy only

one site in coordination sphere• Even if more than one pair of electrons available, if

donation of one pair does not allow for proper positions to make additional bonds, other pairs don’t bond

– Halide ions, SCN- (thiocyanate ions), anions of weak acids

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• Bidentate ligand– 2 donor atoms present and can occupy 2 or

more coordination sites (2 bonds to metal ion)– Most common (diamines/anions of diprotic organic acids)

• (Multi)Polydentate ligand (tri/tetra/hexa)– Can form more than two bonds to metal ion – Appear to grasp metal between 2 or more donor

atoms, called chelating agents (Greek “claw”)

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• Bidentate/polydentate ligands-chelating ligands– Extra stable because two bonds must be broken to

separate metal from ligand– EDTA4

• Excellent chelating ligand• Ethylenediaminetetraacetic acid• Has 6 pairs of electrons to donate

– Molecule flexible enough to allow each of 6 pairs to form bonds with metal ion

• Important for chemical analysis of metal ions using simple titration methods, found in many cosmetics, drugs, foods as preservative by forming complexes with metal ions, acts as catalysts to promote oxidation

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• Ligands:– Coordination sphere of metal-metal

ions/ligands within brackets– Normally either negative ion/polar molecule– Must contain at least one lone pair of

electrons that can serve as electron-pair donors or Lewis bases

– Metal ions (particularly transition metal ions) have vacant valence orbitals which can serve as electron-pair acceptors or Lewis acids

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• Part of ligand that bonds directly with metal-donor atom

– [Co(NH3)5Cl]2+-5 N atoms and 1 Cl atom serve as

donor atoms for Co

• Number of donor atoms surrounding central metal atom-coordination number of the metal

– Above, there are 6 donor atoms, so Co has a coordination number of 6

– Coordination number of a metal is equal to twice its charge-there are many exceptions to this rule, but this can be helpful in completing an equation in reaction question on AP exam

• Coordination number:– Number of bonds formed by metal ions to ligands in

complex ions varies from 2-8 depending on size, charge, electron configuration of transition metal ion

– Many metal ions have more than one– 2 ligands give linear structure, 4-tetrahedral or square

planar, 6-octahedralTypical Coordination #s for some common metal ionsM+ Coor. #s M2+ Coor. #s M3+ Coor. #s Cu+ 2, 4 Mn2+ 4, 6 Sc3+ 6Ag+ 2 Fe2+ 6 Cr3+ 6Au+ 2, 4 Co2+ 4, 6 Co3+ 6

Ni2+ 4, 6 Au3+ 4Cu2+ 4, 6Zn2+ 4, 6

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Examples• [Ag(NH3)2]Cl and K3[Fe(CN)6]

– Complex ion is shown enclosed in brackets– In the silver compound, Cl– is a free chloride

ion, and in the iron compound each K+ is a free potassium ion• K+ and Cl– ions are examples of counter ions

which serve to balance or neutralize the charge of the complex ion

– Coordination number of Pt2+ in [Pt(NH3)4] 2+ is

4, and that of Co2+ in [Co(NH3)6] 2+ is 6.

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Common ligands• Polar molecules:

– Aquo H2O

– Ammine NH3

– Carbonyl CO• Nitrosyl NO

• Neutral Molecules:– Methylamine CH3NH2

– Ethylenediamine (en) H2NCH2CH2NH2

• Anions:– Fluoro-/chloro-/bromo-/iodo- F-/Cl–/Br–/l– – Cyano CN–

– Hydroxo OH–

– Thiosulfato S2O32-

– Carbonato CO32-

– Oxalato C2O42-04/10/23

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Naming complex ions• Ligands named before central metal atom• Anionic ligands names end in “o”

– ide o chloride chloro– ate ato sulfate sulfato

• Neutral ligands named as molecule except– H2O aquo/NH3 ammine/CO carbonyl

• # ligands in complex use Greek prefixes– di for 2/tri for 3/tetra for 4/penta for 5/hex for 6– Prefixes bis-, tris-, tetrakis-, etc. used when other are

already used

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• Name of cationic complex ion ends in name of central metal ion w/oxidation state shown as Roman numeral in () at end of metal’s name

• Name of anionic complex ion ends in “ate,” sometimes Latin name used– chromium(II) chromate(II)– nickel(II) nickelate(II)– platinum(II) platinate(II)– Iron(II) ferrate(II)– Copper(I) cuprate(I)– Lead(II) plumbate(II)– silver=argentate– Gold(I) aurate(I)– Tin(IV) stannate(IV)

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Writing Formula of a Complex

1. Identify central metal ion2. Identify charge on central metal ion in ()3. Identify ligands4. Identify # ligands5. Calculate total chare on ligands6. Calculate charge on complex ion

– Charge on metal ion + total charge on ligands

7. Ligands written first, then central metal ion8. When more than one type of ligand present,

name alphabetically (prefixes don’t affect order)

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Name complex ion w/formula Fe(CN)63-

• Anionic ligands have names ending in 'o'– CN- named as cyano

• # ligands in complex specified using Greek prefix– 6 ligands = hexa → hexacyano

• Oxidation state of central metal atom shown w/Roman numeral in parantheses at end of metal's name– Central metal ion is iron

– Charge on iron: 3- = x + (6 x 1-)

– 3- = x -6

– x = 3+

– Central metal ion: iron (III)

• Complex ion is anion, therefore name will end in ferrate (III) • Ligands named before central metal ion:

– hexacyanoferrate (III) 04/10/23 25

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FormulaLigandName

No. of Ligandsand prefix

Central IonName

Complex Ion Name

Ag(NH3)2+ ammine 2 → di

silver (I)(+1= x + 2(0), x = +1)

diamminesilver (I) ion(complex is a cation)

Ag(CN)2- cyano 2 → di

silver (I) → argentate (I)(-1= x + 2(-1), x = +1)

dicyanoargentate (I) ion(complex is an anion)

Cu(H2O)62+ aquo 6 → hexa

copper (II)(+2= x + 6(0), x = +2)

hexaaquocopper (II) ion(complex is a cation)

CuCl42- chloro 4 → tetracopper (II) → cuprate (II)

(-2= x + 4(-1), x = +2)tetrachlorocuprate (II) ion

(complex is an anion)

Write formula for complex ion tetraamminecopper (II)

• Identify central metal ion : copper, Cu • Identify charge on central metal ion in (): 2+

• Identify ligands: ammine = NH3 (neutral species)

• Identify # ligands: tetra = 4 • Calculate total charge on ligands = 4 x 0 = 0 • Calculate charge on complex ion = charge on metal

ion + total charge on ligands = 2+ + 0 = 2+ • Write formula giving central metal ion first followed

by ligands : Cu(NH3)42+

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NameCentral Ion

FormulaLigand

FormulaNo. of

LigandsComplex Ion

Formula

hexaaquocobalt (II) ion

Co2+

(charge in parentheses)

H2O(aquo = H2O)

hexa = 6Co(H2O)6

2+

(4 x 0 +2 = +2)

tetrachlorocobaltate (II) ion

(ate = anion)

Co2+

(charge in parentheses)

Cl-

(chloro = Cl-)tetra = 4

CoCl42-

(4 x -1 + 2 = -2)

tetracarbonylnickel (II) ion

Ni2+

(charge in parentheses)

CO(carbonyl = CO)

tetra = 4Ni(CO)4

2+

(4 x 0 + 2 = +2)

tetracyanonickelate (II) ion

(ate = anion)

Ni2+

(charge in parentheses)

CN-

(cyano = CN-)tetra = 4

Ni(CN)42-

(4 x -1 +2 = -2)

K2[Ni(CN)4]

• Name cation-potassium

• Name anion-potassium tetracyano

• Oxidation state of central atom-potassium tetracyanonickelate(II)

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[Co(NH3)2(en)2]Cl2

• Name ligands first in alphabetical order-diamminebis(ethylenediamine)

• Name central atom w/oxidation number-diamminebis(ethylenediamine)cobalt(II)

• Name anion- diamminebis(ethylenediamine)cobalt(II)chloride

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• [CoI(NH3)5]Cl2 • pentaammineiodocobalt(III) chloride • [Cu(NH3)4]SO4 • tetraamminecopper(II) sulfate• [CrCl(en)2(H2O)]Cl2• aquachlorobis(ethylenediamine)chromium(III) chloride• (NH4)2[CdCl4] • ammonium tetrachlorocadmate(II)• Na[Rh(EDTA)] • sodium ethylenediaminetetraacetatorhodate(III)• [Pd(en)2][CrCl4(NH3)2]• bis(ethylenediamine)palladium(II)diamminetetrachlorochr

omate(III) • K3[Fe(ox)(ONO)4] • potassium tetranitritooxalatoferrate(III)04/10/23 31

• Ag(NH3)2]+

• diamminesilver(I) • [RuCl5(H2O)]2- • aquapentachlororuthenate(III) • [Fe(CN)6]4- • hexacyanoferrate(II) • Na4[Ni(C2O4)3] • sodium tris(oxalato)nickelate(II) • (NH4)2[CuBr4] • ammonium tetrabromocuprate(II) • [Co(NH3)5Cl](NO3)2 • pentaamminechlorocobalt(III) nitrate • [Co(H2O)6]I3 • hexaaquacobalt(III) iodide • K2[PtCl4]• potassium tetrachloroplatinate(II)

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• Potassium hexafluorocobaltate (III)• K3[CoF6]• tetraamminechloronitrocobalt(III) chloride • [CoClNO2(NH3)4]Cl• tris(ethylenediamine)nickel(II) sulfate • [Ni(en)3]SO4

• tetramminedichloroplatinum(IV) tetrachloroplatinate(II) • [PtCl2(NH3)4][PtCl4]• tris(ethylenediamine)cobalt(II) nitrate• [Co(en)3](NO3)2

• cobalt(II) hexanitrocobaltate(III)• Co3[Co(NO2)6]2 • ammineaquadicarbonyldicyanoiron(III) • [Fe(CN)2(NH3)(H2O)(CO)2]

+ 04/10/23 33

• Sodium tetracyanoosmium(III)• Na[Os(CN)4]• Tris(ethylenediamine)nickel(II) tetraoxomanganate(II) • [Ni(en)3]3[MnO4] • Hexaamminezinc(II) tris(oxalato)chromate(III)• [Zn(NH3)6]3[Cr(ox)3]2

• tris(oxalato)vanadate(II)• [V(ox)3]

4-

• sodium dihydroxodinitritomercurate(II) • Na2[Hg(OH)2(ONO)2]• ammonium tetrabromoaurate(II)• (NH4)2[AuBr4]• Potassium ethylenediaminetetraacetatoferrate(II) • K2[Fe(EDTA)]

diaquabis(ethylenediamine)iridium(III) chloride • [Ir(H2O)2(en)2]Cl3

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In complexation reactions, Lewis bases have many names

• Ligands, complexing agents, chelates, sequestering agents

• Most ligands have one pair of electrons to donate (ammonia)

• Some have two pairs of elections and some up to six pairs

– Ligands that provide more than one electron pair in forming a complex must be large, flexible molecules so that each pair of electrons can be oriented properly to form a bond

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• Complexation reactions can be written generally as

– Mn+ + xLm- ⇋ MLxn-mx where Mn+ is a metal ion

with a charge of +n and Lm- is a liquid with a charge of –m

– Ag tends to accept two electron pairs– Cu accepts four electron pairs– Other metal ions tend to accept six electron

pairs in complexes– This information allows us to accurately

write most complexation reactions once the number of electron pairs that a ligand can donate has been determined

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Complex Ion Formula

No. of LigandsCoordination

NumberShape

Ag(NH3)2+ 2 2 linear

CuCl2- 2 2 linear

Cr(NH3)63+ 6 6 octahedral

Fe(CN)63- 6 6 octahedral

Shapes (Geometry) of Some Complex IonsCoordination number = # ligands = 2 → linear Coordination number = # ligands = 4 → tetrahedral or square-planar Coordination number = # ligands = 6 → octahedral(octahedral geometry is most common for transition metal complexes)

Homework:Read 21.1-21.8, pp. 985-1032Q pp. 1035-1038, #21a, 22a, 24, 30, 32, 34, 46Do 1 additional problem and 1 challenge problemSubmit quizzes by email to me-some you won’t be able to do,

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ace/launch_ace.html?folder_path=/chemistry/book_content/0547125321_zumdahl/ace&layer=act&src=ch21_ace1.xml

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