- multidentate ligand - fe 2+ complex

topic 15: transition metals Flashcards by Thalia Al-Madfai

transition metals are:

d-block elements that form
ion(s) with incompletely-filled d-orbitals

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Why is Zn not a transition metal?

forms Zn 2+
complete d subshell

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Why is Sc not a transition metal?

forms Sc 3+
empty d orbital

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ligand

a species which can donate a lone electron pair to form a dative covalent bond

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monodentate

one covalent bond per ligand

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bidentate

2 covalent bonds per ligand

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complex ion

a central metal ion surrounded by ligands

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how does colour arise? (4)

LIGANDS cause d orbital to split into different energy levels
TM has incomplete d orbital
electrons gain light energy, excited, promoted to higher energy d orbital levels
the light NOT ABSORBED is transmitted and seen as colours

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if coordination number is 6 you are…

octahedral
- usually with smaller ligands eg oh- , h2o, nh3

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if coord number is 4 you are

tetrahedral
usually with larger ligands eg cl-

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cis platin

SQUARE PLANAR
Pt(CL-)2(NH3)2

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WHY IS ONLY THE CIS platin used

in cancer treatment
?????

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coord number of EDTA 4-

6 per ligand !!!

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heamoglobin ligand

multidentate ligand
fe 2+ complex

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what happens with haemoglobin and co

ligand exchange!!!!! co replaces o2
dative covalent bond formed w CO stronger than with O2 therefore prevents O2 binding to haemoglobin
reduces amount of o2 that can be carreid to cells

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vanadium +5 usual compound and colour

V(O2)+
YELLOW

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vanadium +4 usual compound and colour

(VO2)+
Blue

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vanadium +3 usual compound and colour

V 3+
green

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vanadium +2 usual compound and colour

V 2+
violet

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vanadium from +5 to +2 colours

yellow
blue
green
violet

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what do u usually use to reduce the vanadium

zinc

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how to go from Cr2O7 2- to Cr2+ or 3+

zinc
acidic conditions

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why anaeroboic conditions when reducing cr2o7 2- to cr2+

to prevent atmospheric oxygen from re oxidising the cr2+ to cr 3+

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how to stabilise the cr 2+ so its doesnt re oxidise

add a ligand eg ethanedioate as bidentate

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cr2o7 2- colour

orange

cr3+ cloour

green

cr 2+ colour

blue

how to make it easier to oxidise a transition metal in a low oxidation state?

- give it alkali conditions - eg Cr(h2o)6 3+ vs cr(oh)6 3- - easier to remove electrons from a negative complex

what t use to oxidise cr(oh)6 3-

- hydrogen peroxide forms CrO4 2-

CrO4 2- colour

yellow

equilibrium of the chromate vs dichromate

2(CrO4)2- + 2H+ -> Cr2O7 2- + h2o

how to produce Cr2O7 2- ??

- alkali conditions - oxidise cr(oh)6 3- using H2O2 - forms Cro4 2- (yellow). then considering the eqm, add acid to get Cr2O7 2-

Fe 2+ aqua complex AND COLOUR

Fe(H2O) 2+ green

Co 2+ aqua complex AND COLOUR

Co(H2O) 2+ PINK

Cu 2+ aqua complex AND COLOUR

Cu[H2O]6 2+ blue

Fe 3+ aqua complex AND COLOUR

[Fe(H2O)6]3+ brown

Cr 2+ aqua complex AND COLOUR

[Cr(H2O)6]3+ green

equilkibria of the aqueous metal complexes in water

[Fe(H2O)6]2+ + H2O = H3O+ + [Fe(H2O)5(OH)]+

explain how the equilibrium of the aqeous ions shows acidity and which of the 3+ or 2+ complexes are more acidic?

-[M(H2O)6]3+ more acidic than [M(H2O)6]2+ -3+ metal ions higher charge and smaller size - greater polarising power - stronger esa to water molecule (in the equilibria) - strains O-H bond more so it breaks more easily releasing H+ ions

Cu 2+ Fe 2+ Co 2+ from aqeous complex to with limited OH- (include colours)

[M(H2O)4(OH)2] (s) Cu:blue ppt Co:blue ppt Fe: green ppt

Fe 3+ Cr 3+ from aqeous complex to with limited OH- (include colours)

[M(OH)3(H2O)3] Fe: bronwn ppt Cr: green ppt

generic equation M2+ from aquoeous complex to with ammonia

[M(H2O)6]2+ + 2NH3 = [M(OH)2(H2O)4] + 2NH4+

of all of the ions, the only one with a change w excess OH- is

Cr3+ forms a green solution

complexes which do ligand exchange with exces NH3:

- Cr3+ (6x nh3) - Co2+ (6x NH3) Cu2+ (4x nH3)

Cr3+ with EXCESS NH3

[Cr(OH)3(H2O)3] + 6NH3 = [Cr(NH3)6]3+ + 3H2O+ 3OH- PURPLE SOLUTION

Co2+ with EXCESS NH3

[Co(OH)2(H2O)4] + 6NH3 = [Co(NH3)6]2+ + 4H2O + 2OH- PALE YELLOW SOLUTION

Cu2+ with EXCESS NH3

[Cu(OH)2(H2O)4]2+ + 4NH3 = [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH- deep blue solution

adding Cl- ligand changes IMPORTANCE

- Cu2+ and Co2+ - coordinate number from 6 to 4 [(Cu)(Cl)4]2- - BECAUSE Cl- much larger than H2O so more steric hindrance copper complex: yellow/green cobalt: blue TETRAHEDRAL

HOW DOES A CATALYSTIC ONCVERTER WORK?

- decrease CO and NO emissions by -adsorption of CO and NO molecules onto the surface of the catalyst -weakening of bonds and chemical reaction -desorption of CO2 and N2 product molecules from the surface of the catalyst 2 CO + 2 NO = 2 CO2 + N2

reaction between Iodide and persulfate ions - equation - catalysis

(S2O8)2- + 2I- = 2(SO4)2- + I2 - rate is v slow due to repulsion between the negatively charged ions CATALYSED PROPOSITION: - 1. (S2O8)2- + 2Fe2+ = 2(SO4)2- + 2Fe3+ -2. 2I- + 2Fe3+ = 2Fe2+ + I2 possible becase Fe has variabke oxidation states

essential point to note about electrode potential of homogeneous transition metal catalysts

- e cell must lie between the oxidised and reduce - so can first reduce the more positive one, then oxidise the more negative one

autocatalysis exampke Mn 2+ , mno4 - and ethanedioate

2 MnO4- + 5 (C2O4)2- + 16 H+ = 2Mn2+ + 10 CO2 + 8 H2O - REDUCES THEN OXIDISES

coordinate number defintion

number of dative covalent bonds to the central metal atom

ethanedioate is

bidentate o-c=o - o-c=o

only d be not transition metals

Sc and Zn

Why are Zn2+ and Sc3+ colourless?

- complete/empty 3d subshell - electrons can not be promoted to higher d orbitals

why do diff ligands cuase diff colours?

causes diff splitting in d orbitals so diff energy diff between them

difference in colour from flame test vs tm

SIMILARITIES: - electrons promoted to higher E level - difference in E levels determines colour DIFF - TM: light energy absorbed, splitting of d orbital by ligand, colour not absorbed is transmitted and seen - FT: heat energy absorbed, electrons move back down to ground state

how to deterine how many cl - are acting as ligand

- add AgNo3 - those NOT acting as ligands will react

vanadium colours, 5+ down to 2+

Yellow Blue Green Violet

if the acid you're adding is dilute, then its

an acid base NOTTT with Cl- ligands

QUALITIES CHARACTERISTIC of transition metals

- form coloured complexes

cis v trans isomers

cis = ligand on same side

what metals are used in a catalytic converter

platinum palladium rubidium

copper 2+ in xs oh-

no effect

zn 2+ in xs oh-

dissolves to form colurless soln

isomerism in complexes

ONLY IN OCTAHEDRAL if next to each other, then cis if opposite (top v bottom) then trans

topic 15: transition metals Flashcards

(67 cards)