Multidentate ligands Flashcards

1
Q

a monodentate ligand is

A

one that forms one dative bond with a metal ion

this means it uses one lone pair on one atom to form the dative bond

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2
Q

a bidendate ligand is

A

one that forms two dative bonds with a metal ion

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3
Q

a multidentate ligand is

A

one that forms several dative bonds with a metal ion

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4
Q

an example of a bidendate ligand is 1,2-diaminoethane, with formula:
it acts as a bidendate ligand because:

A

NH2CH2CH2NH2
abbreviated to ‘en’
it uses the lone pair of electrons on each nitrogen atom to attack to the metal ion

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5
Q

the equation showing the formation of the [Ni(en)3]2+ is from a haxaaqua metal ion is:

A

[Ni(H2O)6]2+ + 3en → [Ni(en)3]2+ + 6H2O

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6
Q

EDTA ‘s formula is :

A

(COOH-CH2)2-N-CH2-CH2-N-(CH2-COOH)2

EthyleneDiamineTetraAcetic (EDTA)

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7
Q

the EDTA molecule forms the ion……………

A

EDTA4- as each COOH group loses a H+ to form 2 COO- groups on each of the two Nitrogen atoms in the molecule

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8
Q

the EDTA4- ion has ………lone pairs of electrons

A

6 lone pairs, one lone pair on each O in the COO- groups and one lone pair on each N atom
this means the EDTA4- ion forms 6 dative bonds, so is a hexadentate ligand

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9
Q

most complexes are……………….. in the sense that they ……… decompose …………

A

most complexes are stable in the sense that they do not decompose readily

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10
Q

the stability of complexes refers to

A

a comparison of the stabilities of two complexes in which the number of ligands has changed

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11
Q

the equation for the reaction where the monodentate ligands in hexaaquacopper(II) are exchanged by bidentate ligands, en, is:

comment on the stability of the product and refer to the system’s entropy

A

[Cu(H2O)6]2+ + 3en → [Cu(en)3]2+ + 6H2O

here, the number of species has increased from 4 (total of reactants) to 7 (products), meaning the system is more disordered so there is an increase in ∆Ssystem. ligand exchange reactions of this sort lead to an increase in stability of the products compared to the reactants, so the formation of the product is favoured. this is because 6 H2O ligand have been replaced by only 3 en ligands.

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12
Q

the equation for the ligand exchange reaction where the H2O ligands in haxaaquacopper(II) are replaced by the EDTA4- ion is:

A

[Cu(H2O)]2+ + EDTA4- → [Cu(EDTA)]2- + 6 H2O

here six H2O ligands are replaced by one EDTA4- ligand, so the toal number of species has increased from two to seven, meaning ∆Ssystem increases more and the product is favoured more so

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13
Q

the simplified explanation of the role of haemoglobin in oxygen transport is :

A
  • haemoglobin consists of 3 main parts, the largest of which is protein (globin)
  • within the protein, there are 4 haem groups that are made up of mostly C and H atoms
  • inside each haem group, there are 4 N atoms that hold an Fe2+ by forming dative bonds with a square planar structure
  • there is a fifth dative bond to the Fe2+ ion form the protein, globin
  • when blood passes through the lungs, haemoglobin collects oxygen molecules and transports tgem to cells
  • when haemoglobin collects O2, the O2 molecules act as a ligand by using one its its lone pairs of e- to forma dative bond with a Fe2+ ion
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14
Q

the reason why CO, carbon monoxide, is dangerous is :

A
  • the dative bond formed by O2 with haemoglobin is not particularly strong, meaning it can easily be released in the cell
  • the dative bond formed by the lone pair on CO is much stronger, so a ligand exchange reaction occurs, and the CO less easily removed from the haemoglobin, preventing blood from transporting O2 to cells
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