Lecture 20. The d-Block Elements.VII-VIII B groups

PhD. Halina Falfushynska

Manganese• Manganese is obtained mainly from the mineral pyrolusite, MnO2.

• Ferromanganese alloys are wear resistant and shock resistant and are used for railroad tracks, bulldozers, and road scrapers.

• Manganese(IV) oxide is the starting point for making most other manganese compounds.

• Potassium permanganate, KMnO4, is an important oxidizing agent that is used in both analytical and organic chemistry laboratories, and in water treatment.

The Iron Triad: Fe, Co, and Ni• Iron is the fourth most abundant element in Earth’s crust.

Cobalt and nickel are not nearly as common.• All three elements form 2+ and 3+ ions.• The most common ions of Co and of Ni are the 2+. The

most common ion of Fe is the 3+ due to the half-filled d-subshell:

Ferromagnetism• The iron triad exhibits ferromagnetism which is a much

stronger magnetic effect than paramagnetism.• A ferromagnetic solid consists of regions called domains in

which atoms have their magnetic moments aligned.

• When placed in a magnetic field, all the domains are aligned and the solid becomes magnetized.

Examples of variable oxidation states in the transition metals

Iron

Iron has two common oxidation states (+2 and +3) in, for example, Fe2+ and Fe3+. It also has a less common +6 oxidation state in the ferrate(VI) ion, FeO4

2-.

Manganese

Manganese has a very wide range of oxidation states in its compounds. For example:

+2 in Mn2+

+3 in Mn2O3

+4 in MnO2

+6 in MnO42-

+7 in MnO4-

Thinking about a typical transition metal (iron)

Here are the changes in the electronic structure of iron to make the 2+ or the 3+ ion.

Fe [Ar] 3d64s2

Fe2+ [Ar] 3d6

Fe3+ [Ar] 3d5

The 4s orbital and the 3d orbitals have very similar energies. There isn't a huge jump in the amount of energy you need to remove the third electron compared with the first and second.

The figures for the first three ionisation energies (in kJ mol-1) for iron compared with those of calcium are:

metal 1st IE 2nd IE 3rd IE

Ca 590 1150 4940

Fe 762 1560 2960

There is an increase in ionisation energy as you take more electrons off an atom because you have the same number of protons attracting fewer electrons.

Manganese Mn (Manganum)

trace element- cofactor of enzymes: superoxide dismutase

pyruvate carboxylaseKMnO4 Potassium permanganate (INN: Kalii

permanganas)

- in water dissolves to give deep purple solutions

- strong oxidizing agent- dilute solutions can act as desinfectant

Biological role of ManganeseBiological role of Manganese• Manganese is required for the metabolism of

proteins and fats. A partial list of manganese-dependent enzyme families includes oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

• Manganese is involved in the function of numerous organ systems and is needed for normal immune function, regulation of blood sugars, production of cellular energy, reproduction, digestion, and bone growth. Manganese works with vitamin K to support clotting of the blood.

• The National Research Council has recommended an Estimated Safe and Adequate Daily Dietary Intake (ESADDI) for Mn of 2 to 5 mg per day for adults.

Manganese in pharmacyManganese in pharmacy• Manganese has been examined as a treatment for a

variety of conditions, including osteoarthritis and wound healing. However, manganese is often used in combination with other vitamins and/or minerals. Therefore, the effects of manganese alone are difficult to determine.

• Manganese in combination with calcium and zinc may be beneficial in patients with chronic wounds.

• A combination of calcium and manganese may alleviate symptoms associated with premenstrual syndrome.

Source of manganeseSource of manganese• Excellent food sources of manganese include

mustard greens, kale, chard, raspberries, pineapple, strawberries, romaine lettuce, collard greens, spinach, garlic, summer squash, grapes, turnip greens, eggplant, brown rice, blackstrap molasses, maple syrup, cloves, cinnamon, thyme, black pepper, and turmeric.

Iron Fe (Ferrum)important microelementhuman body: 4–5 g Fea) functional form - heme iron proteins

hemoglobin 70 %myoglobin 5 %

some enzymes - non-heme iron proteinsb) tranport form (transferrin)c) storage of iron (ferritin, hemosiderin)-20 %Fe in food 10-30 mg/day absorption: only 7-10%

~ 1 mg/day

HEME iron proteins

Hemoglobin - O2 transport in blood

- in red blood cells- tetramer = 4 subunits

(each subunit: one heme + one globin)

HbA ("adult") 22

HbF ("fetal") 22

Myoglobin - "O2 storage" in muscle cell

Cytochromes - electron transport - their function is based on: Fe2+ (reduced) Fe3+

(oxidized)

heme

Non-heme iron proteins FeII or FeIII bound to protein SH

iron–sulphur proteins (FeS proteins)

Transferrin - blood plasma protein ( 1 globulin )

- transport of Fe - 1 molecule of transferrin can carry 2 iron ions in form of Fe3+

Ferritin - intracellular iron storage protein (liver, bone marrow) - 1 ferritin complex can store about 4500 Fe3+

- ferritin without iron = apoferritin

Hemosiderin - "damaged (Fe-overloaded) ferritin" - Fe from it is less available

OVERVIEW OF IRON METABOLISM

liver FERRITIN HEMOSIDERI

N

blood plasma TRANSFERRIN

bone marrow FERRITIN

red blood cells HEMOGLOBIN

spleen FERRITIN

tissues CYTOCHROMESFe-S proteins

muscles MYOGLOBIN

BLEEDING (Fe losses)

FOOD

Iron metabolism = unique - reutilization ! (closed system)

NO regulated excretion system for Fe !

Fe absorption must be "regulated"

Loss of Fe through loss of blood (females - mestrual bleeding)

Iron deficiency - microcytic anemia "iron deficiency anemia"

Iron overload - hemochromatosis = accumulation of iron in the body (depositions as hemosiderin)

organ dysfunction (liver, heart, ...)

IRON ABSORPTION

FOOD Fe3+

STOMACH

HCl pH 1-2ascorbic acidgastroferrin - iron binding protein

Fe2+

reduction

INTESTINAL MUCOSA CELL

Fe3+

apoferritin

ferritin (Fe3+)

BLOOD transferrin (Fe3+)

Fe2+

Measurement of Iron (Phenanthroline Method)

Interferences : Phosphate Heavy metals

1,10 phenonthroline combines with Fe2+ to form complex ion orange in red color

Color produced confirms Beer’s Law – Visual – Photometric comparison

Phenanthroline MethodSample exposed to atmospfere contains Fe2+ , Fe3+ , ppt of

ferric hydroxide.All iron must be in soluble form

HCl is used Fe(OH)3 + 3 H+ Fe3+ + 3 H2O

1,10 phenonthroline specific for measuring Fe(II)Fe3+ is reduced to Fe2+

Hydroxylamine is used as reducing agent 4Fe(III) + 2 NH2OH 4Fe(II) + N2O + H2O + 4 H+

3 molecules of 1,10 phenantrhroline complex with each Fe2+

Manganese measurement • Colorimetric method depend upon oxidation of

Mn to VII forms highly colored permanganete ion

Obeys Beer’s Law Visual or photometric comparison

•AAS

•ICP

Manganese measurement (Persulphate Method)

Ammonium persulphate oxidizing agent

Cl- interference: Because of reducing action in acid medium.use Hg2+ for interference. HgCl2 complex is formed

Ag2+ is used as catalyst

Oxidation of Mn in lower valence to permanganete by persulfate. Ag+

2Mn2++5S2O82- +8H2O 2MnO4

- +10SO42- +16H+

(permanganete colored)