Applications — biological (haemoglobin, chlorophyll, vit B₁₂), medicinal (cisplatin), industrial (catalysts)

3.4.15 · Chemistry › Coordination Chemistry

KYUN pasand karte hain biology aur industry coordination compounds ko?

Ek free metal ion ( $Fe^{2 +}$ , $Mg^{2 +}$ , $Co^{3 +}$ ) mein hota hai:

variable oxidation states → redox kar sakta hai,
empty d-orbitals → chhoti molecules (O₂, CO, N₂) ko reversibly bind kar sakta hai,
ligands se force ki gayi definite geometry → ek reactive site ko precisely position kar sakta hai.

Life ki trick hai porphyrin / corrin macrocycle — ek flat ring jisme 4 nitrogen donors hain. Yeh metal ko square plane mein pakad leti hai aur 2 axial positions free chhod deti hai chemistry ke liye.

Figure — Applications — biological (haemoglobin, chlorophyll, vit B₁₂), medicinal (cisplatin), industrial (catalysts)

1. Biological systems

(a) Haemoglobin — O₂ transport

Metal: Fe(II) (+2 state zaroori hai; Fe(III) form = methaemoglobin O₂ carry nahi kar sakta).
Ligand: porphyrin (yeh "haem" group hai) plane mein 4 N-donors deta hai; 5th position globin protein ki ek histidine se blocked hoti hai; 6th axial site O₂ ko reversibly bind karti hai.
KYA hota hai: $Hb + O_{2} ⇌ HbO_{2}$ . Binding reversible hai isliye O₂ lungs mein pick up hoti hai (high $p_{O_{2}}$ ) aur tissues mein release hoti hai (low $p_{O_{2}}$ ).

(b) Chlorophyll — photosynthesis

Metal: Mg(II) ek porphyrin-like ring mein.
KYUN Mg, Fe nahi? Mg²⁺ redox-inert hai (oxidation state change aasaan nahi). Iska kaam O₂ bind karna nahi hai — yeh conjugated ring ko rigid rakhta hai taaki yeh visible light (red+blue) absorb kare aur excited electron ko channel kare. Green colour = woh light jo yeh absorb nahi karta.
Role: $CO_{2} + H_{2} O l i g h t carbohydrate + O_{2}$ convert karta hai.

(c) Vitamin B₁₂ (cyanocobalamin)

Metal: Co(III) ek corrin ring mein (porphyrin se chhota; 4 N-donors).
Ek axial site mein –CN hoti hai (vitamin form mein) ya –CH₃/–adenosyl (active coenzyme forms mein).
Role: human biochemistry mein single metal-carbon bond; DNA synthesis aur RBC formation ke liye enzyme. Deficiency → pernicious anaemia.

Recall Table yaad karo cold

System	Metal	Ox. state	Ring	Kaam
Haemoglobin	Fe	+2	porphyrin	O₂ transport
Chlorophyll	Mg	+2	porphyrin	photosynthesis
Vit B₁₂	Co	+3	corrin	DNA/RBC synthesis

2. Medicinal — Cisplatin

KYUN sirf cis isomer kaam karta hai:

Cell ke andar (low Cl⁻ concentration), do cis chlorides hydrolyse ho jaate hain aur inki jagah water leta hai / phir DNA ke guanine bases ke do adjacent N atoms le lete hain.
Kyunki do leaving groups cis hain (90° apart), Pt DNA ke do neighbouring sites se bind kar sakta hai → DNA ko kink karta hai → replication rokta hai → cancer cell mar jaati hai.
Trans-platin mein do Cl 180° apart hain → adjacent bases ko bridge nahi kar sakta → inactive hai. Yeh geometry hai jo life aur death decide karti hai.

3. Industrial catalysts

Coordination complexes homogeneous catalysts ki tarah kaam karte hain — yeh substrate ko bind karte hain, activation barrier ghataate hain, product release karte hain, aur regenerate ho jaate hain.

Catalyst	Formula	Reaction
Wilkinson's	$[RhCl(PPh_{3})_{3}]$	alkenes ka hydrogenation ( $C=C + H_{2} \to$ alkane)
Ziegler–Natta	$TiCl_{4} + Al (C_{2} H_{5})_{3}$	ethene ka polymerisation → polythene
Wacker process	$PdCl_{2} / CuCl_{2}$	ethene → ethanal

Worked reasoning examples

Recall Feynman: ek 12-saal ke bacche ko samjhao

Socho metal atom ek tiny magnet-hand hai. Plants ek magnesium hand ko ek green frame ke andar rakhte hain jo sunlight pakad kar khana banata hai. Tumhara blood ek iron hand ko ek red frame ke andar rakhta hai jo tumhare lungs mein oxygen pakadta hai aur muscles mein drop kar deta hai. Ek vitamin cobalt hand use karta hai tumhara blood banane mein help karne ke liye. Aur ek cancer medicine ek platinum hand use karti hai jisme do "sticky fingers" hain jo zaroor ek doosre ke paas hone chahiye (cis) taaki yeh cancer cell ki instruction book (DNA) ko pakad ke jam kar sake. Same atom, alag cage = bilkul alag kaam.

Flashcards

Haemoglobin mein kaun sa metal aur oxidation state hai?

Fe(II) — Fe²⁺

Chlorophyll ke centre mein kaun sa metal hai, aur kyun yeh metal?

Mg(II); yeh redox-inert hai aur light-absorbing ring ko rigidly hold karta hai

Vitamin B₁₂ mein kaun sa metal aur oxidation state hai?

Co(III), corrin ring ke andar

Haemoglobin aur chlorophyll mein metal ko kaun si macrocyclic ring bind karti hai?

Porphyrin (4 N-donors)

Vitamin B₁₂ mein kaun si ring hai (porphyrin se alag)?

Corrin ring

CO haemoglobin ko poison kyun karta hai?

Yeh 6th (O₂) site ko ~200× zyada strongly bind karta hai, O₂ ko out-compete karta hai (competition, destruction nahi)

Methaemoglobin oxygen kyun carry nahi kar sakta?

Iska Fe oxidise hokar Fe(III) ban jaata hai, jo reversible O₂ site ko block kar deta hai

Cisplatin ka formula aur geometry?

cis-[Pt(NH₃)₂Cl₂], square planar Pt(II)

Sirf cis-platin anticancer drug kyun hai?

Iske do cis (90°) leaving groups DNA pe do adjacent guanine bases ko crosslink karte hain; trans (180°) nahi kar sakta

Wilkinson's catalyst ka formula aur use?

[RhCl(PPh₃)₃]; alkenes ka hydrogenation

Ziegler–Natta catalyst aur use?

TiCl₄ + Al(C₂H₅)₃; ethene ka polymerisation karke polythene banana

Vitamin B₁₂ ki deficiency se kaun si disease hoti hai?

Pernicious anaemia

Metal complexes acche homogeneous catalysts kyun hain?

Variable oxidation states + open coordination sites inhe substrates ko reversibly bind, orient, aur release karne dete hain

Connections

Isomerism in coordination compounds — cis/trans cisplatin ki activity decide karta hai
Crystal Field Theory — haem aur chlorophyll ka colour explain karta hai (d-orbital splitting)
Square planar complexes — Pt(II) d⁸ ki geometry
Stability and chelate effect — macrocyclic rings itne tightly kyun bind karti hain (macrocyclic effect)
Oxidation states of transition metals — Fe(II)/Fe(III), Co(III)