Greenwood & Earnshaw. Chapter 11. Nitrogen

Transcription

1 Greenwood & Earnshaw 2 nd Edition Chapter 11 itrogen

2 Dinitrogen / is chemically very unreactive, mp 210EC, bp 195.8EC its great bond strength, diss = kj/mol, d = pm, and great thermodynamic stability causes many nitrogen compounds to be endothermic. The 2 lone pairs are very low in energy and are much less available for donation than the isoelectronic C. The π* molecular orbitals are very high in energy (π bonds are very strong) and πbackbonding is less favored. A large LU energy gap makes it hard to promote electrons or reduce dinitrogen. Dinitrogen is a nonpolar molecule. isoelectronic with: C, +, C, C 2 2, and similar to C 2, 2 C 2.

3 olecular rbital Diagram Dinitrogen σ LU gap π σ π sp hybridization mixing of s&p σ Lone pairs of electrons σ ote the two πbonds are stronger than the σbond due to bond compression.

4 Reactions of Dinitrogen itrides and nitrogen oxides: 25EC 6 Li Li 3 any small metals (g, Al, Ti) react with dinitrogen at elevated temperatures., hν, elec. dis x Dinitrogen "fixation" during electrical storms and high temperature combustion contributes to soil fertility & "acid rain." Dinitrogen coordinates to some metal complexes: [Ru( 3 ) 5 ( 2 )] [Ru( 3 ) 5 ( 2 )] [ocl 4 (Pe 2 Ph) 2 ] cis [o( 2 ) 2 (Pe 2 Ph) 2 ] toluene, a/g Pe 2 Ph acl Dinitrogen Coordination: η 1 most common bisη 1 impt in fixation µbisη 2 η 2 rare

5 itrides itrido Complexes %, I = %, I = 1 / 2 Ionic: 3 Ca + 2 Ca 3 2 also Li, g, Zn, Ti other small cations. Al C x 2Al + 3 C Covalent: Si 3 4 S 4 4 P 3 5 etwork covalent with alumina in hi tech ceramics. olecular, all have some type of dπpπ bonding. etallic: Transition metals (Zr, Ti, Cr) in cubic and hexagonal close packed littices, fits into octahedral sites.

6 itrido: Linear: 180E Trigonal: itrides itrido Complexes s s Cl 2 Ru Ru 2 Cl Cl Cl Cl Cl Cl Cl [Ir 3 (S 4 ) 6 ( 2 ) 3 ] 4 Tetrahedral: [(ge) 4 ] +

7 Ionic Azides: + 3 Azides Azido Compounds d = = 116 pm isoelectronic with Ionic azides are stable, the ion is symmetrical, the alkali metal salts are commercially available. C Covalent Azides: 3, R 3, Pb( 3 ) 2, g pm 124 pm f E = kj/mol ydrazoic acid, pka = 4.77, pungent, revolting odor, very toxic. Concentated and anhydrous acids are explosive. G f E = kj/mol A very energetic molecule, heavy metal salts are used as detonators for explosives, not hygroscopic, reliable.

8 ydrides Ammonia: 3 Kb = 1.8 X 105 Largest industrial commodity on a molar basis. + RBr + 3 R 3 Br RBr 4 + RBr RBr Ammonia and amines are weak bases ammonium ions are weak acids. Tetraalkylammonium hydroxide is a strong base. + ydrazine: 2 2 Kb = 8.5 X pm gauche conformation torsion angle 90E95E LPLP repulsions make the bond long and weak. Kb = 8.9 X e,2e,4e reducing agent, stronger in base than acid. 1e EEred = 1.74 V acid 1e EEred = 2.42 V base R 4 + Br Ag 2. 2 R 4 + ydrazide Ligand: 2 R A strong acid

9 Diazine: Cyclotriazene: (triaziridine) Less Common Binary ydrides trans more stable cis not stable Ligand important in nitrogen fixation. 1,1isomer Triazane: 2 2 (aminohydrazine) Tetrazane: 2 2 (diaminohydrazine) trans2tetrazene 2 2 Several "binary hydrides" can be made such as ammonium and hydrazinium azide salts; dimers and trimers of hydrazoic acid or triaziridine.

10 ydroxylamine & itrogen Fixation + ydroxylamine: 2 Kb = 6.6 X Trans conformation in the crystal ade by the reduction of ammonium nitrite in a gel using aqueous bisulfate/sulfur dioxide, Raschig Synthesis. 147 pm Industrially used as reducing agent, absorbent for nitrogen oxides. Forms ximes with aldehydes and ketones: C + 2 C + 2 itrogen Fixation: µbisη e diimido 2 2 hydrizido(2) isodiazene

11 4 + F (l) electrolysis itrogen alides 4 + Cl (aq) electrolysis p4 (e 3 Si) 2 Br + 2 BrCl pentane 87EC 3 I 3 + aqueous mp bp F 3 Cl 3 Br 3 I 3 A E 129.0E Stable, GE = 83.3 kj/mol., colorless, low dipole moment (0.234 D), p 102E, pyramidal, low reactivity. 40E +71E ρ 20E = 1.65 g/cc 2,air 2 F 2 + SbF 3 200EC, 100 atm decomposes at 60EC, and very reactive all are shock sensitive and explosive a layer lattice, I 4 tetrahedra linked in infinite chains of II, connected into sheets by II interactions and sheets linked by I 3 interactions. 3 & 3 Cl used commercially to sterilize and bleach flour. + SbF 2 F 5 3 SbF6 2 F 4 2 F 2 mp 165.5EC, bp 73EC D diss = 83.2 kj/mol Cu F [F 4 ] + [SbF 6 ] 2 196EC F electric discharge F 3 any salts known, oxidizer for chemical lasers. F 3 cf. CF 2 & CF 3 F F BF pm pm F [F 2 ] + [BF 4 ]

12 2 F 2 itrogen alides C C F F 2 Cis isomer more reactive, attacks glass. trans isomer does not attack glass. bp 105.7EC mp < 195EC 141 pm F pure cis isomer! F 121 pm F 114E F 2 / 2 2 S 4 F AsF 5 AsF 6 80EC KFAF 2 KF p 12 acl 2 F 4 20EC K+ FF AlCl 3 Low Temp 2 F 2 90 / 10 cis / trans E = 12.5 kj/mol Cis isomer more stable than trans EC F bp 111.4EC mp 172EC 140 pm p 106E 122 pm 100% F AsF5 o Reaction

13 itrosyl halides: X BF 3, AsF 5 AlCl pm itryl halides: X 2 X itrosyl & itryl alides 2 BF 4, AsF 6 AlCl 4 X AsF 5 X F Cl Br mpec bpec ~0 px E f kj/mol 2 X, X + 2 X F Cl mpec bpec px E f kj/mol Potent solvents for dissolving metals. 115 pm AsF 6 X, 2 X + 2

14 xides of itrogen Dinitrogen onoxide: Isoelectronic with carbon dioxide & 2 +. Very (itrous xide) 2 unreactive, very stable gas, anesthetic (laughing gas), greenhouse gas t1/2 = 115 year "lifetime." atural source, microbial degradation of 4 3. itrogen onoxide: (itric xide) 115 pm A stable free radical, paramagnetic, colorless, bp 151.8EC, little tendency to dimerize. xidation to 2 has a negative temperature coefficient. 106 pm xidation of : 2 B 2.5 at 218 pm 112 pm pm 121 pm 2

15 itric xide as a Ligand Bent itrosyls Linear: + A 3 electron donor, 2 's will replace 3 C's in an EA complex. p E Bent: Gp A: ν = cm 1. Common with early transition metals and middle transition metals in higher oxidation states. (2 electron donor) p E ν = cm 1. Common with late transition metals and middle transition metals in lower oxidation states. Gp B: p E (1 electron donor) Bonding odes of :

16 itric xide as a Ligand 243 pm Ph 3 P 117 pm Cl 237 pm Ru p 138E 186 pm 174 pm 242 pm p 178E 116 pm PPh 3 [RuCl() 2 (PPh 3 ) 2 ] + n n n [{(η 5 C 5 5 )n} 3 (µ 2 ) 3 (µ 3 )]

17 Dinitrogen Trioxide: pm p 105E 120 pm 186 pm p 117E p 130E p 113E 122 pm xides of itrogen mp 100.1EC itrogen Dioxide & Dinitrogen Tetroxide colorless redbrown mixed dimer Light blue solid, intense blue liquid, turns green as 2 dissociates, color becomes less intense. 175 pm p 113E 121 pm diss = kj/mol G diss = kj/mol SE = J/KAmol Isoelectronic with B 2 F 4 & C whose CC and BB bonds are of normal length. Does not autoionize, but ionic intermediates form in high dielectric solvents. An intermediate in the production of nitric acid. 3 itric Acid: Pt to be recycled

18 Dinitrogen Pentoxide: 2 3 P xides of itrogen gas Structure poorly understood xoacids xoanions: yponitrous Acid yponitrite also: pka = 6.9 ; 11.6 Isomeric with nitramide pka = Pt(Ph 3 ) ( 3 ) 5 Co Weak dibasic acid of unknown structure. Stable for weeks in acidic solution, decomposes at p > pm Ph 3 P Pt p 78E 139 pm Ph 3 P 200 pm Co( 3 ) pm 4+ 70EC 121 pm + Ionic solid a 3 or a 2 a/g Salts are stable, reducing, "trans" by vibrational spect. "Cis" ion known as a ligand. any "nonea" nitrosyls are cishyponitrites.

19 xoacids xoanions yponitric Acid yponitrates: Acid is known only in solution and is explosive. α form β form a Angeli's Salt "Peroxohyponitrite" a (l) fast slow slow β EC α itroxylic (ydronitrous) Acid itroxolate Anion: "Acid Explosive" 2 a a 3(l)

20 xoacids xoanions itrous Acid itrites 95.4 pm 143 pm p 102E p 111E 118 pm planar 45 kj/mol barrier to rotation nitrite is a very versatile ligand nitro nitrito chelating bridging cisunsymmetrical, bridging trans?? not definitely established

21 itric Acid itrates 141 pm 96 pm p 102E 121 pm p 130E p 114E xoacids xoanions Almost planar gas,p torsion 2E bp 82.6EC. itric Acid will form bonded complexes with nitrate. The nitrate ligand may coordinate in a manner similar to nitrite and may use all three oxygen atoms. rthonitrate: a 2 + a 3 fuse a 3 4 Tetrahedral anion, very short bond due to strong polar interactions. 3 4 unknown pm 3 [ 4 6 ]

22 Coordination odes of itrate Ligand sym bidentate unsym bidentate unidentate µ 2 bridging µ 3 bridging bisµ 2 bridging synsyn ; antianti any metal nitrates melt at "low" temperatures without decomposition Li 3 (255EC); Cs 3 (419EC); Ag 3 (212EC).