The elements of the first transition series.pdf

The metals of the first transitionseries

The metals of the first transitionseries• The Lower Oxidation States

The metals of the first transitionseries• The chemistry of the metals can be classified on thebasis of this table ;• for example,• the d 6 series is V ‐I , Cr o , Mn I , Fe II , Co III , and Ni 1v• Comparisons of this kind can occasionally emphasizesimilarities in spectra and magnetic properties• differences in properties of the d n species due todifferences in the nature of the metal its energy levels,and especially the charge on the ion, often exceed thesimilarities.

The metals of the first transitionseries• The oxidation states less than II.• With the exception of copper, where copper(I) binarycompounds and complexes and the Cu+ ion are known, thechemistry of the I, 0, ‐I, and ‐II formal oxidation states isentirely concerned with:• (a) π‐Acid ligands such as CO, NO, PR3, CN ‐ , and bpy.• (b) Organometallic chemistry in which alkenes, acetylenes,or aromatic systems, such as benzene, are bound to themetal.

The metals of the first transitionseries• The II oxidation state.• Binary compounds in this state are usually ionic.• The metal oxides are basic• have the NaCl structure• are often nonstoichiometric,• particularly for Ti, V, and Fe• The aqua ions• [M(H 2 O) 6 ] 2+ , except for the unknown Ti 2+ ion, are wellcharacterized in solution and in crystalline solids.

The metals of the first transitionseries• V 2+ , Cr 2+ , and Fe 2+ ions are oxidized by air in acidicsolution

The metals of the first transitionseries• halide hydrates do not contain the aqua ion.• VCI 2 . 4H 2 O is trans‐• VCl2 (H2O)4 and MnCI2.4H2O is a polymer with• cis‐MnCI2 (H2O)4 units;• the diaqua species of Mn, Fe, Co, Ni, and Cu have a linearpolymeric edge‐shared chain structure with trans‐[MCl 4(H 2 O) 2 ] octahedra.• The FeCI 2 .6H 2 O compound,contains trans‐FeCl 2 (H 2 O) 4units.• The water molecules of [M(H 2 O) 6 ] 2+ can be displaced byligands such as• NH 3 , en, EDTA 4‐ , CN ‐ , and acac .

The metals of the first transitionseries• complexes may be• Cationic• neutral• anionic• depending on the charge of the ligands• Addition of OH ‐ to the M 2+ solutions gives hydroxides• Some can be crystalised• E.g. Fe(OH)2 , Ni(OH)2• With HCO 3 ,the carbonates of Mn, Fe, Co, Ni, and Cuare precipitated.

The metals of the first transitionseries• The III Oxidation State• All of the elements form at least some compounds in thisstate• Exception: Cu• only a few complexes, not stable toward water, are known• The fluorides (MF3) and oxides (M20 3) are generally ionic• Chlorides, bromides, and iodides , sulfides and similarcompounds• have considerable covalent character.

The metals of the first transitionseries• The elements Ti to Co form octahedral ions,[M(H 2 O) 6 J 3 + .• The C0 3 + and Mn 3+ ions are reduced by water• Ti 3 + and V 3 + ions are oxidized by air.• In aqueous solution high acidities are required toprevent hydrolysis

The metals of the first transitionseries• Crystalline chlorides of V, Fe, and Cr are of the typetrans‐[VCI 2 (H 2 O)4] + Cl ‐ ∙2H 2 O• The alums CsTi(SO4)2.12H2O, or KV(SO4)2.12H2Ocontain the hexaaqua ion .• hydrates like Fe(ClO 4 ) 3 ∙10H 2 O.• There are many anionic, cationic, or neutral M Illcomplexes, which are mostly octahedral.• Cr Ill and Co Ill , hundreds of octahedral complexes thatare substitutionally inert are known

The metals of the first transitionseries• Representative octahedral complexes are• [TiF 6 ] 3‐• [V(CN) 6 ] 3‐• Cr(acac) 3• [Co(NH 3 ) 6 ] 3+• The halides (MX 3 ) act as Lewis acids and formadducts, and• ionic species [VCI4] ‐ ,[CrCI4] ‐

The metals of the first transitionseries• A special feature of the M 3+ ions is the formation ofbasic carboxylates in which an O atom is in the centerof a triangle of metal atoms• This oxo‐centered unit• has been proved• for carboxylates of• V, Cr, Mn, Fe, Co, Ru, Rh, and Ir.

The metals of the first transitionseries• The IV and Higher Oxidation States• The IV state is the most important state for Ti• main chemistry is that ofTiO 2 and TiCl4 and derivatives• VCI4, the main V IV chemistry is that of theoxovanadium(IV) or vanadyl ion VO 2+ .• ion can behave like an M 2+ ion,• forms many complexes• cationic, neutral, or anionic, depending on the ligand.• For the remaining elements, the IV oxidation state is notvery common or well established except in fluorides,fluorocomplex ions, oxo anions, and a few complexes.

The metals of the first transitionseries• The oxidation states V and above are known for• V, Cr, Mn, and Fe• fluorides,• fluorocomplexes• oxo anions• CrF 5• KMn0 4• K 2 FeO 4• All are powerful oxidizing agents.

The metals of the first transitionseries• TITANIUM• Titanium has the electronic structure 3d 2 4s 2• The energy of removal of four electrons is so high• that the Ti 4+ ion may not exist• titanium(IV) compounds are covalent• some resemblances between Ti 1v and Sn IV and theirradii are similar.• TiO 2 (rutile) is isomorphous with SnO 2 (cassiterite)and is similarly yellow when hot

The metals of the first transitionseries• Titanium tetrachloride, like SnCI4 is• a distillable liquid• readily hydrolyzed by water• behaving as a Lewis acid• The bromide and iodide,• form crystalline molecular lattices• are isomorphous with the corresponding Group IVBhalides

The metals of the first transitionseries• Titanium tetrachloride, a colorless liquid (bp 136°C),• has a pungent odor,• fumes strongly in moist air,• and is vigorously, though not violently, hydrolyzed by water.• Partially hydrolyzed species are formed with a deficit ofwater• or on addition of TiCl4 to aqueous HC!.

The metals of the first transitionseries• Titanium oxide has three crystal forms‐• rutile,• anatase,• Brookite• all occur in nature.• The dioxide that is used in large quantities as a white pigment inpaints is made by vapor phase oxidation of TiCl4 with oxygen.• The precipitates obtained by addition of OH ‐ to TiN solutions arebest regarded as hydrous TiO 2 , not a true hydroxide.• This material is amphoteric and dissolves in concentrated NaOH.

The metals of the first transitionseries• VANADIUM• Vanadium is widely distributed but there are few concentrateddeposits.• Occurs in petroleum from Venezuela,• is recovered as V 2 O 5 from flue dusts after combustion.• Very pure vanadium is rare,• is quite reactive toward O2, N2, and C at the elevated temperatures• Chief commercial use is in alloy steels and cast iron, gives ductility andshock resistance,• commercial production mainly as an iron alloy, ferrovanadium.• Vanadium metal is not attacked by air, alkalis, or nonoxidizing acidsother than HF at room temperature.• It dissolves in HNO 3 , concentrated H2SO4, and aqua regia.

The metals of the first transitionseries• CHROMIUM• The chief ore is chromite, FeCr 2 O 4, which is a spinel .It is reduced by C to the carbon‐containing alloyferrochromium.• FeCr 2 O 4 +4C Fe∙2Cr+ 4 CO• When pure Cr is required, the chromite is first treatedwith molten NaOH and O 2 to convert the Cr Ill toCrO 42‐.• The melt is dissolved in water and sodium dichromateis precipitated. This precipitate is then reduced

The metals of the first transitionseries• Chromium is resistant to corrosion, hence its use as anelectroplated protective coating. It dissolvesfairlyreadily inHCI, H 2 SO 4 ,andHCIO 4 ,but it is passivated byHNO 3 .

The metals of the first transitionseries• Acid solutions of dichromate are strong oxidants:• In alkaline solution, the chromate ion is much lessoxidizing:

The metals of the first transitionseries• MANGANESE• Manganese is relatively abundant,• occurs in substantial deposits, mainly oxides, hydrousoxides, or the carbonate.From them, the metal can be obtained by reductionwith AI.• Manganese is quite electropositive, and readilydissolves in dilute, nonoxidizing acids.

The metals of the first transitionseries• The most common compound of Mn lV is manganesedioxide, a gray to black solid found in nature aspyrolusite• Manganese dioxide is inert to most acids except whenheated, but it does not dissolve to give Mn lV insolution; instead, it functions as an oxidizing agent,the exact manner of this depending on the acid. WithHCI, chlorine is evolved.

The metals of the first transitionseries• Solutions of permanganate are intrinsically unstable,decomposing slowly but observably in acid solution.• In basic solution, permanganate is a powerful oxidant.

The metals of the first transitionseries• The addition ofKMn0 4 to concentrated H 2 SO 4 givesstoichiometrically:• the dangerous explosive oil, Mn2O7.• This can be extracted into CCl 4 or chlorofluorocarbonsin which it is reasonably stable and safe.

The metals of the first transitionseries• IRON• Iron is the second most abundant metal, after AI, andthe fourth most abundant element in the earth's crust.The core of the earth is believed to consist mainly of Feand Ni.• The major ores are• Fe 2 O 3 (hematite),• Fe 3 O4 (magnetite),• FeO(OH) (limonite),• FeCO 3 (siderite).

The metals of the first transitionseries• Pure iron is quite reactive. In moist air it is ratherrapidly oxidized to give a hydrous iron(III) oxide (rust)• The metal dissolves readily in dilute mineral acids• With nonoxidizing acids and in the absence of air, Fellis obtained• Very strongly oxidizing media, such as concentratedHNO 3 or acids containing dichromate, passivate iron• Iron is attacked by hot concentrated NaOH

The metals of the first transitionseries• The addition of OH‐to Fe 2 + solutions gives the palegreen hydroxide, which is very readily oxidized by air togive red‐brown hydrous iron (III) oxide.• The iron (II) ion, [Fe(H 2 O) 6 ] 2+ , gives many crystallinesalts.• Mohr's salt, (NH4)2[Fe(H 2 O) 6 ] (SO4)2, is reasonablystable toward air and loss of water,• is commonly used to prepare standard solutions of Fe 2+for volumetric analysis and as a calibration substancein magnetic measurements.

The metals of the first transitionseries• COBALT• The trends toward decreased stability of the very highoxidation states and the increased stability of the II staterelative to the III state• series Ti, V, Cr, Mn, and Fe, persist with Co.• The highest oxidation state is now IV, and only a few suchcompounds are known. Cobalt(III) is relatively unstable insimple compounds,• Addition of OH ‐ to C0 2+ hydroxide,• blue or pink depending on the conditions;• weakly amphoteric dissolving in very concentrated OH ‐ togive a blue solution containing the [CO(OH)4] 2‐ ion.

The metals of the first transitionseries• Cobalt always occurs in association with Ni and willusually occur also with As.• The chief sources of Co are "speisses," which areresidues in the smelting of arsenical ores of• Ni, Cu, and Pb.• Cobalt is relatively unreactive,• although it dissolves slowly in dilute mineral acids.

The metals of the first transitionseries• NICKEL• Nickel occurs in combination with• arsenic, antimony, and sulfur e.g. millerite (NiS)garnierite, a magnesium‐nickel silicate• Nickel is also found alloyed with iron in meteors;• the interior of the earth considerable quantities.• The ore is roasted in air to give NiO,• Reduced to Ni with C.• Nickel is usually purified by electrodeposition

The metals of the first transitionseries• Nickel is quite resistant to attack by air or water• at ordinary temperatures when compact• electroplated as a protective coating.• It dissolves readily in dilute mineral acids.• The metal or high Ni alloys are used to handle F2 and othercorrosive fluorides.• Nickel absorbs considerable amounts of hydrogen when finelydivided and special forms ofNi (e.g., Raney nickel) are used forcatalytic reductions.• The Chemistry of Nickel(II), d 8• The binary compounds, such as NiO and NiCI2, need no specialcomment.• Nickel(II) forms a large number of complexes with coordinationnumbers six, five, and four.

The metals of the first transitionseries• COPPER• single s electron outside the filled 3d shell.• little in common with the alkalis• formal stoichiometries in the +1 oxidation state.• Filled d shell less effective than noble gas shell in shieldingthe s electron from nuclear charge,• first ionization potential of Cu is higher than in the alkali• d shell electrons involved in metallic bonding,• heat of sublimation and melting point of copper are alsomuch higher than those of the alkalis.

The metals of the first transitionseries• Most Cu I compounds are fairly readily oxidized to Cu ll ,but further oxidation to Cu III is difficult.• There is a well‐defined aqueous chemistry of Cu 2+• large number of salts of various anions,• many are water soluble,• exist in addition to a wealth of complexes.

The metals of the first transitionseries• Binary Compounds• Black crystalline CuO is obtained by pyrolysis of the nitrateor other oxo salts; above 800 °c it decomposes to Cu 2 O.• hydroxide is obtained as a blue bulky precipitate on additionof NaOH to Cu 2+ solutions• soluble in strong acids• concentrated NaOH• deep blue anions• halides are the yellow chloride and the almost black bromide• infinite parallel bands of square CuX4 units sharing edges

The metals of the first transitionseries• Catalytic Properties of Copper Compounds• Copper compounds catalyze reactions,• heterogeneously, homogeneously, in the vapor phase, in organicsolvents, and in aqueous solutions.• Many of these reactions, particularly if in aqueous solutions,involve oxidation‐reduction systems• and CU I ‐CU II redox cycle.• Molecular oxygen oxidant, e.g. copper‐catalyzed oxidations ofascorbic acid• Cu + + O 2 =CuO 2+• CuO 2+ + H + = Cu 2 + + HO 2• CU + + HO 2 = Cu 2+ + HO 2‐• H + + HO 2‐ = H 2 O 2