21 Transition metals and coordination chemistry Transition metals in general Importance Cr stainless steel Mn steelmaking Pt, Pd catalysts Fe transport of oygen nitrogen fiation (Mo also) Zn catalyst in biological system vitamin B 12 Similarity within a period adding inner d, f electrons: less effect on chemistry lanthanides and actinides Metallic Ag Cu best heat conductor of heat and e the second Ionic compounds often contain more than one oidation state Forms comple ions usually colored: electron transition between d orbitals often paramagnetic: contain unpaired electrons 1
lectron configurations and oidation states The first row Sc Ti V Cr Mn Fe i Cu Zn 4s 2 3d 1 4s 2 3d 2 4s 2 3d 8 4s 2 3d 10 4s 1 3d 5 4s 1 3d 10 Oid state 3+ 2+ 2+ ntain higher oid states. Mn: 2+, 3+, 4+, 7+ 2+ is very common due to loss of two 4s electrons Oidation potential large stronger reducing ability igher nuclear charge: less higher oid states small Sie atomic radii a Y Sc large small lectron-electron repulsion 3d small 4d large 5d big change atomic number Similar: lanthanide contraction Filling inner 4f orbitals small effect on sie Increasing nuclear charge offsets the increase of n 2
ordination compounds Metal n+ Y n unter ion M n+ + m (M m ) n+ K comple igand using lone electron pair to form a bond to a metal ion Donor atom atom of the ligand bound to the metal ion ordination number the number of donor atoms. [( 3 ) 5 ] 2 : 3+ has a coordination # of 6 igands Monodentate ligand ( 單牙配基 ): forms one bond Bidentate ligand: forms two bonds chelates ( 螯合物 ) Polydentate ligand. 2 C C 2 2 2 ethylenediamine (en) O O O C C O C 2 2 C C 2 C 2 C 2 2 C O C C O O O ethylenediaminetetraacetate (DTA) Chelating agents form more stable complees 3
omenclature. [( 3 ) 5 ] 2 pentaamminechlorocobalt(iii) chloride Rules Cation before anion igands before metal (in formula: metal first) arrange in alphabetical order (prefi does not count) Anionic ligands end in O eutral 3 aido 3 ammine Br bromo 2 O aqua O hydroo CO carbonyl 2 CO 3 carbonato O nitrosyl 2 C 2 O 4 oalato C cyano pyridine Oidation number in ( ) Prefi mono 1 di 2 tri 3 tetra 4 penta 5 hea 6 With complicated ligand name bis( ) 2 tris( ) 3 tetrakis( ) 4 :. [(en) 3 ] 3 tris(ethylenediamine)cobalt(iii) chloride mple is anion: end in -ate. K 4 [Fe(C) 6 ] potassium heacyanoferrate(ii) 4
Isomerism Structural isomerism: different bonding Stereoisomerism: different space arrangement Structural isomerism ordination isomerism [Cr( 3 ) 5 SO 4 ]Br and [Cr( 3 ) 5 Br]SO 4 inkage isomerism nitro nitrito O 3 O 3 O O 3 3 3 3 3 yellow 3 red tetramminechloronitrocobalt(iii) chloride tetramminechloronitritocobalt(iii) chloride Stereoisomerism Geometrical isomers Pt 3 3 cis yellow (cisplatin: a cancer drug) 3 3 3 3 trans green 3 Pt 3 trans pale yellow 3 3 3 3 cis violet 5
Optical isomers nantiomers ( 對掌體 ; 鏡像異構 ) Mirror images but not superimposable (mpounds with this property are chiral ( 掌性的 )) mirror achiral mirror 2 2 2 2 2 2 2 2 same (contain a plane of symmetry: must be achiral) Properties of enantiomers most physical and chemical properties are the same but rotate plane polaried light in different direction 平面偏極光 6
Bonding in comple ion The localied electron model based on the valence bond theory M nsidered as covalent bond Can be viewed as M ewis acid ewis base umber of hybridied metal orbitals = umber of ligands M. ( 3 ) 6 3+ coordination # = 6 d 2 sp 3 octahedral The crystal field model focuses on the energies of d orbitals lor and magnetic properties of transition metals: related to d orbitals Interaction between ions and ligands: lectronic attraction and repulsion Only ionic bonding is considered Five d orbitals same when not used in bonding When ligands approach repulsions occur between ligand electrons and d orbital electrons 7
Octahedral complees d y y d y d y y d 2y 2 The repulsive interactions in d 2 and d 2-y are the highest 2 d 2, d 2-y 2 if field from ligands were spherical y e g t 2g d 2 6Dq 4Dq y d orbitals in free metal ion d y, d, d : crystal field splitting energy (a measurement of crystal field strength of the ligand). 3+ Strong field (large ) Weak field (small ) ow spin igh spin Spectrochemical series C > O 2 > en > 3 > 2 O > O > F > > Br > I Strong field Weak field ligands ligands ( 3 ) 6 3+ : diamagnetic F 6 3 : paramagnetic 8
. Cr 3+ h [Cr( 2 O) 6 ] 3 violet weaker smaller absorbs longer wavelength [Cr( 3 ) 6 ] 3 yellow stronger larger absorbs shorter wavelength ote: For a given ligand As charge on the metal ion increases weak-field ligand may become strong field (M- distance smaller) Tetrahedral crystal field shorter one of the 3d orbitals points to the ligands y longer d y, d, d d 2, d 2-y 2 is smaller than octahedral field Always high spin 9
Square planar field octahedral field remove ligands on ais square planar field d 2 y 2 octahedral d 2 d 2 y 2 if field from ligands were spherical d y d 2 d y d y d d y d inear field octahedral field remove ligands on y plane oactahedral linear field d 2 d 2 d 2 y 2 if field from ligands were spherical d y d d y d y d d y d2y2 10
Biological importance Transition metals easily undergo oid. and red. electron transfer transport and storage of O 2 as catalysts and drugs Iron in cytochrome c ( 細胞色素 ) Cys S Fe S Cys CO 2 CO 2 11