Introduction to d-Block Chemistry - Wits Structural Chemistry

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Introduction to d-Block Chemistry - Wits Structural Chemistry

Introduction to d-Block Chemistry (Inorganic Chemistry, 5 th Ed,7.1-7.11)


Structure & Symmetry:Introduction to d-Block Chemistry


Introduction to d-Block ChemistryStructure & Symmetry:REVISION: Electron ConfigurationsIn neutral atom, energy of 4s < energy of 3dHence:Ca: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2[Ar] 4s 2


Introduction to d-Block ChemistryStructure & Symmetry:REVISON: Electron ConfigurationsSo:Cr:Might expect it to be [Ar] 4s 2 3d4but actually[Ar] 4s 1 3d 5


Introduction to d-Block ChemistryStructure & Symmetry:REVISION: Electron ConfigurationsThere is an energy advantage to having a filled or half-filled fill dshell.4sso3d4sand not3d


Introduction to d-Block ChemistryStructure & Symmetry:REVISION: Electron ConfigurationsUnusual electron configurations in the d block:


Introduction to d-Block ChemistryStructure & Symmetry:REVISION: Electron Configurations• In the representative (s and p) elements, propertieschange dramatically across period.• Not so in the d and f block – very gradual changes.• Electrons being added to inner shells (d or f), so atomic radiirather similar.


Introduction to d-Block ChemistryStructure & Symmetry:REVISION: Electron ConfigurationsBecause of similarity ofatomic radii, metals canreplace each other in themetallic lattice.Hence, alloys readily formed


Introduction to d-Block ChemistryCoordination Compounds:Complex:OOCoNOCentral metal atomor ion (a Lewis acid).....surrounded by a setof ligands (Lewis bases).....OO[Co(OH 2 ) 5 (NH 3 )] 3+


Introduction to d-Block ChemistryCoordination Compounds:Ligand:“An ion or molecule that can have an independent existence”Donor atomBr –E.g.:HNHHHBromido Ammine Aqua 22Bipyridine2,2-BipyridineOHNNOOCoNOAcceptor atomOO


Introduction to d-Block ChemistryCoordination Compounds:Ligand:MemoriseTable 7.1,p. 200‐201


Introduction to d-Block ChemistryCoordination Compounds:Inner-sphere complex:“ligands attached directly to the central metal atom or ion”2+Cl – NH 3Co 3+ [Co(NH 3 ) 5 (Cl)] 2+


Introduction to d-Block ChemistryCoordination Compounds:Outer-sphere complex:“Complex cations can associate electrostatically with anionic ligands and/orsolvent molecules”3+Cl – NH 3Co 3+ {[Co(NH 3 ) 6 ](Cl)] 3+ Cl 3- }


Introduction to d-Block ChemistryCoordination Compounds:Coordination number:“The number of sites around the metal occupied by electron pair donors”OCoNOCOONiOO6-coordinate4-coordinatePreference for coordination numbers 2, 4, & 6, but 3, 5, 7, and 8 also known


Introduction to d-Block ChemistryCoordination Compounds:Types of Ligands and Complexes:The list of potential ligands is a long one.• Ligand must possess an unshared pair of electrons• This includes virtually all anions (e.g. F - , CN - , SCN - , NO 2- , etc)• A large number of neutral molecules (e.g. H 2 O, NH 3 , CO, amines,sulfides, ethers ...)• And even some cations (e.g. H 2 N-NHNH 3+ )


Introduction to d-Block ChemistryCoordination Compounds:Types of Ligands and Complexes:Ligands can be classified as monodentate, or polydentatePolydentate ligands can be bidentate, tridentate, etc.monodentatepolydentateNNNbidentateH 2 NNHtridentateAmbidentate ligands have more than one different potential donor atome.g. Thiocyanate (SCN - )z+Mz+MS C NN C SNH 2


Introduction to d-Block ChemistryCoordination Compounds:Types of Ligands and Complexes:Polydentate ligands can act as chelating agents – polydentate ligands thatform a ring by attaching at two or more sites on the metal, e.g. theethylenediamine ligand (en):OH 2CNenChelate ringCoBite angle(L-M-L angle inchelate ring)Chelatecomplex


Introduction to d-Block ChemistryNaming Coordination Compounds:In the early days, complexes were often named after the investigators whoprepared them. E.g.K[C 2 H 5 PtCl 3 ] NH 4 [Cr(NCS) 4 (NH 3 ) 2 ]-HHNHH+SSCCNNH H HNCrNHHHNNCCSSZeise’s saltReinecke’s salt


Introduction to d-Block ChemistryNaming Coordination Compounds:Modern procedures follow a few simple rules:1. Cation named first, followed by anion2. Ligands named first in alphabetical order. Prefixes not considered whenalphabetizing. E.g. The tri in trichloro is not considered.(a)Any coordinated d anions end in o. (Cl - is chlorido; CN - is cyanido; SCN - isthiocyanato; etc...)(b) Neutral ligands normally named using the name of the molecule(H 2 NCH 2 CH 2 NH 2 is ethylenediamine, C 5 H 5 N is pyridine, etc), but a fewhave special names (H 2O is aqua, NH 3 is ammine, CO is carbonyl, seeTable 7.1, Shriver, 5’th Ed)(c) Any coordinated cations end in ium. Not common, but NH 2 NH 2(c) Any coordinated cations end in ium. Not common, but NH 2 NH 2(hydrazine) can accept a H to form NH 2 NH 3+ and still coordinate to metalthrough 1 st N. Coordinated NH 2 NH 3+ then named as hydrazinium.


Introduction to d-Block ChemistryNaming Coordination Compounds:Modern procedures follow a few simple rules:3. The prefixes di, tri, etc. are used to indicate the number of simple ligandssuch as Cl - , CN - . If the name of the ligand already containes one of theseprefixes, then bis, tris, tetrakis, etc. Isused(eg (e.g. ethylenediamine).4. After naming ligand, name of the metal follows with its oxidations stateindicated by Roman numerals.5. If the complex ion is an anion, the name ends in ate.6. The donor atom of an ambidentate ligand is indicated using the ‘κ (Greekletter kappa) terminology’. E.g. For SCN-, attachment through N is writtenas thiocyanato-κN, t and attachment t through h S is written as thiocyanato-κS. t In the formula, the coordinating atom is sometimes indicated by underliningit, e.g. [Fe(OH 2 ) 5 (NCS)] 2+7. If a polydentate ligand bridges two metals, the ligand is indicated byincluding μ before the name of the ligand.


Introduction to d-Block ChemistryNaming Coordination Compounds:Modern procedures follow a few simple rules:7. cont... E.g.4+CoOCoNH 3μ-oxido-bis(pentaamminecobalt(III))If the number of centres bridged is greater than 2, a subscript is used toindicate the number (E.g. μ 3 if the ligand bridges 3 metal centres)


Introduction to d-Block ChemistryNaming Coordination Compounds:Class Exercises(1) Name the following:[Co(NH 3 ) 6 ]Cl 3


Introduction to d-Block ChemistryNaming Coordination Compounds:Class Exercises(2) Name the following:[Co(NH 3 ) 5 Cl]Cl 2(3) Name the following:[Co(en) 2 (Br) 2 ]Cl(4) N th f ll i(4) Name the following:K[Pt(C 2 H 4 )Cl 3 ]


Introduction to d-Block ChemistryCoordination Numbers and GeometriesThe total number of points of attachment tothe central element is termed thecoordination number (CN) and this can varyfrom 2 to as many as 16, but is usually 6.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesWhat controls the coordination number (CN)?Size of metal ion:2 nd and 3 rd row metals usually have higher CN’s than 1 st rowmetalsSize of metal ion decreases as formal charge increases, e.g.3 2r(Fe 3+ ) < r(Fe 2+ )High coordination numbers most likely with large metal ionsIncreasing C.N..N.easing C.Incre


Introduction to d-Block ChemistryCoordination Numbers and GeometriesWhat controls the coordination number (CN)?Size of ligands:Bulky ligands usually result in low CN’sbecause of steric hindranceHigh coordination numbers most likelyHigh coordination numbers most likelywith small ligands.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesWhat controls the coordination number (CN)?Electronic factors:Metals with large number of electrons (to the right of the d blockusually form complexes with low CN’sIf metal forms multiple bonds with ligands, low CN’s result


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 2:• Uncommon• Largely limited to d 10 metal ionsE.g. [CuCl 2 ] - [Ag(NH 3 ) 2 ] + (R 3 P)AuCl R = alkyl∠L-M-L ≈ 180 o• Bulky ligands may force 2-coordinate environment on metals that usuallyprefer a greater number of ligands.E.g.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 2:Among the common ligands for d 10 ions are the phosphanes:PH 3 - phosphane (common: phosphine)PH 2 CH 3 -PPH 3 -methylphosphanetriphenylphosphane


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 3:• Uncommon• Structures usually trigonal planar.• Favoured by d-block elements with lots of d-electrons (d 8 , d 9 , d 10 )• Trigonal pyrimidal, and T-shape also sometimes found. Arise fromdistortions of the ‘parent’ trigonal planar shape.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 3 cont.:E.g.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 4:• Very common• Tetrahedral (T d ) shape most frequently observed.T d symmetry• T d dominantly found in complexes that are overall neutral or anionic, or whichhave d 0 or d 10 electron counts.E.g. [CuX 4 ] 2− , [FeX 4 ] 2− and [CoX 4 ] 2− (X = halogen anion).RuO 4 , [CdCl 4 ] 2‐• Typical for cases where metal ions are small (high oxidation numbers), andligands are large (e.g. Cl - Br - I - ).


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 4:Typical T d complexes:T d symmetry


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 4:• Square planar (D 4h ) complex are also encountered butrarer than T d• Often associated with d 8 (but not limited to) configurationsof metals belonging g to the 4d- and 5d-series (Rh + , Pd 2+,Au 3+, etc.)D 4hsymmetry• E.g’s of square planar complexes (note, all d 8 ):


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 4 cont.:ClPtNNPtClcis-[PtCl (NH ) ]2 3 2trans-[PtCl (NH ) ]2 3 2• Geometrical isomers have different chemical & biologicalproperties. Cisplatin is an anti-cancer drug; trans isomer noteffective as a drug.• NB: Not all d 8 systems are necessarily sq-planar! d 8 Ni(II)can form octahedral, tetrahedral, and square-planarcomplexes.• Forced sq-planar complex also possible:


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 4 cont.:• Tetrahedral geometry can be converted into square planar geometry (& viceversa) by ligand displacements (no bonds broken):• Tetrahedral & sq-planar are ideal 4-coordinate geometries. In reality,compounds exist which encompass a range of intermediate (D 2h) ) geometriesas well.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 5:• Less common than 4- or 6-coordinate complexes, but still widely found.• Complexes are normally either square-pyrimidal (C 4V symmetry) ortrigonal bipyrimidal (D 3h symmetry).C 4vsymmetryD 3h symmetry• Distortions from these ideal geometries are common, and intermediatestructures between these two geometries are known.• Common for lighter, smaller metal ions, rare for heavier transition metals.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 5 cont.:• Overall trigonal bipyrimidal is found rather than square-pyrimidal, exceptwhere polydentate ligands impose steric constraints, or where π-bondingoccurs. E.g.:ClOWCl-ClCl-[WCl 4(O)]• But since there is little energy difference between trigonal bipyrimidal andsquare-pyrimidal structures, exceptions are common. E.g. In crystals ofNi(CN) 5 ] 3- , both geometries are found.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 5 cont.:• In solution, trigonal bipyrimidal complexes with monodentate ligands are oftenhighly fluxional (able to twist into different shapes).• I.e. An axial ligand at one moment becomes equatorial at the next.• Accomplished by Berry pseudorotation:tiaaeee e aeeeeaaae


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 6:• Most common coordination type by far for d metals.• Seen for all configs from d 0 to d 10 .• Octahedral (O h ) geometry by far the most common. A few examples ofti trigonal prismatic (D 3h symmetry) geometry is also known.• Many structures exist that are intermediate between these two geometries.O hsymmetryTrigonal prismD 3h symmetry


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 6 cont.:• Interconverting octahedral to trigonal prismatic geometries:• Best thought of as two triangles that are either staggered, or eclipsed.• Some chelating ligands with small bite angles can distort octahedralcomplexes into trigonal prismatic complexes.


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 6 cont.:• Deviations from O h geometry:AxialelongationAxialcompressiTetragonal distortions of transligands. Results in D 4h symmetryessionO hsymmetry


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 6 cont.:• Deviations from O h geometry:O hsymmetryRhombic distortion. Results inD 2h symmetry


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 7:• 7-coordination common for the larger d-block metals, especially 4d and 5d.• Limiting ‘ideal’ geometries include pentagonal bipyramid, cappedoctahedron, and capped trigonal prism.Pentagonal bipyramid: id[UO 2 (C 5 H 7 O 2 ) 2 (C 4 H 8 O)]


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 7 cont:Capped octahedron:


Introduction to d-Block ChemistryCoordination Numbers and GeometriesC.N. = 7 cont:Capped trigonal prism:


Introduction to d-Block ChemistryCoordination Numbers and GeometriesPolymetallic Complexes:• Complexes that contain >1 metal atom• Three cases exist:(1) Metal atoms directly attached Called a metal cluster(2) Metal atoms linked through bridging g ligands Called a cage complex(3) A combination of (1) and (2)E.g. (1):


Introduction to d-Block ChemistryCoordination Numbers and GeometriesPolymetallic Complexes:• Complexes that contain >1 metal atom• Three cases exist:(1) Metal atoms directly attached Called a metal cluster(2) Metal atoms linked through bridging g ligands Called a cage complex(3) A combination of (1) and (2)E.g. (2):


Introduction to d-Block ChemistryIsomerism• A molecular formula alone is often not enough to identify a compoundunambiguously.• For example, draw the compound [Co(NH 3 ) 5 (NO 2 )] 2+NOONCoConitrito-κNnitrito-κOAmbidentate ligands give rise to linkage isomerism.


Introduction to d-Block ChemistryIsomerismLinkage Isomerism• Same ligand that can link through different atoms.• Eg. CN - , SCN - , NO-2• In the formula, the link-atom is usually underlined, e.g. [Pt(SCN) 4 ] 2-• One can often predict the more stable linkage isomer on the basis of the hardsoftprinciple.


Introduction to d-Block ChemistryIsomerismIonization Isomerism• Occurs when a ligand and a counterion in one compound exchange places.• Consider [Co(NH 3 ) 5 Cl]NO 2 and [Co(NH 3 ) 5 NO 2 ]Cl• Same empirical formula, but not the same compound.• The complexes are stable enough such that rapid exchange of the ions in thecoordination-sphere and those in the solvent does not occur.• What would happen if exchange did occur?


Introduction to d-Block ChemistryIsomerismHydrate Isomerism• Many complexes are prepared in aqueous solutions, therefore crystallinesolids often contain water of crystallization.•But H 2 O can also act as a ligand.• Consider [Co(NH 3 ) 5 H 2 O](NO 2 ) 3 and [Co(NH 3 ) 5 NO 2 ](NO 2 ) 2 • H 2 O• In one case H 2 O is coordinated in the other it is present as water ofIn one case H 2 O is coordinated, in the other it is present as water ofhydration.


Introduction to d-Block ChemistryIsomerismCoordination Isomerism• Only possible for salts in which both cation & anion are complex ions.• Arise due to interchange of ligands between the two metal centres.• Consider [Pt II (NH 3 3) ][Pt IV Cl 6 ] and [Pt IV (NH 3 Cl ][Pt II 4 6] 3) 4 2 Cl 4 4]


Introduction to d-Block ChemistryIsomerismGeometrical Isomerism• Same composition, different geometrical arrangement of atomsSquare-planar complexes:• Different groups positioned either cis (90 o ) or trans (180 o ) to each other:• E.g. [PtCl 2 (NH 3 ) 2 ] has two ligand arrangements:ClPtNNPtClcis-[PtCl (NH ) ]2 3 2 trans-[PtCl (NH ) ]2 3 2


Introduction to d-Block ChemistryIsomerismGeometrical IsomerismExampleThe two square planar isomers of[PtBrCl(PMe 3 ) 2 ] give the following 31 P NMRspectra. Which is which?Br PMe 3PtBrClPtPtMe 3 PClMe 3 P PMe 3


Introduction to d-Block ChemistryIsomerismGeometrical IsomerismOctahedral complexes:• For a complex having the general formula [MA 4B 2 2]cis and trans isomerismcan occur. E.g. [Co(NH 3 ) 4 Cl 2 ] + :cis-(violet i coloured)trans-(green coloured)


Introduction to d-Block ChemistryIsomerismGeometrical IsomerismOctahedral complexes:• For a complex having the general formula [MA 3B 3 3] there are two ways ofarranging the ligands, either facial (fac) or meridional (mer).• fac carries 3 A ligands in an equilateral triangle on one face of the octahedron,and 3 B ligands on the other face:fac-[MA 3 B 3 ]


Introduction to d-Block ChemistryIsomerismGeometrical IsomerismOctahedral complexes:mer isomer has each of one type of ligand (A) lying in a plane that includes themetal, at right-angles to the plane of the other type of ligand (B).mer-[MA 3 B 3 ]


Introduction to d-Block ChemistryIsomerismGeometrical IsomerismIs the following the fac or the mer isomer of [Co(NO 2 ) 3 (NH 3 ) 3 ]?


Introduction to d-Block ChemistryIsomerismGeometrical IsomerismSpecific conditions, often empirically determined, will lead to the synthesis ofdifferent isomers.


Introduction to d-Block ChemistryIsomerismOptical Isomerism• The occurrence of enantiomers is concerned with chirality.• A pair of enantiomers consists of two molecular species which are nonsuperimposablemirror images of each other.E ti f di ti d t ft h h l ti• Enantiomers of a coordination compound most often occur when chelatingligands are involved.


Introduction to d-Block ChemistryIsomerismOptical IsomerismIf a complex has:Identifying Optical Isomers:ClXzyH NNH33-a centre of inversion, i CoiH 3NNH 3ClChanging x, y, z, to -x, -y, -z for each atom results in the exactsame compound.


Introduction to d-Block ChemistryIsomerismOptical IsomerismIdentifying Optical Isomers:If a complex has:σand/or- a mirror plane, σHN 3OH 2Coσit’s mirror image will besuperimposable and themolecule is achiral.HO2HN3Xzy


Introduction to d-Block ChemistryIsomerismOptical IsomerismIdentifying Optical Isomers:Which of these is chiral, and which is achiral? Explain.AB


Introduction to d-Block ChemistryIsomerismOptical IsomerismIdentifying Optical Isomers:Tris chelate complexes of transition metals are chiralAnd there is a method for assigning their absolute configuration.


Introduction to d-Block ChemistryIsomerismOptical IsomerismIdentifying Optical Isomers:Imagine a view along a three fold rotation axis of the regularoctahedron.LambdaDeltaΛ-[Co(en) 3 ] 3+ Δ-[Co(en) 3 ] 3+

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