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1、Chapter NineCoordination CompoundsCoordination Compound:acompoundinwhichacentralmetalionisattachedtoagroupofsurroundingmoleculesorionsbycoordinatecovalentbonds.Anemia(贫血症)CH2OHCHSHCH2SHCH2OHCHSCH2SHg+HgAnti-tumour（肿瘤）agentCoordination Compounds9-1 Basic Concepts9-2 The Chemical Bond Theory 9-2.1 Val
2、ence Bond Theory 9-2.2 Crystal Field Theory9-3 Coordination Equilibrium 9-4 Chelates 9-1 Basic ConceptsAnintroductiontocomplexionswithanexplanationofwhatligandsareandhowtheybondtothecentralmetalion.centralmetalion transition metals(but not all) complex ion ligands (anions or polar molecules) Transit
3、ionMetals(T.M.)Thisgivesrisetothefollowingproperties:DistinctivecolorparamagneticcompoundscatalyticactivitygreattendencytoformcomplexionsZn,Cd,HgarenotconsideredT.M.LigandsandDonor atomLigands:ionsormoleculesthatisbounddirectlytothemetalatom.e.g.NH3,CN-,H2O,Cl-,I-Donor atom:theatominaligandthatisbou
4、nddirectlytothemetalatom,hasloneelectronpairs.e.g.C,N,O,S,F,Cl,Br,ILigandsDependingonthenumberofdonoratomspresentinthemoleculeorion,ligandscanbeclassifiedas： monodentate : (H2O: :NH3 ) bi dentate ：（：（H2N-CH2-CH2-NH2 ） polydentate： (EDTA) alsocalledchelating agentsCoordination numberCoordination numb
5、er:thenumberofdonoratomssurroundingthecentralmetalatominacomplexion.Commonly,itis2,4,5or6Formonodentate : Cu(NH3)4 SO4,Fe(CN)64- Coordination number = ligand number For bidentate or polydentate： Coordination number ligand numbere.g.Cu(en)2SO4(en=H2N-CH2-CH2-NH2)Coordination number = 4 2Chargesofcoor
6、dinationion:Chargesofcoordinationion=thesumofchargesofcentralionandligandse.g.K3Fe(CN)6Fe3+Fe(H2O)6Cl3Fe3+K4Fe(CN)6Fe2+Containsacomplicatedion-coordinationionCu(NH3)42+,Ag(NH3)2+,Fe(CN)64-MetalionbondedwithotherionormoleculebycoordinationbondHasdefinitestability:KClMgCl26H2O:K+,Cl-,Mg2+KAl(SO4)12H2O
7、:K+,Al3+,SO42+ThefeaturesofcoordinationionSimpleionandcomplexionCuSO4BaCl2BaSO4CuSO4CuSO4NaOHCu(OH)2NH3H2OCu(OH)2BlueNH3H2OCu2+4NH3=Cu(NH3)42+ComplexionAgNO3NaClAgClNH3H2OAg(NH3)2+Cu(NH3)4SO4Ag(NH3)2Cl Thecompositionofcoordinationcompoundthecoordination sphere:1.Thecentralmetalandtheligandsboundtoit
8、constitute.2.squarebracketstosetoffthegroupswithinthecoordinationspherefromotherpartsofthecompound.forexample:Co(NH3)6Cl3 PtCl62+ Cu(NH3)42+SO42-InnerspherecoordinationsphereOutersphereCentralionoratomLigandCoordinationnumberChargesofcoordinationioncoordinationatomordonoratombidentateWhat are the ox
9、idation numbers of the central metal in the complexes below?K3FeF6Na2Ni(CN)4l中文命名原则:1.内界和外界:同一般简单化合物-某化某;某酸某CuCl2;BaSO4Pt(en)2Cl2;Cu(NH3)4SO4;K4Fe(CN)62.内界:按下列次序:Cu(NH3)42+:四氨合铜()离子Fe(CN)64-:六氰合铁()酸根离子配体数-配体名称-“合”-中心离子名称(氧化数)3.当有多种配体时:先无机后有机;先阴性离子后中性分子;先简单后复杂;先常见后不常见;同类按配位原子字母顺序;如先NH3后H2OCo(H2O)(NH3
10、)3Cl2Cl:氯化二氯三氨一水合钴()Pt(NH3)4(NO2)ClCO3:碳酸一氯一硝基四氨合铂()Cu(NH3)4(OH)2:氢氧化四氨合铜()KPt(NH3)Cl5:五氯一氨合铂()酸钾FeFe(CN)6:六氰合铁()酸铁Fe2Fe(CN)6:六氰合铁()酸亚铁Pt(NH3)2Cl2:二氯二氨合铂()Ni(CO)4:四羰基合镍Naming of Coordination CompoundstheInternationalUnionofPureandAppliedChemistry(IUPAC)1.Thecationisnamedbeforetheanion.NaCl:sodiumcho
11、ride2.Withinacomplexiontheligandsarenamedfirst,inalphabeticalorder,andthemetalionisnamedlast.3.Tonametheligands:anionicligandsendin-oneutralligandsusuallycalledthenameofthemoleculeLIGANDNameofLigandinCoord.Cpd.Bromide,Br-BromoChloride,Cl-ChloroCyanide,CN-CyanoHydorxide,OH-HydroxoOixde,O2-OxoCarbonat
12、e,CO32-CarbanatoNitrite,NO3-NitroOxolate,C2O42-OxolatoAmmonia,NH3AmmineCarbonmonoxide,COCarbonylWater,H2OAquoEthylenediamine(en)EthylenediamineNaming Coordination Compounds4.When several ligands of a particular kind are present, we use the Greek prefixes to name them.Di (2)tri (3) tetra (4)Penta (5)
13、Hexa (6)Co(NH3)4Cl2+aretetraamminedichloroIf the ligand itself contains a Greek prefix, we use the prefixes bis, tris, tetrakis to indicate the number of ligands present. e.g. Cu(en)22+ bis(ethylenediamine)5.TheoxidationnumberofthemetaliswritteninRomannumeralsfollowingthenameofthemetal.Cr(NH3)4Cl2+,
14、whichiscalledtetraamminedichlorochromium()ion.6.Ifthecomplexionisananion,itsnameendsin-ate.K4Fe(CN)6theanionFe(CN)64-iscalledhexacyanoferrate(II)ion.MetalinanioncomplexAluminumAluminateChromiumChromateCobaltCobaltateCopperCuprateGoldAurateIronFerrateLeadPlumbateMetalinanioncomplexManganese Manganate
15、NickelNickelateSilverArgentateTinStannateTungstenTungstateZincZincateExample9-1:(a)Ni(CO)4,(b)Co(NH3)4Cl2Cl,(c)K3Fe(CN)6,(d)Cr(en)3Cl3.Solution:(a)tetracarbonylnickel(0)(b)tetraamminedichlorocobalt()chloride(c)potassiumhexacyanoferrate().potassiumferricyanide(d)tris(ethylenediamine)chromium()chlorid
16、e.tetraamminedichlorochromium()ion. hexacyanoferrate(II)ion.thecation Cr(NH3)4Cl2+theanionFe(CN)64-Givetheformulaforthefollowingcoordinationcompounds.tetracarbonylnickel(0)tetraammineaquochlorocobalt(III)chlorideCo(NH3)4H2OClCl2Ni(CO)4,How did I know there had to be two chlorides at the end?9-2 The
17、Chemical Bond TheorySeveral different bonding theories have been applied to transition-metal coordination compounds. We shall consider two of these. the valence-bond theory: being covalent and examines the hybridization of orbitals on the metal. the crystal-field theory: from an ionic point of view
18、and focuses on(集中集中) the effect of the surrounding ligands on the energies of the metal d orbitals 9-2.1ValenceBondTheoryMagnetismIsomerism(异构体异构体)stability9-2.2CrystalFieldTheoryTheSplitting（分裂）（分裂）ofthedorbitalsinoctahedralFieldHigh-spinandLow-SpinCoordinationCompounds Thecolorofcoordinationcompou
19、nds9-2.1thevalence-bondtheoryaligandorbitalcontainingtwoelectronsoverlapsanunoccupiedorbitalonthemetalatom.donateapairofelectronsintoasuitableemptyhybridorbitalonthemetal,1.Centralionbondswithligandsbycoordinationbond.2.Theemptyorbitalsofcentralionmusthybridizetoincreasebondingability.3.Therearetwot
20、ypesofcoordinationcompounds:_ outer-orbitalcoordinationcompounds_ inner-orbitalcoordinationcompoundsl the valence-bond theory Outline :ExampleAg(NH3)2+47AgKr4d105s1Centralion:Ag+4d105s05p0hybridsphybridization(outerorbital)2:NH3Ag(NH3)2+（linear）Ag+:Ni(NH3)42+28Ni3d84s2Centralion:Ni2+3d84s04p0hybrids
21、p3hybridization(outerorbital)4:NH3Ni(NH3)42+(tetrahedral)NiNiNi(CN)42-Centralion:Ni2+3d84s04p0hybriddsp2hybridizationinnerorbitalNi(CN)42-(squareplanar)4:CN-realignmentCo(NH3)63+CoatomCo3+ionCo(NH3)63+3d74s23d6d2sp3hybridization6:NH3Co(NH3)63+(octahedral)(inorbitalcomplex)CoF63+Coatom3d74s2Co3+ionCo
22、F63+3d4s4p4dsp3d2hybridization6:F-(octahedral)3d6MagnetismParamagnetism: substances containing unpaired electrons are paramagnetic.diamagnetic:substances without unpaired electrons are diamagnetic. magnetic moment: = =n (n+2) n (n+2) n : is the number of unpaired electrons Example:ForFe(H2O)6SO4 =5.
23、26B.M accordingtoaboveequation,n=4,sothereare4unpairedelectronsinthiscoordinationcompound.Example:ForK4Fe(CN)6 =0 B.M accordingtoaboveequation,n=0,sothereare0unpairedelectronsinthiscoordinationcompound.Example:ForFe(H2O)6SO4,=5.26B.M accordingtoaboveequation,n=4,sothereare4unpairedelectronsinthiscoo
24、rdinationcompound.3d4s4p4d26Fe:3d64s24p04d0outerorbitalSp3d2hybridizationFe2+:3d64s04p04d0Example:ForK4Fe(CN)6,=0 B.M accordingtoaboveequation,n=0,sothereare0unpairedelectronsinthiscoordinationcompound.Fe2+:3d64s04p04d0d2sp3hybridization,innerorbital3d4s4pTable 9-4:Somecommontypesofhybridizationandg
25、eometries.lIsomerism(异构体)Isomers:Two or more compounds that have the same formula but a different structure (that is, the same collection of atoms but arranged in different ways) are called isomers. Isomers Geometric isomers (Stereo立体立体 isomers)Optical isomersStructural isomers Structural isomerismS
26、tructural isomers are that differ in how the atoms are joined together.Example:Co(NH3)5(SO4)BrredCo(NH3)5BrSO4violet CH3-CH2-CH2-COOH CH3-CH-COOH CH3硝基四氨合钴（）亚硝酸四氨合钴（） Geometric isomerism (Stereoisomerism, cis-trans isomerism)areisomersthathavethesamechemicalbondsbutdifferentspecialarrangements.theis
27、omerwithlikegroupsclosetogetheriscalledthecis-isomer.whereastheonewithlikegroupsfarapartiscalledthetrans-isomer.Geometric Isomerism (stereoisomerism)Pt(NH3)2Cl2ClNH3cisPtClNH3NH3CltransPtClNH3cis-diamminedichloroplatinum(II)bothcoordinationcompoundsarenamed:diamminedichloroplatinum(II)cistransOptica
28、l Isomerism“反应停”的手性结构分子化学名称叫做酞胺呱啶酮酞胺呱啶酮，是一种常用于安定精神和抑制妊娠恶心的镇静药和催眠药。被反应停夺去胳膊的孩子们“海豹”式畸形，不是手足全无，就是缺胳膊少腿，甚至手掌直接长在肩膀上；或者出现心脏等内脏器官畸形、脑障碍、听力或视力丧失、发生自痹症和癫痫症等9-2.2 Crystal Field Theory（中文P217）1.theligandsinatransition-metalcomplexaretreatedaspointcharges.Thus,aligandanionbecomessimplyapointofnegativecharge.m
29、etalionbecomessimplyapointof positivecharged.2.Fortheformationofacomplexionormoleculeistheelectrostaticattraction3.thistheoryexplainsboththeparamagnetismandcolorobservedincertaincomplexes.中心离子中心离子d轨道角度分布图轨道角度分布图The Splitting of the d Orbitals in Octahedral Fieldeg(d)orbitalst2g(d)orbitals=eg-t2g在数值上
30、等于一个电子由在数值上等于一个电子由t2g轨道跃迁到轨道跃迁到eg 轨道所需的激发能。轨道所需的激发能。crystal field splitting energy, High-Spin and Low-Spin Coordination CompoundsFe(H2O)62+Fe3d64s2Fe2+3d6 Figure: Occupationofthe3dorbitalsincomplexesofFe2+.(a)Lowspin.(b)Highspin.pairing energy Ppairing energy P:the energy required to put two electro
31、ns into the same orbital.1.P:thefourthelectronwillgointooneofthehigherdorbitals.ahigh-spincomplex2.P:anelectroninoneofthelowerenergyorbitals.alowspincomplex 影响分裂能影响分裂能( )的因素的因素中心离子和配体构型一定，中心离子和配体构型一定， 值与配体有关：值与配体有关： 配体：配体：配体固定时，中心离子电荷越高，配体固定时，中心离子电荷越高， 值值越大越大 中心离子中心离子 配体：配体：spectrochemical series, W
32、eak-bonding ligandsStrong-bonding ligands I Br Cl SCN F OH H2O NCS edta NH3 en NO2 CN P: low-spin complex 弱场：弱场： o P: high-spin complex 中心离子中心离子M 对对 的影响的影响： CrCl63- MoCl63- o /cm-1 13600 19200 主量子数主量子数n增大，增大， o增大增大: Cr (H2O)63+ Cr (H2O)62 o /cm-1 17600 14000 电荷电荷Z增大，增大， o增大增大:例：下列四种络合物中，d-d跃迁能量(分裂能)
33、最低的是()a.Fe(H2O)62+b.Fe(H2O)63+c.FeF64-d.FeF63-八面体场中电子在八面体场中电子在t 2g和和eg轨道中的分布轨道中的分布1. Crystal Field Stabilization Energy(CFSE)A measure of the net energy ofstabilization gained by a metal ionsnonbonding d electrons as a result ofcomplexformation. 定义定义: :晶体场稳定能晶体场稳定能(Crystal field stabilization energy
34、, CFSE)是指电子占据分裂的是指电子占据分裂的d轨道后而产生的高于平轨道后而产生的高于平 均能量的额外稳定能均能量的额外稳定能 。晶体场理论的应用ligand field stabilization energy:ameasureoftheincreasedstabilityofacomplexshowingligandfieldsplitting.Ingeneral,CFSE=(#electronsint2g)(-0.40)+(#electronsineg)(0.60)CFSE=6(-0.40)+0(0.60)=-2.40CFSE=4(-0.40)+2(0.60)=-0.40 所吸收光子
35、的频率与分裂能所吸收光子的频率与分裂能 大小有关大小有关 颜色的深浅与跃迁电子数目颜色的深浅与跃迁电子数目 有关有关2. 2. 解释配合物离子的颜色解释配合物离子的颜色 过过渡渡金金属属配配合合物物的的颜颜色色产产生生于于d电电子子在在d轨轨道道之之间间的的跃迁（跃迁（d-d跃迁）。跃迁）。Ohh = The larger the crystal-field splitiing （大）大）, the higher will be the frequency of light absorbed most strongly（大）大）, and the shorter its wavelength（
36、短）.The color of coordination compound Many of the colors of octahedral transition-metal compounds arise from the excitation of an electron from an occupied lower energy orbital to an empty higher energy orbital. The frequency () of light that is capable of inducing such a transition is related to th
37、e energy difference between the two states, which is the crystal-field splitting energy. h = 大大大大短小小小小长h = As we have noted earlier, strong-field ligands cause a large split in the energies of the d orbitals of the central metal atom. Transition metal coordination compounds with these ligands are ye
38、llow, orange, or red since they absorb higher-energy violet or blue light. On the other hand, coordination compounds of transition metals with weak-field ligands are blue-green, blue, or indigo since they absorb lower-energy yellow, orange, or red light.Co(NH3)5Cl2+Purplecompoundabsorbsyellowgreenre
39、gion(wavelengthof530nm)Co(NH3)63+orangecompoundabsorbsvioletregion(wavelengthof410nm)d10(Zn2+,Ag+complexes)iscolorless Ti3+：3d1， Ti(H2O)63+ 吸收可见光中吸收可见光中蓝绿色蓝绿色的光，的光， 使溶液呈使溶液呈红色。红色。 = 492.7nm (蓝绿色蓝绿色)，E=h = 242.79 kJmol-1，波数波数1/ =20300cm-1(1cm-1=11.96Jmol-1)，恰好等于该配离子的分裂能恰好等于该配离子的分裂能o=20 300 cm-1例：已知Fe
40、(CN)63-和FeF63-的磁矩分别为1.7B和5.9B，(1)计算这两种络离子中心离子未成对电子数。(2)写出中心离子d轨道上电子排布。(3)它们是强场还是弱场络合物，说明原因。解：(1)Fe(CN)63-中，由n（n2）=1.7B.M,得n=1FeF63中，由n（n2）=5.9B.M,得n=5(2)Fe(CN)63-中，d轨道上电子排布为t2g5eg0，FeF63中，d轨道上电子排布为t2g3eg2，(3)Fe(CN)63-是强场络合物，因为强场低自旋；FeF63是弱场络合物，因为弱场高自旋。9-3 Coordination equilibrium coordinationCu2+(aq
41、)+4NH3(aq)Cu(NH3)42+(aq) ionization Cu(NH3)42+Cu2+NH34Ks =-Kis=-Cu2+NH34Cu(NH3)42+Stabilityconstantorformationconstant(Kf)InstabilityconstantCu2+NH3 Cu(NH3)2+K1 Cu(NH3)2+Cu2+NH3Cu(NH3)2+NH3 Cu(NH3)22+K2 Cu(NH3)22+Cu(NH3)2+NH3Cu(NH3)22+NH3 Cu(NH3)32+K3 Cu(NH3)32+Cu(NH3)22+NH3Cu(NH3)32+NH3 Cu(NH3)42+K
42、4 Cu(NH3)42+Cu(NH3)32+NH3n-AccumulatestabilityconstantCu2+(aq)+NH3(aq)Cu(NH3)2+(aq)K1=1.4104Cu2+(aq)+2NH3(aq)Cu(NH3)22+(aq)K2=3.17103Cu2+(aq)+3NH3(aq)Cu(NH3)32+(aq)K3=7.76102Cu2+(aq)+4NH3(aq)Cu(NH3)2+(aq)K4=1.391023=K1K2K32=K1K2lg4 lgK1lgK2lgK3lgK4Generally,forthesametypecomplexions:thelargervalueof
43、Ks(Kf),thegreatstabilityofthecomplexioninsolutionandaccountsfortheverylowconcentrationofmetalionsatequilibrium.Forthedifferenttypecomplexions:youneedcomparetheirstabilitybycalculation.（见中文p224【例9-1】）1.InfluenceofacidityoncoordinationequilibriumFe(C2O4)33-Fe3+3C2O42-+Equilibriumshift6H+3H2C2O4酸效应酸效应:
44、 当溶液酸度增大时，当溶液酸度增大时，H+离子可与配体结合生成弱酸，离子可与配体结合生成弱酸，使配离子向解离方向移动，配离子的稳定性降低。使配离子向解离方向移动，配离子的稳定性降低。这种因溶液这种因溶液酸度增大而使配合物稳定性降低的现象酸度增大而使配合物稳定性降低的现象.水解效应:因金属离子与溶液中OH结合而使配离子离解的作用叫做金属离子的水解效应。2.InfluenceofprecipitationoncoordinationequilibriumAg(NH3)2+ Ag+ + 2NH3 +EquilibriumshiftBr-AgBrAgBr(s)Ag+Br-+Equilibriumshi
45、ft2S2O32-Ag(S2O3)23-配位平衡与沉淀平衡的转化，取决于沉淀剂与配位剂争夺金属离子能力的大小及其浓度。实验证明一些阴离子或分子争夺Ag+离子的能力：ClNH3BrS2O32ICNS2这个顺序与形成难溶盐的溶度积KSP和形成配离子的KS大小有关例例9-2 向向Ag(CN)2和和CN的浓度均为的浓度均为0.10molL-1溶液中加入溶液中加入NaCl，能否产生，能否产生AgCl沉淀？沉淀？ 若改加若改加Na2S，能否产生，能否产生Ag2S沉淀？沉淀？ 解：溶液中有下列配位平衡：解：溶液中有下列配位平衡： Ag+ + CN Ag(CN)2 KS1.010 21 由平衡式得：由平衡式得
46、： (molL-1) 生成生成AgCl沉淀的条件是沉淀的条件是 Ag+ ClKSP1.771010 假设加入假设加入NaCl后溶液体积无变化，要生成后溶液体积无变化，要生成AgCl沉淀，则沉淀，则: Cl (molL-1) 显然仅靠加入显然仅靠加入NaCl是无法使是无法使Cl1.771010molL-1。 所以向上述溶液加所以向上述溶液加NaCl不可能产生不可能产生AgCl沉淀。沉淀。 加入Na2S产生Ag2S沉淀的条件是:Ag+2S2-KSP6.6910-50S2-假设加入Na2S后溶液体积无明显变化，则有S2(molL-1)加入Na2S很容易使溶液中S2-6.6910-10molL-1，因
47、此向上述溶液加Na2S时可产生Ag2S沉淀。解解：在溶液中有两个平衡：KSP1.810-10KS1.6107将两式相加得总的平衡式：例例9-3 25，在1L氨水中使0.1molAgCl固体溶解，氨水的浓度至少为多少molL-1？此反应的平衡常数式为：设溶解了的Ag+全部转化为Ag(NH3)2+配离子，则Ag(NH3)2+Cl-0.1molL-1由平衡常数表示式解出平衡时NH3的浓度为：NH3(molL-1)氨水的总浓度至少应为:1.8620.12.06（molL-1）计算说明氨水能否溶解AgI沉淀？Influence of redox on coordination equilibriumFe
48、3+I-Fe2+1/2I2+6F-EquilibriumshiftFeF63-FeCl4-Fe3+4Cl-+EquilibriumI-ShiftFe2+1/2I2根据标准电极电势表得知，当加入NaF晶体时，Fe3+与F结合生成FeF63配离子，使Fe3+离子浓度降低，Fe3+/Fe2+电对的电极电势也随之降低，当Fe3+/Fe2+的电极电势小于I2/I的电极电势时，则氧化还原反应方向发生改变.另一方面，配位平衡也可以转化为氧化还原平衡，使配离子离解。如I可使FeCl4配离子中Fe3+还原成Fe2+，从而使FeCl4配离子离解.电极电势改变电极电势改变Cu+/CuAg+/AgAu3+/Au0/v
49、0.520.7991.50Cu(CN)2-/CuAg(CN)2-/AgAu(CN)2+/Au-0.43-0.31-0.58InfluenceofoncoordinationequilibriumAg(NH3)2+ +2CN- Ag(CN)2- + 2NH3 Mn(en)32+ + Ni2+ Ni(en)32+ + Mn2+利用利用KS值可以判断配位平衡转化的方向和程度。值可以判断配位平衡转化的方向和程度。例例9-4 在HgCl42-配离子的溶液中加入KI溶液，能否生成HgI42-配离子？解：解：溶液中存在下列平衡：查表得知HgI42KS=6.81029；HgCl42KS=1.171015代入上
50、式得：K值很大，说明由HgCl42转化为HgI42的反应完全可以实现9-4 Chelatespolydentate ligandshavetwoormoredonoratomssituatedsothattheycansimultaneouslycoordinatetoametalion.chelating agentsappeartograspthemetalbetweentwoormoredonoratoms.clawNHNH2 2-CH-CH2 2-CH-CH2 2-H-H2 2NNpolydentateligandistheethylenediaminetetraacetateion:
51、Thision,abbreviatedEDTA4-,hassixdonoratoms.Itcanwraparoundametalionusingall six of these donor atoms as shown infigure(9-9).Figure 9-9:TheCoEDTA-ionshowinghowtheethylenediamine-tetraacetateionisabletowraparoundametalion,occupyingsixpositionsinthecoordination-sphere.Ingeneral,chelatingagentsformcoord
52、inationcompoundscontainingrings,thesecoordinationcompoundsarecalledchelates.Thechelatesaremorestablethanrelatedmonodentateligands,whichiscalledchelating effect.Ni2+(aq)+6NH3(aq)=Ni(NH3)62+(aq)K=4108Ni2+(aq)+3en(aq)=Ni(en)32+(aq)K=21018Althoughthedonoratomisnitrogen(N)inbothinstances,Ni(en)32+hasastabilityconstantnearly1010timeslargerthanNi(NH3)62+.Thestabilityofchelatedependsonthenumberandsizeofchelatering.Thelargernumberofchelatering,themorestablechelateis.Whenthechelateringisformedby5 or 6members,thechelateismoststable.
