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Coordinationcompound

QuestionAnswer
What are coordination compounds Compounds from due to combination of two or more simple stable salt which retain there identity in solid as well as in dissolved state are called coordination compounds.
What is addition compound Compounds made up of two or more stable compounds by crystallization in a fixed stoichiometric ratio are called addition compound.
Types of addition compounds addition compounds are of two types. First,they lose their identity in solution called double salt and those which retain their identity in solution called coordination or Complex compounds.
What is coordination entity or coordination sphere It constitutes a central metal atom or Ion bonded to a fixed number of Ions or molecules with co-ordinate bonds. For example, in coordination sphere of [CoCl3(NH3)3], cobalt ion (Co3+) is surrounded by three Ammonia molecules and three chloride ions.
What is central atom or ion In coordination entity, the atom or ion to which a fixed number of Ions or groups are attached in a definite geometrical arrangement around it, is called central atom or ion.
Why central atom or ion is called Lewis acid Central metal atom or iron accepts lone pair of electrons from the ligands and hence it act as Lewis acid.
What is ligands The donor atoms, molecules and anions which donate a pair of electrons to the metal atom or ion are called ligands hence ligands are Lewis bases. For example, in [No(NH3)6]Cl2, NH3 is ligand (Lewis base).
What is coordination number It may be defined as number of co-ordinate bonds formed with central atom or Ion by the ligands. For example, in [Ag(CN)2]-, [Cu(NH3)4]2+ and [Cr(H2O)6]3+ , the coordination number of Ag, Cu and Cr is 2, 4 and 6 respectively.
What is the coordination number of Fe and Co in [Fe(C2O4)3]3- and [Co(en)3]3+ ? The coordination number of both Fe and Co is 6 because (C2O4)2-(oxalate) and en (ethylene-1,2-diamine) forms two co-ordinate bonds each with Central metal atom or ion.
How do we determine coordination number of central atom or ion It is determined only by number of Sigma bonds formed by ligands with Central metal atom or ion. Pi bonds, if formed, are not counted for this purpose.
What are counter ions The ionizable groups are written outside the square bracket and are called counterions. For example, in K4[Fe(CN)6] and [Cu(NH3)4]SO4, counter ion is K+ and (SO4)2- respectively.
What is coordination polyhedron The spatial arrangement of ligands around Central metal or ion is called coordination polyhedron.
What is oxidation number Oxidation number of the central metal atom or iron in a complex is the charge present on it if all the ligands are removed along with the electron pairs that are shared with central atom.
What are homoleptic and heteroleptic complexes Complexes which have only one type of ligands are homoleptics for eg., [Co(NH3)6]3+ and have more than one type of ligands for eg., [Co(NH3)4Cl2]+ are heteroleptic complexes.
Excess of aqueous KCN is added to an aqueous solution of copper sulphate. Why there is no precipitate of copper sulphide when H2S(g) is passed through this solution? The complex ion is stable and does not dissociate to give Cu2+ and Cl- ions. Hence, no precipitation with H2S is formed.
Classification of ligands on the basis of charge (i) anionic ligands (negatively charged) for eg., F-, Cl-, CN-, S2-, (SO4)2- etc (ii) neutral ligands (uncharged and electron pair Donor) for eg., CO, NH3, H2O etc. (iii) cationic ligands (positively charged) for eg., NO+, NH2-, NH3+ etc
What is denticity It is number of co-ordinate bonds formed by 1 ligand.
Classification of ligands on the basis of denticity Monodentate, bidentate, polydentate, ambidentate and flexidentate.
Monodentate Ligands having single Donor atom. For eg., Cl-, H20, NH3, NH2-NH3+, etc.
What is bidentate Ligands can bind through two donor atoms (used simultaneously) eg., en (ethylene-1, 2-diamine),ox (oxalate),gly(glycinate),Acetylacetonate (acac) and dimethylglyoxime (dmg) etc.
Polydentate Single ligands having several donor atoms, e.g., EDTA4- ion (hexadentate) (ethylene diamine tetraacetate ion) and diethylenetriamine (dien).
Ambidentate Ligands which can bind through two different atoms (only one at a time) to form coordinate bond, e.g., N02-, SCN- etc.
Flexidentate Ligands having variable denticity. which depends upon nature of metal ion. For e.g., EDTA having denticity 4 or 6. .
Classification of ligands on the basis of type of donation of lone pair Sigma donor, Sigma donor- pi acceptor and pi donor pi acceptor.
Sigma Donor Ligands that donate lone pair and make Sigma bond to central atom/ion, e.g., H20, NH3, etc.
Sigma Donor Pi acceptor Ligands that donate lone pair to central atom/ion by making sigma-bond and accept appreciable amount of electron density from metal atom/ion into its vacant pi or pi star orbital, e.g., CO, NO etc. (these are also called pi-acid ligands).
Pi donor pi acceptor Ligands that donate and accept pi-electrons through pi-bonds with central atom/ion, eg., HC triple bonded to CH, C2H4, C6H6 etc.
Who was Alfred Werner and what did he do Alfred Werner was the first to formulate his ideas about the structures of coordination compounds. He prepared a series of complexes by combination of Cobalt chloride and ammonia called Werner's series.
According to werner's theory, how many types of valencies a metal Ion possess Each metal Ion possesses two types of valencies (a) primary valency (principle or ionizable) and (b) secondary valency (subsidiary or non ionizable.)
What is primary valency These are normally ionizable and are satisfied by anions only. Number of primary valency depends upon Oxidation state of Central metal atom or ion.
What is secondary valency These are non-ionizable, and are satisfied by ions or neutral electron pair donor molecules (i.e., ligands). Number of secondary valencies depends upon size and charge of central metal atom/ion. It represents coordination number of central metal atom/ion.
Which one of the two valencies are directional Primary valencies are non-directional while secondary valencies are directional.
What decides the geometry of complex Geometry of complex is decided by secondary valency. Thus, [Co(NH3)6]3+, [CoCl(NH3)5]2+ and [CoCl2(NH3)4]+ are octahedral entities, while [No(CO)4] and [PtCl4]-2 are tetrahedral and Square planar respectively.
K2[PtCl6] is ionized to 3 ions when dissolved in water. Will it give white precipitate with AgNO3 solution No, because all Cl- are in coordination sphere and are non ionizable.
Write the first two rules for writing the formula of mononuclear coordination entities (i)The central atom is listed first, (ii)Ligands are then listed in alphabetical order and their placement does not depend on their charge.
Write the third rule for writing formula of mononuclear coordination entities (iii)In case of abbreviated ligands (polydentate) the first letter of abbreviation is used to determine the position of ligand in alphabetical order.
Write the fourth and fifth rules for writing formula of mononuclear coordination entities (iv) Entire coordination entity is enclosed in square brackets, whether charged or not. Polyatomic ligands are enclosed in paranthesis, and also their abbreviations. (v)No space is left in between names of ligands and central atom/ion.
Write the 6th and 7th rule for writing the formula of mononuclear coordination entities. (vi)When the formula of a charged coordination entity is to be written without counter ion, the charge is indicated outside square bracket as a right superscript, with the number before sign. (vii)Charge on cation and anion is counter balanced.
Write the first two rules for naming of mononuclear coordination compounds (i)Positive part of complex compounds will be named first, followed by negative part. (ii)Ligands are named first in alphabetical order, followed by central atom (reverse in case of writing formula).
Write the third rule for naming of mononuclear coordination compounds (iii)Prefixes mono, di, tri, tetra etc. are used to indicate number of ligands. Prefixes bis, tris, tetrakis are used for complex ligands (including a numerical prefix). Eg.,[No(H2O)2(en)2]SO4 is named as diaquabis (ethylene diamine) nickel (Il) sulphate.
Write the fourth rule for naming of mononuclear coordination compounds (iv)Name of anionic ligands end with 'o', cationic ligands end with 'ium'. For neutral ligands, regular names are used except 'aqua' for H20, 'ammine' for NH3, 'nitrosyl' for NO, 'carbonyl' for CO. These are placed within ( ).
Write the last two rules for naming of mononuclear coordination compounds (v)Oxidation state of central atom/ion is indicated in roman numerals in bracket after the name of metal. (vi)When coordination entity has negative charge, then name of central metal ends with 'ate', otherwise not.
Examples of anionic ligands HS- (mercapto), CN- (Cyano), NC- (isocyano), F- (fluorido),OH- (hydroxo), N3- (azido), N-3 (nitrido), SCN- (thiocyanato-S), NCS- (thiocyanato-N), ONO- (nitrito-o),N02- (nitrito-N).
Examples of cationic ligands NH2—NH3+ (hydrazinium), NO+(nitrosonium), NO2+ (nitronium).
What is isomerism The compounds having same molecular formula but different arrangement of atoms due to which they differ in one or more physical properties are called isomers and the phenomenon is called isomerism.
Structural isomerism Compounds having same molecular formula but different structures. Further it is divided into ionisation isomerism, linkage isomerism, coordination isomerism, solvate isomerism and coordination-position isomerism.
Ionisation isomerism Isomers when ionized give different ions in solution or in molten state, show ionisation isomerism. Eg.,[CO(NH3)5SO4]Br and [Co(NH3)5Br]SO4.
Created by: sherickp