24. Transition Metals and Coordination Compounds

Which of the following complexes cannot have geometric isomers?

i) [PtCl₂(NH₃)₂]

ii) K₄[Fe(CN)₄(OH)₂]

iii) [Ag(NH₃)₂]Cl

iv) [Ni(H₂O)₂(NH₃)₂]Br₂

The complex [Fe(NH₃)₅OCN]²⁺ has two isomers. Draw their structures.

How many isomers are possible for [Cu(H₂O)₂(NH₃)₂]SO₄? Draw their structures.

In acidic aqueous solution, the complex trans-[Co(en)₂Cl₁]²⁺(aq) undergoes the following substitution reaction:

trans-[Co(en)₁Cl₂]⁺(aq) + H₂O(l) → trans-[Co(en)₂(H₂O)Cl]²⁺(aq) + Cl^–(aq)

The reaction is first order in trans-[Co(en)₂Cl₂]⁺(aq), and the rate constant at 25°C is 3.2×10^–5 s^–1.

(d) Is the reaction product chiral or achiral? Explain.

Constitutional isomers of a ruthenium(II) coordination compound are shown below. <IMAGE>

(a) Give the formula and name for structures 1-3.

(b) Which structures are linkage isomers? 

(c) Which structures are ionization isomers?

Six isomers for a square planar palladium(II) complex that contains two Cl-and two SCN-ligands are shown below.

 <IMAGE>

(a) Which structures are cis-trans isomers?

(b) Which structures are linkage isomers?

Tell how many diastereoisomers are possible for each of the following complexes, and draw their structures. 

(a) Pt(NH₃)₃Cl (square planar) 

(b) [FeBr₂Cl₂(en)]^-

Tell how many diastereoisomers are possible for each of the following complexes, and draw their structures. 

(c) [Cu(H₂O)₄Cl₂]⁺

(d) Ru(NH₃)₃I₃

Refer to the figure showing the structure of various ligands to answer questions 4 and 5. <IMAGE REFERENCE> Which ligand(s) can participate in linkage isomerism?

(a) All of the ligands can participate in linkage isomerism

(b) I, II, and III

(c) I and IV

(d) II and IV

Identify the false statement about the structures of the complex ion [Fe(en)2Cl2]+ shown below. <IMAGE>

(a) Structures I and II are cis-trans isomers.

(b) Structures I and IV are cis-trans isomers.

(c) Structures I and III are enantiomers.

(d) Structures II and IV are enantiomers.

Imagine two complexes, one tetrahedral and one square planar, in which the central atom is bonded to four different ligands (shown here in four different colors). Is either complex chiral? Explain.

<IMAGE>

Which of the following complexes can exist as diastereoisomers?

(a) [Cr(NH₃)₂Cl₄]^-

(b) [Co(NH₃)₅Br]²⁺

(c) [MnCl₂Br₂]^2- (tetrahedral)

(d) [Pt(NH₃)₂Br₂]^2-

Which of the following complexes can exist as enantiomers? Draw their structures.

(a) [Cr(en)₃]³⁺

(b) cis-[Co(NH₃)Cl]²⁺

(c) trans-[Co(en)₂(NH₃)Cl]²⁺

(d) [Pt(NH₃)₃Cl₃]⁺

Draw all possible diastereoisomers of [Cr(C₂O₄)₂(H₂O)₂]^-. Which can exist as a pair of enantiomers?

Draw the three possible diastereoisomers of the triethylenetetramine complex [Co(trend)Cl₂]⁺. Abbreviate the flexible tetradentate trien ligand H₂NCH₂CH₂NHCH₂CH₂NHCH₂CH₂NH₂ as <IMAGE>. Which of the isomers can exist as a pair of enantiomers?

What is a racemic mixture? Does it affect plane-polarized light? Explain.

Draw the structure of all isomers of the octahedral complex [NbX₂Cl₄]^- (X- = NCS^-), and identify those that are linkage isomers.

The glycinate anion, gly-= NH₂CH₂CO₂ ^-, bonds to metal ions through the N atom and one of the O atoms. Using <IMAGE> to represent gly-, sketch the structures of the four stereoisomers of Co(gly)₃.

Draw the structures of all possible diastereoisomers of an octahedral complex with the formula MA₂B₂C₂. Which of the diastereoisomers, if any, can exist as enantiomers?

What is the systematic name for each of the following molecules or ions? Include cis or trans prefixes for diastereoisomers. Platinum is Pt(II) in square planar complexes and Pt(IV) in octahedral complexes. <IMAGE>

(1) <IMAGE>

(2) <IMAGE>

(3) <IMAGE>

(4) <IMAGE>

Consider the following isomers [Cr(NH3)2Cl4]-. <IMAGE> <IMAGE OF MOLECULE 4>

(a) Label the isomers as cis or trans.

(b) Which isomers are identical, and which are different?

(c) Do any of these isomers exist as enantiomers? Explain.

Consider the following ethylenediamine complexes. <IMAGE> <IMAGE OF MOLECULE 1>

(a) Which complexes are chiral, and which are achiral?

(b) Draw the enantiomer of each chiral complex.

(c) Which, if any, of the chiral complexes are enantiomers of one another?

Consider the following ethylenediamine complexes. <IMAGE> <IMAGE OF MOLECULE 2>

(a) Which complexes are chiral, and which are achiral?

(b) Draw the enantiomer of each chiral complex.

(c) Which, if any, of the chiral complexes are enantiomers of one another?

Consider the following ethylenediamine complexes. <IMAGE> <IMAGE OF MOLECULE 3>

(a) Which complexes are chiral, and which are achiral?

(b) Draw the enantiomer of each chiral complex.

(c) Which, if any, of the chiral complexes are enantiomers of one another?

Tris(2-aminoethyl)amine, abbreviated tren, is the tetradentate ligand N(CH2CH2NH2)3. Using <IMAGE> to represent each of the three NCH2CH2NH2 segments of the ligand, sketch all possible isomers of the octahedral complex [Co(tren)BrCl]+.

Consider the octahedral complex [Co(en)(dien)Cl]2+, where dien = H2NCH2CH2NHCH2CH2NH2, which can be abbreivated <IMAGE>

(a) The dien (diethylenetriamine) ligand is a tridentate ligand. Explain what is meant by 'tridentate' and why dien can act as a tridentate ligand.

(b) Draw all possible stereoisomers of [Co(en)(dien)Cl]2+ (dien is a flexible ligand). Which stereoisomers are chiral, and which are achiral?

The reaction of the octahedral complex Co(NH3)3(NO2)3 with HCl yields a complex [Co(NH3)3(H2O)Cl2]+ in which the two chloride ligands are trans to one another.

(a) Draw the two possible stereoisomers of the starting material [Co(NH3)3(NO2)3]. (All three NO2- ligands are bonded to Co through the N atom.)

(b) Assuming that the NH3 groups remain in place, which of the two starting isomers could give rise to the observed product?

There are three coordination compounds with the empirical

formula Co1NH3231NO223 in which all the nitrite ions

are bonded through the N atom. Two isomers have the

same molar mass but different nonzero dipole moments.

The third compound is a salt with singly charged ions and a molar mass twice that of the other compounds.

(a) Draw the structures of the isomeric compounds.

Spinach contains a lot of iron but is not a good source of dietary iron because nearly all the iron is tied up in the oxalate complex [Fe(C₂O₄)₃]^3-.

(d) Draw the structure of [Fe(C₂O₄)₃]^3-. Is the complex chiral or achiral?

Cobalt(III) trifluoroacetylacetonate, Co(tfac)₃, is a sixc oordinate, octahedral metal chelate in which three planar, bidentate tfac ligands are attached to a central Co atom:

<IMAGE>

(a) Draw all possible diastereoisomers and enantiomers of Co(tfac)₃.

Cobalt(III) trifluoroacetylacetonate, Co(tfac)₃, is a sixcoordinate, octahedral metal chelate in which three planar, bidentate tfac ligands are attached to a central Co atom:

<IMAGE>

(b) Diastereoisomers A and B have dipole moments of 6.5 D and 3.8 D, respectively. Which of your diastereoisomers is A and which is B?

Which of the complexes or complex ions has geometric (cis or trans) isomers?

How many geometric isomers are possible for the complex [CrF₃Br₃]₃?

Which of the following two substances are made of the same element but conformed in different ways?