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19.2 Coordination chemistry of transition metals  (Page 9/25)

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In 1965, scientists at Michigan State University discovered that there was a platinum complex that inhibited cell division in certain microorganisms. Later work showed that the complex was cis -diaminedichloroplatinum(II), [Pt(NH 3 ) 2 (Cl) 2 ], and that the trans isomer was not effective. The inhibition of cell division indicated that this square planar compound could be an anticancer agent. In 1978, the US Food and Drug Administration approved this compound, known as cisplatin, for use in the treatment of certain forms of cancer. Since that time, many similar platinum compounds have been developed for the treatment of cancer. In all cases, these are the cis isomers and never the trans isomers. The diamine (NH 3 ) 2 portion is retained with other groups, replacing the dichloro [(Cl) 2 ] portion. The newer drugs include carboplatin, oxaliplatin, and satraplatin.

Key concepts and summary

The transition elements and main group elements can form coordination compounds, or complexes, in which a central metal atom or ion is bonded to one or more ligands by coordinate covalent bonds. Ligands with more than one donor atom are called polydentate ligands and form chelates. The common geometries found in complexes are tetrahedral and square planar (both with a coordination number of four) and octahedral (with a coordination number of six). Cis and trans configurations are possible in some octahedral and square planar complexes. In addition to these geometrical isomers, optical isomers (molecules or ions that are mirror images but not superimposable) are possible in certain octahedral complexes. Coordination complexes have a wide variety of uses including oxygen transport in blood, water purification, and pharmaceutical use.

Chemistry end of chapter exercises

Indicate the coordination number for the central metal atom in each of the following coordination compounds:

(a) [Pt(H 2 O) 2 Br 2 ]

(b) [Pt(NH 3 )(py)(Cl)(Br)] (py = pyridine, C 5 H 5 N)

(c) [Zn(NH 3 ) 2 Cl 2 ]

(d) [Zn(NH 3 )(py)(Cl)(Br)]

(e) [Ni(H 2 O) 4 Cl 2 ]

(f) [Fe(en) 2 (CN) 2 ] + (en = ethylenediamine, C 2 H 8 N 2 )

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Give the coordination numbers and write the formulas for each of the following, including all isomers where appropriate:

(a) tetrahydroxozincate(II) ion (tetrahedral)

(b) hexacyanopalladate(IV) ion

(c) dichloroaurate(I) ion (note that aurum is Latin for "gold")

(d) diaminedichloroplatinum(II)

(e) potassium diaminetetrachlorochromate(III)

(f) hexaaminecobalt(III) hexacyanochromate(III)

(g) dibromobis(ethylenediamine) cobalt(III) nitrate

(a) 4, [Zn(OH) 4 ] 2− ; (b) 6, [Pd(CN) 6 ] 2− ; (c) 2, [AuCl 2 ] − ; (d) 4, [Pt(NH 3 ) 2 Cl 2 ]; (e) 6, K[Cr(NH 3 ) 2 Cl 4 ]; (f) 6, [Co(NH 3 ) 6 ][Cr(CN) 6 ]; (g) 6, [Co(en) 2 Br 2 ]NO 3

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Give the coordination number for each metal ion in the following compounds:

(a) [Co(CO 3 ) 3 ] 3− (note that CO 3 2− is bidentate in this complex)

(b) [Cu(NH 3 ) 4 ] 2+

(c) [Co(NH 3 ) 4 Br 2 ] 2 (SO 4 ) 3

(d) [Pt(NH 3 ) 4 ][PtCl 4 ]

(e) [Cr(en) 3 ](NO 3 ) 3

(f) [Pd(NH 3 ) 2 Br 2 ] (square planar)

(g) K 3 [Cu(Cl) 5 ]

(h) [Zn(NH 3 ) 2 Cl 2 ]

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Sketch the structures of the following complexes. Indicate any cis , trans , and optical isomers.

(a) [Pt(H 2 O) 2 Br 2 ] (square planar)

(b) [Pt(NH 3 )(py)(Cl)(Br)] (square planar, py = pyridine, C 5 H 5 N)

(c) [Zn(NH 3 ) 3 Cl] + (tetrahedral)

(d) [Pt(NH 3 ) 3 Cl] + (square planar)

(e) [Ni(H 2 O) 4 Cl 2 ]

(f) [Co(C 2 O 4 ) 2 Cl 2 ] 3− (note that C 2 O 4 2− is the bidentate oxalate ion, − O 2 CCO 2 − )

(a) [Pt(H 2 O) 2 Br 2 ]:
Two structures are shown. At the center of each is a P t atom. The structure on the left is labeled, “cis.” From this atom, a single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the right to a B r atom. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the right to a second B r atom. Another single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the left to the O atom of an H subscript 2 O group. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the left to a second O atom of an H subscript 2 O group. The structure on the right is labeled, “trans.” From the central P t atom, a single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the right to a B r atom. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the right to the O atom of an H subscript 2 O group. Another single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the left to the O atom of a second H subscript 2 O group. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the left to a second B r atom.;
(b) [Pt(NH 3 )(py)(Cl)(Br)]:
Three structures are shown. At the center of each is a P t atom. From this atom in the first structure on the left, a single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the right to a C l atom. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the right to the N atom of an N H subscript 3 group. Another single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the left to a B r atom. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the left to p y. The middle structure shows a single bond represented by a dashed wedge extending from a vertex at the P t atom up and to the right to a B r atom. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the right to the N atom of an N H subscript 3 group. Another single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the left to p y. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the left to a to a C l atom. The third structure shows a single bond represented by a dashed wedge extending from a vertex at the P t atom up and to the right to p y. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the right to the N atom of an N H subscript 3 group. Another single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the left to a C l atom. Similarly, a single bond represented by a solid wedge extends from a vertex at the P t atom down and to the left to a B r atom.;
(c) [Zn(NH 3 ) 3 Cl] + :
Inside of brackets, a central Z n atom is bonded to a C l atom and three N atoms in N H subscript 3 groups in a tetrahedral spatial arrangement. Short line segments are used to represent a bond extending above to the C l atom and down and to the left to the N of the N H subscript 3 group from the Z n atom. A dashed wedge with the vertex at the Z n atom and wide end at the N atom of an N H subscript 3 group is used to represent a bond down and to the right of the Z n atom. The final bond is indicated by a similar solid wedge again directed down and only slightly right of center beneath the Z n atom to the N of an N H subscript 3 group. Outside the brackets a superscript plus sign is shown.;
(d) [Pt(NH 3 ) 3 Cl] + :
This structure shows a single bond represented by a dashed wedge extending from a vertex at the P t atom up and to the right to the N atom of an N H subscript 3 group. Similarly, two single bonds represented by solid wedges extend from vertices at the P t atom down and to the right and down and to the left to the N atoms of N H subscript 3 groups. Another single bond represented by a dashed wedge extends from a vertex at the P t atom up and to the left to a C l atom. This structure is enclosed in brackets with superscript plus sign appearing to the right of the brackets.;
(e) [Ni(H 2 O) 4 Cl 2 ]:
Two structures are shown. The first is labeled, “trans.” Below this label inside brackets is a central N i atom. From the N i atom, line segments indicate bonds to C l atoms above and below. Above and to both the right and left, dashed wedges with their vertex at the N i atom widening as they move out from the atom indicate bonds with O atoms of H subscript 2 O groups. Similarly, solid wedges below to both the right and left indicate bonds to the O atoms of H subscript 2 O groups. This structure is enclosed in brackets. The second structure is labeled, “cis.” Inside brackets is a central N i atom. From the N i atom, line segments indicate bonds to a C l atom above and the O atom of an H subscript 2 O group below. Above and to both the right and left, dashed wedges indicate bonds with O atoms of H subscript 2 O groups. Similarly, a solid wedge below to the right indicates a bond with a C l atom and a solid wedge to the lower left indicates a bond to the O atoms of an H subscript 2 O group. This structure is also enclosed in brackets.;
(f) [Co(C 2 O 4 ) 2 Cl 2 ] 3− :
This figure includes three structures. The first structure includes a central C o atom that has four O atoms and two C l atoms attached with single bonds. These bonds are indicated with line segments extending above and below, dashed wedges extending up and to the left and right, and solid wedges extending below and to the left and right. C l atoms are bonded at the top and at the upper left of the structure. The remaining four bonds extend from the central C o atom to O atoms. The O atoms are each connected to C atoms which are each connected with double bonds to O atoms extending outward from the central C o atom. These C atoms are connected in pairs with bonds indicated by short line segments, forming two rings in the structure. This entire structure is enclosed in brackets. Outside the brackets to the right is a superscript 3 negative sign. The second structure, which appears to the be mirror image of the first structure, includes a central C o atom that has four O atoms and two C l atoms attached with single bonds. These bonds are indicated with line segments extending above and below, dashed wedges extending up and to the left and right, and solid wedges extending below and to the left and right. C l atoms are bonded at the top and at the upper right of the structure. The remaining four bonds extend from the central C o atom to O atoms. The O atoms are each connected to C atoms which are each connected with double bonds to O atoms extending outward from the central C o atom. These C atoms are connected in pairs with bonds indicated by short line segments, forming two rings in the structure. This entire structure is enclosed in brackets. Outside the brackets to the right is the superscript 3 negative sign. The third structure includes a central C o atom that has four O atoms and two C l atoms attached with single bonds. These bonds are indicated with line segments extending above and below, dashed wedges extending up and to the left and right, and solid wedges extending below and to the left and right. C l atoms are bonded at the top and bottom of the structure. The remaining four bonds extend from the central C o atom to the O atoms. The O atoms are each connected to C atoms which are in turn each double bonded to O atoms extending outward from the central C o atom. These C atoms are connected in pairs with bonds indicated by short line segments, forming two rings in the structure. This entire structure is enclosed in brackets. Outside the brackets, to the right, is a superscript 3 negative sign. This final structure has rings of atoms on opposite sides of the structure.

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Draw diagrams for any cis , trans , and optical isomers that could exist for the following (en is ethylenediamine):

(a) [Co(en) 2 (NO 2 )Cl] +

(b) [Co(en) 2 Cl 2 ] +

(c) [Pt(NH 3 ) 2 Cl 4 ]

(d) [Cr(en) 3 ] 3+

(e) [Pt(NH 3 ) 2 Cl 2 ]

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Name each of the compounds or ions given in [link] , including the oxidation state of the metal.

(a) tricarbonatocobaltate(III) ion; (b) tetraaminecopper(II) ion; (c) tetraaminedibromocobalt(III) sulfate; (d) tetraamineplatinum(II) tetrachloroplatinate(II); (e) tris- (ethylenediamine)chromium(III) nitrate; (f) diaminedibromopalladium(II); (g) potassium pentachlorocuprate(II); (h) diaminedichlorozinc(II)

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Name each of the compounds or ions given in [link] .

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Specify whether the following complexes have isomers.

(a) tetrahedral [Ni(CO) 2 (Cl) 2 ]

(b) trigonal bipyramidal [Mn(CO) 4 NO]

(c) [Pt(en) 2 Cl 2 ]Cl 2

(a) none; (b) none; (c) The two Cl ligands can be cis or trans . When they are cis , there will also be an optical isomer.

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Predict whether the carbonate ligand CO 3 2− will coordinate to a metal center as a monodentate, bidentate, or tridentate ligand.

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Draw the geometric, linkage, and ionization isomers for [CoCl 5 CN][CN].


This figure shows eight structures, each inside brackets in three rows. The first row contains three structures, the second row contains three structures, and the third row contains two structures. These structures are described in increasing order moving left to right and top to bottom in the figure. Each includes a central C o atom with line segments indicating bonds above and below the central atom. Above and to both the left and right, dashed wedges with vertices at the C o atom widening as they move out from the atom indicates single bonds. Similarly, solid wedges below and to both the left and right indicate single bonds. Outside each structure in brackets, to the right, an element or group is identified in brackets as a superscript. In the first structure, the C atom of a C N group is bonded to the C o atom. All 5 remaining bonds are with C l atoms. C N appears in brackets as a superscript outside the structure. In the second structure, the N atom of a C N group is bonded to the C o atom. All 5 remaining bonds are with C l atoms. C N appears in brackets as a superscript outside the structure. In the third structure, the C atom of two C N groups are bonded to the C o atom at the top and bottom of the structure. All 4 remaining bonds are with C l atoms. C l appears in brackets as a superscript outside the structure. In the fourth structure, the C atom of a C N groups is bonded to the C o atom at the top and the N atom of a C N group which is bonded at the bottom of the structure. All 4 remaining bonds are with C l atoms. C l appears in brackets as a superscript outside the structure. In the fifth structure, the N atom of two C N groups are bonded to the C o atom at the top and bottom of the structure. All 4 remaining bonds are with C l atoms. C l appears in brackets as a superscript outside the structure. In the sixth structure, the C atom of two C N groups are bonded to the C o atom at the top and upper right of the structure. All 4 remaining bonds are with C l atoms. C l appears in brackets as a superscript outside the structure. In the seventh structure, the C atom of a C N group is bonded to the C o atom at the top of the structure and the N atom of a C N group is bonded at the upper right of the structure. All 4 remaining bonds are with C l atoms. C l appears in brackets as a superscript outside the structure. In the eighth structure, the N atom of two C N groups are bonded to the C o atom at the top and upper right of the structure. All 4 remaining bonds are with C l atoms. C l appears in brackets as a superscript outside the structure.

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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