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Structures of Coordination Compounds

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Wilkinson's catalyst, chlorotris(triphenylphosphine)rhodium(I), RhCl[P(C6H5)3]3

Depending upon conditions, this catalyst crystallizes in orange or red forms. Both show approximately square planar coordination about the rhodium with the red form showing slightly more deviation toward tetrahedral geometry. The carbon and hydrogen atoms are omitted in the structures shown below.


Potassium hexachloroplatinate(IV), K2[PtCl6]

The chlorine atoms form an octahedral coordination sphere around the platinum.

8 unit cells showing the positions of atoms in the crystal structure.

Space group Fm3m (225) a=969 pm


Tris(ethylenediamine)cobalt(III) chloride, [Co(en)3]Cl3

The nitrogen atoms of the ethylenediamine ligands form an octahedral coordination sphere around the cobalt. The actual compound is [Co(en)3]2Cl6.NaCl.6H2O. The hydrogen atoms are omitted in the five structures shown below.

The coordination sphere of the cobalt.

Unit cell.

Space group P3 (143) a=1147; c=806 pm

Extended structure showing the coordination spheres of the cobalt and sodium.

The ion [Co(en)3]3+ exists in two enanteromeric forms. The images below are arranged to show that each is the mirror image of the other.

d isomer.

l isomer.


Potassium octachlorodirhenate(III), K2[Re2Cl8] 

The rhenium atoms here are linked by a quadruple bond that is responsible for the eclipsed orientation of the sets of four chlorine atoms around the rhenium atoms.

The coordination sphere.

Extended structure showing relationship of Re2Cl92- units to each other.

Space group P1 (2) a=675; b=786; c=761 pm; a=102.0o; b=108.9o; g=104.8o


Potassium nonahydridorhenate(VII), K2[ReH9]

The hydrogen atoms are arranged about the rhenium atom at the corners of a tricapped trigonal prism.

The coordination sphere.

Unit cell.

Space group P62m (189) a=961; c=551 pm


Diamminedichloroplatinum(II), Pt(NH3)2Cl2, cis and trans

The compound cis-platin, cis-Pt(NH3)2Cl2, is a best-selling anticancer drug. The trans isomer is inactive.

cis isomer.

trans isomer.


Zeise's salt, K[PtCl3(H2C=CH2)]

This compound, first prepared in 1825 by Zeise, was the first organometallic compound, although the nature of the bonding was not understood until many years later. The carbon-carbon bond of the ethylene ligand lies at a right angle to the plane of the three chlorine atoms.

The coordination sphere.

Unit cell.

Space group P21c (14) a=1121; b=843; c=970 pm


Dichlorobis(ethylenediamine)cobalt(III), Co(en)2Cl2+, cis and trans

The compound [Co(en)2Cl2]Cl exists in two isomeric forms. The trans compound precipitates from cool aqueous solution and the cis from hot aqueous solution. The hydrogen atoms are omitted in the structures shown below.

cis isomer.

trans isomer.


Chromium(II) acetate, Cr2(OAc)4.2H2O

This compound has four acetate ions bridging between two chromium atoms. A set of four oxyen atoms (one from each of the four acetate ions) occupies the equatorial positions in a nearly octahedral environment around each chromium atom. Water molecules occupy the axial positions. (Hydrogen atoms do appear in this structure.)


Tetrachloroferrate(III), FeCl4-

In concentrated hydrochloric acid, chloride ions form a tetrahedral coordination sphere around the iron(III) ion.


Trichlorotris(pyridine)rhodium(III), Rh(py)3Cl3, fac and mer

Octahedral coordinations compounds having three (monodentate) ligands of one type and three of another can form two geometrical isomers designated as fac (facial) and mer (meriodinal). The structures below show these two isomeric forms for the compound Rh(py)3Cl3. The hydrogen atoms are omitted in these structures.

fac isomer.

mer isomer.


Carbonylchlorodioxygenbis(triphenylphosphine)iridium, IrClCO(O2)(PPh3)2

This compound shows the coordination of both atoms of dioxygen to iridium.

The x-ray crystal structure cannot distinguish the coordinations sites of the chlorine and the carbonyl and thus cannot locate the carbonyl oxygen atom, which is not shown.


Dimanganese decacarbonyl, Mn2(CO)10

Each manganese atoms has a nearly octahedral environment of one manganese atom and five carbonyl ligands. The two sets of carbonyl ligands around the two manganese atoms are in a staggered conformation.

The coordination sphere.

Unit cell.

Space group I2/a (15) a=1409; b=685; c=1424 pm; b=105.08o


Ferrocene, bis(cyclopentadienyl)iron, Fe(h5-C5H5)2

The cyclopentadiene ligands by be viewed as anions containing 6 p-electrons, a number suitable for an aromatic system. The carbon atoms form planar pentagonal rings above and below the iron atom.

The coordination sphere.

Unit cell.

Space group P21/a (14) a=1044; b=757, c=582 pm; b=120.95o


Uranocene, bis(cyclooctatetraenyl)uranium(IV), U(h8-C8H8)2

The cyclooctatetraene ligands by be viewed as dianions containing 10 p-electrons, a number suitable for an aromatic system. The carbon atoms form planar octagonal rings above and below the uranium atom. Hydrogen atoms are not shown.

The coordination sphere.

Unit cell.

Space group P21/n (14) a=708; b=871, c=1063 pm; b=98.75o

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