Ethylenediamine ligand

Ni — N bond breaks and one NH2 group of an ethylenediamine ligand dissociates from the metal complex. 

To indicate the number of ligands of a particular type, the prefixes di, tri, tetra, and so on are used. If the name of the ligand contains one of these prefixes, the number of ligands is indicated by using the prefixes bis, tris, tetrakis, and so forth. For example, two ethylenediamine ligands would be indicated as bis(ethylenediamine) rather than diethylenediamine. 

The dichlorobis(ethylenediamine)cobalt(II) ion can exist in two geometrical isomers. For the trans isomer, there is a plane of symmetry that bisects the cobalt ion and the ethylenediamine ligands, leaving one Cl on either side of the plane. However, the cis isomer has no plane of symmetry so two optical isomers exist. This is also the case for [Co(en)3]3+ as is illustrated in Figure 16.3. 

For example, consider the [Co(en)3]3+ ion, in which three bidentate ethylenediamine ligands bond to the Co3+ ion creating 3 rings in the complex. 

The ethylenediamine ligand is a strong field ligand in the spectrochemical series. 

All attempts to produce optical isomers of [Co(en)3]3+ based upon a trigonal prismatic structure are shown below. The ethylenediamine ligand appears as an arc in each diagram below ... 

A re-investigation of the complex [Pd(en)(enH)Cl]Cl2,H20 has confirmed this formulation containing a protonated ethylenediamine ligand. In addition, the complex was observed to undergo a facile solid-state reaction ... 

One interesting octahedral complex is based on the Ai,A, Ai,Ai -bis[(2-hydroxy ben2yl)(2-methylpyridyl)]ethylenediamine ligand (BBPEN), a derivative of the common Schiff base called salm [31]. The [V(BBPEN)]PF6 complex has the four... 

The tris(ethylenediamine)ruthenium(III) species is obtained by oxidation of [Ru(en)3]2+ with, for example, iodine4 or bromine.6 The oxidizing agent and conditions employed must be chosen carefully to avoid further oxidation of the ethylenediamine ligand to coordinated diimine.7 In the present procedure solid silver anthranilate is used to oxidize [Ru(en)3] [ZnCl4], and [Ru(en)3] Cl3 is isolated. In this heterogeneous procedure the desired [Ru(en)3]Cl3 is the only soluble product and can easily be separated from the insoluble silver, silver chloride, and zinc dianthranilate. Other less soluble [Ru(en)3]3+ compounds can be obtained easily from the soluble chloride. 

On heating K4[Mo2C1s] with ethylenediamine, and then adding hydrochloric acid to an aqueous solution of the crude product, orange crystals of [Mo2(en)4]Cl4 are obtained.17 These give an absorbance (5— 6 ) band at 475 nm. It is unlikely that the ethylenediamine ligand is bridging. Cyclic voltammetry measurements have shown that the complex exhibits an irreversible oxidation at +0.78 V (SCE). 

Both 1- and 1 -A -alkylated ethylenediamine ligands are prochiral and coordination completes the asymmetry at the nitrogen atom. Under favorable conditions, such complexes can be resolved and the absolute configuration determined by X-ray or other methods. Structures (17)-(22) show some representative configurations. 

Complexes of the fully 7V-alkylated ethylenediamine ligand, e.g. l,l,4,4-Me4-en and I,l,4,4-Et4-en, have not been neglected and (23) shows the arrangements of the Et groups in Cu( 1,1,4,4-Et4-en)-(N03)2.4SS This complex shows C2 symmetry and should be compared with the arrangement adopted for Pt(l,l,7,7-Et4-dien)X+ (43) which has a mirror plane. 

Fig. 119. (Top) Crown-cryptand for the analysis of barium and ethylenediamine ligand for anion sensing (tpen). (Bottom) Dendrimer-like ligand for anion sensing.

The complex can exist with both a cis and a trans configuration. Since the compound has two bidentate ethylenediamine ligands, the isomers with both chlorine atoms in the cis configuration will exist as a pair of enantiomers. These will have the descriptors OC-6-2 2-A and OC-6-2 2-A, respectively, and belong to the symmetry point group C2. The trans isomer has a plane of symmetry and three mutually perpendicular C2 axes and therefore belongs... 

Young DA, Freedman TB, Lipp ED et al (1986) Vibrational circular-dichroism in transition-metal complexes. 2. Ion association, ring conformation, and ring currents of ethylenediamine ligands. J Am Chem Soc 108 7255-7263... 

The fiilly N-alkylated ethylenediamine ligand, for example, I,l,4,4-Me4en, is not always carefiilly distinguished from the... 

The complex ion exhibits geometrical isomerism, since the ethylenediamine ligands can be across from or next to each other ... 

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