Ethylenediamine, complex cations

Figure 22.7 (a) Structure of a metal-ethylenediamine complex cation, such as [Cofenjsf. ... 

Figure 22.3 (a) Structure of a metal-ethylenediamine complex cation, such as [Coienls] ". Each ethylenediamine molecule provides two N donor atoms and is therefore a bidentate ligand, (b) Simplified structure of the same complex cation. 

Ms " clusters have 12 framework bonding electrons as has [BsHs]- (p. 161) the anions are also isoelectronic with the well-known cation [Bis]. Similarly, the alloy NaSn. 2.23 reacts with cryptand in ethylenediamine to give dark-red crystals of [Na(ciypt)]4 [Sng] the anion is the first example of a C41, unicapped Archi-median antiprism (Fig. 10. lOc) and differs from the >3/, structure of the isoelectronic cation [Bis] + which, in the salt Bi+[Bi9] +[HfCl6]5 (p. 591), features a tricapped trigonal prism, as in [BgHg] " (p. 153). The emerald green species [Pb9] , which is stable in liquid NH3 solution, has not so far proved amenable to isolation via ciyptand-complexed cations. 

Chelating ligands bind much more tightly to their metal cations than do ligands that possess only one donor atom. A good example is the ethylenediamine complex with. The ethylenediamine complex is much more stable than the analogous ammonia complex ... 

Exchange of complex cations. Complexation of transition metal cations with uncharged ligands such as with amines and with amino acids results in a selectivity enhancement compared to the selectivity of the aqueous metal cation (27, 65-72). Fig. 3 shows an example for the Cu(ethylenediamine) adsorption in montmorillonites of different charge density. Standard thermodynamic data for other cases are given in table IV. In all cases the free ligand concentration in equilibrium solution was... 

Considering the contribution of the solvent and surface terms to the total free energy change, it is apparent that the enhanced selectivity in the presence of e.g. ethylenediamine corresponds in sign to variations in the solution term and is (in part) due to smaller AG values of hydration of the complex cations. This is exemplified for the Ca-Cu and Ag-Cu cases in the presence and absence of ethylenediamine by the equations ... 

With ethylenediamine complexes of the formula Ln(en)3X3 and Ln(en)4X3, where X = C1 , Br , NO, CIOJ have been characterized. IR data indicate that the tris and tetrakis complexes of the fighter lanthanides La-Sm, contain both ionic and coordinated nitrate groups. By contrast tetrakis complexes of heavier lanthanides, Eu-Yb contain ionic nitrate. This is possibly due to steric factors resulting from decreasing cationic radius that force the nitrate out of the coordination sphere of the lanthanides. A coordination number of 8 for tris complexes and a number of 9 for fighter lanthanide tetrakis complexes appears reasonable [234]. The thermodynamic parameters obtained show enthalpy stabilization for... 

Tris(diamine) complexes of chromium(III) have been important from several viewpoints. First, the tris(ethylenediamine) complex is valuable as a synthetic intermediate,1 the action of heat on the chloride salt giving the cis-dichlorobis(ethylenediamine) complex and on the thiocyanate salt giving the irans-bis(iso-thiocyanato) complex. Second, the cations are resolvable, and studies2 of their optical activity have been fruitful in establishing relations between signs of Cotton effects and absolute stereochemistries. A large number of other studies, including kinetic and equilibrium measurements, have shown these complexes to be readily hydrolyzed to bis(ethylenediamine) complexes.3... 

Rh(en)2(ox)]+ equilibrium is established after about 70-75% of the oxalate is aquated, presumably due to the coulombic attraction between ox2- (or Hox") and the cationic ethylenediamine complex.659... 

When the tetradentate ligand trien is substituted by two bidentate ligands, namely ethylenediamine, the resulting compound 2 adopts another type of packing mode, in which each complex cation forms extensive hydrogen bonding interactions with 1,5-... 

Other studies have been concerned with trapping the C0-O2 monomeric complex in an environment where dimerisation is impossible. Nakamoto and co-workers have published a series of papers on Co(II) complexes trapped in 02-doped argon matrices " and a report has appeared of Co " complexed by a nitrogen macrocycle in a micellar phase . Co complexed by ethylenediamine in zeolite cages forms an 1 mononuclear complex at low concentration but j/ dinuclear complexes are observed at higher concentrations. There is some evidence for formation of free Of ion Similar results were found for Go(II) ethylenediamine complexes absorbed on a cation exchange resin ... 

The base can be a co-solvent, such as trialkylamine, or the Lewis base function can be designed into the metal complex using O-bearing ligands such as al-koxyamines, acetylacetonates, etc. The optimum amount of co-solvent is 1-2 equivalents of the metal complex present in the solvent. The nitrogen atoms in ethylenediamine are not sufficiently basic to activate the surface protons from silica, but ethylenediamine complexes of some metal cations, such as Cu(II), readily exchange for the protons in zeolites which are more acidic than silanol protons. ... 

Tris(ethylenediamine)platinum(IV) chloride is a white crystalline solid which is readily soluble in water and stable toward decomposition in both acidic and basic solution. Resolution of the complex cation into its optical isomers has been achieved by fractional precipitation of i-[Pt(en)3]-Cl2(d-C4H406) on addition of ammonium d-tartrate to the racemic mixture. Racemization of the cation occurs only under extreme conditions and is accompanied by little exchange of bound ethylenediamine. A solution of the complex is quantitatively reduced to platinum metal by magnesium and hydrochloric acid. The solid complex is quantitatively reduced to platinum metal upon ignition. 

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