Charge-Compensated Complexes

Formation of Charge-Compensated Complexes with Donor Ligands a. Complexes of Iron... 

Fully or partially charge-compensated complexes of general formulae L2B12H,0 or [LB12HU] can be viewed as derived from [B12H12]2 by substitution of two or one H ligands for two or one neutral 2e donor molecules. When L is a sulfide, the above complexes may be considered as the inner sulfonium salts of the dodecaborane dianion ... 

Figure 4 Chemical hardness vs. vibronic energy diagram for molecules AX3 (X 1 F to I A111 P to Bi) and the charge-compensated complexes PF4 and PF52 (in eV).

Technetium(V) complexes with exclusively phosphorus donors and the [Tc=0] core are obviously not stable. The lack of charge compensation leads to Tc " compounds by further reduction, or to hydrolysis. Pure phosphorus coordination is then possible only if the [0=Tc=0]" core is present, as described in the following section (Scheme 36). 

Two types of Ce centers in calcite were detected by steady-state spectroscopy (Kasyanenko and Matveeva 1987). The first one has two bands at 340 and 370 nm and is connected with electron-hole pair Ce -COj". The second one has a maximum at 380 nm and was ascribed to a complex center with Ce and OH or H2O as charge compensators. Such a center becomes stronger after ionizing irradiation and disappears after thermal treatment. The typical example of Ce luminescence in the time-resolved liuninescence of calcite consists of a narrow band at 357 nm with very short decay time of 30 ns, which is very characteristic for Ce " (Fig. 4.13a). It was found that Ce " excitation bands occurs also in the Mn " " excitation spectrum, demonstrating that energy transfer from Ce to Mn " occurs (Blasse and Aguilar 1984). 

Metal hexacyanoruthenates possess a lower symmetry. Several compounds have highly disordered structures, especially when no alkali cations are present for charge compensation. Such a complex defect structure has been found for a completely potassium free Prussian blue precipitated very slowly from a solution in concentrated hydrochloric acid [25, 26]. Here, the structure still remains cubic face-centered however, one-third of the [M1 -1(CN)6] is vacant, randomly distributed and that space is filled with water molecules. The coordination sphere of the remaining ions is maintained... 

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