First Transition Series Metals

There is reasonable agreement in relation to the stability of the species, Ti2(OH)2, but it is also possible that the species TijfOH) forms, similar to that reported for other trivalent first transition series metals. However, no data have been reported for this species. 

Hydrolysis of Metal Ions, First Edition. Paul L. Brown and Christian Ekberg. 

There are no available data for monomeric titaniumflll) species other than for TiOH. In accord with other trivalent metals in the first transition series, it is probable that species to Ti(OH)4 will form. 

The accepted data for both and Ti2(OH)2 in chloride media have been 

The stability constants determined for TiOH and 112(011)2 , with respect to reaction (2.5), at zero ionic strength from the ionic strength dependence of the species in chloride media, and the associated ion interaction coefficients (Af2 = 0) are 

---

Metal Preferences. LVC s are formed mainly by transition metals to the right in the periodic table (especially elements in Group 8). This is in part due to the availability of d electrons that can be used in back-donation to the 7r-accepting ligands. Moreover, the formation of LVC s is not particularly "row-sensitive" by which I mean that the first-transition-series metals, Fe, Co and Ni, tend to form most of the same cluster compounds as their congeners, Ru, Rh, Pd and Os, Ir, Pt. 

The discussion above has been directed principally to thermally induced spin transitions, but other physical perturbations can either initiate or modify a spin transition. The effect of a change in the external pressure has been widely studied and is treated in detail in Chap. 22. The normal effect of an increase in pressure is to stabilise the low spin state, i.e. to increase the transition temperature. This can be understood in terms of the volume reduction which accompanies the high spin—dow spin change, arising primarily from the shorter metal-donor atom distances in the low spin form. An increase in pressure effectively increases the separation between the zero point energies of the low spin and high spin states by the work term PAV. The application of pressure can in fact induce a transition in a HS system for which a thermal transition does not occur. This applies in complex systems, e.g. in [Fe (phen)2Cl2] [158] and also in the simple binary compounds iron(II) oxide [159] and iron(II) sulfide [160]. Transitions such as those in these simple binary systems can be expected in minerals of iron and other first transition series metals in the deep mantle and core of the earth. 

Most commonly, metal ions M2+ and M3+ (M = a first transition series metal), Li+, Na+, Mg2+, Al3+, Ga3+, In3+, Tl3+, and Sn2+ form octahedral six-coordinate complexes. Linear two coordination is associated with univalent ions of the coinage metal (Cu, Ag, Au), as in Ag(NH3)2+ or AuCL Three and five coordination are not frequently encountered, since close-packing considerations tell us that tetrahedral or octahedral complex formation will normally be favored over five coordination, while three coordination requires an extraordinarily small radius ratio (Section 4.5). Coordination numbers higher than six are found among the larger transition metal ions [i.e., those at the left of the second and third transition series, as exemplified by TaFy2- and Mo(CN)g4 ] and in the lanthanides and actinides [e.g., Nd(H20)93+ as well as UC Fs3- which contains the linear uranyl unit 0=U=02+ and five fluoride ligands coordinated around the uranium(VI) in an equatorial plane]. For most of the metal complexes discussed in this book a coordination number of six may be assumed. 

We first treat those complexes that have only a metal-ligand bonding. Examples of this type of complexes include [M(H20)6] + and [M(NH3)6] +, where M + is a first transition series metal ion and a typical n value is either 2 or 3. A coordinate system for such a complex is shown in Fig. 8.8.1. The representation generated by the six ligand orbitals is... 

Complexes formed by heterocyclic amines with halides and pseudohalides of dipositive first-transition-series metal ions are usually prepared by the reaction between a metallic salt, a soluble thiocyanate, and pyridine in aqueous solution. Although the number of coordinated pyridine molecules varies,... 

It will also be noticed that all the above catalysts contain second transition series metals. Generally, the slower reactions of the third transition series elements are not normally conducive to catalytic efficiency, although some very active iridium catalysts are now known. First transition series metals seldom form stable, lower oxidation state tertiary phosphine complexes. 

Complexes of the rare earth elements provide examples of case (1), many complexes of the first-transition series metals provide examples of case (2), and complexes with covalent bonds provide examples of case (3). Case (2) will be considered here. Excellent monographs cited above are available in which the theory is developed in detail. 

Turner et al. (1981) and Byrne et al. (1988). Turner et al. (1981) used a database of stability constants for more than 500 metal complexes to calculate the inorganic speciation for 58 trace elements in model seawater at pH 8.2, 25 °C, and 1 atm. Byrne et al. (1988) extended this work by considering the influence of temperature and pH on speciation. The free hydrated divalent cation dominates the dissolved inorganic speciation of Zn(II) and the first transition series metals Mn(II), Co(II), and Ni(II). Strongly hydrolyzed trace metals include Be(II), Al(III), Fe(III),... 

Sensitivity. Pulse radiolysis has high sensitivity for weaMy absorbing species, which is especially useftil for monitoring hgand-fleld absorptions of first-transition-series metal ions. 

Other proposed controls on the concentrations of certain of the first transition series metals in soil solutions and natural waters are reviewed and are found to be inadequate to explain the existing data. The princi-... 

For zinc and the first transition series metals manganese, iron, cobalt, and nickel, the free hydrated divalent cation form dominates the dissolved inorganic speciation. The trivalent metal cations Al +, Ga +, Tl +, Fe " ", and Bi + are strongly hydrolyzed (i.e., they form strong complexes with... 

A combined electrochemical, HRS and theoretical DPT investigation has also been carried out on meso-tetraphenylporphyrin (H2TPP) and its first transition series metal complexes (MTPP) (50) [170]. 

In addition to excitations into the id (or Ad) shells, XANES can also be used to probe higher-lying excited states. For atomic spectra, a complete series of Rydberg transitions can be seen. For first transition series metals, the allowed Is Ap transition is sometimes observed. This is the assignment given to the intense transition observed on the rising edge for Cu and for some square-planar Cir and Ni complexes. From studies of model compounds, it is found that the Is Ap" transition is intense for square planar complexes but weak for tetrahedral... 

The lattice energies of bivalent first transition series metal chlorides, MCI2, where is... 

For tetrahedral complexes of the first transition series metals, which electronic conhgu-rations would lead to Jahn-TeUer distortion Upon such distortion, how do the splittings in t2 and e levels compare ... 

---