The First-Row Transition Metals

We have seen that the transition metals are similar in many ways but also show important differences. We will now explore some of the specific properties of each of the 3d transition metals. 

Scandium is a rare element that exists in compounds mainly in the +3 oxidation state— for example, in ScCls, SC2O3, and 802(804)3. The chemistry of scandium 

Unless otherwise noted, all art on this page is Cengage Learning 2014. 

An X ray of a patient who has had a hip replacement. The normal hip joint is on the left the hip joint constructed from the transition metal tantalum is on the right. 

Strongly resembles that of the lanthanides, with most of its compounds being colorless and diamagnetic. This is not surprising as we will see in Section 21.6, the color and magnetism of transition metal compounds usually arise from the d electrons on the metal ion, and Sc + has no d electrons. Scandium metal, which can be prepared by electrolysis of molten ScCls, is not widely used because of its rarity, but it is found in some electronic devices, such as high-intensity lamps. 

Ilmenite is treated with sulfuric acid to form a soluble sulfate, 

Liquid titanium(IV) chloride being added to water, forming a cloud of solid titanium oxide and hydrochloric acid. 

Oxidation States and Species for Vanadium in Aqueous Solution 

When this aqueous mixture is allowed to stand under vacuum, solid FeS04 7H2O forms and is removed. The mixture remaining is then heated, and the insoluble titanium(IV) oxide hydrate (TiOi H2O) forms. The water of hydration is driven off by heating to form pure Ti02  

Niobium was originally called columbium and is still occasionally referred to by that name. 

Transition metals are often used to construct prosthetic devices, such as this hip joint replacement. 

In general, the differences between the 4d and 5d elements in a group increase gradually going from left to right. For example, niobium and tantalum are also quite similar, but less so than zirconium and hafnium. 

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ZINDO/1 IS based on a modified version of the in termediate neglect of differen tial overlap (IXDO), which was developed by Michael Zerner of the Quantum Theory Project at the University of Florida. Zerner s original INDO/1 used the Slater orbital exponents with a distance dependence for the first row transition metals only. Ilow ever. in HyperChein constant orbital expon en ts are used for all the available elein en ts, as recommended by Anderson. Friwards, and Zerner. Inorg. Chem. 2H, 2728-2732.iyH6. 

R. Colton and J. H. Canterford, Halides of the First Row Transition Metals, Wiley-Interscience, New York, 1969. 

Derived from the German word meaning devil s copper, nickel is found predominantly in two isotopic forms, Ni (68% natural abundance) and Ni (26%). Ni exists in four oxidation states, 0, I, II, III, and IV. Ni(II), which is the most common oxidation state, has an ionic radius of —65 pm in the four-coordinate state and —80 pm in the octahedral low-spin state. The Ni(II) aqua cation exhibits a pAa of 9.9. It forms tight complexes with histidine (log Af = 15.9) and, among the first-row transition metals, is second only to Cu(II) in its ability to complex with acidic amino acids (log K( = 6-7 (7). Although Ni(II) is most common, the paramagnetic Ni(I) and Ni(III) states are also attainable. Ni(I), a (P metal, can exist only in the S = state, whereas Ni(lll), a cT ion, can be either S = or S =. ... 

The simple porphyrin category includes macrocycles that are accessible synthetically in one or few steps and are often available commercially. In such metallopor-phyrins, one or both axial coordinahon sites of the metal are occupied by ligands whose identity is often unknown and cannot be controlled, which complicates mechanistic interpretation of the electrocatalytic results. Metal complexes of simple porphyrins and porphyrinoids (phthalocyanines, corroles, etc.) have been studied extensively as electrocatalysts for the ORR since the inihal report by Jasinsky on catalysis of O2 reduction in 25% KOH by Co phthalocyanine [Jasinsky, 1964]. Complexes of all hrst-row transition metals and many from the second and third rows have been examined for ORR catalysis. Of aU simple metalloporphyrins, Ir(OEP) (OEP = octaethylporphyrin Fig. 18.9) appears to be the best catalyst, but it has been little studied and its catalytic behavior appears to be quite distinct from that other metaUoporphyrins [CoUman et al., 1994]. Among the first-row transition metals, Fe and Co porphyrins appear to be most active, followed by Mn [Deronzier and Moutet, 2003] and Cr. Because of the importance of hemes in aerobic metabolism, the mechanism of ORR catalysis by Fe porphyrins is probably understood best among all metalloporphyrin catalysts. 

Solvent exchange on the first-row transition metal [M(solvent)6]2+ species has been subjected to extensive study, as is exemplified by Table III, which contains data for four solvent systems which have been particularly intensively studied (46, 47, 97, 99, 103, 110-117). The solvent exchange mechanism progressively changes from Ia to Id as the number of d-electrons increases and rM decreases for H20, MeOH, and MeCN solvents, as judged from the changes in sign of AV. It is also seen that lability decreases with increase in AHi substantially, as... 

As a consequence of its closed-shell electron configuration, zinc has a negative electron affinity, that is, the removal of an electron from Zn is exothermic. The electronegativity of zinc (1.588 PU) is intermediate between those of the alkaline earth metals and the first row transition metals and remarkably similar to that of beryllium (1.57 PU). 

Among binary transition-metal pnictides, only the first-row transition-metal phosphides have been analysed by XPS extensively, whereas arsenides and antimonides have been barely studied [51-61]. Table 2 reveals some general trends in the P 2p3/2 BEs for various first-row transition-metal monophosphides, as well as some metaland phosphorus-rich members forming for a given transition metal. Deviations of as much as a few tenths of an electron volt are seen in the BEs for some compounds measured multiple times by different investigators (e.g., MnP), but these... 

Our focus is on the most comprehensively studied series, the monophosphides of the first-row transition metals, whose structures successively distort from NaCl-type (ScP) to TiAs-type (TiP), NiAs-type (VP), MnP-type (CrP, MnP, FeP, CoP), and NiP-type, forming stronger metal-metal and phosphorus-phosphorus bonding with greater electron count (Fig. 11) [63-65], The P atoms are six-coordinate, but... 

Most of the first-row transition metals and several in the second and third groups have important uses. For example, iron is the basis of the enormous range of ferrous alloys in which other first-row metals are often combined. The metallurgy of iron-based alloys is a vast and complex field. Among the many... 

The brief discussion of the chemistry of the first-row transition metals presented here shows only a small portion of this vast subject. However, it illustrates some of the differences between the metals and how their chemistry varies throughout the series. For additional details, the reference text by Greenwood and Eamshaw or that by Cotton et al. should be consulted. In Chapters 16 through 22, many other aspects of the organometallic and coordination chemistry of these metals will be presented. 

A measure of the Lewis acidity of a metal ion is determined by its affinity for a pair of electrons, and the greater this affinity, the more stable the complexes formed by the metal ion will be. However, removing electrons from a metal to produce an ion is also related to the attraction the metal atom has for electrons. Therefore, it seems reasonable to seek a correlation between the stability constants for complexes of several metals with a given ligand and the total energy necessary for ionization to produce the metal ions. The first-row transition metal ions react in solution with ethylenediamine, en, to form stable complexes. We will consider only the first two steps in complex formation, which can be shown as follows ... 

The effective atomic number rule (the 18-electron rule) was described briefly in Chapter 16, but we will consider it again here because it is so useful when discussing carbonyl and olefin complexes. The composition of stable binary metal carbonyls is largely predictable by the effective atomic number (EAN) rule, or the "18-electron rule" as it is also known. Stated in the simplest terms, the EAN rule predicts that a metal in the zero or other low oxidation state will gain electrons from a sufficient number of ligands so that the metal will achieve the electron configuration of the next noble gas. For the first-row transition metals, this means the krypton configuration with a total of 36 electrons. 

The vast majority of biochemical processes in which a metal plays a role involve a only a relatively small number of metals. Those metals include Na, K, Mg, Ca, Mo, or the first-row transition metals from V to Zn. Only molybdenum could be considered as a heavy metal. It should also be observed that the metal ions constitute those that can be considered as hard or borderline in hardness. It is a general property that ions of heavy metals having low charge (that is to say "soft") are toxic. These include Hg, Pb, Cd, H, and numerous others. Some heavy metals bind to groups such as the sulfhydryl (-SH) group in enzymes, thereby destroying the ability of the enzyme to promote the reaction in a... 

Rotzinger s calculations confirmed the mechanistic crossover for water exchange on the first-row transition metal ions. The calculations predict Ia mechanisms for V2+ Mn2+ and D (or Id) mechanisms for Mn2+, Fe2+, Cu2+, and Zn2+. A d-activated mechanism for water exchange... 

Both PH3 and S i 114 react similarly with bare transition metal ions except that no simple addition ions [MSiELJ have so far been observed. The Cu+ ion reacts by dehydrogenation and the most unreactive ion, Mn+, does not react in its ground state. The excited-state ion forms [MnH]+. The reactions of several first-row transition metal ions with silane (117-119) have been studied by the GIB method. The major product was [MSiH2]+ for the ground-state ions Ti+, V+, Cr+, Fe+, Co+, Ni+, Cu+, and Zn+. The group 3 (IIIB) ions Sc+, Y+, La+, and Lu+ (49) all reacted with silane in a similar manner to the first-row transition metal ions. 

Sulphides. The partially ionic alkali metal sulphides Me2S have the anti-fluorite-type structure (each Me surrounded by a tetrahedron of S, and each S atom surrounded by a cube of Me). The NaCl-structure type (6/6 coordination) is adopted by several mono-sulphides (alkaline earth, rare earth metals), whereas for instance the cubic ZnS-type structure (coordination 4/4) is observed in BeS, ZnS, CdS, HgS, etc. The hexagonal NiAs-type structure, the characteristics of which are described in 7.4.2.4.2, is observed in several mono-sulphides (and mono-selenides and tellurides) of the first-row transition metals the related Cdl2 (NiAs defect-derivative) type is formed by various di-chalcogenides. Pyrite (cP 12-FeS2 type see in 7.4.3.13 its description, and a comparison with the NaCl type) and marcasite oP6-FeS2 are structural types frequently observed in several sulphides containing the S2 unit. 

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