Chromium atom

In dibenzene chromium, the chromium atom is sandwiched between two benzene rings Figure 13.3)... 

A chromium atom forms a neutral complex with carbon monoxide molecules and 1,10-phenanthroline molecules. The structure of the complex is ... 

An unusual crystal arrangement is exhibited by the isomorphous compounds CrCl and Crl. The close-packed cubic array of Cl or I atoms has two-thirds of the octahedral holes between every other pair of chlorine or iodine planes filled with chromium atoms. Alternate layers of the halogen compounds are held together by van der Waals forces (39,40). 

The binary borides (p. 145), carbides (p. 299), and nitrides (p. 418) have already been discussed. Suffice it to note here that the chromium atom is too small to allow the ready insertion of carbon into its lattice, and its carbide is consequently more reactive than those of its predecessors. As for the hydrides, only CrH is known which is consistent with the general trend in this part of the periodic table that hydrides become less stable across the d block and down each group. 

Chromium (atomic mass = 51.9961 amu) has four isotopes. Their masses are 49.94605 amu, 51.94051 amu, 52.94065 amu, and 53.93888 amu. The first two isotopes have a total abundance of87.87%, and the last isotope has an abundance of2365%. What is the abundance of die third isotope Estimate the abundances of die first two isotopes. 

But similar calculations do not fare as well in other atoms. Consider the case of the chromium atom for example.9... 

The stability of sexivalent chromium, in the chromate ion and related ions, can also be understood. The chromic complexes, involving tervalent chromium, make use of d2sp3 bond orbitals, the three remaining outer electrons of the chromium atom being in three of the 3d orbitals, with parallel spins. The resonance energy of these three atomic electrons in a quartet state helps to stabilise the chromic compounds. However, if all of the nine outer orbitals of the chromium atom were available for bond formation, stable compounds might also be expected... 

The complex might be best described by saying that each oxygen atom could form a double bond with the chromium atom with the. use of either one of its two 7t orbitals and the accompanying pair of electrons, extra stability being achieved through the resonance between the two kinds of double bonds. 

It is found that chromium atoms, manganese atoms, and tin atoms exist in metals in two forms, a small, high-valent form and a larger, low-valent form. The two kinds of manganese atoms coexist in a-manganese and in /3-manganese. 

Fig. 38. Complexes synthesized by the reaction of chromium atoms with 1,4-diphenylbutane at the temperature of liquid nitrogen. From ref. (201).

Nickel and palladium react with a number of olefins other than ethylene, to afford a wide range of binary complexes. With styrene (11), Ni atoms react at 77 K to form tris(styrene)Ni(0), a red-brown solid that decomposes at -20 °C. The ability of nickel atoms to coordinate three olefins with a bulky phenyl substituent illustrates that the steric and electronic effects (54,141) responsible for the stability of a tris (planar) coordination are not sufficiently great to preclude formation of a tris complex rather than a bis (olefin) species as the highest-stoichiometry complex. In contrast to the nickel-atom reaction, chromium atoms react (11) with styrene, to form both polystyrene and an intractable material in which chromium is bonded to polystyrene. It would be interesting to ascertain whether such a polymeric material might have any catal3dic activity, in view of the current interest in polymer-sup-ported catalysts (51). 

Chromium atoms were cocondensed with benzyl sulfide at 77 K (35), the primary result being desulfurization to form bibenzyl and trans-stilbene. Coordination compounds were not characterized in this system. 

In contrast, when chromium atoms were reacted with benzyl ether, complexation to only one phenyl group of the ether was observed. 

Transition-metal atoms have been shown to deoxygenate epoxides to alkenes (36). Chromium and titanium atoms emerged as the most effective species in this regard, abstracting over two equivalents of oxygen. By studying the reaction of a wide range of epoxides with chromium atoms, the reaction... 

When chromium atoms were cocondensed at 77 K with 1,7-cyclodeca-diyne (38), complexation was not observed however, an organic trimer of the starting material was formed. Standard, organic characterization-techniques showed that this trimer is the one depicted, rather... 

A neutral chromium atom has 24 electrons, so the corresponding Cr cation has 21 electrons. The first 18 electrons follow the usual filling order to give the argon core configuration ... 

The chromium atom in Cr04 has an oxidation number of +6, so it must gain three electrons to be converted into Again, water or hydronium ions must supply hydrogen atoms that combine with the... 

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