Alkaline earth metals monovalent derivatives

It is generally accepted that aluminum is tetrahedrally coordinated in aluminosilicate glasses and melts, provided that cations such as alkali metals or alkaline earth metals are present in sufficient amounts to charge compensate the replacement of Si by AF+ [i.e., Si + —> AP" -t- (1/ )M" +, where monovalent or divalent M ions occur in nonframework sites associated with the tetrahedral aluminosilicate framework]. Experimental data for aluminosilicate glasses derived from both low-angle x-ray-scattering experiments and EXAFS studies show that as aluminum is substituted for silicon, the average T (tetrahedrally coordinated ion) -O bond... 

This chapter will cover the monovalent neutral polyatomic derivatives of the alkaline earth elements Be, Mg, Ca, Sr, Ba, and Ra. The alkaline earth metals are naturally divalent in the solid state. Well-known examples of alkaline earth compounds are the widely used Grignard reagents, which have an empirical formula R—Mg—X (R is an alkyl group and X is a halogen) [1]. More recently, the Hanusa group at Vanderbilt has explored the organometallic chemistry of divalent Ca, Sr, and Ba derivatives [8]. In contrast to this normal chemistry, the monovalent derivatives such as CaOH are unstable in the solid state because they readily disproportionate ... 

The monovalent derivatives of the alkaline earth metals are free radicals that are stable in the thermodynamic sense in the gas phase or when isolated in inert matrices. Molecules such as CaOH have strong bonds (dissociation energy, Dca 0 = 92kcal mol-1) [9,10] but are very reactive species because of the unpaired electron localized on the Ca atom. In spite of the transient nature of these monovalent derivatives, it has proved possible to develop an extensive gas-phase inorganic chemistry for Mg, Ca, Sr, and Ba. No monovalent polyatomic derivatives are known for the Be or the Ra members of the alkaline earth group, except for BeOH. There are two experimental reports on the BeOH [11,12] molecule in... 

The alkaline earth metals form a host of unique monovalent free radicals. Most of these molecules can be formed by the laser-driven chemical reactions of metal vapors with a wide variety of organic and inorganic molecules. This photochemical production of new molecules has led to an extensive gas-phase inorganic chemistry and spectroscopy of alkaline earth derivatives. In recent years, the Broida oven source has been displaced by the pulsed molecular beam spectrometer. The chemical dynamics and photochemistry of these new molecules are still at a very early stage of investigation. 

The metal monohydroxides CaOH and SrOH are the simplest monovalent polyatomic derivatives of the alkaline earths. Both CaOH and SrOH have a surprisingly long history in view of their high chemical reactivity. While CaOH and SrOH can only be stored when isolated in rare gas matrices [14], substantial steady-state concentrations exist in a variety of energetic environments. 

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