R is' selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl and alkaryl radicals containing from 1 to 12 carbon atoms, inclusive; each Z is selected from the group consisting of -N= and -C=; D is selected from the group consisting of -O-, --S- and M is an alkali metal selected from the group consisting of sodium, potassium, lithium, rubidium, and cesium; n is a whole integer of fr