The compounds of the invention are monomeric tin compounds characterized by the formula a 2 2) a b 4-ab in which R is selected from the group consisting of the hydrogen atom, lower alkyl radicals, alkoxy radicals, acyloxy radicals, the vinyl group or a phenyl radical; X is a halogen atom; a is an integer having a value of from 1 to 4 inclusive; .1; is an integer having a value of from 0 to 3 inclu