Is there a name for the pair (c, R), where c is the stoichiometric coefficient of a reactant R in some chemical reaction?
In chemistry, often quantities get denoted by an index $i$, which then stands for some compound ($i=\text{A, B, C, ...}$). 

Examples:


The stoichiometric coefficient $\nu_i$
The concentration $c_i$
The amount of substance $n_i$


The notion of grouping together the stoichiometric coefficient with the substance it uses is a novel one for me, and will most likely not have a name.

I suggest you use a name such as "coefpair" or the like and document your code accordingly.