Different reaction pathways were determined between thermolysis and photolysis reactions of the butterfly complex [{Cp^BIGFe(CO)₂}₂(μ,η^1:1-As₄)] (1b). The thermolysis leads to novel arsenic-rich compounds [(Cp^BIGFe)₂(μ,η^4:4-As₄)] (2b), [(Cp^BIGFe)₃(μ₃,η^4:4:4-As₆)] (4) and [Cp^BIGFe(η⁵-As₅)] (5), whereas the photolysis of [{Cp^BIGFe(CO)₂}₂(μ,η^1:1-E₄)] (1a: E = P; 1b: E = As) exclusively results in the decarbonylation products [(Cp^BIGFe)₂(μ,η^4:4-P₄)] (2a), 2b and [(Cp^BIGFe)(μ,η^4:1-As₄)(Cp^BIGFe(CO)₂)] (3). The E₄ complexes 2a and 2b show unique structural differences in the solid state despite their related compositions.