By the reaction of [Cp*Fe(eta(5)-As-5)] (I) (Cp*=C5Me5) with main group nucleophiles, unique functionalized products with eta(4)-coordinated polyarsenide (As-n) units (n=5, 6, 20) are obtained. With carbon-based nucleophiles such as MeLi or KBn (Bn=CH2Ph), the anionic organo-substituted polyarsenide complexes, [Li(2.2.2-cryptand)][Cp*Fe(eta(4)-As5Me)] (1a) and [K(2.2.2-cryptand)][Cp*Fe{eta(4)-As-5(CH2Ph)}] (1b), are accessible. The use of KAsPh2 leads to a selective and controlled extension of the As-5 unit and the formation of the monoanionic compound [K(2.2.2-cryptand][Cp*Fe(eta(4)-As6Ph2)] (2). When I is reacted with [M]As(SiMe3)(2) (M=Li center dot THF; K), the formation of the largest known anionic polyarsenide unit in [M'(2.2.2-cryptand)](2)[(Cp*Fe)(4){mu(5)-eta(4):eta(4):eta(3):eta(3):eta(1):eta(1)-As-20}] (3) occurred (M'=Li (3a), K (3b)).