Neutral, radical [CpNi(dithiolene)] complexes fused with seven-membered rings, formulated as [CpNi{S2C2S2(CH2)2X}] (X = CH2, CF2, C=CH2, S), have been synthesized in 30-60 % yields from the reactions of nickelocene with the corresponding neutral, square-planar, (dithiolene)nickel complexes [Ni{S2C2S2(CH2)2X}2]. [CpNi{S2C2S2(CH2)2X}] (X = C=O) was prepared from nickelocene and [1,3]dithiolo[4,5-b][1,4]dithiepine-2,6-dione under thermal or photochemical conditions. All complexes exhibit reversible oxidation and reduction waves to the cation and anion form, respectively. The terminal groups (X) in the seven-membered ring shift their redox potentials to anodic potentials in the following order: CF2 > C=O > S > C=CH2 > CH2. The singlet EPR responses of [CpNi{S2C2S2(CH2)2(X)}] appear at g 2.0514-2.0529 in dichloromethane solution at room temperature. An NIR absorption is observed at max 798-848 nm ( 1700-2400 M-1 cm-1) in dichloromethane solution. The X-ray structures of the five complexes show two-legged piano-stool geometries around the central nickel atom (formally NiIII) and strong distortions from planarity of the seven-membered C2S2(CH2)2X rings. In the solid state, those radical (S = 1/2) species adopt either one-dimensional alternating chain-like motifs (X = CH2, C=CH2, S) or dimeric entities characterized by a singlet-triplet magnetic behavior (X = CF2, C=O).