Table 3. Spectroscopic properties of the Ni complexes in CH₂Cl₂ solution ^a .

Complex b	λ max [cm–1] (ε × 103 [M–1 cm–1])
1 c	25 400 sh (4.7), 23 900 (8.2), 22 300 sh (5.3), 17 400 w (0.36)
[1˙]+ c	32 000 (100), 26 500 (14.6), 25 000 (10.6), 21 700 (7.1), 19 100 (4.1), 11 000 (3.0), 9100 (9.2), 5900 sh (7.1), 4500 (27.7)
2	23 800 (15.6), 21 800 sh (8.6), 16 700 w (1.7)
[2˙˙]2+	21,00 sh (7.2), 17 800 (3.4), 12 100 (5.8), 8970 (12.3), 4830 (42.9)
3 c	23 800 (13.4), 22 300 sh (9.1), 17 400 w (0.42)
[3˙˙]2+ c	32 000 (100), 26 500 (19.7), 25 000 (16.4), 21 700 (9.9), 19 100 (4.8), 9260 (10.4), 4890 (26.5), 4200 (21.1)
4	23 500 (14.5), 21 850 sh (8.8), 17 500 w (0.8)
[4˙˙]2+	21 500 (9.5), 18 500 (4.4), 9100 (14.0), 5850 sh (8.2), 4850 sh (26.1), 4310 (46.1)
5	23 500 (14.4), 21 600 sh (9.2), 17 400 w (1.1)
[5˙˙]2+	20 200 (28.6), 8700 sh (8.0), 5400 sh (27), 4150 (46.6)

^aNIR transitions in bold.

^bConditions: 0.33 mM (1–4), 0.08 mM (5), CH₂Cl₂, 198 K (1–4), 298 K (5); sh = shoulder, w = weak.

^c Ref. 17.