Azide Binding Controlled by Steric Interactions in Second Sphere. Synthesis, Crystal Structure, and Magnetic Properties of [Ni^II₂(L)(μ_1,1-N₃)][ClO₄] (L = Macrocyclic N₆S₂ Ligand)

Abstract

The dinuclear Ni(II) complex [Ni2(L(2))][ClO4]2 (3) supported by the 28-membered hexaaza-dithiophenolate macrocycle (L(2))(2-) binds the N3(-) ion specifically end-on yielding [Ni2(L(2))(μ(1,1)-N3)][ClO4] (7) or [Ni2(L(2))(μ(1,1)-N3)][BPh4] (8), while the previously reported complex [Ni2L(1)(μ(1,3)-N3)][ClO4] (2) of the 24-membered macrocycle (L(1))(2-) coordinates it in the end-to-end fashion. A comparison of the X-ray structures of 2, 3, and 7 reveals the form-selective binding of complex 3 to be a consequence of its preorganized, channel-like binding pocket, which accommodates the azide anion via repulsive CH···π interactions in the end-on mode. In contrast to [Ni2L(1)(μ(1,3)-N3)][ClO4] (2), which features a S = 0 ground state, [Ni2(L(2))(μ(1,1)-N3)][BPh4] (8) has a S = 2 ground state that is attained by competing antiferromagnetic and ferromagnetic exchange interactions via the thiolato and azido bridges with a value for the magnetic exchange coupling constant J of 13 cm(-1) (H = -2JS1S2). These results are further substantiated by density functional theory calculations. The stability of the azido-bridged complex determined by isothermal titration calorimetry in MeCN/MeOH 1/1 v/v (log K11 = 4.88(4) at I = 0.1 M) lies in between those of the fluorido- (log K11 = 6.84(7)) and chlorido-bridged complexes (log K11 = 3.52(5)). These values were found to compare favorably well with the equilibrium constants derived at lower ionic strength (I = 0.01 M) by absorption spectrophotometry (log K11 = 5.20(1), 7.77(9), and 4.13(3) for N3(-), F(-), and Cl(-) respectively).

Deposition of exchange-coupled dinickel complexes on gold substrates utilizing ambidentate mercapto-carboxylato ligands

“…In contrast to other ω-mercapto-alkanethiols, which adopt an extended zig-zag conformation, the coligand is twisted about the C40–C41 bond (“gauche” conformation) most likely due to steric constraints exerted by the surrounding NMe groups. We have observed similar effects in an azido-bridged complex, where the surrounding alkyl groups dictate the coordination mode of the azido ligand [ 49 ].…”

“…The details of these investigations will be published elsewhere. This method has previously been shown to be a powerful tool to unravel the contribution of the azido and thiolato-bridges for the complex [Ni 2 L Me2H4 (μ-N 3 )]ClO 4 [ 49 ], where L Me2H4 represents a 28-membered variant of the macrocycle L. The results imply that a moderate "ferromagnetic" contribution of ≈30 cm −1 through the μ 1,1 -bridging thiophenolato groups of the supporting macrocycle is counterbalanced by a weak antiferromagnetic interaction ( J ≈ −5 cm −1 ) through the carboxylato-bridges ( J O2CR ), to produce a net ferromagnetic exchange interaction of J ≈ 25 cm −1 . A magneto-structural correlation has recently been reported for related dinuclear nickel complexes of the type [Ni 2 L Me2H4 (μ-L’)] + , where L’ = F − , Cl − , Br − , OH − , and N 3 − ) [ 58 ].…”

Synthesis and Characterisation of Luminescent [CrIII2L(μ‐carboxylato)]3+ Complexes with High‐Spin S=3 Ground States (L=N6S2 donor ligand)

“…This approach has previously proven to be a powerful tool to unravel the contributions of the individual bridges in Ni complexes supported by (L) 2− . [ 76 , 77 ] These results imply that a dominant “ferromagnetic” contribution (39.85 cm −1 ( 1 ), 41.13 cm −1 ( 2 ), Table S3) through the bridging thiolato ligands is counterbalanced by an antiferromagnetic interaction through the carboxylates. Such an orbital countercomplementary effect was also observed for the series of carboxylato‐bridged chromium(III) complexes reported by Rajaraman and Brechin.…”

Thiolate Coordination vs C–S Bond Cleavage of Thiolates in Dinickel(II) Complexes

“…In comparison to these large numbers of literature reports on the synthesis and reactivity of mononuclear nickel–thiolates and heterodinuclear Ni–Fe complexes, reports on the synthesis and reactivity of well-defined, dinuclear Ni­(II)–thiolate and dinuclear Ni­(II)–hydrosulfide complexes are relatively less explored. Almost all of the literature reports on dinuclear Ni­(II)–thiolate − complexes used bi-/tri-/tetra-/multidentate chelating ligands which themselves contain one or more S-donor sites. On the other hand, only a handful of reports on discrete mononuclear − and dinuclear − nickel–-hydrosulfide, and dinuclear nickel–sulfide , complexes are available in the literature.…”