Dependence of the Chemical Properties of Macrocyclic [Ni^II₂L(μ-O₂CR)]⁺ Complexes on the Basicity of the Carboxylato Coligands (L²⁻ = macrocyclic N₆S₂ ligand)

Abstract

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.

Hexaaza‐dithia Macrocycles Containing Pendant Methoxyethyl Groups: Synthesis and Characterization of Mono and Dinuclear Nickel Complexes

“…150 cm -1 (Δν = ν asym -ν sym ) in agreement with a bridging mode. The values are also similar to those of [Ni 2 L1(μ 1,3 -OAc)](BPh 4 ) [21] and provide strong support for the presence of a μ 1,3 -bridging acetate group in 4 and 5. The electronic absorption spectra of 4 and 5 are different from those of 3 as one might expect upon going from a five-to a six-coordinate coordination environment.…”

“…complexes supported by hexaaza-dithiophenolato ligands. [21] In contrast to the compound described above, the 2-methoxyethyl substituents are not involved in bonding interactions with the metal ions. Given the weak affinity of Ni 2+ for ether oxygen donors atoms, this is not surprising.…”

Preparation and Characterization of Dinuclear Nickel(II) Complexes Containing N3Ni(μ1, 3‐SO3R)2(μ‐RCN4)NiN3 Cores: Crystal Structures and Magnetic Properties

“…It should be noted in this respect that there is a large increase of the angle between the N 2 NiS 2 and N 2 Ni(O sulfonato ) 2 planes upon going from the thiophenolato-bridged compounds 1-3 to the sulfonato-bridged species 4-6. Thus, the angles between the normals of the planes through the S 1 can be noted that the absolute value of the exchange interaction in 4-6 compared to that in 1-3 is smaller by an order of magnitude. This observation may be explained with the increased Ni···Ni distance and therefore increased length of the coupling path upon oxidation.…”

“…[1] With first row transition metal ions such as Ni 2+ , Co 2+ , Fe 2+ , and Mn 2+ the doubly deprotonated macrocycle (L1) 2-…”

Synthesis and Characterization of Pentanuclear Complexes Composed of Pairs of Macrocyclic Ni2L and Zn2L Complexes Linked by cis‐[PtCl2(dppba)2] and trans‐[RhCl(CO)(dppba)2] [dppba = (4‐Diphenylphosphanyl)benzoate, L = Macrocyclic Ligand]

“…[1] A particularly large number of [M 2 L(μ-LЈ)] + complexes with carboxylato groups (RCO 2 -) as a coligand (LЈ) has been reported and crystallographically characterized. [2] Besides dinuclear [M 2 L(μ-O 2 CR)] + structures, [3] we have also reported higher-nuclearity complexes of the type [(M 2 L) 2 (μ-O 2 C-R-CO 2 )] 2+ , in which pairs of bioctahedral [M 2 L] 2+ units are united by a dicarboxylate dianion. [4][5][6] The carboxylato groups in these metal complexes are invariably coordinated in a bridging mode thereby generating bisoctahedral N 3 M(μ-SR) 2 + complexes.…”