Formation and Dissociation Kinetics and Crystal Structures of Nickel(II)−Macrocyclic Tetrathiaether Complexes in Acetonitrile. Comparison to Nickel(II)−Macrocyclic Tetramines

Abstract

Complex formation and dissociation rate constants have been independently determined for solvated nickel(II) ion reacting with eight macrocyclic tetrathiaether ligands and one acyclic analogue in acetonitrile at 25 degrees C, mu = 0.15 M. The macrocyclic ligands include 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4) and seven derivatives in which one or both ethylene bridges have been substituted by cis- or trans-1,2-cyclohexane, while the acyclic ligand is 2,5,9,12-tetrathiatridecane (Me2-2,3,2-S4). In contrast to similar complex formation kinetic studies on Ni(II) reacting with corresponding macrocyclic tetramines in acetonitrile and N,N-dimethylformamide (DMF), the kinetics of complex formation with the macrocyclic tetrathiaethers show no evidence of slow conformational changes following the initial coordination process. The differing behavior is ascribed to the fact that such conformational changes require donor atom inversion, which is readily accommodated by thiaether sulfurs but requires abstraction of a hydrogen from a nitrogen (to form a temporary amide). The latter process is not facilitated in solvents of low protophilicity. The rate-determining step in the formation reactions appears to be at the point of first-bond formation for the acyclic tetrathiaether but shifts to the point of chelate ring closure (i.e., second-bond formation) for the macrocyclic tetrathiaether complexes. The formation rate constants for Ni(II) with the macrocyclic tetrathiaethers parallel those previously obtained for Cu(II) reacting with the same ligands in 80% methanol-20% water (w/w). By contrast, the Ni(II) dissociation rate constants show significant variations from the trends in the Cu(II) behavior. Crystal structures are reported for the Ni(II) complexes formed with all five dicyclohexanediyl-substituted macrocyclic tetrathiaethers. All but one are low-spin species.

Cyclopentadienyl Ruthenium–Nickel Catalysts for Biomimetic Hydrogen Evolution: Electrocatalytic Properties and Mechanistic DFT Studies

“…Such a conformational rearrangement is well known for macrocyclic nickel tetraamine complexes and has also been proposed to be facilitated in tetrathioether complexes by the presence of two lone pairs (one of which is coordinated to the metal ion) at the thioether groups. [26] More specifically, another dinuclear compound with similar butterfly structure, 4 ], was reported to be nonrigid in solution, [27] the permutation of the two axial CO ligands at W occurring with an activation barrier of 65 kJ mol À1 , very close to that found for 3 + . This process was tentatively assigned to a mutual buckling of the {NiN 2 S 2 } and {W(CO) 4 } units or to a double inversion at the sulfur atoms, but an isomerization pathway similar to that proposed here for 3 + may also account for the fluxionality of [NiA C H T U N G T R E N N U N G (N 2 S 2 )W(CO) 4 ].…”

Ligand Association/Dissociation Paths and Ill‐Defined Coordination Numbers

“…In [Ni( [14]ane-S 4 )]BF 4 (TTCDNI, Table 1) [36] and the perchlorate of a related macrocyclic complex (MAXSOT, Table 1), [37] moderate deviations from the octahedral shape result from relatively small differences between the bonded NiÀS distances (2.18 ) and the nonbonded contacts between the Ni atom and the BF 4…”

“…Although it would constitute an exciting research topic, it will encounter difficulties, because in many instances the magnetic behavior has gone unreported, and often the high-or low-spin nature of a complex is deduced from interatomic distance criteria without magnetic or spectral evidence. [37] Nevertheless, our shape analysis has allowed us to identify cases of significantly dissociated octahedra for which a lowspin behavior has been reported (see entries PTOCNI10 [38] and LATXOU [39] in Table 1). …”

Poly(amine) biphenyl derivatives as fluorescent sensors for anions and cations

“…NaOH in pellets was added then until pH reached ca. is know to be slow in some cases, 9 the solution was allowed to equilibrate for up to 2 h and no modification of the emission values with time was observed. Fluoride, chloride and bromide were used as their tetrabutylammonium salt.…”