Synthesis, structure, and spectroscopy of an encapsulated nickel(II) complex of the unsymmetrical macrobicyclic ligand 1-methyl-8-amino-3,13-dithia-6,10,16,19-tetraazabicyclo[6.6.6]icosane (AMN4S2sar)

Abstract

The nickel(II) complex of the encapsulating ligand 1 -methyl-8-amino-3,13-dithia-6,10,16,19-tetraazabicyclo[6.6.6]icosane, [Ni(AMN4S2sar)]2+, is reported. Crystals of the complex are monoclinic, space group P2\/c, with Z = 4,a = 9.167(6) Á, b = 19.885(4) Á, c = 13.068(8) Á, ß = 95.37(3)°, and R = 0.055. The low-temperature (~10 K) single-crystal absorption spectrum and ligand field analysis of the complex are reported. The spin-forbidden 3A2g -*• 'Eg.'Aig transitions were observed at low temperature, and from the spectroscopic analysis, a significant differential nephelauxetic effect is shown to occur resulting in much lower values for the Racah B and C parameters for these spin-forbidden transitions in relation to the spin-allowed transitions. introduction Encapsulated transition metal complexes have been studied extensively. In the majority of cases the ligands have been hexaamines of the sar type (sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane),M5 although metal complexes of ligands with donors other than Ng have been reported.16-21 As part of a study directed at the synthesis and properties of potentially octahedral encapsulating ligands with unsymmetrical nitrogen and sulfur donor sets, we have prepared the encapsulating ligands

Pentadentate thioether-oxime macrocyclic and quasi-macrocyclic complexes of copper(II) and nickel(II)

“…Generally, it is known that only two d-d transitions are observed when thioether donors are present, the highest energy band ( 3 T 1g (P) 3 A 2g ) becoming obscured by the charge-transfer processes ( 400 nm) [35]. Two other problems are often encountered in Ni(II) thioether and nitrogen containing systems which are interrelated: (a) The mathematical relation-ships involving spectral transitions and the ligand field parameters break down if there are row-3 donors in the coordination sphere [36]; (b) the lowest energy band ( 3 T 2g 3 A 2g ) often exhibits a double-humped shape due to mixing with a close-lying spin-forbidden transition ( 1 E g 3 A 2g ) through spin-orbit coupling [37,38]. These problems make it difficult to obtain values for 10 Dq as well as Hancock and coworkers have attempted to tackle the problem of determining 10 Dq by 'deconvoluting' the low energy spin-allowed (10 Dq) from the spin-forbidden transition and the method has been used to interpret the spectra of other hexacoordinate Ni(II) systems with thioether and nitrogen donors [36,39].…”

Copper(II) Complexes of a Hexadentate Mixed‐Donor N3S3 Macrobicyclic Cage: Facile Rearrangements and Interconversions

“…The diME-S 6 sar ligand (Scheme 1) is synthesized by means of a metal-free route, [3] but low yields have limited studies of its coordination chemistry beyond cobalt. Mixed-donor N/S sar ligands have been reported (Scheme 1) that comprise combinations such as (N 3 S 3 ), [4][5][6][7] (N 4 S 2 ), [8][9][10][11] and (N 5 S) [12,13] donor atoms, accessible through Co III -directed chemistry of suitably configured, preformed, mixed-donor (N/S) acyclic hexadentate ligands. Complexes of AMME-N 3 S 3 sar (Scheme 1) are the most extensively studied of all N/S mixed-donor cage ligands from this family, and their Co III , [4][5][6][14][15][16] Fe II , [17] and Hg II [18] complexes all exhibit the expected N 3 S 3 hexadentate coordination mode.…”

“…[26,27] The copper(II) chemistry of cage ligands is distinct from other transition metals due to its extreme lability and unusual coordination geometries. The d 9 Cu II metal ion in a six-coordinate environment undergoes a spontaneous distortion from octahedral or trigonal symmetry due to the JahnTeller effect. [28,29] This is nearly always manifested in an elongation of a pair of trans-cooordinated ligands in a sixcoordinate complex.…”

Synthesis, structure and magnetism of iron-(III) and -(II) complexes of 1-thia-4,7-diazacyclononane and N,N ′-dimethyl-1-thia-4,7-diazacyclononane

“…We were interested to investigate the chemical influences of the thioether in the bridged diiron systems in an extension of earlier investigations related to the redox, stereochemical and spectroscopic influences on metal complexes by the replacement of nitrogen donors by thioethers. [18][19][20][21][22][23][24]…”