Conformational and stereochemical flexibility in cadmium(ii) complexes of aza-thioether macrocycles

Abstract

The synthesis and crystal structures of four CdII macrocyclic complexes containing mixed N-, O- and S-donors, [Cd(NO3)2([12]aneN2S2)] (1), [Cd(NO3)2([12]aneNS3)] (2), [Cd(NO3)2([15]aneNO2S2)] (3) and [Cd(NO3)([15]aneN2O2S)]NO3 (4), are presented. The metal ion is coordinated outside of the macrocyclic cavity in the complexes of the smaller macrocycles ([12]aneN2S2 and [12]aneNS3) while the flexibility of the larger macrocycles in and allows very different conformations to be adopted with a 'butterfly' geometry in and a flattened geometry in. No correlation between the number of sulfur donors and Cd-S bond distance in these types of complexes is observed, although the number and binding mode of the nitrato ligands is determined by the conformation and binding mode of the macrocycle. The position of the nitrato ligand also influences, through steric conflicts with the macrocyclic donor atoms, the bond distances in both ligand systems.

Coordination chemistry of N-aminopropyl pendant arm derivatives of mixed N/S-, and N/S/O-donor macrocycles, and construction of selective fluorimetric chemosensors for heavy metal ions

“…The coordination sphere around each metal centre consists of the N 2 SO-donor set of the macrocyclic framework, and two asymmetrically bidentate nitrato ligands (in 1-I, for one of the NO 3 − ions, one Cd-O nitrato distance is only slightly longer than those found for a clearly bidentate nitrato ligand (Fig. 4, Table 3), 44 whereas in 1-II this happens for both coordinated NO 3…”

“…The Cd II ion is displaced out of the plane defined by the four donors of L 3a (by 1. respectively. A similar coordination sphere around the metal centres, and conformation for the macrocyclic ligands has been observed in the complexes [Hg(L 3a )(NO 3 ) 2 ], 37 [Pb(L 3a )NO 3 ) 2 ], 37 [Hg( [12]aneNSO 2 )(NO 3 ) 2 ] ( [12]aneNSO 2 = 1,7-dioxa-4-thia-10-azacyclododecane), 45 [Cd(cis- [12]aneN 2 S 2 )(NO 3 ) 2 ] (cis- [12]aneN 2 S 2 = 1,4-dithia-7,10-diazacyclododecane), 44 and [Cd(L 2a )(NO 3 ) 2 ], 44 thus confirming the inability of 12-membered mixed-donor tetradentate macrocycles to bind a metal in the plane of the donors, and their preference for a folded [2424] conformation with small metal ions such as Cu II and Zn II , or a more planar [3333] conformation with larger metals such as Cd II , Hg II , and Pb II that lack a particular stereochemical preference. Even fewer structural data are available for metal complexes with 15-membered mixed N/S/O-donor pentadentate macrocycles such as L 4a than for the smaller 12-membered macrocyclic ligands.…”

“…Even fewer structural data are available for metal complexes with 15-membered mixed N/S/O-donor pentadentate macrocycles such as L 4a than for the smaller 12-membered macrocyclic ligands. 44,47,51 The greater flexibility and the larger cavity of these systems allows very different conformations to be adopted from a "butterfly" or folded geometry in [Cd(L 4a )(NO 3 ) 2 ], 44 [Ni( [15] The X-ray crystal structure of the compound [Cu(L 4a )(dmf)](ClO 4 ) 2 (2) obtained by reacting L 4a with Cu(ClO 4 ) 2 in MeCN followed by crystallization in dmf/Et 2 O, is not an exception. In this structure the stereochemical demands of the metal centre for an octahedral coordination environment results in a "butterfly" configuration of the macrocycle, with the plane of the ring folded at the S • • • S vector.…”

A Convenient Synthesis of Dithiolane and Benzyloximates Derivatives for Ligand Studies

“…The presence and positioning of multiple sulfur atoms in the rings allow for a variety of multidentate binding modes to transition metals. Recent examples of cyclic thioethers used in this manner include 1,3,5-trithiane [3][4] , 1,4dithiane [5][6] , 1,3-dithiane 7 , 1,4,7-trithiacyclononane 8 , 1,4,8,11-tetrathiacyclododecane 8 , and various macrocyclic thioether-esters 9 and aza-thioethers 10 .…”

Cadmium-113 NMR studies on homoleptic complexes containing thioether ligands: the crystal structures of [Cd([12]aneS4)2](ClO4)2, [Cd([18]aneS4N2)](PF6)2 and [Cd([9]aneS3)2](PF6)2

“…9- 16 The importance of research into Cd(II) macrocyclic thioether complexes has been recently highlighted by Schr öder and co-workers who reported a series of Cd(II) complexes with four coordinate aza-thioether macrocycles. 17 The thioether and related ligands discussed in our paper are illustrated in Chart 1. Our group is interested in examining how structural modifications within thioethers affect their ability to bind toxic heavy metal ions, and we have now prepared a series of new Cd(II) metal complexes with several macrocyclic polythioethers.…”