Threading Salen-type Cu- and Ni-Complexes into One-Dimensional Coordination Polymers: Solution versus Solid State and the Size Effect of the Alkali Metal Ion

Abstract

Compartmentalization of metal ions is crucial in biology as well as in materials science. For the synthesis of single source precursors, the preorganization of different metal ions is of particular interest for the lowtemperature generation of mixed metal oxides. On the basis of a potentially Ω-shaped salen-type ligand providing an N 2 O 2 as well as an O 2 O 2 coordination site, mixed metal coordination compounds with Cu(II) or Ni(II) and alkali metal ions have been studied for their structural and optical properties. UV− vis and 1 H NMR titrations show that the obtained compounds adopt partially different structures in solution compared to the solid state. In the latter case, the coordination geometry is mainly governed by the size of the alkali metal ion as well as the transition metal ion used. ■ INTRODUCTIONThe precise arrangement and compartmentalization of metal ions are important both in biology as well as in materials science.1−5 Siderophores such as iron chelators produced by microbes are for example prototypes for metal specific uptaking agents. These could be used in industrial or environmental cleanup processes to selectively extract metal ions.6 Artificial systems such as salen (N,N′-disalicylidene-ethylenediamine) and its derivatives are commonly employed as versatile chelate ligands in coordination chemistry and obtained by a straightforward condensation reaction. 7 Containing two Schiff base 8 coordinating moieties, this family of ligands is able to bind to transition-metal ions in a tetradentate fashion forming stable complexes through its N 2 O 2 site. Furthermore, they represent versatile ligands type thanks to their tunable design. Several structural studies were undertaken on bi-or trinuclear mono-or heterometallic Schiff base complexes. 33−37Interesting trinuclear structures of Zn-salen based complexes were reported in Cai's work, by tuning the counterions, the solvent, or the reaction conditions. 68 A structural description of a binuclear Zn complex able to undergo transmetalation as well as polynuclear salen compounds was presented by Kleij and coworkers. 69,70 On the basis of salen-type ligands, Nabeshima et al. have described multiple-metal containing host−guest complexes using transmetalation reactions to incorporate the guest ions. 22,71 These ligands can adopt, depending on the ionic radius of the metal ions, a helical conformation in solution. 72,73 They also reported the first efficient and selective introduction of three different metal ions into one ligand under thermodynamic control. 4 While numerous transition metal ions were widely employed along with the salen-derived ligands for multiple purposes, the series with alkali metal ions remain however not entirely investigated. 21,74,75 Previous tests to use alkali ions as guests in larger H 2 L salen-type ligands using also transmetalation were unsuccessful.72 While a recent publication by the Nabeshima group deals with the formation of alkali metal ion complexes with macrocyclic ligands in solution, no 1

Newly synthesized homomultinuclear Co (II) and Cu (II) bissalamo‐like complexes: Structural characterizations, Hirshfeld analyses, fluorescence and antibacterial properties

“…[37][38][39] Salamo-like metal complexes have better flexibilities and selectivities, [40] nitrogen and oxygen atoms in N 2 O 2 cavity are easier to bind to different metal ions. [41][42][43] Of course, it can also be expected to obtain more novel metal complexes because of the different metal ions added. [44][45][46][47] The biological antimicrobial activities of oxime-type metal complexes have been widely studied, [31,32] however, salamo-like complexes are still lacking in this field.…”

“…In addition, it has been reported that some salamo‐like metal complexes are much more stable than corresponding salen‐like metal complexes . Salamo‐like metal complexes have better flexibilities and selectivities, nitrogen and oxygen atoms in N 2 O 2 cavity are easier to bind to different metal ions . Of course, it can also be expected to obtain more novel metal complexes because of the different metal ions added .…”

Compartmentalization of Alkaline-Earth Metals in Salen-Type Cu- and Ni-Complexes in Solution and in the Solid State

“…In a previous work, 71 we have explored the heterometallic systems derived from a 3-methylsalicylaldehyde-diamine ligand (H 2 L) containing two specific coordination sites. 72,73 Its central coordination site was composed of an imine-based N 2 O 2 entity coordinating either Cu(II) or Ni(II) ions.…”

Unprecedented Dinuclear CuII N,O-Donor Complex: Synthesis, Structural Characterization, Fluorescence Property, and Hirshfeld Analysis

“…They can coordinate with alkaline earth, rare earth, and d-block transition metal ions to form stable mononuclear or multinuclear metal coordination compounds [1][2][3][4][5]. It has been found that these salen-like complexes have various special structures and interesting properties [6][7][8]. In recent years, based on the research of salen and its derivatives, a new salamo-like ligand and its derivatives (R-CH=N-O-(CH 2 ) n -O-N=CH-R) have been developed, as the cavity formed by N 2 O 2 is easier to bind with metal ions [9][10][11][12][13].…”