Oligonuclear Copper Complexes of a Bioinspired Pyrazolate-Bridging Ligand:  Synthesis, Structures, and Equilibria in Solution

Abstract

The synthesis of a new bioinspired dinucleating ligand scaffold based on a bridging pyrazolate with appended bis[2-(1-methylimidazolyl)methyl]aminomethyl chelate arms is reported. This ligand forms very stable copper complexes, and a series of different species is present in solution depending on the pH. Interconversions between these solution species are tracked and characterized spectroscopically, and X-ray crystallographic structures of three distinct complexes that correspond to the species present in solution from acidic to basic pH have been determined. Overall, this provides a comprehensive picture of the copper coordination chemistry of the new ligand system. Alterations in the protonation state are accompanied by changes in nuclearity and pyrazolate binding, which cause pronounced changes in color and magnetic properties. Antiferromagnetic coupling between the copper(II) ions is switched on or off depending on the pyrazole binding mode.

Coordination Versatility of Pyrazole‐Based Ligands towards High‐Nuclearity Transition‐Metal and Rare‐Earth Clusters

“…Variation of the side arm chain lengths gives some control over metal-metal separation, while the number and type of side arm donor sites allow the determination of electronic and coordinative properties. An important part of this research has been developed by Meyer and co-workers, [111][112][113][114][115][116][117][118][119][120][121][122][123][124][125][126] who have studied the coordination ability of the 3,5-disubstituted pyrazole ligands with chelating side arms, mainly with N-donor atoms. [11] The main part of the review was dedicated to dinuclear compounds.…”

“…[121] The coordination ability of the HL2a ligand towards other metal ions, such as copper(II) or zinc(II) ions, was also explored. [127] The incorporation of other functional groups in the amino substituents of the pyrazole ring, such as imidazole (HL2j [125] and HL2l [128] ligands) or 1,4,7-triazacyclonanane (HL2m ligand), [129] has also been studied. [112] An octanuclear copper(I) compound, which can be described as a [(MesCu) 4 (µ 4 -O)] 2-(Mes = 2,4,6-trimethylphenyl) anion with two dinuclear copper(I)-pyrazole clamps containing the HL2i ligand, has also been reported.…”

“…The pyrazolato ligand bridges the two metal ions, and in some cases, the dinuclear structures, [M 2 L2a] + (M = Cu II and Zn II ), are linked by carbonates incorporated from air, [111,114] µ 4 -peroxido, [122] phosphato [113] or oxazetidinylacetato ligands. [125,129] Pyrazole Ligands with N-Donor Substituents, Pyridines 2-Pyridylpyrazole derivatives ( Figure 11) have been proven to be good ligands for obtaining different assemblies, such as metallohelicates [130,131] or clusters. [126] The use of more bulky pyrazole ligands (i.e.…”

Siamese‐Twin Porphyrin: A Pyrazole‐Based Expanded Porphyrin of Persistent Helical Conformation

“…[16] Such pyrazole-based chelates proved to be versatile and useful building blocks in bioinorganic coordination chemistry as they offer a good compromise for mimicking the bridging carboxylate donors frequently found in bimetallic enzymes in Nature and because they could be readily incorporated into compartmentalized ligand frameworks. [17] In these complexes, the pyrazoles are monoanionic donors supporting a range of metalmetal distances. [18] The integration of pyrazole moieties (or other heterocycles such as imidazoles, [19] oxazoles, [20] thiadiazoles, or triazoles [21] ) in porphyrinoid macrocyclic compounds is, however, little developed.…”

Der Carboxylat‐Twist – Aufklärung hysteretischer Bistabilität eines High‐Spin‐Dieisen(II)‐Komplexes mithilfe von Mößbauer‐Spektroskopie

“…Hier berichten wir über einen neuen, bioinspirierten High-Spin-(m-Carboxylato)(m-pyrazolato)dieisen(II)-Komplex 1 des doppelt vierzähnigen Liganden HL (Abbildung 1). [5] Komplex 1 zeigt eine ausgeprägte konformative Flexibilität des exogenen Acetatcoliganden. [6] Die entsprechenden Strukturumwandlungen führen zu einer beispiellosen Hysterese in der Temperaturabhängigkeit der Mçßbauer-Spektren und SQUID-Daten (SQUID = superconducting quantum interference device).…”