Tuning Cu^II Coordination Polymers Derived from a Bis(pyrazolecarboxylate) Ligand by Solvothermal C–H Bond Activation: Synthesis, Structures, Catalysis, and Magnetic Properties

Abstract

A new bis(pyrazolecarboxylate) ligand, 1,3-phenylenebis-(1H-pyrazole-5-carboxylic acid) (H 2 PBPC) has been synthesized to study the structure and intriguing properties of the resultant coordination polymers synthesized under solvothermal conditions. The reaction of H 2 PBPC with Cu(ClO 4 ) 2 in the presence of NaOH at two different temperatures (80 and 120°C) resulted in two coordination polymers, namely, [{Cu 2 Na(H 2 OPBPC)}] ϱ (1) and [{Cu 4 Na 2 (H 2 OPBPC) 2 }] ϱ (2), which display 2D corrugated sheet and 3D staircase architectures, respectively; in these structures, the aromatic C-H bond flanked by the pyrazolecarboxylate moieties was oxidized to form a C-O bond. When 2,2Ј-bipyridine (2,2Ј-bpy)[a] 5874 was used instead of NaOH, [{Cu 2 (2,2Ј-bpy) 2 (H 2 PBPC)}-(H 2 O)] ϱ (3) formed, and such C-H bond activation was not observed. Interestingly, one of the coordination polymers, namely, 1, displayed catecholase and phosphatase activity. Variable-temperature magnetic susceptibility data in the range 2-300 K showed that there is antiferromagnetic coupling between the metal centers of 1 and 2 that is mediated through the phenoxo and pyrazole bridges, whereas 3 revealed dominant ferromagnetic interactions between the bis-(pyrazolato)-bridged Cu II centers owing to its very unusual Cu-N-N-Cu torsion angles of 75.28 and 69.52°.

Coordination Driven Self-Assembly in Co(II) Coordination Polymers Displaying Unprecedented Topology, Water Cluster, Chirality, and Spin-Canted Magnetic Behavior

“…N donor heterocyclic ligands particularly pyrazole based flexible or rigid linker are acclaimed for their high thermal stability and interesting structural topologies. [33][34][35][36][37][38] Aromaticpolycarboxylates are used extensively as organic co-linkers since they often produce inherently rigid structures which have potential application in gas adsorption and storage. [39][40][41] But, flexible cyclohexane carboxylate linkers are less explored as co-linkers in designing CPs although they are capable of inducing interesting structural features in the framework.…”

“…In this regard, a very promising approach is the use of mixed ligands such as N-donor heterocyclic ligands together with polycarboxylate organic colinkers in the same system. N-donor heterocyclic ligands, particularly pyrazole-based flexible or rigid linkers, are acclaimed for their high thermal stability and interesting structural topologies. − Aromatic polycarboxylates are used extensively as organic colinkers since they often produce inherently rigid structures which have potential application in gas adsorption and storage. − However, flexible cyclohexane carboxylate linkers are less explored as colinkers in designing CPs, although they are capable of inducing interesting structural features in the framework. The cyclohexane ring of such polycarboxylic acids can adopt various conformations, including boat, chair, twist boat, etc., depending on the coordination requirement of the metal ion, and thus can lead to unexpected and topologically unusual polymeric architectures.…”