Recent advances in the synthesis of piperazine based ligands and metal complexes and their applications

The piperazine scaffold is a privileged structure frequently found in biologically active compounds. Piperazine nucleus is found in many marketed drugs in the realm of antidepressants (amoxapine), antipsychotics (bifeprunox), antihistamines (cyclizine and oxatomide), antifungals (itraconazole), antibiotics (ciprofloxacin), etc. This is one of the reasons why piperazine based compounds are gaining prominence in today's research. In addition to the ring carbons, substitution in the nitrogen atom of piperazine not only creates potential drug molecules but also makes it unique with versatile binding possibilities with metal ions. Piperazine ring-based compounds find their application in biological systems with antihistamine, anticancer, antimicrobial and antioxidant properties. They have also been successfully used in the field of catalysis and metal organic frameworks (MOFs). The present review focuses on the synthesis and application of different piperazine derivatives and their metal complexes having diverse applications.

Syntheses, structures and catalytic properties of Evans–Showell-type polyoxometalate-based 3D metal–organic complexes constructed from the semi-rigid bis(pyridylformyl)piperazine ligand and transition metals

Two 3D Evans–Showell-type POM-based different transition metals–bis-pyrazine–bis-amide complexes act as heterogeneous catalysts for the oxidation of benzyl alcohol.

Crystal structure of catena-poly[hexaaquabis(μ2-3-nitrophthalate-κ2 O:O′)-(μ2-1,4-bis(4-pyridylmethyl)piperazine-κ2 N:N′)dimanganese(II)] dihydrate, C32H42Mn2N6O20

C32H42Mn2N6O20, monoclinic, P21/c (no. 14), a = 10.200(2) Å, b = 19.893(4) Å, c = 11.3785(17) Å, b = 123.118(12)°, V = 1933.7(7) Å3, Z = 2, R gt(F) = 0.0602, wR ref(F 2) = 0.1673, T = 293 K.

The assembly of thiophene-based bis-pyridyl-bis-amide CoII coordination polymers and their polypyrrole-functionalized hybrid materials for boosting their photocatalytic performances

A series of thiophene-based bis-pyridyl-bis-amide coordination polymers have been synthesized and decorated with polypyrrole for boosting their photocatalytic properties under visible light irradiation.

Various pH-Dependent Copper(II) Coordination Architectures Constructed from N,N′-Di(3-pyridyl)succinamide and Two Different Dicarboxylates

Using a bis-pyridyl-bis-amide N,N′-di(3-pyridyl)succinamide (L) and two dicarboxylates as mixed ligands, four 2D copper(ii) metal–organic networks, formulated as [Cu(1,4-chdc)(L)]·3H2O (1), [Cu(1,4-chdc)(L)]·H2O (2), [Cu(2,5-tdc)(L)]·H2O (3), and [Cu(2,5-tdc)(L)]·2H2O (4) (L = N,N′-di(3-pyridyl)succinimide; 1,4-H2chdc = 1,4-cyclohexanedicarboxylic acid; 2,5-H2tdc = thiophen-2,5-dicarboxylic acid) have been hydrothermally synthesized under different pH conditions, and characterized by IR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Compound 1, formed at pH 5.4, contains two rare types of left-, right-handed [Cu-L]n helix chains, which are further connected by [Cu-1,4-chdc]n zigzag chains, affording a 2D wave-like polymeric network. Compound 2 was obtained at pH 5.9, and shows a 2D square-grid layer constructed from zigzag [Cu-L]n chains and linear [Cu-1,4-chdc]n chains. Compounds 3 and 4 possess a similar 2D grid layer to that of 2 with 44-sql topology, formed at pH 4.8 and 5.4 respectively, and are constructed from zigzag [Cu-L]n chains and linear [Cu-2,5-tdc]n chains. The effects of pH and secondary dicarboxylates on the diversity of structures are discussed. In addition, the thermal stabilities, photoluminescence properties, and photocatalytic activity of compounds 1–4 were also studied.

A new three-dimensional coordination polymer of Sr(II) based on dipicolinic acid, with different coordination environments for Sr(II)

A three-dimensional coordination polymer of Sr(II) based on dipicolinic acid (pydcH2) has been synthesized and characterized, namely poly[[diaquabis(μ3-6-carboxypyridine-2-carboxylato)bis(μ4-pyridine-2,6-dicarboxylato)tristrontium(II)] dihydrate], {[Sr3(C7H3NO4)2(C7H4NO4)2(H2O)2]·2H2O}n. The asymmetric unit consists of two unique Sr(II) centres (one of them situated on an inversion centre), two independent pydc(2-) ligands, and one coordinated and one uncoordinated water molecule. The two independent Sr(II) cations are surrounded by water and dipicolinate molecules in distorted square-antiprism and distorted tricapped trigonal prismatic geometries. The dipicolinate ligands adopt μ3- and μ4-bridging modes, linking the alkaline earth metal centres into a three-dimensional coordination framework. One dipicolinate ligand is doubly deprotonated, while the other is singly deprotonated.

Aromatic Polycarboxylate-Tuned Assembly of Three New 2D Copper(II) Complexes Derived from a Flexible Bis(pyridylamide) Ligand

Three new 2D copper(ii) complexes [Cu(NIPH)(L)] (1), [Cu(BDC)(L)(H2O)] (2), and [Cu(HBTC)(L)]·2H2O (3) were hydrothermally synthesized by self-assembly of aromatic polycarboxylates (H2NIPH = 5-nitroisophthalic acid, H2BDC = 1,3-benzenedicarboxylic acid, H3BTC = 1,3,5-benzenetricarboxylic acid) and the flexible bis(pyridylamide) ligand L (L = N,N′-di(3-pyridyl)succinamide), and structurally characterized by single crystal X-ray diffraction, and elemental, IR, and thermogravimetric analyses. Compound 1 is a 2D coordination polymer based on tri-flexural helix chains (left-, right-handed [Cu-L]n helix chains, and left-handed Cu-NIPH helix chain). Compound 2 exhibits a 2D wavelike polymeric layer structure constructed from a 1D [Cu-L]n sinusoidal chain and a 1D [Cu-BDC]n V-like chain. Compound 3 possesses a 2D double-layer network formed from 1D [Cu-L]n zigzag chains and 1D [Cu-HBTC]2n double chains. The fluorescent properties of the three compounds and the electrochemical behaviour of compound 2-bulk-modified carbon paste electrode were also studied.