Mn(II) coordination architectures with mixed ligands of 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons

doi:10.1016/j.ica.2006.12.032

Inorganica Chimica Acta

Volume 360, Issue 8, 30 May 2007, Pages 2532-2540

https://doi.org/10.1016/j.ica.2006.12.032 Get rights and content

Abstract

In our efforts to investigate the factors that affect the formation of coordination architectures, such as secondary coordination donors and pendant skeletons of the carboxylic acid ligands, as well as H-bonding and other weak interactions, two kinds of ligands: (a) 3-(2-pyridyl)pyrazole (L¹) with a non-coordinated N atom as a H-bonding donor, a 2,2′-bipyridyl-like chelating ligand, and (b) four carboxylic ligands with different secondary coordination donors and/or pendant skeletons, 1,4-benzenedicarboxylic acid (H₂L²), 4-sulfobenzoic acid (H₂L³), quinoline-4-carboxylic acid (HL⁴) and fumaric acid (H₂L⁵), have been selected to react with Mn(II) salts, and five new complexes, [Mn(L¹)₂(SO₄)]₂ (1), [Mn(L¹)₂(L²)]_∞ (2), [Mn(L¹)(HL³)₂]_∞ (3), Mn(L¹)₂(L⁴)₂ (4), and [Mn(L¹)₂(L⁵)]_∞ (5), have been obtained and structurally characterized. The structural differences of 1–5 can be attributed to the introduction of the different carboxylic acid ligands (H₂L², H₂L³, HL⁴, and H₂L⁵) with different secondary coordination donors and pendant skeletons, respectively. This result also reveals that the typical H-bonding (i.e. N–H⋯O and O–H⋯O) and some other intra- or inter-molecular weak interactions, such as C–H⋯O weak H-bonding and π⋯π interactions, often play important roles in the formation of supramolecular aggregates, especially in the aspect of linking the multi-nuclear discrete subunits or low-dimensional entities into high-dimensional supramolecular networks.

Graphical abstract

Five new Mn(II) complexes with mixed ligands, 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons have been synthesized and structurally characterized. Their structures are different mainly due to the different secondary coordination donors and pendant skeletons of the carboxylic acid ligands. In addition, intra- or inter-molecular H-bonding and π⋯π interactions also play important roles in the formations of such complexes, and further link the discrete subunits or low-dimensional entities into high-dimensional supramolecular assemblies.

Introduction

Recently, much efforts have been focused on the crystal engineering of metal-organic coordination architectures owing to their fascinating structural diversities and potential applications as functional materials [1], [2]. The advantage of the metal-organic framework approach is to allow a wide choice of different parameters, including electronic properties and coordination geometry of the metal ions, as well as versatile functions and topologies of organic ligands. In a sense, this is also the aspiration for achieving one of the ultimate aims of crystal engineering, i.e., gaining control of the topology and geometry of the networks formed through judicious choice of ligand and metal precursor geometry [3]. However, the rational design and synthesis of anticipant multi-nuclear discrete coordination architectures or polymeric networks with metal ions (or metal clusters) as nodes and organic ligands as bridges or terminal groups is still at an evolutionary stage with the current focus mainly on understanding the factors to determine the crystal packing [4]. Indeed, besides typical coordination bonding [5], [6], some weak interactions, such as H-bonding [7], [8], [9], [10], [11] and π⋯π [12], [13], [14] interactions also affect the structures of coordination complexes, and they may often link multi-nuclear discrete subunits or low-dimensional entities into high-dimensional supramolecular networks [4].

In this field, very often, the skillful combinations of the chelating ligands, carboxylic acid ligands and metal ions have generated some interesting coordination architectures [4]. In our previous works, 3-(2-pyridyl)pyrazole (L¹), and some structurally related pendant carboxylate ligands have been successfully used to construct a series of Cd(II) or Cu(II) complexes with multi-nuclear discrete structures or 1D and 2D frameworks [15]. As a continuation of this study, our idea is to prepare and tune these kinds of metal complexes by carefully selecting two kinds of ligands (Chart 1): (a) 3-(2-pyridyl)pyrazole (L¹) and (b) four carboxylic acid ligands [1,4-benzenedicarboxylic acid (H₂L²), 4-sulfobenzoic acid (H₂L³), quinoline-4-carboxylic acid (HL⁴) and fumaric acid (H₂L⁵)] with the different secondary coordination groups and/or pendant skeletons. Herein, we report their five new Mn(II) complexes, [Mn(L¹)₂(SO₄)]₂ (1) (not introducing carboxylic acid ligand), [Mn(L¹)₂(L²)]_∞ (2), [Mn(L¹)(HL³)₂]_∞ (3), Mn(L¹)₂(L⁴)₂ (4), and [Mn(L¹)₂(L⁵)]_∞ (5), and characterized their structures.

Section snippets

Materials and general methods

All the solvents and reagents for synthesis, including H₂L², H₂L³, HL⁴ and H₂L⁵ were commercially available and used as received or prepared by reported procedures. 3-(2-Pyridyl)pyrazole (L¹) was synthesized by the literature method [16]. IR spectra were measured on a Tensor 27 OPUS (Bruker) FT-IR spectrometer with KBr pellets.

Synthesis of complexes 1–5

[Mn(L¹)₂(SO₄)]₂ (1). Complex 1 was obtained by the reaction of MnSO₄ · H₂O and 3-(2-pyridyl)pyrazole (L¹) in a molar ratio of 1:2 mixed with 12 mL of water under

Synthesis and general characterizations

Complexes 1–5 were synthesized under the hydrothermal conditions and NaOH was introduced to deprotonate for carboxylic acids except 1. The IR spectra for the five complexes show the absorption bands resulting from the skeletal vibrations of the aromatic rings in 1600–1400 cm⁻¹ region. It should be noted that due to the coordination of the pyridyl rings of L¹, the strong absorption band at ∼1575 cm⁻¹ (free L¹) resulting from the skeletal vibrations of the aromatic rings shifted to ∼1600 cm⁻¹. The

Conclusion and comments

In summary, five new Mn(II) complexes with mixed chelating and bridging ligands have been synthesized under the hydrothermal conditions, displaying a systematic structural variations by the employment of the carboxylic acid ligands with the different secondary coordination donors and pendant skeletons and a 2,2′-bipyridyl-like chelating ligand, 3-(2-pyridyl)pyrazole (L¹). These results show that to some extent the structures of such complexes could be adjusted by the secondary coordination

Supplementary material

CCDC 609248, 609249, 609250, 609251, and 609252 contain the supplementary crystallographic data for 1, 2, 3, 4, and 5. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

Acknowledgement

This work was supported by the National Natural Science Funds for Distinguished Young Scholars of China (No. 20225101) and NSFC (No. 20373028).

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Mn(II) coordination architectures with mixed ligands of 3-(2-pyridyl)pyrazole and carboxylic acids bearing different secondary coordination donors and pendant skeletons

Abstract

Graphical abstract

Introduction

Section snippets

Materials and general methods

Synthesis of complexes 1–5

Synthesis and general characterizations

Conclusion and comments

Supplementary material

Acknowledgement

Angew. Chem., Int. Ed.

J. Am. Chem. Soc.

Angew. Chem., Int. Ed.

J. Am. Chem. Soc.

Chem. Rev.

CrystEngComm

Chem. Commun.

Supramolecular Chemistry

Coord. Chem. Rev.

Coord. Chem. Rev.

Chem. Commun.

Angew. Chem., Int. Ed.

Chem. Rev.

Acc. Chem. Res.

Coord. Chem. Rev.

Inorg. Chem.

Inorg. Chem.

Angew. Chem., Int. Ed.

Science

Acc. Chem. Res.

J. Am. Chem. Soc.

Nature

Angew. Chem., Int. Ed. Engl.

Chem. Commun.

Dalton Trans.

Coord. Chem. Rev.

Coord. Chem. Rev.

Acc. Chem. Res.

Acc. Chem. Res.

Chem. Commun.

J. Am. Chem. Soc.