Self-Assembled 3D Heterometallic Cu^II/Fe^II Coordination Polymers with Octahedral Net Skeletons: Structural Features, Molecular Magnetism, Thermal and Oxidation Catalytic Properties

Abstract

The new three-dimensional (3D) heterometallic Cu(II)/Fe(II) coordination polymers [Cu(6)(H(2)tea)(6)Fe(CN)(6)](n)(NO(3))(2n)·6nH(2)O (1) and [Cu(6)(Hmdea)(6)Fe(CN)(6)](n)(NO(3))(2n)·7nH(2)O (2) have been easily generated by aqueous-medium self-assembly reactions of copper(II) nitrate with triethanolamine or N-methyldiethanolamine (H(3)tea or H(2)mdea, respectively), in the presence of potassium ferricyanide and sodium hydroxide. They have been isolated as air-stable crystalline solids and fully characterized including by single-crystal X-ray diffraction analyses. The latter reveal the formation of 3D metal-organic frameworks that are constructed from the [Cu(2)(μ-H(2)tea)(2)](2+) or [Cu(2)(μ-Hmdea)(2)](2+) nodes and the octahedral [Fe(CN)(6)](4-) linkers, featuring regular (1) or distorted (2) octahedral net skeletons. Upon dehydration, both compounds show reversible escape and binding processes toward water or methanol molecules. Magnetic susceptibility measurements of 1 and 2 reveal strong antiferromagnetic [J = -199(1) cm(-1)] or strong ferromagnetic [J = +153(1) cm(-1)] couplings between the copper(II) ions through the μ-O-alkoxo atoms in 1 or 2, respectively. The differences in magnetic behavior are explained in terms of the dependence of the magnetic coupling constant on the Cu-O-Cu bridging angle. Compounds 1 and 2 also act as efficient catalyst precursors for the mild oxidation of cyclohexane by aqueous hydrogen peroxide to cyclohexanol and cyclohexanone (homogeneous catalytic system), leading to maximum total yields (based on cyclohexane) and turnover numbers (TONs) up to about 22% and 470, respectively.

A Rigid Angular Bidentate Ligand for the Design of a New Class of Coordination Polymers Based on Silver(I) Salts – Influence of the Anion on Coordination Assemblies

“…[52] It should be emphasized that we have previously reported the influence of various anions on the self-assembly of supramolecular structures with L 1 and with silver(I) salts. [35] Our results show that CF 3 SO 3 -anions are more coordinating than BF 4 -anions and more recently we have demonstrated that they undergo anion-π interactions with neutral organometallic metal-arene complexes. [53] Scheme 4.…”

“…Although solid state X-ray structures could not be obtained for 1c and 1d so far, we feel that they might have similar packing as those observed for 1a and 1b, respectively. We speculate that the PF 6 -anion should exhibit a similar effect to BF 4 -anion, whereas NO 3 -, a more coordinating anion, may provide a similar packing to that observed with the triflate anion. Moreover, we note that silver coordination polymers in which the coordination of the anion to the metal influences the packing have been previously reported.…”

“…Similarly, white complexes precipitated from solution in high to excellent yield (79-92 %, Scheme 3) and elemental analysis confirmed the formulations of 1a, 1b, 1c and 1d. The IR spectra of these compounds revealed the presence of BF 4 -, NO 3 -and PF 6 -anions for 1b, 1c and 1d, respectively. The 1 H NMR spectra (300 MHz) of 1b, 1c and 1d were recorded in CD 3 CN at room temperature and were analogous to that of 1a.…”

“…[1][2][3] These new metal-containing materials attract attention not only due to their structural diversity but also because of their potential applications in electrical conductivity, magnetism, host-guest chemistry, luminescence and catalysis. [4][5][6][7][8][9][10][11][12][13][14][15] Their topology and properties are determined by several factors such as the metal coordination environment, the topology of spacer ligands employed to connect the metal nodes and weak intermolecular interactions (hydrogen bonding, π-stacking, etc) that stabilize the overall framework. Furthermore, self-assembly has evolved to become an elegant and efficient methodology for the construction of elaborate architectures.…”

“…[35] Recently, we have developed the synthesis of some discrete self-assembled metallosupramolecular 3D capsules of the type M 2 L 4 based on Co II and Cu II , which can encapsulate weakly coordinated anions. [36][37][38][39] Remarkably, they are perfectly designed to house BF 4 -and PF 6 -. As part of our continuing research program, we sought to introduce a highly rigid ligand in our systems that is more coordinating to the metal to investigate whether it was possible to form new cages in which the encapsulation is not only limited to weakly coordinating anions.…”