A Polyoxometalate Containing the {Ni₂N₃} Fragment: Ferromagnetic Coupling in a Ni^II μ‐1,1 Azido Complex with a Large Bridging Angle

Abstract

Dedicated to Professor M. T. Pope on the occasion of his 70th birthday.The chemistry of polyoxometalates (POMs) continues to attract much attention, particularly with respect to potential catalytic activity. [1] In the last few years it has also been noted that POMs are ideal models for the study of exchange interactions in magnetic clusters, as they represent a class of well-insulated complexes of controlled nuclearity and topology.[ [5] and that N 3 À is certainly one of the most interesting magnetic couplers known in molecular chemistry, we have decided to investigate the interaction of this ligand with magnetic POMs. Very recently, we have shown that the paramagnetic center of a Cu II POM can bind an azido group;[3e] nevertheless, the lack of structural information prevents any investigation of the magnetic properties of the compound obtained. We report herein the synthesis, the structural characterization, and the magnetic properties of complex KRb 5 [(PW 10 O 37 )(Ni(H 2 O)) 2 (m-N 3 )]·19 H 2 O (1), which is the first example of a fully characterized azido polyoxometalate. Moreover, the topology of the {Ni(m-1,1-N 3 )Ni} core in 1 is unprecedented, as no corner-sharing azido-bridged Ni II complex has been obtained to date. It follows that the Ni-N-Ni angle q in 1 is by far the largest observed in azido-ligand bridged Ni II compounds, a feature which should help the understanding of the relationships between structural parameters and the value of the magnetic exchange parameter J for m-1,1-N 3 complexes.Compound 1 9À species in solution, is known. [6] Crystal structure analysis of compound 1 [7] shows that 1 can be described as the result of the formal removing of a {W 3 O 13 } group from the [a-PW 12 O 40 ] 3À ion followed by its replacement by a {WO 10 Ni 2 -(H 2 O) 2 N 3 } fragment (Figure 1). Two crystallographically non-6À subunits (1 a and 1 b, containing the ions Ni(1) and Ni(2), respectively) have been found in the unit cell. The dinuclear {[Ni(H 2 O)] 2 N 3 } entities are highly similar in 1 a and 1 b (see Figure 1), and will be considered as identical for the forthcoming discussion. The paramagnetic centers are in an axially distorted octahedral environment. Indeed, an elongated NiÀO(PO 3 ) bond (d Ni-O = 2.273(5), 2.283(4) ) is observed in the position trans to the Ni À OH 2 bond (d NiÀOH 2 = 2.007(2), 2.018(4) ), the remaining Ni-O/N bonds are in the range 1.990(5)-2.081(5) . The two paramagnetic centers are bridged by one of the terminal nitrogen atoms of the azido ligand, which connects the

Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt Clusters

“…[8] Recently, insertion into paramagnetic polyoxometalate matrices of exogenous ligands and especially that of the azido anion [9] has shown that such polydentate ligands can also allow the assembly of magnetic polyoxometalate subunits, [10] but in addition could impose ferromagnetic interactions within the cluster. [11,12] Co II polyoxometalate compounds containing from two to nine interacting paramagnetic centers have been reported.…”

Structural and Magnetic Properties of MnIII and CuII Tetranuclear Azido Polyoxometalate Complexes: Multifrequency High‐Field EPR Spectroscopy of Cu4 Clusters with S=1 and S=2 Ground States

“…Interestingly, we have shown that the synthesis of POM/N 3 À complexes leads to azido compounds characterized by original structural features that differ from those obtained using organic ligands. Complexes with very large [11] or very small [17] M-(N 3 )-M angles have been isolated, as well as a unique Cu II complex in which a m-1,1,1,3,3,3-azido ligand assembles a nine-paramagneticcenter cluster. [17] In this paper, we present the synthesis, X-ray crystal structure analysis, and [17] (2 b) compound, determined by a multifrequency HF-EPR study, and the results are compared and discussed.…”

“…Recently, we have initiated the study of magnetic POM compounds in which the paramagnetic transition-metal ions are connected by azido ligands. [11] For more than two decades, azido-bridged transition-metal complexes have inspired a lot of experimental and theoretical work. [12] It has been established that the end-to-end coordination mode tends to lead to antiferromagnetic coupling, while the end-on coordination generates ferromagnetic coupling.…”

A Nonanuclear Copper(II) Polyoxometalate Assembled Around a μ‐1,1,1,3,3,3‐Azido Ligand and Its Parent Tetranuclear Complex

“…This indicates that an end-on coordination mode is adopted by the N 3 À ion. [5] implying that isomerization occurred during the formation of 1 a; such a process has been previously observed. Indeed, Kortz et 12À species.…”