Structures and Magnetic Properties of Tetranuclear Nickel(II) Complexes with Unusual μ₃‐1,1,3 Azido Bridges

Abstract

Pyrazolate-based dinucleating ligands with thioether-containing chelate arms have been used for the synthesis of a family of novel tetranuclear nickel(II) complexes [L2Ni4(N3)3(O2CR)](ClO4)2 that incorporate three azido bridges and one carboxylate (R = Me, Ph). Molecular structures have been elucidated by X-ray crystallography in four cases, revealing Ni4 cores with a unique topology in which two of the azido ligands adopt an unusual mu3-1,1,3 bridging mode. The compounds were further characterized by mass spectrometry, IR spectroscopy, and variable-temperature magnetic susceptibility measurements. Magnetic data analyses indicate a combination of significant intramolecular ferromagnetic and antiferromagnetic exchange interactions that give rise to an overall S(T) = 0 ground state. The sign and the magnitude of the individual couplings have been rationalized in the framework of the common magnetostructural correlations for end-to-end and end-on azido linkages, suggesting that these correlations also remain valid for the respective fragments of multiply bridging mu3-1,1,3 azido ligands.

Alternating Spin Chains: Controlled Assembly from Bimetallic Building Blocks and QMC Simulation of Spin Correlation

“…The azido ligands thus adopt a rare m-1,1,3 bridging mode in which all NiÀN azide distances lie in the narrow range 2.109(2)-2.189(2) . Genuine m-1,1,3 coordination of azido ligands has only recently been discovered in some molecular Ni 4 systems, [21] while in most previous examples of m 3 -1,1,3-azide binding at least one of the NiÀN azide bonds was much longer and better described as semicoordinating.…”

“…In its deprotonated form L À this ligand was previously shown to nest two high-spin (S = 1) nickel(II) ions in its binding sites and to afford a variety of nickel(II) azido complexes. [21,23,31,32] These may feature unusual azide binding modes in oligonuclear aggregates [21,23] as well as a certain geometrical flexibility of the central azide ion that is hosted between the two metal ions of the bimetallic array, [32] which led us to expect a series of related yet distinct 1D systems from a single dinickel(II) precursor.…”

“…[38] Similar correlations appear to be also valid for m 3 -or m 4 -bridging azide linkages. [21,23] Coupling may be even stronger in the case of secondary bridges such as a pyrazolate. [32] In the case of 2 the Ni-N-N angles are quite acute (111.2(2)/114.9(2)8), while one angle is closer to the normal range for 1 (111.9(2)8/ 119.4(2)8).…”

“…Triply or quadruply bridging azide coordination modes such as m 3 -1,1,1, m 3 -1,1,3, m 4 -1,1,1,1 and m 4 -1,1,3,3 have remained relatively scarce, even though they may be of particular interest with respect to the construction of polynuclear complexes or 2D and 3D polymeric networks. [20][21][22][23] In the search for S = 1 HABA compounds with different alternation parameters g, however, a major drawback of the synthetic strategies followed so far is the lack of control over structure and bond alternation. Usually a nickel(II) salt, potentially bridging ligands and a chelating capping ligand (to avoid polymerization) are mixed, and the solution is then slowly evaporated to give crystalline material.…”

Diverse Structures and Magnetism of Cobalt(II) and Manganese(II) Compounds with Mixed Azido and Carboxylato Bridges Induced by Methylpyridinium Carboxylates

“…Some compounds have been described in which the two different bridges simulA C H T U N G T R E N N U N G taneously connect the same pair of metal ions [11] or separately connect different metal pairs [12] to give clusters [13,14] (including a few SMMs [14] ) and coordination polymers. [11][12][15][16][17][18][19] The compounds were usually derived from anionic carboxylate ligands (in their deprotonated form), such as pyridinecarboxylates and their N-oxides, [15] formate, acetate, [13,16,17] and a few phenyl-based aromatic carboxyl-A C H T U N G T R E N N U N G ates. [11, 12a, 18] Recently, we demonstrated that the use of zwitterionic dicarboxylate ligands with cationic pyridinium and anionic carboxylate groups is an easy and efficient approach to 2D or 3D networks containing 1D chains with azide and carboxylate bridges.…”