Oxamidate-Bridged Dinuclear Five-Coordinate Nickel(II) Complexes:  A Magneto−Structural Study

Abstract

The preparation, spectroscopic characterization, and magnetic study of three new oxamidate-bridged nickel(II) dinuclear complexes of formulas ([Ni(Me3[12]aneN3)]2(mu-oa))(PF6)2 (1), ([Ni(Me3[12]aneN3)]2(mu-dmoa))(PF6)2 (2), and ([Ni(Me3[12]aneN3)]2(mu-dpoa))(PF6)2 (3) (Me3[12]aneN3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene, oa = oxamidate, dmoa = N,N'-dimethyloxamidate, and dpoa = N,N'-diphenyloxamidate) are reported. The crystal structures of two of them (1 and 3) have been determined. 1 and 3 crystallize in the monoclinic system, space group P2(1)/c, with Z = 2 and a = 7.901(4) A, b = 13.597(6) A, c = 17.565(10) A, and beta = 96.46(4) degrees for 1 and a = 13.854(3) A, b = 17.469(4) A, c = 12.543(3) A, and beta = 116.22(3) degrees for 3. The structures of 1 and 3 consist of dinuclear ([Ni(Me3[12]aneN3)]2(mu-oa))2+ and ([Ni(Me3[12]aneN3)]2(mu-dpoa))2+ cations and hexafluorophosphate anions. Each nickel in 1-3 is five-coordinate, and the substitution of the hydrogen atom of the amidate nitrogen of 1 by a methyl (2) or a phenyl (3) group causes a significant modification of the stereochemistry of the nickel(II) ions from square pyramidal toward trigonal bipyramidal (tau values of 0.12 and 0.48 for 1 and 3, respectively). The NOESY spectrum of 3 has allowed us to achieve the assignment of the phenyl protons of the N,N'-diphenyloxamidate. The value of magnetic coupling between the two nickel(II) ions across the oxamidate bridge [J = -57.0 (oa, 1), -38.0 (dmoa, 2) and -30.5 cm(-1) (dpoa, 3)] is very sensitive to this stereochemical change, and its variation is explained on the basis of orbital considerations. DFT type calculations have been performed to analyze and substantiate the trend of the magnetic coupling in 1-3.

Synthesis and Characterization of Heterotrinuclear Complexes of Nickel and Palladium with Pyridinecarboxylate as Bridging Ligands

“…The 1 H NMR spectra of complexes 1-4 show the resonance line pattern observed for the mcN 3 ligands that was assigned on the basis of previous studies of (macrocycle)nickel complexes [10][11][12][13][14] and from the temperature dependence of the resonances. A representative 1 H NMR spectrum for complex 4 is shown in Figure 1.…”

“…This synthetic method has previously been used for the preparation of pentacoordinate nickel(ii) complexes containing N,S-donor, [10] oxamidate, [11] hydroxamate, [12] and pyridonate ligands, [13] as well as phosphate esters and phosphinate derivatives. [14] Complexes 1-4 are air-stable both in the solid state and in solution.…”

Self‐Assembly of Oxamidato‐Chelated ReI‐ and MnI‐Based Flexible Dinuclear Horse‐Stirrup‐Like Metallacycles

“…The oxamide ligands were synthesized as reported previously. [48] The synthesis, workup, and crystallization of the manganese compounds were performed in the dark. Mesitylene and other solvents were purified by standard methods and freshly distilled before use.…”

One-step synthesis of oxamidato bridged fac-Ru(CO)3 core based dinuclear compounds: Spectroscopic and structural characterisation

“…Ru 3 (CO) 12 and iodine were purchased from SigmaeAldrich Chemicals. Oxamide ligands were synthesised as reported in literature [61]. Mesitylene and the other solvents were purified using standard methods and freshly distilled prior to use [62].…”