Synthesis, crystal structure and magnetic properties of the Re(ii) complexes NBu4[Re(NO)Br4(L)] (L = pyridine and diazine type ligands)

Abstract

Four novel Re(II) complexes of formula NBu4[Re(NO)Br4(L)] [NBu4(+) = tetra-n-butylammonium cation and L = pyridine (1), pyrazine (2), pyrimidine (3), pyridazine (4)] have been prepared by a substitution reaction involving NBu4[Re(NO)Br4(EtOH)] and L. Their crystal structures have been determined by single crystal X-ray diffraction. They are all mononuclear complexes whose structure is made up of [Re(NO)Br4L](-) anions and NBu4(+) cations. Each Re(II) ion is six-coordinate with four bromide ligands, a linear nitrosyl group and one monodentate nitrogen donor L building a tetragonally distorted octahedral surrounding. The Re-Br bond distances cover a narrow range [2.5048(8)-2.5333(5) Å] and they are longer than the Re-NO [1.688(15)-1.736(3) Å] and Re-N bonds [2.219(4)-2.234(3) Å]. The magnetic properties of 1-4 have been investigated in the temperature range 1.9-295 K. They behave like quasi magnetically isolated spin doublets with very weak antiferromagnetic interactions through intermolecular BrBr contacts. Their magnetic properties are discussed through a deep analysis of the influence of the ligand field, spin-orbit coupling, tetragonal distortion and covalence effects. The values of the temperature-independent paramagnetism for 1-4 are also substantiated and compared to those previously reported in related systems.

Magnetic anisotropy in two- to eight-coordinated transition–metal complexes: Recent developments in molecular magnetism

“…The magnitude of  for free Re II ranges between 300 and 2000 cm -1 . Dunbar et al investigated the magnetic properties of a series of mononuclear Re II complexes [179,182] [177]. All of these Re II complexes are anisotropic, where g ┴ ranges between 2.30 and 2.34, while g ǁ is in the range of 0.90-1.45, and they are efficient building units for constructing molecule-based magnets [112,178,180,181].…”

“…Examples of low-spin d 5 complexes that exhibit considerable magnetic anisotropy mainly comprise Re II [112,[177][178][179][180][181][182], Ru III [138,[183][184][185][186][187][188][189], and Os III [114,138,[190][191][192][193][194][195]. The magnitude of  for free Re II ranges between 300 and 2000 cm -1 .…”

“…However, for a low-spin d 5 metal ion with octahedral geometry (i.e., with a t 2g 5 electronic configuration), the ground state and excited state energy levels are not as straightforward as those in the highspin analogue. The ground state term ( 2 D) for a t 2g 5 electronic configuration may be considered to be similar to that of a high-spin d 9 metal ion, with a 2 T 2g ground state term under an O h ligand field (Scheme 7) [160,161,177]. The SOC splits the 2 T 2g term into a Kramer's doublet term E′ with J = 1/2 and a quartet term G′ with J = 3/2 (Scheme 7), and with an energy gap of E = -3/2 ( = SOC constant).…”

Aquapentachlororhenate(iv): a singular and promising building block for metal assembly

“…S1), and they are in agreement 50 with those previously reported for other rhenium complexes. 13 1 crystallises in the tetragonal crystal system with space group P4/n, § Table S1 (ESI †). Each Re IV ion in 1 is sixcoordinate and bonded to five chloride ions and one oxygen atom from a water molecule in a somewhat distorted octahedral 60 geometry (Fig.…”

Predicting ESR Peaks in the 4d and 5d Transition Metal Ion Complexes by NMR, ESR and NQR Parameters: A DFT Study

“…Only a limited research work had been done in the experimental determination of number of ESR peaks in complexes of 4d and 5d metal ions [1][2][3][4][5] like Zr (III) [6][7][8] ,Hf (III) [7][8][9] ; Nb (IV) [10][11][12] , Ta (IV) 9 ; Tc (II) 9, 13, 14 , Re (II ) [15][16][17] ; Ru (III) [18][19][20][21][22][23][24] , Os (III) [18][19][20]24 ; Rh (IV) 25-27 , Ir (IV) 26,27 which formed five congeners of 2 nd and 3 rd transition series.…”