A novel series of rhenium-bipyrimidine complexes: synthesis, crystal structure and electrochemical properties

Abstract

Four novel rhenium complexes of formula [ReCl(4)(bpym)] (1), [ReBr(4)(bpym)] (2) PPh(4)[ReCl(4)(bpym)] (3) and NBu(4)[ReBr(4)(bpym)] (4) (bpym = 2,2'-bipyrimidine, PPh(4) = tetraphenylphosphonium cation and NBu(4) = tetrabutylammonium cation), have been synthesized and their crystal structures determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of [ReX(4)(bpym)] molecules held together by van der Waals forces. In both complexes the Re(iv) central atom is surrounded by four halide anions and two nitrogen atoms of a bpym bidentate ligand in a distorted octahedral environment. The structures of 3 and 4 consist of [ReX(4)(bpym)](-) anions and PPh(4)(+) () or NBu(4)(+) (4) cations. The coordination sphere of the Re(iii) metal ion is the same as in 1 and 2, respectively. However, whereas the Re-X bonds are longer the Re-N bonds are shorter than in 1 and 2. This fact reveals that the bpym ligand forms a stronger bond with Re(iii) than with Re(iv) resulting in a stabilisation of the lower oxidation state. [ReX(4)(bpym)] complexes are easily reduced, chemically and electrochemically, to the corresponding [ReX(4)(bpym)](-) anions. A voltammetric study shows that the electron transference is a reversible process characterized by formal redox potentials of +0.19 V (1) and +0.32 V (2) vs. NHE, in acetonitrile as solvent.

Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers

“…The crystal structures of compounds 1 and 2 at ambient pressure have been reported and discussed elsewhere313233. However, it is useful to discuss certain features to understand the structural changes observed with hydrostatic pressure, and the possible effects that such changes may have on the magnetic properties.…”

“…Compound 1 was prepared following the literature procedure32. The synthesis of 2 was performed following an alternative method to that described in the literature and starting from (NBu 4 ) 2 [ReBr 6 ], which was previously prepared by a metathesis reaction of K 2 ReBr 6 in a 0.5 M HBr solution33. A mixture of (NBu 4 ) 2 [ReBr 6 ] (0.15 g, 0.13 mmol) and 2,2′-bipyrimidine (0.02 g, 0.13 mmol) in 5 ml of glacial acetic acid was heated at 90 °C with continuous stirring for 2 h. It was then filtered and the obtained red–orange solution was left to evaporate in a fumehood at room temperature.…”

“…The synthesis and crystal structure of 2 (ref. 33), together with electrochemical33 and preliminary magnetic studies25, are known. 1 and 2 exhibit magnetic ordering via spin canting.…”

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

“…However, the most interesting cases involved Re IV metal ions with octahedral geometry in a series of complexes (Fig. 27), which can be categorized as: (i) hexahalorhenates(IV) [119,[139][140][141][142][143][144][145][146] (79), and I (80)) [139], (ii) pentahalorhenates(IV) with one labile coordination site [147,148] such as (NH 2 Me 2 )[Re IV X 5 (DMF)] (where X = Cl (81) and Br (82)) [147], (iii) tetrahalorhenates(IV) with cis-blocking chelating organic ligands [110,[149][150][151][152][153][154][155][156] such as (NBu 4 ) 2 [Re(ox)X 4 ] (where ox = oxalate, X = Cl (83) and Br (84) For a hexa-coordinated 3d 3 ion with ideal O h geometry, significantly high first-order SOC and thus large magnetic anisotropy will be obtained from the triply degenerate ground state (involving d xy , d xz , and d yz orbitals) if Jahn-Teller distortion, which inevitably breaks the degeneracy and minimizes the SOC, is not present. In octahedral complexes, Jahn-Teller distortion splits the lowest lying triply degenerate d orbitals, thereby leading to two sets of orbitals, i.e., d xy and (d xz , d yz ), irrespective of whether the nature of the distortion is compression (where the energy order is d xy < (d xz , d yz )) or elongation (where the energy order is d xy > (d xz , d yz )).…”

Synthesis and characterization of mono- and dinuclear copper(I) complexes with 3-(2-pyrimidinyl)-1,2,4-triazine

“…Many bpymbased homo-and heterobimetallic complexes including derivatives of Ru [18], Os [19], Pt [20], Re [21], and Cu [22] have been reported. Of these, the Cu(I)-bpym species are found to be emissive in both solution and solid state at ambient temperature [23,24].…”