Structural, electronic and magnetic properties of metal–metal bonded dinuclear rhenium complexes bridged by organocyanide acceptor ligands

Abstract

The syntheses, spectroscopic properties, redox chemistry, and solid-state structures of products obtained from the reaction of Re 2 Cl 4 (dppm) 2 (dppm = bis(diphenylphosphino) methane) with the polycyano acceptors TCNQ (7,7,8,8tetracyanoquinodimethanido) and DM-DCNQI (2,5-dimethyl-N,NЈ-dicyanoquinonediimine) are described. The compounds [Re 2 Cl 4 (dppm) 2 ] 2 (µ-TCNQ), 1, and [Re 2 Cl 4 (dppm) 2 ] 2 (µ-DM-DCNQI), 2, have been prepared by reaction of two equivalents of Re 2 Cl 4 (dppm) 2 with TCNQ and DMDCNQI, respectively, in THF or CH 2 Cl 2 . A single-crystal X-ray crystallographic study of [Re 2 Cl 4 (dppm) 2 ] 2 (µ-TCNQ)ؒ10THF revealed the presence of a trans-µ 2 bidentate mode for the bridging TCNQ ligand that joins two Re 2 Cl 4 (dppm) 2 molecules through equatorial positions. In a similar fashion, the compound [Re 2 Cl 4 (dppm) 2 ] 2 (µ-DM-DCNQI)ؒ10THF consists of two Re 2 units coordinated to the two nitrile positions of the DM-DCNQI ligand. The electronic properties of both compounds are unusual in that they exhibit intense, broad absorptions that span the near-IR region and extend into the mid-IR. The electrochemistry of the compounds consists of numerous oxidation and reduction processes in the range of ϩ2.0 to Ϫ2.0 V as determined by cyclic voltammetry. Both 1 and 2 exhibit temperature independent paramagnetism (TIP) with large χ TIP values of 7.29 × 10 Ϫ3 and 6.23 × 10 Ϫ3 emu mol Ϫ1 , respectively.

Dinuclear and Mononuclear Rhenium Coordination Compounds upon Employment of a Schiff-Base Triol Ligand: Structural, Magnetic, and Computational Studies

“…A fitting of χ M = χ TIP + C/T leads to a value of χ TIP = 6.0 × 10 −3 cm 3 mol −1 and a Curie constant C = 0.30 cm 3 mol −1 K. Such a large TIP value is not unusual for a Re ion because of the large orbital contribution to its magnetic moment. 16,17 Furthermore, the magnetization measurements of 1•2C 7 H 8 (Figure 5, left inset) confirmed this paramagnetic behavior since the theoretical Brillouin function of an S = 1/2 system with an effective g = 1.88 18 and the experimental magnetization curves at various temperatures are superimposable. The magnetic susceptibility measurements of complex 2 (Figure 5, right) suggest again a Curie paramagnetic behavior (S = 1/ 2) with a pronounced TIP contribution with a value of χ TIP = 2.7 × 10 −3 cm 3 mol −1 and a Curie constant C = 0.27 cm 3 mol −1 K (g = 1.63).…”

“…The magnetic susceptibility measurements of 1 ·2C 7 H 8 are shown in Figure (left), revealing a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetic (TIP) contribution. A fitting of χ M = χ TIP + C / T leads to a value of χ TIP = 6.0 × 10 –3 cm 3 mol –1 and a Curie constant C = 0.30 cm 3 mol –1 K. Such a large TIP value is not unusual for a Re ion because of the large orbital contribution to its magnetic moment. , …”

Diverse Reactivity of ECp* (E = Al, Ga) toward Low-Coordinate Transition Metal Amides [TM(N(SiMe3)2)2] (TM = Fe, Co, Zn): Insertion, Cp* Transfer, and Orthometalation

“…Magnetic properties of compound 1 were assessed using a SQUID magnetometer in a temperature range between 50 and 300 K. At ambient temperatures, the determined value for μ eff of 2.1 is slightly above the calculated value of 1.7 for a low spin Co­(II) center with S = 1/2. This deviation is most probably explained by the presence of the Co–Al bond, which might give rise to additional contributions, e.g., from temperature-independent Van Vleck paramagnetism. − The χ M –1 over T plot follows the Curie–Weiss law for paramagnetic compounds with the Curie constant being determined to be 0.58 cm 3 K mol –1 and the Weiss constant to be −12.87 K. Indication for decomposition is observed above 250 K. On the basis of EPR data recorded for frozen solutions of 1 in toluene at 133.15 K, the average g -factor was determined to be 2.06. Note that the high complexity of the obtained spectrum did not allow for a simulation of the hyperfine coupling of 1 .…”

Three alkaline-earth metal complexes with 3D networks constructed from a 7,7,8,8-tetracyanoquinodimethane ligand: synthesis, structure and electrochemical properties

“…4 These chargetransfer complexes, based on reduced TCNQ, have attracted broad interest in view of their extensive and often novel electrical, 5,6 electrochemical, [7][8][9] spectroscopic properties, [10][11][12] potential applications in erasable photochromic laser disks and memory storage, [13][14][15] organic field-effect transistors, [16][17][18] biosensors, [19][20][21] conducting 1,4,22 and magnetic properties. [23][24][25][26][27][28][29][30][31][32] In terms of structure, magnetism and electric-field-induced behavior, the most noticeable example is the TCNQ lanthanide complex {[Gd 2 (TCNQ) 5 (H 2 O) 9 ][Gd(TCNQ) 4 (H 2 O) 3 ]}•4H 2 O behaving as a ferrimagnet. 33 Other representative TCNQ transition metal complexes [M(TCNQ)bpy] (M = Fe(II), Zn(II), Mn(II), Co(II), Cd(II), bpy = 4,4′-bipyridyl) are of a 3D network structure which exhibits metal-dependent guest-responsive color changes and electronic properties.…”