Magnetic dilution

The e.s.r. spectra obtained for several oxovanadium (iv) complexes, including [VO(acac)2], orientated in nematic glasses, compare favourably with those obtained by dilute single-crystal procedures.X-Band e.s.r. spectra of magnetically dilute glasses at 77 K show that EtOH and py form weak complexes with [VO(P-dik)] molecules [P-dik = acac, bzac, tropolone, 3-bromotropolone, (35), or (36)], and that vanadium(iv) in solutions of these... 

The closest Er—Er distance is 11.7 A thus providing the ordered, magnetically dilute erbium ion with a local symmetry of On-... 

One of the oldest and still most common methods of investigating transition metal compounds is the measurement of their magnetic behaviour. In an excellent review Figgis and Lewis 102) have shown, what may be achieved by this method in modem chemistry. They essentially refer to magnetically diluted complexes, including many fluorides, which willnot be discussed further therefore. Magnetic data of such compounds are tabulated 144). 

The PVP-Cr(III) complex is paramagnetic because a Cr(IlI) ion possesses three spins (3d3). The molar magnetic susceptibility of the FVP-Cr(IH) complexes given in Table 3 is the same as that of the pyridine-Cr(III) complex. The ESR spectra of PVP-Cr(III) are similar to that of pyridine-Cr(III). Thus, we considered that the Cr(III) complexes on the FVP chain were magnetically dilute and the Cr(III) ions did not interact with each other, although they coordinated along the PVP chain at high concentration. 

Polymers. The use of HFEPR to measure the ZFS of high spin d5 ions in a distorted octahedral environment was demonstrated43 using the chain polymers Mn[OCPr2SiOCH2-py)z]Cl2(l) and Mn[0(iPr2Si0py)2]Br2(2). The Mn(II) ions in these polymers are well separated and magnetically dilute. The powder... 

The coordination chemistry of zirconium(III) is an ill-defined and relatively unexplored area.19 Only one magnetically dilute zirconium(III) complex has been isolated, [ZrCl3(tfars)]-MeCN [tfars= 1, 2-bis(dimethylarsino)-3,3,4,4-tetrafluorocyclobutene (CFZ)2C2-(AsMe2)2]2° and the first structurally characterized zirconium(III) complex [ ZrCl3(PBu3)2 2] has just recently been reported.21 The known zirconium(III) complexes and their physical properties are listed in Table 2. Even less is known about the coordination chemistry of hafnium(III). Just one complex, HfCl3(py)4, has been reported.22... 

CF2)2C2(AsMe2)2 (tfars), in acetonitrile (sealed tube, eight days at 100 °C, six months at room temperature) yields [ZrCl3(tfars)] -MeCN as a brown solid. A weak IR band at 2255 cm-1 indicates that the acetonitrile is not coordinated to the metal. This compound is a nonelectrolyte in acetonitrile and exhibits a magnetic moment at room temperature of 1.73 BM. It appears to be the first magnetically dilute zirconium(III) complex to have been reported.20... 

Several hydrated halides have been prepared91 by dissolving V205 in acid (hydrochloric, hydrobromic or hydroiodic) and reducing by electrolysis [V(H20)6]X2 (X = Br or I), [V(H20)4X2] (X = Cl, Br or I) and [V(H20)2X2] (X = Cl or Br). The hexa- and tetra-hydrates me magnetically dilute, with moments near the spin-only value and invariant with temperature. On the other hand, the dihydrates have moments which indicate a polymeric structure. 

A complex with 8-mercaptoquinoline [VO(thiooxine)2] is magnetically dilute.823,358 Complexes with Cl and Br derivatives of 8-mercaptoquinoline have also been reported.357 In... 

The monomeric, paramagnetic alkylamides constitute rare examples of magnetically dilute... 

The complexes [CrX2L4] and [CrX2(H20)2L2] are high-spin and magnetically dilute. The former are believed to have trans octahedral structures and there is some evidence that the latter have too.85,90-93... 

Magnetic susceptibility measurements confirm that Cr(NPiJ2)3 and Cr[N(SiMe3)2]3 behave as magnetically dilute species with Ue t values of 3.80 and 3.73 BM respectively over the... 

At the end of this section on the relationship between the electronic properties and the stereochemistry of complexes of the copper(II) ion, it is worth summarizing the most useful physical techniques which offer a criterion for the presence of a polynuclear copper(II) complex rather than a mononuclear complex. These are (i) magnetic susceptibility measurements down to near absolute zero, for the determination of O or / values (ii) ESR spectra of magnetically dilute systems, in the solid state or in solution, to obtain hyperfine data and (iii) cyclic voltammetry to show evidence for a one-step reduction process in a Cu2 species. 

ESR spectra obtained from magnetically dilute samples of the silver(U) complexes doped into the corresponding dimeric zinc complex could be attributed to both homo- (Ag,Ag) and hetero- (Ag,Zn) dinuclear species. In the Ag,Ag dimer the g values were almost equal to those for the Ag,Zn dimer however, the hyperfine coupling constants A were only about half. From this it was concluded that the structures of these two species were very similar.542... 

---