Issue 1, 1981

Chromium(II) chemistry. Part 14. Ferromagnetic and antiferomagnetic tetrabromochromates(II)

Abstract

The dihydrated chromium(II) complex bromides M2[CrBr4(OH2)2], where M = Cs, Rb, NH4, or Hpy (py = pyridine), are magnetically dilute, high-spin compounds. The ammonium salt is isomorphous with the analogous copper(II) bromide which is known to contain trans-[CuBr4(OH2)2]2– anions with two short and two long Cu–Br bonds. The piperazinium salts [H2pipz]2[CrBr6]·2H2O and [H2pipz]2[CrBr6], and the guanidinium salt [C(NH2)3]2[CrBr4]·2MeCO2H, are also magnetically dilute. Their reflectance spectra are as expected for tetragonally distorted octahedral anions. Thermal dehydration gives the compounds M2[CrBr4], where M = Cs, Rb, NH4′ NPhH3′ or Hpy, but the monoalkylammonium salts [NRH3]2[CrBr4], where R = Me, Et, Prn, Bun, n-C5H11,n-C8H17′, or n-C12H25′[NMe2H2]2[CrBr4], and [C(NH2)3]2[CrBr4]·2MeCo2H have been crystallised from glacial acetic acid, and [NEt4]2[CrBr4], from mixed organic solvents. Ferromagnetic behaviour is exhibited by Cs2[CrBr4] and the monoalkylammonium salts, but the other tetrabromochromates(II) are antiferromagnetic. The reflectance spectra indicate tetragonal six-co-ordination of CrII and hence polymeric structures. Like the analogous tetrachlorochromates(II), the magnetic data for the ferromagnetic tetrabromochromates from liquid-nitrogen to room temperature can be reproduced by the high-temperature series-expansion formula for a sheet ferromagnet with S= 2, and JBr > JCl. The reflectance spectra contain very sharp bands at ca. 15 600 and 18 400 cm–1 assigned to spin-forbidden transitions intensified by magnetic coupling. The magnetic behaviour of the antiferromagnetic complexes is reproduced by the high-temperature series-expansion formula with appropriate changes of sign. The stretching vibrations of the short Cr–Br bonds occur near 250 cm–1.

Article information

Article type
Paper

J. Chem. Soc., Dalton Trans., 1981, 27-33

Chromium(II) chemistry. Part 14. Ferromagnetic and antiferomagnetic tetrabromochromates(II)

M. A. Babar, L. F. Larkworthy and A. Yavari, J. Chem. Soc., Dalton Trans., 1981, 27 DOI: 10.1039/DT9810000027

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Spotlight

Advertisements