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Synthesis and Characterization of Some Halogeno, Nitrogen-Donor and Tertiary Phosphine Complexes of Chromium(II).

Siddiqui, Rafiq Ahmed. (1995) Synthesis and Characterization of Some Halogeno, Nitrogen-Donor and Tertiary Phosphine Complexes of Chromium(II). Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

Many new compounds of chromium(II) and one of chromium(III) have been prepared under anaerobic conditions and investigated by spectroscopic, magnetic susceptibility and, in a few instances, X-ray powder and single crystal techniques. New halogenochromate(II) complexes [3-ClC6H4NH3]6[CrCl6]Cl4, [4-HOC6H4NH3]4[CrCl6] and [1-MepipzH2]3[CrCl6]Cl2 have been characterized. The salts are magnetically-normal, high-spin chromium(II) compounds. Reflectance spectra are as expected for highly distorted complexes, confirming the six-coordinate octahedral structure. The compounds [C3H8N6][CrCl6], where C3H8N6 is melaminium, [3-ClC6H4NH3]8[CrBr6]Br4, [4-BrC6H4NH3]2[CrBr4].H2O, [1-MepipzH2]3[CrBr6]Br2 and [HO(CH2)3NH3]8[CrBr6]Br4.2C2H5OH are antiferromagnetic, whereas the compounds [4-BrC6H4NH3]2[CrCl4].CH3CO2H, [2-CH3C6H4NH3]2[CrCl4]-CH3CO2H, [CH3C(O)O(CH2)2NH3]2[CrCl4], [CH3C(O)O(CH2)2NH3]2[CrBr4] [CH3C(O)O(CH2)3NH3]2[CrCl4] and [CH3C(O)O(CH2)3NH3]2[CrBr4] exhibit typical ferromagnetic behaviour. Reflectance spectra are as expected for tetragonally-distorted octahedral chromium(II) compounds. Thus, from the magnetic and spectral results halide-bridged polymeric structures have been assigned. Single crystal X-ray investigations of [CH3C(O)O(CH2)2NH3]2[CrBr4] confirm the assignment, showing that each square planar [CrBr4]2- unit is bridged by bromide to four like units to form -[CrBr4]n- layers. A new series of trihalogenochromates(II) [A][CrX3]-CH3C02H, where A is CH3C(O)O(CH2)2NH3 or CH3C(O)O(CH2)3NH3 and X is Cl or Br, with unexpected magnetic behaviour, has been prepared. They exhibit ferromagnetic behaviour although up till now all trihalogenochromates(II) have been found to be antiferromagnetic compounds with linear chain structures. From the magnetic and spectroscopic results halide-bridged polymeric structures are proposed but crystals suitable for X-ray structure determination could not be obtained. One compound of chromium(III), [4-BrC6H4NH3]6[CrBr6]Br3.2CH3CO2H was inadvertently obtained from a chromium(II) solution. It is magnetically-dilute, and the reflectance spectrum is typical of an octahedral chromium(III) complex. Single crystal X-ray investigations show that it contains [CrBr6]3-octahedral and it is only the second example of this type. The compounds [C3H8N6]0.5[Cr2(CH3CO2)4Cl].CH3CO2H and [Cr2(C8H4O4)2(H2O)2]. 2H2O are believed to be dinuclear chromium(II) compounds from their reflectance spectra and magnetic behaviour. Nitrogen-donor complexes of the type [CrX2(tpam)] (where X = Cl, Br, SCN), [Cr2(H2nn1)(SCN)4], [Cr(H2nn1)(CF3SO3)2].2C2H5OH, [Cr2(H2nn1)I4]-C2H5OH, [Cr(H2nn1)(BF4)2].0.5C2H5OH, and [CrX2(bedp) (where X = Cl, Br, I SCN and BF4) have been characterized. The compounds are antiferromagnetic. Thus, from the magnetic and spectral results bridged polymeric structures have been assigned, whereas [Cr(tpam)2]Br2. 5H2O, [Cr(tpam)I2].7H2O and [CrCl2(ddad)] are magnetically-normal and high-spin and do not have polymeric bridged structures. The complexes [Cr(tpam)2](CF3SO3)2.C2H5OH, [Cr(tpam)2](BF4)2.2H2O, [Cr2(tpen)0.5 Cl4)].C2H5OH, [Cr2(H2nn1)Cl4 2C2H5OH and [Cr2(H2nn1)Br4].2C2H5OH are low-spin. Thus, from the magnetic and spectral results octahedral structures have been assigned. The tertiary diphosphine complexes [CrCl2(dppb)2], [CrCl2(dppen)2], [Cr(MeCN)(depe)2](BPh4)2, [Cr(SCN)2(depe)2].H2O, [Cr(SCN)2(depe)] and [Cr2I4(dppb)] are low-spin. The complexes [CrBr2(dppp)], [Crl2(dppen)] and [Crl2dppp)1.5] are high-spin. The complexes [Cr2(BF4)4(dppp)].2H2O, [Cr2Br4(dppen)] and [Cr2Br4(dppb)] are antiferromagnetic. From the magnetic behaviour tentative structures are assigned.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Siddiqui, Rafiq Ahmed.
Date : 1995
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1995.
Depositing User : EPrints Services
Date Deposited : 06 May 2020 14:37
Last Modified : 06 May 2020 14:43
URI: http://epubs.surrey.ac.uk/id/eprint/856290

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