Table Of ContentProceedings of the Academy of
(Chemical Sciences)
Volume 98
9
CONTENTS
Special issue on Magnetism
Foreword
NdeoupterdownitdhifMfrgac2t*ionVa2n"1"daonpdtiFcea2l+studiesPoJfFtyhneei,onMicTfeHrurtocmhaignngestaRnbd2PCrDCaly4 1-12
,
EPR as a necessary complement ofmagnetic measurements in exchange
coupledsystems
Alessandro Bencini, Cristiano Benelli, Dante Gatteschi and
ClaudiaZanchini 13-22
Magnetic properties and molecular structure of cobalt(II) oxydiacetate
E H
trihydrate William Hatfield,Jeffrey Helms,
BrainRRohrs, PhirtuSingh, JohnR WassonandRobertR Weller 23-31
Irregularspinstatestructuresinheteropolymetallicsystems OliverKahn 33-51
Lowtemperaturehighfieldmagnetisationstudiesonmetalloporphyrins
SamareshMitra 53-68
Spinglassbehaviourinsometernarymetalchalcogens
W
CharlesJO'Connor, Jonathan FoiseandRobertCHaushalter 69-78
Magnetochemistryofcopper(II) RichardL CarlinandRuudBlock 79-97
Structural and electronic properties ofsix-coordinate Lewis-base adducts
of iron(III) Schiff-base complexes. Crystal structure and magnetism of
MeOH
the high spin complex [(imidazole)Fe(salen)(NCS)]-0.5 and of a
relatedcomplexcontainingtwodissimilaraxialligands
Brendan J Kennedy, Keith S Murray, Peter R Zwack, Ernst Horn,
MichaelRSnowandEdwardR TTiekink 99-114
Magneticpropertiesofsomeexchangecoupled [Ni(mnt)2]~dimers
PKuppuswamyandP TManoharan 115-129
Recentprogressinexperimentalone-dimensionalmagnetism
M
/PRenard, SClementand Verdaguer 131-146
Contents
ii
MagneticpropertiesofA2CunX2^+2systems
RogerWillet, ToddGrigereit, KrisHalvorsonandBrianScott 147-K.
Inorganic and Analytical
Lanthanideperchloratecomplexes of2-acetamidopyridine-l-oxide
NSNavaneetham, R Kalyanasundaram, NRajasekarandSSoundararajan 161-K
Solventextraction ofmetalsusingLIX26extractant
G N Rao and V Ramesh 165-K
Quantitative estimation of substances spotted on filter paper by photo-
acousticspectroscopy TSomasundawm, SanjaySR RaoandPGanguly 171-1"
Preconcentration of iodide from saline Water samples and determination
bythe catalyticmethod KR KrishnamoorthyandRKIyer 177-1J
Synthesis, characterisation and chemical reactivity of some new dioxo-
uranium(VI) complexes of 2-aminobenzoylhydrazone of butane-2,3-
dione SaktiprosadGhoshandAmalenduHaiti 185-1$
Copper(II), nickel(II), palladium(II) and iron(III) complexes of 2-(3-
K N
phthalhydrazidylazo)-!,3-diketones Krishnankuttyand Thankarajan 193-1<
Synthesis and spectroscopic studies of platinum(II) and palladium(II)
complexeswithaminoacids andpolypyridylligands
V N Joshi and A S Gijare 241-2*
Potassium ferrocyanide as an analytical reagent for the determination of
rhenium VYathirajam, SirpalKhairaandLR Kakkar 249-2*
Kinetics and mechanism of anation ofhydroxopentaaquo chromium(III)
ion by L-histidine in water ethanol mixtures of different dielectric
constant HGMitraMustofyandGSDe 255-2(
Synthesis and characterization ofadducts ofstannouschloridewith Schiff
bases AnilVarshneyandJP Tandon 265-2<
Ligand based redox series. Comments on its pattern and search for a
parallelprotontransferseries DipankarDatta 269-2"
Sometrivalentlanthanidecomplexesof1-tyrosinehydrazide
TRRaoandIA Khan 273-2'
Oxidation-reduction electron transferoftetra-sulphonatedphthalocyanin
cobalt(II)-apomyoglobin and tetra sulphonated phthalocyanin iron(II)-
apomyoglobin SureshCTyagi 219-21
Contents iii
Interactionofmetalionswithcytidineandaminocarboxylicacids
P Rabindra Reddy and K Sudhakar 289-296
Organic
Kinetic model for micellar catalysed hydrolysis of esters-biomolecular
reactions PSRaghavanand VangalurSSrinivasan 199206
Substituent effects on carbon-13 fcfMR chemical shifts of side chain
carbonylcarbonsof4-substituted 1-naphthamides
KRajasekaran, D Gnanasekaranand TCWong 207-212
Kinetics of oxidation of ethylenediamine tetraacetic acid by aromatic
N-bromaminesinbuffermedium
K Mohan, S Ananda and D S Mahadevappa 213-220
Electrochemicalreductionofdiazepam
L Thomas, JL Vilchez, G Grovettoand]Thomas 221-228
Reactionsofdialkoxynaphthaleneswithcyclica, /3-unsaturated acids
/RMerchantand VCWaghulde 297-304
Physical and Theoretical
Crystalstructureofbenzocaine aloca* anaesthetic
B KSinhaand Vasantha Pattabhi 229-234
Experimentswithflowinggasesinanopenphotoacousticcell
PGanguly and TSomasundaram 305-310
Electrochemicalphaseformation studiesofmercuryon glassycarbon
SJaya, TPrasadaRaoandGPrabhakaraRao 311-318
Volume change on mixing: Binary mixtures ofisomericbutylamineswith
chloroform GopalPathak, KR PatilandSD Pradhan 319-322
A
multistage adsorption process in 15-15' cis /3-carotene crystal: Electri-
calconductivityenhancementonchemicalvapouradsorption
BaniMitraand TNMisra 323-332
AnewB-ZoscillatoryMreaKctRioanmwiRtehddmyi,xeKdoCrgRaanjiacnnsuabsatnrdatPesKSaiprakash 333-340
Rapid Communication
Theroleofsolventmodelsinstabilizingnonclassicalions
CSatheesanBabuandBhalachandraL Tembe 235-240
iv Contents
Special issue on hydrophobic effect
Foreword 341-342
Organizational consequencesofthe hydrophobicinteraction
Charles Tanford 343-356
Onthe roleofwaterin molecularrecognition andself-assembly
A
Ben-Nairn 357-377
The hydrophobicinteraction between macroscopicsurfaces
M M
Hugo KChristenson, Per ClaessonandRichard Pashley 379-389
Photoreactionsinhydrophobicpockets
M
SDevanathan, SSyamalaand VRamamoorthy 391-407
The effect of hydrophobic-lipophilic interaction on chemical reactivity.
9. Puttingthespotlightonlipophilicforces insolvent-effectstudies
Xi-KuiJiang, Xing-Ya LiandBang-ZhouHuang 409-421
The effect of hydrophobic-lipophilic interactions on chemical reactivity.
10. Thecompetition between the aggregation oflong-chain esters and the
formationofinclusioncomplexesofthese esterswithamylose
Xi-KuiJiang, Xing-YaLiandBang-ZhouHuang 423-434
Association models for alcohol-water mixtures
AHRowcandJ
EDesnoyers 435-451
Solubilization of bilirubin by cholate micelles. Spectroscopic and gel
permeationstudies KasturiLahiriPuranamandPBalaram 453-468
Microenvironmental differences amongst micelles ofvarious shapes and
structures /ShobhaandD Balasubramanian 469-478
Role of the hydrophobic region of signal sequences in the targeting of
proteins to membranes and translocation across the hydrophobic
membranebarrier RNagaraj 479-485
SubjectIndex 487-493
AuthorIndex 494-496
Foreword
The area of magnetism in solids is of particular significance in the Indian context
since Indian scientists were among the earliest to contribute to this important field.
Magnetism has both the necessary angles, technological and academic, and has
sustained its growth and importance through the development of new materials,
techniques and theories. Many new concepts such as dimensionality, superex-
change, spin dynamics, magnetic order etc. have emerged in recent years. Indian
science however has not contributed its corresponding share to this area recently.
This issue of Proceedings (Chemical Sciences) is intended to project some of the
present-day chemistry and physics behind magnetism. One would see here a
sampling of inorganic solids with interesting magnetic properties and a variety of
experimental techniques such as simple magnetic susceptibility measurements
(including those of field-cooled and zero-field cooled d.c. susceptibilities), low
frequency EPR and neutron diffraction employed to establish magneto-structural
correlations.
We have not been able to cover all the important aspects of magnetism and
magneticmaterialsinthisissue. We howeverhope thatthis issuewouldbe ofuse to
senior practitioners as well as young research scholars.
We thank all the authors for their excellent contributions.
CNR
P T Manoharan Rao
.
Guest Editor Editor of Publications
Indian Academy of Sciences
Proc. Indian Acad. Sci. (Chem. Sci.), Vol. 98, Nos 1 & 2, January 1987, pp. 1-12.
Printed in India.
Neutron diffraction and optical studies of the ionic ferromagnet
Rb2CrCi4 doped with Mg2+, V2+ and Fe2+
P J FYNE, M T HUTCHINGS+ and P DAY*
Oxford University, Inorganic Chemistry Laboratory, South Parks Road, Oxford
OX1 3QR, England
""Materials Physics Division, AERE Harwell, Didcot, Oxon OX11 ORA, England
Abstract. Powderandsinglecrystalneutrondiffractionandopticalspectroscopyareused
tostudythe effect ofsubstitutingnon-magnetic (Mg2+)ormagnetic (V24, Fe2+) cations
on the Cr24" sites in the ionic ferromagnet Rb2CrO4. Comparison of powder neutron
driafnfgreacotriodnerofatR4b-22CKrCwli4thantdheRmbo2mCernt.7s3Mpagr(a).l2l7eCllt4osthhoewsbastahlatpltahnee.laSttienrglsetilclryesxthailbintesutlroonng
diffraction showsthat substituting 11% Mg2+ lowers the Curie temperature by 19% and
3%V2+ lowers it by 6%. Analysis of satellite fine-structure near the exciton-rnagnon
hFoet2+balnedasdsintotheestviimsaitbelesaobfs6o-r6ptKionansdpe5c-t2raKoffocrrytshtealCsro2f+R-Vb221CraCnld4 Cdro~^efd-Fewi2t1heVxc2h'aanngde
constants.
Keywords. Neutron diffraction; ferromagnet; doped Rb2CrCl4.
I. Introduction
When a ferromagnet is diluted with non-magnetic ions the spin correlations are
reduced and the Curie temperature Tctendstowardszero at acritical concentration
of magnetic ions called the percolation limit, below which there are only finite
clusters of magnetic ions. Rb2CrCl4 is an example of a two-dimensional square
planar Heisenberg ferromagnet (Hutchings el al 1981) for which the theoretical
percolation limit x is 0-59 (Shante and Kirkpatrick 1971). It is therefore of interest
2+
taondobmsaegrnveettihce(efVf2e+ct) odfopinacnrteaisoinnsg Mthe2+coinnceRnbtr2aCtriAo.nMio_fvbColt4h. nAonc-omnavgenneiteinct(wMagy to)
monitor Tcisto measure the temperature dependence ofthe magnetic intensity ofa
suitable reflection by single crystal neutron diffraction, though there is an upper
limit to the concentration of dopant ions that can be incorporated into Rb2CrG4
and still allow preparation of large crystals. In this paper we report measurements
of Tc for crystals of composition Rb2Cr().s<j)Mg<M,Cl4 and Rb2Cr .t;7V .()3Cl4. For
higher concentrations of dopant ions, where only polycrystalline samples are
available, powder neutron diffraction can still indicate the presence of magnetic
order. However, the preferred moment direction is not so unambiguously defined
as by a single crystal experiment. As well as reporting the powder neutron
diffraction of Rb2Cr().73Mg .27Cl4 at 78 and 4-7 K we have measured and refined
powder neutron diffraction profiles of Rb2CrCl4 itself for comparison. The
magnetic structure of the latter has already been determined by single crystal
neutron diffraction (Janke et al 1983) so it is of interest to see how clear an
*To whom all correspondence should be addressed.
M
2 P J Fyne, T Hatchings and P Day
indication of the moment orientation the powder data gives. We also give a brk
account of this method of structure determination.
A further point of interest about Rb2CrCl4 is that it is unique among the sma
groupoftransparentionicferromagnets in-havingdiscrete optical absorption band
in the visible region. These bands have been studied in detail both theoreticall
(Harrop 1981) and experimentally (Janke et al 1982). They arise from magnor
exciton combination excitations via the 'hot-band1 mechanism (Shinagawa an
Tanabe 1971), which involves the coupling of an excitation created by photo
absorption to simultaneous annihilation of a thermally populated magnor
Therefore, as the temperature is raised, the intensity ofthese bands increases wit
the thermal magnon population. We have shown (Wood et al 1982) that whe
Rb2CrCl4 is doped with Mn2+ the exciton-magnon bands develop satellit
sidebands, whose energy separation from the parent absorption bands depends o
the Cr2+-Mn2+ exchange constant. Similar spectra of Rb2CrQ4 doped with V2
and Fe2+ are reported here, together with the spectrum of a crystal doped wit
Mg2+, which demonstrates that the sidebands arise only from magnetic impurities
2. Experimental
CrystalsofRb2CrCl4 doped with Mg2+, V2+ and Fe2+ were grown by the methoc
A
described previously (Walker et al 1982). powder of compositio
Rb2Cr .73Mg .27Cl4-was prepared by quickly cooling a molten mixture of RbC
CrCl2 and MgQ2 in a sealed silica ampoule. The ratio of Cr2+ to Mg2+ in th
powder was determined by atomic absorption spectroscopy.
Powder neutron diffraction data were collected on the Dido Curran diffractc
meter at AERE Harwell using an incident neutron wavelength of 1-37 A. Th
sample was contained in a vanadium can and mounted in a CT14 cryosta
Diffraction patternswere recorded at4-2 K and above Tc. Scansof20from 5 to 9(
were employed with 0-1 steps and a counting time of 2 minutes.
The highest concentration of Mg2+ found in a single crystal boule was 11% in
Czochralski grown sample whose composition varied from 13% to 10% Mg2
across a 0*75 cm section. The boule consisted of two major crystallites with axe
sufficiently well-separated to be treated as distinct crystals. It was aligned on th
crystal axe's of the larger crystallite in a CT14 cryostat. At each temperature th
MK
(0, 0, 4) peak intensity was measured on the Dido VI 2 circle diffractometer;
AERE Harwell using a neutron wavelength of 1-093 A. The procedure employe
was to carry out a scan of the crystal angle a) followed by an CD/20 scan, th
maximum ofthe latter being taken as the intensity ofthe peak. This peak intensit
was corrected for diffuse scattering and background, measured by making an w/2
scan at (0, 0, 3-65). The highest concentration ofV2+ which could be obtained in
single crystal with a small concentration gradient was 3%. The temperatui
variation of (0, 0, 4) intensity in a crystal of Rb2Cro.y7V .()3Cl4 was measure
2+
following the same procedure as that used for the Mg -doped crystal.
Absorption spectra were measured with a McPherson RS10 high resolutio
double beam spectrophotometer equipped with an Oxford Instruments CFH
continuous flow helium cryostat.
