Solid State Communications, Vol. 28, Pp. 243245. 00381098/78/10150243 $02.0O/0 Pergamon Press Ltd. 1978. Printed in Great Britain.

ABSORPTION SPECTRUM OF MANGANESE FORMATE DIHYDRATEJ.L. Rao

Physics Department, S.V. University, Tirupati-5 17502, India

(Received 7 June 1978 by A.R. Verma)

The absorption spectrum of manganese formate dihydrate has been stud-ied at room temperature. The observed bands are assigned as transitionsfrom the 6A1(S) ground state to various excited quartet levels of a Mn

2~ion in a cubic crystalline field. The observed band positions are fitted withfour parametersB, C, Dq and a, and the values obtained for the parametersareB = 800cm, C= 3098 cm ,Dq = 850 cm and a = 76 cm.

1. INTRODUCTION number of doublet states of which 6Ai~lies lowest,

STUDIES on magnetic susceptibility [1, 2] ,proton according to Hund~rule. The other excited electron con-nuclear magnetic resonance [3] , ESR [4] and heat figurations like t~geg,t~ge~and t2ge give rise to

several doublet and quartet states. Thus all the absorp-capacity [5] of manganese formate dthydrate have been

tion bands of Mn2~result from spin forbidden tran-extensively made and reported in the literature. The

sitions.optical absorption spectrum of manganese formate di-hydrate has not been reported earlier. It is studied for 4. RESULTS AND ANALYSISthe first time at room temperature and the results ob-tained are presented in this paper. The observed spectrum at room temperature is

The space group of the crystal belongs to the mono- shown in Fig. 1. It has features characteristic of Mn2~clinic system. In manganese formate dihydrate, four absorption. The spectrum consists of five bands locatedMn2~ions are contained in the unit cell and equally at 18,200, 22,400, 25,000, 27,800 and 29,600 cm1 . Ofdivided between two kinds of inequivalent sites [6]. these bands, the bands at 25,000 and 29,600 cm areMn2~ions on A sites are surrounded octahedrally by six found to be sharp and intense. Ligand field bands areoxygen atoms belonging to formate groups. Mn2~on B sharp either when the energy expressions for the tran-sites are also surrounded by an octahedron composed of sitions are independent of Dq or when the number offour water molecules and two oxygen atoms which be- t

2 electrons is the same in both the excited and groundlong to formate groups. The site symmetry of Mn

2~can states [7]. The sharp bands are therefore attributed totherefore be taken as octahedral in the first approxi- 4Aig(G), 4Eg(G) and 4Eg(D) states respectively, as theirmation. energy expressions are independent of Dq. Using the

TanabeSugano diagram [8] given for d5 configuration,2. EXPERIMENTAL the other three bands at 18,200, 22,400 and 27,800

cm1 are attributed to 4Tig(G), 4T2g(G) and

4T2g(D)

The crystals were kindly supplied by Professor states respectively. The wavelengths and the wavenum-J.M. Thomas of Edward Davies Chemical Laboratories bers of the bands are given in Table 1, along with the(U.K.). The optical absorption spectrum was recorded assignments.with a Unicam SP-800 spectrophotometer at room tem-perature. 5. DISCUSSION

Using the interelectronic repulsion parameters (B3. THEORYand C), the crystal-field splitting parameter (Dq) and

The ground state electron configuration of Mn2~is the Treed correction (a), the energy levels are calculated.

(A) 3d5 where A stands for the closed argon shell. In a Inclusion of Treed correction is found necessary for acubic crystalline field, these five d electrons are distri- good agreement between the observed and calculatedbuted in t2g and eg orbitals, with three in the former values. The correction term introduced by it is relativelyand two in the latter. Thus the ground state configur- small and therefore it is arbitrarily fixed at the free-ionation is written as t~ge.This configuration gives rise to value of 76 cm. Because of the deformation of thethe electronic states 6A 4A 4E 4T , 4T2g and a free-ion orbitals in the crystal, the free-ion values of B

lg, -11g, g, lg243

244 ABSORPTION SPECTRUM OF MANGANESE FORMATE DIHYDRATE Vol. 28, No. 3

0. ~

4A 4E(G)

:~TIG~

C)

~ 0.2 -0

I I I3000 3500 4500 5500 6500

Fig. 1. The absorption spectrum of manganese formate dihydrate at room temperature.

30.0Table 1. The experimental data and the analysis of the 4E~( D)absorption spectrum of manganeseformate dihydrate 29.0(Dq = 850 cm, B = 800 cm1, C = 3098 cm anda = 76 cm1) 28.0 -

~ 4T2~(D)

27.0 --ObservedTransition __________________ Calculated

260 -6Aig(S) (A) (cm~) (cnf) -E 25.0 Aiq(G)4Tig(G) 5500 18,200 18,130 4E~(G)

,~ 24.0 -4T

2g(G) 4470 22,400 22,4104Aig(G),4Eg(G) 4000 25,000 25,010 E 230 ~4T

2g(D) 3600 27,800 27,8004Eg(D) 3380 29,600 29,580 220 - T2q(G)

2L0 -

20.0 -

and C cannot be carried out over to the crystals. The 90parameters B, C and Dq are treated as adjustable para-meters in the calculation. 80 - ~

4Tjg(G)75 -The energy values for quartet electronic states have 700 750 800 850

900Ajq(S)been calculated for different values of Dq withB = Dq in cm800cm,C=3098cm

1 anda=76 cm.Agraph Fig. 2. The energy level diagram of Mn2~in a cubic fieldbetween E and Dq is shown in Fig. 2. A good fit of the showing the variation of the levels with Dq for a caseexperimentally observed band positions is obtained as is withB = 800 cm, C = 3098 cm and a = 76 cm.seen from the graph forDq = 850 cm. It is interesting The solid circles show the experimental energies.to note that the observed and calculated values are ingood agreement justifying the assignments.

for his constant encouragement and advice. Thanks arealso due to Dr. C.A. ten Seldam for much assistance in

Acknowledgements Much of this research was done the calculations. The author wishes to expresshis grate-while the author was a visiting scientist at the Van der ful thanks to Professor S.V.J. Lakshman for many help-Waals Laboratorium, Universiteit Van Amsterdam, ful discussions and suggestions. The author expresses hisAmsterdam. The author is greatly indebted to Professor sincere thanks to Professor J.M. Thomas for his kindN.J. Trappeniers, Director of Van der Waals Laboratory gift of the crystals.

REFERENCES1. FLIPPEN R.B. & FRIEDBERG S.A.,J. Chem. Phys. 38,2652(1963).2. YAMAGATA K. & ABE H.,J. Phys. Soc. Japan 20,906 (1965).3. ABE H. &MATSUURAM.,J. Phys. Soc. Japan 19, 1867 (1964).4. ABE H., MORIGAKI H., MATSUURA M., TORII K. & YAMAGATA K.,J. Phys. Soc. Japan 19, 775 (1964).

Vol. 28, No.3 ABSORPTION SPECTRUM OF MANGANESE FORMATE DIHYDRATE 245

5. PIERCE R.D. & FRIEDBERG S.A.,Phys. Rev. (B) 165,680 (1968).6. OSAKI K.,NAKAI Y.&WATANABE T.,J. Phys. Soc. Japan 19,717(1964).7. BALLHAUSEN C.J., Introduction to Ligand Field Theory. McGraw-Hill, New York (1962).8. TANABE Y.& SUGANO S.,J. Phys. Soc. Japan 9,753 (1954).