Ramanaiah, M Venkata

Ravikumar, R V S S N

Reddy, B J

Srinivasulu, G

Vedanand, S

IACS Institutional Repository

Indian J. Phys. 70B (1), 87-92 (1996)IJP B— an international journalElectronic and vibrational absorption spectra in nickelbloditeM Venkata Ramanaiah, G Srinivasulu, R V S S N Ravikumar, S Vedanand and B J ReddySpectroscopic Laboratories, Department of Physics. S V University, Tirupati-517 502, IndiaReteived 19 May 1995. accepted 30 August 1995Abstract : The electronic absorption bands of nickelblodite at 300 K in the region 200- 1200 nrn are reported here. A successful interpretation of all the bands could be made to Ni(II) ion with octahedral symmetry in the crystal Three broad and intense bands observed at 9010, 14810 and 24995 e n f 1 arc attributed to the transitions, - » 1^ ) -^ 2g(/0 -> *T\kLD) and the other two bands at 13695 and 21730 enr* are assigned to the transitions -» *Eg(D) and ^Ai^F) -> 1 respectively. The crystal field and theRacah parameters are evaluated to be l)q = 900, B = 850 and C = 3500 cm-1 The vibrational spectrum of nickelblodite in IR region exhibited the characteristic bands of H2O and SO^_. The splitting of the degenerate modes V3 and v4 and the appearance of IR inactive modeV| indicate the lowering of SoJ~ from ideal Tj symmetryKeywords : Nickelblodite, absorption spectrum, octahedral symmetry PACS Nos. : 33 20.Ea, 33 20 KfAn attempt has been made to study electronic and vibrational absorption spectra of the nickel rich sulfate mineral, nickelblodite, collected from Carr Boyd Rocks in Western Australia and-to compare with the Ni(II) bearing complexes.Nickelblodite, Na2Ni(S04)2.4H2 0  is the nickel analogue of blodite Na2Mg(S04)2.4H20. Blodite (also called Ashlrakhanite) has monoclinic structure with space group P2,/a (c^)5 and with the cell parameters a = 11.03, b = 8.14, c = 5.49 A and /3= 100°40'[1]. In blodite Mg(II) is in nearly regular octahedral coordination surrounded by oxygen and water molecules. Na(I) is surrounded by four sulfate oxygen atoms and two water oxygen atoms [2]. The crystal structure and chemical analysis of the mineral have been reported [3]. The unit cell parameters of nickelblodite are appreciably smaller than those of blodite due to isomorphous substitution of Mg by Ni in sulfate, generally causes contraction of the unit cell.© 1996IACS88 M  Venkata Ramanaiah et alOn the basis of ionic radii and charge alone, it is expected that Ni(ll) (0.77 A) would readily substitutes for six coordinate Mg(ll) (0.80 A) in hydrous nickel magnesium silicates 14 1. The Ni(II)—Mg(II) diadochy is well established for this and other classes of silicateminerals [5|.A pale green coloured nickelblodite occurs as surface coating intcr-grown with rnorenosite. As the material does not exhibit good crystal forms, its optical absorption spectrum has been recorded in nujol mull form on Cary 2390 spectrophotometer in the wavelength region 200 to 1200 nm. The IR spectrum of the sample is also recorded on Pye IJnicam SP3-300 spectrophotometer in the frequency range 600-4000 cm-1.The ground term of Ni(II) (3d8) ion is *F. The other excited terms arc *D, *G and 1S. When the ion is considered in an octahedral crystal field, the *F term splits intoand 2Tiv levels. Triplet term, transforms into yr ])f while 'D, !Gand *5 gives rise to1 T2>,(D), !AU.(G), '7 U,(G), lEK(G), 1T2f,(G) and lAlft(S) levels respectively.The terms ]EK(D) and '/^ (G ) corresponds to the strong field electronicconfiguration, The terms 37’li;(F), ^^.(F), and ^T2i.{D) to first excitedelectron configuration, e* and the terms 'V^.fG), ’F^G) and ]A]fi(S) to secondexcited electronic configuration, tj e*. fn both the weak and strong crystal I'iclas the 'A2ft(F) is the ground stale according to the Hund's rule. \For Ni(ll) ion, the ground state term is 7\ Another term with the same multiplicity is V1. This leads to the three spin allowed transitions in the crystal field. They arc *A2f( JE and *A2fi —> ^7,  ^ arising Irom the ground state term ]F and *A2f{ —> *T1k from the excited term 7*. Weak and narrow spin forbidden bands are also expected as a result of transitionsFigure 1 . Optical absorption spectrum of nickelblodite in the region 200-1200 nmfrom -/Ufl to ]Ek(D) and '/^(G ) whereas the broad bands with weak intensity arise from the transitions into other singlet levels '7 ^ (0 ) and 17^ A,(G) occurring in the ultraviolet region.Electronic and  vibrational absorption spectra in nickelblodite 89Optica] absorption spectrum is shown in Figure 1. The bands are expected to nickel ion due to higher concentration of nickel. The spectrum consists of three broad and intense bands at 9010, 14810 and 24995 cm"1. The other two bands of less intensity are observed at 13695 and 21730 cm-1. All these band features are characteristic of Ni(II) in octahedral symmetry.The three broad and intense bands observed in the present case at 9010, 14810 and 249.95 cm-1 are attributed to the transitions 3A2g(F) to 3T2fi(F), 3Tlg(F) and *T{g(P) respectively. The energy expressions for Ni(II) in octahedral symmetry are given as follows [6].v, : 3A2k(F) -» Y ,X(P) =* 15Dq + 1.5B + 6 B ( l  + A ) 'nv2 : \ k(F)  Y lg(F) => 15Dq + 1.5B -  6B( \  + A ) 'nvy : \ g(F)  -» Y 2g(F)  => 10Dqwhere A -  (10Dq -  9B)f\2B\ is of the order of 0.01 since Dq and B are of similar magnitudes. If we neglect the value of A, the equation reduces as rjj -  = 12B.Using these expressions, approximate values of Dq and B are calculated as Dq = 900 and B = 850 cm*1. With the help of Tanabe-Sugano diagram, the assignments of the other hands are made. The energy matrices for configuration [71 are solved for different values of Dq, B and C. The values which gave good fit to the observed band energies are Dq =900, B = 850 and C = 3500 cm-1. The observed and calculated energies of the bands forTabic I. Observed and calculated band positions and their assignments of Nifll) in mckelbltxhle B = 850, Dq -  900 and C = 3500 cm-1.Transitions Observed band positions Calculatedfrom Wavelength Wavenumber wavenumber-1 ^ 2S (F) (nm) (cm"1) (cm"1)ro1 11 1 1 0 9010 9000V d > 730 13695 13350Y i* ( f l 670 14810 14730460 21730 219863h g i n 400 24995 25019Ni(ll) in nickelblodite are compared and are presented in Table 1. The three higher energy bands observed at 35705,41655 and 46495 cm-1 are characteristic of charge transfer bands. These bands might be due to electron transfer between the metal ion and the surrounding oxygen ligands [8,9].The infrared spectrum of nickelblodite is shown in Figure 2. It exhibits the bands due to vibrations of H20  and (SO j"). The assignments of bands are given in Table 2. In the present investigation the broad band observed at 1670 cm-1 is attributed to the asymmetric OH stretch (v2) vibrational mode and the other two broad bands at 3160 and 3400 cm*1 are attributed to symmetric O-H stretch (V[) and H-O-H bend (v3) vibrational modes of water90 M Venkata Ramanaiah et almolecule respectively. The other two bands at 730 and 860 cm'1 might be due to twisting (v,) and rocking (vr) vibrational modes of water molecule [10]. Two bands observed at 1100and 1150 citt1 arc attributed to triply degenerate v, mode, the sharp band at 990 cm'1 is attributed to nondegenerate v, vibrational mode of SOj” ion. The other two bands al 610 and 640 cm-' are attributed to triply degenerate v4 vibrational mode. The weak and broad band at 2200 cm'1 might be due to the overtone (2v,) of the v3 fundamental mode of SO^ ".Table 2. Observed vihralional frequencies wnh their »assignments in nickelblodife.Observed band positions Assignments(cm-1)610 v4 ( s o b640730 vt (twisting)800 *V (rocking)990 v\ ( s o b )1 1001150 (S0 j ‘ )1670v2 (H20)2200 CM (SO l~)3160 V] (H20)3400v3 (H20 )The optical absorption spectrum of Ni(II) ion in nickelblodite exhibits features similar to those observed for Oh symmetry with oxygen and 'OH1 ligands [11,12], The crysta reld and inter-electronic repulsion parameters (Dq and B) calculated forElectronic and vibrational absorption spectra in nickelblodite 91nickelblodite are compared with the other nickel bearing minerals and doped complexes in octahedral symmetry and are presented in Table 3, shows that Dq and B values are close to those reported earlier. It confirms the octahedral symmetry for Ni(II) ion in nickelblodite. The lowering of B value (850 cm-1) from that of free ion (1080 cm-1) in nickelblodite indicates the decrease of (20%) in the degree of ionic nature of the metal oxygen bond.Table 3. Crystal field parameters, B and Dq of Ni(II) in octahedral field in different nickel bearing samples.Sample B (cm-1) Dq (Cm-1) ReferencesMgO 890 815 Pappalardo et al [131Olivine 900 870 Wood [6]882 768 Wood [6]Diopside 881 840 White [11]Chnoenstatite 1030 690 White [11]Gamierite 947 910 Faye [14]Zaratite 899 820 Sarma et al [15]Takovite 940 910 Sarma et al [15]Annabergite 833 850 Sarma et al [15]Rh2Cd (SO4^ 6H20 890 920 Sivaprasad et al [16]K2Zn(S04)2.6H20 944 941 Sviridov and Sviridov [17]KMgClS04.3H20 905 940 Rao et al [18]Nickelblodite 850 900 Present workThe vibrational spectrum of nickelblodite in IR region exhibited the characteristic bands of H20  and S 0 4' . The splitting of the degenerate modes, v  ^ and v4 and the appearance of IR inactive mode V\ indicate the lowering of S0J~ from ideal Tj symmetry.AcknowledgmentsThe authors wish to express their thanks to Dr. E H Nickel, Division of Mineralogy, CS1RO, Wembley, Australia for generously donated nickelblodite mineral and the University Grants Commission, New Delhi for financial assistance during the course of investigation.References[ IJ IN  Rumanova and C I Malitskaya Sov. Phys. Crystallogr. 4 381 (1960)[2] R W G Wycoff Crystal Structures (New York : Interscience) (1965)[3] E H Nickel and P J Bridge Mmeralogical. Mag 41 3 (1977)[4] E J W Whittaker and R Muntus Geochim. Cosmachim. Acta 34 945 (1970)[5] G T Faust Am. Mineral. 51 279 (1966)[61 B J Wood Am. Mineral. 59 244 (1974)[7] Y Tanabe and S Sugano J. Phys. Soc. 9 753 (1954)[8] G H Faye, P G Manning and E H Nickel Am. Mineral. 53 1174 (1968)70B (1)—13 '[9] K Longer and K M Abu-Eid Phys. Chem, Minerals 1 273 (1977)(10J S N Rao, S Vedanand and Y P Reddy Solid State Commun 73 665 (1990)| III VV B White Am Mineral. 56 46 (1971)[12] G R Hunt and J W Salisbury Mod Geot 1 283 (1970)113| P Pappalurdo, D L Wood and R C Linares J  Chem Phys 35 1460[14] G H Faye Can Mineral. 12 389 (1974)[15] K B N Sarma, B J Reddy and S V J Lakshman Phy.su a Scripta 28 125 (1983)[16] P Sivaprasad, K Ramesh and Y P Reddy Phystca Scripta 42 100 (1990)[17] D T Svmdov and S D Sviridov 7h Pnkl Spektrosk 49 851 (1988)[18J S N Rao, S Vedanand, R Ravikumar, R V S S N Ravikumnr and Y P Reddy Solid State Commun. 92 (1994)92 M Venkata Ramanaiah et al

Electronic and Vibrational Absorption Spectra in Nickelblodite

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Electronic and Vibrational Absorption Spectra in Nickelblodite

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