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Frost, Ray L. and Reddy, B. Jagannadha and Keeffe, Eloise C. (2010) Structure of selected basic copper (II) sulphate minerals based upon spectroscopy : implications for hydrogen bonding. Journal of Molecular Structure, 977(1-3). pp. 90-99.

Copyright 2010 Elsevier

1

Structure of selected basic copper (II) sulphate minerals based upon 1

spectroscopy - implications for hydrogen bonding 2

3

Ray L. Frost, B. Jagannadha Reddy and Elle C. Keeffe 4

5

6

Inorganic Materials Research Program, School of Physical and Chemical Sciences, 7

Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, 8

Australia. 9

10

11

Abstract: 12

13

The application of near-infrared and infrared spectroscopy has been used for identification 14

and distinction of basic Cu-sulphates that include devilline, chalcoalumite and caledonite. 15

Near-infrared spectra of copper sulphate minerals confirm copper in divalent state. Jahn-16

Teller effect is more significant in chalcoalumite where 2B1g 2B2g transition band shows a 17

larger splitting (490 cm-1) confirming more distorted octahedral coordination of Cu2+ ion. 18

One symmetrical band at 5145 cm-1 with shoulder band 5715 cm-1 result from the absorbed 19

molecular water in the copper complexes are the combinations of OH vibrations of H2O. One 20

sharp band at around 3400 cm-1 in IR common to the three complexes is evidenced by Cu-OH 21

vibrations. The strong absorptions observed at 1685 and 1620 cm-1 for water bending modes 22

in two species confirm strong hydrogen bonding in devilline and chalcoalumite. The multiple 23

bands in 3 and 4(SO4)2- stretching regions are attributed to the reduction of symmetry to the 24

sulphate ion from Td to C2V. Chalcoalumite, the excellent IR absorber over the range 3800-25

500 cm-1 is treated as most efficient heat insulator among the Cu-sulphate complexes. 26

27

Key words: devilline, chalcoalumite, caledonite, Near-IR and Mid-infrared 28

Spectroscopy, cation substitutional effects, OH-overtones, vibrational 29

modes of sulphate anion 30 31

32 Author for correspondence ([email protected])

2

Introduction 33

34

Copper sulphate minerals are formed under specific conditions of pH and sulphate ion 35

concentration [1-3]. The minerals in this group include dolerophanite Cu2OSO4 [4], antlerite 36

Cu3SO4(OH)4 [5, 6], brochantite Cu4SO4(OH)6 [7], posnjakite Cu4SO4(OH)6.H2O, langite 37

Cu4SO4(OH)6·2H2O, wroewulfite Cu4SO4(OH)6·2H2O [8]. Krause and Taebuse [9] 38

formulated a review with 33 references on the diagnostic chemical and physical properties of 39

serpierite, orthoserpierite, and devilline and showed that it is possible to differentiate among 40

these minerals from optical data and chemical analyses. Other basic Cu minerals include 41

devilline, CaCu4(SO4)2(OH)6·3H2O, a calcium copper sulphate hydroxide hydrated mineral; 42

chalcoalumite, CuAl4(SO4)(OH)12·3H2O, a hydrous aluminium copper sulphate and 43

caledonite, a copper lead carbonate sulphate hydroxide, Pb5Cu2(SO4)3(CO3)(OH)6. 44

45

The principal interest in these minerals is many fold: (a) study of possible materials 46

for the restoration of frescoes [10]; (b) studies of the corrosion and restoration of copper and 47

bronze objects [11-16]; (c) corrosion of copper pipes containing reticulated water [17]; (d) 48

synthetic chalcoalumite-type compounds and processes for producing the same-US Patent 49

5980856; [18] (e) Fine particulate synthetic chalcoalumite-type compounds, process for their 50

production, and heat insulator and agricultural film containing the fine particulate synthetic 51

chalcoalumite compounds-US Patent 6306494 [18-21]. 52

53

Recently Raman spectroscopy has been applied to the study of basic copper (II) and 54

some complex copper(II) sulphate minerals and implications for hydrogen bonding were 55

proposed [22]. Many copper (II) sulphate systems exist with quite complex stoichiometry 56

[23-25]. The complexity of these minerals results from the assembly of a wide range of 57

cations in the structure [26-29]. This complexity is reinforced by many multi-anion species 58

incorporated in the structure. These include nitrate, phosphate, arsenate, carbonate and 59

hydroxyl [30-33]. The authors have demonstrated the importance of NIR by observations of 60

the fundamental of anions of OH- and CO32- in addition to the cation contents like Fe and Cu 61

in smithsonite minerals [34]. The near-infrared and mid-infrared spectroscopy have been 62

applied recently on the structure of selected magnesium carbonate minerals [35] and 63

characterisation of some selected tellurite minerals [36]. 64

3

Devilline, a rare hydrated basic copper calcium sulphate of formula, 65

CaCu4(SO4)2(OH)6·3H2O is monoclinic, space group P21/c, with a 20.870, b 6.135, c 22.191 66

Å, and β 102°44'; Z = 8. The crystal structure solved by 3-dimensional Fourier methods, [36] 67

shows each Cu ion, in 4 + 2 coordination, is linked by 6 edges to 6 adjacent Cu ions forming 68

sheets infinitely 2[Cu2(OH)3O]- parallel to (100). Two adjacent parallel sheets are connected 69

by Ca ions in 7-fold coordination, by SO42- tetrahedra, and by a system of hydrogen bonds. 70

Chalcoalumite, a copper alum CuAl4(SO4)(OH)12·3H2O refers to an aluminium copper 71

sulphate. The crystal structure is closely related to nickelalumite, NiAl4 (SO4)(OH)12(H2O)3. 72

The main building unit of the "nickelalumite" structure is a (001) sheet of Al and M 73

octahedra. The Al and M octahedra share common edges to form an interrupted sheet of the 74

form [MAl4(OH)12]2+. Intercalated between the M–Al–OH sheets are layers of (SO4) 75

tetrahedra and (H2O) groups [38]. Caledonite, Pb5Cu2(SO4)3(CO3)(OH)6 is a basic carbonate-76

sulphate of lead and copper. The mineral belongs to the orthorhombic space group Pmn21v 77

with Z = 2, cell parameters are: a = 20.089, b = 7.146 and c = 6.560 Å. Caledonite structure 78

shows edge sharing of the Cu-O42+ pseudo octahedral built around the screw axis, a chain 79

whose repeat unit is infinite [Cu(OH)3O]3-. The three independent lead atoms are irregularly 80

coordinated by oxygen atoms with a wide scattering of Pb-O distances. The CO3 and SO4 81

groups provide the connections among the lead polyhedra, and between these and the copper 82

chains [39]. 83

In this paper, the effects of compositional changes and cations on optical properties of 84

selected copper sulphate minerals-devilline, chalcoalumite and caledonite are studied. A 85

single transition metal ion of copper is common to all the three minerals. Each of these 86

minerals is associated with cations of Ca, Pb or Al. Examples are the minerals: 87

devilline,CaCu4(SO4)2(OH)6·3H2O a calcium copper sulphate hydroxide hydrated mineral; 88

chalcoalumite,CuAl4(SO4)(OH)12·3H2O a hydrous aluminium copper sulphate and caledonite, 89

a copper lead carbonate sulphate hydroxide, Pb5Cu2(SO4)3(CO3)(OH)6. The influence of the 90

cations of Ca, Pb and Al individually with each of the Cu sulphates is expected to show 91

changes in intensity and band positions in electronic and vibrational spectra providing the 92

possible way for distinction and identification of the copper complex minerals. 93

94

Experimental 95

96

Samples description 97

4

The three samples of copper sulphate minerals used in the present work were supplied the 98

Mineralogical Research Company, USA. Devilline originated from Bisbee, Warren District, 99

Mule Mts, Cochise Co., Arizona, USA. The chalcoalumite mineral originated from Bisbee, 100

Cochise Co., and in the Grandview mine, Grand Canyon, Coconino Co.; the caledonite 101

mineral came from the Mammoth Mine at Tiger, Arizona. The minerals were analysed by 102

XRD for phase identification and scanning electronic microscopy (SEM) for morphology. 103

EDX measurements were performed to check the stoichiometry of the minerals. 104

105

Near-infrared (NIR) spectroscopy 106

107

NIR spectra were collected on a Nicolet Nexus FT-IR spectrometer with a Nicolet Near-IR 108

Fibreport accessory (Madison, Wisconsin). A white light source was used, with a quartz 109

beam splitter and TEC NIR InGaAs detector. Spectra were obtained from 13,000 to 4000 110

cm-1 (0.77-2.50 µm) (770-2500 nm) by the co-addition of 64 scans at a spectral resolution of 111

8 cm-1. A mirror velocity of 1.266 m sec-1 was used. The spectra were transformed using the 112

Kubelka-Munk algorithm to provide spectra for comparison with published absorption 113

spectra. 114

115

Mid-IR spectroscopy 116

117

Infrared spectra were obtained using a Nicolet Nexus 870 FTIR spectrometer with a smart 118

endurance single bounce diamond ATR cell. Spectra over the 4000525 cm-1 range were 119

obtained by the co-addition of 64 scans with a resolution of 4 cm-1 and a mirror velocity of 120

0.6329 cm/s. Spectra were co-added to improve the signal to noise ratio. 121

122

Spectral manipulation such as baseline adjustment, smoothing and normalisation were 123

performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, 124

NH, USA). Band component analysis was undertaken using the Jandel ‘Peakfit’ software 125

package which enabled the type of fitting function to be selected and allows specific 126

parameters to be fixed or varied accordingly. Band fitting was done using a Lorentz-Gauss 127

cross-product function with the minimum number of component bands used for the fitting 128

process. The Lorentz- Gauss ratio was maintained at values greater than 0.7 and fitting was 129

5

undertaken until reproducible results were obtained with squared correlations of r2 greater 130

than 0.995. 131

132

Results and discussion 133

134

The Jahn-Teller phenomena 135

Hermann Jahn and Edward Teller based upon group theory elucidated the electronic effect 136

which basically states that non-linear degenerate molecules cannot be stable. This 137

phenomenon is known as the Jahn–Teller effect, sometimes also known as Jahn–Teller 138

distortion. This effect describes the geometrical distortion of non-linear molecules under 139

specific conditions. The Jahn–Teller theorem fundamentally states that any non-linear 140

molecule with a degenerate electronic ground state will undergo a geometrical distortion that 141

removes that degeneracy, because the distortion lowers the overall energy of the complex. 142

The Jahn–Teller effect is most often observed in octahedral complexes of the transition 143

metals, and is very common in six-coordinate copper(II) complexes, including copper(II) 144

minerals. The d9 electronic configuration of this ion gives three electrons in the two 145

degenerate eg orbitals, leading to a doubly-degenerate electronic ground state. Such 146

complexes normally distort along one of the molecular fourfold axes (always labelled the z 147

axis). This has the effect of removing the orbital and electronic degeneracies. This lowers the 148

overall energy. This distortion normally takes the form of elongating the bonds of the ligands 149

lying along the z axis, but may also result in bond shortening. The Jahn–Teller theorem does 150

not predict the direction of distortion, only indicates the presence of an unstable geometry. 151

When such an elongation occurs, the effect is to lower the electrostatic repulsion between the 152

electron-pair on the Lewis basic ligand and any electrons in orbitals with a z component, thus 153

lowering the energy of the complex. If the undistorted complex would be expected to have an 154

inversion centre, this is preserved after the distortion. 155

In octahedral complexes, the Jahn–Teller effect is most pronounced when an odd number of 156

electrons occupy the eg orbitals; i.e., in d9, low-spin d7 or high-spin d4 complexes, all of 157

which have doubly-degenerate ground states. This is because the eg orbitals involved in the 158

degeneracy point directly at the ligands, so distortion can result in a large energetic 159

stabilization. The effect should also occur when there is degeneracy due to the electrons in 160

6

the t2g orbitals (i.e configurations such as d1 or d2, both of which are triply degenerate). 161

However, the effect is much less noticeable, because there is a much smaller lowering of 162

repulsion on taking ligands further away from the t2g orbitals, which don't point directly at the 163

ligands involved. The same is true in tetrahedral complexes; distortion is less because there is 164

less stabilization to be gained because the ligands are not pointing directly at the orbitals. 165

The structural variations result mainly due to diversity of coordination polyhedra associated 166

with the Cu(II) cation. Usually the Cu(II) ion occurs in six-coordinated octahedral and four-167

coordinated square-planar geometries. For Cu(II) ion in a complex, the most common 168

geometry of the coordination polyhedron is octahedral, which invariably undergoes strong 169

distortion. The highly distorted Cu2+φ6 (φ = O2-, OH-, H2O) octahedra in minerals are due to 170

the electronic instability of Cu2+, the d9 configuration in an octahedral ligand-field and is 171

termed as Jahn-Teller distortion of Cu2+φ6 octahedra. As a result of distortion, splitting of the 172

electronic transitions occurs. Such process is observable in the electronic spectrum of the NIR 173

spectral region through the splitting of bands especially for Cu2+ complexes. For Cu(II) in a 174

complex one absorption band (10Dq) is observed with splitting due to Jahn-Teller distortion. 175

For example, Cu(NH3)6 has large distortion with two long M-L bonds along the z axis. Thus 176

Cu(II) ion symmetry is lowered from octahedral to most commonly to D4h. The spin-orbit 177

coupling is significant for copper, causing additional splitting of the energies (See page 448 178

of the text by Douglas et al.). 179

180

The Jahn–Teller effect can be demonstrated experimentally by investigation of the UV-VIS 181

absorbance spectra of inorganic compounds including minerals, where it often causes 182

splitting of bands. It is also readily apparent in the crystal structures of many copper(II) 183

minerals. This is the purpose of this manuscript. 184

185

Near-infrared (NIR) spectroscopy 186

187

Near-infrared spectroscopy is a sensitive method that can provide structural information on 188

the analysis of minerals by identifying the band positions and their energies and to determine 189

electronic transitions of a particular ion or ions involved in the mineral complex. The shift of 190

band positions in the spectra is the result of compositional changes in the three copper 191

7

sulphate minerals. The mineralogical compositions of the samples differ considerably [40]. 192

The main component of the samples is copper. The chemistry of the sulphate minerals data 193

[41] and mineralogy directory [http://webmineral.com/] reveal the ranges of CuO 194

composition percentage are: 48.39 - 44.54 (devilline); 14.56 - 13.61 (chalcoalumite) and 9.73 195

– 8.87 (caledonite). Other cation components Ca, Al and Pb are also found in significant 196

amounts. As highlighted by many authors [42-44], mineralogical differences between the 197

samples are of great importance in terms of spectral properties as well as structural distortions 198

for both transition metal cation and anions. The minerals used in this research are secondary 199

minerals formed in the oxidation zones of primary minerals. As such it is unlikely that any 200

Cu(I) is present in any of the minerals. The presence of Cu(I) in the minerals would enable 201

intervalence charge transfer bands which occur in the visible/NIR region. 202

203

The NIR spectra of the copper sulphate minerals in the range 12000-7600 cm-1 204

produce characteristic absorption bands resulting from the electronic transitions of divalent 205

copper ion. The vibrational spectra in the low wavenumbers, 7600-4000 cm-1 are related to 206

hydroxyl units and also anions like sulphate ion. The observed spectra of the copper 207

complexes are sub-divided into three regions (Figures 1 to 4). First region 12000-7600 cm-1 is 208

the electronic part in which bands result from copper ion. In the second region 7600-6000 209

cm-1 bands are attributed to the overtones of the fundamental OH stretching modes. The third 210

one is 6000 to 4700 cm-1 region where bands appear due to the first overtones of water-OH 211

fundamentals and deformation modes. The low wavenumber bands in the range 4700-4000 212

cm-1 are attributed to the combinations of the stretching and deformation modes of copper 213

sulphate minerals. 214

215

Electronic spectral region: 12000-7600 cm-1 216

217

The three minerals are characterised by divalent copper ion bands in their electronic 218

spectra. Cu(II) (d9) is considered with one unpaired electron and gives one free ion term 2D. 219

The 2D term splits into ground state 2Eg and excited 2Tg state in octahedral crystal field. But 220 2Eg is unstable and splits under the influence of Jahn-Teller effect and the 2Tg excited state 221

also splits. That is why Cu2+complex undergoes distortion from regular octahedral 222

coordination usually to elongated octahedron. As a result of distortion of octahedral 223

symmetry, copper complexes usually show three bands corresponding to 2B1g 2A1g, 2B1g 224

8

2B2g and 2B1g 2Eg transitions [46-47]. Two bands appear in near-infrared and third one 225

is observable in visible spectrum. The Jahn-Teller effect is most often encountered in 226

octahedral complexes of the transition metal ions and is very commonly occurs in six-227

coordinate copper(II) complexes [40,48]. The Jahn–Teller effect can be demonstrated 228

experimentally by investigating the UV-VIS-NIR absorbance spectra of inorganic 229

compounds, where Cu2+ often causes splitting of bands. There have been many studies using 230

UV-VIS-NIR spectroscopy of Cu(II) minerals. Two bands observed in connellite 231

[Cu19(SO4)Cl4(OH)32·3H2O] at 8335 and 12050 cm-1 are assigned to 2B1g 2A1g and 2B1g 232 2B2g transitions [40,48]. Near infrared spectra of smithsonite minerals [47] exhibits bands at 233

8050 and 10310 cm-1 were attributed to Cu(II). It should be noted that increased splitting 234

does not necessarily mean greater Jahn-Teller distortion of the octahedron. Increased 235

splitting may be caused by an increase in the ligand field strength due to covalency or pi 236

bonding. A second cause is spin-orbit coupling by copper or lead. 237

238

The selected minerals under investigation are characterised by divalent copper ion 239

bands in their electronic spectra (Figures 1a, 1b and 1c). By contrast, the behaviour of Cu(II) 240

is very sensitive in each of these spectra due to the compositional changes and also Jahn-241

Teller effect is the cause of splitting of the broad band in the near-infrared. The spectrum of 242

devilline (Figure 1a) displays a strong broad band extending from 8700 to 7900 cm-1 and is 243

related to high concentration of copper in this mineral. Jahn-Teller effect is the cause of 244

splitting of this broad band into three bands at 8465, 8285 and 8110 cm-1. in the near-infrared. 245

The position of this band and the nature of splitting suggest strong support in assigning the 246

bands to the 2B1g 2B2g transition. The intensity of the bands assigned to this transition is 247

interesting. According to the rule of Laporte such a transition ought to be forbidden. 248

However because there is a loss of symmetry such a rule no longer applies. A low intensity 249

band observed at lower wavenumbers 7950 cm-1 may be attributed to 2B1g 2A1g transition. 250

Interestingly the spectrum of chalcoalumite is distinctly different from devilline. At least two 251

reasons may be given: (a) Bands are well resolved due to relatively less concentration of Cu 252

in the sample compared to devilline. (b) The bands shift to 8520, 8030 and 7745 cm-1. The 253

first two bands are identified as 2B1g 2B2g transition whereas the last band is attributed to 254 2B1g 2A1g transition. The spectrum of Cu(II) in caledonite is greatly pronounced at 11275 255

cm-1 with a shoulder 11030 cm-1. The cation of lead in caledonite Pb5Cu2(SO4)3(CO3)(OH)6 is 256

mainly responsible for the band shifts to higher wavenumbers. This shift is attributed to an 257

9

increase in ligand field strength due to increased covalency. The low energy transition band 258

(2B1g 2A1g) is displaced farther to 7415 cm-1. Jahn-Teller effect is more significant in 259

chalcoalumite where 2B1g 2B2g transition band shows a larger splitting (8520-8030 cm-1 = 260

490 cm-1) confirming more distorted octahedral coordination of Cu2+ ion [40]. 261

262

Vibrational spectral region: 7600-4000 cm-1 263

264

Major NIR features of the sulphate minerals are located around 7200-6700 cm-1 and 5700-265

4700 cm-1 (Figures 2 and 3). Near-infrared and mid-infrared spectroscopy has been widely 266

applied to characterise water molecules and hydroxyl groups. Fundamental and overtone 267

vibrational absorptions of H2O and OH- are observed in most of the mineral species. The 268

spectra of the three samples (Figure 2) show a single broad band in the region 7600-6000 269

cm-1. The broad absorption feature is resolved into a number of component bands. Among 270

these, two well defined bands are common in the spectra with variable band positions. These 271

bands correspond to 2OH overtones of the OH fundamental modes of Cu2OH groups which 272

are hydrogen bonded to adjacent sulphate groups. The two peaks located in devilline at 6920 273

and 6700 cm-1 displaced to higher wavenumbers at 7175 and 6965 cm-1 shows the effect of 274

Al in chalcoalumite [50]. Structurally, Al and Cu octahedra share common edges in 275

chalcoalumite to form an interrupted sheet of the form [CuAl4(OH)12]2+. Intercalated between 276

the Cu–Al–OH sheets are layers of (SO4) tetrahedra and (H2O) groups. The 2OH overtones 277

are identified in caledonite at 7080 and 6740 cm-1. The vertically symmetric band at 5145 278

cm-1 with a shoulder band at 5715 cm-1 (Figure 3a) result from molecular water absorption in 279

the mineral structure of devilline and these are similar in nature except for small variations in 280

band maxima in chalcoalumite at 5570 and 5125 cm-1 (Figure3b). These two absorptions are 281

ascribed to the combinations (w + 2δw) and (w + δw) respectively. A computation is made 282

with w, the observed OH- vibrations of water molecules at around 3265 cm-1 and δw, the 283

water bending modes at 1620 cm-1 in IR spectra of devilline and chalcoalumite. For 284

caledonite, the observation of weak combination modes at low wavenumbers, 5450 and 5035 285

cm-1 shows the evidence of molecular water in both, devilline and chalcoalumite, strongly 286

hydrogen bonded. The bands observed in the range 4700-4000 cm-1 (Figure 4) are related to 287

the combinational modes of (SO4)2- ion. The scheme of assignments of the NIR bands 288

tabulated in Table 1 highlights differences in the band maxima that make a distinction 289

between the three copper sulphate containing minerals. 290

10

291

FTIR spectroscopy 292

293

IR spectroscopy is the most sensitive and promising method for the characterisation of 294

hydrogen bonding systems. In particular, this technique is most suitable for diagnosing the 295

mineral species. Most of the information is obtained from the band positions of OH stretching 296

modes which are correlated to OH… O distances. Local disorder at cation sites coordinating 297

the donor oxygen atom of a hydrous species can produce several absorption bands in the OH 298

stretching region, each corresponding to a different local environment. 299

300

Hydroxyl stretching vibrations: 3700-2400 cm-1 spectral region 301

302

The IR spectra of the hydroxyl stretching of the selected multi-anion minerals devilline, 303

chalcoalumite and caledonite are shown in Figures 5a, 5b and 5c. These copper complexes 304

contain two types of groups of hydrogen bonding namely, the water molecules and hydroxyl 305

units. The spectra are characterised by three OH stretching vibrations with variable spectral 306

features and it is possible to differentiate between the three Cu-sulphates minerals devilline, 307

chalcoalumite and caledonite. Three main OH stretching vibrations are observed in IR 308

spectrum of devilline at 3495, 3400 and 3265 cm-1. The dependence of band positions on 309

cations in the complex is remarkable in the spectrum of OH vibrations. The sharp band at 310

3400 cm-1 is identified as Cu-OH vibrations where as the shoulder band at 3265 cm-1 is 311

attributed to OH stretching vibrations of water in devilline [CaCu4(SO4)2(OH)6·3H2O]. The 312

relatively less intense peak located at 3495 cm-1 is assigned to Ca-OH stretch vibrations and 313

the component band at 3545 cm-1 may be attributed to Si-OH. The spectrum of chalcoalumite 314

[CuAl4(SO4)(OH)12·3H2O] is altered and bands also show blue shift. This is due to the cation 315

of Al association apart from Cu in the structure and bands in this case observed at 3620 cm-1 316

is reasonably be attributed to Al(OH) vibrations and OH- vibrations of H2O (w) appeared at 317

3210 cm-1. The cation of lead that makes mainly to cause distortion of the caledonite 318

[Pb5Cu2(SO4)3(CO3)(OH)6] spectrum and the band positions change to 3410, 3380 and 3325 319

cm-1. The 3380 cm-1 band is the Cu-OH stretch and the last one (3325 cm-1) is the w 320

stretching. The Pb-OH stretching vibrations are characterised by a sharp peak at 3410 cm-1. 321

322

H2O bending vibrations (δ H2O): 1800-1300 cm-1 spectral region 323

11

324

For devilline and chalcoalumite, the strong absorption patterns observed in the region 1800-325

1300 cm-1 are related to δw-water bending modes (Fig. 6). For devilline, two strong peaks are 326

observed at 1685 and 1620 cm-1. The first peak shows the evidence of strong hydrogen 327

bonding and the latter peak is due to adsorbed water. A weak band observed at 1395 cm-1 is 328

ascribed to carbonate impurity in devilline. The effect of Al is seen by change in the spectral 329

pattern of chalcoalumite where both the bands at 1670 and 1635 cm-1 are bending modes of 330

water. The unresolved low intensity water bending absorption modes, δw in caledonite near 331

1600 cm-1 shows strong evidence for adsorbed water in devilline and chalcoalumite but not in 332

caledonite. A very low intensity band at around 1395 cm-1 is attributed to the presence of 333

carbonate impurity in the mineral devilline. The same band is strongly enhanced at 1390 334

cm-1 for the mineral caledonite and is related to the presence of the carbonate anion in the 335

structure. 336

337

(SO4)2-stretching vibrations: 1200-500 cm-1 spectral region 338

339

Raman spectroscopy complimented with infrared spectroscopy has been used to 340

characterised synthetic halotrichites, namely, pickingerite MgSO4·Al2(SO4)3·22H2O and 341

apjohnite MnSO4·Al2(SO4)3·22H2O. A number of bands observed for pickingerite at 1145, 342

1109, 1073, 1049 and 1026 cm-1 were assigned to 3 (SO4)2- antisymmetric stretching modes 343

[51-52]. IR spectra of halotrichite FeSO4·Al2(SO4)3·22H2O report by Ross shows bands at 344

645 and 600 cm-1 and for pickingerite bands at 638 and 600 cm-1 [52]. 345

346

IR spectra of devilline and chalcoalumite consists a number of bands in the (SO4)2- stretching 347

region (Figures 7a, 7b and 7c). The overlapping bands is the result of both sulphate and 348

carbonate ions in caledonite. One sharp and strong band looks similar in the spectra as shown 349

in Figure 7 at 1090, 1095 and 1050 cm-1 for devilline, chalcoalumite and caledonite 350

respectively. This band is the characteristic of ν3 antisymmetric stretching mode of sulphate 351

ion. Bands at 985 cm-1 (devilline), 955 cm-1 (chalcoalumite) and 935 cm-1 (caledonite) are 352

assigned to the symmetric stretching mode, 1(SO4)2-. A sequence of two bands in the low 353

wavenumbers at 700-500 region is attributed to 4 bending modes. However, the spectrum of 354

caledonite is complex and the appearance of overlapping bands is related to sulphate and 355

carbonate vibrational modes. IR spectra of the three selected Cu-sulphates reveal continuous 356

12

absorption of IR radiation by chalcoalumite from 3800 to 500 cm-1 where as devilline shows 357

transmission of IR radiation in the regions of 1500-1300 and 900-700 cm-1 and caledonite 358

also shows transmission of infrared radiation in the region 2000-1500 cm-1. Therefore 359

chalcoalumite is treated as most efficient heat insulator among the Cu-sulphate complexes. 360

Novel fine particulate synthetic chalcoalumite compounds are used as heat insulators and 361

water soluble compounds containing Cu and Zn. The synthetic compounds equivalent to the 362

mineral chalcoalumite are treated as a heat insulator in agricultural film in which 363

dispensability of the heat insulator is excellent, and which exhibits very favorable 364

mechanical properties and ultraviolet and visible light transmission and excellent infrared 365

absorption over the range 4000 to 400 cm-1 [19-21] . The knowledge of NIR and IR 366

investigations of copper sulphate minerals leads to the understanding the range of absorption 367

and transmission for the preparation and treatment of synthetic copper sulphate compounds in 368

agriculture. 369

370

Conclusions 371

The electronic spectra of copper sulphate minerals in the NIR confirm that Cu 372

in the Cu2+ state. Jahn-Teller splitting of the broad band in NIR is the character of 373

Cu2+ transition, 2B1g 2B2g in copper complexes and is large (490 cm-1) in 374

chalcoaluminite confirming more distorted octahedral coordination of Cu2+ ion. 375

376

The spectra of different copper complexes are different in the NIR 377

spectral region. Two peaks are resolved around 7000 cm-1 with variable band 378

positions in the mineral species corresponding to 2OH overtones of the OH 379

fundamental modes of Cu2OH groups which are hydrogen bonded to adjacent 380

sulphate groups. A vertically symmetric band at 5145 cm-1 with tailored band 5715 381

cm-1 result from the absorbed molecular water in the mineral structure of devilline 382

appeared with small variations in chalcoalumite are the combinations of OH 383

vibrations of H2O and water bending modes observed in the IR at 3265 and 1620 384

cm-1. One sharp band at around 3400 cm-1 in IR common to the three complexes is 385

evidenced by Cu-OH vibrations. The observation of two strong absorption peaks 386

related δw-water bending modes at 1685 and 1620 cm-1 (devilline) and 1670 and 1635 387

cm-1 (chalcoalumite) is an indication of strongly hydrogen bonded water molecules in 388

two copper sulphate complexes, devilline and chalcoalumite. A sequence of bands 389

13

observed in the range 4700-4000 cm-1 are assigned to the combination modes of 390

(SO4)2- ion. IR spectra of the three selected Cu-sulphates reveal continuous absorption 391

of IR radiation by chalcoalumite from 3800 to 500 cm-1. Chalcoalumite can be treated 392

as most efficient heat insulator among the Cu-sulphate complexes. 393

394

Acknowledgements 395

396

The financial and infra-structure support of the Queensland University of 397

Technology Inorganic Materials Research Program of the School of Physical and Chemical 398

Sciences is gratefully acknowledged. The Queensland University of Technology is also 399

acknowledged for the award of a Visiting Fellowship to B. Jagannnadha Reddy. 400

401

14

References 402

403

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compounds. (Kyowa Chemical Industry Co., Ltd., Japan). Application: EP 425

EP, 1998, p. 14 pp. 426

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EP, 2000, p. 26 pp. 433

15

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16

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Maidenhead, Berkshire, England,, 1972. 479

480

481

482 483

484

485

486

487

488

17

489 490

Devilline CaCu4(SO4)2(OH)6·3H2

O (cm-1)

Chalcoalumite CuAl4(SO4)(OH)12·3H2

O (cm-1)

Caledonite Pb5Cu2(SO4)3(CO3)(OH)

6

(cm-1)

Suggested assignmen

t

8465 8285 8110c

8520 8030

11275 11030

2B1g 2B2g t

7950w 7745 7415 2B1g 2A1g t

6920 6700

7175 6965

7080 6740

2OH a

6495sh 6500sh 6280sh 2w a 5715 5570 5450 (w + 2δw)

a 5145

5030sh 5125

4980sh 5245sh 5035

(w + δw) a

4600 4600 4540 (31+42) b

4510 4555 4430 (33+24) b

4360 4360w 4390 (31+24) b

4270 4250sh 4205

4265 (21+23) b

4110 - 4160 (21+34) b

4035 - 4030

(33+4) b

491 t Electronic transition of Cu2+ 492 a Overtones and combinations of vibrational modes: OH- stretching vibrations (OH) = 3620-493 3380 cm-1; OH- vibrations of water molecules 494 (w) = 3325-2995 cm-1 and water bending vibrations (δw) = 1685-1620 cm-1 495 b Overtones and combination modes of (SO4)

2- fundamentals: 1 = 985-835 cm-1, 2 = 480-496 435 cm-1, 3 = 1115-1000 cm-1 and 4 = 730-595 cm-1 497 c Abbreviations: c-component; sh-shoulder; w-weak 498 499 Table 1 Assignment of the NIR bands of copper(II) sulphate minerals 500

501

502

503

504

505

18

List of Tables 506

Table 1 Assignment of the NIR bands of copper(II) sulphate minerals 507

508

List of Figures 509

Fig. 1a Near-infrared (NIR) spectrum of devilline: 8800-7800 cm-1 region. 510

Fig. 1b Near-infrared (NIR) spectrum of chalcoalumite: 8800-7600 cm-1 region. 511

Fig. 1c Near-infrared (NIR) spectrum of caledonite: 11600-10100 cm-1 region. 512










Fig. 5a 7a Infrared (IR) spectrum of devilline: 3700-2700 cm-1 region. 522

Fig. 5b Infrared (IR) spectrum of chalcoalumite: 3800-2300 cm-1 region. 523

Fig. 5c Infrared (IR) spectrum of caledonite: 3600-2400 cm-1 region. 524

Fig. 6a Infrared (IR) spectrum of devilline: 1800-1300 cm-1 region. 525

Fig. 6b Infrared (IR) Spectrum of chalcoalumite: 1800-1300 cm-1 region. 526


Fig. 7a Infrared (IR) spectrum of devilline: 1200-500 cm-1 region. 528

Fig. 7b Infrared (IR) spectrum of chalcoalumite: 1800-1300 cm-1 region. 529


531

532

533

19

534

535

536

537

538

20

539

Figure 1a 540

541

542

543

544

545

Figure 1b 546

547

21

548

549

550

551

552

Figure 1c553

22

554

555

556

Figure 2a 557

558

23

559

560

561

Figure 2b562

24

563

564

Figure 2c565

25

566

567

Figure 3a 568

569

570

26

571

Figure 3b 572

573

27

574

575

Figure 3c 576

577

578

28

579

580

581

Figure 4a 582

583

29

584

585

586

587

588

Figure 4b 589

590

591

592

593

594

30

595

596

597

Figure 4c598

31

599

600

Figure 5a 601

602

603

32

604

605

606

607

Figure 5b 608

609

33

610

611

612

Figure 5c613

34

614

615

Figure 6a 616

617

618

35

619

620

621

622

623

624

Figure 6b 625

626

627

36

628

629

630

Figure 6c 631

632

37

633

634

635

Figure 7a 636

637

38

638

639

640

641

642

Figure 7b 643

644

645

646

647

39

648

649

Figure 7c 650

651

652

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