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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.

Catalogue from Homo Faber 2007

Copyright 2010 Elsevier 1 Structure of selected basic copper (II) sulphate minerals based upon 2 spectroscopy - implications for hydrogen bonding 3 4 Ray L. Frost,  B. Jagannadha Reddy and Elle C. Keeffe 5 6 7 Inorganic Materials Research Program, School of Physical and Chemical Sciences, 8 Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, 9 Australia. 10 11 12 Abstract: 13 14 The application of near-infrared and infrared spectroscopy has been used for identification 15 and distinction of basic Cu-sulphates that include devilline, chalcoalumite and caledonite. 16 Near-infrared spectra of copper sulphate minerals confirm copper in divalent state. Jahn- 2 2 17 Teller effect is more significant in chalcoalumite where B1g  B2g transition band shows a 18 larger splitting (490 cm-1) confirming more distorted octahedral coordination of Cu2+ ion. 19 One symmetrical band at 5145 cm-1 with shoulder band 5715 cm-1 result from the absorbed

20 molecular water in the copper complexes are the combinations of OH vibrations of H2O. One 21 sharp band at around 3400 cm-1 in IR common to the three complexes is evidenced by Cu-OH 22 vibrations. The strong absorptions observed at 1685 and 1620 cm-1 for water bending modes 23 in two species confirm strong hydrogen bonding in devilline and chalcoalumite. The multiple 2- 24 bands in 3 and 4(SO4) stretching regions are attributed to the reduction of symmetry to the

25 sulphate ion from Td to C2V. Chalcoalumite, the excellent IR absorber over the range 3800- 26 500 cm-1 is treated as most efficient heat insulator among the Cu-sulphate complexes. 27 28 Key words: devilline, chalcoalumite, caledonite, Near-IR and Mid-infrared 29 Spectroscopy, cation substitutional effects, OH-overtones, vibrational 30 modes of sulphate anion 31 32

 Author for correspondence ([email protected]) 1

33 Introduction 34 35 Copper sulphate minerals are formed under specific conditions of pH and sulphate ion

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

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

38 Cu4SO4(OH)6·2H2O, wroewulfite Cu4SO4(OH)6·2H2O [8]. Krause and Taebuse [9] 39 formulated a review with 33 references on the diagnostic chemical and physical properties of 40 serpierite, orthoserpierite, and devilline and showed that it is possible to differentiate among 41 these minerals from optical data and chemical analyses. Other basic Cu minerals include

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

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

44 caledonite, a copper lead carbonate sulphate hydroxide, Pb5Cu2(SO4)3(CO3)(OH)6. 45 46 The principal interest in these minerals is many fold: (a) study of possible materials 47 for the restoration of frescoes [10]; (b) studies of the corrosion and restoration of copper and 48 bronze objects [11-16]; (c) corrosion of copper pipes containing reticulated water [17]; (d) 49 synthetic chalcoalumite-type compounds and processes for producing the same-US Patent 50 5980856; [18] (e) Fine particulate synthetic chalcoalumite-type compounds, process for their 51 production, and heat insulator and agricultural film containing the fine particulate synthetic 52 chalcoalumite compounds-US Patent 6306494 [18-21]. 53 54 Recently Raman spectroscopy has been applied to the study of basic copper (II) and 55 some complex copper(II) sulphate minerals and implications for hydrogen bonding were 56 proposed [22]. Many copper (II) sulphate systems exist with quite complex stoichiometry 57 [23-25]. The complexity of these minerals results from the assembly of a wide range of 58 cations in the structure [26-29]. This complexity is reinforced by many multi-anion species 59 incorporated in the structure. These include nitrate, phosphate, arsenate, carbonate and 60 hydroxyl [30-33]. The authors have demonstrated the importance of NIR by observations of - 2- 61 the fundamental of anions of OH and CO3 in addition to the cation contents like Fe and Cu 62 in smithsonite minerals [34]. The near-infrared and mid-infrared spectroscopy have been 63 applied recently on the structure of selected magnesium carbonate minerals [35] and 64 characterisation of some selected tellurite minerals [36].

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

66 CaCu4(SO4)2(OH)6·3H2O is monoclinic, space group P21/c, with a 20.870, b 6.135, c 22.191 67 Å, and β 102°44'; Z = 8. The crystal structure solved by 3-dimensional Fourier methods, [36] 68 shows each Cu ion, in 4 + 2 coordination, is linked by 6 edges to 6 adjacent Cu ions forming 2 - 69 sheets infinitely [Cu2(OH)3O] parallel to (100). Two adjacent parallel sheets are connected 2- 70 by Ca ions in 7-fold coordination, by SO4 tetrahedra, and by a system of hydrogen bonds.

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

72 sulphate. The crystal structure is closely related to nickelalumite, NiAl4 (SO4)(OH)12(H2O)3. 73 The main building unit of the "nickelalumite" structure is a (001) sheet of Al and M 74 octahedra. The Al and M octahedra share common edges to form an interrupted sheet of the 2+ 75 form [MAl4(OH)12] . Intercalated between the M–Al–OH sheets are layers of (SO4)

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

77 sulphate of lead and copper. The mineral belongs to the orthorhombic space group Pmn21v 78 with Z = 2, cell parameters are: a = 20.089, b = 7.146 and c = 6.560 Å. Caledonite structure 2+ 79 shows edge sharing of the Cu-O4 pseudo octahedral built around the screw axis, a chain 3- 80 whose repeat unit is infinite [Cu(OH)3O] . The three independent lead atoms are irregularly

81 coordinated by oxygen atoms with a wide scattering of Pb-O distances. The CO3 and SO4 82 groups provide the connections among the lead polyhedra, and between these and the copper 83 chains [39].

84 In this paper, the effects of compositional changes and cations on optical properties of 85 selected copper sulphate minerals-devilline, chalcoalumite and caledonite are studied. A 86 single transition metal ion of copper is common to all the three minerals. Each of these 87 minerals is associated with cations of Ca, Pb or Al. Examples are the minerals:

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

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

90 a copper lead carbonate sulphate hydroxide, Pb5Cu2(SO4)3(CO3)(OH)6. The influence of the 91 cations of Ca, Pb and Al individually with each of the Cu sulphates is expected to show 92 changes in intensity and band positions in electronic and vibrational spectra providing the 93 possible way for distinction and identification of the copper complex minerals. 94 95 Experimental 96 97 Samples description 3

98 The three samples of copper sulphate minerals used in the present work were supplied the 99 Mineralogical Research Company, USA. Devilline originated from Bisbee, Warren District, 100 Mule Mts, Cochise Co., Arizona, USA. The chalcoalumite mineral originated from Bisbee, 101 Cochise Co., and in the Grandview mine, Grand Canyon, Coconino Co.; the caledonite 102 mineral came from the Mammoth Mine at Tiger, Arizona. The minerals were analysed by 103 XRD for phase identification and scanning electronic microscopy (SEM) for morphology. 104 EDX measurements were performed to check the stoichiometry of the minerals. 105 106 Near-infrared (NIR) spectroscopy 107 108 NIR spectra were collected on a Nicolet Nexus FT-IR spectrometer with a Nicolet Near-IR 109 Fibreport accessory (Madison, Wisconsin). A white light source was used, with a quartz 110 beam splitter and TEC NIR InGaAs detector. Spectra were obtained from 13,000 to 4000 111 cm-1 (0.77-2.50 µm) (770-2500 nm) by the co-addition of 64 scans at a spectral resolution of 112 8 cm-1. A mirror velocity of 1.266 m sec-1 was used. The spectra were transformed using the 113 Kubelka-Munk algorithm to provide spectra for comparison with published absorption 114 spectra. 115 116 Mid-IR spectroscopy 117 118 Infrared spectra were obtained using a Nicolet Nexus 870 FTIR spectrometer with a smart 119 endurance single bounce diamond ATR cell. Spectra over the 4000525 cm-1 range were 120 obtained by the co-addition of 64 scans with a resolution of 4 cm-1 and a mirror velocity of 121 0.6329 cm/s. Spectra were co-added to improve the signal to noise ratio. 122 123 Spectral manipulation such as baseline adjustment, smoothing and normalisation were 124 performed using the Spectracalc software package GRAMS (Galactic Industries Corporation, 125 NH, USA). Band component analysis was undertaken using the Jandel ‘Peakfit’ software 126 package which enabled the type of fitting function to be selected and allows specific 127 parameters to be fixed or varied accordingly. Band fitting was done using a Lorentz-Gauss 128 cross-product function with the minimum number of component bands used for the fitting 129 process. The Lorentz- Gauss ratio was maintained at values greater than 0.7 and fitting was

130 undertaken until reproducible results were obtained with squared correlations of r2 greater 131 than 0.995. 132 133 Results and discussion 134 135 The Jahn-Teller phenomena

136 Hermann Jahn and Edward Teller based upon group theory elucidated the electronic effect 137 which basically states that non-linear degenerate molecules cannot be stable. This 138 phenomenon is known as the Jahn–Teller effect, sometimes also known as Jahn–Teller 139 distortion. This effect describes the geometrical distortion of non-linear molecules under 140 specific conditions. The Jahn–Teller theorem fundamentally states that any non-linear 141 molecule with a degenerate electronic ground state will undergo a geometrical distortion that 142 removes that degeneracy, because the distortion lowers the overall energy of the complex.

143 The Jahn–Teller effect is most often observed in octahedral complexes of the transition 144 metals, and is very common in six-coordinate copper(II) complexes, including copper(II) 145 minerals. The d9 electronic configuration of this ion gives three electrons in the two

146 degenerate eg orbitals, leading to a doubly-degenerate electronic ground state. Such 147 complexes normally distort along one of the molecular fourfold axes (always labelled the z 148 axis). This has the effect of removing the orbital and electronic degeneracies. This lowers the 149 overall energy. This distortion normally takes the form of elongating the bonds of the ligands 150 lying along the z axis, but may also result in bond shortening. The Jahn–Teller theorem does 151 not predict the direction of distortion, only indicates the presence of an unstable geometry. 152 When such an elongation occurs, the effect is to lower the electrostatic repulsion between the 153 electron-pair on the Lewis basic ligand and any electrons in orbitals with a z component, thus 154 lowering the energy of the complex. If the undistorted complex would be expected to have an 155 inversion centre, this is preserved after the distortion.

156 In octahedral complexes, the Jahn–Teller effect is most pronounced when an odd number of 9 7 4 157 electrons occupy the eg orbitals; i.e., in d , low-spin d or high-spin d complexes, all of

158 which have doubly-degenerate ground states. This is because the eg orbitals involved in the 159 degeneracy point directly at the ligands, so distortion can result in a large energetic 160 stabilization. The effect should also occur when there is degeneracy due to the electrons in

1 2 161 the t2g orbitals (i.e configurations such as d or d , both of which are triply degenerate). 162 However, the effect is much less noticeable, because there is a much smaller lowering of

163 repulsion on taking ligands further away from the t2g orbitals, which don't point directly at the 164 ligands involved. The same is true in tetrahedral complexes; distortion is less because there is 165 less stabilization to be gained because the ligands are not pointing directly at the orbitals.

166 The structural variations result mainly due to diversity of coordination polyhedra associated 167 with the Cu(II) cation. Usually the Cu(II) ion occurs in six-coordinated octahedral and four- 168 coordinated square-planar geometries. For Cu(II) ion in a complex, the most common 169 geometry of the coordination polyhedron is octahedral, which invariably undergoes strong 2+ 2- - 170 distortion. The highly distorted Cu φ6 (φ = O , OH , H2O) octahedra in minerals are due to 171 the electronic instability of Cu2+, the d9 configuration in an octahedral ligand-field and is 2+ 172 termed as Jahn-Teller distortion of Cu φ6 octahedra. As a result of distortion, splitting of the 173 electronic transitions occurs. Such process is observable in the electronic spectrum of the NIR 174 spectral region through the splitting of bands especially for Cu2+ complexes. For Cu(II) in a 175 complex one absorption band (10Dq) is observed with splitting due to Jahn-Teller distortion.

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

177 Cu(II) ion symmetry is lowered from octahedral to most commonly to D4h. The spin-orbit 178 coupling is significant for copper, causing additional splitting of the energies (See page 448 179 of the text by Douglas et al.).

180

181 The Jahn–Teller effect can be demonstrated experimentally by investigation of the UV-VIS 182 absorbance spectra of inorganic compounds including minerals, where it often causes 183 splitting of bands. It is also readily apparent in the crystal structures of many copper(II) 184 minerals. This is the purpose of this manuscript.

185 186 Near-infrared (NIR) spectroscopy 187 188 Near-infrared spectroscopy is a sensitive method that can provide structural information on 189 the analysis of minerals by identifying the band positions and their energies and to determine 190 electronic transitions of a particular ion or ions involved in the mineral complex. The shift of 191 band positions in the spectra is the result of compositional changes in the three copper

192 sulphate minerals. The mineralogical compositions of the samples differ considerably [40]. 193 The main component of the samples is copper. The chemistry of the sulphate minerals data 194 [41] and mineralogy directory [http://webmineral.com/] reveal the ranges of CuO 195 composition percentage are: 48.39 - 44.54 (devilline); 14.56 - 13.61 (chalcoalumite) and 9.73 196 – 8.87 (caledonite). Other cation components Ca, Al and Pb are also found in significant 197 amounts. As highlighted by many authors [42-44], mineralogical differences between the 198 samples are of great importance in terms of spectral properties as well as structural distortions 199 for both transition metal cation and anions. The minerals used in this research are secondary 200 minerals formed in the oxidation zones of primary minerals. As such it is unlikely that any 201 Cu(I) is present in any of the minerals. The presence of Cu(I) in the minerals would enable 202 intervalence charge transfer bands which occur in the visible/NIR region. 203 204 The NIR spectra of the copper sulphate minerals in the range 12000-7600 cm-1 205 produce characteristic absorption bands resulting from the electronic transitions of divalent 206 copper ion. The vibrational spectra in the low wavenumbers, 7600-4000 cm-1 are related to 207 hydroxyl units and also anions like sulphate ion. The observed spectra of the copper 208 complexes are sub-divided into three regions (Figures 1 to 4). First region 12000-7600 cm-1 is 209 the electronic part in which bands result from copper ion. In the second region 7600-6000 210 cm-1 bands are attributed to the overtones of the fundamental OH stretching modes. The third 211 one is 6000 to 4700 cm-1 region where bands appear due to the first overtones of water-OH 212 fundamentals and deformation modes. The low wavenumber bands in the range 4700-4000 213 cm-1 are attributed to the combinations of the stretching and deformation modes of copper 214 sulphate minerals. 215 216 Electronic spectral region: 12000-7600 cm-1 217 218 The three minerals are characterised by divalent copper ion bands in their electronic 219 spectra. Cu(II) (d9) is considered with one unpaired electron and gives one free ion term 2D. 2 2 2 220 The D term splits into ground state Eg and excited Tg state in octahedral crystal field. But 2 2 221 Eg is unstable and splits under the influence of Jahn-Teller effect and the Tg excited state 222 also splits. That is why Cu2+complex undergoes distortion from regular octahedral 223 coordination usually to elongated octahedron. As a result of distortion of octahedral 2 2 2 224 symmetry, copper complexes usually show three bands corresponding to B1g  A1g, B1g

2 2 2 225  B2g and B1g  Eg transitions [46-47]. Two bands appear in near-infrared and third one 226 is observable in visible spectrum. The Jahn-Teller effect is most often encountered in 227 octahedral complexes of the transition metal ions and is very commonly occurs in six- 228 coordinate copper(II) complexes [40,48]. The Jahn–Teller effect can be demonstrated 229 experimentally by investigating the UV-VIS-NIR absorbance spectra of inorganic 230 compounds, where Cu2+ often causes splitting of bands. There have been many studies using 231 UV-VIS-NIR spectroscopy of Cu(II) minerals. Two bands observed in connellite -1 2 2 2 232 [Cu19(SO4)Cl4(OH)32·3H2O] at 8335 and 12050 cm are assigned to B1g  A1g and B1g  2 233 B2g transitions [40,48]. Near infrared spectra of smithsonite minerals [47] exhibits bands at 234 8050 and 10310 cm-1 were attributed to Cu(II). It should be noted that increased splitting 235 does not necessarily mean greater Jahn-Teller distortion of the octahedron. Increased 236 splitting may be caused by an increase in the ligand field strength due to covalency or pi 237 bonding. A second cause is spin-orbit coupling by copper or lead. 238 239 The selected minerals under investigation are characterised by divalent copper ion 240 bands in their electronic spectra (Figures 1a, 1b and 1c). By contrast, the behaviour of Cu(II) 241 is very sensitive in each of these spectra due to the compositional changes and also Jahn- 242 Teller effect is the cause of splitting of the broad band in the near-infrared. The spectrum of 243 devilline (Figure 1a) displays a strong broad band extending from 8700 to 7900 cm-1 and is 244 related to high concentration of copper in this mineral. Jahn-Teller effect is the cause of 245 splitting of this broad band into three bands at 8465, 8285 and 8110 cm-1. in the near-infrared. 246 The position of this band and the nature of splitting suggest strong support in assigning the 2 2 247 bands to the B1g  B2g transition. The intensity of the bands assigned to this transition is 248 interesting. According to the rule of Laporte such a transition ought to be forbidden. 249 However because there is a loss of symmetry such a rule no longer applies. A low intensity -1 2 2 250 band observed at lower wavenumbers 7950 cm may be attributed to B1g  A1g transition. 251 Interestingly the spectrum of chalcoalumite is distinctly different from devilline. At least two 252 reasons may be given: (a) Bands are well resolved due to relatively less concentration of Cu 253 in the sample compared to devilline. (b) The bands shift to 8520, 8030 and 7745 cm-1. The 2 2 254 first two bands are identified as B1g  B2g transition whereas the last band is attributed to 2 2 255 B1g  A1g transition. The spectrum of Cu(II) in caledonite is greatly pronounced at 11275 -1 -1 256 cm with a shoulder 11030 cm . The cation of lead in caledonite Pb5Cu2(SO4)3(CO3)(OH)6 is 257 mainly responsible for the band shifts to higher wavenumbers. This shift is attributed to an

258 increase in ligand field strength due to increased covalency. The low energy transition band 2 2 -1 259 ( B1g  A1g) is displaced farther to 7415 cm . Jahn-Teller effect is more significant in 2 2 -1 260 chalcoalumite where B1g  B2g transition band shows a larger splitting (8520-8030 cm = 261 490 cm-1) confirming more distorted octahedral coordination of Cu2+ ion [40]. 262 263 Vibrational spectral region: 7600-4000 cm-1 264 265 Major NIR features of the sulphate minerals are located around 7200-6700 cm-1 and 5700- 266 4700 cm-1 (Figures 2 and 3). Near-infrared and mid-infrared spectroscopy has been widely 267 applied to characterise water molecules and hydroxyl groups. Fundamental and overtone - 268 vibrational absorptions of H2O and OH are observed in most of the mineral species. The 269 spectra of the three samples (Figure 2) show a single broad band in the region 7600-6000 270 cm-1. The broad absorption feature is resolved into a number of component bands. Among 271 these, two well defined bands are common in the spectra with variable band positions. These

272 bands correspond to 2OH overtones of the OH fundamental modes of Cu2OH groups which 273 are hydrogen bonded to adjacent sulphate groups. The two peaks located in devilline at 6920 274 and 6700 cm-1 displaced to higher wavenumbers at 7175 and 6965 cm-1 shows the effect of 275 Al in chalcoalumite [50]. Structurally, Al and Cu octahedra share common edges in 2+ 276 chalcoalumite to form an interrupted sheet of the form [CuAl4(OH)12] . Intercalated between

277 the Cu–Al–OH sheets are layers of (SO4) tetrahedra and (H2O) groups. The 2OH overtones 278 are identified in caledonite at 7080 and 6740 cm-1. The vertically symmetric band at 5145 279 cm-1 with a shoulder band at 5715 cm-1 (Figure 3a) result from molecular water absorption in 280 the mineral structure of devilline and these are similar in nature except for small variations in 281 band maxima in chalcoalumite at 5570 and 5125 cm-1 (Figure3b). These two absorptions are

282 ascribed to the combinations (w + 2δw) and (w + δw) respectively. A computation is made - -1 283 with w, the observed OH vibrations of water molecules at around 3265 cm and δw, the 284 water bending modes at 1620 cm-1 in IR spectra of devilline and chalcoalumite. For 285 caledonite, the observation of weak combination modes at low wavenumbers, 5450 and 5035 286 cm-1 shows the evidence of molecular water in both, devilline and chalcoalumite, strongly 287 hydrogen bonded. The bands observed in the range 4700-4000 cm-1 (Figure 4) are related to 2- 288 the combinational modes of (SO4) ion. The scheme of assignments of the NIR bands 289 tabulated in Table 1 highlights differences in the band maxima that make a distinction 290 between the three copper sulphate containing minerals.

291 292 FTIR spectroscopy 293 294 IR spectroscopy is the most sensitive and promising method for the characterisation of 295 hydrogen bonding systems. In particular, this technique is most suitable for diagnosing the 296 mineral species. Most of the information is obtained from the band positions of OH stretching 297 modes which are correlated to OH… O distances. Local disorder at cation sites coordinating 298 the donor oxygen atom of a hydrous species can produce several absorption bands in the OH 299 stretching region, each corresponding to a different local environment. 300 301 Hydroxyl stretching vibrations: 3700-2400 cm-1 spectral region 302 303 The IR spectra of the hydroxyl stretching of the selected multi-anion minerals devilline, 304 chalcoalumite and caledonite are shown in Figures 5a, 5b and 5c. These copper complexes 305 contain two types of groups of hydrogen bonding namely, the water molecules and hydroxyl 306 units. The spectra are characterised by three OH stretching vibrations with variable spectral 307 features and it is possible to differentiate between the three Cu-sulphates minerals devilline, 308 chalcoalumite and caledonite. Three main OH stretching vibrations are observed in IR 309 spectrum of devilline at 3495, 3400 and 3265 cm-1. The dependence of band positions on 310 cations in the complex is remarkable in the spectrum of OH vibrations. The sharp band at 311 3400 cm-1 is identified as Cu-OH vibrations where as the shoulder band at 3265 cm-1 is

312 attributed to OH stretching vibrations of water in devilline [CaCu4(SO4)2(OH)6·3H2O]. The 313 relatively less intense peak located at 3495 cm-1 is assigned to Ca-OH stretch vibrations and 314 the component band at 3545 cm-1 may be attributed to Si-OH. The spectrum of chalcoalumite

315 [CuAl4(SO4)(OH)12·3H2O] is altered and bands also show blue shift. This is due to the cation 316 of Al association apart from Cu in the structure and bands in this case observed at 3620 cm-1 - 317 is reasonably be attributed to Al(OH) vibrations and OH vibrations of H2O (w) appeared at 318 3210 cm-1. The cation of lead that makes mainly to cause distortion of the caledonite

319 [Pb5Cu2(SO4)3(CO3)(OH)6] spectrum and the band positions change to 3410, 3380 and 3325 -1 -1 -1 320 cm . The 3380 cm band is the Cu-OH stretch and the last one (3325 cm ) is the w 321 stretching. The Pb-OH stretching vibrations are characterised by a sharp peak at 3410 cm-1. 322 -1 323 H2O bending vibrations (δ H2O): 1800-1300 cm spectral region

324 325 For devilline and chalcoalumite, the strong absorption patterns observed in the region 1800- -1 326 1300 cm are related to δw-water bending modes (Fig. 6). For devilline, two strong peaks are 327 observed at 1685 and 1620 cm-1. The first peak shows the evidence of strong hydrogen 328 bonding and the latter peak is due to adsorbed water. A weak band observed at 1395 cm-1 is 329 ascribed to carbonate impurity in devilline. The effect of Al is seen by change in the spectral 330 pattern of chalcoalumite where both the bands at 1670 and 1635 cm-1 are bending modes of

331 water. The unresolved low intensity water bending absorption modes, δw in caledonite near 332 1600 cm-1 shows strong evidence for adsorbed water in devilline and chalcoalumite but not in 333 caledonite. A very low intensity band at around 1395 cm-1 is attributed to the presence of 334 carbonate impurity in the mineral devilline. The same band is strongly enhanced at 1390 335 cm-1 for the mineral caledonite and is related to the presence of the carbonate anion in the 336 structure. 337 2- -1 338 (SO4) stretching vibrations: 1200-500 cm spectral region 339 340 Raman spectroscopy complimented with infrared spectroscopy has been used to

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

342 apjohnite MnSO4·Al2(SO4)3·22H2O. A number of bands observed for pickingerite at 1145, -1 2- 343 1109, 1073, 1049 and 1026 cm were assigned to 3 (SO4) antisymmetric stretching modes

344 [51-52]. IR spectra of halotrichite FeSO4·Al2(SO4)3·22H2O report by Ross shows bands at 345 645 and 600 cm-1 and for pickingerite bands at 638 and 600 cm-1 [52]. 346 2- 347 IR spectra of devilline and chalcoalumite consists a number of bands in the (SO4) stretching 348 region (Figures 7a, 7b and 7c). The overlapping bands is the result of both sulphate and 349 carbonate ions in caledonite. One sharp and strong band looks similar in the spectra as shown 350 in Figure 7 at 1090, 1095 and 1050 cm-1 for devilline, chalcoalumite and caledonite

351 respectively. This band is the characteristic of ν3 antisymmetric stretching mode of sulphate 352 ion. Bands at 985 cm-1 (devilline), 955 cm-1 (chalcoalumite) and 935 cm-1 (caledonite) are 2- 353 assigned to the symmetric stretching mode, 1(SO4) . A sequence of two bands in the low

354 wavenumbers at 700-500 region is attributed to 4 bending modes. However, the spectrum of 355 caledonite is complex and the appearance of overlapping bands is related to sulphate and 356 carbonate vibrational modes. IR spectra of the three selected Cu-sulphates reveal continuous

357 absorption of IR radiation by chalcoalumite from 3800 to 500 cm-1 where as devilline shows 358 transmission of IR radiation in the regions of 1500-1300 and 900-700 cm-1 and caledonite 359 also shows transmission of infrared radiation in the region 2000-1500 cm-1. Therefore 360 chalcoalumite is treated as most efficient heat insulator among the Cu-sulphate complexes. 361 Novel fine particulate synthetic chalcoalumite compounds are used as heat insulators and 362 water soluble compounds containing Cu and Zn. The synthetic compounds equivalent to the 363 mineral chalcoalumite are treated as a heat insulator in agricultural film in which 364 dispensability of the heat insulator is excellent, and which exhibits very favorable 365 mechanical properties and ultraviolet and visible light transmission and excellent infrared 366 absorption over the range 4000 to 400 cm-1 [19-21] . The knowledge of NIR and IR 367 investigations of copper sulphate minerals leads to the understanding the range of absorption 368 and transmission for the preparation and treatment of synthetic copper sulphate compounds in 369 agriculture. 370 371 Conclusions 372 The electronic spectra of copper sulphate minerals in the NIR confirm that Cu 373 in the Cu2+ state. Jahn-Teller splitting of the broad band in NIR is the character of 2+ 2 2 -1 374 Cu transition, B1g  B2g in copper complexes and is large (490 cm ) in 375 chalcoaluminite confirming more distorted octahedral coordination of Cu2+ ion. 376 377 The spectra of different copper complexes are different in the NIR 378 spectral region. Two peaks are resolved around 7000 cm-1 with variable band

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

380 fundamental modes of Cu2OH groups which are hydrogen bonded to adjacent 381 sulphate groups. A vertically symmetric band at 5145 cm-1 with tailored band 5715 382 cm-1 result from the absorbed molecular water in the mineral structure of devilline 383 appeared with small variations in chalcoalumite are the combinations of OH

384 vibrations of H2O and water bending modes observed in the IR at 3265 and 1620 385 cm-1. One sharp band at around 3400 cm-1 in IR common to the three complexes is 386 evidenced by Cu-OH vibrations. The observation of two strong absorption peaks -1 387 related δw-water bending modes at 1685 and 1620 cm (devilline) and 1670 and 1635 388 cm-1 (chalcoalumite) is an indication of strongly hydrogen bonded water molecules in 389 two copper sulphate complexes, devilline and chalcoalumite. A sequence of bands

390 observed in the range 4700-4000 cm-1 are assigned to the combination modes of 2- 391 (SO4) ion. IR spectra of the three selected Cu-sulphates reveal continuous absorption 392 of IR radiation by chalcoalumite from 3800 to 500 cm-1. Chalcoalumite can be treated 393 as most efficient heat insulator among the Cu-sulphate complexes.

394

395 Acknowledgements

396 397 The financial and infra-structure support of the Queensland University of 398 Technology Inorganic Materials Research Program of the School of Physical and Chemical 399 Sciences is gratefully acknowledged. The Queensland University of Technology is also 400 acknowledged for the award of a Visiting Fellowship to B. Jagannnadha Reddy. 401

402 References 403 404 [1] G. Fowles, J. Chem. Soc., (1926) 1845-1858. 405 [2] W.E. Richmond, C.W. Wolfe, Amer. Min., 25, (1940) 606-610. 406 [3] H. Ungemach, Bull. Soc. Franc. Min., 47, (1924) 124-129. 407 [4] W.E. Richmond, C.W. Wolfe, Amer. Min., 25 (1940) 606-610. 408 [5] J.J. Finney, T. Araki, Nature 197 (1963) 70. 409 [6] T. Araki, Mineral. J. (Tokyo) 3 (1961) 233-235. 410 [7] M. Helliwell, J.V. Smith, Acta Cryst.C53 (1997) 1369-1371. 411 [8] A.M. Pollard, R.G. Thomas, P.A. Williams, Stud. Conserv. 35 (1990) 148-152. 412 [9] W. Krause, H. Taeuber, Aufschluss 43 (1992) 1-25. 413 [10] D. Bersani, G. Antonioli, P.P. Lottici, L. Fornari, M. Castrichini, Proc. The Inter. Soc. 414 Opt. Engin. 4402 (2001) 221-226. 415 [11] A. Kratschmer, I. Odnevall Wallinder, C. Leygraf, Corr. Sc.44 (2002) 425-450. 416 [12] R.A. Livingston, Environ. Sci. Technol. 25 (1991) 1400-1408. 417 [13] R. Lobnig, R.P. Frankenthal, C.A. Jankoski, D.J. Siconolfi, J.D. Sinclair, M. Unger, 418 M. Stratmann, Proc. Electrochem.Soc. 99-29 (1999) 97-126. 419 [14] g. Mankowski, J.P. Duthil, A. Giusti, Cor. Sc.39 (1997) 27-42. 420 [15] S. Matsuda, S. Aoki, W. Kawanobe, Hozon Kagaku 36 (1997) 1-27. 421 [16] A.G. Nord, E. Mattsson, K. Tronner, Neues Jahrb.Min.(1998) 265-277. 422 [17] M. Bouchard-Abouchacra, PhD Thesis (2001). 423 [18] US patents 5980856 and 6306494 424 [19] A. Okada, K. Oda, K. Shimizu, Manufacture of synthetic chalcoalumite-type 425 compounds. (Kyowa Chemical Industry Co., Ltd., Japan). Application: EP 426 EP, 1998, p. 14 pp. 427 [20] A. Okada, K. Shimizu, K. Oda, Manufacture and composition of chalcoalumite 428 compounds. (Kyowa Chemical Industry Co., Ltd., Japan). Application: EP 429 EP, 1997, p. 17 pp. 430 [21] H. Takahashi, A. Okada, Novel fine synthetic chalcoalumite particles and their 431 production as thermal insulators in agricultural films for greenhouses. (Kyowa 432 Chemical Industry Co., Ltd., Japan). Application: EP 433 EP, 2000, p. 26 pp.

434 [22] Ray L. Frost, Wayde Martens, Peter Leverett, J. Theo Kloprogge, , Amer. 435 Miner.1130-1137 89 (2004) 1130-1137. 436 [23] H. Effenberger, Tschermaks Mineral. Petrogr. Mitt. 34 (1985) 279-288. 437 [24] H. Effenberger, Neues Jahrb. Mineral., (1988) 38-48. 438 [25] H. Effenberger, J. Zemann, Min. Mag. 48 (1984) 541-546. 439 [26] G. Giuseppetti, C. Tadini, Neues Jahrb. Mineral., (1987) 71-81. 440 [27] H. Hess, P. Keller, H. Riffel, Neues Jahrb. Mineral., (1988) 259-264. 441 [28] M. Mellini, S. Merlino, Z. Kristallogr., Kristallgeom., Kristallphys., Kristallchem. 147 442 (1978) 129-140. 443 [29] K. Mereiter, Tschermaks Mineral. Petrogr. Mitt. 30 (1982) 47-57. 444 [30] P. Orlandi, N. Perchiazzi, Eur. J. Mineral. 1 (1989) 147-149. 445 [31] R. Pierrot, P. Sainfeld, Bull. Soc. Franc. Mineral. 84 (1961) 90-91. 446 [32] R. Von Hodenberg, W. Krause, H. Taeuber, Neues Jahrb. Mineral., (1984) 17-24. 447 [33] N.V. Zubkova, D.Y. Pushcharovsky, G. Giester, E. Tillmanns, I.V. Pekov, D.A. 448 Kleimenov, Mineral. Petrol. 75 (2002) 79-88. 449 [34] B. Jagannadha Reddy, R.L. Frost, M.C. Hales, D.L. Wain, Journal of Near Infrared 450 Spectroscopy 16 (2008) 75-82. 451 [35] R.L. Frost, Jessica Graham, B. Jagannadha Reddy, Polyhedron 27 (2008) 2069-2076. 452 [36] B. Jagannadha Reddy, R.L. Frost, Eloise C. Keeffe, Transition Metal Chemistry 34 453 (2009) 23-32. 454 [37] C. Sabelli, Acta Cryst. B28 (1972) 1182-1189. 455 [38] E.S. Yulia A. Uvarova , Frank C. Hawthorne, Vladimir V. Karpenko, Atali A. 456 Agakhanov, Leonid A. Pautov, Can. Min. 43 (2005) 1511-1519. 457 [39] S.M. C. Giacovazzo, F. Scordari, Acta Cryst. B29 (1973) 1986-1990. 458 [40] B. E. Douglas, D. H. McDaniel, J. J.Alexander. Concepts and Models of Inorganic 459 Chemistry, 3rd Edition. Wiley Publishers, New York. 460 [41] J.W. Anthony, K.W. Bladh, M.C. Nichols, Hand Book of Mineralogy,, Mineral Data 461 Publishing:, Tucson, Arizona,, 2003. 462 [42] V.C. Farmer, Mineralogical Society Monograph 4: The Infrared Spectra of Minerals, 463 1974. 464 [43] R.G. Burns, Mineralogical Applications of Crystal Field Theory, Cambridge 465 University Press, London, U.K., 1993. 466 [44] J.W. Salisbury, G.R. Hunt, Modern Geology, 5 (1976) 211-217. 467 [45] C.J. Ballhausen, McGraw-Hill Book Co., Inc., New York, (1962). 15

468 [46] A.B.P. Lever, Studies in Physical and Theoretical Chemistry, Vol. 33: Inorganic 469 Electronic Spectroscopy. 2nd Ed, 1984. 470 [47] E.A.M. Rob Janes (Ed.), Metal-ligand bonding, Royal Society of Chemistry, London, 471 U.K., 2004. 472 [48] K.M.R. P. Sreeramulu, A.S. Jacob, B.J. Reddy, J. Crystall. Spectrosc. Res. 20 (1990) 473 93-96. 474 [49] B. Jagannadha Reddy, Ray L. Frost, Matthew C. Hales, Daria L. Wain, J. Near 475 Infrared Spectrosc.16 (2008) 75-82. 476 [50] J.W. Salisbury, G.R. Hunt, Modern Geology, 1 (1970) 283-300. 477 [51] R.L. Frost, S.J. Palmer, Polyhedron 25 (2006) 3379-3396. 478 [52] S.D. Ross, Inorganic Infrared and Raman Spectra,, McGraw-Hill Book Co.: , 479 Maidenhead, Berkshire, England,, 1972. 480 481 482 483 484 485 486 487 488

489 490 Devilline Chalcoalumite Caledonite Suggested CaCu4(SO4)2(OH)6·3H2 CuAl4(SO4)(OH)12·3H2 Pb5Cu2(SO4)3(CO3)(OH) assignmen O O 6 t -1 -1 -1  (cm )  (cm )  (cm )

2 2 8465 8520 11275 B1g  B2g 8285 8030 11030 t 8110c 2 2 7950w 7745 7415 B1g  A1g t a 6920 7175 7080 2OH 6700 6965 6740 a 6495sh 6500sh 6280sh 2w 5715 5570 5450 (w + 2δw) a 5145 5125 5245sh (w + δw) 5030sh 4980sh 5035 a 4600 4600 4540 (31+42) b 4510 4555 4430 (33+24) b 4360 4360w 4390 (31+24) b 4270 4250sh 4265 (21+23) 4205 b 4110 - 4160 (21+34) b b 4035 - 4030 (33+4)

491 492 t Electronic transition of Cu2+ a - 493 Overtones and combinations of vibrational modes: OH stretching vibrations (OH) = 3620- 494 3380 cm-1; OH- vibrations of water molecules -1 -1 495 (w) = 3325-2995 cm and water bending vibrations (δw) = 1685-1620 cm b 2- -1 496 Overtones and combination modes of (SO4) fundamentals: 1 = 985-835 cm , 2 = 480- -1 -1 -1 497 435 cm , 3 = 1115-1000 cm and 4 = 730-595 cm 498 c Abbreviations: c-component; sh-shoulder; w-weak 499 500 Table 1 Assignment of the NIR bands of copper(II) sulphate minerals 501 502 503 504 505 17

506 List of Tables 507 Table 1 Assignment of the NIR bands of copper(II) sulphate minerals 508 509 List of Figures 510 Fig. 1a Near-infrared (NIR) spectrum of devilline: 8800-7800 cm-1 region. 511 Fig. 1b Near-infrared (NIR) spectrum of chalcoalumite: 8800-7600 cm-1 region. 512 Fig. 1c Near-infrared (NIR) spectrum of caledonite: 11600-10100 cm-1 region. 513 Fig. 2a Near-infrared (NIR) spectrum of devilline: 7600-6000 cm-1 region. 514 Fig. 2b Near-infrared (NIR) spectrum of chalcoalumite: 7600-6200 cm-1 region. 515 Fig. 2c Near-infrared (NIR) spectrum of caledonite: 7700-5700 cm-1 region. 516 Fig. 3a Near-infrared (NIR) spectrum of devilline: 5900-4800 cm-1 region. 517 Fig. 2b Near-infrared (NIR) spectrum of chalcoalumite: 6200-4700 cm-1 region. 518 Fig. 3c Near-infrared (NIR) spectrum of caledonite: 5700-4700 cm-1 region. 519 Fig. 4a Near-infrared (NIR) spectrum of devilline: 4700-4000 cm-1 region. 520 Fig. 4b Near-infrared (NIR) spectrum of chalcoalumite: 4700-4100 cm-1 region. 521 Fig. 4c Near-infrared (NIR) spectrum of caledonite: 4700-4000 cm-1 region. 522 Fig. 5a 7a Infrared (IR) spectrum of devilline: 3700-2700 cm-1 region. 523 Fig. 5b Infrared (IR) spectrum of chalcoalumite: 3800-2300 cm-1 region. 524 Fig. 5c Infrared (IR) spectrum of caledonite: 3600-2400 cm-1 region. 525 Fig. 6a Infrared (IR) spectrum of devilline: 1800-1300 cm-1 region. 526 Fig. 6b Infrared (IR) Spectrum of chalcoalumite: 1800-1300 cm-1 region. 527 Fig. 6c Infrared (IR) spectrum of caledonite: 2000-1200 cm-1 region. 528 Fig. 7a Infrared (IR) spectrum of devilline: 1200-500 cm-1 region. 529 Fig. 7b Infrared (IR) spectrum of chalcoalumite: 1800-1300 cm-1 region. 530 Fig. 7c Infrared (IR) spectrum of caledonite: 1800-1300 cm-1 region. 531 532 533

534 535 536 537 538

539 540 Figure 1a 541

542 543 544 545 546 Figure 1b 547

548 549 550 551 552 553 Figure 1c

554

555 556 557 Figure 2a 558

559 560 561 562 Figure 2b

563 564 565 Figure 2c

566 567 568 Figure 3a 569 570

571 572 Figure 3b 573

574 575 576 Figure 3c 577 578

579 580

581 582 Figure 4a 583

584 585 586 587

588 589 Figure 4b 590 591 592 593 594

595 596 597 598 Figure 4c

599 600 601 Figure 5a 602 603

604 605 606 607 608 Figure 5b 609 32

610

611 612 613 Figure 5c

614 615 616 Figure 6a 617 618

619 620 621 622

623 624 625 Figure 6b 626 627

628 629

630 631 Figure 6c 632

633

634 635 636 Figure 7a 637

638 639 640

641 642 643 Figure 7b 644 645 646 647

648 649 650 Figure 7c 651 652