Titanium3+ Hexacyanometallates(II): Preparation and Porous Framework

ARTICLE

DOI: 10.1002/zaac.201000104

Titanium3+ Hexacyanometallates(II): Preparation and Porous Framework

Manuel Ávila,[a] Claudia Vargas,[a] Hernani Yee-Madeira,[b] and Edilso Reguera*[a,c]

Keywords: Prussian blue analogues; Porous solids; Hydrogen storage; Crystal structure; Titanium

Abstract. The studied compounds were prepared by the precipitationmethod mixing Ti3+ in concentrated HCl with aqueous solution of[M(CN)6]4– where M = Fe, Ru, Os. The formed solids,Ti3Cl[M(CN)6]2·10H2O, were characterized by IR spectroscopy, X-raydiffraction, thermogravimetry, Mössbauer spectroscopy, energy-dis-perse X-ray spectroscopy, UV/Vis spectroscopy, adsorption data, andchemical analyses. Their crystal structures were solved and refinedfrom the recorded X-ray powder patterns in the Fm3̄m space group.This series of compounds has a porous framework with a relatively

Introduction

Within titanium hexacyanometallates the most studied mem-ber is Ti4+ hexacyanoferrate(II) because of its ability for 137Cssorption [1, 2]. This compound is usually prepared from solu-tions of Ti4+ chloride and K+ or Na+ hexacyanoferrate(II),where the mixed complex salt TiA2[Fe(CN)6]·xH2O (A = Na,K) precipitates. Its crystal structure is formed by a 3D frame-work of –Ti–N≡C–Fe–C≡N–Ti– chains with the alkali metalatoms occupying all the available interstitial spaces. Its abilityfor the cesium sorption is supported in the ionic exchange ofthese interstitial alkali metal atoms by cesium. Cesium is a bigatom, which practically occupies all the available volume ofthe interstitial void and from this fact the ionic exchange ishighly favorable [3]. For the 137Cs sorption other divalent tran-sition metal (T) mixed salts, TA2[Fe(CN)6]·xH2O can also beused [4, 5]. In addition, metal hexacyanoferrates are relativelystable materials in acid media, which favors their applicationfor the 137Cs recovery from nuclear waste plants [1–3]. Theformed precipitate from solutions of Ti3+ chloride and K+ hex-acyanoferrate(III) has also been studied, in which the solid pre-cipitation is accompanied of an inner charge transfer to form

* Prof. Dr. E. RegueraE-Mail: [email protected]

[a] Centro de Investigación en Ciencia Aplicada y TecnologíaAvanzada del IPNUnidad LegariaLegaria 694, México, D.F

[b] Escuela Superior de Física y Matemáticas del IPNUP ALMLindavista, México, D.F

[c] Instituto de Ciencia y Tecnología de MaterialesUniversidad de La HabanaLa Habana, CubaSupporting information for this article is available on the WWWunder http://dx.doi.org/10.1002/zaac.201000104 or from theauthor.

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high free volume, which is occupied by coordinated and hydrogenbonded water molecules. The charge balancing Cl– ion was found coor-dinated to titanium atoms. This series of porous solids was studied inorder to explore the hydrogen interaction with the titanium atomsfound at the surface of the cavities. On the water removal by moderateheating their porous framework collapses as reveal the nitrogen, CO2,and hydrogen adsorption but without complex salt decomposition. Onthe solids rehydration the porous framework is partially restored.

Ti4+ hexacyanoferrate(II) [6]. From Ti3+ and ferrocyanic acid,H4[Fe(CN)6], the formation of a solid with formula unitT4[Fe(CN)6]3·xH2O was reported [6]. The structure of thesesolids can be interpreted according to a structural model forPrussian blue (PB) analogues nowadays surpassed.To the best of our knowledge, the preparations and character-izations of Ti3+ hexacyanometallates(II) with RuII and OsII asinner metal atoms, have not been reported. In this contribution,the preparation of the Ti3+ hexacyanometallates(II) series andtheir characterization from energy-disperse X-ray spectroscopy(EDS), X-ray diffraction (XRD), infrared (IR) spectroscopy,Mössbauer spectroscopy, thermogravimetry (TG), UV/Visspectroscopy, adsorption data and chemical analyses are dis-cussed.The interest for the Ti3+ hexacyanometallates(II) series was

motivated by the possibility of obtaining porous solids of PBtype, Ti4[M(CN)6]3, with Ti3+ atoms at the surface of the cavi-ties with available coordination sites in the anhydrous material.Such a solid could be a prototype of porous material for molec-ular hydrogen storage through formation of a coordinationbond between the metal and the hydrogen molecule [7]. Theavailability of open metal sites at the surface of cavities in PBanalogues has stimulated their study for hydrogen storage [8–16]. For Ti3+ located at a silica surface hydrogen adsorptionheats close to –22 kJ·mol–1 were reported [17]. That value is inthe required ideal range of adsorption energy for technologicalapplications of hydrogen storage in porous solids [18]. Tita-nium has extended 3d orbitals and this facilitates its coordina-tion interaction with the hydrogen molecule. The obtained sol-ids, Ti3Cl[M(CN)6]2·10H2O (M = Fe, Ru, Os) in the followingTi3ClM2, were found to be not appropriate for studies relatedto the hydrogen adsorption in porous materials because on thecrystal water removal a partial collapse for the porous frame-work was observed; nevertheless, valuable information on the

Titanium3+ Hexacyanometallates(II)

structure and related properties of the formed precipitates wasobtained, which is discussed in this contribution.

Results and DiscussionCharacterization of the Formed Solids

When solutions of Ti3+ and [M(CN)6]4– are mixed, after twodays a dark blue, practically black, fine precipitate is formed,which increases in amount and crystalline order on aging. TheUV/Vis spectra correspond to a wide absorption in practicallyall the visible spectral region with slight differences relative tothe spectrum found for genuine PB (see Supporting Informa-tion). Such spectral features suppose the existence of a reversi-ble light-induced metal–metal charge transfer through the CNbridge, a behavior also observed in genuine PB blue and CoIII

hexacyanoferrate(II) samples [19]. The nature of these solidsas transition-metal hexacyanometallates(II) was unequivocallyestablished from IR spectroscopy. Their ν(CN) absorption bandwas observed around 2080 cm–1, a frequency value typical ofmetal hexacyanometallates(II). In the spectra also the low fre-quency vibrations δ(MCN) and ν(MC) were observed (see Ta-ble 1 and Supporting Information). According to the EDSspectra, the Ti:M atomic ratio in the obtained powders is closeto 3:2 and always a peak corresponding to the presence ofchlorine was detected (see Supporting Information) for anatomic ratio Ti:M:Cl of 3:2:1. The presence of chlorine in thesolids is maintained for samples dehydrated above 120 °C andthen rehydrated at room temperature and rewashed with dis-tilled water. All these spectroscopic evidence on the nature ofthe studied solids was complemented with chemical analysesfor Cl, C, H, and N, in wt.-%: Ti3ClFe2 (found: Cl 4,60; C18.21; H 2.49; N 21.38; calcd.: Cl 4.52; C 18.40; H 2.57; N21.45), Ti3ClRu2 (found: Cl 4,21; C 16.39; H 2.28; N 19.02;calcd.: Cl 4.06; C 16.50; H 2.31; N 19.23), Ti3ClOs2 (found:Cl 3,89; C 14.99; H 2.11; N 17.37; calcd.: Cl 3.72; C 15.14;H 2.12; N 17.65). From these analytical data, the followingformula unit Ti3Cl[M(CN)6]2·10H2O resulted. This formulaunit corresponds to PB analogues with 1/3 of vacancies for theoctahedral building block, [M(CN)6], where the charge balan-cing ion Cl– is probably found in the coordination environmentof titanium atoms. For M = Fe, the Mössbauer spectrum is asingle line with an isomer shift (δ) value of 0.12 mm·s–1 (rela-tive to sodium nitroprusside). This value of δ is characteristicof low spin FeII in PB analogues [15].The IR spectra of the obtained powders also show ν(OH)bands from coordinated and weakly bonded water molecules;which are particularly broad and intense for the last ones. Suchpattern of ν(OH) vibrations is characteristic of porous PB ana-

Table 1. Vibrations /cm–1 observed in the IR spectra of the materials under study and their assignment.

Ti3Cl[Fe(CN)6]2·10H2O Ti3Cl[Ru(CN)6]2·10H2O Ti3Cl[Os(CN)6]2·10H2O Assignment

3340 3340 3354 ν(OH)2080 2086 2069 ν(CN)1609 1610 1608 δ(OH)932 928 924 ν(M–C)528 510 536 δ(M–C–N)

Z. Anorg. Allg. Chem. 2010, 1968–1973 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 1969

logues, where a fraction of the crystal water molecules is foundcoordinated to the outer metal (Ti3+ in this case) and the re-maining ones are stabilized within the cavity through hydrogenbonding interactions with the coordinated ones. The TG curvesalso suggest the formation of a porous framework; on heatingpronounced weight loss is observed which ends close to150 °C (Figure 1). Such weight loss corresponds to approxi-mately ten water molecules per formula unit. The dehydrationtemperature follows the order Os > Ru > Fe. That order sug-gests the existence of a certain effect of the inner metal (Os,Ru, Fe) on the effective charge on the metal linked at the nitro-gen end of the CN group (titanium). In hexacyanometallatesthe electronic structure of the metal atoms remains stronglycoupled through the CN bridges [13, 14]. A low dehydrationtemperature supposes a strong metal–ligand interaction at thenitrogen end subtracting a relatively large charge from the CNgroup by its 5σ orbital, which has certain antibonding charac-ter. Such charge subtraction leads to a reduction for the effect-ive positive charge on the metal, which lowers its ability toretain the coordinated waters. The same mechanism explainsthe Os > Ru > Fe order observed for the thermal stability (Fig-ure 1). Analogue behaviors were observed for homologous se-ries of hexacyanometallates(II) with manganese, zinc, and cad-mium as outer metal [20, 21].

Figure 1. TG curves for the studied series of Ti3+ hexacyanometal-lates(II). The observed weight loss on moderate heating correspondsto the evolution of water molecules from the porous framework. Above200 °C, decomposition of the material is observed.

Crystal StructurePB analogues are usually obtained as aggregates of smallcrystals of nanometric size and their crystal structure must be

E. Reguera et al.ARTICLE

solved and refined from XRD powder patterns. For the seriesof solids under study the XRD powder patterns correspond tothe cubic unit cell characteristic of PB analogues (Fm3̄m spacegroup) (Figure 2) [22]. This structural model supposes a ran-dom distribution for the vacancies within the framework. Fora non-random distribution the structure corresponds to theprimitive Pm3̄m space group [23], which is observed for in-stance in PB samples, Fe4[Fe(CN)6]3·xH2O, recrystallized inconcentrate HCl solution [24]. The possibility of a non-randomvacancy distribution for the series Ti3Cl[M(CN)6]2·xH2O wasdiscarded by the absence of reflections that behaves as finger-print for the Pm3̄m structure (see Supporting Information). Therecorded patterns for the Ti3+ series are formed by relativelybroad reflections indicating that the material is formed by anaggregate of nanometric size crystals. From the peak width atthe half height and using the Scherrer equation [25], the crys-tallite size was estimated to be 9.5, 9.0 and 7.0 nm for iron,ruthenium, and osmium, respectively.In the Fm3̄m there is a position for the metal linked at thenitrogen end (Ti) (4a sites) and also a position for the innermetal (Fe, Ru, Os) (4b sites). In this structural model the car-bon and nitrogen atoms and also the oxygen atom of coordi-nated water molecules occupy 24e sites and the oxygen atomof zeolitic water molecules are found in 8c positions. At aninitial stage, the crystal structure was refined using that struc-tural model ignoring the Cl– ion. The position of this last onewas then located from the Fourier mapping for the residualcharge density and it was found close to the titanium positions,in their coordination sphere (24e sites), with a statistical occu-pation since there is a Cl– ion for three titanium atoms. In thesecond refinement stage the position for Cl– ion was also re-fined, and the final atomic positions, occupation and thermalfactors for all the atoms were obtained. Since this structuralmodel contains 1.33 formula units per unit cell, the inner metaland also all the atoms in 24e positions are found with fractionaloccupation. The refined atomic positions and the calculatedbond lengths and angles, thermal and occupation factors areavailable from Supporting Information and were also depositedat the ICSD data base [Fachinformationszentrum Karlsruhe(FIZ)].From the calculated occupation factors, the coordination en-vironment for the titanium atom resulted: TiN4(H2O)5/3Cl1/3(see Figure 3). The figures of merit from refinement processare reported in Table 2. Figure 2 shows the experimental, fittedand difference patterns for the crystal structure refinement inthe series of materials under study. The thermal factors foroxygen atoms corresponding to weakly bonded water molecu-les resulted relatively high suggesting that these water molecu-les have a high thermal-induced mobility within the cavity. Forchlorine a high thermal factor was also observed. This ischarge balancing species, which is stabilized within the cavitythrough an electrostatic interaction with the titanium atomfound at the surface of the cavity and from this fact its highthermal-induced mobility probably results.Figure 4 shows atomic packing within the unit cell for thisseries of Ti3+ hexacyanometallates(II). This family of com-pounds shows an open-framework structure. If that framework

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Figure 2. Experimental XRD powder patterns and the calculated anddifference profiles obtained from the Rietveld refinement of the crystalstructure for the studied materials. These fitting correspond to a cubicunit cell in the Fm3̄m space group.

Figure 3. Coordination environments for the metal atoms inTi3Cl[M(CN)6]2·xH2O (M = Fe, Ru, Os). The Cl– anion was foundcoordinated to titanium atoms but with a statistical occupation becausethere is a Cl– for three titanium atoms.


Table 2. Details of the structural refinement by the Rietveld method for the materials under study.

Ti3Cl[Fe(CN)6]2·10H2O Ti3Cl[Ru(CN)6]2·10H2O Ti3Cl[Os(CN)6]2·10H2O

Unit cellSpace group Fm3̄m [225] Fm3̄m [225] Fm3̄m [225]Cell parameters /Å a = 10.2135(7) a = 10.4774(7) a = 10.4867(1)Volume /Å3 1065.42(5) 1150.16(2) 1153.23(3)Z 4/3 4/3 4/3RefinementExperimental points 3001 3001 3001Effective reflections 36 37 37Constrain distances 2 2 2Refined parametersProfile 8 8 8Structural 15 15 15Figures of meritRexp 5.40 4.66 5.02Rwp 6.35 7.08 6.61RB 4.75 7.45 4.81S 1.17 1.51 1.31

remains stable on the water removal the resulting free volumecould be used for the adsorption of small molecules, amongthem hydrogen.

Figure 4. Atomic packing within the cubic unit cell forTi3Cl[M(CN)6]2·xH2O (M = Fe, Ru, Os). Indicated are the vacanciesof the building unit [M(CN)6].

Porous Framework and its Collapse on the Water Molecu-les Removal

In porous PB analogues all the crystal water molecules arefound occupying the cavity volume resulting from the buildingblock vacancy. From this fact, the cavity volume can be esti-mated from the amount of water molecules per formula unit,considering, for instance, a water density within the cavity of1 g·cm–3 (the water density at 4 °C and at atmospheric pres-sure). This is a reasonable density value for the water molecu-


les within the cavity since they are confined to a small volumeand participating of relatively strong hydrogen interactions be-tween them. From these considerations, the expected availablecavity volume for the studied series of Ti-PB analogues isclose to 300 Å3, ≈ 0.300 cm3·g–1 for Ti3Cl[Fe(CN)6]2. Thisvalue is slightly smaller than that found from nitrogen and H2Oadsorption data for the isostructural series T3[Co(CN)6]2 (T =Mn, Co, Ni, Cd), which is close to 0.400 cm3·g–1 [26]. Relativeto Ti3+-PB analogues, this last series also contains a largeramount of water molecules within the cavity, about 13 H2Omolecules per formula unit. The difference in available cavityvolume between these two series can be attributed to the vol-ume occupied by the chlorine ion. For genuine PB,Fe4[Fe(CN)6]3, up to 16 water molecules per vacancy (cavity)was reported [22]. Such large amount of water molecules percavity for PB is probably favored by the presence of Fe3+ spe-cies at the surface of the cavity. The high polarizing power ofFe3+ enhances the coordination bond with water molecules andalso the strength for the hydrogen bonding interactions withthe zeolitic ones.Figure 5 shows the recorded hydrogen adsorption isothermsfor the series Ti3+ hexacyanometallates(II) and for the refer-ence material Co3[Co(CN)6]2. As already-mentioned,Co3[Co(CN)6]2 is isostructural to the Ti3+ series with slightlygreater available free volume. For the Ti3+ complex salts theamount of hydrogen adsorbed resulted relatively low comparedwith the adsorption isotherm recorded for the reference mate-rial. Such behavior was interpreted as resulting from a partialcollapse of the porous framework, which was corroboratedfrom nitrogen and CO2 adsorption data (see Supporting Infor-mation). The nitrogen and CO2 adsorption isotherms corre-spond to non-porous solids. The low stability on the watermolecules removal for the Ti3+ series was ascribed to their lowparticle size, below 10 nm, and also to the relatively highertemperature of heating required to obtain an anhydrous solid,close to 150 °C, well above the dehydration temperature forthe cobalt compound, which is around 80 °C [16]. The low

E. Reguera et al.ARTICLE

thermal stability of Ti3+-PB analogues represents a limitationfor the use of this family of coordination polymers as prototypeof solids for the study of the hydrogen interaction with Ti3+

atoms located at the surface of cavities, which was the initialmotivation of this study.

Figure 5. Excess hydrogen adsorption isotherms in the Ti3+ series,Ti3Cl[M(CN)6]2, and in the reference material Co3[Co(CN)6]2.

The samples used for the adsorption studies were aged atroom temperature in humid air for at least a weak and thencharacterized using the above mentioned spectroscopic andstructural techniques. The removal of the crystal water molecu-les under moderate heating leads to the porous framework col-lapse but not to a change in their nature as Ti3+ hexacyanomet-allates(II). The IR and UV/Vis spectra of the rehydratedsamples were found to be similar to those obtained for the as-synthesized samples and the XRD powder pattern shows cer-tain crystalline order (see Supporting Information).

ConclusionsWhen aqueous solutions of [M(CN)6]4– (M = Fe, Ru, Os)

and Ti3+ in concentrated HCl solution are mixed, solids of for-mula unit Ti3Cl[M(CN)6]2·xH2O and crystallite size about10 nm are obtained. These solids crystallize with an open-framework structure based on the Fm3̄m space group, typicalof PB analogues with Z = 1.33 formula unit per unit cell. Theircrystal structure was solved and refined from the recordedXRD powder patterns. The Cl– ions were found to be in thecoordination environment of the titanium atom through a ran-dom occupation. On moderate heating to remove the crystalwater molecules, the porous framework collapses limiting itspotential application for hydrogen storage through specific in-teraction of the hydrogen molecule with the titanium atomfound at the surface of the cavities.

Experimental SectionThe samples of Ti3+ hexacyanometallates(II) were prepared mixing anaqueous solution of K4[M(CN)6]·3H2O (M = Fe, Ru, Os) with a solu-

1972 www.zaac.wiley-vch.de © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2010, 1968–1973

tion of Ti3+ salt in concentrated HCl. The mixture was aged two daysand the formed precipitate was separated by centrifugation, washedseveral times with acidic distilled water and finally air dried until ithad constant weight. All the reagents used were analytical grade fromSigma–Aldrich. The obtained powders were characterized by EDS, IRspectroscopy, Mössbauer spectroscopy, TG, XRD, UV/Vis spectro-scopy, adsorption data and chemical analyses.

The TG curves were recorded with a high-resolution TA Instrumentsequipment Q 5000 under a nitrogen flow. The IR spectra were run asKBr pressed disks with a Spectrum One spectrophotometer from Per-kin–Elmer. Mössbauer spectra were collected at room temperature witha constant acceleration spectrometer (from Wissel) operating in thetransmission mode and 57Co/Rh source. The Mössbauer spectra werefitted using pseudo-Lorentzian line shape and the obtained isomer shift(δ) values are reported relative to sodium nitroprusside. XRD powderpatterns were obtained Cu-Kα radiation in D8 Advance diffractometer(from Bruker) in the 10–100 °/2θ range and 0.025 of angular step. Thecrystal structures were refined from the recorded XRD powder patternsusing the Rietveld method implemented in the FullProf code [27]. Peakprofiles were calculated within 10 times the full width at half maxi-mum. The background was modeled by a third-order polynomial. Theinteratomic C–N distance was constrained to take values within certainlimits considering results from single-crystal studies in PB analogues[22]. The intermolecular contacts for the water molecules within thecavities were estimated from the refined atomic positions for the oxy-gen atom of water molecules. In Table 2 the refinement parameters arereported.

The hydrogen adsorption isotherms were recorded up to 10 atm. withan ASAP 2050 analyzer (from Micromeritics). The samples were acti-vated (dehydrated) by moderate heating from room temperature at aheating rate of 2 °C·min–1 and then maintained at the dehydration tem-perature indicated by the TG curve until to have an outgas rate below0.1 μm Hg. After volume measurement with helium, the degassing wascontinued for 24 h at 80 °C in the sample port. Measurements wereperformed at a liquid nitrogen bath. The hydrogen adsorption data withcomplemented with the recording of nitrogen and CO2 isotherms usingnitrogen and ice-water baths, respectively. The recorded hydrogen ad-sorption data were compared with the reported hydrogen adsorptionisotherm for Co3[Co(CN)6]2 [23], a compound, which also crystallizesin the Fm3̄m space group found for the Ti3+ complex salts.

Structural information been deposited at ICSD Fachinformationszen-trum Karlsruhe (FIZ), 76344 Eggenstein-Leopoldshafen, Germany(Fax: +49-7247-808-666; E-Mail: [email protected], http://www.fiz-karlsruhe.de/request for deposited data.html) on quoting theCSD numbers CSD-421482 (Ti3Cl[Fe(CN)6]2·10H2O), CSD-421483(Ti3Cl[Ru(CN)6]2·10H2O) and CSD-421484 (Ti3Cl[Os(CN)6]2·10H2O).

Supporting Information (see footnote on the first page of this article):EDS, UV/Vis, and IR spectra, as well as XRD powder patterns, atomicpositions, main bond distances/angles, and N2 and CO2 adsorption iso-therms for the title compounds.

Acknowledgement

The partial support from ICyTDF PIFUTP08-158 project is acknowl-edged. The authors thank the help of J. Roque for the H2 adsorptiondata recording.


References

[1] W. Bao, S. Xu, L. Li, C. Song, J. Zhong, Y. Zhu, J. Nucl. Mater.2002, 301, 237–241 and references cited therein.

[2] J. Narbutt, J. Wiwinski, B. Bartos, A. Bickwicz, J. Radioanal.Nucl. Chem. 1986, 89, 41–49.

[3] R. Martinez-Garcia, E. Reguera, J. Rodriguez, J. Balmaseda, J.Roque, Powder Diffract. 2004, 19, 255–264.

[4] C. P. Zhang, P. Gu, J. Zhao, D. Zhang, Y. Deng, J. Hazard. Mater.2009, 167, 1057–1062.

[5] M. V. Logunov, A. S. Skobtsov, B. V. Soldatov, A. P. Paznikov,Y. A. Voroshilov, S. I. Rovny, C. R. Chim. 2004, 7, 1185–1190.

[6] K. G. Maer Jr., M. L. Beasley, R. L. Collins, W. O. Milligan, J.Am. Chem. Soc. 1968, 90, 3201–3208.

[7] G. J. Kubas, Chem. Rev. 2007, 107, 4152-4205.[8] S. S. Kaye, J. R. Long, J. Am. Chem. Soc. 2005, 127, 6506–6507.[9] K. W. Chapman, P. D. Southon, C. L. Weeks, C. J. Kepert, Chem.

Commun. 2005, 3322–3324.[10] J. T. Culp, C. Matranga, M. Smith, E. W. Bittner, B. Bockrath, J.

Phys. Chem. B 2006, 110, 8325–8328.[11] S. S. Kaye, J. R. Long, Catal. Today 2007, 120, 311–316.[12] S. Natesakhawat, J. T. Culp, C. Matranga, B. Bockrath, J. Phys.

Chem. C 2007, 111, 1055–1060.[13] L. Reguera, C. P. Krap, J. Balmaseda, E. Reguera, J. Phys. Chem.

C 2008, 112, 10490–10501.[14] L. Reguera, C. P. Krap, J. Balmaseda, E. Reguera, J. Phys. Chem.

C 2008, 112, 15893–15899.


[15] M. Ávila, L. Reguera, J. Rodríguez-Hernández, J. Balmaseda, E.Reguera, J. Solid State Chem. 2008, 181, 2899–2907.

[16] C. P. Krap, J. Balmaseda, L. F. del Castillo, B. Zamora, E. Re-guera, Energy Fuels 2010, 24, 581–589.

[17] A. Hamaed, M. Trudeau, D. M. Antonelli, J. Am. Chem. Soc.2008, 130, 6992–6999.

[18] http://www.energy.gov/energysources/hydrogen.htm.[19] E. Reguera, E. Marín, A. Calderón, J. Rodríguez-Hernández,

Spectrochim. Acta A 2007, 68, 191–197.[20] J. Rodríguez-Hernández, A. Gómez, E. Reguera, J. Phys. D: Appl.

Phys. 2007, 40, 6076–6082.[21] M. Ávila, L. Reguera, C. Vargas, E. Reguera, J. Phys. Chem.

Solids 2009, 70, 477–482.[22] A. Ludi, H. U. Gudel, Struct. Bonding (Berlin) 1973, 14, 1–21.[23] J. Jiménez-Gallego, J. Rodríguez-Hernández, H. Yee-Madeira, E.

Reguera, J. Phys. Chem. C 2010, 114, 5043–5048.[24] F. Herren, P. Fisher, A. Ludi, W. Halg, Inorg. Chem. 1980, 19,

956–959.[25] A. Guinier, X-ray Diffraction; Dover Publications: Mineola, NY,

1994.[26] J. Roque, E. Reguera, J. Balmaseda, J. Rodríguez-Hernández, L.

Reguera, L. F. del Castillo, Microporous Mesoporous Mater.2007, 103, 57–71.

[27] J. Rodríguez-Carvajal, FullProf 2005, Institute Louis Brillouin,Saclay, France, 2005.

Received: February 25, 2010Published Online: May 18, 2010

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Titanium3+ Hexacyanometallates(II): Preparation and Porous Framework