BACKGROUND: The Prussian blue analogues represent well-known and extensively studied group of coordination species which has many remarkable applications due to their ion-exchange, electron transfer or magnetic properties. Among them, Co-Fe Prussian blue analogues have been extensively studied due to the photoinduced magnetization. Surprisingly, their suitability as precursors for solid-state synthesis of magnetic nanoparticles is almost unexplored. In this paper, the mechanism of thermal decomposition of [Co(en)3][Fe(CN)6] ∙∙ 2H2O (1a) is elucidated, including the topotactic dehydration, valence and spins exchange mechanisms suggestion and the formation of a mixture of CoFe2O4-Co3O4 (3:1) as final products of thermal degradation. RESULTS: The course of thermal decomposition of 1a in air atmosphere up to 600°C was monitored by TG/DSC techniques, (57)Fe Mössbauer and IR spectroscopy. As first, the topotactic dehydration of 1a to the hemihydrate [Co(en)3][Fe(CN)6] ∙∙ 1/2H2O (1b) occurred with preserving the single-crystal character as was confirmed by the X-ray diffraction analysis. The consequent thermal decomposition proceeded in further four stages including intermediates varying in valence and spin states of both transition metal ions in their structures, i.e. [Fe(II)(en)2(μ-NC)Co(III)(CN)4], Fe(III)(NH2CH2CH3)2(μ-NC)2Co(II)(CN)3] and Fe(III)[Co(II)(CN)5], which were suggested mainly from (57)Fe Mössbauer, IR spectral and elemental analyses data. Thermal decomposition was completed at 400°C when superparamagnetic phases of CoFe2O4 and Co3O4 in the molar ratio of 3:1 were formed. During further temperature increase (450 and 600°C), the ongoing crystallization process gave a new ferromagnetic phase attributed to the CoFe2O4-Co3O4 nanocomposite particles. Their formation was confirmed by XRD and TEM analyses. In-field (5 K / 5 T) Mössbauer spectrum revealed canting of Fe(III) spin in almost fully inverse spinel structure of CoFe2O4. CONCLUSIONS: It has been found that the thermal decomposition of [Co(en)3][Fe(CN)6] ∙∙ 2H2O in air atmosphere is a gradual multiple process accompanied by the formation of intermediates with different composition, stereochemistry, oxidation as well as spin states of both the central transition metals. The decomposition is finished above 400°C and the ongoing heating to 600°C results in the formation of CoFe2O4-Co3O4 nanocomposite particles as the final decomposition product.

Department of Inorganic Chemistry Institute of Chemistry Faculty of Sciences P J Šafárik University in Košice Moyzesova 11 Košice SK 041 54 Slovakia

Regional Centre of Advanced Technologies and Materials and Department of Inorganic Chemistry Palacký University Tř 17 listopadu 12 Olomouc CZ 77146 Czech Republic

Regional Centre of Advanced Technologies and Materials and Department of Physical Chemistry Palacký University Tř 17 listopadu 12 Olomouc CZ 77146 Czech Republic

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Verdaguer M, Girolami GS, Miller JS, Drillon M. Magnetism: Molecules to Materials, Volume 5. Weinheim: Wiley-VCH Verlag GmbH & Co. KGaA; 2005. Magnetic Prussian Blue Analogs.

Catala L, Volatron F, Brinzei D, Mallah T. Functional Coordination Nanoparticles. Inorg Chem. 2009;48:3360–3370. doi: 10.1021/ic8012574. PubMed DOI

Ricci F, Palleschi G. Sensor and biosensor preparation, optimisation and applications of Prussian Blue modified electrodes. Biosens Bioelectron. 2005;21:389–407. doi: 10.1016/j.bios.2004.12.001. PubMed DOI

Jayalakshmi M, Scholz FJ. Performance characteristics of zinc hexacyanoferrate/Prussian blue and copper hexacyanoferrate/Prussian blue solid state secondary cells. J Power Sources. 2000;91(2):217–223. doi: 10.1016/S0378-7753(00)00475-4. DOI

Hu B, Fugetsu B, Yu H, Abe Y. Prussian blue caged in spongiform adsorbents using diatomite and carbon nanotubes for elimination of cesium. J Hazard Mater. 2012;217–218:85–91. PubMed

Okubo M, Asakura D, Mizuno Y, Kim JD, Mizokawa T, Kudo T, Honma I. Switching Redox-Active Sites by Valence Tautomerism in Prussian Blue Analogues AxMny[Fe(CN)6].nH2O (A: K, Rb): Robust Frameworks for Reversible Li Storage. J Phys Chem Lett. 2010;1:2063–2071. doi: 10.1021/jz100708b. DOI

Uemura T, Ohba M, Kitagawa S. Size and Surface Effects of Prussian Blue Nanoparticles Protected by Organic Polymers. Inorg Chem. 2004;43:7339–7345. doi: 10.1021/ic0488435. PubMed DOI

Liang C, Liu P, Xu J, Wang H, Wang W, Fang J, Wang Q, Shen W, Zhao J. A Simple Method for the Synthesis of Fe-Co Prussian Blue Analogue with Novel Morphologies, Different Structures, and Dielectric Properties. Synth React Inorg, Met-Org, Nano-Met Chem. 2011;41(9):1108. doi: 10.1080/15533174.2011.591354. DOI

Koncki R. Chemical Sensors and Biosensors Based on Prussian Blues. Crit Rev Anal Chem. 2002;32:79–96. doi: 10.1080/10408340290765452. DOI

DeLongchamp DM, Hammond PT. Multiple-Color Electrochromism from Layer-by-Layer-Assembled Polyaniline/Prussian Blue Nanocomposite Thin Films. Chem Mater. 2004;16:4799–4805. doi: 10.1021/cm0496624. DOI

Bustos L, Godinez LA. Modified Surfaces with Nano-Structured Composites of Prussian Blue and Dendrimers. New Materials for Advanced Electrochemical Applications. Int J Electrochem Sci. 2011;6:1–36.

de Tacconi NR, Rajeshwar K. Metal Hexacyanoferrates: Electrosynthesis, in Situ Characterization, and Applications. Chem Mater. 2003;15:3046–3062. doi: 10.1021/cm0341540. DOI

Verdaguer M, Bleuzen A, Marvaud V, Vaissermann J, Seuleiman M, Desplanches C, Scuiller A, Train C, Garde R, Gelly G, Lomenech C, Rosenman I, Veillet P, Cartier C, Villain F. Molecules to build solids: high TC molecule-based magnets by design and recent revival of cyano complexes chemistry. Coord Chem Rev. 1999;192:1023–1047.

Dunbar KR, Heintz RA. Progress in Inorganic Chemistry, Volume 45. New York: Karlin KD. John Wiley; 2007. Chemistry of Transition Metal Cyanide Compounds: Modern Perspectives; pp. 283–391.

Herrera JM, Bachschmidt A, Villain F, Bleuzen A, Marvaud V, Wernsdorfer W, Verdaguer M. Mixed valency and magnetism in cyanometallates and Prussian blue analogues. Phil Trans R Soc A. 2008;366:127–138. doi: 10.1098/rsta.2007.2145. PubMed DOI

Sato O. Optically Switchable Molecular Solids: Photoinduced Spin-Crossover, Photochromism, and Photoinduced Magnetization. Acc Chem Res. 2003;36:692–700. doi: 10.1021/ar020242z. PubMed DOI

Talham DR, Meisel MW. Thin films of coordination polymer magnets. Chem Soc Rev. 2011;40:3356–3365. doi: 10.1039/c1cs15015d. PubMed DOI

Holmes SM, Girolami GS. Sol–gel Synthesis of KVII[CrIII(CN)6].2H2O: A Crystalline Molecule-Based Magnet with a Magnetic Ordering Temperature above 100°C. J Am Chem Soc. 1999;121:5593–5594. doi: 10.1021/ja990946c. DOI

Sato O. Photoinduced magnetization in molecular compounds. J Photochem and Photobiol C: Chem. 2004;5:203–223. doi: 10.1016/j.jphotochemrev.2004.10.001. DOI

Sato O, Tao J, Zhang YZ. Control of Magnetic Properties through External Stimuli. Angew Chem Int Ed. 2007;46:2152–2187. doi: 10.1002/anie.200602205. PubMed DOI

Culp JT, Park JH, Frye F, Huh YD, Meisel MW, Talham DR. Magnetism of metal cyanide networks assembled at interfaces. Coord Chem Rev. 2005;249:2642–2648. doi: 10.1016/j.ccr.2005.05.011. DOI

Bleuzen A, Lomenech C, Escax V, Villain F, Varret F, Cartier dit Moulin C, Verdaguer M. Photoinduced Ferrimagnetic Systems in Prussian Blue Analogues CIxCo4[Fe(CN)6]y (CI = Alkali Cation). 1. Conditions to Observe the Phenomenon. J Am Chem Soc. 2000;122:6648–6652. doi: 10.1021/ja000348u. DOI

Sato O, Einaga Y, Fujishima A, Hashimoto K. Photoinduced Long-Range Magnetic Ordering of a Cobalt-Iron Cyanide. Inorg Chem. 1999;38:4405–4412. doi: 10.1021/ic980741p. PubMed DOI

Ohba M, Okawa H. Synthesis and magnetism of multi-dimensional cyanide-bridged bimetallic assemblies. Coord Chem Rev. 2000;198:313–328. doi: 10.1016/S0010-8545(00)00233-2. DOI

Colacio E, Ghazi M, Stoeckli-Evans H, Lloret F, Moreno JM, Perez C. Cyano-Bridged Bimetallic Assemblies from Hexacyanometalate, [M(CN)6]3- (M = MnIII and FeIII), and [M(N4-macrocycle)]2+ (M = FeIII, NiII and ZnII) Building Blocks. Syntheses, Multidimensional Structures, and Magnetic Properties. Inorg Chem. 2001;40:4876–4883. doi: 10.1021/ic0103446. PubMed DOI

Marvaud V, Decroix C, Scuiller A, Guyard-Duhayon C, Vaissermann J, Gonnet F, Verdaguer M. Hexacyanometalate Molecular Chemistry: Heptanuclear Heterobimetallic Complexes; Control of the Ground Spin State. Chem Eur J. 2003;9:1677–1691. doi: 10.1002/chem.200390192. PubMed DOI

Funck KE, Hilfiger MG, Berlinguette CP, Shatruk M, Wernsdorfer W, Dunbar KR. Trigonal-Bipyramidal Metal Cyanide Complexes: A Versatile Platform for the Systematic Assessment of the Magnetic Properties of Prussian Blue Materials. Inorg Chem. 2009;48:3438–3452. doi: 10.1021/ic801990g. PubMed DOI

Newton GN, Nihei M, Oshio H. Cyanide-Bridged Molecular Squares – The Building Units of Prussian Blue. Eur J Inorg Chem. 2011;20:3031–3042.

Černák J, Orendáč M, Potočňák I, Chomič J, Orendáčová A, Skoršepa J, Feher A. Cyanocomplexes with one-dimensional structures: preparations, crystal structures and magnetic properties. Coord Chem Rev. 2002;224:51–66. doi: 10.1016/S0010-8545(01)00375-7. DOI

Billing R. Optical and photoinduced electron transfer in ion pairs of coordination compounds. Coord Chem Rev. 1997;159:257–270.

Billing R, Vogler A. Optical and photoinduced electron transfer in tris(ethylenediamine)cobalt(III)-cyanometallate ion pairs. J Photochem Photobiol A: Chem. 1997;103(3):239–247. doi: 10.1016/S1010-6030(96)04562-5. DOI

Poulopoulou VG, Li ZW, Taube H. Comparison of the rates of substitution in [Ru(NH3)5H2O]3+ and [Os(NH3)5H2O]3+ by hexacyano complexes: substitution coupled to electron transfer. Inorg Chim Acta. 1994;225:173–184. doi: 10.1016/0020-1693(94)04045-1. DOI

Allen FH, Bellard S, Brice MD, Cartwright BA, Doubleday A, Higgs H, Hummelink T, Hummelink-Peters BG, Kennard O, Motherwell WDS, Rodgers JR, Watson DG. Cambridge Structural Database System (CSDS) Cambridge, U.K; 1994.

Bernhardt PV, Bozoglian F, Macpherson BP, Martinez M. Molecular mixed-valence cyanide bridged CoIII–FeII complexes. Coord Chem Rev. 2005;249:1902–1916. doi: 10.1016/j.ccr.2004.11.014. PubMed DOI

Bernhardt PV, Bozoglian F, Gonzalez G, Martınez M, Macpherson BP, Sienra B. Dinuclear Cyano-Bridged CoIII-FeII Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity. Inorg Chem. 2006;45:74–82. doi: 10.1021/ic0511423. PubMed DOI

Bernhardt PV, Martınez M, Rodrıguez C. Molecular CoIII/FeII Cyano-Bridged Mixed-Valence Compounds with High Nuclearities and Diversity of CoIII Coordination Environments: Preparative and Mechanistic Aspects. Inorg Chem. 2009;48:4787–4797. doi: 10.1021/ic802198s. PubMed DOI

Seitz K, Peschel P, Babel D. On the Crystal Structure of the Cyanido Complexes [Co(NH3)6][Fe(CN)6], [Co(NH3)6]2[Ni(CN)4]3⋅ 2H2O, [Cu(en)2][Ni(CN)4] Z Anorg Allg Chem. 2001;627:929–934. doi: 10.1002/1521-3749(200105)627:5<929::AID-ZAAC929>3.0.CO;2-7. DOI

Bok LD, Leipoldt JG, Basson SS. The crystal structure of tris(ethylenediamine), cobalt(III) hexacyanoferrate(III)dihydrate, Co(C2H8N2)3[Fe(CN)6]2 · H2O. Z Anorg Allg Chem. 1972;389:307–314. doi: 10.1002/zaac.19723890311. DOI

Elder RC, Kennard GJ, Payne MD, Deutsch F. Synthesis and Characterization of Bis(ethylenediamine)cobalt(III) Complexes Containing Chelated Thioether Ligands. Crystal Structures of [(en)2Co(S(CH3)CH2CH2NH2)][Fe(CN)6] and [(en)2Co(S(CH2C6H5)CH2COO)](SCN)2. Inorg Chem. 1978;17:1296–1303. doi: 10.1021/ic50183a039. DOI

Maľarová M, Trávníček Z, Zbořil R, Černák J. [Co(en)3][Fe(CN)6]⋅ H2O and [Co(en)3][Fe(CN)6]: A dehydration process investigated by single crystal X-ray analysis, thermal analysis and Mössbauer spectroscopy. Polyhedron. 2006;25:2935–2943. doi: 10.1016/j.poly.2006.04.021. DOI

Matiková-Maľarová M, Černák J, Massa W, Varret F. Three Co(III)–Fe(II) complexes based on hexacyanoferrates: Syntheses, spectroscopic and structural characterizations. Inorg Chim Acta. 2009;362:443–448. doi: 10.1016/j.ica.2008.04.038. DOI

Ohashi Y, Yanagi K, Mitsuhashi Y, Nagata K, Kaizu Y, Sasada Y, Kobayashi H. Absolute Configuration of (−)D-Tris(2,2′-bipyridine)cobalt(III) J Am Chem Soc. 1979;101:4739–4740. doi: 10.1021/ja00510a056. DOI

Yanagi K, Ohashi Y, Sasada Y, Kaizu Y, Kobayashi H. Crystal structure and Absolute Configuration of (−)589-Tris(2,2′-bipyridine)cobalt(III) Hexacyanoferrate(III) Octahydrate. Bull Chem Soc Jpn. 1981;54:118–126. doi: 10.1246/bcsj.54.118. DOI

Singh N, Diwan K, Drew MGB. Supramolecular assemblies of metal ions in complex bimetallic and trimetallic salts based on hexacyanoferrate(III) ion. Polyhedron. 2010;29:3192–3197. doi: 10.1016/j.poly.2010.08.032. DOI

Zhuge F, Wu B, Yang J, Janiak C, Tang N, Yang XJ. Microscale hexagonal rods of a charge-assisted second-sphere coordination compound [Co(DABP)3][Fe(CN)6] Chem Commun. 2010;46:1121–1123. doi: 10.1039/b914216a. PubMed DOI

Ulas G, Brudvig GW. Redirecting Electron Transfer in Photosystem II from Water to Redox-Active Metal Complexes. J Am Chem Soc. 2011;133:13260–13263. doi: 10.1021/ja2049226. PubMed DOI

Kersting B, Siebert D, Volkrner D, Kolm MJ, Janiak C. Synthesis and Characterization of Homo- and Heterodinuclear Complexes Containing the N3M(μ2-SR)3MN3 Core (M = Fe, Co, Ni) Inorg Chem. 1999;38:3871–3882. doi: 10.1021/ic990087t. DOI

Mohai B. Thermolysis of cyano complexes. VII. On the thermal decomposition of hexacyanocobaltate(III); ligand exchange during thermolysis. Z Anorg Allg Chem. 1972;392:287–294. doi: 10.1002/zaac.19723920313. DOI

Horváth A, Mohai B. Thermolysis of complex cyanides - XIII Structural transformations at thermal decomposition of [M(en)3][M’(CN)5NO] double complexes. J Inorg Nucl Chem. 1980;42:195–199. doi: 10.1016/0022-1902(80)80239-9. DOI

Ng CW, Ding J, Gan LM. Microstructural Changes Induced by Thermal Treatment of Cobalt(II) Hexacyanoferrate(III) Compound. J Solid State Chem. 2001;156:400–407. doi: 10.1006/jssc.2000.9013. DOI

Ng CW, Ding J, Shi Y, Gan LM. Structure and magnetic properties of copper(II) hexacyanoferrate(III) compound. J Phys Chem Solids. 2001;62:767–775. doi: 10.1016/S0022-3697(00)00248-1. DOI

Pechenyuk SI, Domonov DP, Gosteva AN, Kadyrova GI, Kalinnikov VT. Synthesis, Properties, and Thermal Decomposition of Compounds [Co(En)3][Fe(CN)6] · 2H2O and [Co(En)3]4[Fe(CN)6]3 · 15H2O. Russ J Coord Chem. 2012;38:596–603. doi: 10.1134/S1070328412090060. DOI

Kaupp G. Solid-state reactions, dynamics in molecular crystals. Curr Opin Solid State Mater Sci. 2002;6:131–138. doi: 10.1016/S1359-0286(02)00041-4. DOI

Nicketic SR, Rasmussen K. Conformational Analysis of Coordination Compounds. IV. Tris(1,2-ethanediamine)- and Tris(2,3-butanediamine)cobalt(III) complexes. Acta Chem Scand. 1978;A32:391–400.

Matsuki R, Shiro M, Asahi T, Asai H. Absolute configuration of Λ-(+)589-tris(ethylenediamine)cobalt(III) triiodide monohydrate. Acta Crystallogr., Sect. E: Struct. Rep. Online. 2001;57:m448–m450. doi: 10.1107/S1600536801015008. DOI

Ueda T, Bernard GM, McDonald R, Wasylishen RE. Cobalt-59NMR and X-ray diffraction studies of hydrated and dehydrated (±)-tris(ethylenediamine) cobalt(III) chloride. Solid State Nucl Magn Reson. 2003;24:163–183. doi: 10.1016/S0926-2040(03)00049-3. PubMed DOI

Moron MC, Palacio F, Pons J, Casabo J, Solans X, Merabet KE, Huang D, Shi X, Teo BK, Carlin RL. Bimetallic Derivatives of [M(en)3I3+ Ions (M = Cr, Co): An Approach to Intermolecular Magnetic Interactions in Molecular Magnets. Inorg Chem. 1994;33:746–753. doi: 10.1021/ic00082a021. DOI

Saha MK, Lloret F, Bernal I. Inter-String Arrays of Bimetallic Assemblies with Alternative Cu2+-Cl-Cu2+ and Cu-NC-M (M = Co3+, Fe+3, Cr+3) Bridges: Syntheses, Crystal Structure, and Magnetic Properties. Inorg Chem. 2004;43:1969–1975. doi: 10.1021/ic034897n. PubMed DOI

Salah El Fallah M, Rentschler E, Caneschi A, Sessoli R, Gatteschi D. A Three-Dimensional Molecular Ferrimagnet Based on Ferricyanide and [Ni(tren)]2+ Building Blocks. Angew Chem Int Ed Engl. 1996;35:1947–1949. doi: 10.1002/anie.199619471. DOI

Herchel R, Tuček J, Trávníček Z, Petridis D, Zbořil R. Crystal Water Molecules as Magnetic Tuners in Molecular Metamagnets Exhibiting Antiferro-Ferro-Paramagnetic Transitions. Inorg Chem. 2011;50:9153–9163. doi: 10.1021/ic201358c. PubMed DOI

Reguera E, Férnandez-Bertrán J. Effect of the water of crystallization on the Mössbauer spectra of hexacyanoferrates (II and III) Hyperfine Interact. 1994;88:49–58. doi: 10.1007/BF02068701. DOI

Nakamoto I. Infrared Spectra of Inorganic and Coordination Compounds. New York: John Wiley and Sons; 2002.

Landolt-Bornstein GII. Atomic and Molecular Physics, Volume 2. Verlag: Springer; 1966.

Comba P. Prediction and Interpretation of EPR Spectra of Low-Spin Iron(III) Complexes with the MM-AOM Method. Inorg Chem. 1994;33:4511–4583.

Tang HY, Lin HY, Wang MJ, Liao MY, Liu JL, Hsu FC, Wu MK. Crystallization and Anisotropic Properties of Water-Stabilized Potassium Cobalt Oxides. Chem Mater. 2005;17:2162–2164. doi: 10.1021/cm047707v. DOI

Viertelhaus M, Henke H, Anson CE, Powell AK. Solvothermal Synthesis and Structure of Anhydrous Manganese(II) Formate, and Its Topotactic Dehydration from Manganese(II) Formate Dihydrate. Eur J Inorg Chem. 2003;12:2283–2289.

Song Y, Zavalij PY, Suzuki M, Whittingham MS. New Iron(III) Phosphate Phases: Crystal Structure and Electrochemical and Magnetic Properties. Inorg Chem. 2002;41:5778–5786. doi: 10.1021/ic025688q. PubMed DOI

Greve J, Jess I, Nather C. Synthesis, crystal structures and investigations on the dehydration reaction of the new coordination polymers poly[diaqua-(μ2-squarato-O, O’)-(μ2–4,4′-bipyridine-N, N’)Me(II)] hydrate (Me = Co, Ni, Fe) J Sol State Chem. 2003;175:328–340. doi: 10.1016/S0022-4596(03)00306-2. DOI

Feist M, Troyanov SI, Mehner H, Witke K, Kemnitz E. Halogeno Metallates of Transition Elements with Cations of Nitrogen-containing Heterocyclic Bases. VII Two Oxidation States and Four Different Iron Coordinations in one Compound. Synthesis, Crystal Structure, and Spectroscopic Characterization of 1,4-Dimethylpiperazinium Chloroferrate (II,III), (dmpipzH2)6[FeIICl4]2 [FeIIICl4]2[FeIICl5] [FeIIICl6] Z Anorg Allg Chem. 1999;625:141–146. doi: 10.1002/(SICI)1521-3749(199901)625:1<141::AID-ZAAC141>3.0.CO;2-W. DOI

Wyrzykowski D, Maniecki T, Pattek-Janczyk A, Stanek J, Warnke Z. Thermal analysis and spectroscopic characteristics of tetrabutylammonium tetrachloroferrate(III) Thermochim Acta. 2005;435:92–98. doi: 10.1016/j.tca.2005.05.007. DOI

Roodburn HM, Fisher JR. Reaction of Cyanogen with Organic Compounds. X. Aliphatic and Aromatic Diamines. J Org Chem. 1957;22:895–899. doi: 10.1021/jo01359a010. DOI

Zsakó J, Pokol G, Novák C, Várhelyi C, Dobó A, Liptay G. KINETIC ANALYIS OF TG DATA XXXV. Spectroscopic and thermal studies of some cobalt(III) chelates with ethylenediamine. J Therm Anal Calorim. 2001;64:843–856. doi: 10.1023/A:1011577319016. DOI

Nihei M, Sekine Y, Suganami N, Nakazawa K, Nakao A, Nakao H, Murakami Y, Oshio H. Controlled Intramolecular Electron Transfers in Cyanide-Bridged Molecular Squares by Chemical Modifications and External Stimuli. J Am Chem Soc. 2011;133:3592–3600. doi: 10.1021/ja109721w. PubMed DOI

Sakai T, Ohgo Y, Hoshino A, Ikeue T, Saigon T, Takahashi M, Nakanuta M. Electronic Structures of Five-Coordinate Iron(III) Porphyrin Complexes with Highly Ruffled Porphyrin Ring. Inorg Chem. 2004;43:5034–5043. doi: 10.1021/ic049825q. PubMed DOI

Fejitha KS, Mathew S. Thermoanalytical investigations of tris(ethylenediamine)nickel(II) oxalate and sulphate complexes. J Therm Anal Calorim. 2010;102:931–939. doi: 10.1007/s10973-010-0823-8. DOI

Persoons RM, Degrave E, Van Denberghe RE. Mössbauer study of Co-substituted magnetite. Hyperfine Interact. 1990;54:655–660. doi: 10.1007/BF02396107. DOI

Haneda K, Morrish AH. Noncollinear magnetic structure of CoFe2O4 small particles. J Appl Phys. 1988;63:4258–4261. doi: 10.1063/1.340197. DOI

Greenwood NN, Gibb TC. Mössbauer spectroscopy. New York: Barnes and Noble Inc; 1971.

Fedotova YA, Baev VG, Lesnikovich AI, Milevich IA, Vorobeva SA. Magnetic Properties and Local Configurations of 57Fe Atoms in CoFe2O4 Powders and CoFe2O4/PVA Nanocomposites. Phys Sol State. 2011;53:647–653.

Ngo AT, Bonville P, Pileni MP. Nanoparticles of CoxFey_zO4: Synthesis and superparamagnetic properties. Eur Phys J. 1999;B9:583–592.

Vivier V, Aguey F, Fournier J, Lambert JF, Bedioui F, Che M. Spectroscopic and Electrochemical Study of the Adsorption of [Co(en)2Cl2]Cl on γ-Alumina: Influence of the Alumina Ligand on Co(III)/(II) Redox Potential. J Phys Chem B. 2006;110:900–906. doi: 10.1021/jp058224x. PubMed DOI

Diffraction O. CrysAlis CCD. Abingdon, England: Oxford Diffraction Ltd; 2006.

Altomare A, Burla MC, Camalli M, Cascarano GL, Giacovazzo C, Guagliardi A, Moliterni AGG, Polidori G, Spagna R. SIR97: a new tool for crystal structure determination and refinement. J Appl Cryst. 1999;32:115–119. doi: 10.1107/S0021889898007717. DOI

Farrugia LJ. WinGX suite for small-molecule single-crystal crystallography. J Appl Cryst. 1999;32:837–838. doi: 10.1107/S0021889899006020. DOI

Sheldrick GM. A short history of SHELX. Acta Crystallogr, Sect A: Found Crystallogr. 2008;64:112–122. doi: 10.1107/S0108767307043930. PubMed DOI

Brandenburg K. DIAMOND. Visual Crystal Structure Information System. Version 2.1e. Bonn, Germany: Crystal Impact GbR; 2000.