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26
N. I. Naumkina, O. V. Mikhailov, T. B. Tatarintseva,
T. Z. Lygina
NON-TYPICAL (CdCo)HETEROBINUCLEAR HEXACYANOFERRATES(II) FORMED
INTO MOLECULAR NANO-REACTORS
Keywords: gelatin-immobilized matrix; ionic exchange; heterobinuclear hexacyanoferrate(II);
cadmium; cobalt.
Ionic exchange Co(II)^Cd(II) and Cd(II)^Co(II) reactions proceeding into molecular nano-reactors of corresponding metal(II)hexacyanoferrate(II) gelatin-immobilized matrix materials (C02[Fe(CN)6j -GIM and Cd2[Fe(CN)6]-GIM) under their contact with water solutions of cadmium(II) and cobalt(II) chloride, respectively, have been studied. It has been shown that a formation of heterobinuclear hexacyanoferrates(II) having COdCd55[Fe(CN)6]32 and Cdn Co5[Fe(CN)6]8 formulas occurs as a result of this process.
Ключевые слова: желатин-иммобилизован-ная матрица; ионный обмен; гетеробиядерный
гексацианоферрат(П); кадмий; кобальт.
Изучены ионообменные реакции Co(II)^ Cd(II) и Cd(II)^Co(II), протекающие в молекулярных нанореакторах соответствующих металлгексацианоферрат(П)ных желатин-иммобилизованных матричных материалов (Co2[Fe(CN)6]-GIM и Cd2[Fe(CN)6]-GIM) при их контакте с водными растворами хлоридов кадмия(П) и кобальта(П) соответственно. Отмечено, что в результате этих процессов имеет место образование гетеробиядерных гексацианоферратов(П) Co9Cd55[Fe(CN)6]32 и
CdiiC0e[Fe(CN)6]8-
Introduction
A lot of the works devoted to synthesis and application so-called gelatin-immobilized matrix materials (GIM), and, also, to studying of complexing processes proceeding in them, was published in the literature in the last 10 years. The information concerning these publications can be found in reviews [1-6]. However, all these works were devoted to research of reactions of nucleophilic substitution or template synthesis. Reactions of ionic exchange till now were considered only in [7,8] and were used for development of the general methodology of obtaining metalhexacyanoferrate(II) GIM [7] and metalsulfide ones. In this connection, it is interesting to study reactions of ionic exchange proceeding in various 3d-metal(II)hexacyanoferrate(II) gelatin-immobilized matrix materials (M2[Fe(CN)6]-GIM) when they are in contact with water solutions of metal(II) chloride MCl2 (M -d-element). Heteronuclear hexacyanoferrates(II) containing atoms of three various d-elements in a crystal lattice, might be formed theoretically as a result of these reactions. Such (dd)heterobinuclear hexacyanoferrates(II) are little-studied even now, more than 30 years after publication of the basic monography [9]. An importance of studying these reaction increases if to pay into attention that such compounds, and, for example, cyanocomplexes of cobalt(II) and cadmium(II), according to data [10-13], might be perspective in a design of
molecular ferromagnetic substances. The given paper devoted to studying Co2[Fe(CN)6]^-Cu(II) and Cd2[Fe(CN)6]^Co(II) ionic exchange reactions proceeding in the cobalt(II)- and cadmium(II)hexacyanoferrate(II) GIM systems at their contact to water solutions of cadmium(II)chloride CdCl2 and cobalt(II) chloride CoCl2, respectively.
Experimental
Initial Co2[Fe(CN)6]- and Cd2[Fe(CN)6]-GIM were synthesized by the techniques described in [7]. Metalhexacyanoferrate(II) GIM prepared then were in a contact of CdCl2 and CoCl2, respectively. Concentration of MCl2 in the water solutions (M= Co, Cd) contacting with these matrices was (0,01-0.10) mol-dm-3, time of contact the GIM/solution was varied within 1-10 minutes at temperature (20.0±0.1)°C. After the completion of this procedure, gelatin-immobilized matrices synthesized was washed out 15-20 minutes in the running water, washed with distilled water and dried 2-3 hours at room temperature.
In order to study structure and properties of (aW)heteronuclear hexacyanoferrates(II) formed in gelatin-immobilized matrix, corresponding matrices were destroyed by influence on them of solutions proteolytic enzymes (for example, Bacillus mesentericus) according to a technique [14]. The measurements of pH values of solutions contacting with GIM were carried out with the using pH-150 potentiometer. The optical densities of GIM obtained (D) were measured with using Macbeth TD-504 photometer (Kodak, USA) with an accuracy + 2% (rel.) in the 0.1-5.0 range. The kinetics of complexing process was described by D= f(CF, CMo, t) dependences where D is metalcomplex gelatin-immobilized matrix optical density corresponding to initial concentration of Co2[Fe(CN)6] or Cd2[Fe(CN)6] in a GIM (CF, mol-dm-3), concentration of CdCl2 or CoCl2 in a solution contacting to a matrix (CMo, mol-dm-3) and the complexing process (ionic exchange) time (t, min). Examples of these dependences in coordinate sections [CF=const, varied CMo, argument t] and [CMo=const, varied t, argument CF] are shown in figs. 1 and 2. Electronic absorption spectra of the GIM were recorded with using Specord UV-VIS (Karl Zeiss, Germany) and PU-8710 (Philips, The Netherlands) spectrophotometers in the 400-800 nm range; examples of such spectra are presented in fig. 3. For recording i.r. spectra in the 400-4000 cm-1 range, a 16PCFT-IR spectrometer (Perkin Elmer, USA) was employed. X-ray fluorescence analysis of metalcomplex gelatin-immobilized GIM was carried out with a spectrometer VRA 20L. An intensity of fluorescence of samples was parameter measured in this method. X-ray phase analysis carried out with using diffraction instrument DR0N-4-07. A scanning was carried out in an interval from 3 up to 65o 20, a step was 0,05 20.
Results and discussion
In the Co2[Fe(CN)6]-GIM- CdCl2 system, at the contact GIM/CdCl2 solution, the change of colour of gelatin mass from green to greenish-yellow accompanied by slight increase of D values with t growth; it is significant that D values become constant already at t= 2 min (Fig. 1, part A) and in the future does not change even at long (1 hour and more) time of such a contact. Besides, D= f(CF, CMo, t) dependence for the GIM formed after t= 6 min, in coordinate sections [CMo=const, varied t, argument CF] are higher than the similar curves corresponding Co2[Fe(CN)6]-GIM and Cd2[Fe(CN)6]-GIM (fig. 1, part B). A chemical analysis of CdCl2 solutions contacting with Co2[Fe(CN)6]-GIM showed that all they contained cobalt(II) ion, the quantity of which increased with D values growth. This circumstance evidences that in the system studied, complexing process accompanied by cobalt(II)^ cadmium(II) ionic exchange, occurs. When the gelatin layer formed as a result of such a contact, is destroyed by the procedure [14], the yellow-green substance may be isolated. According to data of chemical analysis and X-ray fluorescence analysis, it has the simplest CogCd55Fe32Ci98Ni98 formula (table 1). In the i.r. spectrum of this compound, a low-frequent displacement of frequency of valence oscillation v(CN) in comparison with v(CN) frequency in the i.r. spectrum of Co2[Fe(CN)6], without change of intensity of corresponding band, takes place. The frequency of band v(Fe-C)
compared with one in the i.r. spectrum of Co2[Fe(CN)6] slightly increase and intensity of band indicated increases. The frequency of 5(Fe-CN) in comparison with one in the i.r. spectrum of Co2[Fe(CN)6] increases whereas its intensity does not change (table 1). U.v.-vis. spectral curve for compound obtained is higher than similar curves corresponding to cobalt(II)hexacyanoferrate(II) and cadmium(II)hexacyanoferrate(II), resembles in a character the curve of Cd2[Fe(CN)6] with a «splitting» of absorption maximum (fig. 3). In the Cd2[Fe(CN)6]-GIM- C0CI2 system, at the contact GIM/CoCl2 solution, the change of gelatin mass from yellowish-white to emerald-green accompanied by increase of D values with t growth; as in the Co2[Fe(CN)6]-GIM- CdCl2 system, D values become constant already at t= 2 min (fig. 2, part A) and in the future does not change.
Fig. 1 - D= f(CF, CMo, t) dependences in the Co2[Fe(CN)6]-GIM- Cd(II) system. A) In the coordinate section [CF = const, varied CMo, argument t] at CF = 0.19 (1), 0.40 (2) and 0.70 mol-dm"3 (3) for CMo= 7.0-10"2 mol-dm"3. B) In the coordinate section [CMo= const, varied t, argument CF] at CMo= 7.0-10"2 mol-dm"3, t= 6 min (1), for initial Co2[Fe(CN)6] (2) and Cd2[Fe(CN)6] (3). The optical densities were measured using a blue filter with a transmission maximum at 450 nm
D= f(CF, CMo, t) dependence for the GIM forming after t= 6 min, in coordinate sections [CMo=const, varied t, argument CF] are between the similar curves corresponding Co2[Fe(CN)6]-GIM and Cd2[Fe(CN)6]-GIM (fig. 2, part B). A chemical analysis of CoCl2 solutions contacting with Cd2[Fe(CN)6]-GIM evidenced that all these solutions contained cadmium(II) ion the quantity of which increased with D values growth. No doubt in this connection, in the system under examination complexing process accompanied by cadmium(II) ^ cobalt(II) ionic exchange takes place. When the gelatin layer formed as a result of such a contact, is destroyed by the procedure [14], the dark-green substance may be isolated. According to data of chemical analysis and X-ray fluorescence analysis, it has the a simplest Cd11Co5Fe8C48N48 formula (table 1). In the i.r. spectrum of compound obtained, a high-frequent displacement of frequency of valence oscillation v(CN) in comparison with one in the i.r. spectrum of Cd2[Fe(CN)6] without change of intensity of corresponding band, takes place. The frequency of band v(Fe-C) compared with one in the i.r. spectrum of Cd2[Fe(CN)6] slightly decreases but its intensity increases. Finally, the frequency of 5(Fe-CN) in comparison with one in the i.r. spectrum of Cd2[Fe(CN)6] decreases, its intensity slightly increase (table 1). U.v.-vis. spectral curve for compound obtained, is between similar curves
corresponding to cobalt(II)hexacyanoferrate(II) and cadmium(II)hexacyanoferrate(II), resembles in a character the curve of Co2[Fe(CN)6] (fig. 3).
The character of change of i.r. and u.v.-vis. spectra of products of processes studied evidences that a formation of novel coordination compounds but not solid solution between Co2[Fe(CN)6] and Cd2[Fe(CN)6], occurs in the systems under examination. The chemical analysis data of solutions contacting with Co2[Fe(CN)6]- and Cd2[Fe(CN)6]-GIM, shows that there is not even small concentrations of CN" -anion and products of its chemical conversion (H3N, CO, CO2 et al) in such solutions. This circumstance provides evidence synonymously that at the course of processes studied, cyanide grouping keeps without change. In this connection, ConCdmFek(CN) formula may be postulated for the substances obtained by us [n, m, k, / - positive (not necessary whole) numbers]. It is significant that even after long (t>1 hour) contact between GIM and CoCl2/CdCl2 solutions, neither iron(II) nor iron(III) ion are accumulated in these solutions even in very small concentrations. Hence, [Fe(CN)6] grouping having in the initial gelatin-immobilized Co2[Fe(CN)6] and Cd2[Fe(CN)6], is kept in substances obtained after completion of contact indicated, too. By taking into account simplest compositions of substances obtained (Co9Cd55Fe32C198N198 and Cd11Co5Fe8C48N48), formulas Co9Cd55[Fe(CN)6]32 and Cd11Co5[Fe(CN)6]8, respectively, may be proposed for them. As can be seen from all aforesaid, the compositions of final products formed in the Co2[Fe(CN)6]-GIM- CdCl2 system and Cd2[Fe(CN)6]-GIM- CoCl2 one, do not tally and, moreover, differ from each other rather sharply. It should be noted specifically that the compositions indicated are unchanged at any, plenty of long time (even during several days) of contact between corresponding metalhexacyanoferrate(II) GIM and MCl2 solution.
Fig. 2 - D= f(CF, CMo, t) dependences in the Cd2[Fe(CN)6]-GIM- Co(II) system. A) In the coordinate section [CF = const, varied CMo, argument t] at CF = 0.40 (1), 1.00 (2) and 1.90 mol-dm'3 (3) for CMo= 7.0-10'2 mol-dm'3. B) In the coordinate section [CMo= const, varied t, argument CF] at CMo= 7.0-10'2 mol-dm'3, t= 6 min (1), for initial Co2[Fe(CN)6] (2) and Cd2[Fe(CN)6] (3). The optical densities were measured using a blue filter with a transmission maximum at 450 nm
1,5
0 4----------1---------1---------- -----------1—
400 500 600 700 800
X(nm)
Fig. 3 - Spectral characteristics of GIM containing Co2[Fe(CN)6] (curve 1), Cd2[Fe(CN)6] (2), Co9Cd55[Fe(CN)6]32 (3) and Cd11Co5[Fe(CN)6]8 (4). The concentration of absorbing substance in the GIM is 0.10 mol-dm-3
Table 1 - Spectral parameters and analytical data for (CoCd)heterobinuclear hexacyanoferrates(II) prepared in the Co2[Fe(CN)6]- and Cd2[Fe(CN)6]-GIM
Complex U.v.-vis. I.r. max* Found (Calcd.) (%)
max, nm cm-1 Fe Co Cd C N
Co2[Fe(CN)6] - Cd(II) system
Co2[Fe(CN)6] 640 2090 596 472
C09Cd55[Fe(CN)6]32 630, 670 2068
600 13.9 4.1 46.0 16.7 19.4
485 (13.43) (3.92) (45.77) (17.03) (19.85)
Cd2[Fe(CN)6] - Co(II) system
Cd2[Fe(CN)6] 635, 670 2062 607 498
CdnCo5[Fe(CN)6]8 650 2076
598 13.5 9.0 38.6 18.1 20.9
480 (14.06) (9.11) (38.22) (17.82) (20.79)
* v(CN), v(Fe-C), S(Fe-CN).
As can be found easily from the data presented in the table 1, the ratio of number of cobalt atoms to number of iron atoms (n:k) for the complexing reaction product in the Co2[Fe(CN)6]-GIM- CdCl2 system is 0.28, the ratio of number of cadmium atoms to number of iron atoms (m:k) for the complexing reaction product in the Cd2[Fe(CN)6]-GIM- CoCl2 system is 1.37. These values differ sharply between itself and from value 2.00, which must be observed, if rather quickly reaching of
constant values of optical densities on D= f(t) curves with t growth (figs. 1,A and 2,A) would be caused by only process of physical sorption of cadmium(II) ions by Co2[Fe(CN)6]-GIM and cobalt(II) ions by Cd2[Fe(CN)6]-GIM. This fact is evidence that in the systems studied, cobalt(II)^cadmium(II) substitution in the crystalline lattice of Co2[Fe(CN)6] and cadmium(II)^cobalt(II) substitution in the one of Cd2[Fe(CN)6] but not a process of physical sorption, occurs.
X-ray phase analysis of substances obtained shows that each of them is one phase and has specific totality of reflexes. This fact provides evidence synonymously that in the Co2[Fe(CN)6]-GlM- CdCl2 system as well as in the Cd2[Fe(CN)6]-GIM- CoCl2 one, a formation of namely one (CdCo)heterobinuclear hexacyanoferrate(II) but not solid solutions between Co2[Fe(CN)6] and Cd2[Fe(CN)6], occurs. Also, it excludes the supposition that phenomena observed in the systems considered are connected with only sorption processes of cadmium(II) and cobalt(II) ions by corresponding hexacyanoferrates(II) (in this case, X-ray patterns of products of contact of Co2[Fe(CN)6]-GIM with CdCl2 and Cd2[Fe(CN)6]-GIM with CoCl2 practically coincide with ones of initial cobalt(II)hexacyanoferrate(II) and cadmium(II) hexacyanoferrate(II), respectively, that indeed does not occur). The data about inter-plane distances (d, A) u relative intensities of lines of reflexes (I, %) of mononuclear and both (CdCo)heterobinuclear hexacyanoferrates(II) is presented in the table 2.
Table 2 - X-ray phase analysis data for (CdCo)heteronuclear hexacyanoferrates(II) prepared in the Co2[Fe(CN)6]- and Cd2[Fe(CN)6]-GIM
Parameter Co2[Fe(CN)6] Compound Cd2[Fe(CN)6] C09Cd55[Fe(CN)6]32 Cd^Co5[Fe(CN)6]8
D, A 5,00 (69) 5,08 (80) 6.92 (67) 5.90 9)
(I, %)* 3,54 (100) 3,86 (27) 5.54 (41) 5.08 100)
2,99 (90) 3,59 (100) 5.10 (100) 4.66 (47)
2,51 (39) 3,41 (24) 3.61 (61) 3.80 35)
2,25 (6) 3,11 (6) 3.06 (12) 3.62 (86)
1,78 (14) 3,01 (11) 2.74 (10) 3.51 (7)
1,59 (18) 2,53 (43) 2.56 (35) 3.25 81)
2,27 (21) 2.28 (20) 3.18 12)
2,03 (24) 2.08 (17) 3.08 21)
1,80 (10) 1.97 (7) 2.80 16)
1,61 (13) 2.78 (44)
2.72 23)
2.55 (42)
2.49 35)
2.34 (56)
2.29 14)
2.18 12)
2.10 12)
2.05 21)
1.86 10)
1.80 11)
1.69 (40)
1.67 14)
* An intensity is given relatively of the most intensive line.
It is significantly that both (CdCo)heteronuclear hexacyanoferrates(II) are iso-structural to mononuclear cobalt(II)hexacyanoferrate(II), and there are reflexes with mainly even whole-numerical indexes (hkl) on X-ray patterns of the each of them. In this connection, it may be presumed that like initial cobalt(II)hexacyanoferrate(II), (CdCo)heteronuclear
hexacyanoferrates(II) obtained, have face-centered cubic crystalline lattice Fm3m. Unfortunately, full X-ray diffraction analysis of compounds synthesized was found to be impossible because by the method of their isolation from GIM, they were obtained as extremely small crystals unsuitable for such an analysis.
As can be shown with using the data [15], a process of full substitution Co(II)—> Cd(II) with Cd2[Fe(CN)6] formation proceeding accordingly general scheme (1) Co2[Fe(CN)6](crystal) + Cd2+ (solution) — Cd2[Fe(CN)6](crystal) + Co2+ (solution) (1) is thermodynamically possible (AG298° = -1302.1 kJ). It is noteworthy in this connection that either full substitution Co(II)—— Cd(II) in the Co2[Fe(CN)6]-CdCl2 system or full substitution Cd(II)—— Co(II) in the Cd2[Fe(CN)6]-CoCl2 system and a formation of corresponding mononuclear metal(II)hexacyanoferrate(II) does not observed. The circumstance noticed provides well-defined evidence that (CdCo)heterobinuclear hexacyanoferrates(II) forming in the systems under examination, are more stable in comparison with initial mononuclear cobalt(II)- and cadmium(II) hexacyanoferrate. It is not unexpected something; it is known a long time ago that heteronuclear metalhexacyanoferrates(II) containing alkaline metal ions and ion of any d-element M(II), as a rule, are more stable than corresponding mononuclear hexacyanoferrates(II) M2[Fe(CN)6] [9]. Moreover, high kinetic inertness of [Fe(CN)6]4- - anion is greatly conductive to formation and accumulation of heteronuclear metalhexacyanoferrates(II) at the course of complexing process into gelatin-immobilized matrix, too. It should be noted in this connection that formation of Co9Cd55[Fe(CN)6]32 and Cd11Co5[Fe(CN)6]8 is observed only in the GIM and does not occur when solutions containing CdCl2 or CoCl2, are in contact with solid phase of corresponding M2[Fe(CN)6]. This circumstance indicates the specific role of gelatin-immobilized matrix as organizing system in ionic exchange reactions studied.
Ionic exchange in the M2[Fe(CN)6]-GIM- M'Cl2 solution systems should be regarded as a specific phenomenon which can be described by a model different from used for a description of similar process in solution and solid phase. Although these are typical heterogeneous systems, ionic exchange therein with a good approximation may be considered as quasi-homogeneous since it occurs not at the solid/liquid interface (matrix/ M'Cl2 solution), but in the volume of the polymer layer of above matrix. Every such a matrix represents the totality of molecular reaction nano-volumes which is in the polymer, and the reagents of the chemical reaction enter this volume by means of diffusion from a solution that is in contact with it. The particles of the reactive substance of metalhexacyanoferrate(II) matrix can be regarded with a good approximation as coordination polymers with a relatively small molecular weight and a sufficiently regular structure that are enclosed in the voids between the polypeptide chains of gelatin molecules. Actually, ionic exchange in our case proceeds in the molecular nano-reactors. As it was shown in [6], linear size of «average» such a molecular nano-reactor assuming in to be of globular form is equal to (89.1-102.2)A, assuming a cubic form, equal to (71.8-82.4)A. No doubt, the entropy (S) of M2[Fe(CN)6]- M'Cl2 reactionary system in such a nano-reactor must be considerably lower than entropy of this system in the that case when M(II)—— M'(II) ionic exchange proceeds in the solution or solid phase. That is why, it can be expected that products of M(II)—— M'(II) ionic exchange reaction proceeding into M2[Fe(CN)6]-GIM, will be distinguished
from products of the same reaction proceeding in the solution or solid phase. Inasmuch as process of formation of (dd)heterobinuclear hexacyanoferrates(II) from mononuclear ones must be accompanied by general decrease of S values, preliminary decrease of entropy promotes a formation of compounds indicated in the course of M(II)—>М'(!1) ionic exchange in the metal(II)hexacyanoferrate(II) GIM s.
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© N. I. Naumkina - канд. геол.-мин. наук, ст. науч. сотр. Центрального научно-исследовательского института геологии нерудных ископаемых, E-mail: root@geolnerud.net; O. V. Mikhailov - д-р хим. наук, проф. каф. аналитической химии, сертификации и менеджмента качества КГТУ. E-mail: ovm@kstu.ru; T. B. Tatarintseva - канд. хим. наук, доц. каф. материаловедения КГЭУ. E-mail: ovm@kstu.ru; T. Z. Lygina - д-р геол.-мин. наук, зам. директора Центрального научноисследовательского института геологии нерудных ископаемых, E-mail: lygina@geolnerud.net.
