The chemical identity of “[Ag(py)2]MnO4” organic solvent soluble oxidizing agent and new synthetic routes for the preparation of [Ag(py)n]XO4 (X = Mn, Cl, and Re, n = 2–4) complexes

Article abstract of DOI:10.1080/00958972.2018.1493464

A widely used oxidizing agent in organic chemistry with an assumed structure of “[Ag(py)₂]MnO₄” and its perchlorate and perrhenate analogues are studied. Their synthesis in pure form is challenging. In order to clarify the chemical nature of the known compounds and find routes to new derivatives, a systematic study is presented for the synthesis of [Ag(py)_n]XO₄ (X = Mn, Cl, and Re, n = 2–4) complexes. Ten complexes including four new derivatives, [Ag(py)₄]MnO₄, [Ag(py)₄]MnO₄·4[Ag(py)₂]MnO₄, [Ag(py)₂]ClO₄·0.5 py, and [Ag(py)₂]ReO₄, are synthesized and characterized. The chemical identity of “Ag(py)₂MnO₄” is also clarified. A novel route to prepare [Ag(py)₂]MnO₄ is developed. The reaction of AgXO₄ salts with neat pyridine followed by various crystallization techniques is used to prepare [Ag(py)₂]XO₄, [Ag(py)₄]XO₄, [Ag(py)₄]XO₄·4[Ag(py)₂]XO₄, and [Ag(py)₂]XO₄·0.5py (X = Cl, Mn) complexes. The solid phase structure of [Ag(py)₂]MnO₄·0.5py is determined (a = 19.410 ?, b = 7.788 ?, c = 21.177 ?, β = 104.20°, C2/c (15), Z = 4 (3a)). [Ag(py)₂]⁺ cations in the crystal form dimeric units where silver ions are connected by oxygen atoms of two MnO₄^– anions. The Ag…Ag distance is indicative of argentophilic interactions. The pyridine ring π…π interactions contribute to the stability of the crystal lattice.

Full text of DOI:10.1080/00958972.2018.1493464

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
The chemical identity of ‘[Ag(py)2]MnO4’ organic
solvent soluble oxidizing agent and new synthetic
routes for the preparation of [Ag(py)n]XO4 (Xꢀ=ꢀMn,
Cl, Re, nꢀ=ꢀ2-4) complexes
István E. Sajó, Gréta B. Kovács, Tibor Pasinszki, Petra A. Bombicz, Zoltán
May, Imre M. Szilágyi, Anna Jánosity, Kalyan K. Banerji, Rajni Kant & László
Kótai
To cite this article: István E. Sajó, Gréta B. Kovács, Tibor Pasinszki, Petra A. Bombicz, Zoltán
May, Imre M. Szilágyi, Anna Jánosity, Kalyan K. Banerji, Rajni Kant & László Kótai (2018):
The chemical identity of ‘[Ag(py)2]MnO4’ organic solvent soluble oxidizing agent and new
synthetic routes for the preparation of [Ag(py)n]XO4 (Xꢀ=ꢀMn, Cl, Re, nꢀ=ꢀ2-4) complexes, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2018.1493464
To link to this article: https://doi.org/10.1080/00958972.2018.1493464
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The chemical identity of ‘[Ag(py)2]MnO4’ organic solvent soluble oxidizing
agent and new synthetic routes for the preparation of [Ag(py)n]XO4
(X=Mn, Cl, Re, n=2-4) complexes
ISTVÁN E. SAJÓ†, GRÉTA B. KOVÁCS‡,§ TIBOR PASINSZKI¶, PETRA A. BOMBICZ‡, ZOLTÁN MAY‡,
IMRE M. SZILÁGYI§, ANNA JÁNOSITY‡, KALYAN K. BANERJIǁ, RAJNI KANT†† and
LÁSZLÓ KÓTAI*‡,‡‡
†University of Pécs, János Szentágothai Research Centre, Ifjúság útja 20, Pécs, H-7624 Hungary
‡Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar Tudósok krt. 2.,
Budapest, H-1117 Hungary
§Budapest University of Technology and Economics, Department of Inorganic and Analytical Chemistry,
Műegyetem rakpart 3, Budapest, H-1111 Hungary
¶Fiji National University, Department of Chemistry, Faculty of Sciences, College of Engineering,
Science & Technology, Nasinu, Suva, P.O.Box 7222, Fiji Islands
ǁDepartment of Chemistry, JNV University, Jodhpur 342005, India
††X-ray Crystallography Laboratory, Department of Physics, University of Jammu, Jammu-Tawi, 180006
‡‡Deuton-X Ltd., Érd, Selmeci. u. 89., H-2030 Hungary
A widely used oxidizing agent in organic chemistry with an assumed structure of
‘[Ag(py)2]MnO4’ and its perchlorate and perrhenate analogues are studied. Their synthesis in
pure form is challenging. In order to clarify the chemical nature of the known compounds and
find routes to new derivatives, a systematic study is presented for the synthesis of [Ag(py)n]XO4
(X = Mn, Cl, Re, n = 2-4) complexes. Ten complexes including four new derivatives,
[Ag(py)4]MnO4, [Ag(py)4]MnO4·4[Ag(py)2]MnO4, [Ag(py)2]ClO4·0.5py and [Ag(py)2]ReO4,
are synthesized and characterized. The chemical identity of ‘Ag(py)2MnO4’ is also clarified. A
novel route to prepare [Ag(py)2]MnO4 is developed. The reaction of AgXO4 salts with neat
pyridine followed by various crystallization techniques is used to prepare [Ag(py)2]XO4,
[Ag(py)4]XO4, [Ag(py)4]XO4·4[Ag(py)2]XO4 and [Ag(py)2]XO4·0.5py (X = Cl, Mn) complexes.
The solid phase structure of [Ag(py)2]MnO4·0.5py is determined (a = 19.410 Å, b = 7.788 Å, c =
21.177 Å,  = 104.20°, C2/c (15), Z = 4(8)). [Ag(py)2]+ cations in the crystal form dimeric units
–
where silver ions are connected by oxygen atoms of two MnO4 anions. The Ag…Ag distance is
indicative of argentophilic interactions. The pyridine ring … interactions contribute to the
stability of the crystal lattice.
*Corresponding author. Email: kotai.laszlo@ttk.mta.hu

Keywords: Metal organic permanganates; Perchlorates; Perrhenates; Synthesis; Structure; X-ray
diffraction
Introduction
Silver permanganate (AgMnO4, 1a), silver perchlorate (AgClO4, 1b), and silver perrhenate
(AgReO4, 1c) readily dissolve in pyridine (py) with the formation of various pyridine complexes.
The available information about these complexes in the literature, however, is quite
controversial. Considering the silver ion coordination number of two or four, lattice pyridine
molecules, and mixed silver coordination numbers, six series of pyridine complexes can be
derived, [Ag(py)2]XO4 (2), [Ag(py)2]XO4·xpy (3), [Ag(py)2]XO4·y[Ag(py)4]XO4 (4),
[Ag(py)4]XO4 (5), [Ag(py)4]XO4·xpy (6) and [Ag(py)2]XO4·y[Ag(py)4]XO4·xpy (7), where X =
Mn, Cl, or Re. It is a critical question whether x and y are concrete numbers for these complexes
or varied. Out of the possible 18 complexes of these series, only six are known to date. The most
frequently synthesized compound is bis(pyridine)silver(I) permanganate ([Ag(py)2]MnO4, 2a).
Due to its solubility in polar organic solvents, it is widely used as a mild oxidizing agent in
organic synthesis [1-11]. The chemical identity of the compound used in these reactions,
however, is doubtful [12, 13]. Bis(pyridine)silver(I) perchlorate (2b) has been known since 1960
[14]. Interestingly, an intermediate complex with the formula of [Ag(py)4]ClO4·4[Ag(py)2]ClO4
(4b) ([Ag(py)2.4]ClO4) could be isolated during its synthesis [15]. The four py coordinated
tetrakis(pyridine)silver(I) perchlorate (5b) and perrhenate (5c) have been synthesized and
characterized earlier [16, 17]. Although a complex with the formula of [Ag(py)2.5]MnO4 was
described by Klobb [18], its identity as [Ag(py)2]MnO4·0.5py (3a) has not been confirmed yet.
No member of the series of 6 and 7 has been synthesized to date. The controversial and missing
literature data of [Ag(py)n]XO4·xpy complexes prompted us to perform a systematic study on the
effect of anions and synthesis conditions on the formation of these complexes in the AgXO4-py-
water, AgXO4-py-benzene, AgNO3-MXO4-py-H2O and Ag2SO4-MXO4-py-H2O systems (X =
Cl, Mn, Re; M = Na, K; n = 2-4). In this paper, we present the synthesis of 10 pure silver(I)-py
complexes and their identification based on powder X-ray diffraction (PXRD), elemental
analysis, and in a selected case on single crystal X-ray diffraction (SXRD).

Results and discussion
General considerations on the synthesis of permanganate complexes [Ag(py)n]MnO4 (n = 2-4)
(2a-5a)
Firouzabadi et al. [10] synthesized a purple material by reaction of AgNO3 with KMnO4 in dilute
aq. pyridine and declared that the elemental analysis was in agreement with the formula of the
[Ag(py)2]MnO4 (2a) complex. Unfortunately, numerical data of elemental analysis were not
provided. Repeating the published method, including the purification step by recrystallization
from acetone-benzene, however, resulted in the isolation of [Ag(py)2]MnO4·0.5py (3a)
([Ag(py)2.5]MnO4) [12, 13]. The PXRD investigation of the raw product (before
recrystallization) (Suppl. figure S1) unambiguously indicated that the precipitate contained the
compounds described by Klobb with the formulas [Ag(py)2]MnO4 and [Ag(py)2.5]MnO4 [18].
These two compounds were synthesized by reaction of silver sulfate and potassium
permanganate. The compound [Ag(py)2.5]MnO4 prepared by the Klobb [18] method, however,
was found to be isomorphic with the known complex [Ag(py)4]ClO4·4[Ag(py)2]ClO4
([Ag(py)2.4]ClO4) (4b) [15], indicating the same structure and composition for the cationic part
of these two materials. Consequently, Klobb’s formula of [Ag(py)2.5]MnO4 seems to be
incorrect. In order to clarify product composition, all previously described experiments were
repeated and our results are summarized in table 1. Product compositions were confirmed by
PXRD. As data in table 1 shows, all products based on previous methods provided mixtures of
complexes. Besides Ag:py ratio, other factors such as the cooling procedure played a key role in
the composition of the crystalline precipitates formed. The cooling rate and time were not
provided in the original articles [10, 18]. In order to isolate pure 2a, 3a and 4a, novel methods
were developed by us.
Synthesis of [Ag(py)2]MnO4 (2a)
To synthesize 2a, we prepared bis(pyridine)silver(I) nitrate first by reaction of AgNO3 with aq.
pyridine [19]. [Ag(py)2]NO3 was treated in the subsequent step with a concentrated sodium
permanganate solution and the product was crystallized using 25/0, 10/0, and 0/0 °C temperature
gradients. Pure 2a was isolated with 50-58% yields in all cases.
[Ag(py)2]NO3 + NaMnO4 → [Ag(py)2]MnO4 + NaNO3

Synthesis of [Ag(py)2]MnO4·0.5py (3a)
Recrystallizing a mixture of 2a+4a, prepared by the Firouzabadi method [10] from 1:1 acetone-
benzene (v/v), led to the formation of platelet-like crystal bunches of pure 3a and some
amorphous brown decomposition product. Since the solvent did not contain pyridine, the
decomposition of [Ag(py)4]+ cations seemed to be the source of pyridine to convert 2a to 3a
(3a is richer in pyridine than 2a). It is in line with this that the recrystallization of pure 4a from
acetone-benzene (1:1, v/v) led to the formation of a mixture of 3a and 4a in a 1:10 ratio.
Interestingly, the recrystallization of pure 2a gave a 4:1 mixture of 3a and 2a under analogous
conditions. This suggests that the main source of free pyridine to form 3a is the py ligand
dissociation from 2a. It may be also concluded that 4a is more stable in 1:1 acetone-benzene
solution than 2a. Recrystallization of the 2a:4a (1:1) mixture from a pyridine-chloroform (1:5,
v/v) solvent mixture resulted in the formation of a completely amorphous decomposition
product. It might be explained by the formation and fast decomposition of unstable 5a
([Ag(py)4]MnO4) due to high pyridine concentration ensured by the solvent mixture.
Compound 3a was grown as a bunch of platelet-like purple monoclinic single crystals.
Synthesis of [Ag(py)4]MnO4·4[Ag(py)2]MnO4 (4a) and [Ag(py)4]MnO4 (5a)
1a is well soluble in pyridine.† The solution contains tetrakis(pyridine)silver(I) and
bis(pyridine)silver(I) cations, and their ratio depends on the AgMnO4 concentration. In principle,
any of the permanganate compounds containing these cations (2a, 3a, 4a or 5a) could be
precipitated/crystallized from this solution due to equilibria between the pyridine solvent and
complex cationic species influenced by temperature and solvent composition. Accordingly, the
slow crystallization at room temperature led to pure 4a with the appearance of 5a as an
intermediate product. Cooling the saturated solution to –18 °C, however, led to 5a. Since
pyridine is a polar and aromatic solvent, it is miscible with water and benzene. Adding these co-
solvents to pyridine has great influence on the composition of the crystallized compounds.
Addition of water to the pyridine solution of AgMnO4 in 1:10 ratio (v/v) (Ag:py molar ratio =
†Freshly prepared wet silver(I) permanganate (1a) can easily and safely be dissolved in pure pyridine resulting in a
deep purple solution. Using dried or older sample of silver permanganate, however, may result in a violent flame
phenomena (silver manganese oxides (Körbl’s catalyst) [11] formed on the surface of 1a which catalyze the ignition
and combustion of pyridine). Thus, adding of solid AgMnO4 to pyridine has to be done with care.

1:50) led to pure 4a. Trituration of solid AgMnO4 with a 1:1 pyridine:water mixture gave a 4a:5a
mixture. Upon adding benzene as co-solvent to a pyridine solution of AgMnO4 in 1:1 (v/v) ratio,
pure 5a could be isolated when crystals were in contact with the mother liquor. However, 5a
transformed into 4a during evaporation of the solvent to dryness. Upon increasing the benzene
amount to 1:10 (v/v), first 5a then 4a, and finally a 2a:4a mixture (1:10) could be isolated by the
solvent evaporating process. [Ag(py)4]MnO4 (5a) was found to be a relatively unstable solid,
which easily decomposed during its isolation and analysis.
Studies on interconversion of compounds 1a-5a
Surprisingly, the behavior of neat 2a, 4a, and their mixtures was not identical during
recrystallization from acetone-benzene. The reason for these differences might be attributed to
the different Ag/py ratio in the solutions of pure compounds and mixtures. This prompted us to
study the effect of various polar solvents such as dichloromethane, benzene, and pyridine in the
recrystallization process of pure 2a and 4a, as well as 2a+4a mixtures (see table 2).
Recrystallization of either pure 2a or 4a from dichloromethane resulted in mixtures of 2a:4a in
3:1 and 1:9 ratio, respectively, which indicates that 2a and 4a can transform into each other in
this solvent (2a in 25%, 4a in 10% amount). It must be noted that the analogous perchlorate (2b)
and perrhenate (2c) salts can be recrystallized from dichloromethane without any transformation.
Recrystallization of a 2a and 4a mixture (1:1) from dichloromethane, however, gave 2a:3a =
1:30 mixture showing that 4a almost completely transformed into 3a.
Using pyridine as the solvent, the crystallization of a 1:1 mixture of 2a:4a resulted in the
transformation of 2a into 4a (1:10 mixed product was formed), while in pyridine-chloroform
(1:5, v/v) a mixture of amorphous decomposition products was obtained only. Pure 2a or 4a
crystallization in pyridine resulted in the formation of 5a, but due to the decomposition of 5a, 4a
could be isolated as the final product. Recrystallization of pure 2a from acetone-benzene (1:1,
v/v) resulted in a mixture of 3a and 4a (3a:4a = 4:1). Pure 4a behaved similarly, but produced
only small amounts of 3a (3a:4a = 1:10). Trituration of solid 4a with this solvent mixture and
with pure benzene resulted in increasing the 3a:4a ratio to 1:4 and 3:2, respectively. Gentle
heating (40 °C) caused the most remarkable effect, the 3a:4a ratio was changed to 6:1. Results of
recrystallization experiments performed with pure 2a, 4a, and their mixtures in various solvents

are summarized in table 2. The general interconversion scheme for compounds 1a-5a can be
seen in figure 1.
An unexpected result was observed during the vacuum treatment of the 2a+4a (1:1)
mixture. This treatment resulted in the formation of 4a instead of 2a. It is surprising, because the
pyridine vapor pressure above the higher coordinated tetrakis(pyridine)silver(I) complex 4a
should be higher than in the case of bis(pyridine)silver(I) compound 2a, as it was observed in the
case of 2b and 4b. It is worth noting that 2b can be prepared from 4b or 5b by vacuum treatment
[14, 20]. This uncommon behavior of 2a both in the solid phase and in solution compared to the
behavior of 2b and 2c might be attributed to the appearance of a redox reaction between part of
the pyridine ligands and permanganate ion [12, 13] with the destruction of the cation symmetry
and pyridine loss. Note that free pyridine is liberated from 2a, because only one of the pyridine
rings is oxidized [12, 13]. The low decomposition point of 2a (65 °C [18]) compared to 2b and
2c (144 °C [14] (perchlorate) and 140 °C (perrhenate), respectively) supports this hypothesis,
taking into consideration the low oxidation ability of perchlorate and perrhenate ions towards the
pyridine ring. Compound 4a decomposes almost at the same temperature as 4b (100 and 95.6 °C
[14, 21], respectively), which indicates that there is no key role for the anion in the
decomposition of 4a and 4b. The reason of this might be hidden in the different crystal packing
of 2a,b and 4a,b [15, 20].
General considerations on the synthesis of perchlorate complexes [Ag(py)n]ClO4 (n = 2-4)
(2b-5b)
There are three known pyridine-silver(I) perchlorate complexes, the bis(pyridine)silver(I)
perchlorate (2b) [14, 20], the tetrakis(pyridine)silver(I) perchlorate (5b) [16] and the mixed
complex [Ag(py)4]ClO4·4[Ag(py)2]ClO4 (4b) [15]. Compound 3b has not been synthesized
previously, and the complex [Ag(py)2.25]ClO4 [21] was proven to be identical with 4b. In order
to synthesize perchlorate complexes, we treated AgNO3 and Ag2SO4 with pyridine and NaClO4
following procedures discussed above for permanganate complexes. The products formed during
the synthesis are summarized in table 3.
Almost all reaction products of the perchlorate complex synthesis proved to be mixtures
of [Ag(py)2]ClO4 (2b), [Ag(py)2]ClO4·0.5py (3b) and [Ag(py)4]ClO4·4[Ag(py)2]ClO4 (4b).
Thus, not surprisingly, Kauffman [14] could prepare pure [Ag(py)2]ClO4 (2b) only in a three-

step process by reaction of silver nitrate with sodium perchlorate in aq. pyridine in the first step
(Ag:ClO4:py = 1:1.3:6, py/water ratio = 5/9 (v/v)), recrystallizing the primary product in the
second step, and vacuum treating the secondary product in the third step. Dyason confirmed that
the intermediate product formed in the second step (recrystallization of the primary product from
pyridine-chloroform 1:5, v/v) was the compound [Ag(py)4]ClO4·4[Ag(py)2]ClO4 (4b) [15]. Chen
et al. confirmed the importance of vacuum treatment by synthesizing [Ag(py)2]ClO4 (2b) by
dissolving AgClO4 (1b) in pyridine and evaporating the mixture to dryness [20]. Colorless
crystals of [Ag(py)4]ClO4 were also prepared by dissolving AgClO4 (1b) in pyridine and cooling
the saturated solution [16]. We repeated the work of Kauffman and our PXRD studies
unambiguously confirmed that the primary product of this reaction was a mixture of two known
and one newly isolated compounds, [Ag(py)2]ClO4 (2b), [Ag(py)4]ClO4·4[Ag(py)2]ClO4 (4b)
and [Ag(py)2]ClO4·0.5py (3b). The main product was compound 4b, while 3b was only a minor
component. The molar ratio of 4b:2b was >2:1.
Synthesis of compound [Ag(py)2]ClO4·0.5py (3b)
Complex 3b could be synthesized by triturating a 1:1 mixture of 2b and 4b with an
acetone:benzene (1:1, v/v) mixture. The separated solid phase was found to be pure 3b while the
solid product isolated from the dissolved part proved to be a mixture of 2b and 3b. This result
suggested that the free pyridine source for the formation of 3b was mainly the 4b content of the
2b+4b mixture. This is, however, in contrast to the formation of the analogous permanganate 3a,
where the pyridine source to form 3a was mainly the 2a content of the 2a+4a mixture. Similarly
to permanganates, an interchangeability of phases could be observed for perchlorates depending
on the solvent, namely the ratio of 2b and 4b could be altered in a substantial way. The formed
3b is stable in contact with the mother liquor only and slowly decomposes to 2b on drying in the
air. Compound 3b was formed only in the case of an acetone-benzene solvent mixture.
Recrystallization of the 1:1 mixture of 2b:4b from dichloromethane resulted in the enrichment of
2b (2b:4b = 2:1), while pyridine or a pyridine:chloroform (1:5) mixture led to the enrichment of
4b (2b:4b = 1:4 and 1:9, respectively). Recrystallization results are summarized in table 4.
Compound 5b could be isolated from a saturated solution of AgClO4 (1b) in pyridine by
cooling to –18 C. By allowing the solution to evaporate to dryness at room temperature,
however, only pure 2b was obtained. It is interesting to note that the crystalline phase formed

during the evaporation was a 1:2 mixture of 4b and 5b while it was in contact with the mother
liquor. This indicates that both 4b and 5b change to 2b upon standing in air at room temperature,
or in vacuum [20]. Diluting the pyridine solution of 1b with water or benzene and evaporating
these diluted solutions to dryness had a strong impact on the identity of isolated products. A 2-
and 10-fold dilution with benzene resulted in the formation of a 4b:5b (1:3) mixture and pure 5b,
respectively. Evaporation always resulted in the formation of a mixture of 2b+4b. These results
are summarized in table 5, and the interphase relationships between compounds of the AgClO4–
py–H2O system (compounds 1b-5b) are shown in figure 2.
General considerations on [Ag(py)n]ReO4 complexes and the synthesis of [Ag(py)2]ReO4
Only one pyridine complex of silver(I) perrhenate, the tetrakis(pyridine)silver(I) perrhenate,
[Ag(py)4]ReO4 (5c), was known previously. 5c was isolated from the pyridine solution of
silver(I) nitrate and perrhenic acid or ammonium perrhenate on cooling [17]. We attempted the
synthesis of novel perrhenate complexes by adopting methods used to prepare analogous
permanganates and perchlorates (2a-5a and 2b-5b). However, only one compound, the
previously unknown [Ag(py)2]ReO4 (2c), could be isolated in pure form. All of our efforts to
prepare 3c and 4c compounds led to multiphase reaction products with 2.3-3.5 pyridine/AgReO4
average pyridine content. These results are summarized in tables 6 and 7.
The recrystallization of 2c and multiphase products obtained from various solvents did
not result in pure 3c or 4c. Application of dichloromethane and acetone-benzene (1:1, v/v)
solvents yielded compound 2c, while in the case of pyridine or pyridine containing mixed
solvents (py-CHCl3 1:5), a higher pyridine containing product mixture was isolated, which
transformed back with pyridine loss into 2c on standing in air (in the dark) for several days.
Compound 5c is very unstable and loses its pyridine content very easily at room temperature.
Therefore, it has to be stored and dried for analysis under pyridine vapor atmosphere.
Comparing synthetic results of perchlorate, permanganate, and perrhenate complexes, it
can be concluded that the nature of the anion plays a key role in the composition of isolated
pyridine-silver(I) complexes. Compounds belonging to one cationic series with different anions
could be prepared only under different experimental conditions. All permanganate and
perchlorate complexes (2a,b-5a,b) were isolated in pure form, but in the case of perrhenate, only
2c and 5c compounds could be synthesized in pure form. Our efforts to isolate pure 3c and 4c

were unsuccessful, although a mixture of compounds in which the average pyridine content is
higher than the pyridine content of 2c and lower than the pyridine content of 5c could be
synthesized.
Crystal and molecular structure of compound 3a
Attempts to grow single crystals of pure, isolated compounds with appropriate size and quality
were successful in the case of compounds 3a and 2b, only. The structure of 2b at 150 K has
already been published [20]. There is no phase transition of 2b in the temperature range of 150 to
298 K proved by the unchanged cell parameters, slightly extended by the increase of the
temperature only. The main crystallographic parameters of the silver complexes are summarized
in table 8.
The purple, platelet-shaped single crystals of compound 3a were grown from acetone-
benzene (1:1) by slow evaporation of the solvents at room temperature. 3a crystallizes in the
monoclinic crystal system, space group C2/c. A crystal of 3a with the size of 0.40 × 0.30 ×
0.07 mm was measured at room temperature using MoK radiation. The atomic positions were
determined by direct methods and hydrogen atoms were placed into calculated positions [22].
Crystal data and details of the structure determination and refinement are listed in table 9, while
intermolecular interactions of 3a are presented in table 10.
There is one [Ag(py)2]MnO4·0.5py in the asymmetric unit, Z’=0.5 (figure 3). The
permanganate anion is disordered over two positions in 66:34 ratio. The Kitaigorodskii packing
–
coefficient (calculated with the main disordered positions of MnO4 ) is 67.4% [23]. The space
available for the guest pyridine is 604.5 Å3 in the unit cell, which is 19.5% of the total unit cell
volume of 3103.4 Å3. There is no additional residual solvent accessible void in the crystal lattice.
–
Two [Ag(py)2]+ cations and two MnO4 anions form a dimeric complex molecule,
–
[Ag(py)2]2(MnO4)2, where silver ions are connected by oxygen atoms of two MnO4 anions
(figure 4). In the central centrosymmetric square of Ag-O-Ag-O, the Ag…Ag distance is
3.4213(9) Å, while the Ag…O distances are 2.548(14) Å and 2.745(9) Å (figure 4a).
Cα-H(pyridine ligand)…O(permanganate) interactions support the complex formation
(table 10, figure 4b). … interactions contribute to the stability of the crystal lattice (figure 5).
The distance between the aromatic rings containing N1 and N2 is 3.740(5) Å, while the distance
between the aromatic rings containing N2 and N2, respectively, is 3.782(5) Å. The

stoichiometric ratio of the dimer [Ag(py)2]2(MnO4)2 and the solvent pyridine is 1:1. The
neighboring dimers are connected by the weak C12-H12…O3 intermolecular interaction
(table 10). The packing arrangement in the crystal of 3a, viewed from the b crystallographic axis,
is shown in figure 6.
Table 11 contains the Ag….Ag, Ag-N and the pyridine α-CH…..O(F)-X (X = central
atom of the anion) distances of some pyridine-silver complexes. These distances indicate the
strength of interactions between neighboring silver atoms and the possibilities of reaction
between the most reactive C-H group of pyridine and the anion. Argentophilic interactions must
be considered to be present in all molecular and crystal structures where two or more low-
coordinated silver cations with a [Kr]4d10 electronic configuration appear in pairs or groups with
sub van der Waals contacts between the metal atoms (shorter than 3.44) [26]. The weak forces
such as p–p stacking established between the ligands can influence the mode and strength of
aggregation and thus determine the Ag–Ag distance between the neighboring fragments. The
argentophilic interaction in 3a seems to be weaker (Ag…Ag = 3.421 Å) than in non-solvated
–
–
–
bis(pyridine)silver(I) compounds (~3 Å in the case of complexes with BF4 , PF6 and ClO4
anions). Compared to these and 3a, the Ag…Ag distance is much longer in the hydrated nitrate
compound (4.703 Å) and in 4b containing both [Ag(py)2]+ and [Ag(py)4]+ cations with
perchlorate anion (4.843 Å). There is no argentophilic interaction between [Ag(py)4]+ cations of
4b and 5b.
The Ag-N distances in compound 3a are close to those of other bis(pyridine)silver(I)
compounds, indicating only small dependence from the counter anion and presence of solvate
molecule. The distance between the most reactive ring CH and permanganate oxygen is very
similar in the listed compounds, so differences between the reactivity and stability of these
compounds might be attributed to the strong oxidizing nature of permanganate compared to
perchlorate or nitrate.
Conclusion
A series of [Ag(py)n]XO4 compounds have been isolated from AgXO4-pyridine-water, AgXO4-
pyridine-benzene, AgNO3-MXO4-py-H2O and Ag2SO4-MXO4-py-H2O systems (M = Na, K; X =
Cl, Mn, Re; n = 2-4), and reaction conditions for synthesizing pure compounds have been
presented. Ten pyridine-silver(I) complexes belonging to the [Ag(py)2]XO4,

[Ag(py)2]XO4·0.5py, [Ag(py)4]XO4·4[Ag(py)2]XO4 and [Ag(py)4]XO4 series have been
synthesized using metathesis reactions and selective precipitation. Interconversion of these
complexes during recrystallization experiments has been discussed. Co-crystallization of several
complexes is pointed out. It is observed that formation and isolation of these compounds are
strongly influenced by conditions of the synthetic procedure and crystallization parameters,
namely starting material, solvent, and crystallization temperature and gradient.
The crystal lattice parameters of three permanganate [Ag(py)2]MnO4,
[Ag(py)4]MnO4·4[Ag(py)2]MnO4, and [Ag(py)4]MnO4, one perrhenate, [Ag(py)2]ReO4, and two
perchlorate, [Ag(py)2]ClO4 and [Ag(py)2]ClO4·0.5py compounds have been determined using
PXRD. The crystal and molecular structure of [Ag(py)2]MnO4·0.5py based on SXRD
measurement is analyzed.
During the synthetic work it was learned that methods described previously in the
literature for synthesizing [Ag(py)2]MnO4 from the AgNO3-KMnO4-py-H2O or Ag2SO4-
KMnO4-py-H2O systems resulted in mixtures of compounds. Therefore, in light of the present
study we reveal that the compound used in previous synthetic reactions [1-11] as an oxidizing
agent was not pure [Ag(py)2]MnO4 as stated, but a mixture of various complexes. The chemical
activity and usefulness of pure complexes in oxidizing reactions will be clarified in future
research.
Experimental
Synthetic procedures
Caution: Perchlorate, permanganate, and nitrate salts of metal organic complexes are potentially
explosive and should be handled with great care. Reagent grade silver(I) nitrate, sodium sulfate,
sodium perrhenate, pyridine, sodium perchlorate, sodium permanganate and potassium
permanganate were supplied by Deuton-X Ltd., Hungary.
Preparation of AgXO4 (X = Mn (1a), Cl (1b) and Re (1c)) salts
Silver(I) permanganate (1a)
Silver nitrate (1.036 g, 6.10 mmol) was dissolved in ca. 5 ml of water; then this solution was
added to a 3.3 ml solution of 40% aq. NaMnO4 (d = 1.391) (30% excess to the stoichiometric
amount). The purple precipitate was separated by filtration, washed 3 times with a copious

amount of water, and finally dried in a desiccator over CaCl2. The yield was 0.87 g, 63.0%.
Elem. anal. (ICP, uncorrected): found: Ag-47.70%, Mn-25.81%; calcd. for AgMnO4:
Ag-47.55%, Mn-25.98%.
Silver(I) perchlorate (1b)
Silver nitrate (10 mmol, 1.72 g) was dissolved in 17 ml of water then mixed with 5.8 g
(20 mmol, excess) of sodium carbonate decahydrate in 10 ml H2O. The yellowish white
precipitate was washed successively 6 times with water; then the precipitate was suspended in a
minimal amount of water and dissolved in 20% aq. HClO4. The solution was filtered and
evaporated to dryness in an oven at 150 °C. The yield was 1.58 g, 76.2%. The compound is very
hygroscopic, absorbing water during weighing. Phase identity was confirmed by XRD.
Silver(I) perrhenate (1c)
The procedure given for the synthesis of silver permanganate was followed using sodium
perrhenate instead of KMnO4. A white precipitate was formed with 1.63 g (74.5%) yield. Elem.
anal.: Ag-29.45%; Re-51.71%; Calcd.: Ag-29.64%; Re-51.18%.
Attempts for the synthesis of [Ag(py)2]XO4 (X = Mn (2a), Cl (2b), Re (2c)) and
[Ag(py)2]XO4·0.5py (X = Mn (3a), Cl (3b), Re (3c))
Bis(pyridine)silver(I) permanganate (2a) and its hemipyridine solvate (3a)
a) Ag2SO4 (0.4 g, 1.28 mmol) was dissolved in 100 ml of water and a freshly prepared mixture
of 12 cm3 of 0.2 M KMnO4 and 15 cm3 of 10% aq. pyridine was added to this solution. A fine
fibrous crystalline mass was obtained immediately, and rapid cooling of the solution to +10 °C
yielded a further crop of product. The combined yield was 0.68 g. The product contained more
than one compound.
b) 2.0 g Ag2SO4 was dissolved in a mixture of 500 ml of water and 90 ml of 10% aq.
pyridine, the mixture was stirred until complete dissolution of the silver salt and cooled to
+10 °C, and a cooled (+10 °C) solution of 60 ml of 0.2 M KMnO4 was added. The reaction
mixture was cooled to 0 °C and filtered. The purple crystals obtained were dried in the dark over
pyridine containing CaCl2. The yield was 4.4 g as a mixture of products.

c) Bis(pyridine)silver(I) nitrate (0.6 gram, 1.8 mmol) was dissolved in 9 ml of water then
1.8 mmol of sodium permanganate (40% aq. soln., d = 1.391, 0.46 ml) was added at room
temperature. The mixture was cooled to 0 °C. The experiment was repeated with mixing the
reactants at +10 °C and 0 °C as well. The mixture formed by mixing the reactants at 0 °C was
kept at this temperature for 15 min to complete the crystallization process. The yields were
varied between 0.35-0.41 g (50.6-58.4%) of 2a depending on the mixing and the cooling
temperatures. Elem. anal.: Ag-28.00%, Mn-14.17%, C-30.98%, H-2.73%, N-7.11%. Calcd.: Ag-
28.05%, Mn-14.29%, C-31.17%; H-2.60%, N-7.27%. IR (ATR): aromatic C-H bands: 3103,
3070, 3039 and 3002 cm-1; pyridine ring vibrations (numbering of pyridine ring vibrations given
by [25]: 1602 (8a), 1486 (19a), 1448 (19b), 1220 (9a), 1154 (15), 1074 (18a), 1042 (12),
1015 (1), 891(5), 745 (4), 700 (11), 640 (6a), 412 (16b) cm-1; permanganate bands: νas(MnO) 919
(very strong, triplet) and νs(MnO): 830 cm-1 (weak, singlet).
d) A mixture of products (2a and 4a, ~1:1) formed in the reaction described by
Firouzabadi [8] was recrystallized from acetone-benzene (1:1, v/v) at room temperature. The
crystals of 3a were removed from the mother liquor and analyzed (CHN, ICP, single crystal
X-ray diffraction and IR spectroscopy). Elem. anal.: Ag-25.44%, Mn-12.96%, C-35.34%,
H-2.95%, N-8.25%. Calcd.: Ag-25.75%, Mn-13.21%, C-35.04%; H-2.65%, N-8.17%. IR (ATR):
aromatic C-H bands: 3102, 3067, 3038 and 3000 cm-1; pyridine ring vibrations: 1600 (8a),
1485 (19a), 1447 (19b), 1219 (9a), 1152 (15), 1070 (18a), 1041 (12), 1014 (1), 880(5), 750 (4),
697 (11), 636 (6a), 414 (16b) cm-1; permanganate bands: νas(MnO) 920-910 (very strong, triplet)
and νs(MnO): 831 cm-1 (weak, singlet).
Bis(pyridine)silver(I) perchlorate (2b) and its hemipyridine solvate (3b)
a) An equivalent amount of silver nitrate (10 mmol) dissolved in ten times of its weight distilled
water was added to a mixture of pyridine (30 mmol) and a saturated solution of sodium
perchlorate (10 mmol) in distilled water at 10 °C. The white crystalline precipitate formed was
washed with cold distilled water and then with dry benzene and Et2O several times, and dried
over anhydrous calcium chloride. Yield was 3.61 g. The product was a mixture of 2b and 4b.
The mixture was triturated with 1:1 acetone-benzene mixture at room temperature, and the solid
formed (3b) was filtered off. Yield: 1.0 g (25%). Elem. anal.: Ag-26.55%, C-36.11%, H-3.23%,
N-8.51%. Calcd: Ag-26.67%, C-37.04%, H-3.09%, N-8.64%; IR (ATR): aromatic C-H bands:

3109, 3071 and 3045 cm-1; pyridine ring vibrations (numbering of pyridine ring vibrations given
by [25]: 1603 (8a), 1488 (19a), 1447 (19b), 1222 (9a), 1155 (15), 1074 (18a), 1041 (12),
1015 (1), 750 (4), 692 (11), 638 (6a), 413 (16b) cm-1; perchlorate bands: νas(ClO) 1067-1057
(very strong, multiplet) and νs(ClO): 930 cm-1 (weak, singlet).
b) Silver(I) perchlorate (1.00 g, 5 mmol) was allowed to stir in 5 ml of pyridine
overnight. After completing the reaction, the solvent was removed completely at room
temperature in vacuum. The residue was proved by PXRD to be pure [Ag(py)2]ClO4 (2b). The
yield was 99.8%. Ag-29.57%, C-26.5%, H-2.81%, N-7.63%. Calcd.: Ag-29.54%, C-27.3%,
H-2.74%, N-7.67%. IR (ATR): aromatic C-H bands: 3113, 3080, 3049 and 3008 cm-1; pyridine
ring vibrations: 1607 (8a), 1491(19a), 1452 (19b), 1224 (9a), 1156 (15), 1046 (12), 1017 (1),
751 (4), 641 (6a), 414 (16b) cm-1; perchlorate bands: νas(ClO) 1132 (very strong,
singlet/shoulder) and νs(ClO): 945 cm-1 (weak, singlet).
Bis(pyridine)silver(I) perrhenate (2c) and its hemipyridine solvate (3c)
a) The method (a) used to prepare the analogous permanganate complex was followed, using
0.2 M aq. NaReO4 solution. On cooling the reaction mixture to 0 °C a white precipitate
appeared, which was filtered off. The yield was 0.75 g for 2c, 56.8% of the theoretical value. The
white crystals were dried in the dark over pyridine containing CaCl2. Ag-20.85%, Re-36.01%,
C-23.11%, H-2.01%, N-5.32%. Calcd.: Ag-20.93%, Re-36.07%, C-23.26%, H-1.94%, N-5.43%.
IR (ATR): aromatic C-H bands: 3043-3000 cm-1; pyridine ring vibrations (numbering of pyridine
ring vibrations given by [25]: 1601 (8a), 1483 (19a), 1450 (19b), 1223 (9a), 1149 (15),
1065 (18a), 1043 (12), 1015 (1), 875(5), 748 (4), 708 (11), 639 (6a), 425 (16b) cm-1; perrhenate
bands: νas(ReO) 952,959 (very strong) and νs(ReO): 933 cm-1 (weak, singlet).
b) The procedure (b) used to prepare the analogous permanganate complex was followed
but using a saturated solution of sodium perrhenate. A multiphase white crystalline precipitate
(4.77 g) was obtained.
c) Silver(I) perrhenate (1.00 g, 2.8 mmol) was stirred in 5 ml of pyridine overnight. After
completing the reaction, the solvent was removed at room temperature. This solid was proved to
be pure [Ag(py)2]ReO4. Recrystallization of 2c from acetone:benzene (1:1) and dichloromethane
at room temperature resulted in the formation of white crystals of the starting 2c. The expected
3c did not form at all.

Attempts to synthesize [Ag(py)4]XO4·4[Ag(py)2]XO4 (X = Mn (4a), Cl (4b), and Re (4c)
Tetrakis(pyridine)silver(I)permanganate-co-tetrakis[(bis(pyridine)silver(I) permanganate]
(4a)
a) Silver nitrate (1.72 g, 10 mmol) dissolved in 17 ml of distilled water was added to a mixture of
pyridine (30 mmol) and a saturated solution of potassium permanganate (1.60 g, 10 mmol) in
distilled water (40 ml) at 10 °C. The purple crystalline precipitate formed was washed with cold
distilled water several times, dried in air in the dark, and then dried under vacuum for 24 h. A
mixture of [Ag(py)4]MnO4·4[Ag(py)2]MnO4 and [Ag(py)2]MnO4 was formed (2.5 g).
b) 1.72 g (10 mmol) of silver nitrate was dissolved in 7 ml of water, then a mixture of
5 ml of pyridine (60 mmol) and 2.6 ml of 40% aq. solution of the sodium permanganate (d =
1.391) was added with continuous stirring. The mixture was cooled to +10 °C in an ice bath, the
purple precipitate was collected by filtration, washed thoroughly with water, then dried in air.
Yield was 3.85 g, based on PXRD analysis. The primary product was
[Ag(py)4]MnO4·4[Ag(py)2]MnO4, and only a small amount of [Ag(py)2]MnO4 was present as a
contaminant.
c) Ag2SO4 (0.4 g, 1.28 mmol) was dissolved in 100 ml of water and a freshly prepared
mixture of 12 ml of 0.2 M KMnO4 and 100 ml of 20% aq. pyridine was added to this solution. A
fine fibrous crystalline mass was obtained immediately, and rapid cooling of the solution to
+8 °C resulted in further precipitation of the product. The yield was 0.496 g, and the product was
proved to be impure (a mixture of 2a and 4a).
d) The above-mentioned synthesis has been modified. First, the pyridine was added to the
silver sulphate solution until complete dissolution of the silver salt, then the mixture was cooled
to +10 °C, and a cooled (+10 °C) solution of KMnO4 was added. A light purple fine precipitate
was formed immediately. The whole mixture was cooled to 0 °C and filtered. The purple crystals
(0.68 g, a mixture of 2a and 4a) were dried in the dark over pyridine containing CaCl2.
e) Freshly prepared silver(I) permanganate (1 g, 4.5 mmol) was allowed to stir in 18 ml
of pyridine overnight. After completing the reaction, the solvent was removed at room
temperature. When the purple mass was kept in equilibrium with the mother liquor, the isolated
product was pure 4a. The yield ws 0.85 g (47%). The evaporation of the mixture to dryness
resulted in a mixture of [Ag(py)4]MnO4·4[Ag(py)2]MnO4 and [Ag(py)4]MnO4.

f) Freshly prepared wet silver(I) permanganate (2.27 g) was dissolved in pure pyridine,
then the saturated purple solution formed was immediately diluted with water to reach a pyridine
content of 50 or 10%. A thixotropic mass and a precipitate were immediately formed,
respectively. The product formed at 10-fold dilution (H2O) was proved to be pure 4a (elem.
anal.: Ag-25.81%, Mn-13.25%, C-33.09%, H-2.98%, N-8.00%, calcd.: Ag-25.92%, Mn-13.20%,
C-34.56%, H-2.88%, N-8.07%). IR (ATR): aromatic C-H bands: 2999 and 3039 cm-1; pyridine
ring vibrations (numbering of pyridine ring vibrations given by [25]: 1592(8a), 1485 (19a),
1448 (19b), 1214 (9a), 1154 (15), 1071 (18a), 40,1033 (12), 1012 (1), 891(5), 756 (4), 707 (11),
413 (16b) cm-1; permanganate bands: νas(MnO) 909, 917 (very strong) and νs(MnO): 826 cm-1
(weak, singlet). The yield was 2.3g (55%). At two-fold dilution with water a mixture of 4a and
2a was formed.
Tetrakis(pyridine)silver(I)perchlorate-co-tetrakis[bis(pyridine)silver(I) perchlorate] (4b)
a) The procedure (a) used to prepare the analogous permanganate complex was followed but
using a solution of sodium perchlorate. On cooling the mixture to +10 °C in an ice bath, a white
precipitate (2.77 g) was isolated with 4b as the main component.
b) The procedure (c) used to prepare the analogous permanganate complex was followed
but using 0.2 M sodium perchlorate. The mixture was left at 0 °C for half an hour for
crystallization. A colorless crystalline mass appeared, which was filtered. Yield was 0.432 g
(84.7%). Ag-27.31%, C-36.01%, H-3.15%, N-8.31%. Calcd.: Ag-27.20%, C-36.26%, H-3.02%,
N-8.46%. IR (ATR): aromatic C-H bands: 3095, 3063 and 3043 cm-1; pyridine ring vibrations:
1592(8a), 1482 (19a), 1440 (19b), 1215 (9a), 1155 (15), 1079 (18a), 1034 (12), 1002 (1), 885(5),
751 (4), 700 (11), 407 (16b) cm-1; perchlorate bands: νas(ClO) 1064 (very strong) and νs(ClO):
944 cm-1 (weak, singlet).
Attempts
on
preparation
of
tetrakis(pyridine)silver(I)perrhenate-co-
tetrakis[bis(pyridine)silver(I)) perrhenate] (4c)
a) 0.86 g (5 mmol) of silver nitrate was dissolved in 3.5 ml of water, then a mixture of 2.5 ml of
pyridine and 5 mmol (1.35 g) sodium perrhenate in 2.5 ml of water was added slowly with
continuous stirring. A white precipitate formed immediately; then the mixture was cooled to

+10 °C in an ice bath. The white precipitate was collected by filtration, washed thoroughly with
water, then dried in air. The yield of multiphase product was 2.37 g.
b) Ag2SO4 (0.4 g, 1.28 mmol) was dissolved in 100 ml of water and 100 ml of a 20% aq.
pyridine solution was added to this solution with stirring until complete dissolution of the silver
salt. The solution was then cooled to +10 °C, and 12 ml of a cold (+10 °C) solution of 0.2 M
NaReO4 was added. A fluffy white precipitate formed immediately, which dissolved in seconds;
then during cooling the mixture to 0 °C a white cotton like precipitate was deposited. The white
crystalline mass was isolated by filtration and dried over pyridine containing CaO in a desiccator
placed in a refrigerator. The yield of multiphase product was 0.85 g.
[Ag(py)4]MnO4 (5a), [Ag(py)4]ClO4 (5b)
Silver(I) permanganate (2.27 g) was dissolved in pyridine, then 2-fold excess of benzene was
added. The mixture was left to crystallize, when purple crystals of 5a were formed (1.5 g,
27.6%). The crystals were dried in a refrigerator at -18 °C using a desiccator containing pyridine
and CaO. Elem. anal. Ag-16.97%, Mn-14.45%, C-35.91%, H-3.00%, N-8.35%. Calcd.:
Ag-16.59%, Mn-14.56%, C-36.87%, H-3.07%, N-8,60%. IR (ATR): aromatic C-H bands: 3056-
2999 cm-1 (wide multiplet); pyridine ring vibrations (numbering of pyridine ring vibrations given
by [25]: 1591 (8a), 1483 (19a), 1440 (19b), 1214(9a), 1152 (15), 1033 (12), 1003 (1), 885(5),
750 (4), 697 (11), 618 (6a), 411 (16b) cm-1; permanganate bands: νas(MnO) 884, 897(very
strong) and νs(MnO): 825 cm-1 (weak, singlet).
Silver(I) perchlorate (2.08 g) was dissolved until saturation in pyridine at room
temperature, then the mixture was cooled to –18 °C and left to crystallize 5b. The yield was
0.78 g, 14.9%. Elem. anal. Ag-18.01%, C-36.23%, H-3.01%, N-8.15%. Calcd.: Ag-17.10%,
C-38.00%, H-3.17%, N-8.87%. IR (ATR): aromatic C-H bands: 3062 cm-1 (wide multiplet);
pyridine ring vibrations: 1592 (8a), 1481 (19a), 1440 (19b), 1215 (9a), 1155 (15), 1035 (12),
1003 (1), 885(5), 751 (4), 700 (11), 618 (6a), 408 (16b) cm-1; perchlorate bands: νas(ClO)
1064,1078(very strong) and νs(ClO): 944 cm-1 (weak, singlet).
[Ag(py)2]NO3
30 mmol of AgNO3 (5.16 g) was dissolved in 50 ml of water, and 9 ml of pyridine was added at
room temperature. A white crystalline precipitate was deposited after several minutes and was

separated by filtration on a glass filter. The precipitate was washed with a minimum amount of
water, benzene, and diethyl ether. The yield was 4.16 g (42.2%). Its solubility in water is
4.65 g/100 g at room temperature.
Instrumental methods
The Ag, Mn and Re content of the compounds were determined by atomic emission
spectroscopy using a Spectro Genesis ICP-OES (SPECTRO Analytical Instruments GmbH,
Kleve, Germany) simultaneous spectrometer with axial plasma observation. Multielement
standard solutions for ICP (Merck Chemicals GmbH, Darmstadt, Germany) were used for
calibration. The carbon, hydrogen and nitrogen content were measured by elemental analysis
(Fisons model CHN 1018S). FT-IR spectra of solid samples were recorded in the attenuated total
reflection (ATR) mode on a Bruker Tensor 27 Platinum ATR FT-IR spectrometer at 2 cm-1
resolution between 4000 and 400 cm−1.
The components of mixtures were identified by powder X-ray diffractometry. X-ray
powder diffraction measurements were performed using a Philips PW-1050 Bragg-Brentano
parafocusing goniometer. It was equipped with a Cu tube operated at 40 kV and 35 mA tube
power, a secondary beam graphite monochromator, and a proportional counter. Scans were
recorded in step mode. Evaluation of the diffraction patterns was obtained by full profile fitting
techniques.
Single crystal diffraction intensity data were collected on an Enraf-Nonius CAD4
diffractometer (carbon monochromator; Mo-Kα radiation,  = 0.710730 Å) at 293(2) K in the
range 2.16 ≤  ≤ 23.96 [22]. A crystal of 3a was mounted on a glass fiber. Cell parameters were
determined by least-squares using 25 (10.03 ≤  ≤ 13.32) reflections. A total of 2569 reflections
were collected of which 2423 were unique [R(int) = 0.0092, R() = 0.0526]; intensities of 1303
reflections were greater than 2(I). Completeness to  = 1.000. A psi-scan absorption correction
was applied to the data (the minimum and maximum transmission factors were 0.6931 and
0.8647).
The crystal structure was solved by direct methods [22]. Anisotropic full-matrix least-
squares refinement [22] on F2 for all non-hydrogen atoms yielded R1 = 0.0451 and wR2 =
0.1143for 1332 [I>2(I)] and R1 = 0.1038 and wR2 = 0.1317 for all (2423) intensity data,
(number of parameters = 238, goodness-of-fit = 0.793, the maximum and mean shift/esd is 0.011

and 0.001). The maximum and minimum residual electron density in the final difference map
was 0.849 and -0.713 e.Å-3. The weighting scheme applied was
w
=
2
2
1/[2(Fo )+(0.10000.0000P)2+0.0000P], where P = (Fo +2Fc2)/3. Hydrogen atomic positions
were calculated from assumed geometries. Hydrogen atoms were included in structure factor
calculations but they were not refined. The isotropic displacement parameters of the hydrogen
atoms were approximated from the U(eq) value of the atom they were bonded to.
Acknowledgements
The research within project No. VEKOP-2.3.2-16-2017-00013 was supported by the European
Union and the State of Hungary, co-financed by the European Regional Development Fund.
P. Bombicz is grateful for the Hungarian Scientific Research Found (K-124544). I.M. Szilágyi
thanks for a János Bolyai Research Fellowship of the Hungarian Academy of Sciences and an
ÚNKP-17-4-IV-BME-188 grant supported by the ÚNKP-17-4-IV New National Excellence
Program of the Ministry of Human Capacities, Hungary. An NRDI K 124212 and an NRDI
TNN_16 123631 grants are acknowledged. The authors are grateful to Dr. Gyula Argay for the
crystal structure determination of 3a and Ms. Tünde Kocsis for the synthetic experiments and
PXRD measurements.
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Figure 1. The interconversion scheme for compounds 1a-5a.
Figure 2. The interconversion scheme for compounds 1b-5b.

Figure 3. ORTEP presentation of the molecular structure and atomic numbering scheme of
compound 3a. The asymmetric unit contains [Ag(py)2]MnO4 and the half of the pyridine,
arranged by a twofold axis, Z’=0.5. The displacement ellipsoids are drawn at the 30% probability
level.
Figure 4. The dimer of [Ag(py)2]2(MnO4)2. a) The Ag…O distances are indicated. b) The
Cα-H(pyridine ligand)…O(permanganate) interactions which support the complex stability are shown.

Figure 5. The … interactions formed between pyridine ligands. The distances of the ring
centroids are indicated.

Figure 6. The packing arrangement of complex molecules 3a (capped sticks) and the solvent
pyridine (ball and stick representation) viewed from the b crystallographic axis.

Table 1. The effect of reaction conditions on the composition of the reaction products (AgX: MMnO4 = 1:1;
M = K, Na; X = NO3 or 1/2SO4).
Temp.
X
M
Ag:Py molar ratio Pyridine conc., wt.%
gradient,
Product
start °C/end °C
SO4
SO4
SO4
SO4
NO3
NO3
K
K
1:50
1:50
1:100
1:100
1:3
6
25/0
10/0
25/8
10/8
10/0
10/10
2a:4a = 1:50
2a:4a = 1:2
6
K
10.5
10.5
1.25
36.5
2a:4a = 1:50
K
2a:4a = 1:100
2a:3a:4a = 10:1:10
2a:4a = 1:6
K
Na
1:6

Table 2. Compounds formed during crystallization of 2a and 4a from various
solvents.
Compound
Solvent
Product
pyridine
CH2Cl2
4a+5a*
2a+4a(3:1)
3a+4a (4:1)
4a+5a*
2a
2a
C6H6-acetone (1:1, v/v)
pyridine
2a
4a
CH2Cl2
2a+4a (1:9)
3a+4a (1:10)
3a+2a (6:1)
3a+4a (1:4)
3a+4a (3:2)
3a+2a (30:1)
3a
4a
4a
C6H6-acetone (1:1, v/v)
C6H6-acetone (1:1, v/v, heating)
C6H6-acetone (1:1, v/v, trituration)
benzene, trituration
CH2Cl2
4a
4a
4a
2a:4a (1:1)
2a:4a (1:1)
2a:4a (1:1)
C6H6-acetone (1:1, v/v)
pyridine
2a+4a (1:10)
*The 4a:5a ratio could not be determined exactly because 5a partly
decomposed during the powder X-ray measurement done at room
temperature.

Table 3. The effect of reaction conditions on the composition of the reaction products
(AgX: NaClO4 = 1:1, X=NO3 or 1/2SO4).
Ag:Py
molar ratio
Pyridine
conc., wt.%
Temp. gradient,
start °C/end °C
X
Product
SO4
SO4
NO3
NO3
1:100
1:50
1:3
10.5
6
25/0
25/25
10/10
25/10
4b
2b:4b = 1:6
1.25
36.5
2b:4b = 1:1
1:6
2b:3b:4b = 3:1:15

Table 4. Recrystallization experiments on 2b+4b (1:1) mixture with various organic solvents.
Solvent
Product
Remark
Pyridine
2b:4b (1:4)
(5b) 4b*
evaporated to dryness
mother liquor
Pyridine-CHCl3 (1:5, v/v)
Dichloromethane
2b:4b (1:9)
2b:4b (2:1)
3b
evaporated to dryness
evaporated to dryness
solid phase, trituration
C6H6-acetone (1:1, v/v)
2b:3b (1:10)
evaporation of liquid
phase/trituration
*The wet product contacted with the mother liquor was proved to be 5b which decomposes
during the XRD measurement into 4b on drying.