Crystal structure of poly[μ-aqua-bis(μ3-2-methylpropanoato-κ4O:O,O′:O′)dipotassium]

Fábry, J.; Samolová, E.

doi:10.1107/S2056989020012591

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ISSN: 2056-9890

Volume 76| Part 10| October 2020| Pages 1669-1674

https://doi.org/10.1107/S2056989020012591

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Crystal structure of poly[μ-aqua-bis(μ₃-2-methylpropanoato-κ⁴O:O,O′:O′)dipotassium]

Jan Fábry ^a ^* and Erika Samolová ^a

^aInst. of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Praha 8, Czech Republic
^*Correspondence e-mail: fabry@fzu.cz

Edited by G. Diaz de Delgado, Universidad de Los Andes, Venezuela (Received 15 May 2020; accepted 16 September 2020; online 22 September 2020)

The structure of the title compound, [K₂(C₄H₇O₂)₂(H₂O)]_n, is composed of stacked sandwiches, which are formed by cation–oxygen bilayers surrounded by methylethyl hydrophobic chains. These sandwiches are held together by van der Waals interactions between the methylethyl groups. The methylethyl groups are disordered over two positions with occupancies 0.801 (3):0.199 (3). The potassium cations are coordinated by seven O atoms, which form an irregular polyhedron. There is a water molecule, the oxygen atom of which is situated in a special position on a twofold axis (Wyckoff position 4e). The water H atoms are involved in O_water—H⋯O_carboxyl hydrogen bonds of moderate strength. These hydrogen bonds are situated within the cation–oxygen, i.e. hydrophilic, bilayer.

Keywords: methylpropanoate; metal–organic framework compounds; Cambridge Structural Database; crystal structure.

CCDC reference: 2032320

1. Chemical context

The structures of simple alkali 2-methylpropanoates (isobutyrates) have not been determined so far (as shown by a search of the Cambridge Structural Database, version 5.41, update of November 2019; Groom et al., 2016 ) . In this context, `simple' means a compound containing just one cationic species. The reason for this rather surprising fact may follow from the expected difficult crystallization (Mirnaya et al., 1991 ). Moreover, the phases of isobutyrate salts are supposedly prone to undergo phase transitions due to the ordering of voluminous hydrophobic methylethyl chains by analogy to the phase transitions observed in alkali propionates and 2-methylpropanoates (Ferloni et al., 1975 ).

The chemistry of water solutions and the corresponding solid phases of 2-methylpropanoates and other carboxylates where the number of carbon atoms is greater than two differs from that of formates and acetates. The structures and chemistry of the former compounds are also affected by hydration (Mirnaya et al., 1991). Hydration may take place because water molecules compete with the carboxylates in inclusion into the coordination sphere of the cations. Moreover, a rather tedious structure determination can be expected in alkanoates where the number of carbon atoms is greater than two because the organic chains tend to be positionally disordered and tend to exert large thermal agitation. This disorder, as well as the large displacement parameters, is related to the tendency to form different phases as pointed out above.

The structure determinations of 2-methylpropanoates as well as those of chemically related compounds with carboxylates other than the formates and acetates show that their structures share the same tendency for the separation of metal cations, carboxylate groups and sometimes water molecules on the one hand from the organic chains on the other. The former groups are hydrophilic while the latter are hydrophobic. The separation of these groups in these structures may be considered as an illustration of the alchemists' experience expressed by the slogan similis similibus solvuntur on a microstructural level. This separation also refers to solvate molecules and affects their orientation with regard to their hydrophilic and hydrophobic ends. The compound catena-[tetrakis(μ₂-isobutyrato-O,O,O′)bis(isobutyrato-O,O′)triaquadicerium ethanol solvate] (refcode XALZAN; Malaestean et al., 2012 ) can serve as an example.

Thus, the intermolecular bonds in these structures can be divided into metal–oxygen bonds, O—H⋯O hydrogen bonds and van der Waals bonds between the hydrophobic groups. The water molecules as well as the solvate molecules can be either coordinated to the cation or not while completing the hydrophilic part of the structures. At the same time, they are included into the hydrogen-bond pattern.

Correspondingly, the structures can be divided into the following classes (Table 1):

Table 1
Overview of structural types observed in isobutyrates

Compound	Refcode	Reference
Water-free clusters
1	OHOXUF	Malaestean et al. (2009 )
2	GEWFUL	Malaestean et al. (2013a )
3	NAGQUI	Coker et al. (2004 )

Clusters interconnected by water molecules
4	NAGQUI	Coker et al. (2004)

Water-free columns
5	PENJUN	Ilina et al. (1992 )
6	TAHXOR	Boyle et al. (2010)
7	TAHXOR01	Bierke & Meyer (2008 )
8	TAHXOR02	Kotal et al. (2010)

Columns interconnected by water molecules
9	MECVAU	Skelton & Deacon (2017 )
10	XALZAN	Malaestean et al. (2012)

Water-free layered structures
11	KELKOE	Skelton & Deacon (2017)
12	LUHGOK	Yuranov & Dunaeva (1989 )

Structures with layers interconnected by water molecules
13	VIQTOG	Malaestean et al. (2013b )
14	POSCIJ	Troyanov et al. (1993 )
15	SAJMUO	Fischer et al. (2017 )
Compound names, 1: bis(μ₄-oxo)dodecakis(μ₃-isobutyrato)hexakis(μ₂-isobutyrato)bis(isobutyric acid)-bis(propanol)-octa-manganese(II)-di-manganese(III) dihydrate; 2: hexakis(μ₃-isobutyrato)hexakis(μ₂-isobutyrato)hexakis(2-methylpropanoic acid)hexamanganese; 3: hexakis[bis(μ₂-2-methylpropanoato)(2-methylpropanoic acid)magnesium]; 4: bis(μ₄-oxo)dodecakis(μ₃-isobutyrato)hexakis(μ₂-isobutyrato)bis(isobutyric acid)bis(propanol)octamanganese(II)dimanganese(III) propanol solvate; 5: bis[(μ₃-isobutyrylato-O,O′)(μ₂-isobutyrylato)copper(II)]; 6: catena-[tetrakis(μ₂-2-methylpropanoato)dizinc]; 7: catena-[tetrakis(μ₂-2-methylpropanoato)dizinc]; 8: catena-[tetrakis(μ₂-2-methylpropanoato)dizinc); 9: catena-[tetrakis(μ-2-methylpropanoato)bis(2-methylpropanoato)triaquadilanthanum(III) hydrate; 10: catena-[tetrakis(μ₂-isobutyrato-O,O,O′)bis(isobutyrato-O,O′)triaquadicerium ethanol solvate]; 11: catena-[hexakis(μ-methylpropanoato)dilutetium]; 12: diaquabis(isobutyrato)dioxouranium(VI); 13: catena-[(μ₂-2-methylpropanoato)(2-methylpropanoato)triaquamagnesium monohydrate]; 14: catena-[hexakis(μ₂-isobutyrato)aquadierbium monohydrate]; 15: catena-[bis(μ-2-methylpropanoato)(μ-aqua)cobalt(II) monohydrate].

(i) Structures that are composed of clusters where the inner part is formed by hydrophilic parts while the outer skin is formed by hydrophobic groups.

(ii) Structures that are formed by columns, the interior of which is composed of the hydrophilic parts while the outer skin is hydrophobic.

(iii) Layered structures that are composed of stacked sandwiches formed by cation–oxygen bilayers surrounded by hydrophobic organic groups. These sandwiches are bonded by van der Waals forces.

In all of these structural types, water molecules can occur; examples are given in Table 1.

So far, the structures of 2-methylpropanoates (isobutyrates) have been reviewed. The motif of stacked layers, however, seems to be typical for simple alkali alkanoates M⁺C_nH_2n+1COO⁻, n > 2, as follows from the known structures of Li(C₃H₅O₂) (refcodes OMERUV, OMERUV01 and OMERUV02; Martínez Casado et al., 2009 ), and the recently determined series of structures of Na, K, Rb and Cs propanoates (Fábry & Samolová, 2020 ), Tl(C₃H₅O₂), catena-[(μ₂-propanoato)thallium(I)(propanoato)thallium(I)] (WEWKAM; Martínez Casado et al., 2010 ) and further from the structures of potassium acrylate and potassium methacrylate (refcodes VOVWOV and VOVWAH, respectively; Heyman et al., 2020 ) as well as from the known structures with alkanoates with longer organic chains, e.g. potassium palmitate KC₁₆H₃₁O₂ (KPALMA; Dumbleton & Lomer, 1965 ).

Thus, the typical motif of separated hydrophobic and hydrophilic parts of the molecules can be generalized for carboxylates other than formates and acetates.

The physical properties of 2-methylpropanoates as well as other related carboxylates C_nH_2n+1COO⁻, n > 2, hinder possible applications of these compounds, although there are some exceptions such as lanthanide zinc butyrates or their analogues, which have been applied for the synthesis of lanthanide–zinc–oxygen nanoparticles (Boyle et al., 2010 ) or for gelation induced by ultrasound in presence of ZnO nanoparticles (Kotal et al., 2010 ).

The aim of the present study was the preparation of potassium 2-methylpropanoate in order to fill the gap in the knowledge of these structures. Moreover, it was even more attractive to compare the sodium and potassium propanoate structures (Fábry & Samolová, 2020) in which the methyl groups are situated in two positions related by rotation of 180° because such a positional disorder mimics the arrangement of both methylethyl chains in 2-methylpropanoates by the demand for space. However, a crystal of a hydrated phase has been obtained, the structure of which is reported here. Still, the authors believe that this reported structure determination adds a piece of knowledge that could be helpful in understanding the structural features in simple alkali carboxylates with C_nH_2n+1COO⁻, n > 2, and related structures.

2. Structural commentary

The structural unit of the title compound is shown in Fig. 1, which shows that the central cation is surrounded by seven oxygen atoms up to ∼3.33 Å. All of the oxygens stem from the carboxylates except for the atom O3, which is a part of the coordinated water molecule. The K—O bond distances are listed in Table 2. Five of them, i.e. O2, O2ⁱⁱ, O2ⁱⁱⁱ, O3 and O3^iv, form a tetragonal pyramid with O2 as its apex. Atoms O1 and O1ⁱ complete the coordination polyhedron [symmetry codes: (i) 1 − x, y, $[{1\over 2}]$ − z; (ii) $[{3\over 2}]$ − x, − $[{1\over 2}]$ + y, $[{1\over 2}]$ − z; (iii) $[{3\over 2}]$ − x, $[{1\over 2}]$ + y, $[{1\over 2}]$ − z; (iv) x, −1 + y, z.) It is also worth mentioning that the distances between the cation and the oxygen atoms belonging to the same carboxylate are quite different: K1—O1 = 3.1113 (13) Å and K1—O2 = 2.8056 (13) Å.

Table 2
Selected bond lengths (Å)

K1—O1	3.1113 (13)	K1—O2ⁱⁱⁱ	2.7330 (12)
K1—O1ⁱ	2.6951 (14)	K1—O3^iv	3.3351 (13)
K1—O2	2.8056 (13)	K1—O3	2.7693 (12)
K1—O2ⁱⁱ	2.7360 (12)
Symmetry codes: (i) $[-x+1, y, -z+{\script{1\over 2}}]$ ; (ii) $[-x+{\script{3\over 2}}, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) $[-x+{\script{3\over 2}}, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iv) x, y-1, z.

Figure 1
A view of the structural motif in the title compound (DIAMOND; Brandenburg, 2005

): Displacement ellipsoids are shown at the 30% probability level. K, O, C and water H atoms are shown as green, red, black ellipsoids as well as gray spheres, respectively. Symmetry codes: (i) 1 − x, y, $[{1\over 2}]$ − z; (ii) $[{3\over 2}]$ − x, − $[{1\over 2}]$ + y, $[{1\over 2}]$ − z; (iii) $[{3\over 2}]$ − x, $[{1\over 2}]$ + y, $[{1\over 2}]$ − z; (iv) x, −1 + y, z.

3. Supramolecular features

The prominent feature of the title structure is the presence of an oxygen–metal bilayer, which is surrounded by methylethyl chains on both sides (Fig. 2). This bilayer is composed of the cations and the oxygen atoms.

Figure 2
The packing of the molecules in the title compound (DIAMOND; Brandenburg, 2005

) viewed along the b axis. Displacement ellipsoids are shown at the 30% probability level. The colours are assigned to the atoms are as in Fig. 1

Table 3 lists a pair of symmetry-equivalent O_water—H⋯O_carboxylate hydrogen bonds of moderate strength (Gilli & Gilli, 2009 ). These hydrogen bonds take place within the cation–oxygen bilayer (Fig. 2). Interestingly, the water hydrogen atoms, supposedly positively charged, are directed towards the more distant cation K1 [H1O3⋯K1^v and H1O3ⁱ⋯K1^v = 3.033 (19) and 3.01 (2) Å, respectively, see Fig. 3 and its caption]. This means that the positive-charge interaction diminishes a cohesive weak interaction O3⋯K1^v, the bond valence of which is 0.0385 (1) (Brese & O'Keeffe, 1991 ). Other cohesive hydrogen-bonding interactions are listed in Table 3.

Table 3
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H1O3⋯O1^v	0.83 (2)	1.92 (2)	2.7358 (17)	167 (2)
O3—H1O3ⁱ⋯O1^vi	0.83 (2)	1.92 (2)	2.7358 (17)	167 (2)
Symmetry codes: (i) $[-x+1, y, -z+{\script{1\over 2}}]$ ; (v) x, y+1, z; (vi) $[-x+1, y+1, -z+{\script{1\over 2}}]$ .

Figure 3
The structural motif showing the interaction of a water molecule to K1^v. Displacement ellipsoids are shown at the 30% probability level. The colours are assigned to the atoms are as in Fig. 1

. Symmetry codes as in Fig. 1

and (v) x, 1 + y, z.

As stated above, methylethyl chains surround the hydrophilic inner bilayer on both sides. The packing of these sandwiches forms the title structure. The sandwiches are held together by van der Waals forces. Table 4 lists these weak interactions. Their distances are about the same as those in dicalcium barium hexakis(propanoate) Ca₂Ba(C₃H₅O₂)₆ [4.05 (2) Å; Stadnicka & Glazer, 1980 ] where disorder of the ethyl groups occurs. On the other hand, these intermolecular distances are somewhat longer than in sodium and potassium propanoates, where disorder of the ethyl groups has also been observed (Fábry & Samolová, 2020). In the latter structures, the distances between two ethyl groups while one of them is in a disordered position are as short as 2.609 (8) and 2.651 (9) Å, respectively, which is an indication of a dynamic disorder: cf. the discussion about the disorder in Ca₂Ba(C₃H₅O₂)₆ by Stadnicka & Glazer (1980) according to whom the disorder is related to close C—C distances that are shorter than the sum of the van der Waals radii (about 4.5 Å). In the structurally related rubidium and caesium propanoates, however, such an occupational disorder does not take place, most probably because of the longer distances between the ethyl groups in the latter structures. The shortest C—C distances in rubidium and caesium propanoates are 3.908 (12) and 3.882 (13) Å, respectively.

Table 4
C_methylene—C_methyl and C_methyl—C_methyl intermolecular distances (Å) in the title structure of up to 4.5 Å

C2, C2a correspond to the methylene carbon atoms while C3, C3a and C4, C4a correspond to methyl atoms.

C2⋯C4^v	4.251 (6)	C3⋯C4^vi	3.992 (6)
C3⋯C4^viii	4.136 (6)	C4⋯C4^ix	3.984 (5)
C3a⋯C4a^vii	4.17 (2)	C3a⋯C4a^vi	4.25 (2)
C4a⋯C4a^ix	4.31 (2)	C2a⋯C3a^x	3.97 (2)
C2a⋯C4a^x	3.884 (19)	C2⋯C2a^v	3.960 (10)
C2⋯C4a^x	4.479 (16)	C3⋯C2a^v	4.128 (11)
C3⋯C3a^x	4.44 (2)	C3⋯C4a^vii	4.000 (15)
C3⋯C4a^vi	4.207 (15)	C4⋯C3a^x	4.48 (2)
C4⋯C3a^xi	4.087 (14)	C4⋯C3a^viii	4.43 (3)
C4⋯C4a^x	3.767 (17)	C4⋯C4a^ix	4.051 (17)
Symmetry codes: (v) x, y + 1, z; (vi) x − $[{1\over 2}]$ , y + $[{1\over 2}]$ , z; (vii) x − $[{1\over 2}]$ , y − $[{1\over 2}]$ , z; (viii) −x + 1, −y, −z; (ix) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , −z; (x) x, y − 1, z; (xi) x + $[{1\over 2}]$ , y − $[{1\over 2}]$ , z; (xii) x + $[{1\over 2}]$ , y + $[{1\over 2}]$ , z.

4. Synthesis and crystallization

Preparation of potassium 2-methylpropanoate was intended. The compound was prepared by dissolving potassium carbonate sesquihydrate (1.50 g) with 2-methylpropanoic acid (0.80 g) in the molar ratio 1:2 in water. The pH of the solution was adjusted to 6–7 by addition of several tenths of a ml of the acid.

The solution was filtered and the excess amount of water was evaporated at 313 K. Shortly before crystallization, a layer with a pronounced viscosity appeared on the surface of the solution. The crystals grew in the form of elongated colourless plates of several tenths of a mm in their longest direction.

5. Structure determination and refinement

Crystal data, data collection and structure refinement details are summarized in Table 5. The refinement was carried out on the averaged set of independent diffractions. All of the non-hydrogen atoms were determined by SHELXT (Sheldrick, 2015 ). The structure was treated with consideration of a positional disorder of the methylethyl chain. This disorder was revealed by a relatively high peak of residual electron density (0.68 e Å⁻³) in the vicinity of atom C2 (Fig. 4a), which was pertinent to a model without assumed disorder. This residual peak was on the opposite side of the vector C2—H1C2 and was observable in the difference electron-density map using a model without the atoms C2, C3 and C4 as well as without the hydrogens attached to the latter carbons. This peak was assigned to a disordered atom C2 and denoted as C2a. Correspondingly, the carbon C3 was also disordered in the difference electron-density map (Fig. 4b). Atoms C3 and C4 were split into the positions C3, C3a and C4, C4a after inclusion into the difference electron-density map.

Table 5
Experimental details

Crystal data
Chemical formula	[K₂(C₄H₇O₂)₂(H₂O)]
M_r	270.4
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	240
a, b, c (Å)	11.9190 (5), 4.5454 (2), 24.3172 (9)
β (°)	97.517 (1)
V (Å³)	1306.10 (9)
Z	4
Radiation type	Cu Kα
μ (mm⁻¹)	6.45
Crystal size (mm)	0.34 × 0.14 × 0.04

Data collection
Diffractometer	Bruker D8 VENTURE Kappa Duo PHOTON 100 CMOS
Absorption correction	Multi-scan (SADABS; Bruker, 2017 )
T_min, T_max	0.219, 0.765
No. of measured, independent and observed [I > 3σ(I)] reflections	10532, 1269, 1212
R_int	0.036
(sin θ/λ)_max (Å⁻¹)	0.618

Refinement
R[F > 3σ(F)], wR(F), S	0.028, 0.082, 2.48
No. of reflections	1269
No. of parameters	82
No. of restraints	9
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.19, −0.22
Computer programs: Instrument Service and SAINT (Bruker, 2017), SHELXT (Sheldrick, 2015), JANA2006 (Petříček et al., 2014 ) and DIAMOND (Brandenburg, 2015).

Figure 4
(a) The maximum (0.6025, 0.0146, 0.1014), which is indicated by the arrow, is in the vicinity of C2. The increment of positive (solid lines) and negative (dashed) contours are 0.1 e Å⁻³. The height of the indicated maximum is 0.33 e Å⁻³ in the depicted section. The structural model did not contain the atoms C2, C2a, C3, C3a, C4 and C4a and the attached H atoms. (b) The maximum (0.4677, 0.5409, 0.0940), which is indicated by the arrow, is in the vicinity of C3. The increment of positive (solid lines) and negative (dashed) contours are 0.1 e Å⁻³. The height of the maximum is 0.27 e Å⁻³ in the depicted section. The model did not contain the atoms C2, C2a, C3, C3a, C4 and C4a and the attached H atoms.

The occupational parameters of these pairs of atoms, as well as of the attached hydrogens, were constrained so that their sum is equal to 1; the occupational parameter of atom C4 was refined. Each pair of these carbon atoms was constrained in such a way that the atom with the minor occupancy was assigned the same displacement parameters as the atom with the major occupancy. The carboxylate carbon C1 was not split; the present model with the non-split carboxylate carbon C1 was given preference because a splitting was too small and called for severe restraints of the C1—O1 and C1—O2 distances.

The methanetriyl hydrogens H1c2 and H1c2a, although observable, were placed in calculated positions. The latter hydrogens were refined under the following constraints: C_methanetriyl—H_methanetriyl = 0.99 Å, U_iso(H_methanetriyl) = 1.2U_eq(C_methanetriyl). Subsequently, after the anisotropic refinement of the non-hydrogen atoms with the methanetriyl hydrogen, the difference electron-density map revealed the methyl hydrogens. All of the methyl hydrogens were discernible in the difference electron-density maps. The hydrogens belonging to the major disorder component were found at first and then, after the refinement had converged, the other methyl hydrogens were found and refined. The methyl hydrogens were refined under the following constraints: C_methyl—H_methyl = 0.96 Å, U_iso(H_methyl) = 1.5U_eq(C_methyl). A following difference electron-density map revealed the water hydrogen, which was situated in a general position in contrast to its carrier O3. The water hydrogen was refined using the angle restraint H1O3—O3—H1O3ⁱ [symmetry code: (i) 1 − x, y, $[{1\over 2}]$ − z] = 105.00 (1)° while U_iso(H1O3) = 1.5U_eq(O3). A trial refinement showed that the water oxygen was fully occupied. The C1—C2, C1—C2a bonds were restrained to be equal [1.540 (1) Å] as were C2—C3, C2—C3a and C2—C4, C2—C4a [1.500 (1) Å]. These values were found to yield the lowest R factors. Moreover, angle restraints to C3—C2—C4 and C3a—C2a—C4a were also applied. Of course, these C—C distances are affected by a large thermal agitation and are less reliable, as are the geometric parameters, compared to those of atom C1.

Supporting information

CCDC reference: 2032320

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989020012591/dj2009sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989020012591/dj2009Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989020012591/dj2009Isup3.smi

checkCIF report

Computing details top

Data collection: Instrument Service (Bruker, 2017); cell refinement: SAINT (Bruker, 2017); data reduction: SAINT (Bruker, 2017); program(s) used to solve structure: SHELXT (Sheldrick, 2015); program(s) used to refine structure: JANA2006 (Petříček et al., 2014); molecular graphics: DIAMOND (Brandenburg, 2015); software used to prepare material for publication: JANA2006 (Petříček et al., 2014).

Poly[µ-aqua-bis(µ₃-2-methylpropanoato-κ⁴O:O</i),O':O')dipotassium] top

Crystal data top

[K₂(C₄H₇O₂)₂(H₂O)]	F(000) = 568
M_r = 270.4	There have been used diffractions with I/σ(I)>20 for the unit cell determination.
Monoclinic, C2/c	D_x = 1.375 Mg m⁻³
Hall symbol: -C 2yc	Cu Kα radiation, λ = 1.54178 Å
a = 11.9190 (5) Å	Cell parameters from 8438 reflections
b = 4.5454 (2) Å	θ = 7.4–72.2°
c = 24.3172 (9) Å	µ = 6.45 mm⁻¹
β = 97.517 (1)°	T = 240 K
V = 1306.10 (9) Å³	Plate, colourless
Z = 4	0.34 × 0.14 × 0.04 mm

Data collection top

Bruker D8 VENTURE Kappa Duo PHOTON 100 CMOS diffractometer	1269 independent reflections
Radiation source: IµS micro-focus sealed tube	1212 reflections with I > 3σ(I)
Helios Cu multilayer optic monochromator	R_int = 0.036
φ and ω scans	θ_max = 72.2°, θ_min = 7.4°
Absorption correction: multi-scan (SADABS; Bruker, 2017)	h = −14→14
T_min = 0.219, T_max = 0.765	k = −5→5
10532 measured reflections	l = −30→30

Refinement top

Refinement on F²	94 constraints
R[F > 3σ(F)] = 0.028	Primary atom site location: dual
wR(F) = 0.082	H atoms treated by a mixture of independent and constrained refinement
S = 2.48	Weighting scheme based on measured s.u.'s w = 1/(σ²(I) + 0.0004I²)
1269 reflections	(Δ/σ)_max = 0.035
82 parameters	Δρ_max = 0.19 e Å⁻³
9 restraints	Δρ_min = −0.22 e Å⁻³

Special details top

Refinement. The reflections 2 2 0, 4 2 0, 5 1 7 and 3 3 0 were excluded from the refinement because |I_obs-I_calc|>15σ(I_obs).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
K1	0.65739 (3)	0.08834 (7)	0.292673 (13)	0.03769 (13)
O1	0.54092 (11)	−0.0749 (2)	0.17459 (5)	0.0474 (4)
O2	0.71739 (10)	0.0879 (2)	0.18489 (5)	0.0451 (4)
O3	0.5	0.5048 (4)	0.25	0.0442 (5)
H1o3	0.521 (2)	0.616 (3)	0.2262 (8)	0.0664*
C1	0.62018 (14)	0.0693 (3)	0.15869 (6)	0.0357 (4)
C2	0.59779 (18)	0.2545 (5)	0.10542 (7)	0.0445 (6)	0.801 (3)
H1c2	0.62015	0.458674	0.115969	0.0533*	0.801 (3)
C2a	0.5957 (9)	0.124 (2)	0.09573 (13)	0.0445 (6)	0.199 (3)
H1c2a	0.590888	−0.055688	0.072613	0.0533*	0.199 (3)
C3	0.4752 (2)	0.2726 (12)	0.0811 (2)	0.0828 (14)	0.801 (3)
H1c3	0.433861	0.380314	0.105886	0.1242*	0.801 (3)
H2c3	0.468892	0.371338	0.045975	0.1242*	0.801 (3)
H3c3	0.444536	0.077688	0.076086	0.1242*	0.801 (3)
C3a	0.4876 (10)	0.297 (4)	0.0912 (13)	0.0828 (14)	0.199 (3)
H1c3a	0.442774	0.254928	0.056368	0.1242*	0.199 (3)
H2c3a	0.44613	0.243332	0.120994	0.1242*	0.199 (3)
H3c3a	0.504672	0.50346	0.093401	0.1242*	0.199 (3)
C4	0.6678 (4)	0.1371 (12)	0.06307 (12)	0.1008 (19)	0.801 (3)
H1c4	0.743884	0.103888	0.080315	0.1512*	0.801 (3)
H2c4	0.635891	−0.044833	0.048302	0.1512*	0.801 (3)
H3c4	0.668259	0.277338	0.033579	0.1512*	0.801 (3)
C4a	0.6882 (11)	0.314 (4)	0.0786 (7)	0.1008 (19)	0.199 (3)
H1c4a	0.669733	0.367954	0.040336	0.1512*	0.199 (3)
H2c4a	0.695838	0.487804	0.101114	0.1512*	0.199 (3)
H3c4a	0.758165	0.20639	0.083389	0.1512*	0.199 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
K1	0.0335 (2)	0.0384 (2)	0.0413 (2)	0.00132 (11)	0.00537 (14)	0.00039 (11)
O1	0.0463 (7)	0.0488 (7)	0.0492 (7)	−0.0052 (5)	0.0138 (5)	0.0043 (5)
O2	0.0387 (6)	0.0496 (6)	0.0457 (7)	0.0038 (5)	0.0002 (5)	0.0011 (4)
O3	0.0510 (10)	0.0318 (7)	0.0490 (9)	0	0.0031 (7)	0
C1	0.0375 (8)	0.0359 (7)	0.0345 (8)	0.0047 (6)	0.0075 (6)	−0.0002 (5)
C2	0.0494 (10)	0.0422 (12)	0.0417 (10)	0.0012 (11)	0.0056 (8)	0.0081 (9)
C2a	0.0494 (10)	0.0422 (12)	0.0417 (10)	0.0012 (11)	0.0056 (8)	0.0081 (9)
C3	0.0537 (14)	0.127 (3)	0.061 (3)	0.0035 (16)	−0.0173 (15)	0.0378 (19)
C3a	0.0537 (14)	0.127 (3)	0.061 (3)	0.0035 (16)	−0.0173 (15)	0.0378 (19)
C4	0.109 (3)	0.155 (5)	0.0460 (19)	0.053 (3)	0.038 (2)	0.029 (2)
C4a	0.109 (3)	0.155 (5)	0.0460 (19)	0.053 (3)	0.038 (2)	0.029 (2)

Geometric parameters (Å, º) top

K1—O1	3.1113 (13)	C2—C4	1.505 (4)
K1—O1ⁱ	2.6951 (14)	C2a—H1c2a	0.99
K1—O2	2.8056 (13)	C2a—C4a	1.500 (18)
K1—O2ⁱⁱ	2.7360 (12)	C3—H1c3	0.96
K1—O2ⁱⁱⁱ	2.7330 (12)	C3—H2c3	0.96
K1—O3^iv	3.3351 (13)	C3—H3c3	0.96
K1—O3	2.7693 (12)	C3a—H1c3a	0.96
O1—C1	1.252 (2)	C3a—H2c3a	0.96
O2—C1	1.2499 (19)	C3a—H3c3a	0.96
O3—H1o3	0.83 (2)	C4—H1c4	0.96
O3—H1o3ⁱ	0.83 (2)	C4—H2c4	0.96
C1—C2	1.539 (2)	C4—H3c4	0.96
C1—C2a	1.541 (4)	C4a—H1c4a	0.96
C2—C3	1.505 (4)	C4a—H2c4a	0.96
C2—C3a	1.328 (13)	C4a—H3c4a	0.96

O1—K1—O1ⁱ	84.51 (4)	O2—C1—C2a	122.5 (4)
O1—K1—O2	43.54 (3)	C1—C2—H1c2	106.47
O1—K1—O2ⁱⁱ	98.72 (3)	C1—C2—C3	114.4 (2)
O1—K1—O2ⁱⁱⁱ	123.27 (4)	C1—C2—C4	109.3 (2)
O1—K1—O3^iv	50.08 (2)	H1c2—C2—C3	105.38
O1—K1—O3	67.58 (3)	H1c2—C2—C4	110.8
O1ⁱ—K1—O2	128.05 (4)	C3—C2—C4	110.4 (3)
O1ⁱ—K1—O2ⁱⁱ	100.88 (4)	H1c2a—C2a—C3a	113.92
O1ⁱ—K1—O2ⁱⁱⁱ	130.31 (4)	H1c2a—C2a—C4a	107.85
O1ⁱ—K1—O3^iv	52.67 (3)	C3a—C2a—C4a	109.5 (12)
O1ⁱ—K1—O3	73.84 (3)	C2—C3—H1c3	109.47
O2—K1—O2ⁱⁱ	89.24 (4)	C2—C3—H2c3	109.47
O2—K1—O2ⁱⁱⁱ	89.30 (4)	C2—C3—H3c3	109.47
O2—K1—O3^iv	84.87 (2)	H1c3—C3—H2c3	109.47
O2—K1—O3	83.88 (2)	H1c3—C3—H3c3	109.47
O2ⁱⁱ—K1—O2ⁱⁱⁱ	112.43 (4)	H2c3—C3—H3c3	109.47
O2ⁱⁱ—K1—O3^iv	70.78 (3)	C2a—C3a—H1c3a	109.47
O2ⁱⁱ—K1—O3	165.48 (4)	C2a—C3a—H2c3a	109.47
O2ⁱⁱⁱ—K1—O3^iv	173.34 (3)	C2a—C3a—H3c3a	109.47
O2ⁱⁱⁱ—K1—O3	80.35 (4)	H1c3a—C3a—H2c3a	109.47
O3^iv—K1—O3	95.81 (3)	H1c3a—C3a—H3c3a	109.47
K1—O1—K1ⁱ	87.96 (4)	H2c3a—C3a—H3c3a	109.47
K1—O2—K1ⁱⁱ	90.76 (4)	C2—C4—H1c4	109.47
K1—O2—K1ⁱⁱⁱ	90.70 (4)	C2—C4—H2c4	109.47
K1ⁱⁱ—O2—K1ⁱⁱⁱ	112.43 (4)	C2—C4—H3c4	109.47
K1—O3—K1^v	95.806 (12)	H1c4—C4—H2c4	109.47
K1—O3—K1ⁱ	93.77 (5)	H1c4—C4—H3c4	109.47
K1—O3—K1^vi	170.43 (4)	H2c4—C4—H3c4	109.47
K1^v—O3—K1ⁱ	170.43 (4)	H1c2—C4a—C2a	66.18
K1^v—O3—K1^vi	74.62 (3)	C2a—C4a—H1c4a	109.47
K1ⁱ—O3—K1^vi	95.806 (12)	C2a—C4a—H2c4a	109.47
H1o3—O3—H1o3ⁱ	105.0 (16)	C2a—C4a—H3c4a	109.47
O1—C1—O2	124.40 (13)	H1c4a—C4a—H2c4a	109.47
O1—C1—C2	119.45 (14)	H1c4a—C4a—H3c4a	109.47
O1—C1—C2a	109.8 (4)	H2c4a—C4a—H3c4a	109.47
O2—C1—C2	116.04 (14)

Symmetry codes: (i) −x+1, y, −z+1/2; (ii) −x+3/2, y−1/2, −z+1/2; (iii) −x+3/2, y+1/2, −z+1/2; (iv) x, y−1, z; (v) x, y+1, z; (vi) −x+1, y+1, −z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O3—H1O3···O1^v	0.83 (2)	1.92 (2)	2.7358 (17)	167 (2)
O3—H1O3ⁱ···O1^vi	0.83 (2)	1.92 (2)	2.7358 (17)	167 (2)

Symmetry codes: (i) −x+1, y, −z+1/2; (v) x, y+1, z; (vi) −x+1, y+1, −z+1/2.

Overview of structural types observed in isobutyrates top

Number	Refcode	Reference
	Water-free clusters
1	OHOXUF	Malaestean et al. (2009)
2	GEWFUL	Malaestean et al. (2013a)
3	NAGQUI	Coker et al. (2004)

	Clusters interconnected by water molecules
4	NAGQUI	Coker et al. (2004)

	Water-free columns
5	PENJUN	Ilina et al. (1992)
6	TAHXOR	Boyle et al. (2010)
7	TAHXOR01	Bierke & Meyer (2008)
8	TAHXOR02	Kotal et al. (2010)

	Columns interconnected by water molecules
9	MECVAU	Skelton & Deacon (2017)
10	XALZAN	Malaestean et al. (2012)

	Water-free layered structures
11	KELKOE	Skelton & Deacon (2017)
12	LUHGOK	Yuranov & Dunaeva (1989)

	Structures with layers interconnected by water molecules
13	VIQTOG	Malaestean et al. (2013b)
14	POSCIJ	Troyanov et al. (1993)
15	SAJMUO	Fischer et al. (2017)

Notes: 1: Bis(µ₄-oxo)dodecakis(µ₃-isobutyrato)hexakis(µ₂-isobutyrato)bis(isobutyric acid)-bis(propanol)-octa-manganese(II)-di-manganese(III) dihydrate; 2: hexakis(µ₃-isobutyrato)hexakis(µ₂-isobutyrato)hexakis(2-methylpropanoic acid)hexamanganese; 3: hexakis[bis(µ₂-2-methylpropanoato)(2-methylpropanoic acid)magnesium]; 4: bis(µ₄-oxo)dodecakis(µ₃-isobutyrato)hexakis(µ₂-isobutyrato)bis(isobutyric acid)bis(propanol)octamanganese(II)dimanganese(III) propanol solvate; 5: bis[(µ₃-isobutyrylato-O,O')(µ₂-isobutyrylato)copper(II)]; 6: catena-[tetrakis(µ₂-2-methylpropanoato)dizinc]; 7: catena-[tetrakis(µ₂-2-methylpropanoato)dizinc); 8: catena-[tetrakis(µ₂-2-methylpropanoato)dizinc); 9: catena-[tetrakis(µ-2-methylpropanoato)bis(2-methylpropanoato)triaquadilanthanum(III) hydrate; 10: catena-[tetrakis(µ₂-isobutyrato-O,O,O')bis(isobutyrato-O,O')triaquadicerium ethanol solvate]; 11: catena-[hexakis(µ-methylpropanoato)dilutetium]; 12: diaquabis(isobutyrato)dioxouranium(VI); 13] catena-[(µ₂-2-methylpropanoato)(2-methylpropanoato)triaquamagnesium monohydrate]; 14: catena-[hexakis(µ₂-isobutyrato)aquadierbium monohydrate]; 15] catena-[bis(µ-2-methylpropanoato)(µ-aqua)cobalt(II) monohydrate].

C_methylene—C_methyl and C_methyl—C_methyl intermolecular distances (Å) in the title structure of up to 4.5 Å top

C2, C2a correspond to the methylene carbon atoms while C3, C3a and C4, C4a correspond to methyl atoms.

C2···C4^v	4.251 (6)	C3···C4^vi	3.992 (6)
C3···C4^viii	4.136 (6)	C4···C4^ix	3.984 (5)
C3a···C4a^vii	4.17 (2)	C3a···C4a^vi	4.25 (2)
C4a···C4a^ix	4.31 (2)	C2a···C3a^x	3.97 (2)
C2a···C4a^x	3.884 (19)	C2···C2a^v	3.960 (10)
C2···C4a^x	4.479 (16)	C3···C2a^v	4.128 (11)
C3···C3a^x	4.44 (2)	C3···C4a^vii	4.000 (15)
C3···C4a^vi	4.207 (15)	C4···C3a^x	4.48 (2)
C4···C3a^xi	4.087 (14)	C4···C3a^viii	4.43 (3)
C4···C4a^x	3.767 (17)	C4···C4a^ix	4.051 (17)

Symmetry codes: (v) x, y + 1, z; (vi) x - 1/2, y + 1/2, z; (vii) x - 1/2, y - 1/2, z; (viii) -x + 1, -y, -z; (ix) -x + 3/2, -y + 1/2, -z; (x) x, y - 1, z; (xi) x + 1/2, y - 1/2, z; (xii) x + 1/2, y + 1/2, z.

Acknowledgements

Dr Ivana Císařová from the Faculty of Science is thanked for the generous measurement of the sample.

Funding information

The authors express their gratitude for the support provided by Project NPU I – LO1603 of the Ministry of Education of the Czech Republic to the Institute of Physics of the Academy of Sciences of the Czech Republic.

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