Versatile Reactivity of MnII Complexes in Reactions with N-Donor Heterocycles: Metamorphosis of Labile Homometallic Pivalates vs. Assembling of Endurable Heterometallic Acetates

Reaction of 2,2′-bipyridine (2,2′-bipy) or 1,10-phenantroline (phen) with [Mn(Piv)2(EtOH)]n led to the formation of binuclear complexes [Mn2(Piv)4L2] (L = 2,2′-bipy (1), phen (2); Piv− is the anion of pivalic acid). Oxidation of 1 or 2 by air oxygen resulted in the formation of tetranuclear MnII/III complexes [Mn4O2(Piv)6L2] (L = 2,2′-bipy (3), phen (4)). The hexanuclear complex [Mn6(OH)2(Piv)10(pym)4] (5) was formed in the reaction of [Mn(Piv)2(EtOH)]n with pyrimidine (pym), while oxidation of 5 produced the coordination polymer [Mn6O2(Piv)10(pym)2]n (6). Use of pyrazine (pz) instead of pyrimidine led to the 2D-coordination polymer [Mn4(OH)(Piv)7(µ2-pz)2]n (7). Interaction of [Mn(Piv)2(EtOH)]n with FeCl3 resulted in the formation of the hexanuclear complex [MnII4FeIII2O2(Piv)10(MeCN)2(HPiv)2] (8). The reactions of [MnFe2O(OAc)6(H2O)3] with 4,4′-bipyridine (4,4′-bipy) or trans-1,2-(4-pyridyl)ethylene (bpe) led to the formation of 1D-polymers [MnFe2O(OAc)6L2]n·2nDMF, where L = 4,4′-bipy (9·2DMF), bpe (10·2DMF) and [MnFe2O(OAc)6(bpe)(DMF)]n·3.5nDMF (11·3.5DMF). All complexes were characterized by single-crystal X-ray diffraction. Desolvation of 11·3.5DMF led to a collapse of the porous crystal lattice that was confirmed by PXRD and N2 sorption measurements, while alcohol adsorption led to porous structure restoration. Weak antiferromagnetic exchange was found in the case of binuclear MnII complexes (JMn-Mn = −1.03 cm−1 for 1 and 2). According to magnetic data analysis (JMn-Mn = −(2.69 ÷ 0.42) cm−1) and DFT calculations (JMn-Mn = −(6.9 ÷ 0.9) cm−1) weak antiferromagnetic coupling between MnII ions also occurred in the tetranuclear {Mn4(OH)(Piv)7} unit of the 2D polymer 7. In contrast, strong antiferromagnetic coupling was found in oxo-bridged trinuclear fragment {MnFe2O(OAc)6} in 11·3.5DMF (JFe-Fe = −57.8 cm−1, JFe-Mn = −20.12 cm−1).

In this work manganese complexes were chosen as the objects of research due to some specific features of this ion, which are manifested in the reactivity of its polynuclear complexes [25,26]. The reasons for such differences include the wide range of stable oxidation states of manganese with low energy barriers for redox-transformations [36,37], as well as, in the case of Mn II , the relatively high kinetic lability of this ion [36]. The additional reasons for interest to homo-and heterometallic manganese complexes is that such species have found applications as building blocks for the synthesis of single-molecule magnets [9,15,38] or various coordination polymers capable of absorbing guest molecules [39,40]. It is also known that molecular manganese compounds can oligomerize upon crystallization during solvent changes, giving rise to complexes with higher nuclearity [9,26,26].
Previously reported carboxylate complexes of transition metals ions formed polymeric compounds with pyrimidine [50], so the formation of the molecular complex 5 is uncommon. At the same time, the formation of the mixed valence hexanuclear fragment {Mn II 4Mn III 2(µ4-O)2(Piv)10} is similar to that in 5 and quite typical, for example, oxidation of [Mn(Piv)2(EtOH)]n (the same starting compound as in formation of 5) by air led to [Mn II 4Mn III 2(µ4-O)2(Piv)10(HPiv)(EtOH)3] [51]; a similar hexanuclear Mn6 core was found in polymeric compounds [40,52]. Introduction of pyrimidine ligands resulted in formation of new coordination polymers.
The use of pyrazine (pz) instead of pyrimidine in the reaction with [Mn(Piv)2(EtOH)]n in MeCN under an argon atmosphere led to the formation of the 2D-coordination polymer [Mn4(OH)(Piv)7(µ2-pz)2]n (7). This complex was stable in air and was not soluble in MeCN, and this reason probable precluding oxidation of Mn II . Pyrazine is a quite typical bridging ligand in the chemistry of manganese, forming polymers with Mn II carboxylates [53,54], as well as with the mixed-valence hexanuclear fragment {Mn II 4Mn III 2(µ4-O)2(O2CR)10} [54][55][56]. From an analysis of literature, as well as from the results of this study it can be noted that the tetranuclear unit {Mn II 2Mn III 2O2(O2CR)6} usually forms in the presence of chelating ligands, such as 2,2′-bipy and phen, while the hexanuclear unit {Mn II 4Mn III 2O2(O2CR)10} is produced in reactions with monodentate N-donor ligands or in the absence of such ligands.
The synthesis of compounds 9-11 was based on substitution of coordinated water molecules in [Fe2MnO(OAc)6(H2O)3] by 4,4′-bipyridine (4,4′-bipy) or 1,2-trans-(4pyridyl)ethene (bpe). In compounds 9 and 10 all vacancies in the coordination spheres of the metal ions are filled by the nitrogen atoms of 4,4′-bipy or bpe ligands, while 4,4′-bipy or bpe molecules act both as bridging and non-bridging (capping) ligands, as will be described in details in the X-ray structures description (vide infra). In compound 11 all bpe molecules link trinuclear blocks but only two of three possible "vacant" positions in the coordination spheres of metal ions are occupied by a pyridine group of bpe; the third position is filled by DMF.

Crystal and Molecular Structures
The crystal structures of molecular complexes 1-5, 8 and coordination polymers 6, 7, 9-11 were determined by single crystal X-ray analysis.
The aromatic rings of 2,2′-bipy ligands of the neighboring molecules in 1 are not parallel, and the angle between the mean planes of these molecules is 7.6(3)°. The closest distance between centroids of pairs rings of different 2,2′-bipy ligands is 3.591(4) Å (the slippage is 0.707 Å). This leads to the formation of a supramolecular chain along the c axis (Figure 3b), probably due to π-stacking interactions. The aromatic rings of two phen ligands in one molecule of 2 are not parallel, and the angle between the mean planes of these molecules is 9.8(2)°. The closest distance between centroids of pairs rings (N2C18-C22, C14-C19), belonging to these different phen ligands, is 3.695(4) Å (the slippage is 1.055 Å). The mean planes of phen ligands from the neighboring different molecules of 2 are parallel and the centroids of these pairs of phen rings are located in 3.730(4) Å (the slippage is 1.561 Å). Such an arrangement of aromatic phen molecules can allow for π-stacking interactions between them and as a result formation of a supramolecular pile structure along the c axis ( Figure 3c). However, it cannot be excluded that intramolecular π-stacking between phen molecules in 2 may be the reason for the difference between structures of this compound and 1: the 2,2′-bipy molecules in 1 are located on different sides in respect to the inversion center, located between the Mn II ions.

Compounds 3 and 4
The molecules of compounds 3 and 4 are centrosymmetric (an inversion center lies between the central metal ions) and possess a similar tetranuclear Mn4O2(Piv)6 core (Figure 3a) of a "butterfly" type, which is quite typical for Mn carboxylates [63][64][65][66]. Each Mn III ion in the center of the butterfly is located in a square pyramidal coordination polyhedron (MnO5 chromofore, τ = 0.15 [63][64][65][66]   . , The molecular structure of 3 ((a), atoms with an additional character in the atom labels are at (-x, 1-y, 1-z)), intra-(only for 2) and intermolecular (for 1 and 2) π-stacking interaction and formation of supramolecular chain structure in crystal lattices of 1 (a) and 2 (b) (H atoms at carbon atoms and methyl groups of pivalate ions are omitted for clarity, (c) the displacement ellipsoids are drawn at the 30% probability level).

Compound 5
Compound 5 crystallizes in the monoclinic space group P21/n as a discrete centrosymmetric hexanuclear complex (the inversion center lies between the central metal ions Mn2, Mn3, Mn2A and Mn3A). The hexanuclear core of 5 can be considered as two identical triangular fragments {Mn3(OH)(Piv)3(pym)2} linked by four carboxylic acid groups (two µ2-Piv and two µ3-Piv) (Figure 4a). In each trinuclear fragment Mn II ions are linked by µ3-OH (bond lengths Mn-O are equal to 2.049(2)-2.184(2) Å), and the O atom is located on 0.66(2) Å above the Mn1Mn2Mn3 plane, which can be an additional proof that the central oxygen atom belongs to a µ3-hydroxo group rather than a µ3-oxo (Mn3(µ3-O) unit that is expected to be planar [67][68][69][70]). One µ-O2C bridging group links Mn1 and Mn2, and two µ2-O2C groups link Mn1 with Mn3 (bond lengths Mn-O(Piv) and lie in the 2.095(3)-2.142(3) Å) range. In addition to the oxygen atoms of carboxylate groups, the nitrogen atoms of two pyrimidine molecules are coordinated to Mn1, completing its coordination polyhedron to form a distorted octahedron

Compound 6
This compound crystallizes as a 1D polymer in the space group Pn, in which hexanuclear units {Mn II 4Mn III 2O2(Piv)10} are linked by pyrimidine bridges (Figure 4b). Generally, the structure of the Mn6 core in 6 is similar to that of the hexanuclear units observed in [M II 4M III 2(O)2(O2CR)10(L)4] complexes, where L is a neutral N-or O-donor ligands [71][72][73][74] with the difference that one Mn4 atom in 6 possesses coordination number four and is located in a coordination polyhedron, close to a distorted square-pyramid (τ = 0.12) [75].   . H atoms at carbon atoms and methyl groups of pivalate ions are omitted for clarity, the displacement ellipsoids are drawn at the 30% probability level.

Compounds 9-11
Coordination polymers 9-11 are built by linking a neutral trinuclear block, {Fe2MnO(OAc)6}, with neutral pyridine-containing bridges. The structure of the {Fe2MnO(OAc)6} unit in all these complexes is almost the same (such unit in compound 9 is shown on Figure 7 as example). In this block three metal ions (two Fe III and Mn II ) are located in the corners of an irregular triangle and generally cannot be distinguished by Xray crystallography, so the assignment of metal ions was arbitrary. These metal ions are linked by µ3-O atoms and six bridging acetates, so oxygen donors occupy five positions in the coordination sphere of each metal ion. The sixth positions are taken up by a donor atom (N or O) from other ligands (4,4′-bipy, bpe or DMF), so that each metal ion is located in a distorted octahedral donor set.
The twofold axis passes through µ3-O atoms of trinuclear blocks B and C. Also the local inversion centers are located between the pyridine groups of 4,4′-bipy molecules which bind two A type trinuclear blocks. The crystal lattice of 9 does not contain continuous channels (see Figure S2, Supporting Information).

Complexes 10 and 11
These are built from trinuclear units {Fe2MnO(OAc)6} bound by bpe molecules ( Figure  10a). Two metal ions in each trinuclear block coordinate with pyridine rings from bridging bpe, leading to 1D-chain formation. The third metal ion is bound to a nitrogen atom of a terminal (non-bridging) bpe in 10 or oxygen atom of coordinated DMF in 11 (Figure 10b).
Chains of compound 10 are parallel and directed along the a-½b vector. The noncoordinated pyridine ring of bpe in one chain and the pyridine ring of a bridging bpe ligand from the neighboring chain are almost parallel (the angle between mean planes of these rings is 4.1(5)°), and the closest distance between these rings is 3.38(2) Å (the distance between centroids of the rings is 3.634(6) Å), the slippage is 1.179 Å, which can allow for π-interactions (Figure 11a). Chains of compound 11 are also parallel and directed along the c vector ( Figure 11). No specific interactions between different chains are found. Due to this peculiarities of the chain packing channels of dimensions 5 × 12 Å directed along the a axis form in the crystal lattice ( Figure 12). Estimation of solvent-accessible volume, performed by PLATON software [76], gives a value of 36% for 11, containing DMF molecules coordinated to metal ions, or 45% for a structure, if coordinated DMF is removed assuming that such removal does not lead to crystal lattice collapse (calculated for a probe molecule with r = 1.4 Å). These values correspond to ca. 0.32 cm 3 g -1 pore volume, occupied by solvent in 11, assuming that the volume occupied by coordinated DMF is not included in this value, or 0.40 cm 3 g -1 , if the volume of coordinated DMF is included.

Thermal Stability and Sorption Properties of 11·3.5DMF
The thermal stability of 11·3.5DMF was studied by thermogravimetry. Upon heating to 275 °C, compound 11·3.5DMF lost 26% of its weight, which corresponds to the release of both non-coordinated and coordinated solvent ( Figure 13). An abrupt weight loss began at 275 °C, which was completed at 400 °C and could be associated with decomposition of the compound. The total weight loss was equal to 76.6% and corresponded to the formation of Fe2O3·1/3Mn3O4 (Figure 13a). Loss of solvent and coordinated DMF led to significant lattice disorder, as it can be concluded by comparison of the powder XRD pattern of vacuum-dried product at 145 °C and the powder XRD pattern, calculated from the single-crystal structure (Figure 13b).  For sorption experiments compound 11·3.5DMF was heated in vacuum at 153 °C during 6 h, which led to removal of non-coordinated and coordinated DMF. The desolvated sample is hereinafter referred to as 11′.
Compound 11′ showed only surface sorption of N2 or H2 at 78 K, which is evidence of crystal lattice collapse and is consistent with the powder XRD data. In contrast, 11′ absorbed significant quantities of methanol and ethanol at 298 K (Figure 14). Such a difference between absorption of gases and alcohols can be caused by expansion of crystal lattice of 11′ upon interaction with methanol and ethanol, similarly to reported gate-opening phenomena [77] and previously reported cases of alcohol absorption by coordination polymers [18]. Both in the cases of methanol and ethanol, the sorption capacity gradually increased to ca. 0.42 cm 3 ·g −1 (methanol) or 0.35 cm 3 ·g −1 (ethanol), which is in good agreement with the value of solvent-accessible volume estimated from the crystallographic data (vide supra).
The plateau in the methanol absorption isotherm at PPS −1 ca. 0.07-0.3 (Vabs. about 0.05 cm 3 g −1 ) corresponds to a methanol to Fe2Mn molar ratio 1:1 and can be associated with methanol coordination to the metal ion (in a position which was occupied by coordinated DMF in 11). It can be concluded from the presence of such a plateau that there is a noticeable difference between the energy of methanol coordination to a metal ion in 11′ and the energy of further methanol interaction with 11′·CH3OH. In contrast, a similar plateau was not found in the ethanol absorption isotherm: ethanol binding by 11′ after filling of unsaturated metal sites seems to be as efficient as ethanol binding due to its coordination (which most probably does occur). Anyhow, the maximal achieved sorption capacity of 11′ corresponds to ca. 10.5 moles of methanol or ca. 5 moles of ethanol per 1 mole of Fe2Mn, which is significantly higher than the sorption capacity associated with coordination.

EPR Spectroscopy
X-band EPR experiments for polycrystalline samples 1 and 2 were performed at 293 K. The spectra of 1 and 2 show an intense singlet without hyperfine structure with g ≈ 2.00. In the low magnetic field lines of low intensity are observed; their origin can be explained by the exchange interactions between paramagnetic manganese ions ( Figure 15).   Since antiferromagnetic interactions with J = −1.03 cm −1 were found in 1 and 2 by magnetic data analysis (see below), all possible magnetic states of dimer of two Mn 2+ ions with spins S1,2 = 5/2, notably, S = 0, 1, 2, 3, 4, 5 (S = S1 + S2) were equally populated. Furthermore, since |J| > hν ≈ 0.3 cm −1 , transitions between states with different total spin S can be neglected. Thus, the spin Hamiltonian for 1 and 2 is the sum of spin Hamiltonians of five dimers with different total spins. The spin Hamiltonian (1) for single ion in 1 or 2 has a rhombic symmetry: where giz, gix, giy-z, x, y-g-tensor components of monomer i, where i = 1, 2; Siz, Six, Siyprojections of spin operator of monomer on coordinate axes, Si = 5/2; di, ei-component of fine interaction tensor (so-called, single-ion). Mn 2+ ion has half-filled d 5 shell and S-state, so g-tensor is isotropic and close to spin-only value, so, giz =gix = giy = g=2.0023.
Spin Hamiltonian (2) of dimer is the sum of two Hamiltonians for interactions within mononuclear fragments of molecule and the part of their interaction: where d12, e12 are the components of fine interaction tensor, caused by dipole interaction of manganese ions.
For the total spin of dimer and neglecting of transitions between multiplets with different total spin S = S1 + S2, spin Hamiltonian (3) can be used: where D and E are the components of fine interaction tensor, associated with parameters d1,2, e1,2, d12 и e12 by the following formula [78]: The spin Hamiltonian (3) was diagonalized numerically. Calculations of resonance fields of spin Hamiltonian (3) required to build a theoretical spectrum were carried out by the Belford method [79], which involves finding the values of magnetic field H, for which two eigenvalues of spin Hamiltonian (3) matrix, corresponding to two different eigenvectors, would differ on the hν.
The spin Hamiltonian parameters for compounds 1 and 2 are given in Table 1. Thus, while isotropic exchange of two dimers is same, fine interaction tensor causes a noticeable difference in the EPR spectra.

Magnetic Properties of Complexes 1 and 2
For both compounds χMT values (here and below χM is the magnetic susceptibility per formula unit and T is the temperature in K) monotonously decrease upon lowering the temperature from 8.17 (for 1) or 8.64 (for 2) cm 3 ·K·mole −1 at 300 K to 7.81 (for 1 at 60 K) or 7.74 (for 2 at 68 K) cm 3 ·K·mole −1 , after which it falls sharply to 4.01 (for 1 at 5 K) or 0.82 (for 2 at 2 K) cm 3 ·K·mole −1 . Room-temperature values of χMT are close to the expected spinonly value (8.75 cm 3 ·K·mole −1 for a system with two non interacting magnetic centers with S = 5/2).
The spin Hamiltonian for dinuclear blocks Mn2 in 1 and 2 is shown as Equation (5).
where the first summand corresponds to the superexchange interactions between Heisenberg spins localized at metal sites (JMn-Mn), and the second summand corresponds to the isotropic interactions between local spins and the external field through Zeeman interactions [80].
It should be noted that the spin-Hamiltonian proposed for interpretation of the magnetic properties differed from the one employed for interpretation of the EPR spectra of the same compounds. There was no contradiction between these Hamiltonians, as both of them were "partial" variations of the complete spin-Hamiltonian describing the system of the unpaired electron within the species of the compounds. This complete spin-Hamiltonian had to include all the terms: (i) Zeeman interactions with the external magnetic field; (ii) exchange interactions between the ions; (iii) zero-field splitting. However, the variations of exchange interaction parameters could not notably influence the studied EPR spectra (vide supra), while the influence of zero-field splitting on the magnetization curves was negligible compared to the influence of the exchange interactions. Thus, introduction of the corresponding terms into the spin-Hamiltonians and efforts to extract the corresponding parameters from the data simulations would not produce any reliable values. Regarding Zeeman interactions, their principal parameters-g-factors-were consistent (within accuracy of the methods) for the EPR and magnetochemical data.
Temperature-independent paramagnetism (tip) term was also introduced. Intermolecular interactions were taken into account within molecular field model (zJ' term).
Analytical expression for the χMT values for the Mn2 unit [80] is the following: Absolute values of JMn-Mn for 1 and 2 are higher than those reported for benzoato-and phtalato-bridged dinuclear blocks Mn2(µ-O2C)2(η-O2C)2 [81,82], which is consistent with the higher electron-donating ability of the tert-butyl groups in pivalates compared to phenyl group.

Magnetic Properties of Complex 7 ·2MeCN.
For the compound 7 2MeCN the χMT value monotonically decreases upon lowering the temperature from 15.78 cm 3 ·K·mole -1 at 300 K to 0.53 cm 3 ·K·mole −1 at 3 K. The roomtemperature value of χMT is lower than the expected spin-only value (17.5 cm 3 ·K·mole −1 for a system with four non-interacting magnetic centers with S = 5/2). The coupling scheme within a tetranuclear unit is presented in Figure 17. The spin Hamiltonian for tetranuclear block Mn4 takes the form: where the first five summands correspond to the superexchange interactions between Heisenberg spins localized at metal sites (J1-J5), and the last summand corresponds to the isotropic interactions between local spins and the external field through Zeeman interactions (gMn), respectively [80]. A temperature-independent paramagnetism (tip) term was also introduced. Calculation of the exchange coupling parameters were performed by full-matrix diagonalization using the Mjöllnir software [16,83]. Uncertainty values of simulation parameters were estimated as described previously [33]. Briefly, digits in brackets indicated deviation of the value, which caused 10% increase of R 2 .
The best correspondence between experimental and calculated χMT values for compound 7 was achieved for the parameters J1 =  Exchange coupling parameters have larger values for magnetic interactions of Mn1 ion with Mn2 and Mn3 which agree with the structural data: the Mn1 ion has in its coordination sphere two N atoms from two pyrazine molecules which increase its electron density and amplify the antiferromagnetic interactions. Additionally, the most effective way of magnetic interactions transfer through the OH group in the trinuclear Mn1Mn2Mn3 unit which also agrees with the received data.
The Mn4 units can be selected in the 2D-coordination polymer [Mn4(µ3-OH)(Piv)7(µpz)2]n, and exchange coupling within these units can be presented by five integrals J1-J5 ( Figure 17). From the experimental χMT vs. T curve the following values could be calculated by full-matrix diagonalization (performed using the Mjöllnir software [16,83] It should be noted that fitting of the χMT vs. T curve for 7 2MeCN could be fitted with simpler Hamiltonian (8): with J1 = −2.08 ± 0.02 cm -1 , J2 = −3.92 ± 0.07 cm −1 , g = 2 (fixed), however there are no reasons to neglect interactions between other Mn II ions, since structural features of the bridges between them are similar. The χMT vs. T curve calculated with these parameters is visually the same as shown on Figure 17.

Magnetic Properties of Complex 11·3.5DMF
For compound 11·3.5DMF, the value of χMT at 300 K was 4.66 cm 3 ·K·mol −1 , which is significantly lower than the expected spin-only value for three non-interacting spins 5/2 (13.125 cm 3 ·K·mol −1 ). On cooling, the χMT vs. T curve decreased monotonically to 3.20 cm 3 ·K/mol at 50 K, after which it sharply fell to 2.08 cm 3 ·K·mol −1 at 2 K.
The coupling scheme within a trinuclear unit is represented on Figure 18. The spin Hamiltonian for trinuclear blocks Fe2Mn takes the form: where first line corresponds to the superexchange interactions between Heisenberg spins localized at metal sites (JFe-Fe and JFe-Mn), the second line corresponds to the isotropic interactions between local spins and the external field through Zeeman interactions (gFe and gMn), respectively [80]. Intermolecular interactions were taken into account within molecular field model.  [31], which is consistent with the higher electron-donating ability of the methyl group in acetate relative to CF3-group. However, for {Fe2MnO(Piv)6} blocks exchange coupling parameters [58] have close values to exchange coupling parameters for 11·3.5DMF. It can be explained by different nitrogen ligands: pyridine group in 11·3.5DMF in comparison with hexamethylenetetramine [58] compensates lower electron donor efficiency of acetate group in comparison with pivalate group [84].

Materials and Methods
Reagents and solvents were commercially available (Sigma-Aldrich, Aldrich, St. Louis, MO, USA) and were used without further purification. Manganese pivalate [Mn(Piv)2(EtOH)]n and trinuclear acetate [MnFe2O(OAc)6(H2O)3], used as starting compound, were prepared as previously reported [30,51]. C,H,N-analyses were performed using a 1106 instrument (Carlo Erba, Instruments, Egelsbach, Germany). IR-spectra were measured in KBr pellets on a Spectrum BX FT-IR spectrometer (Perkin Elmer, Waltham, MA, USA) in 400-4000 cm −1 range. The X-ray powder diffraction analysis of 6 was carried out on a G670 (HUBER, Offenburg, Germany) Guinier camera using CuKα1 radiation on air. The X-ray powder diffraction analysis of 11 was performed on a D8 Advance instrument (Bruker, Billerica, MA, USA) in air.
Thermogravimetric analyses (TGA) were performed in air on Q1500 instrument, (Paulik-Paulik-Erdey, Budapest, Hungary). The heating rate was 5 °C per minute. Sorption of methanol and ethanol by [MnFe2O(OAc)6(dpe)] was studied gravimetrically, using a tungsten microbalance at 293 K. Each point on the absorption and desorption isotherms corresponds to equilibrium conditions (no change of sample weight at certain p·pS −1 , where pS is the pressure of saturated vapor of the compound at 293 K). This sample was thermally activated at 150 °C in vacuum at 10 −2 Torr. Volume of pores was estimated from the quantity of adsorbed alcohol using its density in liquid phase at 293 K.
Magnetic measurements were performed on a MPMS-XL (for 11), MPMS-5S (for 7) and PPMS (for 1 and 2) SQUID magnetometers (Quantum Design, San Diego, CA, USA) and intrinsic diamagnetic corrections were calculated using Pascal's constants [80]. The X-band EPR spectra for 1 and 2 were measured on a Bruker Elexsys E680-X spectrometer at T = 293 K.

X-ray Structure Determination
For X-ray structure determination single crystals of the compounds 1-8 were isolated from the mother liquors and mounted on a Bruker APEX II diffractometer equipped with a CCD camera and a graphite monochromated MoKα radiation source (λ = 0.71073 Å) at the N. S. Kurnakov Institute of General and Inorganic Chemistry (Moscow, Russia). X-ray structure determination for compounds 9-11 was performed using a a Kappa-Nonius four circle diffractometer equipped with a CCD camera and a graphite monochromated MoKα radiation source (λ = 0.71073 Å), located at the Centre de Diffractométrie (CDIFX), Université de Rennes 1 (Rennes, France).
Effective absorption correction was performed using SCALEPACK. Structures of the complexes were solved by the direct method using SHELXS-97 [85] or Sir-97 [86] software, and refined with a full matrix least squares method on F 2 using SHELXL-97, SHELX-2014 or SHELX-2018 program [87]. H atoms were treated by a riding model. Solvent molecules, which could not be localized, were removed by SQUEEZE procedure for compounds 9-11 [88]. The structure of 6 was solved taking into account crystal twinning (Flack parameter is 0.42(4)). Crystallographic data and structure refinement parameters for 1-11 are presented in Tables 2-4. Supplementary crystallographic data for the compounds synthesized are given in CCDC numbers 2055493-2055503 for 1-11, respectively. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

DFT Calculations
The signs and the magnitudes of exchange coupling parameters J were independently estimated by DFT calculations similar to the previously reported by us in details [89], brief description of the methodology is provided in this section.
The calculations were performed via ORCA software [90]. TPSSh [91][92][93] exchangecorrelation potential was employed for the calculation together with LANLTZ basis sets [94] for 3d ions and def2-SVP [95] basis set for the rest of the elements.
The atomic coordinates were taken from the crystallographic data. For calculation of each J value, all Mn 2+ ions in Mn4 core except the two ions taking part in the coupling were "substituted" by diamagnetic Zn 2+ ions in order to simplify the system of spin states of the species. Broken symmetry DFT approach was applied for the calculation of J: first, a single-point calculation was performed for the high-spin state of the Mn2Zn2 species, then the broken symmetry state was constructed by artificial flipping the spin projections of the unpaired electrons localized on one of the Mn 2+ ions, and a single-point calculation was performed again. J value was obtained using the energies EHS and EBS resulted from the two converged single-point calculations as J = − (EHS − EBS)/(<S 2 >HS−<S 2 >BS) [96] (<S 2 >HS and <S 2 >BS-the total spin operator expectation values derived from the calculations).

Conclusions
In this study a variety of transformations of Mn-containing complexes in reactions with N-donor heterocycles was shown. In was found that homometallic Mn pivalates underwent metamorphosis while heterometallic acetates with a Fe2MnO core preserved their structure, giving rise to coordination polymers. Different behavior of Mn II or Ni II and Co II pivalates in reactions with FeCl3 was also revealed: while the first complex produced a hexanuclear [Mn II 4Fe III 2O2(Piv)10(MeCN)2(HPiv)2] compound, the latter (Ni II and Co II ) pivalates under similar conditions gave trinuclear pivalates with a Fe2MnO core.
Magnetic properties of the compounds were in line with those expected for Mn carboxylates. The temperature dependence of the magnetic susceptibility of [Mn4(µ3-OH)(Piv)7(µ-pz)2]n could be fitted with five exchange coupling parameters, and their reliability was independently checked by DFT calculations.
Supplementary Materials: The following are available online. Figure S1: PXRD data for 6; Figure  S2

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.