Synthesis, crystal structure and thermal properties of poly[bis[μ-3-(aminomethyl)pyridine-κ2 N:N′]bis(thiocyanato-κN)manganese(II)]

In the crystal structure of the title compound, the manganese cations are octahedrally coordinated by the N atoms of four 3-(aminomethyl)pyridine co-ligands and two terminal N-bonded thiocyanate anions. The metal cations are linked into layers by the co-ligands, and these are further connected into a three-dimensional network by intermolecular N—H⋯S hydrogen bonding.

The reaction of Mn(NCS) 2 with a stoichiometric amount of 3-(aminomethyl)pyridine in ethanol led to the formation of the title compound, [Mn(NCS) 2 (C 6 H 8 N 2 ) 2 ] n , which is isotypic to its Zn, Co and Cd analogues. The manganese cation is located on a centre of inversion and is octahedrally coordinated in an all-trans configuration by two terminal N-bonded thiocyanate anions as well as four 3-(aminomethyl)pyridine co-ligands, of which two coordinate with the pyridine N atom and two with the amino N atom. The 3-(aminomethyl)pyridine co-ligands connect the Mn II cations into layers extending parallel to (101). These layers are further connected into a threedimensional network by relatively strong intermolecular N-HÁ Á ÁS hydrogen bonding. Comparison of the experimental X-ray powder diffraction pattern with the calculated pattern on the basis of single-crystal data proves the formation of a pure crystalline phase. IR measurements showed the CN stretching vibration of the thiocyanate anions at 2067 cm À1 , which is in agreement with the presence of terminally N-bonded anionic ligands. TG-DTA measurements revealed that the title compound decomposes at about 500 K.

Chemical context
In contrast to other small-sized ligands such as azide or cyanide anions, thiocyanate anions show many more coordination modes. Therefore, a variety of structures including discrete complexes (Prananto et al., 2017;Małecki et al., 2011;Wö hlert et al., 2014), dimers (Mautner et al., 2015;Wei & Luo, 2010;Jochim et al., 2018), chains (Mautner et al., 2018;, layers (Suckert et al., 2016 or in very rare cases three-dimensional networks  can be observed. This structural variability is further enhanced by isomerism, because for an octahedral coordination with three pairs of identical ligands, five different isomers exist, including the all-trans, all-cis and three different cis-cis-trans configurations. These features are found in compounds with structures where the metal cations are linked by pairs of anionic ligands into chains. The majority of compounds with -1,3bridging thiocyanate anions shows this behaviour. Depending on the actual metal coordination (all-trans or cis-cis-trans), linear or corrugated chains are observed (Jin et al., 2007;Rams et al., 2017;Bö hme et al., 2020;Jochim et al., 2020). Moreover, even for compounds with layered thiocyanate structures, different networks are realized, in which the metal cations are linked exclusively by single anionic ligands or by both singly and doubly -1,3-bridging thiocyanate anions. For less chalcophilic metal cations like Mn II , Fe II , Co II or Ni II , the majority ISSN 2056-9890 of compounds consist of structures with only terminally N-bonding thiocyanate anions, because in this case this coordination is energetically favoured. With only monocoordinating ligands this usually leads to the formation of discrete metal complexes with an octahedral coordination. If bridging co-ligands are used, chain structures can be realized and networks of higher dimensionality are available if additional -1,3-bridging thiocyanate anions are present.
Thiocyanate coordination polymers are of interest not only because of their variable structural behaviour, but also because this ligand is able to mediate reasonable magnetic exchange. We and other groups have reported many new compounds in which the metal cations are linked by -1,3bridging thiocyanate anions into chains or layers (Werner et al., 2015;Bassey et al., 2020;Mekuimemba et al., 2018;Palion-Gazda et al., 2015;Neumann et al., 2019;Mousavi et al., 2020). In this context, we became interested in 3-(aminomethyl)pyridine, because this ligand is able to link metal cations via the pyridine and the amino N atom. Surprisingly, with Co II we always obtained only one crystalline phase in which the Co II cations are coordinated by only terminally N-bonding thiocyanate anions but linked into layers by the 3-(aminomethyl)pyridine co-ligands (Krebs et al., 2021). In contrast to the Co II cation, the Mn II cation is more chalcophilic and usually behaves like Cd II , for which compounds with -1,3-bridging thiocyanate anions are much easier to obtain. Therefore, we used Mn(NCS) 2 in the present study. However, irrespective of the ratio between Mn(NCS) 2 and 3-(aminomethyl)pyridine, we always obtained only one crystalline phase with composition Mn(NCS) 2 (C 6 H 8 N 2 ) 2 . Single-crystal structure analysis revealed isotypism with the Co II analogue reported recently (Krebs et al. 2021). Comparison of the experimental X-ray powder diffraction pattern with the calculated pattern based on single-crystal data proved that a pure crystalline phase was obtained (see Fig. S1 in the supporting information); IR investigations revealed that the CN stretching vibration is observed at 2067 cm À1 , in agreement with the presence of only terminally N-bound thiocyanate anions (Fig. S2). TG-DTA measurements showed decomposition of the compound at about 500 K, which is accompanied by an endothermic event in the DTA curve (Fig. S3). The first decomposition step might be associated with the removal of the 3-(aminomethyl)pyridine co-ligand. On further heating, an exothermic signal is observed, which indicates the decomposition of the co-ligand.

Structural commentary
Mn(NCS) 2 (C 6 H 8 N 2 ) 2 is isotypic with its recently reported Cd II , Zn II and Co II analogues (Neumann et al., 2017;Krebs et al., 2021). The asymmetric unit consists of one Mn II cation that is located on a centre of inversion as well as one 3-(aminomethyl)pyridine co-ligand and one thiocyanate anion (Fig. 1). The Mn II cation is octahedrally coordinated by the N atoms of four symmetry-equivalent 3-(aminomethyl)pyridine coligands and two symmetry-equivalent thiocyanate anions. Two of these co-ligands coordinate through the pyridine N atom whereas the other two coordinate with the amino N atom. Each pair of identical donor atoms is in a trans-position (Fig. 1). The Mn-N bond length to the negatively charged thiocyanate N atom is significantly shorter than that to the The coordination of the Mn II cation in the title compound with displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (A) Àx, Ày + 1, Àz, (B) 1 2 À x, À 1 2 + y, 1 2 À z, (C) À 1 2 + x, 3 2 À y, À 1 2 + z.] Table 1 Selected geometric parameters (Å , ).
3-(aminomethyl)pyridine co-ligand; the Mn-N bond length to the pyridine N atom is significantly longer than that to the amino N atom of the 3-(aminomethyl)pyridine ligand ( Table 1). As expected, all Mn-N bond lengths are significantly longer and shorter, respectively, compared to the Co II and Cd II analogues. The bond angles around Mn II indicate a considerable distortion (Table 1). This is also indicated by the mean octahedral quadratic elongation of 1.0013 and the octahedral angle variance of 0.8258 (Robinson et al., 1971). The Mn II cations are connected by bridging 3-(aminomethyl)pyridine ligands into chains, which are further linked into layers extending parallel to (101) by additional co-ligands (Fig. 2).

Supramolecular features
The layers are linked into a three-dimensional network by intermolecular N-HÁ Á ÁS hydrogen bonds between the amino H atoms and the thiocyanate S atoms (Fig. 3, Table 2). The N-HÁ Á ÁS angles indicate a relatively strong interaction and the thiocyanate S atom acts as an acceptor for two of these hydrogen bonds. There is also a C-HÁ Á ÁS interaction but the bonding angle is far from linearity, which points to a weak interaction (Table 2).

Database survey
In Crystal structure of the title compound in a view of a layer along the crystallographic a axis.

Synthesis and crystallization
Synthesis Mn(NCS) 2 and 3-(aminomethyl)pyridine were purchased from Alfa Aesar and all chemicals were used without further purification. Single crystals were obtained by reacting 1 mmol of Mn(NCS) 2 (175.1 mg) with 1 mmol of 3-(aminomethyl)pyridine (108.1 mg) in 4 ml of ethanol. After approximately one week, light-brown crystals were obtained, which were suitable for single crystal X-ray analysis. For the synthesis of crystalline powders, the same amounts of reactants were stirred in 2 ml of ethanol for 1 d and the precipitate was filtered off and dried in air. Experimental details The elemental analysis was performed using a EURO EA elemental analyzer fabricated by EURO VECTOR Instruments. The IR spectrum was measured using an ATI Mattson Genesis Series FTIR spectrometer, control software: WINFIRST, from ATI Mattson. The PXRD measurement was performed with Cu K 1 radiation ( = 1.540598 Å ) using a Stoe Transmission Powder Diffraction System (STADI P) that is equipped with a MYTHEN 1K detector and a Johanssontype Ge(111) monochromator. Thermogravimetry and differential thermoanalysis (TG-DTA) measurements were performed in a dynamic nitrogen atmosphere in Al 2 O 3 crucibles using a STA-PT 1000 thermobalance from Linseis. The instrument was calibrated using standard reference materials.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were located in a difference-Fourier map but were positioned with idealized geometry (N-H = 0.91 Å , C-H = 0.95-0.99 Å ) and were refined in a riding model with U iso (H) = 1.2U eq (C) or 1.5U eq (C) for amino H atoms.

Poly[bis[µ-3-(aminomethyl)pyridine-κ 2 N:N′]bis(thiocyanato-κN)manganese(II)]
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.