Reaction of different molar ratios of Ni(NCS)2 and 3‐bromopyridine in water, methanol or acetonitrile leads to the formation of two polymorphs of composition Ni(NCS)2(3‐bromopyridine)4 (1‐I and 1‐II), as well as Ni(NCS)2(3‐bromopyridine)2(H2O)2 (2), Ni(NCS)2(3‐Bromopyridine)2(CH3OH)2 (3), Ni(NCS)2(3‐bromopyridine)2 ⋅ CH3CN (4) and Ni(NCS)2(3‐bromopyridine)2 (5). Compounds 1‐I, 1‐II, 2 and 3 consist of discrete octahedral complexes with terminal N‐bonded anionic ligands. In compound 4 the Ni cations are cis‐cis‐trans coordinated and linked into corrugated chains by pairs of μ‐1,3‐bridging thiocyanate anions. Solvent mediated conversion experiments prove that form 1‐I represents the thermodynamically stable polymorph at room temperature. TG‐DTA measurements reveal that upon heating compounds 1‐I, 1‐II, 2 and 3 lose their coligands stepwise and transform into the new crystalline phase 5 that can also be obtained from solution if the reaction is performed in n‐butanol. If the acetonitrile solvate molecules are removed from compound 4, it also transforms into 5. DC magnetic measurements for compound 4 show a maximum, which is indicative for antiferromagnetic ordering, whereas for compound 5 no magnetic ordering is observed. For both compounds, the ferromagnetic exchange constants were determined.

Acetic acid, an alternative green solvent, was utilized for the solvothermal synthesis of four 2D materials of composition [Zr2O2(OAc)2(BDC-F)], [Zr2O2(OAc)2(BDC-F4)], [Zr2O2(OAc)2(BDC)], and [Zr2O2(OAc)2(NDC)] (BDC, terephthalate; BDC-F, 2-fluoroterephthalate; BDC-F4, tetrafluoroterephthalate; NDC, 2,6-naphthalenedicarboxylate). The first three compounds were subsequently reacted with terephthalic acid in solid-state reactions to form porous MIL-140A-type metal–organic frameworks and mixed-linker derivatives ([ZrO­(BDC)1–x (BDC-Y) x ], x = 0–0.18, Y = F, F4). The reaction kinetics of the formation of MIL-140A were investigated with the aid of time-resolved synchrotron and temperature-resolved in-house X-ray powder diffraction experiments. Thorough compositional analyses and solid-state NMR spectroscopic experiments were used to assess the crystallographic ordering of the different linker molecules. Additionally, acetic acid-based routes for the direct synthesis of MIL-140A-NO2 and a novel MIL-140A-(CH3)2 derivative were discovered.

The reaction of Co­(NCS)2 with 3-bromopyridine leads to the formation of discrete complexes [Co­(NCS)2(3-bromopyridine)4] (1), [Co­(NCS)2(3-bromopyridine)2(H2O)2] (2), and [Co­(NCS)2(3-bromopyridine)2(MeOH)2] (3) depending on the solvent. Thermogravimetric measurements on 2 and 3 show a transformation into [Co­(NCS)2(3-bromopyridine)2] n (4), which upon further heating is converted to [{Co­(NCS)2}2(3-bromopyridine)3] n (5), whereas 1 transforms directly into 5 upon heating. Compound 5 can also be obtained from solution, which is not possible for 4. In 4 and 5, the cobalt­(II) cations are linked by pairs of μ-1,3-bridging thiocyanate anions into chains. In compound 4, all cobalt­(II) cations are octahedrally coordinated (OC-6), as is usually observed in such compounds, whereas in 5, a previously unkown alternating 5- and 6-fold coordination is observed, leading to vacant octahedral (vOC-5) and octahedral (OC-6) environments, respectively. In contrast to 4, the chains in 5 are very efficiently packed and linked by π···π stacking of the pyridine rings and interchain Co···Br interactions, which is the basis for the formation of this unusual chain. The spin chains in 4 demonstrate ferromagnetic intrachain exchange and much weaker interchain interactions, as is usually observed for such linear chain compounds. In contrast, compound 5 shows almost single-ion-like magnetic susceptibility, but the magnetic ordering temperature deduced from specific heat measurements is twice as high as that in 4, which might originate from π···π stacking and Co···Br interactions between neighboring chains. More importantly, unlike all linear Co­(NCS)2 chain compounds, a dominant antiferromagnetic exchange is observed for 5, which is explained by density functional theory calculations predicting an alternating ferro- and aniferromagnetic exchange within the chains. Theoretical calculations on the two different cobalt­(II) ions present in 5 predict an easy-axis anisotropy that is much stronger for the octahedral cobalt­(II) ion than for the one with the vacant octahedral coordination, with the magnetic axes of the two ions being canted by an angle of 84°. This almost orthogonal orientation of the easy axis of magnetization for the two cobalt­(II) ions is the rationale for the observed non-Ising behavior of 5.

Dedicated to Prof. Dr. Josef Breu on the occasion of his 60th birthday.Reactions of Ni(NCS) 2 and 3-cyanopyridine in different solvents lead to the formation of Ni(NCS) 2 (3-cyanopyridine) 4 (1) already reported in the literature, Ni(NCSThe crystal structures of 1-4 consist of discrete octahedral complexes, in which the thiocyanate anions, as well as the 3cyanopyridine coligands, are only terminally N-bonded. In compound 5 the Ni cations are octahedrally coordinated and linked by pairs of thiocyanate anions into dinuclear units that are further connected into layers by single μ-1,3-bridging anionic ligands. TG-DTA measurements of the discrete complex 1 reveal that in the first step half of the coligands are emitted leading to the formation of compound 5. In contrast, compounds 2 and 3 transform into a new crystalline phase of the same composition ( 6) upon heating that should also contain μ-1,3-bridging anionic ligands, but the outcome of this reaction strongly depends on the reaction conditions. The acetonitrile complex 4 is unstable at room temperature and decomposes into a mixture of different phases including the aqua complex 2. Magnetic measurements of compound 5 prove a ferromagnetic transition at T c = 6.0 K. This result is compared to those obtained for other thiocyanate compounds exhibiting a similar layer topology.

The reaction of Co(NCS)2 with 3-(aminomethyl)pyridine as coligand leads to the formation of crystals of the title compound, [Co(NCS)2(C6H8N2)2] n , that were characterized by single-crystal X-ray analysis. In the crystal structure, the CoII cations are octahedrally coordinated by two terminal N-bonded thiocyanate anions as well as two pyridine and two amino N atoms of four symmetry-equivalent 3-(aminomethyl)pyridine coligands with all pairs of equivalent atoms in a trans position. The CoII cations are linked by the 3-(aminomethyl)pyridine coligands into layers parallel to the ac plane. These layers are further linked by intermolecular N—H...S hydrogen bonding into a three-dimensional network. The purity of the title compound was determined by X-ray powder diffraction and its thermal behavior was investigated by differential scanning calorimetry and thermogravimetry.