Transition Metal Halide Salts and Complexes of 2-Aminopyrimidine: Cobalt(II) and Nickel(II) compounds, Crystal Structures of Bis(2-Aminopyrimidinium)MX4 [M = Co, Ni; X = Cl, Br] and 2-Aminopyrimidinium(+2) [NiBr2(H2O)4]Br2

Towards ferroelectricity-inducing chains of halogenoantimonates(iii) and halogenobismuthates(iii)

In halogenoantimonate(iii) and halogenobismuthate(iii) organic–inorganic hybrids, chains of trans-connected octahedra, trans-[MX₅]_∞, are considered attractive anionic structures for inducing ferroelectricity. The latter is realized by displacing the bridging halogen atoms along the chain direction – the process that changes the polarity of the whole unit. Advances in the identification of such materials have been hindered, however, by substantial difficulty in obtaining such structures. Here we investigate structural and dielectric properties of three families of compounds based on 2-mercaptopyrimidinium, 2-aminopyrimidinium, and 2-amino-4-methylpyrimidinium cations in which 8 out of 12 compounds show trans-[MX₅]_∞ chains in their crystal structures. Two of the compounds adopt a polar P2₁ space group and are potentially ferroelectric. We perform a detailed structural analysis of all compounds with trans-[MX₅]_∞ chains discovered by far to understand the factors that lead to the chains' formation. We reveal that the size of a cation predominantly defines the accessibility of structures with this anionic form and we provide rules for designing hybrids with trans-[MX₅]_∞ chains to help guide future efforts to engineer materials with interesting non-linear electrical properties.

A discovered abundance of structures with rare and highly-desired anionic chains is examined to identify structural factors leading to the chains' formation.

A Three-Dimensional Nickel(II) Framework from a Semi-Flexible Bipyrimidyl Ligand Showing Weak Ferromagnetic Behavior

A semi-flexible bipyrimidyl ligand, 5,5'-bipyrimidin (bpym), was used for the self-assembly of a transition metal coordination polymer, resulting in the formation of a nickel(II) compound, [Ni(Br)₂(bpym)₂]n (1) with a three-dimemsional (3D) structure. Single-crystal X-ray analysis showed that compound 1 crystallizes in the monoclinic space group C2/c and the structure represents a 3D (4,4)-connected bbe topological framework constructed of nickel(II) ions, twisted cis-μ-bpym and planar trans-μ-bpym groups. Magnetic characterization revealed that 1 shows antiferromagnetic coupling between the pyrimidyl-bridged Ni(II) ions along with weak ferromagnetism due to spin canting with a magnetic ordering below Tc = 3.4 K.

Hydroboration of Terminal Olefins with Pinacolborane Catalyzed by New Mono(2-Iminopyrrolyl) Cobalt(II) Complexes

The 5-substituted 2-aryliminopyrrolyl ligand precursors of the type 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]-1 H-pyrrole (R = 2,6-Me₂-C₆H₃ (1a), 2,4,6-ⁱPr₃-C₆H₂ (1b), 2,4,6-Ph₃-C₆H₃ (1c; reported in this work), anthracen-9-yl (1d), CPh₃ (1e; reported in this work)) were treated with K[N(SiMe₃)₂] in toluene to yield the respective 5-R-2-[ N-(2,6-diisopropylphenyl)formimino]pyrrolyl potassium salts 2a-e in high yields. The paramagnetic 15-electron Co(II) complexes of the type [Co{κ² N,N'-5-R-NC₄H₂-2-C(H)═N(2,6-ⁱPr₂-C₆H₃)}(Py)Cl] (3a-e; Py = pyridine) were prepared by salt metathesis of CoCl₂(Py)₄ with the respective potassium salts 2a-e in moderate to good yields. When the CoCl₂(THF)_1.5 precursor was combined with the in situ prepared sodium salt of ligand precursor 1b, the trinuclear complex [Co{κ² N, N'-5-(2,4,6-ⁱPr₃-C₆H₂)-NC₄H₂-2-C(H)═N(2,6-ⁱPr₂-C₆H₃)}(μ-Cl)]₂[(μ-Cl)₂Co(THF)₂] (4) was obtained in high yields. Complexes 3a-e have high-spin electronic configurations both in solution and in the solid state. X-ray diffraction studies of complexes 3a,e confirmed distorted tetrahedral coordination geometries. Complex 4, on the other hand, is a linear trinuclear Co(II)-Co(II)-Co(II) complex with two terminal distorted tetrahedral four-coordinate sites and a central octahedral six-coordinate site, all in the high-spin state, S = 3/2, as confirmed by the magnetization measurements and DFT calculations. Solid-state magnetic measurements in both complexes 3a and 4 point to paramagnetic behavior with a significant contribution of spin-orbit coupling. Additionally, intramolecular antiferromagnetic coupling of the adjacent cobalt atoms is observed in 4. The Co(II) family 3a-d, on activation with K(HBEt₃), catalyzed the hydroboration of several α-olefins with pinacolborane, in good to high yields (50-80%). This system almost exclusively yielded the anti-Markovnikov (a-Mk) addition product, except when styrene was used, where the selectivity in the Markovnikov (Mk) product increased with increasing steric bulkiness of the 5-R-2-iminopyrrolyl substituent, with the a-Mk:Mk molar ratio varying from 2.33:1 (3a, R = 2,6-Me₂-C₆H₃) to 0.75:1 (3c, R = 2,4,6-Ph₃-C₆H₃). Preliminary mechanistic studies indicate that the activation by K(HBEt₃) gave rise to a Co(I) species, the catalyst system likely following an oxidative addition pathway.

catena-Poly[[(2-amino-pyrimidine-κN(1))(thio-cyanato-κS)mercury(II)]-μ-thio-cyanato-κ(2)S:N]

In the title coordination polymer, [Hg(NCS)(2)(C(4)H(5)N(3))], the Hg(II) atom is four-coordinated by one aromatic N atom from a 2-amino-pyrimidine ligand, one S atom from a terminal thio-cyanate ligand, and one S atom and one N atom from a bridging thio-cyanate ligand. The crystal structure features polymeric chains running along the b axis which are stabilized by N-H⋯N hydrogen bonds.

(2-Amino-pyrimidine-κN)diaqua(pyridine-2,6-dicarboxyl-ato-κO,N,O)-nickel(II) monohydrate

The reaction of Ni(NO₃)₂·6H₂O with pyridine-2,6-dicarboxylic acid, NaOH and 2-amino­pyrimidine in aqueous solution leads to the formation of the title complex, [Ni(C₇H₃NO₄)(C₄H₅N₃)(H₂O)₂]·H₂O. The Ni^II ion is coordinated by one N and two O atoms of the tridentate chelating pyridine-2,6-dicarboxyl­ate anion, one heterocyclic N atom of the 2-amino­pyrimidine ligand, and two water mol­ecules. The resulting geometry for the [NiN₂O₄] coordination environment can be described as distorted octa­hedral. One uncoord­inated water mol­ecule completes the asymmetric unit. Extensive O—H⋯O and N—H⋯O hydrogen-bonding inter­actions between the NH₂ group of 2-amino­pyrimidine, carboxyl­ate groups, and coordinated and uncoordinated water mol­ecules contribute to the formation of a three-dimensional supra­molecular structure.

1-(2-Pyrid-yl)-N,N'-dipyrimidin-2-ylmethane-diamine

In the title compound, C₁₄H₁₃N₇, inter­molecular N—H⋯N and C—H⋯N hydrogen bonds link the mol­ecules into infinite one-dimensional chains along (100). A C—H⋯π inter­action also occurs in the crystal.