Halogen Bonding Channels for Magnetic Exchange in Cu(II) Complexes with 2,5-Di(methylthio)-1,3,4-thiadiazole

Copper(II) complexes with 2,5-bis(methylthio)-1,3,4-thiadiazole (tda) formulated as [Cu(tda)_n X₂ ] (n=2, X=Cl^- , Br^- , C₂ N₃ ^- ; n= 1, X=C₂ N₃ ^- ) have been isolated and fully characterized. The crystal structures of all compounds have been determined using single-crystal X-ray diffraction (SCXRD). A study of the magnetic susceptibility in the range 1.77-300 K has shown that magnetic properties of the [Cu(tda)₂ Cl₂ ] and [Cu(tda)₂ Br₂ ] complexes match those of 1D chains of antiferromagnetically-coupled Cu²⁺ ions. The intrachain interaction J in [Cu(tda)₂ Cl₂ ] turns out to be ∼1.2 times weaker than in its bromide analogue. In its turn, [Cu(tda)₂ (C₂ N₃ )₂ ] exhibits J being an order of magnitude smaller and of the opposite ferromagnetic sign. Halogen bonding (HB) between adjacent complexes is much stronger than the H-bonds or π-π interactions between tda ligands according to the DFT calculations.

Halogen bond and polymorphism in trans-bis(2-iodo-5-halopyridine)dihalocopper(ii) complexes: crystallographic, theoretical and magnetic studies

As the halogen atom on position 5 of the 2I5YP ligand gets heavier the probability of crystallizing the syn-conformer increases; 2I5Cl-Cl crystallizes as the anti-conformer whereas 2I5Br-Cl crystallizes as syn- and anti-conformers.

Two-Dimensional and Three-Dimensional Coordination Polymers Based on Ln(III) and 2,5-Diiodoterephthalates: Structures and Luminescent Behavior

Five new coordination polymers based on Ln3+ and 2,5-diiodoterephthalates (2,5-I-bdc)— {[La2(2,5-I-bdc)3(DMF)4]}·2DMF (1) and {[Ln2(2,5-I-bdc)3(DMF)4]} (Ln = La (2), Nd (3), Sm (4) and Eu (5))—were prepared and characterized by single crystal and powder X-ray diffractometry. Luminescent behavior was examined (the highest quantum yield is 4.5%); thermal stability was examined using thermogravimetric analysis.

Zn(II) and Co(II) 3D Coordination Polymers Based on 2-Iodoterephtalic Acid and 1,2-bis(4-pyridyl)ethane: Structures and Sorption Properties

Metal-organic frameworks [M₂(2-I-bdc)₂bpe] (M = Zn(II) (1), Co(II) (2), 2-I-bdc = 2-iodoterephtalic acid, and bpe = 1,2-bis(4-pyridyl)ethane) were prepared and characterized by X-ray diffractometry. Both compounds retain their 3D structure after the removal of guest DMF molecules. Selectivity of sorption of different organic substrates from the gas phase was investigated for both complexes.

Polymorphism and isomorphism in trans-bis(2,5-diiodopyridine)dihalocopper(ii) complexes: theoretical and crystallographic studies

Two conformational polymorphs of [Cu(25dIpy)2Cl2] have been prepared, the anti-polymorph crystallized from 2-propanol at room temperature (green) and the syn-polymorph crystallized from acetonitrile at 60 °C (brown).

Zn(II) Heteroleptic Halide Complexes with 2-Halopyridines: Features of Halogen Bonding in Solid State

Reactions between Zn(II) dihalides and 2-halogen-substituted pyridines 2-XPy result in a series of heteroleptic molecular complexes [(2-XPy)₂ZnY₂] (Y = Cl, X = Cl (1), Br (2), I (3); Y = Br, X = Cl (4), Br (5), I (6), Y = I, X = Cl (7), Br (8), and I (9)). Moreover, 1-7 are isostructural (triclinic), while 8 and 9 are monoclinic. In all cases, halogen bonding plays an important role in formation of crystal packing. Moreover, 1-9 demonstrate luminescence in asolid state; for the best emitting complexes, quantum yield (QY) exceeds 21%.

Two new canted antiferromagnetic systems: magnetic, theoretical, and crystallographic studies on trans-bis(2-iodopyridine)dihalocopper(ii)

The two complexes Cu(2ip)X₂ were prepared (where 2ip = 2-iodopyridine and X = Cl or Br), and their crystal structures were determined. The two complexes are isomorphous and form a magnetic chain based on the two-halide exchange pathway. The powder and single crystal magnetic susceptibility data were measured down to 1.8 K. The exchange is antiferromagnetic along the chain; the exchange is stronger in the bromide complex than in the corresponding chloride complex. In the ordered state, weak moments appear along some of the axes, indicative of spin-canting. The calculated spin densities and the mapped surface of spin density on total electron density were used to rationalize qualitatively the observed magnetic behavior. Low temperature structures are compared with the room temperature data; the C-IX-Cu and Cu-XX-Cu distances are shorter at low temperatures; in contrast, the covalent bonds of the organic ligand (2-iodopyridine) are longer (negative thermal expansion of the covalent bonds). The anomalous behavior is rationalized using charge transfer from Cu-X group to the anti-bonding orbital of the organic ligand. Quantum theory of atoms in molecules was used to analyze C-IX halogen bonding interactions.

Spin-Lattice Coupling Across the Magnetic Quantum-Phase Transition in Copper-Containing Coordination Polymers

We measured the infrared vibrational properties of two copper-containing coordination polymers, [Cu(pyz)₂(2-HOpy)₂](PF₆)₂ and [Cu(pyz)_1.5(4-HOpy)₂](ClO₄)₂, under different external stimuli in order to explore the microscopic aspects of spin-lattice coupling. While the temperature and pressure control hydrogen bonding, an applied field drives these materials from the antiferromagnetic → fully saturated state. Analysis of the pyrazine (pyz)-related vibrational modes across the magnetic quantum-phase transition provides a superb local probe of magnetoelastic coupling because the pyz ligand functions as the primary exchange pathway and is present in both systems. Strikingly, the PF₆^- compound employs several pyz-related distortions in support of the magnetically driven transition, whereas the ClO₄^- system requires only a single out-of-plane pyz bending mode. Bringing these findings together with magnetoinfrared spectra from other copper complexes reveals spin-lattice coupling across the magnetic quantum-phase transition as a function of the structural and magnetic dimensionality. Coupling is maximized in [Cu(pyz)_1.5(4-HOpy)₂](ClO₄)₂ because of its ladderlike character. Although spin-lattice interactions can also be explored under compression, differences in the local structure and dimensionality drive these materials to unique high-pressure phases. Symmetry analysis suggests that the high-pressure phase of the ClO₄^- compound may be ferroelectric.

Ferroelectricity and antiferromagnetism in organic–inorganic hybrid (1,4-bis(imidazol-1-ylmethyl)benzene)CuCl4·H2O

A new [CuCl₄]²⁻ based organic–inorganic hybrid, (bix)CuCl₄·H₂O (bix = 1,4-bis(imidazol-1-ylmethyl)benzene), is synthesized via simple solution method, which shows the coexistence of ferroelectric and antiferromagnetic ordering in (bix)CuCl₄·H₂O.

Halogen Bonds in 2,5-Dihalopyridine-Copper(I) Halide Coordination Polymers

Two series of 2,5-dihalopyridine-Cu(I)A (A = I, Br) complexes based on 2-X-5-iodopyridine and 2-X-5-bromopyridine (X = F, Cl, Br and I) are characterized by using single-crystal X-ray diffraction analysis to examine the nature of C2-X2···A-Cu and C5-X5···A-Cu halogen bonds. The reaction of the 2,5-dihalopyridines and Cu(I) salts allows the synthesis of eight 1-D coordination polymers and a discrete structure. The resulting Cu(I)-complexes are linked by C-X···A-Cu halogen bonds forming 3-D supramolecular networks. The C-X···A-Cu halogen bonds formed between halopyridine ligands and copper(I)-bound halide ions are stronger than C-X···X'-C interactions between two 2,5-dihalopyridine ligands. The C5-I5···I-Cu and C5-Br5···Br-Cu halogens bonds are shorter for C2-fluorine than C2-chlorine due to the greater electron-withdrawing power of fluorine. In 2,5-diiodopyridine-Cu(I)Br complex, the shorter C2-I2···Br-Cu [3.473(5) Å] distances are due to the combined polarization of C2-iodine by C2-I2···Cu interactions and para-electronic effects offered by the C5-iodine, whilst the long halogen bond contacts for C5-I5···Br-Cu [3.537(5) Å] are indicative that C2-iodine has a less para-electronic influence on the C5-iodine. In 2-fluoro-5-X-pyridine-Cu(I) complexes, the C2-fluorine is halogen bond passive, while the other C2-halogens in 2,5-dihalopyridine-Cu(I), including C2-chlorine, participate in halogen bonding interactions.

Four-Center Nodes: Supramolecular Synthons Based on Cyclic Halogen Bonding

The isocyanide trans-[PdBr₂ (CNC₆ H₄ -4-X')₂ ] (X'=Br, I) and nitrile trans-[PtX₂ (NCC₆ H₄ -4-X')₂ ] (X/X'=Cl/Cl, Cl/Br, Br/Cl, Br/Br) complexes exhibit similar structural motif in the solid state, which is determined by hitherto unreported four-center nodes formed by cyclic halogen bonding. Each node is built up by four Type II C-X'⋅⋅⋅X-M halogen-bonding contacts and include one Type I M-X⋅⋅⋅X-M interaction, thus giving the rhombic-like structure. These nodes serve as supramolecular synthons to form 2D layers or double chains of molecules linked by a halogen bond. Results of DFT calculations indicate that all contacts within the nodes are typical noncovalent interactions with the estimated strengths in the range 0.6-2.9 kcal mol^-1 .

Halogen bonds in 2,5-dihalopyridine-copper(ii) chloride complexes

In the (2,5-dihalopyridine)₂·CuCl₂ complexes varying the C5-position halogens affects the halogen bonding properties so that the C5–X5⋯Cl–Cu halogen bonds follow the order F5 < Cl5 < Br5 < I5 when the substituent at 2-position is chlorine and Cl5 < Br5 < I5 when it is bromine.

May halogen bonding interactions compete with Cu⋯Cl semi-coordinate bonds? Structural, magnetic and theoretical studies of two polymorphs of trans-bis(5-bromo-2-chloro pyridine)dichlorocopper(ii) and trans-bis(2,5-dichloropyridine)dichlorocopper(ii)

Interaction of the negative potential area from one molecule with the positive areas I and II from two different molecules produces polymorphs 1 and 2.

New organically templated thiocyanatocadmates and chlorocuprate(II): synthesis and structural characterization

With various organic base molecules as the countercations, five new thiocyanatocadmates [H2(tmen)][Cd(SCN)4] (tmen = N,N,N',N'-tetramethylethylenediamine) 1, [H2(tmba)][Cd2(SCN)6] (tmba = N,N,N',N'-tetramethyl-1,4-butanediamine) 2, [H2(teen)][Cd2(SCN)6] (teen = N,N,N',N'-tetra-ethylethylenediamine) 3, [H(amp)][Cd(SCN)2(CH3COO)] (amp = 2-amino-6-methylpyridine) 4 and [H(abp)]4[Cd(SCN)4]SO4·H2O (abp = 2-amino-6-bromopyridine) 5, and one new chlorocuprate(II) [H2(cha)][CuCl4] (cha = 1,4-cyclohexanediamine) 6 were obtained from a series of simple room-temperature self-assemblies at pH = 2 or 6.5. X-ray single-crystal diffraction analysis reveals that (i) templated by [(CH3)2NH(CH2)2NH(CH3)2](2+) (H2(tmen)(2+)), the anion [Cd(SCN)4](2-) in 1 shows a 1-D linear single-chain structure, whereas templated by [(CH3)2NH(CH2)4NH(CH3)2](2+) (H2(tmba)(2+)), the anion [Cd2(SCN)6](2-) in 2 shows a 1-D linear double-chain structure. The number of C atoms between the two N atoms in the templating agent controls the width of the anionic chain through the N(amino)-H···N(SCN) interactions; (ii) templated by [(C2H5)2NH(CH2)2NH(C2H5)2](2+) (H2(teen)(2+)), the anion [Cd2(SCN)6](2-) in 3 exhibits a 3-D open-framework structure, which is based on zigzag anionic chains. A direct change of the substituent group from -CH3 to -C2H5 alters indirectly the shape of the anionic chain from a linear shape to a zigzag shape; (iii) 4 shows a 3-D supramolecular network structure, which is built up from the 1-D zigzag anionic structures by the H(amp)(+) molecules via N-H···O interactions. The formation of the zigzag chain derives from the chelation of the CH3COO(-) groups to the Cd(2+) centers; (iv) 5 is indeed a double salt of [H(abp)]2[Cd(SCN)4] and [H(abp)]2SO4. SO4(2-) and H(abp)(+) form a supramolecular aggregation. Surrounded by the aggregations, the anion [Cd(SCN)4](2-) only shows a dinuclear structure; and (v) templated by H2(cha)(2+), the anion [CuCl4](2-) in 6 displays a 2-D perovskite layer structure. The photoluminescence analysis indicates that upon excitation (λ(ex) = 335 nm for 4, λ(ex) = 395 nm for 5), and emit light (λ(em) = 365 nm for 4, λ(em) = 470 nm for 5), which can be seen clearly under the UV lamp.

New 1-D and 3-D thiocyanatocadmates modified by various amine molecules and Cl−/CH3COO− ions: synthesis, structural characterization, thermal behavior and photoluminescence properties

Reactions of CdCl₂/Cd(CH₃COO)₂, SCN⁻ and various organic amines yielded five new thiocyanatocadmates; structural, thermal and photoluminescence properties are reported.

Tailoring magnetic properties of molecular materials through non-covalent interactions

This Chemistry Frontier highlights how supramolecular non-covalent interactions can be employed as effective tools in tailoring the magnetic properties of crystalline functional molecular materials.