Semicoordinate Bonds Research Articles

Copper (II) halide compounds with cationic N-donor ligands: Design, synthesis, structure and magnetism

Copper (II) complexes of the cationic ligands 1-(4′-pyridyl)-pyridinium (L1) and 1-(4′-pyridyl)-pyridin-4-ol (L2) have been prepared and characterized by single crystal X-ray diffraction and variable temperature magnetic susceptibility measurements: [Cu(L1)2X2]X2 [where X = Cl (1), Br (2)], and [Cu(L2)2X2]X2 [where X = Cl (3), Br (4)]. The complexes are fundamentally square planar with L2X2 coordination planes and long, semi-coordinate bonds to the additional halide ions. All compounds crystallize in monoclinic systems with 1 and 2 in the P21/n space group and 3 and 4 in the P21/c space group. The crystal structures are stabilized by both non-classical (in the case of 1 and 2) and classical (3 and 4) hydrogen bonds. EPR data for 1–4 support a rhombohedral structure, in good agreement with the local geometry as seen in the crystal structures. Magnetic susceptibility measurements show the presence of very weak antiferromagnetic interactions. In addition, the syntheses and magnetic properties of two neutral complexes, [Cu(L3)2X2]·2H2O [L3 = 1-(4′-pyridino)-4-pyridone; X = Cl (5), Br (6)] are reported. Magnetic susceptibility data indicate the presence of moderate antiferromagnetic exchange interactions [J ∼ 28 K (5), 60 K (6)] which were well modeled by the S = 1/2 Heisenberg uniform chain model.

Competition between Cu-Br semi-coordinate bond and C-H∙∙∙Br, C-H∙∙∙S and S∙∙∙S interactions; new two thioalkylazothiophenol (SNS) copper (II) dimers [Cu(L)(µ-Br)

Two new copper dimers [Cu(L)(µ-Br)]2, HL = 2(RS)C6H4N = NC(COCH3)-SC6H5, where R = CH3 (1), C6H5 (2) were synthesized and characterized using a variety of physicochemical methods, including single crystal X-ray diffraction. The molecular structures of the two binuclear copper(II) complexes show that Cu∙∙∙Cu inter-nuclei distances are 3.662 \\AA and 3.392 \\AA in 1 and 2, respectively. Structural analysis of the two dimers supported by QTAIM analysis of electron density indicates the presence of competition between Cu∙∙∙Br semi-coordinate bond and CH∙∙∙Br and CH∙∙∙S hydrogen bonding interactions and S∙∙∙S chalcogen bonding interactions. In complex 1, CH∙∙∙Br and CH∙∙∙S hydrogen bonding interactions exist, in contrast, they are absent in 2. Cu∙∙∙Br semi-coordinate bonds are stronger in 2 as indicated by Cu∙∙∙Br bond distances; Cu∙∙∙Br bond distances are 2.955 and 2.858 Å in 1 and 2.746 Å in 2. There are two weaker S∙∙∙S interactions in 2 and one stronger interaction in 1 as indicated by S∙∙∙S interatomic distances. The two copper dimers and their ligands exhibited good anticancer efficacy against breast (MCF-7), lung (HCT115), and colon human (A549) cancer cell lines. Complex 1 demonstrated strong cancer cell death compared to complex 2. Additionally, the complexes exhibited higher activity than the ligands. Dimer 2 exhibits two quasi-reversible one-electron reduction waves at −0.05 V and −0.37 V. The comproportionating constant for forming the Cu(I/II) mixed-valence complex was 2.57 × 105. The absence of Intervalence transfer (IT) bands in the electronic absorption spectrum for the mixed-valence complex suggested that a single unpaired electron is localized on one copper center.

Pyridyl-imidazole copper compounds

Three 4-(2’-pyridyl)imidazole (4-pyim) complexes of copper(II) have been synthesized and studied structurally and magnetically. The structures of [CuCl2(4-pyim)] (1), [CuCl(4-pyim)2]2Cl2(H2O)10 (2), and [Cu(CuCl4)(4-pyim)2][Cu(H2O)(4-pyim)2](CuCl4)(H2O)4 (3) are reported. Single-crystal X-ray diffraction measurements show that 1 crystallizes in the monoclinic space group P21/n with a four-coordinate Cu(II) ion forming dimers via semi-coordinate bonds to bridging chloride ions. The structure of 1 shows the copper and chloride ions disordered over two sites. Compound 2 crystallizes in the triclinic space group P – 1 with five-coordinate Cu(II) ions in a highly distorted geometry between square pyramidal and trigonal bipyramidal. It has an extensive hydrogen bonding network created by 10 lattice water molecules, chloride ions, and nitrogen atoms in the ligands. Compound 3 crystallizes in the monoclinic space group Cc with both four- and five-coordinate Cu(II) ions present in the lattice; the five-coordinate Cu(II) ions display highly distorted geometries. All three compounds have hydrogen bonding and π-stacking interactions among the 4-pyim rings. Magnetic susceptibility data were collected on 1. Magnetic susceptibility data of 1 shows that it exhibits modest antiferromagnetic interactions which are best fit using a honeycomb model [(2J = −2.6(2) K), 2J’ = −1.6(2) K, ]. Disorder in the crystal structure decreases the rate of growth of the correlation length at low temperatures, lowering the temperature of the expected maximum in χ below the range of the data.

Theoretical Investigation on Non-Covalent Interactions

This editorial is dedicated to announcing the Special Issue “Theoretical investigation on non-covalent interactions” of Crystals. The Special Issue covers the most recent progress in the rapidly growing fields of data science, artificial intelligence, and quantum and computational chemistry in topics relevant to the problem of theoretical investigation on non-covalent interactions (including, but not limited to, hydrogen, halogen, chalcogen, pnictogen, tetrel, and semi-coordination bonds; agosic and anagosic interactions; stacking, anion-/cation–π interactions; metallophilic interactions, etc.). The main successes of my colleagues and I in the field of fundamental theoretical studies of non-covalent interactions in various chemical compounds over the past year are briefly highlighted.

Structure-directing sulfur...metal noncovalent semicoordination bonding

The abundance and geometric features of nonbonding contacts between metal centers and `soft' sulfur atoms bound to a non-metal substituent R were analyzed by processing data from the Cambridge Structural Database. The angular arrangement of M, S and R atoms with ∠(R-S...M) down to 150° was a common feature of the late transition metal complexes exhibiting shortened R-S...M contacts. Several model nickel(II), palladium(II), platinum(II) and gold(I) complexes were chosen for a theoretical analysis of R-S...M interactions using the DFT method applied to (equilibrium) isolated systems. A combination of the real-space approaches, such as Quantum Theory of Atoms in Molecules (QTAIM), noncovalent interaction index (NCI), electron localization function (ELF) and Interacting Quantum Atoms (IQA), and orbital (Natural Bond Orbitals, NBO) methods was used to provide insights into the nature and energetics of R-S...M interactions with respect to the metal atom identity and its coordination environment. The explored features of the R-S...M interactions support the trends observed by inspecting the CSD statistics, and indicate a predominant contribution of semicoordination bonds between nucleophilic sites of the sulfur atom and electrophilic sites of the metal. A contribution of chalcogen bonding (that is formally opposite to semicoordination) was also recognized, although it was significantly smaller in magnitude. The analysis of R-S...M interaction strengths was performed and the structure-directing role of the intramolecular R-S...M interactions in stabilizing certain conformations of metal complexes was revealed.

Pentacoordinated silver(I) complex featuring 8-phenylquinoline ligands: Interplay of coordination bonds, semicoordination, and stacking interactions

A rare example of pentacoordinated silver(I) complex featured unconventional type of coordination of 8-phenylquinoline has been prepared. DFT calculations indicated that the silver(I) center forms two strong coordination bonds with the N atoms (21.8–29.8 kcal/mol) and an electrostatically provided bond with the triflate anion (the charges at the silver(I) center and the triflate O atom are estimated as +0.64 and −1.02 e, respectively). The coordination polyhedron is complemented by two semicoordination bonds with the C atoms of the phenyl rings (4.3–6.0 kcal/mol). These silver(I)–phenyl π-interactions are significantly stronger than such interactions observed previously for other systems exhibiting energy lower than 2 kcal/mol.

Light‐Induced Spin‐State Switching of the MoIV Centre in Trinuclear [CuII(diamine)2]2[MoIV(CN)8] Molecules

New trinuclear molecules [Cu(meen)2]2[MoIV(CN)8]·5H2O (1) and [Cu(eten)2]2[Mo(CN)8]·7H2O (2) (meen = N‐methyl‐ethylenediamine; eten = N‐ethyl‐ethylenediamine) have been prepared and characterised by X‐ray diffraction and dc magnetometry. The crystal structure of 1 and 2 consists of trinuclear Cu2Mo molecules interacting through weak semicoordination bonds and resulting in the formation of 2D and 3D supramolecular networks, respectively. In the ground state, both molecules exhibit simple paramagnetic behaviour, with very weak antiferromagnetic interaction present at low temperatures. The photomagnetic studies of 1 and 2, performed using 436 nm light, have shown a significant increase in the magnetisation upon irradiation that might be explained in terms of a singlet–triplet transition at MoIV.

Copper(II) complexes with pyridine-2,6-dicarboxylic acid from the oxidation of copper(I) iodide

Via an oxidation reaction of Cu(I) iodide with pyridine-2,6-dicarboxylic acid (H2L) in DMF three copper(II) complexes, [(CH3)2NH2]2[CuL2] (1), K2[CuL2]∙H2L∙H2O (2) and [Cu(L)(H2O)]n (3), were synthesized and characterized. The structures of 1–3 were determined by single crystal X-ray diffraction studies. In-situ DMF decomposition produces dimethylamine base under solvothermal conditions and a proton transfer reaction takes place for the complex formation of 1. 3-D networks are stabilized in 1 and 2 via hydrogen bonds. Complex 3 is a 1-D coordination polymer with Cu-O semi-coordination bonds. Thermal decomposition of the complexes results in the corresponding metal oxides. Also, the electrochemical behavior of 1 was determined to be a metal-centered and diffusion-controlled, one-electron reduction process.

Syntheses and structures of eight-semi-coordinate M(II) (M=Mn, Fe, Co, Ni, Cu, Zn) complexes and density functional theory study of bond dissociation energies for the MO semi coordinate bonds

Abstract Six new complexes 1–6 with the common formula [M(NiL)4][M(NCS)4] (M = Mn, Fe, Co, Ni, Cu and Zn for 1, 2, 3, 4, 5 and 6, respectively; the same below) were synthesised and structurally characterised by X-ray single crystal analysis. NiL acts as a complex ligand. L denotes the dianion of dimethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo-[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate. Each M(II) centre of the [M(NiL)4]2 + complex cations in 1–6 adopts a distorted square-antiprism coordination geometry with a O8 donor set. All the M O bonds in the six complexes are abnormally long (2.444–2.528 A). M(II) complexes having such weak coordination environments have not been reported, and eight-coordinate M(II) complexes with all the eight oxygen donor atoms coming from metalloligands have also not been documented. Each M(II) centre of the [M(NCS)4]2 − anions in 1–6 has a distorted tetrahedral coordination environment with a N4 donor set. Theoretical calculations for the bond dissociation energies (BDEs) of the M O semi coordinate bonds were performed using density functional theory at B3LYP level. The calculated BDE values are 23.8, 25.5, 20.0, 22.3, 19.8 and 18.2 kcal/mol for 1, 2, 3, 4, 5 and 6, respectively. The BDE values suggest that the long Mn O bonds in 1 and the long Co O bonds in 3 are significantly weaker than their significantly shorter counterparts in the formerly reported [Mn(NiL)2(NCS)2] and [Co(NiL)2(NCS)2], respectively.

Structures of [(n-C4H9)2NH2]2Cd9Cl20·2H2O and [Cu(C14H24N4)]2Cu13Cl30(H2O)2·xH2O: Perforated Layer Structures Based on the CdCl2 Layer Network

The crystal structures are reported for two compounds containing novel perforated layer structures, [DBA] 2Cd 9Cl 20.2H 2O and [Cu(TIM)] 2Cu 13Cl 30(H 2O) 2. xH 2O, where [DBA] (+) = di n-butylammonium and TIM = 2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo- 1,4,8,11-tetraazatetradecane. In the former compound, single Cd (2+) ions are excised from the parent CdCl 2 layers, with water molecules hydrogen bonded to chloride ions on both sides of the excision. Lattice stability is provided by the DBA (+) cations, which have an all-trans conformation. These lie between the layers, hydrogen bonding to the adjacent [Cd 9Cl 20(H 2O) 2] n (2 n- ) sheets. In the copper compound, the modification of the parent CuCl 2 structure is much more complex. In this compound, [Cu 2Cl 2] (2+) moieties are excised in a regular fashion. In addition, at 50% of the Cu1 sites, CuCl 2 species are replaced by pairs of water molecules in a random fashion. The Cu(TIM) (2+) cations bridge the layers via the formation of two semicoordinate bonds to chloride ions at the edge of the [Cu 2Cl 2] (2+) excision sites of adjacent layers.

Dimethylammonium Trichlorocuprate(II): Structural Transition, Low-Temperature Crystal Structure, and Unusual Two-Magnetic Chain Structure Dictated by Nonbonding Chloride−Chloride Contacts

Catena(dimethylammonium-bis(mu2-chloro)-chlorocuprate), (CH3)2NH2CuCl3, forms chains of Cu2Cl6(2-) bifold dimers linked along the structural chain axis by terminal chlorides forming long semicoordinate bonds to adjacent dimers. The structural chains are separated by dimethylammonium ions that hydrogen bond to chloride ions of the dimers. A structural phase transition below room temperature removes disorder in the hydrogen bonding, leaving adjacent dimers along the chain structurally and magnetically inequivalent, with alternating ferromagnetic and antiferromagnetic pairs. The coupled dimers are magnetically isolated from each other along the structural chain axis by the long semicoordinate Cu-Cl bond. However, the dimers couple to like counterparts on adjacent chains via nonbonding Cl...Cl contacts. The result is two independent magnetic chains, one an alternating antiferromagnetic chain and the other an antiferromagnetic chain of ferromagnetically coupled copper dimers, which run perpendicular to the structural chains. This magnetostructural analysis is used to fit unusual low-temperature (1.6 K) magnetization vs field data that display a two-step saturation. The structural phase transition is identified with neutron scattering and capacitance measurements, and the X-ray crystal structures are determined at room temperature and 84 K. The results appear to resolve long-standing confusion about the origins of the magnetic behavior of this compound and provide a compelling example of the importance of two-halide magnetic exchange.

The Electrostatic Nature of Aryl−Bromine−Halide Synthons: The Role of Aryl−Bromine−Halide Synthons in the Crystal Structures of the trans-Bis(2-bromopyridine)dihalocopper(II) and trans-Bis(3-bromopyridine)dihalocopper(II) Complexes

The role of C−Br···X synthons in the structures of Cu(nbp)2X2 (nbp = n-bromopyridine; n = 2 and 3) are investigated. A comparison of the role of these synthons in these and in the previously published (nBP)2CuX4 and (nBP)X structures (nBP = n-bromopyridinium cations; X = Br- or Cl-; n = 2, 3, or 4) indicate that electrostatic effects, the positive charge on the bromopyridinium cation and the negative charge on the halide anion, play a major role in the strength and directionality of C−Br···X synthons. The data indicates that the C−Br···X synthons are stronger in the (nBP)2CuX4 and (nBP)X salts compared with the Cu(nbp)2X2 compounds. The supramolecular assembly of these Cu(nbp)2X2 complexes is dominated by nontraditional C−Br···X synthons and Cu···X semicoordinate bonds. The bromine−halide distances are almost equal to the sum of their van der Waals radii (rvdW) in Cu(3bp)2X2 but less than the sum of the rvdW by ∼0.24 Å in Cu(2bp)2X2. The C−Br···X angles are close to linear, ranging from 158.15(8)° to 167.90(8)° for Cu(3bp)2Cl2 and Cu(2bp)2Cl2 respectively. The Cu(2bp)2X2 units form chain structures based on the C−Br···X synthons. These chains interact via C−H···X and π−π stacking to form the three-dimensional structure. In contrast, the chain structures in Cu(3bp)2X2 compounds are based on the Cu···X semicoordinate bond. These chains interact via C−Br···X synthons to form the three-dimensional structure.

Aqua(2,2′-bi-1H-imidazole)chlorocopper(II) chloro(iminodiacetato)copper(II) monohydrate

In the title compound, [CuCl(C6H6)N4)(H2O)][Cu(C4H5NO4)Cl].H2O, the Cu(II) atom in the cation is coordinated by one Cl- ion, two N atoms of the 2,2'-biimidazole ligand and one aqua ligand. Within the anion, the Cu(II) atom is bonded to one Cl- ion, and one N and two O atoms of the iminodiacetate ligand. Neighbouring cations and anions are connected to each other by Cu...Cl semi-coordination bonds of 2.830 (12) and 3.071 (12) A, forming a Cu2Cl2 rectangular unit. The dinuclear units further link into a polymeric chain along the a axis through Cu...O(aqua) interactions of 2.725 (3) A. Including the long coordination bonds, the geometries around the Cu atoms in the cation and anion are square-pyramidal and distorted octahedral, respectively.

Thermal and Photo-Responsibility of Axial Semi-Coordination Bonds in a Copper(II) Complex

Abstract The thermal and photo-responsibility of the axial semi-coordination Cu–O bonds in [Cu(en)2](ClO4)2 (1) (en = ethylenediamine) have been investigated. We discovered a new photoresponsive behavior that was attributed to photo-induced ClO4− cleavage accompanied by compression of the Cu–O bonds using the structural degree of freedom of the semi-coordination bonds.

Synthesis and Structure of Bis(2-Amino-5-Cyanopyridinium) Diaquadichlorocopper(II) Dichloride

The reaction of CuCl2 with 2-amino-5-cyanopyridine and HCl in 1-propanol gave bis(2-amino-5-cyanopyridinium) diaquadichlorocopper(II) dichloride (1). Crystal data for 1 are: monoclinic, space group: P21/c, a = 8.461(3) Å, b=14.665(5) Å, c=7.883(3) Å, g =96.105(4)°, V=972.6(6) Å 3 , Z=2, Dcalc =1.645 Mg/m3, w =1.691 mm−1, F(OOO)=486, MoK f( u =0.71073 Å), R1=0.0431 for [∣I∣ S 2 σ (I)] and R1=0.0680 for all 1944 unique reflections and 130 parameters. The structure exists as square planar Cu(H2O)2Cl2 units with long semi-coordinate bonds to the cyano nitrogens of the 2-amino-5-cyanopyridinium ions. Hydrogen bonding from the water molecules and N―H hydrogens to the chloride irons stablises the lattice.

A redetermination of bis(ethylenediamine-N,N')bis(perchlorato-O)copper(II)

Reaction of copper(II) perchlorate with excess ethylenediamine (en) in aqueous solution gave the title complex, [Cu(ClO 4 ) 2 (C 2 H 8 N 2 ) 2 ]. The cation is centrosymmetric with a mean Cu-N distance of 2.016 (2) A. There are semi-coordinate bonds to the perchlorate ions with a Cu-O distance of 2.579 (4) A. The N-Cu-N angle is 84.69 (9)°, as expected for chelating en. The structure is stabilized by hydrogen bonds from three of the perchlorate O atoms to amino H atoms within each molecule and between molecules, linking them into chains.

Redetermination of [Cu5Cl10(n-C3H7OH)2

The structure of the title compound octa-μ-chloro-1:2κ4Cl, 2:3κ4Cl, 3:4κ4Cl, 4:5κ4Cl-dichloro-1κCl,5κCl- bis(propanol)-1κO, 5κO-pentacopper(II), consists of planar bibridged pentameric Cu5Cl10L2 (L = n-propanol) units. Each Cu2+ ion assumes an approximate square-planar coordination geometry, with Cu—Cl distances ranging between 2.258 (2) and 2.297 (3) A. The oligomers form stacks parallel to b through the formation of longer semicoordinate bonds which range in length from 2.687 (2) to 3.158 (3) A. The stacking pattern leaves one semicoordinate site vacant on the Cu(3) atom. The stacks then aggregate into sheets lying parallel to the (\overline{1}01) planes through the formation of semicoordinate Cu(3)—Cl(5) bonds of 2.681 (2) A. The n-propyl groups separate these sheets. Large atomic displacements of the C atoms [particularly for atoms C(2) and C(3)] indicate substantial disorder of the propyl group.

Anomalous magnetic properties of planar bibridged trinuclear copper(II)-halide compounds

The magnetic susceptibilities of five trinuclear pseudoplanar bibridged copper(II) chloride species have been measured from approximately 5 to 300 K. The compounds all show antiferromagnetic intratrimer and generally weaker ferromagnetic intertrimer spin coupling. These compounds show systematic deviations from the susceptibility as calculated from an isotropic Heisenberg Hamiltonian with nearest-neighbor coupling. The deviations arise from intertrimer interactions through the formation of semicoordinate bonds and result in a spin-frustrated state at low temperatures. The results of a phenomenological mean field theory model support spin-frustration occurrence by accurately modeling the non-Boltzmann depopulation of the excited quartet state. Preliminary cluster expansion calculations have not lent support to the postulate but more extended calculations may be necessary to include a sufficient number of intermolecular interactions in order to accurately describe the crystalline state.

Organoboron compounds 396. Crystal and molecular structure of dipropylboryl-(2-formimidoylaminopyridinate)

1. X-ray structure analysis has been used to determine the crystal and molecular structure of dipropylboryl-(2-forminimidoylaminopyridinate). 2. In the chelate ring of dipropylboryl-(2-forminimidoylaminopyridinate), six of the π-electrons form a nonclosed five-center π-system (NCNCN), and the B-N bonds are semicoordination bonds. 3. Protonation of dipropylboryl-(2-forminimidoylaminopyridinate) takes place through the N2 atom.

Synthesis and certain properties of 1,3,5-triphenylcyclotriborothian (phenylmercaptoborane trimer)

1. Diborane reacts with thiophenol in ethereal solution at room temperature to form phenylmercaptoborane trimer, 1,3,5-triphenylcyclotriborothian. 2. Phenyl radicals reduce the strength of the semicoordinate bonds in 1,3,5-substituted cyclotriborothians. 3. In tetrahydrofuran the phenylmercaptoborane trimer dissociates and forms a complex with tetrahydrofuran. 4. With trimethylamine the phenylmercaptoborane trimer is converted to trimethylamine-phenylmercaptoborane. 5. On heating the phenylmercaptoborane trimer reacts with thiophenol by replacing the hydrogen atoms at the boron with phenylmercapto groups.