1 A 1 ⇄ 5 T 2 Spin Transition in New Thermochromic Iron(II) Complexes with 1,2,4-Triazole and 4-Amino-1,2,4-Triazole

New complexes of iron(II) chloride and bromide with 1,2,4-triazole (Htrz) and 4-amino-1,2,4-tri-azole (NH₂trz) of composition Fe(Htrz)₃Cl₂ · 1.5H₂O, Fe(NH₂trz)₃Cl₂ · 2H₂O, Fe(Htrz)₃Br₂ · 2H₂O, and the Fe(NH₂trz)₃SO₄ · H₂O complex were synthesized and studied by magnetochemical, electronic, IR and Mössbauer spectroscopy methods. Magnetochemical studies showed that these complexes exhibit ¹ A ₁ ⁵ T ₂ spin transition accompanied by thermochromism (a reversible pink white change of color).     

Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged {HAT ⋅ (FeIICl2)3}n (n=2- and 3-) Assemblies of Hexaazatriphenylenes (HAT)

Hexaazatrianthracene (HATA) and hexaazatriphenylenehexacarbonitrile {HAT(CN)₆} are reduced by metallic iron in the presence of crystal violet (CV⁺)(Cl⁻). Anionic ligands are produced, which simultaneously coordinate three Fe^IICl₂ to form (CV⁺)₂{HATA ⋅ (Fe^IICl₂)₃}²⁻ ⋅ 3 C₆H₄Cl₂ ( 1 ) and (CV⁺)₃{HAT(CN)_6. (Fe^IICl₂)₃}³⁻ ⋅ 0.5CVCl ⋅ 2.5 C₆H₄Cl₂ ( 2 ). High-spin (S=2) Fe^II atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between Fe^II in {HATA ⋅ (Fe^IICl₂)₃}²⁻ ( 1 ) with a Weiss temperature (Θ) of −80 K, the PHI estimated exchange interaction (J) is −4.7 cm⁻¹. The {HAT(CN)₆ ⋅ (Fe^IICl₂)₃}³⁻ assembly is obtained in 2 . The formation of HAT(CN)₆^.3− is supported by the appearance of an intense EPR signal with g=2.0037. The magnetic behavior of 2 is described by a strong antiferromagnetic coupling between the Fe^II and HAT(CN)₆^.3− spins with J₁=−164 cm⁻¹ (−2 J formalism) and by a weaker antiferromagnetic coupling between the Fe^II spins with J₂=−15.4 cm⁻¹. The stronger coupling results in the spins of the three Fe^IICl₂ units to be aligned parallel to each other in the assembly. As a result, an increase of the χ_MT values is observed with the decrease of temperature from 9.82 at 300 K up to 15.06 emu ⋅ K/mol at 6 K, and the Weiss temperature is also positive being at +23 K. Thus, a change in the charge and spin state of the HAT-type ligand to ⋅3⁻ results in ferromagnetic alignment of the Fe^II spins, yielding a high-spin (S=11/2) system. DFT calculations showed that, due to the high symmetry and nearly degenerated LUMO of both HATA and HAT(CN)₆, their complexes with Fe^IICl₂ have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.     

1,2,4‐Triazole Controlled CdII/MnII Complexes with Discrete Mononuclear,Polymeric 1D Chain,and 2D Layer Motifs

Three Htrz‐based metal complexes, [Cd(trz)(CH₃OH)(nb)]_n ( 1 ), [Cd(Htrz)(H₂O)(nb)₂]_n ( 2 ), and {[Mn(Htrz)₂(H₂O)₄] · 2nb} ( 3 ) (Htrz = 1,2,4‐triazole, Hnb = 4‐nitrobenzoic acid), have been synthesized by diffusion or solvent evaporation method and structurally characterized by single crystal X‐ray crystallography, elemental analysis, IR and fluorescence spectroscopy, and TG‐DTA. Structural determinations revealed that complex 1 has a two‐dimensional (2D) layer structure constructed by tridentate μ_N1,N2,N4‐bridging trz anions and Cd^II ions. Complex 2 presents a 1D polymeric chain structure bridged by bidentate μ_N1,N4‐bridging Htrz molecule and Cd^II ions, whereas compound 3 is a supramolecular assembly containing a mononuclear [Mn(Htrz)₂(H₂O)₄]²⁺ dication and two free nb anions for charge compensation. Thus, the structural diversity of the three complexes is significantly governed by the coordination modes of the neutral/deprontated Htrz ligand, rather than the terminal/lattice nb anion. Additionally, the thermal stability of the complexes is observed to be dependent on the polymeric or discrete structure nature. At room temperature, the three solid complexes show Htrz‐based intraligand fluorescent emission.     

Magnetic investigations of a two‐dimensional coordination polymer with a three‐dimensional supramolecular framework: poly[[bis[μ2‐1,4‐bis(1,2,4‐triazol‐1‐yl)butane]bis(thiocyanato‐κN)cobalt(II)] dihydrate]

In the title mixed‐ligand metal–organic polymeric complex, {[Co(NCS)₂(C₈H₁₂N₆)₂]·2H₂O}_n, the asymmetric unit contains a divalent Co^II cation, which sits on an inversion centre, two halves of two crystallographically distinct and centrosymmetric 1,4‐bis(1,2,4‐triazol‐1‐yl)butane (BTB) ligands, one N‐bound thiocyanate ligand and one solvent water molecule. The Co^II atom possesses a distorted {CoN₆} octahedral geometry, with the equatorial positions taken up by triazole N atoms from four different BTB ligands. The axial positions are filled by thiocyanate N atoms. In the crystal, each Co^II atom is linked covalently to four others through the distal donors of the tethering BTB ligands, forming a neutral (4,4)‐topology two‐dimensional rhomboid grid layer motif, which is coincident with the (11) crystal planes. Magnetic investigations show that weak antiferromagnetic coupling exists between Co^II atoms in the complex.     

A 3D Polyoxometalate‐Based Framework Constructed from Ag/trz Metal‐Organic Ribbons and P2W18 Polyoxoanions: Synthesis,Structure and Electrochemical Properties

A Wells‐Dawson Polyoxometalate‐based hybrid, Ag₉(trz)₃(Htrz)₄ (H₂O)(P₂W₁₈O₆₂)·3H₂O ( 1 ) (Htrz = 1,2,4‐1H‐triazole) was hydrothermally synthesized through using trz ligand and silver nitrate in the presence of [P₂W₁₈O₆₂]^6– polyoxoanion. In the 3D framework structure of compound 1 , two kinds of wave‐like Ag/trz chains originated from trz ligands and silver cations are aggregated in a “2+1” mode by {Ag₂/trz} linkages to result in a 1D Ag/trz metal‐organic ribbon, which is further extended into a 3D framework structure by [P₂W₁₈O₆₂]^6– polyoxoanions through Ag‐O covalent bonds. Additionally, the electrochemical properties of compound 1 have also been investigated.     

Varieties in structures of Co(II), Ni(II) and Cu(II) coordination compounds based on dimethyl pyridin-2-ylcarbamoylphosphoramidate

A series of new 3d metal complexes based on dimethyl pyridin-2-ylcarbamoylphosphoramidate (HL) was synthesized. The compounds with general formula M(HL)₂Cl₂·nH₂O and M(L)₂·nH₂O (M=Co²⁺, Cu²⁺, Ni²⁺) were characterized by means of single-crystal X-ray analysis and IR spectroscopy. The organic ligands in all complexes are coordinated via oxygen atom of the carbonyl group and nitrogen atom of the heterocycle. The coordination environment of the central atoms is a distorted octahedron. The axial positions in the Co(II) and Ni(II) complexes with deprotonated ligands are occupied by water molecules. The Co(II) and Cu(II) complexes with phosphoryl ligands in a neutral form have different ligands in the axial positions: in the Co(II) complex, the positions are occupied by two water molecules, whereas in the Cu(II) complex, the positions are occupied by two chlorine anions. The structure of HL was experimentally and theoretically obtained by utilizing single-crystal X-ray analysis and DFT calculations. The computationally optimized geometric parameters for HL show a good agreement with the experimental results.     

Novel heteroligand complexes of Co(II), Cu(II), Ni(II) and Mn(II) formed by 2,2′-dipyridyl or 1,10-phenanthroline and phosphortriamide ligands: Synthesis and structure

This paper presents examples of mixed-ligand Co(II), Cu(II), Ni(II) and Mn(II) complexes, with a distorted octahedral coordination geometry, with 2,2′-dipyridyl or 1,10-phenanthroline and phosphortriamide ligands. The complexes of the general type ML₂·Lig (where M = Co(II), Cu(II), Ni(II), Mn(II); L⁻ = {Cl₃C(O)NP(O)R₂}⁻ (R = NHBz, NHCH₂CHCH₂, NEt₂); Lig = 2,2′-dipyridyl or 1,10-phenanthroline) were synthesised and characterised by means of X-ray diffraction, IR and UV–Vis spectroscopy. The phosphortriamide ligands are coordinated via oxygen atoms of phosphoryl and carbonyl groups involved in six-membered metal cycles. The additional ligands 2,2′-dipyridyl or 1,10-phenanthroline are coordinated to the central atom, forming five-membered cycles.     

Magnetic Anisotropy Transfer from Mono- to Polymetallic Complexes

The reaction of multi-bidentate oxamate-based copper(II) complexes with the [Ni(ⁱPrtacn)Cl₂] complex (ⁱPrtacn:1,4,7-triisopropyl-1,4,7-triazacyclononane) has been investigated. X-ray diffraction studies reveal that for all compounds the oxamato κO,κΟ’ bidentate coordination site replaces the two chloride ions in [Ni(iPrtacn)Cl₂] to form trimetallic {CuNi₂} ( 1 – 3) , hexametallic {Cu₂Ni₄} ( 4 ) and enneametallic {Cu₃Ni₆} ( 5 ) complexes. The investigation of the magnetic properties shows that Cu−Ni interactions through the oxamato bridge are in the expected range (−111 cm⁻¹, −68 cm⁻¹). For 1 – 3 , both the sign and strength of the magnetic couplings are computed independently from DFT calculations, and these estimates broadly agree with the experiments. The magnetization measurements and EPR studies reveal that 1 – 3 are anisotropic: a significant portion of the large anisotropy of the [Ni(ⁱPrtacn)Cl₂] complex is retained, resulting in a D value for the S=3/2 ground state of 5 cm⁻¹ on average. This is no longer the case for 4 and 5 where the anisotropy of the Ni(II) complexes is diluted due to the high nuclearity of the final edifices. These results show that it is possible to obtain trimetallic complexes with a high anisotropy and a high spin value for the ground state by a judicious choice of the interacting metal ions.     

New homoleptic metal complexes of Schiff bases derived from 2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-one

New bidentate Schiff-base ligands 2-(2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazinecarbothioamide HL¹ and 2-(2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazinecarboxamide HL² were synthesized from the condensation of 2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-one with thiosemicarbazide and semicarbazide, respectively. Homoleptic complexes of these ligands, of general formula K[Cr(L ⁿ )₂Cl₂], K₂[Mn(L ⁿ )₂Cl₂], K₂[Fe(L¹)₂Cl₂] and [M(L ⁿ )₂] (where M = Co(II), Ni(II) Cu(II), Zn(II), Cd(II), and Hg(II) ions; n = 1 or 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometry for Cr(III), Mn(II), and Fe(II) complexes, square planar for Cu(II), Co(II), and Ni(II) complexes and tetrahedral for Zn(II), Cd(II), and Hg(II) complexes.     

Comparison of the methyl ester of l‐tyrosine hydrochloride and its methanol monosolvate

Solvent‐free (2S)‐methyl 2‐ammonio‐3‐(4‐hydroxy­phenyl)­propionate chloride, C₁₀H₁₄NO₃⁺·Cl⁻, (I), and its methanol solvate, C₁₀H₁₄NO₃⁺·Cl⁻·CH₃OH, (II), are obtained from different solvents: crystallization from ethanol or propan‐2‐ol gives the same solvent‐free crystals of (I) in both cases, while crystals of (II) were obtained by crystallization from methanol. The structure of (I) is characterized by the presence of two‐dimensional layers linked together by N—H⋯Cl and O—H⋯Cl hydrogen bonds and also by C—H⋯O contacts. Incorporation of the methanol solvent mol­ecule in (II) introduces additional O—H⋯O hydrogen bonds linking the two‐dimensional layers, resulting in the formation of a three‐dimensional network.     

Synthesis,crystal structure and magnetic properties of the cyano-bridged heteropolynuclear complex [{(Cu(dien))2Co(CN)6}n][Cu(dien)(H2O)Co(CN)6]n·5nH2O

The reaction of [Cu(dien)(H₂O)](NO₃)₂ with K₃[Co(CN)₆] leads to the cyano-bridged heteropolynuclear complex, [{(Cu(dien))₂Co(CN)₆}_n][Cu(dien)(H₂O)Co(CN)₆]_n·5nH₂O, {Cu₃Co₂}, whose crystal structure has been solved. The structure consists of two distinct ionic units, namely one-dimensional cationic chains [{(Cu(dien))₂Co(CN)₆}_n]ⁿ⁺, and discrete binuclear anionic entities [(H₂O)(dien)Cu–NC–Co(CN)₅]⁻. The cryomagnetic investigation of the title compound reveals a very weak antiferromagnetic coupling between the Cu(II) ions within the cationic chain (J=−1.02 cm⁻¹, g=2.14). The complete elimination of the water molecules from the isomorphous {Cu₃Co₂}, {Cu₃Fe₂} and {Cu₃Cr₂} complexes causes the modification of the magnetic properties. The most dramatic one is observed with the Cu(II)–Fe(III) system, where the magnetic behavior changes from ferro- to antiferromagnetic. The dehydrated chromium derivative preserves the ferromagnetic coupling, which is observed at lower temperatures (below 30 K) in comparison with the parent compound (below 150 K).     

The thermodynamic properties of Fe(II) complexes with 1,2,4-triazoles

The temperature dependences of the heat capacities at 106–330 K of the monoligand Fe(NH₂trz)₃I₂ (I) and mixed-ligand Fe(Htrz)_0.3(NH₂trz)_2.7SiF₆ · H₂O (II) complexes (Htrz is 1,2,4-triazole, and NH₂trz is 4-amino-1,2,4-triazole) were studied by adiabatic vacuum calorimetry. The ¹A₁ ⇔ ⁵T₂ spin transition was observed in these compounds. The thermodynamic parameters of phase transitions in I and II were determined.     

Diazabutadiene cobalt(II) complexes

Summary Studies on the chelates of cobalt(II) with the bidentate ligands 1,4-diphenyl(2,3-dimethyl-1,4-diazabutadiene) (PMB) and 1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene (MPMB) have been carried out. On the basis of elemental analyses, the complexes are [Co(PMB)Cl₂], [Co(PMB)₂(C1O₄)₂], [Co(MPMB)Cl₂] and [Co(MPMB)₂(ClO₄)₂].Both ligands are bidentatevia nitrogen atoms in all the complexes. The magnetic susceptibility and i.r. and u.v.-visible spectra are reported and discussed. The chloro-compounds involving two chlorine ligands and, in the perchlorate compounds, the ClO ₄ ^– groups are bound to the cobalt(II) centre.     

7‐Carboxyl­ato‐8‐hydroxy‐2‐methyl­quinolinium monohydrate and 7‐carboxy‐8‐hydroxy‐2‐methyl­quinolinium chloride monohydrate at 100 K

Both 7‐carboxyl­ato‐8‐hydroxy‐2‐methyl­quinolinium monohydrate, C₁₁H₉NO₃·H₂O, (I), and 7‐carboxy‐8‐hydroxy‐2‐methyl­quinolinium chloride monohydrate, C₁₁H₁₀NO₃⁺·Cl⁻·H₂O, (II), crystallize in the centrosymmetric P space group. Both compounds display an intramolecular O—H⋯O hydrogen bond involving the hydroxy group; this hydrogen bond is stronger in (I) due to its zwitterionic character [O⋯O = 2.4449 (11) Å in (I) and 2.5881 (12) Å in (II)]. In both crystal structures, the HN⁺ group participates in the stabilization of the structure via intermolecular hydrogen bonds with water mol­ecules [N⋯O = 2.7450 (12) Å in (I) and 2.8025 (14) Å in (II)]. In compound (II), a hydrogen‐bond network connects the Cl⁻ anion to the carboxylic acid group [Cl⋯O = 2.9641 (11) Å] and to two water mol­ecules [Cl⋯O = 3.1485 (10) and 3.2744 (10) Å].     

Proton‐bifurcated C—H⋯(O,O) hydrogen bonds in 2,3‐dichloro‐6‐nitro­benzyl­aminium chloride

In the crystal structure of the title salt, C₇H₇Cl₂N₂O₂⁺·Cl⁻, the chloride anions participate in extensive hydrogen bonding with the aminium cations and indirectly link the mol­ecules through multiple N⁺—H⋯Cl⁻ salt bridges. There are two independent mol­ecules in the asymmetric unit, related by a pseudo‐inversion center. The direct inter­molecular coupling is established by C—H⋯O, C—H⋯Cl and C—Cl⋯Cl⁻ inter­actions. A rare three‐center (donor bifurcated) C—H⋯(O,O) hydrogen bond is observed between the methyl­ene and nitro groups, with a side‐on intra­molecular component of closed‐ring type and a head‐on inter­molecular component.     

Cobalt(II) Complexes with N‐Thioacylamidophosphates and 2,2′‐Bipyridyl and 1,10‐Phenathroline. Crystal Structures,Solution 1H NMR Spectral and Magnetic Properties

Structure and magnetic properties of N‐diisopropoxyphosphorylthiobenzamide PhC(S)‐N(H)‐P(O)(OiPr)₂ ( HL^I ) and N‐diisopropoxyphosphoryl‐N′‐phenylthiocarbamide PhN(H)‐C(S)‐N(H)‐P(O)(OiPr)₂ ( HL^II ) complexes with the Co^II cation of formulas [Co{PhC(S)‐N‐P(O)(OiPr)₂}₂] ( 1 ), [Co{PhN(H)‐C(S)‐N‐P(O)(OiPr)₂}₂] ( 2 ), [Co{PhC(S)‐N(H)‐P(O)(OiPr)₂}₂{PhC(S)‐N‐P(O)(OiPr)₂}₂] ( 1a ) and [Co{PhC(S)‐N‐P(O)(OiPr)₂}₂}(2,2′‐bipy)] ( 3 ), [Co{PhC(S)‐N‐P(O)(OiPr)₂}₂(1,10‐phen)] ( 4 ), [Co{PhN(H)‐C(S)‐N‐P(O)(OiPr)₂}₂(2,2′‐bipy)] ( 5 ), [Co{PhN(H)‐C(S)‐N‐P(O)(OiPr)₂}₂(1,10‐phen)] ( 6 ) were investigated. Paramagnetic shifts in the ¹H NMR spectrum were observed for high‐spin Co^II complexes with HL^I,II , incorporating the S‐C‐N‐P‐O chelate moiety and two aromatic chelate ligands. Investigation of the thermal dependence of the magnetic susceptibility has shown that the extended materials 1‐2 and 6 show ferromagnetic exchange between distorted tetrahedral ( 1 , 2 ) or octahedral ( 1a , 6 ) metal atoms whereas 3 and 5 show antiferromagnetic properties. Compound 4 behaves as a spin‐canted ferromagnet, an antiferromagnetic ordering taking place below a critical temperature, T_c = 115 K. Complexes 1 and 1a were investigated by single crystal X‐ray diffraction. The cobalt(II) atom in complex 1 resides a distorted tetrahedral O₂S₂ environment formed by the C=S sulfur atoms and the P=O oxygen atoms of two deprotonated ligands. Complex 1a has a tetragonal‐bipyramidal structure, Co(O^ax)₂(O^eq)₂(S^eq)₂, and two neutral ligand molecules are coordinated in the axial positions through the oxygen atoms of the P=O groups. The base of the bipyramid is formed by two anionic ligands in the typical 1,5‐O,S coordination mode. The ligands are in a trans configuration.     

2,2′‐(Iminodimethylene)bis(1H‐benzimidazolium)(1+) chloride

The title compound, C₁₆H₁₆N₅⁺·Cl⁻ (nbbH⁺·Cl⁻), displays N—H⋯N, N—H⋯Cl and π–π inter­actions in the crystal packing. The Cl⁻ anion is chelated by the nbbH⁺ cation via two N—H⋯Cl hydrogen bonds. Inter‐ion N—H⋯N and N—H⋯Cl hydrogen bonds link ions related by 2₁ screw axes into chains along the c axis. These chains are further linked by glide‐plane operations to generate a three‐dimensional network, which is additionally stabilized by inter­chain π–π inter­actions.     

Copper complexes of 1-[(2-carboxyethyl)benzene]-3-[2-pyridine]triazene

The triazenide, 1-[(2-carboxyethyl)benzene]-3-[2-pyridine]triazene (HL), has been synthesized. In the presence of Et₃N, the reaction of HL with Cu(OAc)₂·H₂O or CuCl₂·2H₂O gives the tetranuclear copper(II) complexes {Cu₄(L)₂(μ₂-OH)₂(OAc)₄} 1 and {Cu₄L₄(μ₄-O)Cl₂} 2, respectively. The X-ray crystal structures of both complexes have been obtained. Magnetic studies indicate significant antiferromagnetic coupling between the copper(II) centers for both complexes, with coupling constants (J) of −493.4 cm⁻¹ for 1 and −165 cm⁻¹ for 2.     

Effect of Intermolecular Interactions on Metal‐to‐Metal Charge Transfer: A Combined Experimental and Theoretical Investigation

Understanding the effects of intermolecular interactions on metal‐to‐metal charge transfer (MMCT) is crucial to develop molecular devices by grafting MMCT‐based molecular arrays. Herein, we report a series of solvent‐free {Fe₂Co₂} compounds sharing the same cationic tetranuclear {[Fe(PzTp)(CN)₃]₂[Co(dpq)₂]₂}²⁺ (PzTp^?=tetrakis(pyrazolyl)borate, dpq=dipyrido[3,2‐d:2′,3′‐f]quinoxaline) square units but having anions with different size, including BF₄^?, PF₆^?, OTf^?, and [Fe(PzTp)(CN)₃]^?. Intermolecular π???π interactions between dpq ligands, which coordinate to cobalt ions in the {[Fe(PzTp)(CN)₃]₂[Co(dpq)₂]₂}²⁺ units, can be modulated by introducing different counterions, regulating the distortion of the CoN₆ octahedron and ligand field around the cobalt ions. This change results in different MMCT behavior. Computational analyzes reveal the substantial role of the intermolecular interactions tuned by the presence of different counteranions on the MMCT behavior.     

l‐Methioninium chloride and l‐seleno­methioninium chloride at 103 K

The crystal structures of the title compounds, (S)‐1‐carboxy‐3‐(methyl­sulfanyl)­propanaminium chloride, C₅H₁₂NO₂S⁺·Cl⁻, and (S)‐1‐carboxy‐3‐(methyl­selanyl)­propanaminium chloride, C₅H₁₂NO₂Se⁺·Cl⁻, are isomorphous. The proton­ated l ‐methionine and l ‐seleno­methionine mol­ecules have almost identical conformations and create very similar contacts with the Cl⁻ anions in the crystal structures of both compounds. The amino acid cations and the Cl⁻ anions are linked viaN—H⋯Cl⁻ and O—H⋯Cl⁻ hydrogen bonds.