A Sequential Method to Prepare Polymorphs and Solvatomorphs of [Fe(1,3‐bpp)2](ClO4)2⋅nH2O (n=0, 1, 2) with Varying Spin‐Crossover Behaviour

Two polymorphs of the spin crossover (SCO) compound [Fe(1,3‐bpp)₂](ClO₄)₂ ( 1 and 2 ; 1,3‐bpp=2‐(pyrazol‐1‐yl)‐6‐(pyrazol‐3‐yl)pyridine) were prepared using a novel, stepwise procedure. Crystals of 1 deposit from dry solvents, while 2 is obtained from a solid‐state procedure, by sequentially removing lattice H₂O molecules from the solvatomorph [Fe(1,3‐bpp)₂](ClO₄)₂?2 H₂O ( 2 ?2 H₂O), using single‐crystal‐to‐single‐crystal (SCSC) transformations. Hydrate 2 ?2 H₂O is obtained through the same reaction as 1 , now with 2.5 % of water added. Compounds 2 and 2 ?2 H₂O are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3‐bpp)₂](ClO₄)₂?H₂O ( 2 ?H₂O), also following SCSC processes. The four derivatives have been characterised by single‐crystal X‐ray diffraction (SCXRD). Furthermore, the homogeneity of the various compounds as well as their SCSC interconversions have been confirmed by powder X‐ray diffraction (PXRD). Polymorphs 1 and 2 exhibit abrupt SCO behaviour near room temperature with T_1/2↑=279/316 K and T_1/2↓=276/314 K (near 40 K of shift) and different cooperativity.     

[Fe(TPT)2/3{MI(CN)2}2]⋅nSolv (MI=Ag,Au): New Bimetallic Porous Coordination Polymers with Spin‐Crossover Properties

Two new heterobimetallic porous coordination polymers with the formula [Fe(TPT)_2/3{M^I(CN)₂}₂] ? nSolv (TPT=[(2,4,6‐tris(4‐pyridyl)‐1,3,5‐triazine]; M^I=Ag (nSolv=0, 1 MeOH, 2 CH₂Cl₂), Au (nSolv=0, 2 CH₂Cl₂)) have been synthesized and their crystal structures were determined at 120 K and 293 K by single‐crystal X‐ray analysis. These structures crystallized in the trigonal R‐3m space group. The Fe^II ion resides at an inversion centre that defines a [FeN₆] coordination core. Four dicyanometallate groups coordinate at the equatorial positions, whilst the axial positions are occupied by the TPT ligand. Each TPT ligand is centred in a ternary axis and bridges three crystallographically equivalent Fe^II ions, whilst each dicyanometallate group bridges two crystallographically equivalent Fe^II ions that define a 3D network with the topology of NbO. There are two such networks, which interpenetrate each other, thereby giving rise to large spaces in which very labile solvent molecules are included (CH₂Cl₂ or MeOH). Crystallographic analysis confirmed the reversible structural changes that were associated with the occurrence of spin‐crossover behaviour at the Fe^II ions, the most significant structural variation being the change in unit‐cell volume (about 59 ų per Fe^II ion). The spin‐crossover behaviour has been monitored by means of thermal dependence of the magnetic properties, Mössbauer spectroscopy, and calorimetry.     

A Ferroelectric Iron(II) Spin Crossover Material

A dual‐function material in which ferroelectricity and spin crossover coexist in the same temperature range has been obtained. Our synthetic strategy allows the construction of acentric crystal structures in a predictable way and is based on the high directionality of hydrogen bonds. The well‐known iron(II) spin crossover complex [Fe(bpp)₂]²⁺ (bpp=2,6‐bis(pyrazol‐3‐yl)pyridine), a four‐fold noncentrosymmetric H‐bond donor, was combined with a disymmetric H‐bond acceptor such as the isonicotinate (isonic) anion to afford [Fe(bpp)₂](isonic)₂⋅2 H₂O. This low‐spin iron(II) compound crystallizes in the acentric nonpolar I space group and shows piezoelectricity and SHG properties. Upon dehydration, it undergoes a single‐crystal to single‐crystal structural rearrangement to a monoclinic polar Pc phase that is ferroelectric and exhibits spin crossover.     

2,6‐Bis(pyrazol‐3‐yl)pyridine as Meridional Capping Ligand: Synthesis,Characterization, and Crystal Structure of the First Corresponding Hexanuclear Iron(III) Complex

Based on the 2,6‐bis(pyrazol‐3‐yl)pyridine ligand (H₂bpp) the hexanuclear iron(III) complex [Fe₆(bpp)₄(μ₃‐O)₂(μ‐OMe)₃(μ‐OH)Cl₂] ( 1 ) was synthesized. The reaction with iron(II) chloride and additional pyridine leads to the exclusive formation of the complex through self‐assembly process. Six octahedrally coordinated iron atoms are linked through the pyrazolido groups of four H₂bpp ligands. These are further linked through bridging hydroxido, methoxido, and oxido groups. The complex has been characterized by IR spectroscopy, ESI mass spectrometry, elemental analysis and X‐ray crystallography. Temperature‐dependent magnetic measurements indicate strong antiferromagnetic exchange interaction between the high‐spin iron(III) ions within the complex, which leads to an S = 0 spin ground state. As a result of the two Fe3(μ₃‐O) fragments two frustrated exchange pathways are present. In addition the properties of H₂bpp as a potential capping ligand for the synthesis of heteroleptic trinuclear complexes based on the triaminoguanidine core is investigated.     

A Reversible Hydrogen-Bond Isomerization Triggered by an Abrupt Spin Crossover near Room Temperature

The spin crossover salt [Fe(bpp)₂](isonicNO)₂⋅ 2.4 H₂O ( 1 ⋅2.4 H₂O) (bpp=2,6-bis(pyrazol-3-yl)pyridine; isonicNO=isonicotinate N-oxide anion) exhibits a very abrupt spin crossover at T_1/2=274.4 K. This triggers a supramolecular linkage (H-bond) isomerization that responds reversibly towards light irradiation or temperature change. Isotopic effects in the thermomagnetic behavior reveal the importance of hydrogen bonds in defining the magnetic state. Further, the title compound can be reversibly dehydrated to afford 1 , a material that also exhibits spin crossover coupled to H-bond isomerization, leading to strong kinetic effects in the thermomagnetic properties.     

Local Coordination Geometry and Spin State in Novel FeII Complexes with 2,6‐Bis(pyrazol‐3‐yl)pyridine‐Type Ligands as Controlled by Packing Forces: Structural Correlations

A substituted 2,6‐bis(pyrazol‐3‐yl)pyridine (3‐bpp) ligand, H₄L, created to facilitate intermolecular interactions in the solid, has been used to obtain four novel Fe^II complexes: [Fe(H₄L)₂](ClO₄)₂ ? 2 CH₃NO₂ ? 2 H₂O, [Fe(H₄L)(H₂LBF₂)](BF₄) ? 5 C₃H₆O (H₂LBF₂ is an in situ modified version of H₄L), [Fe(H₄L)₂](ClO₄)₂ ? 2 C₃H₇OH and [Fe(H₄L)₂](ClO₄)₂ ? 4 C₂H₅OH. Changing of spin‐inactive components (solvents, anions or distant ligand substituents) causes differences to the coordination geometry of the metal that are key to the magnetic proper‐ ties. Magnetic measurements show that, contrary to the previously published complex [Fe(H₄L)₂](ClO₄)₂ ? H₂O ? 2 CH₃COCH₃, the newly synthesised compounds remain in the high‐spin (HS) state at all temperatures (5–300 K). A member of the known family of Fe^II/3‐bpp complexes, [Fe(3‐bpp)₂](ClO₄)₂ ? 1.75 CH₃COCH₃ ? 1.5 Et₂O, has also been prepared and characterised structurally. In the bulk, this compound exhibits a gradual and incomplete spin transition near 205 K. The single‐crystal structure is consistent with it being HS at 250 K and partially low spin at 90 K. Structural analysis of all these compounds reveals that the exact configuration of intermolecular interactions affects dramatically the local geometry at the metal, which ultimately has a strong influence on the magnetic properties. Along this line, the geometry of Fe^II in all published 3‐bpp compounds of known structure has been examined, both by calculating various distortion indices (Σ, Θ, θ and Φ) and by continuous shape measures (CShMs). The results reveal correlations between some of these parameters and indicate that the distortions from octahedral geometry observed on HS systems are mainly due to strains arising from intermolecular interactions. As previously suggested with other related compounds, we observe here that strongly HS‐distorted systems have a larger tendency to remain in that state.     

An Investigation of Photo‐ and Pressure‐Induced Effects in a Pair of Isostructural Two‐Dimensional Spin‐Crossover Framework Materials

Two new isostructural iron(II) spin‐crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)₂(NCX)₂] (dpms=4,4′‐dipyridylmethyl sulfide; X=S ( SCOF‐6(S) ), X=Se ( SCOF‐6(Se) )) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF‐6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high‐spin (HS) to low‐spin iron(II) sites over the temperature range 300–4 K (T_1/2=75 K). In contrast, the NCSe^? analogue, SCOF‐6(Se) , displays a complete SCO transition (T_1/2=135 K). Photomagnetic characterizations reveal quantitative light‐ induced excited spin‐state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF‐6(S) and SCOF‐6(Se) , respectively. Variable‐pressure magnetic measurements were performed on SCOF‐6(S) , revealing that with increasing pressure both the T_1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF‐6(S) at ambient pressure due to an interplay between close T_1/2 and T(LIESST) values.     

A Redox‐Active Bridging Ligand to Promote Spin Delocalization,High‐Spin Complexes,and Magnetic Multi‐Switchability

A dinuclear Co^II complex, [Co₂(tphz)(tpy)₂]ⁿ⁺ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T_1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an S_T=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature.     

A Brønsted‐Ligand‐Based Iron Complex as a Molecular Switch with Five Accessible States

A mononuclear Fe^II complex, prepared with a Brønsted diacid ligand, H₂L (H₂L=2‐[5‐phenyl‐1H‐pyrazole‐3‐yl] 6‐benzimidazole pyridine), shows switchable physical properties and was isolated in five different electronic states. The spin crossover (SCO) complex, [Fe^II(H₂L)₂](BF₄)₂ ( 1_A ), exhibits abrupt spin transition at T_1/2=258 K, and treatment with base yields a deprotonated analogue [Fe^II(HL)₂] ( 1_B ), which shows gradual SCO above 350 K. A range of Fe^III analogues were also characterized. [Fe^III(HL)(H₂L)](BF₄)Cl ( 1_C ) has an S=5/2 spin state, while the deprotonated complexes [Fe^III(L)(HL)], ( 1_D ), and (TEA)[Fe^III(L)₂], ( 1_E ) exist in the low‐spin S=1/2 state. The electronic properties of the five complexes were fully characterized and we demonstrate in situ switching between multiple states in both solution and the solid‐state. The versatility of this simple mononuclear system illustrates how proton donor/acceptor ligands can vastly increase the range of accessible states in switchable molecular devices.     

Anion Recognition with Hydrogen‐Bonding Cyclodiphosphazanes

Modular cyclodiphosph(V)azanes are synthesised and their affinity for chloride and actetate anions were compared to those of a bisaryl urea derivative ( 1 ). The diamidocyclodiphosph(V)azanes cis‐[{ArNHP(O)(μ‐tBu)}₂] [Ar=Ph ( 2 ) and Ar=m‐(CF₃)₂Ph ( 3 )] were synthesised by reaction of [{ClP(μ‐NtBu)}₂] ( 4 ) with the respective anilines and subsequent oxidation with H₂O₂. Phosphazanes 2 and 3 were obtained as the cis isomers and were characterised by multinuclear NMR spectroscopy, FTIR spectroscopy, HRMS and single‐crystal X‐ray diffraction. The cyclodiphosphazanes 2 and 3 readily co‐crystallise with donor solvents such as MeOH, EtOH and DMSO through bidentate hydrogen bonding, as shown in the X‐ray analyses. Cyclodiphosphazane 3 showed a remarkably high affinity (log[K]=5.42) for chloride compared with the bisaryl urea derivative 1 (log[K]=4.25). The affinities for acetate (AcO^?) are in the same range ( 3 : log[K]=6.72, 1 : log[K]=6.91). Cyclodiphosphazane 2 , which does not contain CF₃ groups, exhibits weaker binding to chloride (log[K]=3.95) and acetate (log[K]=4.49). DFT computations and X‐ray analyses indicate that a squaramide‐like hydrogen‐bond directionality and C_α?H interactions account for the efficiency of 3 as an anion receptor. The C_α?H groups stabilise the Z,Z‐ 3 conformation, which is necessary for bidentate hydrogen bonding, as well as coordinating with the anion.     

A Redox‐Active Bridging Ligand to Promote Spin Delocalization,High‐Spin Complexes,and Magnetic Multi‐Switchability

A dinuclear Co^II complex, [Co₂(tphz)(tpy)₂]ⁿ⁺ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T_1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an S_T=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature.     

Multi‐Dimensional Cobalt(II) and Nickel(II) Coordination Polymers

A series of metal coordination polymers, [Co₂(NB)₄(bpp)₂(H₂O)]·H₂O ( 1 ), [Co₂(e,e‐trans‐chdc)(e,a‐cis‐chdc)(bpp)₂] ( 2 ), [Ni(e,e‐trans‐chdc)(bpp)(H₂O)₂] ( 3 ), [Ni₂(PDA)₂(bpp)₂(H₂O)₃]·H₂O ( 4 ), and [Ni‐(mBDC)(bpp)] ( 5 ) (NB = 3‐nitrobenzoate anion; bpp = 4,4′‐trimethylene dipyridine; chdc = cyclohexane‐1,4‐dicarboxylate anion; PDA = 1,4‐phenylenediacetate anion; mBDC = 1,3‐benzene dicarboxylate anion), were synthesized from metal ions and organic mixed‐ligands by hydrothermal reactions. The single crystal structure analysis revealed that 1, 3, and 4 were 2D sheets with bilayer (1 and 4) and 2‐fold interpenetrated layers (3), 2 is a 3D binodal (4,5)‐connected framework, and 5 is a 1D chains. The non‐covalent interactions of H‐bonds and π–π stacking caused this conformation of highly cross‐linked networks. Compounds 1‐5 were further characterized by thermal gravimetric analysis, powder X‐ray diffraction, UV‐vis, infrared, and PL spectroscopy.     

FeIII Quinolylsalicylaldimine Complexes: A Rare Mixed‐Spin‐State Complex and Abrupt Spin Crossover

A new synthesis of (8‐quinolyl)‐5‐methoxysalicylaldimine (Hqsal‐5‐OMe) is reported and its crystal structure is presented. Two Fe^III complexes, [Fe(qsal‐5‐OMe)₂]Cl ? solvent (solvent=2 MeOH ? 0.5 H₂O ( 1 ) and MeCN ? H₂O ( 2 )) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal‐5‐OMe)₂] Cl ? 2 MeOH ? 0.5 H₂O ( 1 ) exhibits rare crystallographically independent high‐spin and low‐spin Fe^III centres at 150 K, whereas [Fe(qsal‐5‐OMe)₂]Cl ? MeCN ? H₂O ( 2 ) is low spin at 100 K. In both structures there are extensive π–π and C? H???π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped‐spin crossover with T_1/2=245 K and 275 K for steps 1 and 2, respectively, with a slight hysteresis of 5 K in the first step and a plateau of 15 K between the steps. In contrast, 1 is found to undergo an abrupt half‐spin crossover also with a hysteresis of 10 K. The two compounds are the first Fe^III complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by ⁵⁷Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe^II at ?0.18 V and irreversible oxidation of the coordinated qsal‐5‐OMe ligand at +1.10 V.     

Synthesis of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl) pyrrole‐based donor polymers and their bulk heterojunction solar cell applications

A series of three new 1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole‐based polymers such as poly[1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole] ( PTPT ), poly[1,4‐(2,5‐bis(octyloxy)phenylene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PPTPT ), and poly[2,5‐(3‐octylthiophene)‐alt‐5,5'‐(1‐(2,6‐diisopropylphenyl)‐2,5‐di(2‐thienyl)pyrrole)] ( PTTPT ) were synthesized and characterized. The new polymers were readily soluble in common organic solvents and the thermogravimetric analysis showed that the three polymers are thermally stable with the 5% degradation temperature >379 °C. The absorption maxima of the polymers were 478, 483, and 485 nm in thin film and the optical band gaps calculated from the onset wavelength of the optical absorption were 2.15, 2.20, and 2.13 eV, respectively. Each of the polymers was investigated as an electron donor blending with PC₇₀BM as an electron acceptor in bulk heterojunction (BHJ) solar cells. BHJ solar cells were fabricated in ITO/PEDOT:PSS/polymer:PC₇₀BM/TiO_x/Al configurations. The BHJ solar cell with PPTPT :PC₇₀BM (1:5 wt %) showed the power conversion efficiency (PCE) of 1.35% (J_sc = 7.41 mA/cm², V_oc = 0.56 V, FF = 33%), measured using AM 1.5G solar simulator at 100 mW/cm² light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Photomagnetism of a sym‐cis‐Dithiocyanato Iron(II) Complex with a Tetradentate N,N′‐Bis(2‐pyridylmethyl)1,2‐ethanediamine Ligand

A comprehensive study of the magnetic and photomagnetic behaviors of cis‐[Fe(picen)(NCS)₂] (picen=N,N′‐bis(2‐pyridylmethyl)1,2‐ethanediamine) was carried out. The spin‐equilibration was extremely slow in the vicinity of the thermal spin‐transition. When the cooling speed was slower than 0.1 K min^?1, this complex was characterized by an abrupt thermal spin‐transition at about 70 K. Measurement of the kinetics in the range 60–70 K was performed to approach the quasi‐static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin‐state‐trapping (TIESST) effect, was measured. At 10 K, this complex also exhibited the well‐known light‐induced excited spin‐state‐trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light‐induced excitation, was studied. Single‐crystal X‐ray diffraction as a function of speed‐cooling and light conditions at 30 K revealed the mechanism of the spin‐crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin‐crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin‐transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect.     

Poly[(μ2‐1,3‐di‐4‐pyridylpropane‐κ2N:N′)(μ3‐glutarato‐κ3O:O′:O′′)dizinc(II)]

The title compound, [Zn₂(C₅H₆O₄)₂(C₁₃H₁₄N₂)]_n or [Zn₂(glu)₂(bpp)]_n, is a novel zinc polymer based on mixed flexible glutarate (glu) and 1,3‐di‐4‐pyridylpropane (bpp) ligands. The Zn^II center has a distorted tetra­hedral geometry and the central atom of the bpp ligand is located at a special site with a C₂ axis passing through it. A layer is formed by Zn–glu bonding. Such layers are pillared by bpp ligands, forming a three‐dimensional framework with large channels. The inverted inter­penetration of two three‐dimensional frameworks completes the mol­ecular structure.     

Two Coordination Polymers based on 2‐Ethyl‐1H‐imidazole‐4,5‐dicarboxylic Acid and 1,3‐Bis(4‐pyridyl)propane: Synthesis,Crystal Structures,and Photoluminescent Properties

Two coordination polymers, [Cd(Heidc)(bpp)]_n ( 1 ) and [Zn₃ (eidc)₂(bpp)(H₂O)₂] · 2H₂O}_n ( 2 ) (H₃eidc = 2‐ethyl‐4,5‐imidazole dicarboxylic acid, bpp = 1,3‐bis(4‐pyridyl)propane) were hydrothermally synthesized and characterized by elemental analysis, IR, spectroscopy single‐crystal X‐ray diffraction, and thermogravimetric analyses. Compound 1 features a 2D layer formed by C–H ··· π stacking interactions between adjacent chains, whereas compound 2 shows a 3D (8³)₂(8⁵.10)‐tfc framework constructed of the 2D (6,3) layer. The result demonstrates that the central metal atoms play a key role in governing the coordination motifs. Moreover, solid‐state properties such as thermal stabilities and photoluminescence of 1 and 2 were also investigated.     

Thermal‐ and Light‐Induced Spin Crossover in a Guest‐Dependent Dinuclear Iron(II) System

We previously reported the dinuclear material [Fe^II₂(ddpp)₂(NCS)₄] ? 4 CH₂Cl₂ ( 1? 4 CH₂Cl₂; ddpp=2,5‐di(2′,2′′‐dipyridylamino)pyridine) and its partially desolvated analogue ( 1? CH₂Cl₂), which undergo two‐ and one‐step spin‐crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one‐ or two‐step spin transition can be specifically targeted. The chloroform clathrate 1? 4 CHCl₃ undergoes a relatively abrupt one‐step SCO, in which the two equivalent Fe^II sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1? 4 CHCl₃ to form 1? 3 CHCl₃ and 1? CHCl₃ occurs through single‐crystal‐to‐single‐crystal processes (monoclinic C2/c to P2₁/n to P2₁/n) in which the two equivalent Fe^II sites become inequivalent sites within the dinuclear molecule of each phase. Both 1? 3 CHCl₃ and 1? CHCl₃ undergo one‐step spin transitions, with the former having a significantly higher SCO temperature than 1? 4 CHCl₃ and the latter, and each has a broader SCO transition than 1? 4 CHCl₃, attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials through reversibly resolvating the partially desolvated material with chloroform to produce the original one‐step SCO, or with dichloromethane to produce a two‐step SCO reminiscent of that seen for 1? 4 CH₂Cl₂. Furthermore, we investigate the light‐induced excited spin state trapping (LIESST) effect on 1? 4 CH₂Cl₂ and 1? CH₂Cl₂ and observe partial LIESST activity for the former and no activity for the latter.     

[Cu(bpp)2(bpdc)(H2O)2]×2H2O and [Cu(bpp)2](tdc)×7.5H2O的合成、晶体结构和热稳定性

在室温下, 由Cu(NO3)2 、1,3 -二（4 -吡啶基）丙烷(bpp)、4,4 ’ -联苯二甲酸(H2bpdc)和2,5-噻吩二甲酸(H2tdc)制备出两种新型铜( II)配位聚合物[Cu(bpp)2(bpdc)(H2O)2]n·2nH2O, 1 和[Cu(bpp)2]n·n(tdc) 7.5nH2O, 2。两个配位聚合物均为一维线型结构,铜原子均采取变形的八面体结构,在轴线方向上的两个水分子与铜原子存在较弱的配位作用。在配合物1中,两个bpdc羧酸根离子与铜原子配位,而2中的tdc羧酸离子没有与铜原子键合,只是作为反离子平衡电荷。在两个产物中, 配体bpp具有不同的构象。热重分析表明配合物1与2分别在110°C和160°C以下是稳定的。     

Heteroleptic FeII Complexes of 2,2′‐Biimidazole and Its Alkylated Derivatives: Spin‐Crossover and Photomagnetic Behavior

Three iron(II) complexes, [Fe(TPMA)(BIM)](ClO₄)₂?0.5H₂O ( 1 ), [Fe(TPMA)(XBIM)](ClO₄)₂ ( 2 ), and [Fe(TPMA)(XBBIM)](ClO₄)₂ ?0.75CH₃OH ( 3 ), were prepared by reactions of Fe^II perchlorate and the corresponding ligands (TPMA=tris(2‐pyridylmethyl)amine, BIM=2,2′‐biimidazole, XBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐biimidazole, XBBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐bibenzimidazole). The compounds were investigated by a combination of X‐ray crystallography, magnetic and photomagnetic measurements, and Mössbauer and optical absorption spectroscopy. Complex 1 exhibits a gradual spin crossover (SCO) with T_1/2=190 K, whereas 2 exhibits an abrupt SCO with approximately 7 K thermal hysteresis (T_1/2=196 K on cooling and 203 K on heating). Complex 3 is in the high‐spin state in the 2–300 K range. The difference in the magnetic behavior was traced to differences between the inter‐ and intramolecular interactions in 1 and 2 . The crystal packing of 2 features a hierarchy of intermolecular interactions that result in increased cooperativity and abruptness of the spin transition. In 3 , steric repulsion between H atoms of one of the pyridyl substituents of TPMA and one of the benzene rings of XBBIM results in a strong distortion of the Fe^II coordination environment, which stabilizes the high‐spin state of the complex. Both 1 and 2 exhibit a photoinduced low‐spin to high‐spin transition (LIESST effect) at 5 K. The difference in the character of intermolecular interactions of 1 and 2 also manifests in the kinetics of the decay of the photoinduced high‐spin state. For 1 , the decay rate constant follows the single‐exponential law, whereas for 2 it is a stretched exponential, reflecting the hierarchical nature of intermolecular contacts. The structural parameters of the photoinduced high‐spin state at 50 K are similar to those determined for the high‐spin state at 295 K. This study shows that N‐alkylation of BIM has a negligible effect on the ligand field strength. Therefore, the combination of TPMA and BIM offers a promising ligand platform for the design of functionalized SCO complexes.