Spin Crossover in [Fe(2-Picolylamine)3](2+) Adjusted by Organosulfonate Anions.

Three mononuclear spin crossover (SCO) compounds [Fe(2-pic)3]·A2·Solv (A = m-ABS(-), Solv = MeOH, 1; A = p-ABS(-), 2; A = OTf(-), 3) were prepared and characterized magnetically and structurally (2-pic = 2-picolylamine, m-HABS = m-aminobenzenesulfonic acid, p-HABS = p-aminobenzenesulfonic acid, HOTf = trifluoromethanesulfonic acid). Single-crystal X-ray analyses show that they are constructed from the charge-assisted hydrogen bonds between the 2-pic donors and the organosulfonate acceptors, forming the hydrogen-bonded three-dimensional networks for 1 and 2 and one-dimensional columns for 3. While the [Fe(2-pic)3](2+) cations in compounds 1 and 2 are in the meridional (mer-) configuration, it has a facial (fac-) configuration in complex 3. Magnetic susceptibility measurements revealed the SCO transitions and the SCO properties in all three complexes are quite different. Compound 1 undergoes an abrupt SCO with critical temperatures T1/2↓ = 100 K and T1/2↑ = 103 K, while compound 2 exhibits a gradual SCO with T1/2 = 218 K. Compound 3, with the fac-configuration, has an abrupt SCO transition accompanied by the structural phase transition with critical temperatures T1/2↓ = 333 K and T1/2↑ = 343 K. The SCO transitions were further confirmed by the detailed structural analyses of the coordination environments of the Fe(II) centers in both spin states and also by differential scanning calorimetry. Compared to the famous [Fe(2-pic)3]·A2·Solv compounds in the literature, compound 2 has the highest transition temperature for the mer-[Fe(2-pic)3](2+)-containing compounds, while compound 3 represents the first example of the structurally characterized compound of the fac-[Fe(2-pic)3](2+) motif showing SCO behavior. These results show that the organosulfonate anions are very promising to adjust the hydrogen-bonded structures of the SCO compounds and improve the SCO properties of those structures.

[1]  Azzedine Bousseksou,et al.  Molecular spin crossover phenomenon: recent achievements and prospects. , 2011, Chemical Society reviews.

[2]  K. Törnroos,et al.  Interplay of spin conversion and structural phase transformations: re-entrant phase transitions in the 2-propanol solvate of tris(2-picolylamine)iron(II) dichloride. , 2006, Chemistry.

[3]  M. Ward,et al.  Regulating the architectures of hydrogen-bonded frameworks through topological enforcement. , 2015, Journal of the American Chemical Society.

[4]  K. Törnroos,et al.  Challenges in engineering spin crossover: structures and magnetic properties of six alcohol solvates of iron(II) tris(2-picolylamine) dichloride. , 2004, Angewandte Chemie.

[5]  P. Gütlich,et al.  Mössbauer effect study on low-spin 1A1 ⇌ high spin 5T2 transition in [Fe(2-pic)3]Cl2: II. Influence of non-coordinating solvent molecule in [Fe(2-pic)3] Cl2 · X1 X = C2H5OH, CH3OH, H2O and 2H2O , 1977 .

[6]  K. Hagen,et al.  Iron(II) triflate salts as convenient substitutes for perchlorate salts: crystal structures of [Fe(H2O)6](CF3SO3)2 and Fe(MeCN)4(CF3SO3)2. , 2000, Inorganic chemistry.

[7]  Giannis S. Papaefstathiou,et al.  Supramolecular control of reactivity in the solid state: from templates to ladderanes to metal-organic frameworks. , 2008, Accounts of chemical research.

[8]  H. Goodwin,et al.  Structural, Magnetic and Mössbauer Spectral Studies of Salts of Bis[2,6-bis(pyrazol-3-yl)pyridine]iron(II)—a Spin Crossover System , 1994 .

[9]  Angiolina Comotti,et al.  Supramolecular Archimedean Cages Assembled with 72 Hydrogen Bonds , 2011, Science.

[10]  M. Ward,et al.  Architectural diversity and elastic networks in hydrogen-bonded host frameworks: from molecular jaws to cylinders. , 2007, Journal of the American Chemical Society.

[11]  M. Ward,et al.  Controlled orientation of polyconjugated guest molecules in tunable host cavities. , 2010, Journal of the American Chemical Society.

[12]  G. Shimizu,et al.  Exploiting Complementary Second-sphere Effects in Supramolecular Coordination Solids , 2003 .

[13]  M. Ward,et al.  Nanoporous Molecular Sandwiches: Pillared Two-Dimensional Hydrogen-Bonded Networks with Adjustable Porosity , 1997, Science.

[14]  David Casanova,et al.  Shape and symmetry of heptacoordinate transition-metal complexes: structural trends. , 2003, Chemistry.

[15]  Philipp Gütlich,et al.  Thermal and Optical Switching of Iron(II) Complexes , 1994 .

[16]  Graham N. Newton,et al.  Programmable spin-state switching in a mixed-valence spin-crossover iron grid , 2014, Nature Communications.

[17]  P. Gütlich,et al.  Mössbauer effect study on low-spin 1A1 ⇌ high-spin 5T2 transition in tris(2-picolylamine) iron chloride I. Dilution effect in [FexZn1-x(2-pic)3]Ch2·C2H5OH , 1976 .

[18]  S. Iijima,et al.  Interlayer interaction of two-dimensional layered spin crossover complexes [FeIIH3L(Me)][FeIIL(Me)]X (X-=ClO4-, BF4-, PF6-, AsF6-, and SbF6-; H3L(Me)=tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine). , 2003, Inorganic chemistry.

[19]  G. Shimizu,et al.  Selective guest inclusion in a non-porous H-bonded host. , 2006, Chemical communications.

[20]  Xin-Yi Wang,et al.  Hydrogen-bonded host frameworks of cationic metal complexes and anionic disulfonate linkers : Effects of the guest molecules and the charge of the metal complex , 2007 .

[21]  M. Halcrow,et al.  Structure:function relationships in molecular spin-crossover complexes. , 2011, Chemical Society reviews.

[22]  Xin-Yi Wang,et al.  A Series of Guest-Defined Metal-Complex/Disulfonate Frameworks of Hydrogen-Bonded [Co(en)2(ox)]+ and 2,6-Naphtalenedisulfonate , 2008 .

[23]  K. Törnroos,et al.  Ordering phenomena and phase transitions in a spin-crossover compound-uncovering the nature of the intermediate phase of [Fe(2-pic)3]Cl2.EtOH. , 2003, Angewandte Chemie.

[24]  K. Yoshizawa,et al.  A light-induced spin crossover actuated single-chain magnet , 2013, Nature Communications.

[25]  J. Vittal,et al.  Stacking of double bonds for photochemical [2+2] cycloaddition reactions in the solid state. , 2008, Chemical communications.

[26]  O. Kahn,et al.  Spin-Transition Polymers: From Molecular Materials Toward Memory Devices , 1998 .

[27]  G. Shimizu,et al.  Second-sphere coordination networks : 'Tame-ing' (Tame = 1,1,1-Tris (aminomethyl)ethane) the hydrogen bond , 2006 .

[28]  J. Real,et al.  Thermal- and pressure-induced cooperative spin transition in the 2D and 3D coordination polymers {Fe(5-Br-pmd)z[M(CN)x]y} (M=AgI, AuI, NiII, PdII, PtII). , 2007, Inorganic chemistry.

[29]  Lan-sun Zheng,et al.  Synergetic spin crossover and fluorescence in one-dimensional hybrid complexes. , 2015, Angewandte Chemie.

[30]  M. Ward,et al.  Lamellae-Nanotube Isomerism in Hydrogen-Bonded Host Frameworks. , 2001, Angewandte Chemie.

[31]  B. Skelton,et al.  Variable-temperature magnetic, spectral, and x-ray crystallographic studies of "spin-crossover" iron(III) Schiff-base-Lewis-base adducts. Influence of noncoordinated anions on spin-state interconversion dynamics in [Fe(salen)(imd)2]Y species (Y = ClO4-, BF4-, PF6-, BPh4-; imd = imidazole) , 1987 .

[32]  C. O'connor,et al.  High- and Low-spin Interconversion in a Series of (α-picolylamine)iron(II) Complexes , 1979 .

[33]  J. Let́ard,et al.  Photo-induced spin-transition: the role of the iron(II) environment distortion. , 2005, Acta crystallographica. Section B, Structural science.

[34]  M. Shatruk,et al.  Photomagnetic response in highly conductive iron(II) spin-crossover complexes with TCNQ radicals. , 2015, Angewandte Chemie.

[35]  J. Obel,et al.  An iron(II) spin-crossover complex with a 70 K wide thermal hysteresis loop. , 2008, Angewandte Chemie.

[36]  B. Katz,et al.  Spin-state isomerism of tris(2-picolylamine)iron(II). The diiodide and the hydrated dichloride , 1980 .

[37]  G. Shimizu,et al.  A family of supramolecular inclusion solids based upon second-sphere interactions. , 2003, Angewandte Chemie.

[38]  P. Guetlich,et al.  MOESSBAUER-EFFECT STUDY OF THE THERMALLY INDUCED SPIN TRANSITION IN TRIS(2-PICOLYLAMINE)IRON(II) CHLORIDE. DILUTION EFFECT IN MIXED CRYSTALS OF (FEXZN1-X(2-PIC)3)CL2.C2H5OH (X = 0.15, 0.029, 0.0009) , 1978 .

[39]  Ashis Bhattacharjee,et al.  Cause for Unusually Large Thermal Hysteresis of Spin Crossover in [Fe(2-pic)3]Cl2·H2O , 2004 .

[40]  K. Chapman,et al.  Single-crystal to single-crystal structural transformation and photomagnetic properties of a porous iron(II) spin-crossover framework. , 2008, Journal of the American Chemical Society.

[41]  M. Ward,et al.  Guest exchange through single crystal-single crystal transformations in a flexible hydrogen-bonded framework. , 2014, Journal of the American Chemical Society.

[42]  E. Müller,et al.  Unusual spin-transition anomaly in the crossover system [Fe(2-pic)3]Cl2·EtOH , 1982 .

[43]  F. Thétiot,et al.  Spin crossover iron(II) coordination polymer chains: syntheses, structures, and magnetic characterizations of [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II), Pt(II), aqin = quinolin-8-amine). , 2014, Inorganic chemistry.

[44]  Tomoyuki Matsuda,et al.  Observation of an iron(II) spin-crossover in an iron octacyanoniobate-based magnet. , 2008, Angewandte Chemie.

[45]  O. Roubeau.  Triazole-based one-dimensional spin-crossover coordination polymers. , 2012, Chemistry.

[46]  M. Tong,et al.  Tuning the spin-crossover behaviour of a hydrogen-accepting porous coordination polymer by hydrogen-donating guests. , 2015, Chemistry.

[47]  A. Beatty.  Open-framework coordination complexes from hydrogen-bonded networks: toward host/guest complexes , 2003 .

[48]  Gautam R. Desiraju,et al.  The C-h···o hydrogen bond:  structural implications and supramolecular design. , 1996, Accounts of chemical research.

[49]  M. Ward,et al.  Sterically Controlled Architectural Reversion in Hydrogen-Bonded Crystalline Clathrates , 1999 .

[50]  Yann Garcia,et al.  Spin state switching in iron coordination compounds , 2013, Beilstein journal of organic chemistry.

[51]  M. R. Snow,et al.  The crystal structure of bis[N-(2-aminoethyl)salicylaldiminato] iron (III) chloride monohydrate, a low spin oron(III) complex stabilized by lattice water ☆ , 1978 .

[52]  K. Biradha,et al.  Crystal engineering of topochemical solid state reactions. , 2013, Chemical Society reviews.

[53]  Epiphane Codjovi,et al.  A spin transition system with a thermal hysteresis at room temperature , 1993 .

[54]  E. Sinn,et al.  High-spin and Low-spin Α-picolylamine Iron(II) Complexes , 1978 .

[55]  J. Wolny,et al.  A range of spin-crossover temperature T1/2>300 K results from out-of-sphere anion exchange in a series of ferrous materials based on the 4-(4-imidazolylmethyl)-2-(2-imidazolylmethyl)imidazole (trim) ligand, [Fe(trim)2]X2 (X=F, Cl, Br, I): comparison of experimental results with those derived from de , 2006, Chemistry.

[56]  M. Halcrow.  Spin-crossover materials : properties and applications , 2013 .

[57]  Linda S. Shimizu,et al.  Functional materials from self-assembled bis-urea macrocycles. , 2014, Accounts of chemical research.

[58]  Marinela M. Dîrtu,et al.  Influence of Hydrogen Bonding on the Hysteresis Width in Iron(II) Spin-Crossover Complexes , 2011 .

[59]  P. Gütlich,et al.  Deuterium isotope effect on the high-spin α low-spin transition in deuterated solvates of tris(2-picolylamine) iron(II) chloride , 1980 .

[60]  P. Gütlich,et al.  Spin Crossover in Transition Metal Compounds II , 2004 .

[61]  H. Goodwin,et al.  NON-FIRST-ORDER KINETICS OF THE HIGH SPIN-LOW SPIN RELAXATION IN FE(BPP)2(BF4)2 AFTER LIESST AND THERMAL SPIN TRAPPING , 1994 .

[62]  M. Ward,et al.  Metric engineering of soft molecular host frameworks. , 2001, Accounts of chemical research.

[63]  J. Real,et al.  Thermo-, piezo-, photo- and chemo-switchable spin crossover iron(II)-metallocyanate based coordination polymers , 2011 .

[64]  K. Hashimoto,et al.  Observation of an Fe(II) spin-crossover in a cesium iron hexacyanochromate. , 2005, Journal of the American Chemical Society.

[65]  G. Renovitch,et al.  Spin equilibrium in tris(2-aminomethylpyridine)iron (II) halides , 1967 .

[66]  S. Iijima,et al.  An unprecedented homochiral mixed-valence spin-crossover compound. , 2003, Angewandte Chemie.

[67]  Song Gao,et al.  Synthesis, magnetic and photomagnetic study of new iron(II) spin-crossover complexes with N₄O₂ coordination sphere. , 2010, Dalton transactions.

[68]  G. Shimizu,et al.  The first example of a functional pillared metal sulfonate network , 2001 .

[69]  Sukhjinderjit Singh,et al.  Second sphere coordination complexes: Synthesis, characterization, single crystal structure and packing analyses of [trans-Cu(en)2(H2O)2](L1/L2)2 where L1 = p-toluenesulphonate, L2 = 5-bromo-2-methoxybenzenesulphonate , 2010 .

[70]  G. Shimizu,et al.  Crystal engineering of a permanently porous network sustained exclusively by charge-assisted hydrogen bonds. , 2007, Journal of the American Chemical Society.

[71]  K. Törnroos,et al.  Chemical disorder and spin crossover in a mixed ethanol–2-propanol solvate of FeII tris(2-picolylamine) dichloride , 2009 .

[72]  J. G. Haasnoot,et al.  High-spin α low-spin transition in [Fe(NCS)2(4,4′-bis-1,2,4-triazole)2](H2O). X-ray crystal structure and magnetic, mössbauer and EPR properties , 1990 .

[73]  Xin-Yi Wang,et al.  Hydrogen-bonded metal-complex sulfonate (MCS) inclusion compounds: effect of the guest molecule on the host framework. , 2007, Inorganic chemistry.

[74]  M. Ward,et al.  Engineering Crystal Symmetry and Polar Order in Molecular Host Frameworks , 2001, Science.

[75]  Y. Garcia,et al.  Large thermal hysteresis for iron(II) spin crossover complexes with N-(pyrid-4-yl)isonicotinamide. , 2014, Inorganic chemistry.

[76]  A. Bond,et al.  Second-sphere coordination in hexaamminecobalt(III) salt with organic sulphonate anion: Synthesis, characterisation and X-ray crystal structure of [Co(NH3)6](CH3SO3)3 , 2007 .