Journal ArticleDinuclear [(TPyA)FeII(THBQ22)FeII(TPyA)](BF4)2 (1) possesses hydrogen bonding interactions that form a 1-D chain, and p-p interactions between the 1-D chains that give rise to a 2-D supramolecular-layered structure, inducing hysteresis in the spin crossover behavior; 1 has shown spin crossover behavior around 250 K with thermal hysteresis and ferromagnetic interactions at low temperature

Miller, Joel Steven

Min, Kil Sik

English

The University of Utah: J. Willard Marriott Digital Library

COMMUNICATION www.rsc.org/chemcomm | ChemCommA  d i n u c l e a r  i r o n ( l l )  c o m p l e x ,  [ ( T P y A ) F e n ( T H B Q 2 ) F e n ( T P y A ) ] ( B F 4 ) 2 [ T P y A  =  t r i s ( 2 - p y r i d y l m e t h y l ) a m i n e ;  T H B Q 2 ^  =  2 , 3 , 5 , 6 - t e t r a h y d r o x y - l , 4 -  b e n z o q u i n o n a t e ]  e x h i b i t i n g  b o t h  s p i n  c r o s s o v e r  w i t h  h y s t e r e s i s  a n d  f e r r o m a g n e t i c  e x c h a n g eKil Sik Min,"* Krzysztof Svvierczek," Antonio G. DiPasquale,1 Arnold L. Rheingold,1 William M. Reiff,rf Atta M. Arif' and Joel S. Miller*"Received (in Austin, TX, USA) 4th October 2007, Accepted 8th November 2007 First published as an Advance Article on the web 26th November 2007 DOI: 10.1039/b715271jDinuclear [(TPyA)Fe"(THBQ2 )Fe"(TPyA)KBF4)2 (1) pos­sesses hydrogen bonding interactions that form a 1-D chain, and n-n  interactions between the 1-D chains that give rise to a 2-D supramolecular-layered structure, inducing hysteresis in the spin crossover behavior; 1 has shown spin crossover behavior around 250 K  with thermal hysteresis and ferromagnetic interactions at low temperature.Multifunctional magnetic materials have attracted attention because of their potential use as electronic switches, displays, and data storage devices.1 In particular, spin crossover (SCO) materials are very useful for these aims in which physical properties can be tuned by external stimuli, i.e. temperature, light, and/or pressures Many metal complexes with chloranilate (CA~ ) analogues have been studied because of their interesting redox and magnetochemistry, due to the noninnocent nature of this delocalized n system.3 Recently, dinuclear Fe(n) complexes exhibiting spin crossover behavior or ferromagnetic coupling have been reported for :[(TPyA)Fe“(DBQ2")Fe“(TPyA)](BF4)2, DBQ’ = 2,5-di-/«-/-butyl-3,6-dihydroxy-[l ,4]-benzoquinonate; TPyA = tris(2-pyridylmethyl)amine} and I[(TPyA)Fe"(CA2 )- FeH(TPyA)](BF4)2 }, respectively.4 Although the former displays SCO behavior around room temperature, it does not exhibit thermal hysteresis. Thus, to induce thermal hysteresis, greater interdinuclear cation interactions were sought, and introduction of interdinuclear H-bonding was targeted. Hence, 2,3,5,6-tetrahy- droxy-l,4-benzoquinone (H/THBQ) was identified as a bridging ligand, and we report [(TPyA)Fe"(THBQ2 )Fe"(TPyA)](BF4 )2  (l)t and its coexisting spin crossover with thermal hysteresis behaviors in addition to an intradimer ferromagnetic interaction.The structure of 1 was determined at 208 (Fig. 1) and 295 K.{ Each Fe(ii) ion in the dinuclear [(TPyA)Fe"(THBQ2 )Fe"- (TPyA)f+ cation has a distorted octahedral geometry with the four nitrogen atoms of TPyA and the two oxygen atoms of"Departm ent o f  Chemistry, University o f  Utah, 315 S. 1400 E. R M  2124, Salt Lake City, U T  84112-0850, USA.E-mail: fsntiller&chem. Utah, edu; Fax: +1-S01-5S1-8433;Tel: +1-801-585-5455hD epartm ent o f  Chem istry Education, Kyungpook National University, Daegu, 702-701, Republic o f  Korea1D epartm ent o f  Chemistry, University o f  California, San Diego, T,a Jolla, CA 92093-0358, USAdD epartm ent o f  Chem istry and Chemical Biology, Northeastern University, Boston, M A  02115, USATHBQ~ in the cis positions. The asymmetric unit consists of two halves of two independent Fe(n) dimers, each possessing a crystallographic center of symmetry at both 208 and 295 K. The two unique dinuclear compounds in an asymmetric unit at 208 K have similar structures, but have very different bond lengths around the Fe".At 208 K the average Fe-O and Fe-N bond distances are 1.953(2) and 1.958(2) A in one asymmetric unit, and 2.089(2) and 2.180(2) A in the other asymmetric unit. Thus, the former unique dinuclear complex is predominantly low spin (LS), while the other is predominantly high spin (HS). The latter HS species has longer Fe-O and Fe-N distances with respect to the LS species by 0.136 and 0.222 A, respectively, due to the Fe(ii) spin states difference at 208 K.5 Hence, the unit cell is composed of two dinuclear Fe(ii) complexes, one with spin singlet and the other with quintet Fe(ll) sites. The cell volume increases by 149 A3 (3.2%) upon wanning from 208 to 295 K. The average Fe-O and Fe-N bond distances at 295 K are 2.087(3) and 2.163(2) A for the asymmetric unit. TheFig. 1 ORTF.P (30% probable thermal ellipsoid) view of 1 at 208 K. The dication with predominately IIS Fe(ii)s in 1 is similar and not shown. II atoms of carbon and BF4~ are omitted for clarity. Key distances (A) and angles ( ): asymmetric unit with predominately LS Fe(n)s: Fel O l 1.974(3). Fel 02 1.931(3). Fel NI 1.984(4). Fel-N2 1.930(3). Fel-N3 1.955(4). Fel-N4 1.973(3). Cl C2 1.486(5). C2-C3 1.387(5). C3-CP 1.391(5). Cl 01 1.285(4). C2 02 1.290(4). C3 03 1.368(4). Ol Fel 02 83.22(11). Asymmetric unit with predominately IIS Fe(ii)s. Fel O l 2.148(3). Fel 02 2.029(3). Fel NI 2.175(4). Fel-N2 2.145(3). Fel-N3 2.168(4). Fel-N4 2.223(3). C1-C2 1.523(5). C2-C3 1.362(5). C3-CP 1.402(5). Cl 01 1.254(4). C2 02 1.284(4). C3 03 1.377(4). 01 Fel 02 77.71(10).This journa l is © The Royal Society o f Chem istry 2008 Chem. Commun., 2008, 317-319 | 317difference in the average Fe L bond distances disappears upon warming to 295 K. indicating that both dinuclear complexes are predominantly high spin states at room temperature. The average C O and CI-C2 bond distances of TIIBQ2- are 1.288(3) and 1.486(5) A for the dimer possessing LS Fe(n)s. and 1.269(3) and 1.523(5) A for the dimer possessing I IS Fe(n)s. In the I IS species of1. the C O and C-C bond lengths are clearly in good agreement with those of a CA2~ type ligand.4 I lowever. in LS species the bond lengths of C O and C-C lie in middle of CA2~ and CA3~ type ligands. This is attributed to the low-spin Fe(ii) ion. That is. a low-spin Fe(n) ion bonds to the O atom of the TI IBQ2 ligand more strongly than a high-spin Fe(n) ion as shown in the structure. The average C2-C3 and C3-C1' bond lengths are 1.389(4) A for the dimers possessing LS Fe(ii)s and 1.382(4) A for the dimer possessing I IS Fe(n)s. showing that the bonds are delocalized regardless of the Fe(n) spin states.Based upon the bond distances, the TI IBQ2 ions in the two different dinuclear complexes in 1 are slightly different from each other, due to the LS and I IS states of the Fe(n) ions. This confirms S  = 0 TI IBQ2 bridged ligands, not spin-bearing TI IBQ-3-. in accord to that reported for [(TPyA)Co(CA)Co(TPyA)]+ 4h The shortest intradimer Fe---Fe separation is 7.614(1) A and is 18% greater than the shortest interdimer Fe- • -Fe distance of 6.448(1) A.As anticipated, intermolecular O - I I - O  hydrogen bonding interactions exist between the hydroxyl groups of TI IBQ2 ions, giving rise to a 1-D chain motif.6 Interestingly, the 1-D chains consist of ••■ABAB-" units. The TPyA pyridyl groups are involved in offset face-to-face jt-jt interactions between the Fe(ii) dimers in a 1-D polymer and between the 1-D chains.7 in which complex 1 gives rise to 2-D supramolecular layered structure.The 2-350 K magnetic susceptibility. /. was obtained on a SQUID magnetometer (Fig. 2). At 350 K. the effective moment. faff l= (OkfJN j.ifC)yT)V2]. is 7.34 /in/Fcj. and decreases slightly with decreasing temperature to 7.24 /t,/Pc2 at 270 K. followed by an abrupt decrease to 5.77 /(b/Fct at 230 K. indicating a spin crossover behavior related to the high and low spin transition of the Fe dimer (1). Fig. 2 (inset) shows the thermal dependence of the /<efr(7) upon warming and cooling. LIpon cooling, the /<en(7) value abruptly drops from 6.86 /in/Fe? at 255 K to 5.76 /in/Fe? at 215 K. As shown in Fig. 2 (inset), the magnetic moment recovered to the original values after both warming and cooling. The widthFig. 3 Mossbauer spectrum of 1 confirming intensity LS a fully consistent with X-ray results [<>I S = 0.37 mm s_l. AEls  - <*h s  = 0.98 mm s~'. AEHs = 3.21 mm s-1].intensity HS. 0.52 mm s_l:Fig. 2 per asymmetric unit for 1 at 1 kOe upon wanning andthermal hysteresis around 250 K (inset).of the thermal hysteresis was ca. 10 K. Remarkably, after the SCO /ierr(7) gradually decreases with decreasing temperature to 5.53 /(h/Fct at 45 K. then it increases to maximum of 6.25 /tRfFc2 at 9 K. indicative of a ferromagnetic interaction between the Fe(ii) centers, and again decreases to 5.54 /in/Fo? at 2 K due to the interdimer antiferromagnetic exchange and/or zero field splitting. Unexpected ferromagnetic coupling as observed for 1 has been reported for [(TPyA)Fe(CA)Fe(TPyA)](BF4)2 (Jlkn = +1.0 K).4* Surprisingly. 1 exhibits dual magnetic properties, such as a spin transition at "250 K with thermal hysteresis (width ^  10 K) as well as a ferromagnetic coupling below 45 K. The existence of the hysteresis effect can be attributed to hydrogen bonding interactions between hydroxyl groups of bridged TIIBQ2- ligand in l.8 The rise in /<err(7) at low temperature suggests the onset of magnetic coupling and is under further investigation.The Mossbauer spectrum of 1 gives evidence of incipient formation of LS Fe(ii) at room temperature while SCO behavior is obvious at "270 K in accord with the SQUID data. The combination of Mossbauer spectroscopy and X-ray results for 1 definitively confirm the presence of dinuclear pairs of Fe(ii) for which one pair is all I IS and the other is all LS. as opposed to 50 : 50 LS : I IS within each dinuclear Fe(ii) complex at 77 K (Fig. 3). The zero field Mossbauer spectrum of Fig. 3 does not distinguish the latter possibility by itself.9In conclusion, the first dinuclear Fe(ii) complex bridged with a tetraoxolene-type ligand, exhibiting the dual magnetic functions of a spin crossover with hysteresis and a ferromagnetic interaction, is reported. Further studies on the mechanism of the SCO and fabrication of new dinuclear complexes showing a hysteresis at room temperature are ongoing.We appreciate the continued partial support by the U  S. Department of Energy Division of Material Science (Grant No. DE-FG03-93ER45504) and AFOSR (Grant No. F49620-03-1- 0175).Notes and references+ Synthesis: 1 was synthesized from a MeOH solution (50 mL) of [FefOtLfeKBFah (232 mg. 0.688 mmol) added to MeOH solutions (10 mL)318 | Chem. Commun., 2008, 317-319 This journa l is © The Royal Society o f Chemistry 2008of TPyA (200 mg, 0.688 mmol) and 11 11IBQ (39 mg, 0.344 mmol) in a wet box !<1 ppm CM. The solution turned dark brown, was neutralized with NEti (0.20 mL, 1.38 mmol), and heated to reflux for 1 h. After filtration while hot, the filtrate was allowed to stand at room temperature for 2 or 3 days. Dark brown crystals formed which were collected by filtration, washed with MeOII, and dried in vacuo to afford 195 mg (55%) of 1. IR (KBr): \'on 3406. vCn 3069, 2924, vCN 1604, vco 1531. vB|.- 1053 cm-1. Anal, calcd for C4JI«B,F«Fe,N«06: C. 48.69: II. 3.70: N. 10.81. Found: C, 48.83: II, 3.75: N, 10.36%.J Crystal and structure refinement parameters for 1: At 208(2) K, C^II^BiFjiFeiNgOfi. fw = 1036.12 g mol-1. monoclinic, space group l% lc,a = 14.414(2) A ./> = 21.922(2) A. r = 14.955(2) A ./i= 97.225(2)“. V= 4688.0(9) A3. Z  = 4. 4 lU = 1.468 g cm-3. /((MoKot) = 0.705 mm-1. Rim = 0.0979, RI = 0.0653, wR2 = 0.1260!/ > 2cr(/)), CCDC 662710. At 295(2) K, monoclinic, space group P2]/c, a = 15.190(1) A, b = 21.590(1) A, c = 14.818(1) A. IS = 95.508! 1)“. V = 4837.2(3) A3. Z  = 4. 4 lU = 1.423 g cm-3. /((MoKa) = 0.683 mm-1, Rhn = 0.0906, R\ = 0.1053, wR2 = 0.3040 (/ > 2cr( f)), CCDC 662711. Data were collected on Bruker SMART/Enraf- Nonius KappaCCD automatic diffractometers using graphite monochro- mated MoKot (/. = 0.71073 A) radiation. Structures were solved by direct methods and refined by fui-matrix least-squares refinement using the SIIELXL9710 programs. For crystallographic data in CIF or other electronic format, see DOI: 10.1039/b715271j1 Ui) O. Kahn and C. J. Martinez, Science, 1998, 279,44: (b) A. B. Caspar, V. Ksenofontov. M. Seredyuk and P. Gutlich. Cvoni Chem. Re\\, 2005. 249, 2661: id  M. Nihei, M. Ui, M. Yokota, L. Ilan, A. Maeda,II. Kishida, II. Okamoto and II. Oshio, Angetv. C'hem., Int. Ed, 2005,44. 6484: (rf) O. Sato. J. Tao and Y.-Z. Zhang. Angew. Chem., Int. Ed,, 2007, 46, 2152.2 la) Spin Crossover in Transition Metal Compounds I, ed. P. Gutlich andII. A. Goodwin. Springer. New York. 2004. vol. 233: {b) J. A. Real. A. B. Caspar, V. Niel and M. Munoz, Coord Chem. Re\\, 2003, 236,121: (i) S. Bonhommeau, T. Guillon, L. M. L. Daku, P. Demont, J. S. Costa. J.-F. Letard. C. Molnar and A. Bousseksou, Angetv. C'hem., Int. Ed, 2006, 45, 1625.3 {a) S. Kitagawa and S. Kawata, Coord Chem. Rev., 2002, 224, 11: {b) J. Tao, II. Maruyama and O. Sato, J. Am. Chem. Soc., 2006,128, 1790.4 (a) K. S. Min, A. DiPasquale, A. L. Rheingold and J. S. Miller, Inorg. Chem, 2007, 46, 1048: W) K. S. Min, A. C. DiPasquale, J. A. Golen, A. L. Rheingold and J. S. Miller, J. Am. Chem. Soc., 2007, 129, 2360.5 {a) D. L. Reger, J. R. Gardinier, W. R. Gemmill, M. D. Smith, A. M. Shahin. C. J. Long. L. Rebbouh and F. Grandjean. J. Am. Chem. Soc., 2005, 127, 2303: lb) S. Alvarez, J. Am. Chem. Soc., 2003, 125, 6795: (i ) N. Brtfuel, S. Imatomi, II. Torigoe, II. Ilagiwara,S. Shova, J.-F. Meunier, S. Bonhommeau, J.-P. Tuchagues and N. Matsumoto, Inorg. Chem., 2006, 45, 8126: (rf) K. W. Tomroos, M. Ilostettler, D. Chernyshov, B. Vangdal and II.-B. Burgi, Chem. Eur. J., 2006, 12, 6207.6 At 208 K. 03- -03B = 2.802(4) A. Z03-II3-03B = 148.32“: 03B-"F4(-.\- + 1. -v . - r  + 1) = 2.641(4) A. Z03B-II3B-F4 = 153.35“. At 295 K. 03---03B(x - v  + 1/2. r  -  1/2) = 2.764(7) A. Z 03- II3-03B = 150.15“: 03B---F4(-x. r  + 1/2. - r  + 1/2) = 2.623(9) A. Z03B-II3B-F4 = 151.89“.7 ia) G. R. Desiraju, Crystal Engineering: The Design o f  Organic Soliiis, Elsevier. New York. 1989. ch. 4: (b) A. S. Shetty. J. Zhang and J. S. Moore, J. Am. Chem. Soc., 1996, 118, 1019.8 II. Ilagiwara. S. Ilashimoto. N. Matsumoto and S. Lijima. Inorg. Chem, 2007, 46, 3136.9 In the absence of X-ray data, these possibilities have been distinguished for SCO Fe(ll) dimers viii applied field Mossbauer spectroscopy. V. Ksenofontov, II. Spiering, S. Reiman, Y. Garcia, A. Caspar, N. Moliner. J. Real and P. Gutlich. Chem. Phvs. Ijett.. 2001. 348. 381.10 G. M. Sheldrick, SHELXL-97, Program for refinement o f  crystal structures. University of Gottingen, Germany, 1997.This journa l is © The Royal Society o f Chem istry 2008 Chem. Commun., 2008, 317-319 | 319

Dinuclear iron(II) complex, [(TPyA)FeII(THBQ 2-)FeII(TPyA)](BF4)2 [TPyA = tris(2-pyridylmethyl)amine; THBQ2- = 2,3,5,6-tetrahydroxy-1,4- benzoquinonate] exhibiting both spin crossover with hysteresis and ferromagnetic exchange

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Dinuclear iron(II) complex, [(TPyA)FeII(THBQ 2-)FeII(TPyA)](BF4)2 [TPyA = tris(2-pyridylmethyl)amine; THBQ2- = 2,3,5,6-tetrahydroxy-1,4- benzoquinonate] exhibiting both spin crossover with hysteresis and ferromagnetic exchange

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