Crystal Structure and Magnetic Property of Cobalt Glutarate, Co[O 2 C(CH 2 ) 3 CO 2 ] * 이 윤 원, 김 유 진, 정 덕 영 * Department of Chemistry - BK21, SungKyunKwan University

Introduction A reasonable approach to build three-dimensional structures based on layered structural motifs is to control the packing of layers by organic pillars of changeable length and type. Pillared structures are potentially important for applications in catalysis, magneto material and etc. A variety of layered structure with transition metal and dicarboxylate have been synthesized. Single crystal of Co-glutarate, Co[O 2 C(CH 2 ) 3 CO 2 ], was synthesized as single crystal under hydrothermal condition, characterized by XRD, IR, TG, UV-vis, and SQUID. It is interesting to note that this structure represents the first example of carboxylate pillared structures containing only tetrahedral sites of cobalt(II) with two different conformation of glutarate ligands(anti/gauche-form).

Experimental Procedure aqueous KOH 1.5 M 5 mL Metal ion source; CoCl 2 ·6H2O 5 mmol Ligand; Glutaric acid 5 mmol oven 180ºC Heat in oven at 180 °C for 24 h under hydrothermal condition Quench in cold water Dark purple crystals (Filter, wash with alcohol, yields in ~70%) Co-glutarate, Co[O 2 C(CH 2 ) 3 CO 2 ] Teflon Vessel ~pH 4.5

Crystal Structure Data Empirical formulaCoC 5 H 6 O 4 Formula weight Crystal systemmonoclinic Space groupP2/c Unit cell dimensionsa = (3) Å b = (10) Å c= 9.274(3) Å α= 90º β= 90.50(2)º γ= 90º Volume, Z624.1(3) Å 3, 4 Density (calculated)2.012 mg/m 3 Final R indicesR 1 = wR 2 = R indices (all data)R 1 = wR 2 = Co O1 O4 O3 O2 C4 C5 C6 C1 C2 C3 Asymmetric Unit

Gauche-form Anti-form Two Different Conformations of Glutarate Ligands 115.6º 115.2º 109.8º

Inorganic Layer b c c a b a c 4.81 Å 4.63 Å 7.01 Å 90.5° 6.99 Å = Gauche-form = Anti-form

(syn-anti / syn-anti mode) syn anti (syn-anti / syn-anti mode) syn anti Gauche-form Anti-form Bridging mode of Carboxylate c a 90.5°

Crystal Structure View c(100) 90° b a(001) Gauche-form Anti-form b

Decomposition of Organic Chains Rate = 10 °C/min Under N 2 -gas Blowing 39% Co[O 2 C(CH 2 ) 3 CO 2 ] CoO (39.6%) (~ 450 o C) No hydrate water C-O stretching C-C stretch No C=O stretch IR and TG IRTG

UV-Vis Spectrum Color : Dark purple Peak Assignment 1274 nm (7849 cm -1 ): 4 A 2g (F) 4 T 1g (F) 558 nm (179211cm -1 ): 4 A 2g (F) 4 T 1g (P) Crystal Field Strength:  t = 4418 cm -1 Racah parameter: B t = 788 cm Co 2+ (d 7 ) in T d Strong field ground configuration : e 4 t 2 3 Strong field ground term : 4 A 2

Magnetization C = 0.18 cm 3 K/mol  = K  eff = 3.69  B (at 300 K) *  eff (expt):  B for H.S  B for L.S. state of Co 2+ 1/  = T/C -  /C (at T > 50 K) = 0.57 T (100G, MPMS-SQUID magnetometer) Co 2+ (in T d ) ; 3d 7

Conclusion All cobalt atoms were coordinated to four oxygen atoms (T d symmetry) by carboxylate groups to form an organic/inorganic hybrid compound in three-dimension. Interestingly, two different conformations of alkyl chain in glutarate ligands (anti-form and gauche-form) were observed in the crystal structure of the prepared Co-gluatarate compounds. Magnetic measurement showed long range with  eff = 3.69  B (at 300 K). Acknowledgement We acknowledge financial support from the Electron Spin Science Center at POSTECH, which established as the excellent science research center by the KOSEF. The Korea Basic Science Institute provided us with SQUID magnetometer measurements for the present study.