Crystal Structure and Magnetic Property of Cobalt Glutarate, Co[O 2 C(CH 2 ) 3 CO 2 ]

1. Crystal Structure and Magnetic Property of Cobalt Glutarate, Co[O2C(CH2)3CO2] 이 윤 원, 김 유 진, 정 덕 영* Department of Chemistry - BK21, SungKyunKwan University

2. 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[O2C(CH2)3CO2], 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).

3. Experimental Procedure Teflon Vessel Metal ion source; CoCl2·6H2O 5 mmol Ligand; Glutaric acid 5 mmol aqueous KOH 1.5 M 5 mL ~pH 4.5 Heat in oven at 180 °C for 24 h under hydrothermal condition oven 180ºC Quench in cold water Dark purple crystals (Filter, wash with alcohol, yields in ~70%) Co-glutarate, Co[O2C(CH2)3CO2]

4. Crystal Structure Data Asymmetric Unit Empirical formula CoC5H6O4 Formula weight 189.03 Crystal system monoclinic Space group P2/c Unit cell dimensions a = 14.002(3) Å b = 4.8064(10) Å c= 9.274(3) Å α= 90º β= 90.50(2)º γ= 90º Volume, Z 624.1(3) Å3, 4 Density (calculated) 2.012 mg/m3 Final R indices R1 = 0.0480 wR2 = 0.1316 R indices (all data) R1 = 0.0566 wR2 = 0.1601 C6 C5 C4 O1 O2 O4 Co O3 C1 C2 C3

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

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

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

8. (001) (100) b b Anti-form Anti-form Gauche-form 90° 90° a c Crystal Structure View

9. IR and TG IR No C=O stretch TG Rate = 10 °C/min Under N2-gas Blowing C-C stretch No hydrate water 39% Decomposition of Organic Chains C-O stretching Co[O2C(CH2)3CO2] CoO (39.6%) (~ 450 oC)

10. 116.4 103.3 99.0 121.4 106.5 110.3 UV-Vis Spectrum Color : Dark purple Co2+(d7) in Td Strong field ground configuration : e4t23 Strong field ground term : 4A2 Peak Assignment 1274 nm (7849 cm-1): 4A2g(F) 4T1g(F) 558 nm (179211cm-1): 4A2g(F) 4T1g(P) Crystal Field Strength: Dt = 4418 cm-1 Racah parameter: Bt= 788 cm-1

11. Magnetization Co2+(in Td) ; 3d7 C = 0.18 cm3K/mol Q = -1.01 K eff = 3.69 B (at 300 K) *eff (expt): 4.30-5.20B for H.S. 1.73 B for L.S. state of Co2+ 1/c = T/C - Q/C (at T > 50 K) = 0.57 T + 5.61 (100G, MPMS-SQUID magnetometer)

12. Conclusion All cobalt atoms were coordinated to four oxygen atoms (Td 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.