Indo. J. Chem., 2012, 12 (1), 89 - 93 Fahimah Martak et al. 89 * Corresponding author. Tel/Fax : +62-81572535690 Email address : fahimahm@chem.its.ac.id SYNTHESIS AND MAGNETIC PROPERTIES OF BINUCLEAR COMPLEX [N(n-C 4 H 9 ) 4 ][Mn II Fe III (ox) 3 ] Fahimah Martak*, Hamzah Fansuri, and Sekarayu Dianing Putri Department of Chemistry, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo Surabaya 60111 Received September 7, 2011; Accepted February 10, 2012 ABSTRACT Binuclear complex, [N(n-C 4 H 9 ) 4 ][Mn II Fe III (ox) 3 ] (ox=oxalate), has been synthesized and characterized. Binuclear complex with formula of [N(n-C 4 H 9 ) 4 ][Mn II Fe III (ox) 3 ] was synthesized by forming precursor K 3 [Fe(ox) 3 ] which was followed by adding manganese chloride and tetrabutyl ammonium chloride. Characterization of the complex was made by microanalysis, FT-IR spectroscopy, x-ray diffraction and Magnetic Susceptibility Balance. Magnetic moment of binuclear complex [N(n-C 4 H 9 ) 4 ][Mn II Fe III (ox) 3 ] is 7.81 BM. The compound has higher magnetic moment than the previously reported compound with different organic cation, [N(n-C 5 H 11 ) 4 ][Mn II Fe III (ox) 3 ]. This behavior might be associated with the decreasing range among layers on polymeric network. Keywords: Binuclear complex; oxalato network; iron complex; magnetic properties; X-ray powder diffraction ABSTRAK Kompleks Binuklir, [N(n-C 4 H 9 ) 4 ][Mn II Fe III (ox) 3 ] (ox=oxalate), telah disintesis dan dikarakterisasi. Kompleks binuklir dengan formula, [N(n-C 4 H 9 ) 4 ][Mn II Fe III (ox) 3 ] disintesis melalui pembentukan precursor kristal K 3 [Fe(ox) 3 ] yang selanjutnya dilakukan penambahan mangan klorida dan tetrabutil ammonium klorida. Padatan hasil sintesis dikarakterisasi dengan analisis unsur, teknik difraksi sinar-X (XRD), spektroskopi FTIR dan Suseptibilitas magnetik balans. Pada penelitian ini diketahui bahwa moment magnetik kompleks binuklir adalah 7,81 BM. Nilai moment magnetik senyawa ini lebih tinggi dari yang dilaporkan sebelumnya dengan kation yang berbeda, [N(n- C 5 H 11 ) 4 ][Mn II Fe III (ox) 3 ]. Sifat magnetik yang lebih tinggi ini dihubungkan dengan menurunnya jarak antar lapisan pada jejaring polimer. Kata Kunci: Kompleks binuklir; jejaring oksalat; kompleks besi; sifat magnetik; difraksi sinar-X INTRODUCTION Molecular magnet based on polynuclear complexes has superior magnetic properties than mononuclear complexes. For example, the magnetic moment of [N(n- C 5 H 11 ) 4 ][Mn II Fe III (Ox) 3 ] is 7.5 BM [1], while the magnetic moment of its respective mononuclear complex K 3 Fe(Ox) 3 is 5.8 BM [2]. Interactions among metal ions in the polynuclear complex improve their total magnetic moment. The magnetic moment of polynuclear complexes is a function of the size of organic cation. Decreasing the cation size will increase the magnetic moment followed by the increase in temperature of paramagnetic- antiferomagnetic transition. Studies on the effect of organic cation size to magnetic moment of polynuclear complexes have been reported. For an example, Mathoriene et al. (1996) reported that binuclear complex [N(n-C 5 H 11 ) 4 ] [Mn II Fe III (ox) 3 ] had paramagnetic-antiferomagnetic transition at 27 K and effective magnetic moment 7.71 BM. The crystal structure of the complex was investigated later [3]. Tetra-Butylamine [N(n-C 4 H 9 ) 4 ] + is an organic cation which is smaller than tetra-pentylamine, [N(n- C 5 H 11 ) 4 ] + . Therefore, when the former cation replaces the [N(n-C 5 H 11 ) 4 ] in [N(n-C 5 H 11 ) 4 ][Mn II Fe III (Ox) 3 ], the magnetic moment of the complex will increase. This paper reports the research results of the substitution and its effect on the complex magnetic moment. The polyanion complex was synthesized from K 3 Fe(Ox) 3 precursor. EXPERIMENTAL SECTION Materials All chemicals were reagent grade and were used as commercially obtained, such as MnCl 2 .4H 2 O, [(NH 4 ) 2 Fe(H 2 O) 2 (SO 4 ) 2 ].4H 2 O, H 2 SO 4 6M, methanol,