An iron(III) phosphonate cluster containing a nonanuclear ring
  This communication reports the first example of cyclic ferric clusters with an odd number of iron atoms capped by phosphonate ligands, namely, [Fe9(m-OH)7(m-O)2(O3PC6H9)8-(py)12]. The magnetic studies support a S = 1/2 ground state with an exchange coupling constant of about J = -30 K. 
H. C. Yao, J. J. Wang, Y. S. Ma, O. Waldmann, W. X. Du, Y. Song, Y. Z.   Li, L. M. Zheng, S. Decurtins, X. Q. Xin