Three bis-tetradentate acyclic amine ligands differing only in the arm length of the pyridine pendant arms attached to the 4,6-positions of the pyrimidine ring, namely, 4,6-bis[N,N-bis(2'-pyridylethyl)aminomethyl]-2-phenylpyrimidine (L(Et)), 4,6-bis[N,N-bis(2'-pyridylmethyl)aminomethyl]-2-phenylpyrimidine (L(Me)), and 4,6-[(2'-pyridylmethyl)-2'-pyridylethyl)aminomethyl]-2-phenylpyrimidine (L(Mix)) have been used to synthesize nine air-sensitive diiron(II) complexes: [Fe(II)(2)L(Et)(NCS)(4)]·MeOH·¾H(2)O (1·MeOH·¾H(2)O), [Fe(II)(2)L(Et)(NCSe)(4)]·H(2)O (2·H(2)O), [Fe(II)(2)L(Et)(NCBH(3))(4)]·(5/2)H(2)O (3·(5/2)H(2)O), [Fe(II)(2)L(Me)(NCS)(4)]·½H(2)O (4·½H(2)O), [Fe(II)(2)L(Me)(NCSe)(4)] (5), [Fe(II)(2)L(Me)(NCBH(3))(4)]·(3/2)H(2)O (6·(3/2)H(2)O), [Fe(II)(2)L(Mix)(NCS)(4)]·½H(2)O (7·½H(2)O), [Fe(II)(2)L(Mix)(NCSe)(4)]·(3/2)H(2)O (8·(3/2)H(2)O), and [Fe(II)(2)L(Mix)(NCBH(3))(4)]·(3/2)H(2)O (9·(3/2)H(2)O). Complexes 3·(5/2)H(2)O, 4·½H(2)O, 5, 6·(3/2)H(2)O, and 8·(3/2)H(2)O were structurally characterized by X-ray crystallography, revealing, in all cases, both of the iron(II) centers in an octahedral environment with two NCE (E = S, Se, or BH(3)) anions in a cis-position relative to one another. Variable temperature magnetic susceptibility measurements showed that all nine diiron(II) complexes are stabilized in the [HS-HS] state from 300 K to 4 K, and exhibit weak antiferromagnetic coupling. Mössbauer spectroscopy confirmed the spin and oxidation states of eight of the nine complexes (the synthesis of air-sensitive complex 3 was not readily reproduced).