A new family of oxalate-bridged chains of formula (C-1)[Mn(H2O)(3)Cr(ox)(3)]center dot H2O ( 1), (C-2)(4)[Mn-2(H2O)(3)ClCr2(ox)(6)]Cl center dot H2O center dot 2C(2)H(6)O (2a), (C-2)(4)[Co-2(H2O)(3)ClCr2(ox)(6)]Cl center dot 2H(2)O center dot 2C(2)H(6)O (2b), [Mn(C-3)(H2O)(2)Cr(ox)(3)]center dot H2O (3), and (C-4)(4)[Mn(H2O){Cr(ox)(3)}(2)]center dot H2O (4) [C-1(+) = tetramethylammonium, C-2(+) = 4-N,N-dimethylaminopyridinium, C-3(+) = 1-hydroxyethyl-4.N,N-dimethylaminopyridinium, C-4(+) = 1-hydroxyethyl-4-(4'-dimethylamino-alpha-styryl)-pyridinium, ox(2)(-) = oxalate] have been synthesized by self-assembly of the (C-n)(3)[Cr(ox)(3)] (n = 1-4) mononuclear compound and the chloride salts of the corresponding metal(II) ions. The crystal structures of the five chain compounds have been determined by single-crystal X-ray diffraction. Compounds 1 and 2 crystallize in the Pc and P2(1)/c centrosymmetrical space groups, respectively, whereas 3 and 4 crystallize in the C2cb and PI noncentrosymmetrical space groups, respectively. Compounds 1, 2, and 3 adopt a zigzag chain structure while 4 exhibits a comb-like chain structure consisting of the repetition of the [Mn(H2O){Cr(mu-ox)(ox)(2)}{Cr(mu-ox)(2)(ox)}](4)(-) entities. Compound 3 displays large second-order optical nonlinearity. The magnetic properties of 1-4 have been investigated in the temperature range 2-300 K. Monte Carlo simulations on 1, 2a, 2b, and 3 provide a quantitative description of the magnetic properties indicating ferromagnetic interactions through the bis(bidentate) oxalate bridges [J = +0.55 cm(-1) (1), J = +1.02 cm(-1) (2a), J = +3.83 cm(-1) (2b), and J = +0.75 cm(-1) (3) using Hamiltonian (H) over cap = -J((S) over cap (i),(S) over cap (j))]. On the other side, the fit of the magnetic susceptibility data of 4 by full-matrix diagonalization agrees with a ferromagnetic exchange interaction within the [Mn(H2O){Cr(mu-ox)(ox)(2)}(Cr(mu-ox)(2)(ox)}](4)(-) trinuclear units (J = +2.07 cm(-1)) antiferromagnetically coupled along the chain. Compound 2b exhibits a metamagnetic behavior, the value of the critical field being H-C = 1000 G, due to the occurrence of weak interchain antiferromagnetic interactions.