An out-of-plane dimeric Mn-III quadridentate Schiff-base compound, [Mn-2(salpn)(2)(H2O)(2)](ClO4)(2) (salpn(2-) = N,N'-(propane)bis(salicylideneiminate)), has been synthesized and structurally characterized. The crystal structure reveals that the [Mn-2(salpn)(2)(H2O)(2)](2+) units are linked through weak H-bonds (OHwater center dot center dot center dot O-Ph) in one dimension along the c-axis, forming supramolecular chains. The exchange interaction between Mn-III ions via the biphenolate bridge is ferromagnetic (J/k(B) = +1.8 K), inducing an S-T = 4 ground state. This dinuclear unit possesses uni-axial anisotropy observed in the out-of-plane direction with D-Mn2/k(B) = -1.65 K. At low temperatures, this complex exhibits slow relaxation of its magnetization in agreement with a single-molecule magnet (SMM) behavior. Interestingly, the intermolecular magnetic interactions along the one-dimensional organization, albeit weak (J'/k(B) = -0.03 K), influence significantly the thermally activated and quantum dynamics of this complex. Thus, unique features such as M vs H data with multiple steps, hysteresis effects, and peculiar relaxation time have been explained considering SMMs in small exchange-field perturbations and finite-size effects intrinsic to the chain arrangement. The magnetic properties of this new complex can be regarded as an intermediate behavior between SMM and single-chain magnet (SCM) properties.