Lattice- and spin-dimensionality crossovers in a linear-chain-molecule-based ferrimagnet with weak spin anisotropy

[MnOEP][HCBD], a member of the metalloporphyrin family of donor-acceptor molecule-based magnets, consists of isolated ferrimagnetic chains of alternating $S=2,$ [MnOEP], and $s=1/2,$ [HCBD] units ($\mathrm{O}\mathrm{E}\mathrm{P}=\mathrm{o}\mathrm{c}\mathrm{t}\mathrm{a}\mathrm{e}\mathrm{t}\mathrm{h}\mathrm{y}\mathrm{l}\mathrm{p}\mathrm{o}\mathrm{r}\mathrm{p}\mathrm{h}\mathrm{y}\mathrm{r}\mathrm{i}\mathrm{n}\mathrm{a}\mathrm{t}\mathrm{o}$ and $\mathrm{H}\mathrm{C}\mathrm{B}\mathrm{D}=\mathrm{h}\mathrm{e}\mathrm{x}\mathrm{a}\mathrm{c}\mathrm{y}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{b}\mathrm{u}\mathrm{t}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{e}$). Analysis of the exchange pathways reveals an exchange along one interchain axis ${(J}_{\mathrm{inter}})$ almost 3 orders of magnitude weaker than the intrachain exchange ${(J}_{\mathrm{intra}}),$ and a negligible exchange along the other interchain axis. From the susceptibility and magnetization data we determine $J_{\mathrm{intra}}$ and $J_{\mathrm{inter}}$ to be antiferromagnetic with values of $-172\mathrm{K}$ and $-0.4\mathrm{K},$ respectively. At 19.6 K, the system undergoes both lattice and spin dimensionality crossovers in which the ferrimagnetic chains couple antiferromagnetically as two-dimensional Ising sheets.