Two quaternary metal chalcogenides, Ba2AlSbS5 and Ba2GaBiSe5, were successfully synthesized by solid-state reaction in sealed silica tubes. Both of them crystallize in the same orthorhombic space group Pnma, but they appear with obviously different construction features. For example, Ba2AlSbS5 exhibits [SbS3](3-) units and zero-dimensional (0D) [AlSbS5](4-) clusters, which is different from those ([BiSe6](3-) units and 1D [GaBiSe5](4-) chains) of Ba2GaBiSe5. We also systematically investigated the entire series of (Ba2MMIII)-M-III'Q(5) (M-III = Al, Ga, In; M-III' = As, Sb, Bi; Q = S, Se, Te) compounds, and the results showed that the interconnection of M(III)Q(4) and M-III'Q(n) (n = 3, 5, 6) units can form three different structural types, including 0D [(MMIII)-M-III'Q(5)] clusters, single [M-III'Q(3)] chains and isolated [M(III)Q(4)] units, or [M(III)Q(3)](n) and [M-III'Q(3)](n) double chains, which may be induced by the flexible coordination and on-link modes of M-III' atoms. Spectral investigation shows that their bandgaps are about 2.57 eV for Ba2AlSbS5 and 2.14 eV for Ba2GaBiSe5. Theoretical calculation was also used to analyze their structure-property relationships, and the results indicate that the title compounds exhibit larger birefringences (Delta n > 0.10), thus having potential as the IR birefringent materials.