The fundamental chemistry of the f-elements is relatively underexplored compared to any other block of elements on the periodic table. The synthesis, structure determination, and characterization of new f-element compounds may lead to the elucidation of novel materials and structure-property relationships which may in turn have innovative real world applications. The goal of this research is to synthesize new lanthanide and actinide selenites that are relevant for their optical, ion-exchange, sorption, and magnetic properties. To this end, the research contained herein will address the synthesis and characterization of inorganic materials containing f-elements. In this work, the structural chemistry and resultant physico-chemical properties were probed using selenite as a ligand, often in combination with other metals or counter-ions. Multiple characterization techniques were utilized including single crystal X-ray diffraction, powder X-ray diffraction, superconducting quantum interference device magnetometery, scanning electron microscopy, energy-dispersive X-ray spectrometry, and solid-state ultraviolet-visible-near infrared spectroscopy. In an effort to synthesize lanthanide- and actinide- containing selenite materials to compare bonding and other chemical properties several new 4f and 5f compounds were discovered including: isotypic structures displaying an unusual case of aliovalent substitution, Th(VO₃)₂(SeO₃) and Ln(VO₃)₂(IO₃) (Ln = Ce, Pr, Nd, Sm, and Eu) (Chapter 2), mixed anion materials including three noncentrosymmetric structures, Pr₂(SeO₃)2(SO₄)(H₂O)₂, KGd₂(SeO₃)₃(H₂O), KEu₂(SeO₃)₃(H₂O), and Ce₂(SeO₃)₃(VO₂) (Chapter 3), isomorphous open-framework structures, Na₃Ln₄(SeO₃)₇O·nH₂O (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb) (Chapter 4), a 3d-4f heterobimetallic material, DyCo(SeO₃)₃Cl(O)(H₂O) (Chapter 5), and the first example of a lanthanide carbonate selenite, KHo(CO₃)(SeO₃) (Chapter 6).