Crystals of the tetragonal form of Na 2 CoP 2 O 7 have been grown and characterized by single crystal X-ray di4raction. This compound crystallizes in the tetragonal system, space group P4 2 /mnm with a β«Ψβ¬ 7.7058(12), c β«Ψβ¬ 10.301(2) A s , and Z β«Ψβ¬ 4. The structure was solved by Patterson and Fourier methods, and re5ned to 5nal agreement factors R(F 2 ) β«Ψβ¬ 5.8%, Rw (F 2 ) β«Ψβ¬ 12.4%, S(F 2 ) β«Ψβ¬ 1.07. Their structure can be described as layered since it is formed by slabs of [CoP 2 O 7 ] with Na cations lying between the layers. The Co 2Ψ cation adopts a tetrahedral coordination geometry unusual in inorganic solids. CoO 4 tetrahedra share four oxygens with P 2 O 7 pyrophosphate groups and the Na Ψ cations appear in a NaO 8 quadrangular prismatic coordination geometry. Magnetic measurements reveal the presence of antiferromagnetic interactions in the Co 2Ψ sublattice, at about 10 K. Magnetic correlations are also studied from the analysis of possible superexchange pathways in the structure. Impedance measurements (frequency range: 1+5 Ψ 10 6 Hz; temperature range: 90+5403C) show Na 2 CoP 2 O 7 an ionic conductor being the conductivity at 3003C 2 Ψ 10 Ψ5 Scm Ψ1 and the activation energy 0.61 eV. The possible motion of the Na Ψ ions in the interlayer surface plane and through adjacent layers (c axis) is discussed.