  We report the structural and magnetic characterizations of Ba3TeCo3P2O14,
Pb3TeCo3P2O14, and Pb3TeCo3V2O14, compounds that are based on the mineral
Dugganite, which is isostructural to Langasites. The magnetic part of the
structure consists of layers of Co2+ triangles. Nuclear and magnetic structures
were determined through a co-refinement of synchrotron and neutron powder
diffraction data. In contrast to the undistorted P321 Langasite structure of
Ba3TeCo3P2O14, a complex structural distortion yielding a large supercell is
found for both Pb3TeCo3P2O14 and Pb3TeCo3V2O14. Comparison of the three
compounds studied along with the zinc analog Pb3TeZn3P2O14, also characterized
here, suggests that the distortion is driven by Pb2+ lone pairs; as such, the
Pb compounds crystallize in a pyroelectric space group, P2. Magnetic
susceptibility, magnetization, and heat capacity measurements were performed to
characterize the magnetic behavior. All three compounds become
antiferromagnetic with N\'eel temperatures TN ~ 21 K (Ba3TeCo3P2O14), ~ 13 K
(Pb3TeCo3P2O14), and ~ 8 K (Pb3TeCo3V2O14), and they exhibit magnetic
transitions at high applied magnetic fields, suggesting intrinsically complex
magnetic behavior for tetrahedrally coordinated d7 Co2+ in this structure type.
