Abstract The hydrothermal syntheses and crystal structures of two novel cobalt carboxylate− phosphonates with 4, 4′-bipyridine (4, 4′-bipy) as the secondary metal linker are reported. Compound 1,[Co 3 (H 2 L) 2 (H 2 O) 4 (4, 4′-bipy)], where H 5 L= 4-HO 2 CC 6 H 4 CH 2 N (CH 2 PO 3 H 2) 2, crystallizes in the monoclinic space group C2/c with a= 25.9281 (5), b= 9.76310 (10), c= 17.3671 (5) Å, β= 103.290 (2), V= 4278.6 (2) Å 3, and Z= ...