Dispersion engineering in optical waveguides allows applications relying on the precise control of phase matching conditions to be implemented. Although extremely effective over relatively narrow band spectral regions, dispersion control becomes increasingly challenging as the bandwidth of the process of interest increases. Phase matching can also be achieved by exploiting the propagation characteristics of waves exciting different spatial modes of the same waveguide. Phase matching control in this case relies on achieving very similar propagation characteristics across two, and even more, waveguide modes over the wavelengths of interest, which may be rather far from one another. We demonstrate here that broadband (>40??nm) four-wave mixing can be achieved between pump waves and a signal located in different bands of the communications spectrum (separated by 50?nm) by exploiting interband nonlinearities. Our demonstration is carried out in the silicon-rich silicon nitride material platform, which allows flexible device engineering, allowing for strong effective nonlinearity at telecommunications wavelengths without deleterious nonlinear-loss effects.